JP2015114539A - Light source device, correlation photon pair generator, polarization quantum-entangled photon pair generator and time position quantum-entangled photon-pair generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a wavelength conversion equivalent to a SHG (Second Harmonic Generation) by a conventional laser excitation and the like to be efficiently attained using an incoherent light source such as spontaneous emission light and the like, and in this case, to enable expansion of an allowable range as to an input wavelength and the like.SOLUTION: Output light outputted from an incoherent light source 2 is configured to be input to a first non-linear optical device 1 via an optical coupling system 3. In the first non-linear optical device, a SFG (Sum Frequency Generation) is generated among optical spectrum components owned by the incoherent light source 2, and short wavelength light of an optical frequency as twice as a central optical frequency of the incoherent light source 2. The generated short wavelength light is configured to be externally output via the optical coupling system 4.

Description

  The present invention is characterized by a light source device including an incoherent light source and a nonlinear optical device, a correlated photon pair generating device that generates a correlated photon pair by natural parametric fluorescence using incoherent light as excitation light, and generation of a polarization entangled photon pair. The present invention relates to a polarization entangled photon pair generation device and a time-position entangled photon pair generation device specialized for time-position entangled photon pair generation.

Outputs light with a wavelength that is 1 / n of the input light wavelength (where n is an integer of 2 or more) using a nonlinear optical device that uses a nonlinear optical crystal such as lithium niobate (LiNbO ₃ ). The light source device has a high industrial utility value as a light source that generates light having a wavelength that is difficult to realize with a short wavelength light source or a laser light source such as an existing semiconductor laser. For example, optical second harmonic generation (hereinafter abbreviated as SHG) corresponding to n = 2 is often used to generate green light, which is one of the three primary colors of light. Used in display technology. In addition, it is possible to increase the recording density of the optical recording medium by shortening the wavelength of the light source using SHG.

Further, a correlated photon pair generating device that generates a correlated photon pair by using a short wavelength light generated from the above-described device as a pumping light by natural parametric down conversion (SPDC), which is a second-order nonlinear optical effect. And a entangled photon pair generating apparatus using the same (see Non-Patent Document 1, for example). In Non-Patent Document 1, in a first periodically poled LiNbO ₃ (Periodically poled lithium noibate, hereinafter abbreviated as PPLN) waveguide type device, 779.5 nm SHG light is generated for input laser light having a wavelength of 1559 nm, In the second PPLN waveguide type device, a correlated photon pair of 1.5 μm wavelength band is generated by SPDC using SHG light as excitation light, and a time-position entangled photon pair is generated.

  A similar correlated photon pair generator can also be realized by using spontaneous four wave mixing (hereinafter abbreviated as SFWM), which is a third-order nonlinear optical effect. Hereinafter, SPDC and SFWM are collectively referred to as natural parametric fluorescence. In particular, a correlated photon pair generator specialized for generation of polarization entangled photon pairs is a polarization entangled photon pair generator, and a correlated photon pair generator specialized for time position entangled photon pair generation is a time position entangled photon pair. It may also be called separately from the generator.

  Here, for convenience in the following description, the correlation photon pair, the polarization entangled photon pair, and the time position quantum entangled photon pair are defined.

  When excitation light is input to a nonlinear optical crystal that exhibits a nonlinear optical effect, the nonlinear optical effect that manifests in the nonlinear optical crystal, for example, on the wave number, angular frequency, polarization state, and time axis of signal light, idler light, etc. The converted light having a quantum correlation with respect to the time position and the like is generated. A correlated photon pair refers to a pair of photons having a quantum correlation in this way, and a correlated photon pair generator refers to an apparatus that generates a correlated photon pair.

  A polarization quantum entangled photon pair is a photon in which the polarization of each photon is not determined, but the polarization between two photons has a definite polarization correlation such as parallel or orthogonal to each other. Say a pair. That is, the polarization quantum entangled photon pair is a correlated photon pair in which a plurality of combinations of polarizations are superimposed on the photon pair, and there is a polarization correlation between the photon pairs.

  On the other hand, a time-position entangled photon pair has a plurality of time slots in which photons can exist, and it is not determined in which time slot each photon exists, but two photons must be identical. A photon pair that exists in a time slot. That is, the time-entangled entangled photon pair is in a state where the distribution method of each of the plurality of photons existing for the photon pair is superimposed, and the correlated photon pair having a correlation in the time position between the photon pairs. It is. In addition, the time-entangled entangled photon pair not only has a correlation in the measurement related to the generation time of the two-photons, but also has a phase difference corresponding to the relative delay time τ. The result is also correlated with whether the image is overlaid.

Qiang Zhang, Hiroki Takesue, Sae Woo Nam, Carsten Langrock, Xiuping Xie, Burm Baek, MM Fejer, and Yoshihisa Yamamoto, "Distribution of Time-Energy Entanglement over 100 km fiber using superconducting single-photon detectors", Optics Express, vol 16 , No. 8, pp. 5776-5781 (2008)

  As disclosed in many literatures and the like, the excitation light source that has been conventionally used exclusively for producing nonlinear optical effects such as SHG is a laser light source. This is because the laser light source has high spatial and temporal coherence, which is useful for producing non-linear optical effects efficiently, i.e. with high conversion efficiency at low excitation intensity. .

  Here, spatial coherence means that the wavefront is aligned in the direction perpendicular to the traveling direction (lateral direction), and temporal coherence means that the wavefront is aligned in the traveling direction (vertical direction). To do. If a wide wavelength component is included in the light traveling direction, it will be difficult to align the wavefront in the traveling direction. Therefore, in order to achieve temporal coherence, the width of the included wavelength is required to be narrow. . That is, a laser light source by optical amplification based on stimulated emission light is a coherent light source that satisfies such conditions and outputs light having high spatial and temporal coherence. On the other hand, a light source that outputs incoherent light that is based on spontaneously emitted light, such as lamps, light bulbs, fluorescent lamps, light emitting diodes, sunlight, etc., that has a uniform wavefront in both the horizontal and vertical directions is called an incoherent light source. .

  In general, preparing a laser light source is more difficult than preparing an incoherent light source based on spontaneous emission. This is because preparing a laser light source requires a stable optical resonator as well as an amplifying material that realizes an inversion distribution in order to effectively cause stimulated emission. In contrast, incoherent light is present throughout the natural world without any special preparation.

  In order to efficiently realize the nonlinear optical effect, it is indispensable to realize phase matching, but the phase matching conditions include the wavelength of the input light and output light, including quasi-phase matching. Very sensitive to. Therefore, the wavelength of the excitation laser light source must be sufficiently controlled. Furthermore, it is necessary to operate with sufficient control over the input optical wavelength (phase matching wavelength) that realizes phase matching on the nonlinear optical device side. For example, according to an experimental example by the inventors of the present invention described later, SHG is generated by using a PPLN waveguide type device having an element length of 6 cm and realizing quasi-phase matching for an input light wavelength near 1.5 μm. In this case, the accuracy of the allowable input light wavelength is as narrow as about 0.2 nm. From the PPLN waveguide type device side, this corresponds to the fact that the operating temperature must be controlled within a temperature fluctuation range of about 1.6 ° C. Hereinafter, unless there is a particular need for distinction, it may be simply referred to as phase matching even for pseudo phase matching.

  Therefore, if an incoherent light source such as spontaneous emission light can be used to efficiently achieve wavelength conversion equivalent to SHG by conventional laser excitation, and the allowable range for the input light wavelength can be widened at that time, more A low-cost and highly efficient light source device is realized. Furthermore, by using this light source device, it is possible to provide a low-cost and high-efficiency correlated photon pair generator and a entangled photon pair generator.

  Accordingly, an object of the present invention is to provide an incoherent light source and a non-linear optical device, and use the output light from the incoherent light source to generate converted light having a wavelength of 1 / n of the output light wavelength by the non-linear optical device. And a correlated photon pair generating device that generates a correlated photon pair by natural parametric fluorescence using the converted light output from this device as excitation light, and in particular, a polarization entangled photon pair generation It is an object of the present invention to provide a polarization entangled photon pair generation device specialized in the above and a time position quantum entangled photon pair generation device specialized in the generation of time position quantum entangled photon pairs. In addition, the output light from the incoherent light source is used to generate wavelength-converted light generated by sum frequency generation (SFG) and SPDC in a single second-order nonlinear optical device. It is another object of the present invention to provide a correlated photon pair generating device, a polarized quantum entangled photon pair generating device, and a time position quantum entangled photon pair generating device for generating correlated photon pairs.

  When incoherent light is input to the second-order nonlinear optical device, SFG appears between the optical frequency spectral components contained in the incoherent light, and the optical frequency is twice (half the wavelength) the center frequency of the incoherent light. Short wavelength light is generated. Here, SHG is included as a special case of SFG. That is, SFG is a process in which one high frequency light is generated from two low frequency spectral components of incoherent light, and SHG is a special case where the frequencies of the two low frequency spectral components are equal.

The inventor of the present application, when using a second-order nonlinear optical device, the full width at half maximum Δf _{pump of the} curve that gives the optical frequency spectrum of the incoherent excitation light source, and the curve that gives the SHG light intensity with respect to the optical frequency of the SHG light (hereinafter, SHG curve). Through the examination of the relationship between the full width at half maximum (hereinafter also referred to as SHG bandwidth) Δf _SHG and the wavelength dependency of differential frequency generation (hereinafter referred to as DFG), I got the knowledge.

As a result of detailed calculations, it has been found that when the relationship Δf _pump ≦ 1.2 Δf _SHG is satisfied, the SFG conversion efficiency according to the method of the present invention exceeds the conventional SHG conversion efficiency.

Further, when the relationship of Δf _pump > 0.7Δf _SHG is satisfied, the phase matching required for the SHG conversion obtained by the incoherent light source according to the method of the present invention from the phase matching condition required for the SHG conversion obtained by the conventional coherent light source The knowledge that the conditions are relaxed was obtained.

  Therefore, according to the gist of the present invention, a light source device having the following configuration is provided.

The light source device includes a non-linear optical device having an n-th order nonlinear optical effect in which n is an integer of 2 or more and a phase matching wavelength is λ _PMW , and an incoherent spectrum having a continuous optical frequency spectrum including a wavelength component of λ _PMW The incoherent light output from the incoherent light source is input to the nonlinear optical device, and the nth-order optical sum frequency generation for the incoherent light is generated to generate the sum frequency light of wavelength λ _PMW / n It is characterized by making it.

In order to increase the wavelength conversion efficiency, the full width at half maximum Δf _pump of the optical frequency curve that gives the optical frequency spectrum characteristics of incoherent light and the full width at half maximum Δf _{SHG of the} curve that gives the SHG light intensity with respect to the optical frequency of SHG light are Δf _It is preferable to satisfy the relationship of _pump ≦ 1.2Δf _SHG .

To relax the phase matching condition, the full width at half maximum Δf _pump of the optical frequency curve giving the optical frequency spectral characteristics of incoherent light and the full width at half maximum Δf _{SHG of the} curve giving the SHG light intensity with respect to the optical frequency of SHG light are Δf _pump It is preferable to satisfy the relationship> 0.7Δf _SHG .

According to the light source device of the present invention, incoherent light having a continuous optical frequency spectrum including a wavelength component of λ _PMW output from an incoherent light source is input to a nonlinear optical device having an nth-order nonlinear optical effect. Since it is configured, it is possible to generate converted light having a wavelength of λ _PMW / n.

And when using a second-order nonlinear optical device, by narrowing or widening the relationship between the full width at half maximum Δf _pump of the optical frequency curve and the full width at half maximum Δf _{SHG of the} curve giving the SHG light intensity as described above, Compared with a light source device using a conventional coherent light source, the wavelength conversion efficiency can be increased and the phase matching condition can be relaxed.

  Therefore, according to the light source device of the present invention, it is only necessary to prepare an incoherent light source instead of the laser light source, and the procurement of the light source is facilitated. Since an expensive coherent light source is not required, a light source device can be realized at low cost. That is, since the light source device can be constructed using an incoherent light source, it is possible to design a device other than a light source device that requires a conventional coherent light source. Can contribute to increase.

  In addition, if a light source device using the incoherent light source of the present invention, or a technique for increasing the wavelength conversion efficiency or a technique for relaxing the phase matching condition using the incoherent light source of the present invention is applied, A correlated photon pair generating device that generates correlated photon pairs can be realized, and in particular, a polarization entangled photon pair generating device or a time-position entangled photon pair generating device can be realized. Furthermore, using the output light from the incoherent light source, similarly, a correlated photon pair generating device, a polarization quantum entangled photon pair generating device, and a time position quantum entangled photon pair generating device for generating a correlated photon pair can be realized. It becomes possible.

  That is, since the correlation photon pair generation device can be constructed using an incoherent light source, it is realized using an incoherent light source in addition to a correlation photon pair generation device that requires a conventional coherent light source. Since the apparatus can be designed, it is possible to contribute to an increase in the degree of freedom in designing the correlated photon pair generating apparatus.

1 is a block configuration diagram schematically showing a basic configuration of an embodiment of a first light source device of the present invention. FIG. It is a graph with which it _uses for description about _SHG bandwidth (DELTA) f _SHG and input light spectrum width (DELTA) f _pump . It is a figure which shows the optical frequency spectrum which divided | segmented and displayed the amplitude of the photoelectric field of input light for 2N pieces for every minute frequency (DELTA) f. It is a figure which uses for description about ratio of SFG light intensity by wavelength conversion of this invention and SHG light intensity by wavelength conversion of a conventional system, and input light spectrum width dependence of SFG spectrum width by wavelength conversion of this invention. It is a figure which shows the measurement result of the input light intensity dependence of SFG light intensity according to the change of input light spectrum width. It is a figure which shows the experimental result which evaluated P _SFG / P _SHG ratio and SFG light spectrum width with respect to input light spectrum width under fixed input light intensity. Center optical frequency, was conducted to evaluate the tolerance for shift amounts [delta] _p from f _0/2, the experimental results for the variation of the SFG light intensity when changing the operating temperature of the fixed input light intensity device FIG. It is a block block diagram which shows roughly about the structural example of the incoherent light source utilized for the light source device of this invention. FIG. 5 is a block configuration diagram schematically showing a basic configuration of an embodiment of a second light source device of the present invention. FIG. 3 is a block configuration diagram schematically showing a basic configuration of an embodiment of a first correlated photon pair generating device using excitation light generated by a first light source device or a second light source device. FIG. 3 is a schematic block configuration diagram of an optical rejection filter and an optical separation circuit suitable for using SFWM in the first correlated photon pair generation device. 1 is a block configuration diagram schematically illustrating a configuration example of a polarization entangled photon pair generation device using a type-I type second-order nonlinear optical device. FIG. FIG. 10 is a block configuration diagram schematically illustrating another configuration example of a polarization entangled photon pair generation device using a type-I type second-order nonlinear optical device. It is a block block diagram which shows roughly the example of a structure of the polarization entangled photon pair generator using the type-II type | mold secondary nonlinear optical device. FIG. 5 is a block configuration diagram schematically showing a basic configuration of an embodiment of a second correlated photon pair generation device. FIG. 5 is a schematic block configuration diagram of an optical rejection filter and an optical separation circuit suitable for using SFWM in the second correlated photon pair generation device. FIG. 10 is a block configuration diagram schematically illustrating another configuration example of a polarization entangled photon pair generation device using a type-I type second-order nonlinear optical device. It is a block block diagram which shows schematically the structural example of a mode converter.

  Hereinafter, referring to FIG. 1 to FIG. 18, the light source device of the present invention, a correlated photon pair generating device, a polarization entangled photon pair generating device specialized for polarization entangled photon pair generation, and a time-position entangled photon pair generation An embodiment of a time-position entangled photon pair generation device specialized in the present invention will be described. In the following description, specific elements and operating conditions may be taken up, but these elements and operating conditions are only one preferred example, and are not limited to these. Each of the diagrams showing schematic configurations of the light source device, the correlated photon pair generating device, the polarization entangled photon pair generating device, and the time-position quantum entangled photon pair generating device is the whole or a part of the device according to the present invention. However, the present invention is not limited to the illustrated example, but merely illustrates the arrangement relationship of each component to the extent that the present invention can be understood.

<First light source device>
≪1≫
A first light source device according to an embodiment of the light source device of the present invention will be described with reference to FIG. The first light source device includes a first nonlinear optical device 1 having a second-order nonlinear optical effect whose phase matching wavelength is λ _PMW , and a continuous optical frequency spectrum including a wavelength component of λ _PMW (hereinafter simply referred to as optical And an incoherent light source 2 that outputs incoherent light having a spectrum (may be abbreviated as spectrum). Then, the incoherent light is input to the nonlinear optical device, and the sum frequency light having the wavelength λ _PMW / 2 is generated by the second-order nonlinear optical effect on the incoherent light.

  The output light output from the incoherent light source 2 is input to the first nonlinear optical device 1 via the optical coupling system 3 including a lens or the like. In the first nonlinear optical device 1, SFG occurs between optical spectral components of the incoherent light source 2, and short wavelength light having an optical frequency twice as high as the center optical frequency of the incoherent light source 2 is generated. The generated short-wavelength light is output to the outside via an optical coupling system 4 composed of a lens or the like, if necessary, for practical use.

Here, in the first nonlinear optical device 1, when SHG light is generated by inputting laser light having a single wavelength as in the prior art, light of maximum intensity SHG light obtained by realizing phase matching. Let f ₀ be the frequency. The optical frequency of the input single wavelength laser beam (excitation light) at this time is f _0/2 . In general, the value 2c / f ₀ obtained by converting the optical frequency of the input single-wavelength laser light into a wavelength at this time is called a phase matching wavelength (λ _PMW ). Here, c is the speed of light in vacuum. The optical frequency f ₀ of the SHG light corresponds to the optical frequency of the SHG light when the SHG light having the maximum intensity is obtained, and this f ₀ corresponds to λ _PMW / 2 when converted into a wavelength.

With reference to FIGS. 2A and 2B, the SHG bandwidth Δf _SHG and the input optical spectrum width Δf _pump will be described. Fig. 2 (A) is a graph showing the relationship (SHG curve) of SHG light intensity to SHG optical frequency, and Fig. 2 (B) is the relationship of optical frequency spectrum intensity to input pumping light frequency (optical frequency spectrum of incoherent light source). ). As shown in FIG. 2 (A), when the wavelength (or optical frequency) of the input single-wavelength laser light is changed, the light of the SHG light when the SHG light intensity is obtained more than half the maximum SHG light intensity described above. The variable frequency range (full width at half maximum) is the SHG bandwidth Δf _SHG . As is well known, the SHG curve generally has a shape given by the square of the sinc function. Further, as shown in FIG. 2 (B), the optical frequency spectrum of the incoherent light source is assumed optical frequency is a continuous light spectrum spread around its comprise components of f _0/2. The full width at half maximum of this optical spectrum is defined as the input optical spectral width Δf _pump .

Curve giving the optical frequency spectrum of the incoherent light source, it is most desirable is symmetric with respect to the optical frequency axis about the optical frequency f _0/2. Although details will be described later, it is desirable that the input optical spectrum width Δf _pump of the optical spectrum is equal to or narrower than the _SHG bandwidth Δf _SHG of the SHG curve. However, these conditions are not necessarily required in order to realize a part of the effect obtained by the first light source device.

  Next, SHG and SFG generated by incoherent light having the optical frequency spectrum shown in FIG. 2 (B) will be considered.

  First, regarding the SHG, if the optical frequency of the generated SHG light is f, the SHG light is generated only from the component of the optical frequency f / 2 among the optical frequency components of the input light. Since the input light has a continuous spectral shape, such frequency components are only a fraction of the total spectral components, and the generated SHG light is very weak compared to SFG light described later.

  On the other hand, for SFG, if the optical frequency of the SFG light is f, this SFG light has the optical frequency (f / 2) + δf frequency component and the optical frequency (f / 2)-δf among the optical frequency components of the input light. It is generated from the frequency component. Since there are an infinite number of combinations of Δf within the range of the optical spectrum band, SFG light is basically generated with a much stronger intensity than SHG light.

  That is, it can be considered that the short wavelength light generated in the first light source device is due to SFG, and there is almost no light due to SHG.

≪2≫
Next, the intensity of short wavelength light generated by SFG will be considered.

First, for the sake of simplicity, the optical frequency spectrum of the amplitude of the photoelectric field of the input light will be considered by dividing it into 2N for each minute frequency Δf. FIG. 3 shows an optical frequency spectrum of the amplitude of the photoelectric field of the input light divided into 2N for each minute frequency Δf, with the horizontal axis representing the optical frequency and the vertical axis representing the magnitude of the photoelectric field amplitude. _Let the amplitude of the photoelectric field per unit frequency in each optical frequency region be _er (r = -N, -N + 1, -N + 2,..., -1, 1, 2,..., N).

Here, the order of r, in order from the center region than the optical frequency f _0/2 high frequency side, 1, 2, ..., N Distant from the center of the area than the optical frequency f _0/2 low-frequency side In order, -1, -2, ..., -N. If fine frequency Δf is sufficiently small, and the light of the r-th amplitude e _r of the optical field light and -r th optical electric field amplitude e _-r, it may be considered to generate an SFG light of optical frequency f ₀ . Since there are N combinations of (e _r , e _−r ), if the nonlinear polarization per unit frequency generated by the SFG at the optical frequency f ₀ is p ^{(f 0)} , the following equation (1) is obtained. Here, d is SHG tensor, k _r is the wave number of the light amplitude of the r-th light field is e _r, the phi _r is the r-th light relative phase amplitude of the light field is e _r .

If the above equation (1) is substituted into the coupled mode equation and solved, the SFG light intensity can be calculated. For simplicity, if the propagation loss of the input light and SFG light is zero and there is no attenuation of the input pumping light, the amplitude of the SFG light photoelectric field of the unit frequency value generated at the optical frequency f ₀ e _f0 follows the coupled mode equation given by the following equation (2).

Here, Δk _r represents a phase mismatch amount defined as Δk _r ≡k _f0 −k _r −k _−r −K, and k _f0 is the wave number of SFG light. K is a parameter corresponding to the polarization inversion period for quasi-phase matching, and is given by Λ / 2π with respect to the polarization inversion period Λ. Furthermore, A is a proportional coefficient including a refractive index.

Here, for convenience, it is assumed that phase matching is established for all combinations of (e _r , e _−r ). That is, it is assumed that Δk _r = 0. As will be explained later, this assumption is valid. Solving equation (2) yields equation (3) below. Here, L is the device length.

Now, since the generated SFG light is proportional to | e _f0 | ² , if the SFG light intensity per unit frequency is i _SFG (f ₀ ), i _SFG (f ₀ ) is given by the following equation (4). . Here, B is a proportional coefficient including a dielectric constant and the like.

In the last product (Σ) × (Σ) on the right side of Equation (4), the phase φ _r fluctuates randomly because the input light is incoherent light. Therefore, the time average value of the product term r ≠ m is zero, and as a result, Equation (4) becomes the following Equation (5).

Here, considering that | e _r | ² is proportional to the spectral intensity i _r (spectral density) per unit frequency of the input light, equation (5) becomes the following equation (6). Here, C is a proportional coefficient.

Now, the input light spectrum, the peak spectral intensity around the f _0/2 is I _0, the full width at half maximum (input optical spectral width) is assumed to be Gaussian type is Delta] f _pump. That is, the spectrum intensity waveform is given by the following equation (7).

  At this time, if the minute frequency Δf corresponding to the division width when the optical frequency spectrum of the amplitude of the photoelectric field of the input light is divided into 2N pieces is sufficiently small, the following expression (8) is given.

Further, the average intensity P _pump of the input light is given by the following equation (9).

  Substituting equations (8) and (9) into equation (6) yields the following equation (10).

Since the input incoherent light has a continuous spectrum, SFG light having various frequency components is generated. Although details will be described later, the spectral shape of the SFG light, Delta] f _pump is is sufficiently wider than the Delta] f _SHG, full width at half maximum as shown in FIG. 2 (A) the sinc ² function of Delta] f _SHG. That is, it matches the SHG curve. Total intensity P _SFG of SFG light has a peak intensity of formula (10), the following equation since given by the total integrated value of the sinc ² function of FWHM Delta] f _SHG with the nature of the sinc ² function (11) can get.

From the expressions (10) and (11), the intensity P _{SFG of the SFG} light and the intensity P _{pump of the} input light have a relationship given by the following expression (12).

When the same argument is applied to conventional SHG pumped by single-wavelength laser light, the relationship between the SHG light intensity P _SHG and the input light intensity P _pump when phase matching is obtained is given by the following equation (13): It is done.

Comparing equation (12) and equation (13), the following can be said. That is, when the optical spectrum width Δf _pump of the input light is 1.5 times the _SHG bandwidth Δf _SHG of the SHG curve, the first light source device has a conversion efficiency equivalent to that of a conventional light source device using SHG by laser light excitation. When the optical spectrum width Δf _pump of the input light is narrower than this, the first light source device has higher conversion efficiency than the conventional light source device using SHG by laser light excitation. That is, the first light source device has a high short-wavelength light intensity obtained for the same excitation light intensity.

Although the above discussion fully explains the approximate characteristics of the first light source device, more rigorous discussion is required. For example, according to the equation (12), as the optical spectrum width Δf _pump of the input light becomes narrower, the SFG light intensity diverges infinitely, but this does not happen in reality. This is because as the optical spectrum width Δf _pump of the input light becomes narrower, the SFG spectrum also becomes narrower accordingly. Therefore, as shown in the calculation results below, the first light source device has a conversion efficiency equivalent to that of a conventional SHG light source device excited by laser light because the optical spectrum shape of the input light is a Gaussian curve. When given, the optical spectrum width Δf _pump of the input light is about 1.2 times the _SHG bandwidth Δf _SHG of the SHG curve.

Therefore, a more rigorous theoretical consideration is given. Referring to the approximate discussion so far, the SFG light intensity i _SFG (f) per unit frequency at the optical frequency f is expressed by the following equation (14) in consideration of the effect of phase mismatch.

Here, S _in (x) is the spectral intensity per unit frequency of the input light at the optical frequency x. Further, the phase mismatch amount Δ is given by the following equation (15).

Further, the total SFG light intensity P _SFG is given by the total integral of the following equation (16).

Here, it is assumed that the wavelength dependence of the refractive index of the first nonlinear optical device 1 (second-order nonlinear optical device) is linear within the spectrum band of the input incoherent light. That is, it is assumed that the refractive index is approximated by the following equation (17) as a function of the wavelength λ, where a and b are constants.
n = aλ + b (17)

At this time, the wavelengths corresponding to the optical frequencies f, (f / 2) + x, and (f / 2) -x are λ _f , λ _{(f / 2) + x} , and λ _{(f / 2) -x} , respectively. , SFG Energy Conservation Law
_{(1 / λ f) = (} 1 / λ (f / 2) + x) + (1 / λ (f / 2) -x)
The wave numbers corresponding to the optical frequencies f, (f / 2) + x, (f / 2) -x are k _f , k _{(f / 2) + x} , k _{(f / 2)- As x} , the phase mismatch amount Δ is
Δ≡k _f −k _{(f / 2) + x} −k _{(f / 2) -x} −K = (2π / λ _f ) −4πa− (2πb / λ _f ) −K
Thus, the phase mismatch amount Δ is independent of x, and the sinc ² function part in the equation (14) can be out of the integration. Further, the phase mismatch amount Δ is set such that the wavelength and wave number corresponding to the optical frequency f / 2 are λ _{f / 2} and k _{f / 2} , respectively.
Δ≡ (2π / λ _f ) −4πa− (2πb / λ _f ) −K = (2π / λ _f ) −4πa− (4πb / λ _{f / 2} ) −K = k _f −2k _{f / 2} −K
Therefore, it is equal to the phase mismatch amount in the SHG curve. Where
It was used that 1 / λ _f = 2 / λ _{f / 2} .

The validity of the above-mentioned linear approximation of the refractive index can be evaluated from the wavelength dependence of the conversion efficiency of DFG, for example. That is, in the range where the above-described linear approximation is established, the phase matching is established, so that the conversion efficiency does not change. For example, Reference A (Tadashi Kishimoto and Koji Nakamura, “Periodically Poled MgO-doped Stoichiometric LiNbO ₃ Wavelength Converter With Ridge-Type Annealed Proton-Exchanged Waveguide”, IEEE Photonics Technology Letters, vol. 23, No. 3, pp. 161-163 According to the results of experiments conducted by the inventors of the present application disclosed in (2011)), in a PPLN waveguide type device having an element length of 6 cm, the conversion efficiency typically does not change in a wavelength range of about 60 nm. I know that. Therefore, if the spectral band of the input light is about this level, it may be assumed that the above-described linear approximation holds and the following discussion holds.

Similar to the strict theoretical consideration described above, it is assumed that the input light has a spectral shape given by a Gaussian curve having a full width at half maximum Δf _pump . Further, the center optical frequency is assumed to shift [delta] _p from f _0/2. Also, the sinc ² function part is expressed by the following equation (18) because it matches the SHG curve and the full width at half maximum is Δf _SHG .

Based on the above assumption, when the integration of Expression (14) is executed, the intensity i _SFG (f) of the SFG light per unit frequency is expressed by the following Expression (19).

Similarly, the SHG light intensity P _{SHG in} the case of SHG using conventional laser light is given by the following equation (20).

Comparing Equation (10) with Equation (19), the last term on the right side of Equation (19) shows the narrowing of the SFG spectrum when the spectrum band of the input light is narrowed. Similarly, the effect of deviation from the optimum value (f _0/2 ) of the center optical frequency of the input light is shown.

≪3≫
Next, using the expressions (16), (19), and (20), the ratio P _SFG / P _SHG between the SFG light intensity by the first light source device and the SHG light intensity by the conventional single wavelength laser light excitation The results of calculating the input light spectrum width dependence are shown in FIGS. 4 (A) and (B). In FIG. 4A, the horizontal axis represents the input optical bandwidth ratio Δf _pump / Δf _SHG (normalized by Δf _SHG ), and the vertical axis represents the ratio of SFG light intensity / SHG light intensity (P _SFG / P _SHG ). Is taken. In Fig. 4 (B), the horizontal axis represents the input optical bandwidth ratio Δf _pump / Δf _SHG , and the vertical axis represents the SFG bandwidth / SHG bandwidth ratio Δf _SFG / Δf _SHG (normalized by Δf _SHG ). It is shown. An ideal case where δ _p = 0 is assumed.

As shown in FIG. 4 (A), the wavelength conversion method of the present invention has a higher conversion efficiency than the conventional SHG method using a coherent light source. The input optical spectrum width is about 1.2 times the _SHG bandwidth Δf _SHG or less. It can be seen that Here, the input optical spectrum width where P _SFG / P _SHG = 1 is referred to as a critical spectral width.

  This critical spectral width depends on the spectral shape of the input light. FIG. 4A also shows calculation results when the input light spectrum is a rectangular waveform (dotted line) and a Lorentz waveform (dashed line). The critical spectral widths were estimated to be about 1.6 times (rectangular) and about 0.45 times (Lorentz waveform), respectively. That is, the steeper spectral shape increases the critical spectral width (the conversion efficiency is reversed with a wider spectral width). This is because the spectral density at the center increases as the spectrum becomes steeper, and the SFG light intensity is proportional to the square of the spectral density.

In either waveform, the maximum value of P _SFG / P _SHG converges to 2. When δ _p = 0 (no deviation) in equation (19) and the input optical spectrum width becomes narrower than the SHG bandwidth, the sinc ² function portion in equation (19) is approximately 1 and the result The shape of the SFG spectrum is approximated to a full width at half maximum Gaussian waveform. The total SFG light intensity P _{SFG at} this time is given by the following equation (21).

  That is, it can be seen that the improvement of the conversion efficiency with respect to the conventional SHG method by narrowing the bandwidth of the input light spectrum converges at a maximum of 2 times.

If [delta] _p is not zero, SFG light intensity is reduced. It [delta] _p is not zero, it means that the input spectrum is asymmetric with respect to the optical frequency axis about the optical frequency f _0/2. That is, in order to maximize the effect of the present invention, it is most desirable that the input optical spectrum is symmetric about the optical frequency axis with f _0/2 as the center. On the other hand, however, if the bandwidth of the input optical spectrum is sufficiently wide, the portion of Exp {} at the end of the right side of Equation (19) does not change much from 1 even if _Δp increases to some extent. This means that the tolerance for δ _p is increased.

From Equation (19), the tolerance of δ _{p at which} the SFG light intensity is about half is approximately Δf _pump / (2 ^1/2 ), which increases in proportion to the input light spectrum width. On the other hand, in the case of SHG using conventional laser light excitation, the tolerance for _Δp is about half of Δf _SHG from Equation (20). Therefore, when the relationship of Δf _pump > Δf _SHG / (2 ^1/2 ) ≈0.7Δf _SHG is satisfied, the incoherent light source according to the method of the present invention is obtained from the phase matching condition required for the SHG conversion obtained by the conventional coherent light source. The phase matching condition required for the SHG conversion obtained by the above is relaxed.

These means that in the first light source device, if the bandwidth of the input light spectrum is sufficiently wide, the conversion efficiency can be kept constant even if the center frequency of the input light spectrum is shifted. Furthermore, even if the temperature of the nonlinear optical device changes, for example, the value of f ₀ changes, it means that the reduction in conversion efficiency can be reduced. On the other hand, the conventional SHG based on laser beam excitation is very sensitive to the wavelength of the input laser beam and the temperature of the nonlinear optical device, and these have to be precisely controlled.

At first glance, the first light source device can be used as long as the input laser beam is a longitudinal multimode laser and has a sufficient spectral spread even when wavelength conversion using conventional laser beam excitation is used. It seems that the same effect of increasing the conversion efficiency and the tolerance of δ _p can be obtained. However, such an effect does not occur for the reason described below.

That is, for example, it is assumed that the input laser beam is a longitudinal multi-mode laser and has N laser oscillation modes, one of which matches f _0/2 . At this time, SHG is generated for the matched oscillation mode, and SFG is generated between the other longitudinal modes. If the total intensity of the laser beam is P, the intensity of each longitudinal mode is at most P / N. The combination of the longitudinal modes that generate SFG is (N-1) / 2. As a result, the total intensity of SFG and SHG is at most given by the following equation (22), which is the same as the value when excited by a single longitudinal mode laser.

  Further, the above discussion is a case where the longitudinal modes are arranged at the same frequency interval and in phase. A general longitudinal multimode laser does not do this, and the efficiency is further reduced.

Furthermore, when δ _p is given, if it is larger than Δf _SHG , SHG does not occur due to large phase mismatch, and SFG does not occur as well. That is, the tolerance for δ _p is not different from the case where it is excited by a single longitudinal mode laser. That is, the effect of the first light source device is generated because the input light is an incoherent light source having a continuous spectrum, and the first multi-mode laser having a discrete spectral structure determined by the resonator structure is used for the first light source device. The effect of the light source device cannot be obtained.

Next, the spectral width of SFG light is considered. FIG. 4B shows the calculation result of the dependence of the spectrum width of SFG light on the input light spectrum width. As described above in FIG. 4B, the input optical spectrum width on the horizontal axis is normalized by the _SHG bandwidth Δf _SHG as in FIG. 4A. Also, the SFG light spectrum width on the vertical axis is normalized by the _SHG bandwidth Δf _SHG . The ideal case where δ _p = 0 was assumed.

When the input light spectral width Δf _pump is sufficiently wide, the SFG spectral width is almost the same as the _SHG bandwidth Δf _SHG and does not change. This can be understood from the fact that in the equation (19), when Δf _pump >> Δf _SHG , the SFG spectrum shape almost coincides with the SHG curve. As the input light spectral width Δf _pump becomes narrower, the SFG spectral width also becomes narrower. This is a monotonic decrease and as a result, the SFG spectral width will never be wider than the SHG spectral width.

  As will be described later, for example, when a PPLN waveguide type device having a length of 6 cm is used, the SHG bandwidth is as narrow as about 0.1 nm (optical frequency is 50 GHz). This value is wider than the spectral width (typically several hundred kHz to MHz) of a longitudinal single-mode laser such as a so-called distributed feedback laser, but on the other hand, such as a Fabry-Perot laser. It is very narrow compared to the spectral width (several nm) of a multimode laser. That is, according to the first light source device, it is possible to output wavelength-converted light having high time coherence that is not inferior to the wavelength-converted light obtained by normal laser light or SHG of the laser light.

  The inventor of the present application conducted a verification experiment to verify the theoretical consideration described above. A PPLN waveguide device similar to that described in the above-mentioned document A was used for the experiment. Evaluations were made on devices with element lengths of 6 cm and 2 cm.

The device with an element length of 6 cm had a pseudo phase matching wavelength (= 2c / f ₀ ) of 151.55 nm at a temperature of 41.5 ° C., and the SHG conversion efficiency at this time was about 650% / W. The SHG bandwidth (Δf _SHG ) was about 50 GHz (0.1 nm wavelength). On the other hand, the device with an element length of 2 cm had a pseudo phase matching wavelength of 1548.54 nm at a temperature of 25.0 ° C., and the SHG conversion efficiency at this time was about 62% / W. The SHG bandwidth (Δf _SHG ) was about 150 GHz (0.3 nm).

As the incoherent light source, an amplified spontaneous emission (Amplified Spontaneous Emission, hereinafter referred to as ASE light) generated by a commercially available erbium-doped fiber amplifier (Er ³⁺ -doped fiber amplifier, hereinafter referred to as EDFA) was used. By passing the ASE light from EDFA through optical bandpass filters with various transmission bandwidths, the input light spectral width of the input light source was changed. Also, in order to measure various characteristics such as input light intensity dependence, multiple EDFAs and optical bandpass filters were connected in multiple stages.

  In addition, an SHG generation experiment using a single-wavelength semiconductor laser was also conducted as a reference for the conventional SHG method using laser light excitation. The laser light source used is a commercially available tunable single wavelength semiconductor laser light source, which is a typical single wavelength laser light source having a line width of about 100 kHz.

  In the following experiments, a PPLN waveguide type device was used in which a polarization maintaining optical fiber pigtail was coupled to both end faces to form an optical module. The input intensity referred to below is the input intensity to the fiber pigtail. The SFG light intensity or SHG light intensity is the output intensity from the fiber pigtail. Therefore, although the input light intensity and SFG (or SHG) intensity actually input / output to / from the device are different from the experimental values this time, evaluation of each relative value is sufficient as a demonstration experiment of the first light source device. is there.

≪4≫
Next, with reference to FIG. 5, the measurement result of the dependence of the SFG light intensity on the input light intensity when the input light spectrum width is changed for a device having an element length of 6 cm will be described. In the figure, the input light spectrum width is converted to a value in the wavelength region. The dotted line in the figure is the result when SHG is generated by laser input. Both the laser light wavelength in the case of SHG and the center wavelength in the case of the SFG of the present invention by ASE light input were matched with the quasi phase matching wavelength. In FIG. 5, the input light spectrum width is indicated by ■ for 0.128 nm, the input light spectrum width is indicated by ▲, and the input light spectrum width is indicated by ● for 0.84 nm. The spectrum width is indicated by □ for 2.6 nm, the input light spectrum width is indicated by Δ for 5.15 nm, and the input light spectrum width is indicated by ◯ for 14.55 nm.

  In any spectral width, the SFG light intensity is proportional to the square of the input light intensity. On the other hand, with the same excitation light intensity, the generated SFG light intensity increased as the input light spectrum width narrowed. In particular, when the input optical spectrum width is about 0.45 nm (optical frequency is about 56 GHz), the SFG light intensity almost coincides with the SHG light intensity by the laser input of the conventional example. This input spectral width is about 1.13 times the SHG bandwidth (50 GHz), which is in good agreement with the theoretical results described above. Furthermore, when the input light spectrum width was narrower than 0.45 nm, the SFG light intensity by the first light source device was higher than the SHG light intensity by the conventional light source device, and the results supporting the effect of the first light source device were obtained. .

  When the same experiment was performed on an element with a length of 2 cm, and the input optical spectrum width was about 1.3 nm (optical frequency was about 162.5 GHz), the SFG light intensity was the SHG light intensity from the conventional laser input. Almost matched. This input spectral width is about 1.08 times the SHG bandwidth (150 GHz), which is in good agreement with the theoretical results. Similarly, when the input light spectrum width was narrower than 1.3 nm, the SFG light intensity increased compared to the conventional SHG light intensity.

6 (A) and 6 (B) show the experimental results evaluated at a constant input light intensity (0 dBm). _6A shows the P _SFG / P _SHG ratio with respect to the input light spectrum width, and FIG. 6B shows the relationship of the SFG light spectrum width with respect to the input light spectrum width. 6 (A) and 6 (B), the horizontal axis indicates the input light spectrum width in units of nm. The experimental value for an element with an element length of 6 cm is indicated by ◯, and the experimental value for an element with an element length of 2 cm is indicated by ●. In addition, the theoretical calculation result for an element having an element length of 6 cm is indicated by a solid line in the figure, and the theoretical calculation result for an element having an element length of 2 cm is indicated by a dotted line. The experimental value and the theoretical value showed a very good agreement, and an experimental result demonstrating the effect of the present invention was obtained.

Next, in order to evaluate the tolerance for δ _p , the following experiment was performed on a device having an element length of 6 cm. In other words, we investigated the change in SFG light intensity when the input light intensity was fixed and the device operating temperature was changed. Changing the operating temperature of the device changes the quasi phase matching wavelength, which results in δ _p . The temperature variation of the quasi-phase matching wavelength was estimated from the temperature variation of the input wavelength that maximizes the SHG light intensity in the normal SHG method, and was approximately 0.13 nm / ° C.

  Fig. 7 shows the experimental results. In FIG. 7, the horizontal axis represents the device temperature, and the vertical axis represents the SHG light intensity in units of dBm. A temperature range in which the intensity of the converted SHG light and SFG light is more than half of the maximum intensity is defined as an allowable temperature range. Here, the dotted line shows the experimental result in the case of SHG with laser light input, which is a conventional method, and the allowable temperature range was about 1.6 ° C. That is, the change in the quasi phase matching wavelength is 0.13 × 1.6 = 0.208 nm. This is about 25 GHz in terms of optical frequency, which is about half of the SHG bandwidth (50 GHz) as described above.

  On the other hand, FIG. 7 also shows the allowable temperature range in the case of SFG light by the incoherent light input of the present invention. That is, devices with input light spectral widths of 0.208 nm (indicated by a circle), 2.87 nm (indicated by a triangle), 5.45 nm (indicated by a square), and 10.8 nm (indicated by a black circle). The change in the intensity of SFG light with respect to temperature is shown. In the case of the SFG light by the incoherent light input of the present invention, the tolerance increases as the input light spectral width becomes wider. For example, when the input light spectrum width is 10.8 nm, the SFG light intensity hardly changed with respect to a temperature change of 15 ° C. or more.

  From the above experimental results, the effect of the first light source device could be verified. In implementing the first light source device, various configurations can be used particularly for the configuration of the incoherent light source. As the incoherent light source, various light sources such as a spontaneous emission light source can be basically used. From the viewpoint of outputting a higher light intensity and thereby outputting a wavelength-converted light having a higher intensity, it is a preferable example to use an ASE light source having an optical amplification function as an incoherent light source. For example, an EDFA, a semiconductor optical amplifier, or a light emitting diode (hereinafter abbreviated as LED) light source used in the demonstration experiment is a suitable example.

≪5≫
Various forms can be applied as the incoherent light source of the first light source device. With reference to FIGS. 8A to 8E, various configuration examples of the incoherent light source will be described.

  As the incoherent light source, output light from a plurality of incoherent light sources (spontaneous emission light sources) that output incoherent light may be collected at one place and the collected incoherent light may be used. That is, as shown in FIG. 8 (A), the output light from a plurality of incoherent light sources 2 such as an LED array is formed into an appropriate optical coupling system 3 to form an appropriate location on the first nonlinear optical device 1. The light can be condensed and used. The output light from multiple incoherent light sources 2 such as LED arrays is collected by the optical coupling system 3, and the incoherent light output from the optical coupling system 3 is input to the first nonlinear optical device 1 to obtain the first nonlinear The converted light output from the optical device 1 is beam-shaped by the optical coupling system 4 and output.

  Further, as shown in FIG. 8 (B), output light from a plurality of incoherent light sources is irradiated to each appropriate plurality of locations on the first nonlinear optical device 1 to output SFG light. The same effect as in the case of FIG. 8A can also be obtained by condensing the generated SFG light at an appropriate location by an appropriate optical coupling system 4 and outputting it.

Considering that there is no coherence between multiple incoherent light sources, the effect of time-averaged zeroing between different frequency modes considered in Equations (4) to (5) above is the same. The resulting SFG light is thought to be enhanced in proportion to the square of the sum of the light output of each light source. In other words, using four LEDs increases the SFG light intensity by 16 times. The same thing is technically possible with SHG generation using multiple laser sources, but in order to obtain an enhancement effect, it is necessary to control the wavelength and phase between individual laser sources. In the case of an incoherent light source, there is an advantage that such a countermeasure is unnecessary. Also you do it by changing the wavelength of each of the incoherent light source gradually, so it is possible to increase the spectral width of the total, thereby also take high tolerance [delta] _p. Such a configuration is particularly effective when, for example, it is desired to obtain a constant wavelength-converted light intensity without temperature control in an environment where the temperature changes greatly.

  The incoherent light source may be composed of a spontaneous emission light source and an optical amplifier. That is, as shown in FIG. 8C, a configuration in which the output light from the incoherent light source 2 that is a spontaneous emission light source is amplified by the optical amplifier 5 and then input to the first nonlinear optical device 1 is also a suitable example. is there. The incoherent light output from the incoherent light source 2 is input to the optical amplifier 5 and amplified, and the output light is collected by the optical coupling system 3 and input to the first nonlinear optical device 1. Then, the converted light output from the first nonlinear optical device 1 is beam-shaped by the optical coupling system 4 and output.

  The effect of the present invention can be realized even if the output light from the original incoherent light source 2 is weak. A configuration in which a plurality of optical amplifiers 5 are cascade-connected may be used. By adopting such a configuration, a general spontaneous emission light source having no light amplification function can be used as the original incoherent light source 2.

  Further, as described above, when the input light spectrum width of the incoherent light source is narrower than the SHG bandwidth of the SHG curve, wavelength conversion with higher efficiency than the conventional SHG method by laser light excitation can be realized. In order to realize this, a configuration as shown in FIG. 8D can also be used.

  Output light from the incoherent light source 2 is input to the optical bandpass filter 6 and amplified by the optical amplifier 5. Output light from the optical amplifier 5 is collected by the optical coupling system 3 and input to the first nonlinear optical device 1. Then, the converted light output from the first nonlinear optical device 1 is beam-shaped by the optical coupling system 4 and output.

That is, of the output light from the incoherent light source 2 which is the original spontaneous emission source, extracts only the optical frequency f _0/2 near the optical components (lambda _PMW wave component near) by the optical band-pass filter 6, an optical amplifier Amplify with 5. Such a configuration, an optical amplifier 5 can centrally amplified by stimulated emission only light components of f _0/2 vicinity, can prepare high incoherent light source peak spectral intensity I ₀ in the narrow spectral width. Further, a configuration in which such an optical bandpass filter and an optical amplifier are connected in a multistage cascade may be used.

  Furthermore, the incoherent light source includes a free space light acquisition device that acquires free space light such as sunlight and illumination light, an optical amplifier, and an optical bandpass filter. A configuration in which the light intensity is amplified with a filter and the optical spectrum band is narrowed to be input to the nonlinear optical device may be employed. That is, as shown in FIG. 8 (E), free space light such as sunlight or illumination light can be used as the incoherent light source instead of a light source device or light source device such as an LED. The free space light acquisition device 8 includes a light source such as an LED for inputting incoherent light to an element such as an optical coupling system, an optical amplifier, or an optical bandpass filter suitable for the light source device of the present invention. A general term for an optical component or a set of these elements that are adjusted so that the beam shape of the incoherent light has a suitable shape. When using sunlight, the free space light acquisition device 8 includes a device for automatically following the movement of the sun, a light collection system, and the like.

  The incoherent light output from the free-space light acquisition device 8 is collected by an optical coupling system 7 such as a lens or an optical fiber for optical routing, and the optical bandpass filter 6 narrows the optical spectrum band, and the light Amplified by the amplifier 5. Output light from the optical amplifier 5 is collected by the optical coupling system 3 and input to the first nonlinear optical device 1. Then, the converted light output from the first nonlinear optical device 1 is beam-shaped by the optical coupling system 4 and output. By adopting such a configuration, it is possible to provide a light source device having a high degree of freedom with respect to the light source.

  In the embodiment shown in FIGS. 8C to 8E, the optical amplifier 5 is used. However, it is not always necessary if the intensity of the incoherent light input to the first nonlinear optical device 1 is sufficient. And not.

≪6≫
According to the first light source device, the following effects can be expected. That is, wavelength-converted light having a half wavelength can be generated using an incoherent light source as an excitation light source. By making the spectral width of the light source narrower than the bandwidth of the SHG curve of the second-order nonlinear optical device, wavelength-converted light can be generated more efficiently than the conventional SHG method. Alternatively, by making the spectrum width of the light source sufficiently wider than the bandwidth of the SHG curve of the second-order nonlinear optical device, wavelength-converted light that is less sensitive to phase mismatch than the conventional SHG method and is resistant to changes in ambient temperature, etc. Can occur. Furthermore, the degree of freedom in selecting the excitation light source is increased.

<Second light source device>
≪1≫
With reference to FIG. 9, a second light source device according to an embodiment of the light source device of the present invention will be described by taking up a case where a nonlinear optical device of the third or higher order is used.

The second light source device includes a non-linear optical device having an n-order nonlinear optical effect where n is an integer of 3 or more and a continuous optical frequency spectrum including a wavelength (λ _PMW ) component that realizes phase matching (hereinafter simply referred to as an optical device). And an incoherent light source that outputs incoherent light having a spectrum (which may be abbreviated as spectrum). Then, the incoherent light is input to the nonlinear optical device, and the sum frequency light having the wavelength λ _PMW / n is generated by the nth-order nonlinear optical effect on the incoherent light.

The output light of the incoherent light source 22 is input to the nth-order nonlinear optical device 21 through an optical coupling system 23 configured with a lens or the like. In the nth-order nonlinear optical device 21, high-order sum-frequency generation (hereinafter abbreviated as HO-SFG) occurs between optical frequency spectral components of the incoherent light source 22, and the incoherent light source 22 Short wavelength light having an optical frequency f _{0 which} is n times the optical frequency f ₀ / n is generated. If necessary, the generated short wavelength light is output to the outside through an optical coupling system 24 composed of a lens or the like for practical use.

In the second light source device, n is an integer of 3 or more, and phase matching or quasi-phase matching is realized in n-order harmonic generation using an n-order nonlinear optical device, so that the n-order harmonic intensity is maximized. In this case, the wavelength of the input single wavelength laser light is referred to as a phase matching wavelength or a quasi phase matching wavelength λ _PMW .

≪2≫
In order to discuss the effects of the second light source device, the conditions under which the effects obtained by the second light source device are manifested are summarized. The effects of the second light source device are obtained under the conditions shown in the following (1) to (3).
(1) An incoherent light source having a continuous optical spectrum has an infinite number of combinations of pumping light frequencies that generate SFG light having an optical frequency f within the optical spectrum band.
(2) Since there is no phase correlation between different frequency modes, the SFG light intensity per unit frequency can be transformed as shown in equations (4) to (5).
(3) If there is a wavelength-dependent linearity of the refractive index as shown in equation (17), the phase mismatch amount does not depend on the combination of pumping light frequencies for any SFG optical frequency (equation (14 ) Do not depend on x). This condition means that when the SFG optical frequency is f ₀ , all combinations of pumping light frequencies in the input optical spectrum satisfy the phase matching condition.

Based on this, for example, a case where short wavelength light corresponding to third harmonic generation (hereinafter referred to as THG) in a third-order nonlinear optical device is generated will be considered. In this case, assuming that the THG optical frequency is f _THG , the combination of the _three pumping light frequency components f ₁ , f ₂ , and f ₃ that satisfy the following equation (23) is a short wavelength light equivalent to _THG of the optical frequency f _THG. Occur.
f _THG = f ₁ + f ₂ + f ₃ (23)
This effect is a third-order SFG, and higher-order optical sum frequency generation (HO-SFG) as described above.

If the input light is an incoherent light source having a continuous light spectrum with f _THG / 3 as the central optical frequency, there are innumerable combinations of pumping light satisfying the above equation (23). Condition (1) is satisfied. Further, since there is no phase correlation between different optical frequency modes, it can be considered that the HO-SFG light intensity is given in the same manner as the above condition (2).

Next, if the optical frequency components f ₁ , f ₂ , and f ₃ are in the same optical frequency band and there is a linearity of refractive index dispersion, the THG wavelength is λ _THG and the optical frequency components f ₁ , f ₂ , f _If the wavelengths corresponding to ₃ are λ ₁ , λ ₂ , and λ ₃ , respectively, the energy conservation law
1 / λ _THG = (1 / λ ₁ ) + (1 / λ ₂ ) + (1 / λ ₃ )
It is expressed. The phase mismatch amount Δ is the polarization inversion period for the quasi-phase matching described above, where the wave numbers corresponding to the optical frequency components f ₁ , f ₂ , and f ₃ are k ₁ , k ₂ , and k ₃ , respectively. If the parameter corresponds to
Δ≡k _THG −k ₁ −k ₂ −k ₃ −K = (2π / λ _THG ) −6πa− (2πb / λ _THG ) −K
Thus, the phase mismatch amount Δ does not depend on the combination of the optical frequency components f ₁ , f ₂ , and f ₃ . That is, the above condition (3) is satisfied.

  From the above, as in the case of the first light source device, by using a third-order HO-SFG effect using an incoherent light source and a third-order nonlinear optical device, light having a short wavelength corresponding to THG can be obtained. It is thought that it can be generated efficiently. Furthermore, if this is generalized, using an incoherent light source and a nonlinear optical device having an nth-order nonlinear optical effect, and using the nth-order HO-SFG effect, the optical frequency is n times that of the input incoherent light. It is considered that short wavelength light (1 / n in wavelength) can be efficiently generated.

≪3≫
According to the second light source device, the following effects can be expected in addition to the effects of the first light source device. That is, it is possible to efficiently generate short-wavelength light having a 1 / n wavelength of input incoherent light by using a non-linear optical device having incoherent light and an nth-order nonlinear optical effect.

<First correlated photon pair generator>
≪1≫
Correlated photon pair generating device that generates correlated photon pairs by SPDC or SFWM using the wavelength converted light as excitation light if wavelength converted light generated by the first light source device or the second light source device is used, and the same A polarization entangled photon pair generation device and a time-position entangled photon pair generation device are realized. Hereinafter, the polarization entangled photon pair generator and the time position quantum entangled photon pair generator may be collectively referred to as a quantum entangled photon pair generator. Further, in order to distinguish from the same type of device described later, the correlated photon pair generating device described here is referred to as a first correlated photon pair generating device.

  With reference to FIG. 10, the configuration of the first correlated photon pair generating device using the excitation light generated by the first light source device or the second light source device will be described.

The first correlated photon pair generation device includes a light source device 30, an optical high-pass filter 32, a second nonlinear optical device 31, an optical rejection filter 33, and an optical separation circuit. The second nonlinear optical device 31 is a second-order nonlinear optical device that expresses SPDC by the second-order nonlinear optical effect, or a third-order nonlinear optical device that expresses SFWM by the third-order nonlinear optical effect. The optical high-pass filter 32 removes a light component in the vicinity of the optical frequency f ₀ / n of the incoherent light source and transmits a light component in the vicinity of the optical frequency f ₀ (high-order SFG light). The optical rejection filter 33 removes high-order SFG light and transmits only the correlated photon pair component by SPDC or SFWM. The light separation circuit 34 finally spatially separates and outputs correlated photon pairs composed of signal photons and idler photons generated by SPDC or SFWM.

  The wavelength-converted light output from the light source device 30 is input to the second nonlinear optical device 31 after passing through the optical high-pass filter 32. In the second nonlinear optical device 31, SPDC or SFWM using this wavelength converted light component as excitation light is generated, and a correlated photon pair consisting of a signal photon and an idler photon is generated. The generated correlation photon pair passes through the optical rejection filter 33, and then is spatially separated into a signal photon component and an idler photon component in the light separation circuit 34 and output.

≪2≫
The wavelength-converted light output from the light source device 30 passes through the optical high-pass filter 32 and is input to the second nonlinear optical device 31. The optical high-pass filter 32 removes the incoherent light component near the optical frequency f ₀ / n output from the light source device 30, and outputs only the wavelength converted light component near the optical frequency f ₀ . Such an optical high-pass filter is commercialized using a dielectric multilayer filter or the like. As a result, only the wavelength converted light component in the vicinity of the optical frequency f ₀ is input to the second nonlinear optical device 31. Then, in the second nonlinear optical device 31, SPDC or SFWM using this wavelength converted light component as excitation light is generated, and a correlated photon pair including signal photons and idler photons is generated.

When the SPDC is used, the optical frequency f _s of the signal light and the optical frequency f _i of the idler light satisfy the following expression (24) that defines the energy conservation law.

f ₀ = f _s + f _i (24)
Signal photon, when the idler photon is in the same wavelength band (f _s ≒ f _i), the signal light from the above equation (24), the optical frequency of the idler light, according to the first light source device, the incoherent light source optical frequency It matches or is very close to f _0/2 . Therefore, the optical high-pass filter 32 is used to prevent the incoherent light component from being input to the second nonlinear optical device 31 so that the incoherent light component and the correlated photon pair component are not confused.

On the other hand, the optical frequency f _s of the signal light and the optical frequency f _i of the idler light satisfy the following equation (25) that defines the energy conservation law when SFWM is used.

2f ₀ = f _s + f _i (25)
When the signal photon and idler photon are in the same wavelength band (f _s ≈f _i ), the optical frequency of the signal light and idler light is close to the optical frequency f ₀ of the wavelength converted light from the above equation (25), but incoherent light Is significantly different from the optical frequency f _0/2 . In such a case, the optical high pass filter 32 may be omitted. The output light from the second nonlinear optical device 31 passes through the optical rejection filter 33. At this time, it is desirable that the wavelength conversion light component used as the excitation light of SPDC or SFWM is removed, and only the correlated photon pair component is output from the optical rejection filter 33.

  When SPDC is used, the optical frequency of the correlated photon pair component is approximately half the optical frequency of the wavelength-converted light according to Equation (24). Therefore, an optical low-pass filter can be used as the optical rejection filter 33. Such an optical low-pass filter is also commercialized using a dielectric multilayer filter or the like.

  On the other hand, when SFWM is used, the optical frequency of the wavelength-converted light and the optical frequency of the correlated photon pair component are very close according to Equation (25). In this case, an example of a suitable optical rejection filter is a so-called AWG (Arrayed Waveguide Grating) filter. That is, it is only necessary to set two of the plurality of output ports of the AWG filter so that the signal light wavelength and the idler light wavelength satisfy Expression (25). The wavelength converted light component may be set so as to be output to another output port or attenuated without being coupled to the output port. When the AWG filter is used in this way, the signal light component and the idler light component are spatially separated and output, so that the light separation circuit 34 operates simultaneously.

Alternatively, an optical bandpass filter that can output both transmitted light and reflected light is also suitable as the optical rejection filter 33. If the transmission center wavelength is set to the optical frequency f ₀ , it is possible to obtain signal light and idler light components generated at optical frequencies far from them as reflected outputs. Alternatively, a fiber Bragg grating (hereinafter abbreviated as FBG) can also be used as such an optical rejection filter 33. That is, if an FBG whose Bragg wavelength is the wavelength-converted light wavelength is prepared, the wavelength-converted light component of the input light is reflected, but the correlated photon pair component can be transmitted.

≪3≫
Further, the first correlated photon pair generating device can also be realized by combining two optical high-pass filters as shown in FIG. Here, the first optical high-pass filter 35 is an optical high-pass filter that selectively transmits light having a frequency higher than the optical frequency f ₀ of the wavelength-converted light and reflects other light components. That is, the first optical high-pass filter 35, the incoherent light source device 30 outputs the optical frequency f _0/2 near or optical frequency f _0/3 to remove photosynthesis vicinity photosynthesis optical frequency f ₀ near Transmits only SFG light. The second optical high-pass filter 36 is an optical high-pass filter that selectively reflects light having a frequency lower than the optical frequency f ₀ of the wavelength-converted light. Such an optical high-pass filter is commercially available using a dielectric multilayer filter or the like.

  The output light from the second nonlinear optical device 31 that exhibits the second-order or third-order nonlinear optical effect is first input to the first optical high-pass filter 35. The transmitted light does not include the wavelength-converted light component, and only the high frequency component (referred to as the signal light component) of the correlated photon pair is selectively output. The reflected light (including the wavelength converted light component) of the first optical high-pass filter 35 is then input to the second optical high-pass filter 36. The reflected light does not include the wavelength-converted light component, and only the low frequency component (assumed idler light) of the correlated photon pair is selectively output.

  As a result, the signal light component from the transmission output of the first optical high-pass filter 35 and the idler light component from the reflection output of the second optical high-pass filter 36 are spatially separated and output without including the wavelength conversion light component. The A configuration may be adopted in which optical bandpass filters 37 and 38 are additionally connected to the respective output terminals as necessary to limit the band. As described above, in the configuration of FIG. 11, like the AWG filter, the two optical high-pass filters serve as both the optical rejection filter 33 and the optical separation circuit. A plurality of optical rejection filters as described above may be connected and used.

  In many applications such as quantum key distribution, it is desirable that the generated correlated photon pair components are output in a spatially separated manner. This is executed in the light separation circuit 34. Here, a nonlinear optical device that realizes type-I phase matching in which the correlation photon pair of the generated signal light and idler light has the same polarization direction is defined as a type-I type second-order nonlinear optical device. On the other hand, a nonlinear optical device that realizes type-II type phase matching in which a correlation photon pair of generated signal light and idler light is orthogonally polarized is defined as a type-II type second-order nonlinear optical device.

  When the second nonlinear optical device 31 is a type-II type second-order nonlinear optical device, the polarization of the signal photon and the idler photon is orthogonal to each other. Therefore, a polarization beam splitter can be used as the light separation circuit 34. On the other hand, when the second nonlinear optical device 31 is a type-I type second-order nonlinear optical device, the signal photon and the idler photon have the same polarization direction. In such a case, a combination of different wavelengths satisfying the equation (24) or the equation (25) is selected as the signal photon and the idler photon, and a WDM (Wavelength Division Multiplexing) filter such as a so-called AWG filter is used as the optical separation circuit 34. What is necessary is just to separate wavelength using. Alternatively, two optical high-pass filters may be used in combination as shown in FIG.

Using the correlation photon pair generated in this way, a entangled photon pair can also be generated. For example, in the same configuration as that shown in FIG. 10, if the wavelength-converted light intensity, that is, the incoherent light source intensity is appropriately set, the time-position quantum entangled photon pair is changed as disclosed in Non-Patent Document 1 described above. Can occur. Alternatively, a type-II type second-order nonlinear optical device is used as the second nonlinear optical device 31, degenerate SPDC in which the signal photon and idler photon have the same wavelength is used, and no polarization is generated as the optical separation circuit 34. If you use a dependent half mirror, Reference B (Go Fujii, Naoto Namekata, Masayuki Motoya, Sunao Kurimura, and Shuichiro Inoue, "Bright narrowband source of photon pairs at optical telecommunication wavelengths using a type-II periodically poled lithium niobate waveguide" , Optics Express, vol. 15, No. 20, pp. 12769-12776 (2007).). Document B discloses a light source for generating a high-brightness narrow wavelength band photon pair based on a type-II pseudo-phase matching using a nonlinear optical tensor component d ₂₄ by an optical waveguide type PPLN.

  Further, the Sagnac loop interferometer shown in FIGS. 12 to 14 may be configured to generate the polarization entangled photon pair.

<Polarized quantum entangled photon pair generator>
≪1≫
With reference to FIG. 12, a configuration example of a polarization entangled photon pair generation apparatus using a type-I type second-order nonlinear optical device as the second nonlinear optical device 31 will be described.

  First, the outline of the polarization entangled photon pair generating device shown in FIG. 12 will be described as follows.

  The polarization entangled photon pair generator using this type-I type nonlinear optical device transmits only the first or second light source device (light source device 30) of the present invention and the SFG light output from the light source device 30. Optical high-pass filter 32, type-I type second nonlinear optical device 31, optical rejection filter 33 that removes SFG light, and correlated photon pairs generated by second nonlinear optical device 31 as signal light components And an optical separation circuit 34 that spatially separates and outputs the idler light component, a polarization rotator 39 that rotates the polarization of the SFG light by 45 degrees, a dichroic filter 40 that is a kind of optical multiplexer / demultiplexer, a polarization beam splitter 41, A 90-degree polarization rotator 42 that rotates the polarization of input light by 90 degrees is provided.

  The dichroic filter 40 outputs SFG light input from the first port 40-1 to the second port 40-2, and a correlated photon composed of a signal light component and an idler light component input from the second port 40-2. The pair component is output to the third port 40-3.

  The polarization beam splitter 41 separates and outputs the SFG light input from the first port 41-1 to polarization components orthogonal to each other to the second and third ports (41-2, 41-3), When a correlated photon pair having the same polarization direction as the polarization components separated from each other is input to the second port 41-2 and the third port 41-3, they are combined into the first port 41-1. Output.

  Then, the second nonlinear optical device 31 and the 90-degree polarization rotator 42 are arranged on the loop path (Sagnac loop path) connecting the second port 41-2 and the third port 41-3 of the polarization beam splitter 41. The polarization rotator 39 is connected to the first port 40-1 of the dichroic filter 40, the first port 41-1 of the polarization beam splitter 41 is connected to the second port 40-2 of the dichroic filter 40, and the dichroic The optical rejection filter 33 is connected to the third port 40-3 of the filter 40.

  The output light from the light source device 30 passes through the optical high-pass filter 32 and the polarization rotator 39, passes through the first port 40-1 and the second port 40-2 of the dichroic filter 40, and is polarized as a 45-degree polarized light. The signal is input to the first port 40-1 of the splitter 41.

  The first and second SFG lights propagating clockwise and counterclockwise through the Sagnac loop path output from the second port 41-2 and the third port 41-3 of the polarization beam splitter 41 are the second nonlinear optics. First and second correlated photon pairs that are input bidirectionally to the device 31 and propagate in the Sagnac loop path clockwise and counterclockwise, respectively, consisting of signal light and idler light by parametric fluorescence are generated in both directions.

  The first and second correlated photon pairs are polarized and combined in the polarization beam splitter 41 and output to the first port 40-1, and the polarized and combined correlated photon pairs are output to the second port 40-2 and the second port 40-2 of the dichroic filter 40. After passing through the third port 40-3, the optical rejection filter 33, and the optical separation circuit 34, a quantum entangled photon pair is generated.

As described above, the wavelength-converted light from the light source device 30 passes through the optical high-pass filter 32, is then converted into 45-degree linearly polarized light by the polarization rotator 39, and is input to the first port 40-1 of the dichroic filter 40. The In the dichroic filter 40, the wavelength conversion light component of the optical frequency f ₀ near is outputted from the second port 40-2 is input from the first port 40-1. On the other hand, the correlated photon pair component is input from the second port 40-2 and output from the third port 40-3. Such a dichroic filter 40 can be realized using a technique of a commercially available dielectric multilayer filter when SPDC is used. In addition, when SFWM is used, it can be realized by using the above-described AWG filter type or an optical bandpass filter type optical rejection filter 33 that can output both transmitted light and reflected light.

The wavelength-converted light output from the second port 40-2 of the dichroic filter 40 is then input to the first port 41-1 of the polarization beam splitter 41. In the polarization beam splitter 41, among the wavelength converted light component of the optical frequency f ₀ near input from the first port 41-1, p polarized light component is output to the second port 41-2, therewith s polarizing orthogonal The polarization component is output to the third port 41-3. Here, the p-polarized component is the excitation light polarization direction that causes the strongest SPDC or SFWM in the second nonlinear optical device 31.

  Similarly, in the polarization beam splitter 41, of the correlated photon pair components input from the second port 41-2, the p-polarized component is output to the first port 41-1. Further, when the s-polarized light component orthogonal to the polarization is input to the third port 41-3, it is output to the first port 41-1. Such a polarization beam splitter 41 can be realized by using a technique such as a dielectric multilayer filter. The 90-degree polarization rotator 42 rotates the polarization of the wavelength converted light and the correlated photon pair light by 90 degrees. As such a 90-degree polarization rotator 42, it is preferable to use a fusion-bonded one obtained by rotating the optical axis of the polarization plane holding fiber by 90 degrees.

  The p-polarized wavelength-converted light output from the second port 41-2 of the polarization beam splitter 41 generates a p-polarized correlated photon pair by SPDC or SFWM in the second nonlinear optical device 31. This correlated photon pair passes through the 90-degree polarization rotator 42 and is converted into s-polarized light, input to the third port 41-3 of the polarization beam splitter 41, and output to the first port 41-1. Then, the signal is input to the second port 40-2 of the dichroic filter 40 and output from the third port 40-3. On the other hand, the wavelength-converted light of s-polarized light output from the third port 41-3 of the polarization beam splitter 41 passes through a 90-degree polarization rotator 42 and is converted to p-polarized light, and is converted into SPDC in the second nonlinear optical device 31. Alternatively, a p-polarized correlated photon pair is generated by SFWM. This correlated photon pair is input to the second port 41-2 of the polarization beam splitter 41 and output to the first port 41-1. Then, the signal is input to the second port 40-2 of the dichroic filter 40 and output from the third port 40-3.

  As a result, the s-polarized correlated photon pair and the p-polarized correlated photon pair are output from the third port 40-3 of the dichroic filter 40. By appropriately adjusting the intensity of the wavelength-converted light (that is, the intensity of the incoherent light source), it is possible to realize these superposition states, that is, polarization entangled states. After that, the wavelength conversion light component and the like are removed by the optical rejection filter 33, and the polarization quantum entangled photon pair is spatially separated by using an optical separation circuit 34 such as an AWG filter, and a signal photon and an idler photon are output. That's fine.

≪2≫
In a non-linear optical device, for example, an s-polarized correlated photon pair component may be generated for p-polarized excitation light. Such an example occurs when the d ₃₁ component of the third-order polar tensor that gives the second-order nonlinear optical constant is used in SPDC. In such a case, a configuration as shown in FIG. 13 is adopted.

  The polarization entangled photon pair generator shown in FIG. 13 is a polarization entangled photon pair generator using a type-I type second-order nonlinear optical device. This polarization quantum entangled photon pair generating device includes a first or second light source device (light source device 30) of the present invention, an optical high-pass filter 32 that transmits only SFG light output from the light source device 30, and a type-I type The second nonlinear optical device 31, the optical rejection filter 33 that removes SFG light, and the correlated photon pair generated by the second nonlinear optical device 31 are spatially separated into a signal light component and an idler light component and output. And a polarization rotator 39 that rotates the polarization of the SFG light by 45 degrees, a polarization beam splitter 41, and a 90-degree polarization rotator. The polarization beam splitter 41 separates and outputs the SFG light input from the first port 41-1 to polarization components orthogonal to each other to the second and third ports (41-2, 41-3). When a correlated photon pair having a polarization direction orthogonal to the polarization components separated by polarization is input to the second port 41-2 and the third port 41-3, the pair of polarized photons is polarized to the fourth port 41-4. Combine and output.

  In the Sagnac loop path connecting the second port 41-2 and the third port 41-3 of the polarization beam splitter 41, the second nonlinear optical device 31 and the 90-degree polarization rotator 42 are arranged.

  The polarization rotator 39 is connected to the first port 41-1 of the polarization beam splitter 41, and the optical rejection filter 33 is connected to the fourth port 41-4 of the polarization beam splitter 41.

  After the output light from the light source device 30 passes through the optical high-pass filter 32 and the polarization rotator 39, it is input to the first port 41-1 of the polarization beam splitter 41 as 45-degree polarized light, and the first and second SFG lights And output from the second port 41-2 and the third port 41-3. The first and second SFG lights propagating clockwise and counterclockwise through the Sagnac loop path output from the second port 41-2 and the third port 41-3 of the polarization beam splitter 41 are second nonlinear First and second correlated photon pairs, which are input bidirectionally into the optical device 31 and propagate in the Sagnac loop path clockwise and counterclockwise, respectively, consisting of signal light and idler light by parametric fluorescence, are generated bidirectionally. Then, the first and second correlated photon pairs are combined in the polarization beam splitter 41 and output to the fourth port 41-4, and the combined polarization photons pass through the optical rejection filter 33 and the optical separation circuit 34. And output as a entangled photon pair.

  That is, in this case, a polarizing beam splitter having four input / output ports is used as the polarizing beam splitter 41. That is, in addition to the operation described above, in the polarization beam splitter 41, the s-polarized component of the correlated photon pair component input from the second port 41-2 is output to the fourth port 41-4. Further, when the p-polarized light component orthogonal to the polarization is input to the third port 41-3, it is output to the fourth port 41-4. Such a polarization beam splitter 41 can also be realized by using a technique such as a dielectric multilayer filter.

  At this time, correlated photon pairs of p-polarized light and s-polarized light input to the third port 41-3 and the second port 41-2 of the polarization beam splitter 41 are output to the fourth port 41-4. Therefore, the optical rejection filter 33 and the optical separation circuit 34 may be connected to the fourth port 41-4 side of the polarization beam splitter. In such a case, since the correlated photon pair component does not pass through the dichroic filter 40, the dichroic filter 40 becomes unnecessary.

≪3≫
When the second nonlinear optical device 31 is a type-II type second-order nonlinear optical device, the configuration shown in FIG. 14 may be used. Here, the polarization beam splitter 41 having the above-described four input / output ports is used.

  The polarization entangled photon pair generator shown in FIG. 14 is a polarization entangled photon pair generator using a type-II type second-order nonlinear optical device. This polarization quantum entangled photon pair generating device includes a first or second light source device (light source device 30) of the present invention, an optical high-pass filter 32 that transmits only SFG light output from the light source device 30, and a first optical reject. Filter 33-1 and second optical rejection filter 33-2, type-II type second nonlinear optical device 31, polarization rotator 39 that rotates the polarization of SFG light by 45 degrees, and dichroic filter 40 A polarization beam splitter 41 and a 90-degree polarization rotator 42 that rotates the polarization of the input light by 90 degrees.

  The dichroic filter 40 outputs the SFG light input from the first port 40-1 to the second port 40-2, and the correlation composed of the signal light component and the idler light component input from the second port 40-2. The photon pair component is output to the third port 40-3.

  The polarization beam splitter 41 separates and outputs the SFG light input from the first port 41-1 to polarization components orthogonal to each other to the second and third ports (41-2, 41-3), When a correlated photon pair having a polarization direction orthogonal to the polarization-separated polarization component is input to the second and third ports (41-2, 41-3), respectively, the first port 41-1 and the fourth port Output to the port 41-4.

  The second nonlinear optical device 31 and the 90-degree polarization rotator 42 are arranged in the Sagnac loop path connecting the second port 41-2 and the third port 41-3 of the polarization beam splitter 41, and the second dichroic filter 40 The polarization rotator 39 is connected to the 1 port 41-1.

  The first port 41-1 of the polarization beam splitter 41 is connected to the second port 40-2 of the dichroic filter 40, the first optical rejection filter 33-1 is connected to the third port 40-3, The second optical rejection filter 33-2 is connected to the fourth port 41-4 of the polarization beam splitter 41.

  The output light from the light source device 30 passes through the optical high-pass filter 32 and the polarization rotator 39, passes through the first port 40-1 and the second port 40-2 of the dichroic filter 40, and is polarized as a 45-degree polarized light. The signal is input to the first port 41-1 of the splitter 41.

  The first and second SFG lights propagating clockwise and counterclockwise through the Sagnac loop path output from the second port 41-2 and the third port 41-3 of the polarization beam splitter 41 are the second nonlinear optics. First and second correlated photon pairs that are input bidirectionally to the device 31 and propagate in the Sagnac loop path clockwise and counterclockwise, respectively, consisting of signal light and idler light by parametric fluorescence are generated in both directions.

  Correlated photon pairs generated in both directions are polarized and separated into a signal light component and an idler light component in the polarization beam splitter 41, respectively, and output to the first port 41-1 and the fourth port 41-4, respectively. A quantum entangled photon pair is output from the optical rejection filter 33-1 and the second optical rejection filter 33-2. The signal light component output from the first port 41-1 of the polarization beam splitter 41 is input to the second port 40-2 of the dichroic filter 40 and output from the third port 40-3 to output the first light. Input to the rejection filter 33-1.

  As described above, when the second nonlinear optical device 31 is a type-II nonlinear optical device, the correlated photon pair is an s-polarized and p-polarized photon pair. Assuming that the signal light is p-polarized light and the idler light is s-polarized light, the signal light is the first of the polarization beam splitter 41 compared to the SPDC or SFWM light generated by the wavelength converted light propagating clockwise in the Sagnac loop path in FIG. The first port 41-1 is output as s-polarized light, and the idler light is output as p-polarized light to the fourth port 41-4. On the other hand, for SPDC or SFWM light generated by wavelength converted light propagating counterclockwise in the Sagnac loop path, the signal light is p-polarized at the first port 41-1 of the polarization beam splitter 41, and the idler light is the fourth Is output as s-polarized light to port 41-4. Similarly, if the intensity of the wavelength-converted light (that is, the intensity of the incoherent light source) is appropriately adjusted, these superposition states, that is, polarization entangled states can be realized. In this case, since the signal light and the idler light are output to different ports of the polarization beam splitter 41, the light separation circuit 34 for spatially separating and outputting them is basically unnecessary.

  A further effect of the correlated photon pair generating apparatus and polarized quantum entangled photon pair generating apparatus of the present invention is that it is easy to generate photon pairs (or quantum entangled photon pairs) that cannot be distinguished in time. Generation of photon pairs that cannot be discriminated in time is an indispensable technique for various quantum signal processing circuits, for example, realization of quantum teleportation using bell measurement.

  Reference C (Hugues de Riedmatten, Valerio Scarani, Ivan Marcikic, Antonio, Acin, Wolfgang Tittel, Hugo Zbinden and Nicolas Gisin, "Two independent photon pairs versus four- According to photon entangled states in parametric down conversion ", J. Mod. Opt. 51, 1637 (2004).) To generate photon pairs (or entangled photon pairs) that are indistinguishable in time, The coherence time of the excitation light that causes SPDC or SFWM needs to be as short as the coherence time of the correlated photon pair by SPDC or SFWM.

  The coherence time of an SPDC or SFWM correlated photon pair is the optical band when the band limitation is imposed by an optical bandpass filter for the entire spectral bandwidth of the correlated photon pair generated by SPDC (or SFWM) or for spatial separation, etc. It is given by the reciprocal of the transmission bandwidth of the pass filter. The minimum value of the spectral width that can be realized by the SPDC (or SFWM) spectral width or the optical bandpass filter is at most about sub-nm to several nanometers with reference to the prior art. This corresponds to an optical frequency of several tens of GHz or more in the 1.5 μm wavelength band.

  On the other hand, since the coherence time of pumping light is the reciprocal of the line width (generally several MHz or less) in the case of continuous laser light, it is generally difficult to satisfy the above conditions with pumping of continuous laser light. Therefore, conventionally, in order to generate photon pairs that are indistinguishable in time (and quantum entangled photon pairs), a pulsed laser beam, mainly an ultrashort pulsed laser beam whose pulse width reaches the femtosecond region, is used as the laser beam. There were many cases to do. Such ultrashort pulse laser light sources and pulse laser light sources are generally large and expensive experimental equipment.

  On the other hand, in the case of the correlated photon pair generator of the present invention, and further the entangled photon pair generator, the coherence time of the excitation light is given by the reciprocal of the SHG bandwidth in the case of the first light source device, for example. The value is about several tens of GHz as shown in the demonstration experiment example, which is much wider than the line width of continuous laser light. An optical bandpass filter having such a band can be sufficiently realized by existing optical filter technology. Shortening the device length of the nonlinear optical device makes the SHG bandwidth even wider, making it easier to implement.

≪4≫
According to the first correlated photon pair generator, a photon pair (and also a entangled photon pair) that cannot be distinguished temporally by an incoherent light source in a continuous light state without using a pulsed light-like excitation light source. Can be generated. That is, according to the first correlated photon pair generator, the following effects can be expected. That is, a low-cost, high-conversion-efficiency correlated photon pair generator and a entangled photon pair generator using incoherent light output from the first light source device or the second light source device of the present invention as excitation light Can be provided. Furthermore, correlated photon pairs and entangled photon pairs that cannot be distinguished in time can be easily generated without using a pulse light source.

<Second correlated photon pair generator>
≪1≫
The configuration of the second correlated photon pair generating device will be described with reference to FIG. The difference between the second correlated photon pair generating device and the first correlated photon pair generating device is that wavelength-converted light generation by SFG and SPDC are generated by a single second-order nonlinear optical device.

Second correlation photon pair generating device, the incoherent light source 52 including the optical frequency f _0/2 near the frequency components, the optical bandpass filter 53 that transmits the optical frequency f _0/2 near the optical component only, A secondary nonlinear optical device 51, an optical low-pass filter 54, an optical rejection filter 55, and an optical separation circuit 56 are provided.

The second-order nonlinear optical device 51 generates SFG light from incoherent light with a phase matching wavelength of 2c / f ₀ and expresses SPDC. Light low-pass filter 54, an optical frequency f ₀ near the optical components are removed, it transmits a light component including the optical frequency f _0/2 wavelength components of SPDC photon pairs in the vicinity. Light rejection filter 55 transmits only the wavelength component of the SPDC photon pair to remove the optical frequency f _0/2 near the incoherent light component. The light separation circuit 56 spatially separates and outputs correlated photon pairs composed of signal photons and idler photons generated by SPDC.

Output light from the incoherent light source 52 is input to the second-order nonlinear optical device 51 after being band-limited to an optical frequency f _0/2 near the optical components by optical bandpass filter 53. In the second-order nonlinear optical device 51, SFG is generated using the input incoherent light component as excitation light, and short wavelength light is generated. At the same time, SPDC is generated using this short wavelength light as excitation light, and a correlated photon pair consisting of a signal photon and an idler photon is generated. Of the output light from the second-order nonlinear optical device 51, unnecessary wavelength components other than the correlated photon pair wavelength component are removed by the optical low-pass filter 54 and the optical rejection filter 55, and then the correlated photon pair is separated by the optical separation circuit 56. The signal photon component and the idler photon component are output after being spatially separated.

  Note that the portion constituted by the incoherent light source 52 and the optical bandpass filter 53 shown in FIG. 15 may be configured by cascading a plurality of optical amplifiers and optical bandpass filters.

Here, the operation of the second correlated photon pair generator shown in FIG. 15 will be described. The excitation light output from the incoherent light source 52 passes through the optical bandpass filter 53 and is input to the second-order nonlinear optical device 51. Optical bandpass filter 53, of the broad light spectrum with incoherent light source 52 to the common practice is to extract only the optical frequency f _0/2 optical component near incoherent inputted to second-order nonlinear optical device 51 Limit the optical bandwidth. This is because the wavelength component of the correlated photon pair generated in the first correlated photon pair generator described above is very close to the wavelength component of the incoherent light source 52, so that the incoherent light input to the second-order nonlinear optical device 51 is This is because the correlation photon pair component and the incoherent light component cannot be separated if the optical spectrum remains wide. Such an optical bandpass filter is commercialized using a dielectric multilayer filter or the like.

In second-order nonlinear optical device 51, SFG that the incoherent light component and the pumping light is generated, SFG light of optical frequency f ₀ is generated. At the same time, SPDC is generated in the same second-order nonlinear optical device 51 using this SFG light as excitation light, and a correlated photon pair consisting of a signal photon and an idler photon is generated. Such a cascaded second-order nonlinear optical effect can occur because the inventors of the present application use a cascade χ ⁽²⁾ process that appears in a PPLN ridge waveguide nonlinear optical device to apply polarization quantum in the optical communication wavelength band. Reference D (Shin Arahira, Naoto Namekata, Tadashi Kishimoto, Hiroki Yaegashi, and Shuichiro Inoue, “Generation of polarization entangled photon pairs at telecommunication wavelength using cascaded χ ⁽²⁾ processes in a periodically poled LiNbO ₃ ridge waveguide "Optics Express vol. 19, No. 17, pp. 16032-16043, (2011)).

The optical frequency f _s of the signal light and the optical frequency f _i of the idler light satisfy the equation (24) that defines the energy conservation law in the SPDC process, and the signal photon and the idler photon are in the same wavelength band (f _s ≒ f _i ) when in the signal light from the equation (24), the optical frequency of the idler light match or become very close to the optical frequency f _0/2 of the incoherent light source. Therefore, it is necessary to limit the bandwidth of the input incoherent light by the optical bandpass filter 53.

  As a result of such band limitation, the intensity of input incoherent light generally decreases, and as a result, it may be difficult to obtain the number of SPDC photon pairs that are sufficient for practical use. In such a case, an optical amplifier or an optical bandpass filter may be additionally inserted before and after the optical bandpass filter 53 as shown in the description of the first correlated photon pair generation device described above. . Even if a plurality of these optical amplifiers and optical bandpass filters are used, the same effect can be obtained.

  The output light from the secondary nonlinear optical device 51 first passes through the optical low-pass filter 54. At this time, the SFG light component used as the SPDC excitation light is removed, and as a result, only the incoherent light component and the correlated photon pair component are output from the optical low-pass filter 54.

  Next, the optical rejection filter 55 removes the incoherent light component and transmits only the correlated photon pair component. An example of such a suitable optical rejection filter is a so-called AWG filter. That is, it is only necessary to set two of the plurality of output ports of the AWG filter so that the signal light wavelength and the idler light wavelength satisfy Expression (24). The incoherent light component may be set so as to be output to another output port or attenuated without being coupled to the output port.

An optical bandpass filter that can output both transmitted light and reflected light is also suitable as the optical rejection filter 55. If the transmission center wavelength is set to the optical frequency f _0/2 and the transmission bandwidth is set wider than that of the optical bandpass filter 53, the reflected output does not include the incoherent light component, only the correlated photon pair component Is output. Such an optical rejection filter 55 is commercially available using a dielectric multilayer filter or the like.

  An FBG can also be used as such an optical rejection filter 55. That is, if an FBG whose Bragg wavelength is a phase matching wavelength is prepared, an incoherent light component of input light is reflected, whereas a correlated photon pair component can be transmitted and output.

  A plurality of optical rejection filters as described above may be connected and used. Further, in many applications, it is desirable that the generated correlated photon pair components are output after being spatially separated from each other. This is executed in the light separation circuit 56.

  When the second-order nonlinear optical device 51 is a Type-II type second-order nonlinear optical device, the signal photon and the idler photon are orthogonal to each other in polarization. Therefore, a polarization beam splitter can be used as the light separation circuit 56.

  On the other hand, when the second-order nonlinear optical device 51 is a type-I type second-order nonlinear optical device, the signal photon and the idler photon have the same polarization direction. In such a case, a combination of different wavelengths satisfying Equation (24) is selected as the signal photon and idler photon, and WDM (Wavelength Division), which is a type of optical multiplexer / demultiplexer such as a so-called AWG filter, is used as the optical separation circuit 56. Multiplexing) may be used for wavelength separation. In such a case, it is also possible to play the roles of the optical rejection filter 55 and the optical separation circuit 56 with a single AWG filter.

≪2≫
It is also possible to configure the optical rejection filter 55 and the optical separation circuit 56 with two optical high-pass filters. Referring to FIG. 16, in the second correlated photon pair generation apparatus, a case where the optical rejection filter 55 and the optical separation circuit 56 are configured by two optical high-pass filters will be described.

  The first optical high-pass filter 57 selectively transmits light on a higher frequency side than the transmission incoherent light band determined by the optical band-pass filter 53 and reflects other light components. The second optical high-pass filter 58 selectively reflects light on the lower frequency side than the transmission incoherent light band determined by the optical band-pass filter 53. As such first and second optical high-pass filters, those using a dielectric multilayer filter or the like are commercially available.

  The output light from the optical low pass filter 54 is first input to the first optical high pass filter 57. The transmitted light does not include an incoherent light component, and only a high frequency component (referred to as a signal light component) of the correlated photon pair is selectively output. The reflected light (including the incoherent light component) of the first optical high-pass filter 57 is then input to the second optical high-pass filter 58. The reflected light does not contain an incoherent light component, and only the low frequency component (assumed idler light) of the correlated photon pair is selectively output. As a result, the signal light component from the transmission output of the first optical high-pass filter 57 and the idler light component from the reflection output of the second optical high-pass filter 58 are spatially separated and output without including the incoherent light component. The A configuration may be adopted in which optical bandpass filters 59 and 60 are additionally connected to the respective output terminals as necessary to limit the band.

  Using the correlation photon pair generated in this way, a entangled photon pair can also be generated. For example, in the second correlated photon pair generation device having the same configuration as that of FIG. 15, if the incoherent light source intensity is appropriately set, a time-position quantum entangled photon pair can be generated. Also, a polarization entangled photon pair can be generated by configuring a Sagnac loop interferometer as in the first correlated photon pair generating apparatus shown in FIG.

≪3≫
Next, a polarization entangled photon pair generating device, which is a second correlated photon pair generating device using a type-I type second-order nonlinear optical device as a nonlinear optical device, will be described with reference to FIG.

The polarization entangled photon pair generating device, the incoherent light source 52 including the optical frequency f _0/2 near the frequency component, the phase matching wavelength _{λ PMW (= 2c / f 0} ) optical bandpass that transmits the wavelength component near A filter 53, a type-I type second-order nonlinear optical device 51, an optical low-pass filter 54 that removes the sum frequency light of the wavelength component in the vicinity of λ _PMW / 2, an optical rejection filter 55, and an optical separation circuit 56 A polarizer 61, a polarization rotator 62, a WDM filter 63 that is a kind of optical multiplexer / demultiplexer, a polarization beam splitter 64, and a 90-degree polarization rotator 65 that rotates the polarization of input light by 90 degrees. Yes.

  The optical rejection filter 55 removes incoherent light components that pass through the optical bandpass filter 53. The light separation circuit 56 spatially separates the correlated photon pair composed of the signal light component and the idler light component generated by the secondary nonlinear optical device 51 into the signal light component and the idler light component, and outputs them. The polarization rotator 62 rotates the polarization of the incoherent light component transmitted through the polarizer 61 by 45 degrees. The WDM filter 63 includes a first port 63-1, a second port 63-2, and a third port 63-3, and the incoherent light component input from the first port 63-1 is converted to the second port 63-1. A correlated photon pair component consisting of a signal light component and an idler light component input to the port 63-2 and input from the second port 63-2 is output to the third port 63-3. The polarization beam splitter 64 includes a first port 64-1, a second port 64-2, and a third port 64-3, and the light input from the first port 64-1 is second and second. The three polarized light components are separated and output to the three ports (64-2, 46-3), and light having the same polarization direction as the polarized light components separated and polarized is output to the second and third ports (64, 64-3). -2, 46-3), the light is combined and output to the first port 64-1.

Then, the second-order nonlinear optical device 51 and the 90-degree polarization rotator 65 are arranged in the Sagnac loop path connecting the second port 64-2 and the third port 64-3 of the polarization beam splitter 64, and the WDM filter 63 An optical bandpass filter 53, a polarizer 61, and a polarization rotator 62 are connected between the first port 63-1 and the incoherent light source 52. The light output from the polarization rotator 62 is input to the WDM filter 63. The operation of the WDM filter 63 is the same as that of the optical rejection filter 55 using the optical bandpass filter that can output both transmitted light and reflected light described above. That is, incoherent light component of the optical frequency f _0/2 vicinity is outputted from the second port 63-2 is input from the first port 63-1 (transmission), while the optical frequency corresponding to the SPDC correlated photon pairs component of f _0/2 vicinity is inputted from the second port 63-2 is output from the third port 63-3 (reflection). Such a WDM filter 63 can be realized by using a commercially available optical band filter technology. The WDM filter 63 also serves to remove the input incoherent light component output from the Sagnac loop interferometer, and thus also serves as the optical rejection filter 55 described above.

Further, the first port 64-1 of the polarization beam splitter 64 is connected to the second port 63-2 of the WDM filter 63, and the optical low-pass filter 54 is connected to the third port 63-3 of the WDM filter 63. Yes. The incoherent light output from the second port 63-2 of the WDM filter 63 is then input to the first port 64-1 of the polarization beam splitter 64. In the polarization beam splitter 64, among the optical frequency f _0/2 near the incoherent light component input from the first port 64-1, for example, p-polarized light component is output to the second port 64-2, the same polarization The orthogonal s-polarized components are output to the third port 64-3. Here, it is assumed that the p-polarized component is the excitation light polarization direction that causes SFG and SPDC most strongly in the second-order nonlinear optical device 51.

Similarly, in the polarization beam splitter 64, among the optical frequency f _0/2 near the SPDC correlated photon pairs component input from the second port 64-2, p-polarized light component is output to the first port 64-1 . In addition, when the s-polarized light component orthogonal to the polarization is input to the third port 64-3, it is output to the first port 64-1. Such a polarizing beam splitter 64 can be realized by using a technique such as a dielectric multilayer filter.

In addition 90 degree polarization rotator 65, the optical frequency f _0/2 near the input incoherent light and SPDC correlated photon pairs polarization rotated 90 degrees. As such a 90-degree polarization rotator 65, a fusion-bonded member obtained by rotating the optical axis of the polarization plane holding fiber by 90 can be used as in the embodiment of the present invention. Furthermore, in this case, since the input incoherent light and the SPDC correlated photon pair are in the same wavelength region, a half wavelength version can be used.

  The output light from the incoherent light source 52 passes through the first band 63-1 and the second port 63-2 of the WDM filter 63 after passing through the optical bandpass filter 53, the polarizer 61, and the polarization rotator 62. The 45-degree polarized light is input to the first port 64-1 of the polarization beam splitter 64. That is, the output light from the incoherent light source 52 is band-limited by the optical bandpass filter 53, converted to linearly polarized light by the polarizer 61, and converted to 45-degree obliquely polarized light by the polarization rotator 62.

  The p-polarized input incoherent light output from the second port 64-2 of the polarization beam splitter 64 generates SFG in the second-order nonlinear optical device 51, and accordingly generates a p-polarized correlated photon pair by SPDC. . This correlated photon pair passes through the 90-degree polarization rotator 65 and is converted into s-polarized light, which is input to the third port 64-3 of the polarization beam splitter 64 and output to the first port 64-1. Then, the signal is input to the second port 63-2 of the WDM filter 63 and, as a result, output from the third port 63-3.

  On the other hand, the s-polarized input incoherent light output from the third port 64-3 of the polarization beam splitter 64 passes through the 90-degree polarization rotator 65 and is converted to p-polarized light, and the second-order nonlinear optical device 51 similarly SFG is generated, and as a result, a p-polarized correlated photon pair is generated by SPDC. The correlated photon pair is input to the second port 64-2 of the polarization beam splitter 64 and output to the first port 64-1. Then, the signal is input to the second port 63-2 of the WDM filter 63 and, as a result, output from the third port 63-3.

  The polarizer 61 is inserted to use only a certain linearly polarized light component when using an incoherent light source of indefinite polarization such as a polarization-independent EDFA. This is because there is no coherence between orthogonal polarizations, and such an operation is necessary to improve the coherence of the entangled photon pair to be generated. On the other hand, when the output light from the incoherent light source 52 is close to linearly polarized light like an LED light source, the polarizer 61 is not necessary.

  The incoherent light component propagating clockwise and counterclockwise through the loop path output from the second port 64-2 and the third port 64-3 of the polarization beam splitter 64 is bidirectional to the second-order nonlinear optical device 51. SFG light for the incoherent light component passing through the optical bandpass filter 53 in the second-order nonlinear optical device 51 is generated, and a correlated photon pair consisting of signal light and idler light by parametric down-conversion to this SFG light Occurs in both directions. The correlated photon pair generated in both directions is polarized and synthesized by the polarization beam splitter 64 and output to the first port 64-1, and the correlated photon pair synthesized by polarization is the second port 63-2 and third of the WDM filter 63. After passing through the port 63-3, the optical low-pass filter 54, the optical rejection filter 55, and the optical separation circuit 56, a quantum entangled photon pair is generated.

As a result, the third port 63-3 of the WDM filter 63, an optical frequency f _0/2 near the s-polarized correlated photon pairs correlated photon pairs and p-polarized light is outputted. If the intensity of the input incoherent light source is appropriately adjusted, these superposition states, that is, polarization entangled states can be realized. After that, the SFG light component is removed by the optical low-pass filter 54, and if the input incoherent light is not sufficiently removed by the WDM filter 63, it passes through the additional optical rejection filter 55 as appropriate, and then the AWG filter, etc. Thus, the signal light component and the idler light component can be spatially separated and output for practical use.

In the polarization entangled photon pair generating apparatus described with reference to FIG. 17, the nonlinear optical device only needs to include one second-order nonlinear optical device, as described above. As a result, the cost and size of the apparatus can be reduced. In addition, since the short-wavelength SFG light component is generated by the second-order nonlinear optical device 51 itself, it is not necessary to propagate or couple the short-wavelength light through other optical paths. Therefore, for example, the WDM filter 63 and the polarizing beam splitter 64,90 degree polarization rotator 65 may be those that operate only in the wavelength region of the optical frequency f _0/2 near the input incoherent light and SPDC correlated photon pairs, the wavelength conversion Operation at the optical wavelength is not required. Therefore, a high-performance device configuration with lower cost and lower insertion loss is possible.

<Time-entangled entangled photon pair generator>
Referring to FIG. 12, FIG. 13, FIG. 14, FIG. 17, and FIG. 18, a mode converter 70 is further added to the first or second correlated photon pair generator (polarized quantum entangled photon pair generator) described above. A correlated photon pair generating device (time position entangled photon pair generating device) configured by providing the device will be described.

  The mode converter 70 is in a state where a plurality of photons present in the photon pair are distributed in a time slot, and a correlated photon pair is correlated with the time position between the photon pairs. A relative delay time difference is generated between optical paths between two photons whose polarization planes are orthogonal to each other. As a mechanism for generating this relative delay time difference, for example, a polarization beam splitter that separates photons into a relationship in which the planes of polarization are orthogonal to each other and a half mirror that combines photons in which the planes of polarization are orthogonal to each other are used. An optical path is provided, and the optical time delay generated in the two optical paths is set to be different.

  When the mode converter 70 is added to the polarization entangled photon pair generating device shown in FIGS. 12 to 14, the optical rejection filter 33 (in FIG. 14, the first optical rejection filter 33-1 or the second optical Insert into the front or back of the rejection filter 33-2). Alternatively, when the mode converter 70 is added to the polarization quantum entangled photon pair generating device shown in FIG.

  The configuration and operation of mode converter 70 will be described with reference to FIG. 18 is added to the polarization entangled photon pair generating device shown in FIG. 12, the mode converter 70 is connected to the third port 40-3 of the dichroic filter 40 and the optical converter. The case where it arrange | positions between the rejection filters 33 is shown in figure. The configuration of the mode converter 70 is the same when it is added to the polarization entangled photon pair generating device shown in FIG. 13, FIG. 14 and FIG.

  The mode converter 70 includes a second polarization beam splitter 71 that separates photons into a relationship in which the planes of polarization are orthogonal to each other, a second 90-degree polarization rotator 72 that generates a relative delay time difference, and a plane of polarization that is mutually And a half mirror 73 for aligning photons that are orthogonal to each other. The half mirror 73 is a half mirror having at least three input / output ports 73-1 to 73-3. Here, the port 73-4 corresponding to the fourth port is not practically used, but FIG. 18 is shown for convenience of explanation.

  The second polarization beam splitter 71 converts the correlated photon pair input from the first port 71-1 to the second and third ports (71-2, 71-3) into polarization components that are orthogonal to each other. Separate output. The second 90 degree polarization rotator 72 rotates the polarization of the correlated photon pair by 90 degrees. The half mirror 73 equally branches the correlated photon pair input from the first port 73-1 to the second and fourth ports (73-2 and 73-4) and inputs from the third port 73-3 The correlated photon pair thus made is equally branched to the second and fourth ports (73-2, 73-4).

  The third port 71-3 of the second polarizing beam splitter 71 and the first port 73-1 of the half mirror 73 are connected, and the second port 71-2 and the second port of the second polarizing beam splitter 71 are connected. The 90-degree polarization rotator 72 and the third port 73-3 of the half mirror 73 are connected in this order. The optical delay time generated in the optical path between the third port 71-3 of the second polarizing beam splitter 71 and the first port 73-1 of the half mirror 73, and the second of the second polarizing beam splitter 71 The optical delay time difference generated in the optical path between the port 71-2 and the third port 73-3 of the half mirror 73 is set to be different.

  That is, the optical path connecting the third port 71-3 of the second polarizing beam splitter 71 and the first port 73-1 of the half mirror 73, and the second port 71-2 of the second polarizing beam splitter 71 A relative delay time difference τ is provided between the optical path connecting the third port 73-3 of the half mirror 73 via the second 90-degree polarization rotator 72.

  The polarization entangled photon pair output from the third port 40-3 of the dichroic filter 40 is input to the first port 71-1 of the second polarization beam splitter 71, and is polarized and separated to the second port 71. -2 is output to the third port 71-3. The output light from the third port 71-3 is input as it is to the first port 73-1 of the half mirror 73, and is branched and output to the second port 73-2 and the fourth port 73-4. On the other hand, the output light from the second port 71-2 is input to the third port 73-3 of the half mirror 73 after the polarization is rotated by 90 degrees in the second 90-degree polarization rotator 72, The output is branched to the second port 73-2 and the fourth port 73-4.

  The third port 40-3 of the dichroic filter 40 corresponds to the output end of the fourth port 41-4 of the polarization beam splitter 41 for the polarization entangled photon pair generator shown in FIG. This corresponds to the output terminal of the third port 63-3 of the WDM filter 63 for the polarization entangled photon pair generator shown.

  The polarization quantum entangled photon pair output from the third port 40-3 of the dichroic filter 40 is input to the first port 71-1 of the second polarization beam splitter 71 and subjected to polarization separation. As a result, the p-polarized correlated photon pair is output to the third port 71-3, while the s-polarized correlated photon pair is output to the second port 71-2. The correlated photon pair output from the third port 71-3 of the second polarization beam splitter 71 is input to the first port 73-1 of the half mirror 73, and the second port 73-2 and the fourth port The output is split and output as p-polarized light to port 73-4. On the other hand, the s-polarized correlated photon pair output from the second port 71-2 of the second polarizing beam splitter 71 is converted into p-polarized light by the second 90-degree polarization rotator 72, The signal is input to the third port 73-3 of the half mirror 73, and is branched and output to the second port 73-2 and the fourth port 73-4 as p-polarized light.

Here, attention is focused on the output from the second port 73-2 of the half mirror 73. The second port 73-2 of the half mirror 73 is coupled to the light rejection filter 33 and the light separation circuit 34. Here, when photons are simultaneously output from the two output ports of the light separation circuit 34, it is either (1) or (2) shown below. That is,
(1) After the correlated photon pair of p-polarized light passes through the third port 71-3 of the second polarization beam splitter 71 and the first port 73-1 of the half mirror 73, the second pair of the half mirror 73 Was output as p-polarized light to port 73-2?
(2) The correlated photon pair of s-polarized light passes through the second port 71-2 of the second polarization beam splitter 71, the second 90-degree polarization rotator 72, and the third port 73-3 of the half mirror 73. After that, it is output to the third port 73-2 of the half mirror 73 as p-polarized light.

  Under such a condition that the signal light and the idler light are simultaneously output from the two output ports of the light separation circuit 34, the signal light and the idler light generated in the cases (1) and (2). A delay time of τ is given between the correlated photon pairs.

  If the incoherent light source is optically pulsed and the delay time τ is sufficiently larger than the pulse width, the correlated photon pair output from the two output ports of the optical separation circuit 34 is a correlated photon with zero relative delay time. The pair and the correlated photon pair of relative delay time τ are superposed, that is, a conditional time-position quantum entangled photon pair can be generated.

  The difference between the correlated photon pair generating apparatus described with reference to FIGS. 12, 13, 14, and 17 and the first and second correlated photon pair generating apparatuses described with reference to FIGS. It occurs as follows.

  That is, the coherence in time-position quantum entanglement is determined by the coherence time of the excitation light source that generates SPDC or SFWM. In the case of the time-position quantum entangled photon pair output from the first and second correlated photon pair generators shown in FIGS. 10 and 15, the coherence time is several tens of ps (reciprocal of the SHG bandwidth). For example, quantum key distribution must be performed using a delay interferometer with a shorter delay time τ.

  On the other hand, in the time-position entangled photon pair output from the correlated photon pair generator described with reference to FIGS. 12, 13, 14, and 17, the p-polarized light generated by the original polarization entanglement Correlated photon pairs and s-polarized correlated photon pairs have high coherence. Therefore, the time-position quantum entangled photon pair generated by using it also has high coherence. That is, regardless of the coherence time of the excitation light source, the delay time τ can be freely designed according to the system configuration requirements and the like. Therefore, in addition to the effects of the first and second correlated photon pair generation devices, the following effects can be expected. That is, a time-position quantum entangled photon pair having a high degree of freedom in designing the delay time τ and having high coherence can be generated.

  In addition, in the time-position entangled photon pair generator, the incoherent light source inserts an optical modulator at any appropriate location constituting the incoherent light source, or pulses the current or light source that excites the incoherent light source, etc. By taking the means, it is assumed that the light source is an incoherent light source that generates incoherent light in the form of light pulses.

<Modification of correlated photon pair generator>
The connection order of the optical bandpass filter, the optical lowpass filter, and the like in the first and second correlated photon pair generation apparatuses described above is not limited to the order of the configuration diagram of the embodiment of the present invention. For example, in FIGS. 12 to 14, the arrangement of the optical high-pass filter 32 and the polarization rotator 39 may be interchanged. In addition, the optical bandpass filter 53 in FIG. 17 may be inserted in any place on the optical path connecting the incoherent light source 52 and the first port 63-1 of the WDM filter 63. Further, the arrangement of the optical low-pass filter 54 and the optical rejection filter 55 in FIGS. 15 and 17 may be interchanged. Further, the order of the first optical high-pass filters 35 and 57 and the second optical high-pass filters 36 and 58 in FIGS. 11 and 16 may be switched. An optical low-pass filter may be used instead of the optical high-pass filter.

  In addition, in the polarization entangled photon pair generation device using the Sagnac loop interferometer shown in FIGS. May be left and right circularly polarized light. In addition, if the insertion loss of subsequent dichroic filters or polarizing beam splitters is polarization-dependent, or if the optical coupling efficiency is bi-directionally input to the nonlinear optical device, these are compensated. For this reason, it may be preferable that the polarization state of the light after the polarization rotators 39 and 62 is slightly deviated from the 45 degree polarization. Even in this case, the effect of the present invention can be obtained. In order to cope with such a case, it is most desirable to use a half-wave plate whose optical axis direction is rotatable as the polarization rotators 39 and 62.

  Further, as the nonlinear optical device, an optimal device may be selected as appropriate according to the required wavelength conversion light wavelength, the entangled photon pair wavelength, etc. It is not limited. That is, a waveguide type device or a bulk crystal may be used. Further, ultraviolet light or infrared light may be handled.

  In the present invention, an operation verification experiment was performed in the case of a quasi-phase matched second-order nonlinear optical device having a periodic polarization reversal structure. The effect of the present invention is, for example, that the polarization reversal period is changed along the light propagation direction. Even in the case of the quasi phase matching second-order nonlinear optical device having a so-called chirped grating structure, the operation principle of the present invention can be considered.

  In addition, as in the time-position entangled photon pair generating device, and also in the first and second correlated photon pair generating devices, an optical modulator is inserted at any appropriate location constituting the incoherent light source, or Prepare a pulsed incoherent light source using a method such as exciting the current of the coherent light source or pulsing the light source, and as a result, generate a pulsed wavelength-converted light, correlated photon pair, or entangled photon pair This is also included in the embodiment of the present invention.

1: First nonlinear optical device
2, 22, 52: Incoherent light source
3, 4, 7, 23, 24: Optical coupling system
5: Optical amplifier
6, 37, 38, 53, 59, 60: Optical bandpass filter
8: Free space light acquisition device
21: nth-order nonlinear optical device
30: Light source device
31: Second nonlinear optical device
32: Optical high-pass filter
33, 55: Optical rejection filter
33-1: First optical rejection filter
33-2: Second optical rejection filter
34, 56: Optical separation circuit
35, 57: First optical high-pass filter
36, 58: Second optical high-pass filter
39, 62: Polarization rotator
40: Dichroic filter
41, 64, 71: Polarizing beam splitter
42, 65, 72: 90 degree polarization rotator
51: Second-order nonlinear optical device
54: Optical low-pass filter
61: Polarizer
63: WDM filter
70: Mode converter
73: Half mirror

Claims (23)

n is an integer of 2 or more, light velocity in vacuum is c, phase matching for n-th order sum frequency generation (SFG) is realized, and maximum intensity converted light is obtained. A first nonlinear optical device having an n-order nonlinear optical effect in which the optical frequency of the converted light is f ₀ and the phase matching wavelength or the pseudo phase matching wavelength is λ _PMW (= nc / f ₀ ),
An incoherent light source that outputs incoherent light having a continuous optical frequency spectrum including the wavelength component of λ _PMW ,
A light source device, wherein the first nonlinear optical device generates SFG light having a wavelength λ _PMW / n by n-th order SFG for the incoherent light.   The light source apparatus according to claim 1, wherein the first nonlinear optical device is a second-order nonlinear optical device. The curve giving the optical frequency spectrum of the incoherent light source is symmetric about the optical frequency axis about the optical frequency f _0/2 ,
The full width at half maximum Δf _pump of the optical frequency curve and the full width at half maximum Δf _{SHG of the} curve giving the SHG light intensity with respect to the optical frequency of the SHG light by the second harmonic generation (hereinafter referred to as SHG) are Δf _pump ≦ The light source device according to claim 2, wherein a relationship of 1.2Δf _SHG is satisfied. The curve giving the optical frequency spectrum of the incoherent light source is symmetric about the optical frequency axis about the optical frequency f _0/2 ,
The full width at half maximum Δf _pump of the optical frequency curve and the full width at half maximum Δf _{SHG of the} curve that gives the SHG light intensity with respect to the optical frequency of the SHG light by second harmonic generation (hereinafter referred to as SHG) are Δf _pump > The light source device according to claim 2, wherein a relationship of 0.7Δf _SHG is satisfied. The incoherent light source is configured to collect output light from a plurality of spontaneous emission light sources that output incoherent light in one place,
The light source apparatus according to claim 1, wherein the condensed incoherent light is input to the first nonlinear optical device. The incoherent light source includes a plurality of spontaneous emission light sources that output incoherent light,
Irradiating the plurality of locations on the first nonlinear optical device with output light from the plurality of incoherent light sources to output SFG light,
5. The light source device according to claim 1, wherein the SFG light generated at the plurality of locations is collected and output. The incoherent light source includes a spontaneous emission light source and an optical amplifier,
5. The light source device according to claim 1, wherein incoherent light output from the spontaneous emission light source is amplified by the optical amplifier and then input to the first nonlinear optical device. . The incoherent light source includes a spontaneous emission light source and an optical bandpass filter,
The incoherent light output from the spontaneous emission light source is narrowed in the optical spectrum band by the optical bandpass filter and input to the first nonlinear optical device. The light source device according to claim 1. The incoherent light source includes a spontaneous emission light source, an optical bandpass filter, and an optical amplifier,
The incoherent light output from the spontaneous emission light source is narrowed in the optical spectrum band by the optical bandpass filter, amplified by the optical amplifier, and then input to the first nonlinear optical device, The light source device according to any one of claims 1 to 4. The incoherent light source includes a free space light acquisition device that acquires free space light and an optical bandpass filter,
The free space light, which is incoherent light, is narrowed in the optical spectrum band by the optical bandpass filter and input to the first nonlinear optical device. The light source device according to item. The incoherent light source includes a free space light acquisition device that acquires free space light, an optical bandpass filter, and an optical amplifier,
The free-space light, which is incoherent light, is narrowed in an optical spectrum band by the optical bandpass filter, amplified by the optical amplifier, and then input to the first nonlinear optical device. Item 5. The light source device according to any one of Items 1 to 4. The light source device according to any one of claims 1 to 11,
An optical high-pass filter that removes light components in the vicinity of the optical frequency f ₀ / n of the incoherent light output from the light source device and transmits only the SFG light by transmitting the light component in the vicinity of the optical frequency f ₀ ;
A second nonlinear optical device;
An optical rejection filter for removing the SFG light;
An optical separation circuit,
After the output light from the light source device passes through the optical high-pass filter, it is input to the second nonlinear optical device,
In the second nonlinear optical device, the correlated photon pair consisting of a signal light component and an idler light component generated by natural parametric down-conversion that is a second-order nonlinear optical effect or natural four-wave mixing that is a third-order nonlinear optical effect Generate
The correlated photon pair generated by the second nonlinear optical device is spatially separated into a signal light component and an idler light component by the light rejection filter and the light separation circuit, and is output. Twin generator. The light source device according to any one of claims 1 to 11,
An optical high-pass filter that removes light components in the vicinity of the optical frequency f ₀ / n of the incoherent light output from the light source device and transmits only the SFG light by transmitting the light component in the vicinity of the optical frequency f ₀ ;
A second nonlinear optical device that exhibits a second-order or third-order nonlinear optical effect;
A first optical high-pass filter that selectively transmits light at a frequency higher than the optical frequency f ₀ of the wavelength-converted light and reflects other light components;
A second optical high-pass filter that selectively reflects light at a frequency lower than the optical frequency f ₀ of the wavelength-converted light,
After the output light from the light source device passes through the optical high-pass filter, it is input to the second nonlinear optical device,
In the second nonlinear optical device, the correlated photon pair consisting of a signal light component and an idler light component generated by natural parametric down-conversion that is a second-order nonlinear optical effect or natural four-wave mixing that is a third-order nonlinear optical effect Generate
Output light from the second nonlinear optical device is input to the first optical high-pass filter, and reflected light of the first optical high-pass filter is input to the second optical high-pass filter,
A correlated photon pair generating apparatus, wherein a signal light component is output from a transmission output of the first optical high-pass filter and an idler light component is output from a reflection output of the second optical high-pass filter after being spatially separated. The light source device according to any one of claims 1 to 11,
An optical high-pass filter that transmits only SFG light output from the light source device;
A second nonlinear optical device of type-I type that exhibits a second-order nonlinear optical effect;
An optical rejection filter for removing the SFG light;
A light separation circuit that spatially separates and outputs a correlated photon pair generated by the second nonlinear optical device into a signal light component and an idler light component;
A polarization rotator that rotates the polarization of the SFG light by 45 degrees;
The SFG light that is input from the first port is output to the second port, and the optical coupling / demultiplexing that outputs the correlated photon pair component including the signal light component and the idler light component input from the second port to the third port And
Separates and outputs the SFG light input from the first port of the optical multiplexer / demultiplexer to the second and third ports into polarization components that are orthogonal to each other, and has the same polarization direction as the polarization components that have undergone polarization separation A pair of correlated photons of the polarization beam splitter that is input to the second and third ports, respectively, and combined and output to the first port;
A 90-degree polarization rotator that rotates the polarization of input light by 90 degrees,
The second nonlinear optical device and the 90-degree polarization rotator are arranged in a loop path connecting the second port and the third port of the polarization beam splitter;
The polarization rotator is connected to a first port of the optical multiplexer / demultiplexer;
A first port of the polarization beam splitter is connected to a second port of the optical multiplexer / demultiplexer;
The optical rejection filter is connected to a third port of the optical multiplexer / demultiplexer;
After the output light from the light source device passes through the optical high-pass filter and the polarization rotator, the light passes through the first port and the second port of the optical multiplexer / demultiplexer, and passes through the first port and the second port as 45-degree polarized light. Input to port 1,
First and second SFG lights propagating clockwise and counterclockwise through the loop path output from the second port and the third port of the polarization beam splitter are bidirectionally transmitted to the second nonlinear optical device. The first and second correlated photon pairs propagating clockwise and counterclockwise in the loop path, which are input and composed of signal light and idler light by parametric fluorescence, are generated in both directions,
The first and second correlated photon pairs are polarized and combined in the polarization beam splitter and output to the first port;
The correlated photon pair synthesized by polarization is output as a entangled photon pair after passing through the second port, the third port, the optical rejection filter, and the optical separation circuit of the optical multiplexer / demultiplexer. Polarized quantum entangled photon pair generator. The light source device according to any one of claims 1 to 11,
An optical high-pass filter that transmits only SFG light output from the light source device;
A second nonlinear optical device of type-I type that exhibits a second-order nonlinear optical effect;
An optical rejection filter for removing the SFG light;
A light separation circuit that spatially separates and outputs a correlated photon pair generated by the second nonlinear optical device into a signal light component and an idler light component; a polarization rotator that rotates the polarization of the SFG light by 45 degrees;
The SFG light input from the first port is separated and output to the second and third ports as polarization components that are orthogonal to each other, and the correlated photon pair having a polarization direction orthogonal to the polarization components that have been polarized and separated A polarization beam splitter that is input to the second and third ports respectively, and is combined with the polarization and output to the fourth port;
A 90-degree polarization rotator that rotates the polarization of input light by 90 degrees,
The second nonlinear optical device and the 90-degree polarization rotator are arranged in a loop path connecting the second port and the third port of the polarization beam splitter;
The polarization rotator is connected to a first port of the polarization beam splitter;
The optical rejection filter is connected to a fourth port of the polarizing beam splitter;
After the output light from the light source device passes through the optical high-pass filter and the polarization rotator, it is input to the first port of the polarization beam splitter as 45-degree polarized light,
First and second SFG lights propagating clockwise and counterclockwise through the loop path output from the second port and the third port of the polarization beam splitter are bidirectionally transmitted to the second nonlinear optical device. The first and second correlated photon pairs propagating clockwise and counterclockwise in the loop path, which are input and composed of signal light and idler light by parametric fluorescence, are generated in both directions,
The first and second correlated photon pairs are polarized and combined in the polarization beam splitter and output to the fourth port;
The polarization entangled photon pair generating apparatus characterized in that the correlated photon pair synthesized by polarization is output as a entangled photon pair after passing through the optical rejection filter and the optical separation circuit. The light source device according to any one of claims 1 to 11,
An optical high-pass filter that transmits only SFG light output from the light source device;
Type-II type second nonlinear optical device that expresses the second-order nonlinear optical effect;
First and second optical rejection filters for removing the SFG light;
A polarization rotator that rotates the polarization of the SFG light by 45 degrees;
The SFG light that is input from the first port is output to the second port, and the optical coupling / demultiplexing that outputs the correlated photon pair component including the signal light component and the idler light component input from the second port to the third port And
The SFG light input from the first port is separated and output to the second and third ports into polarization components that are orthogonal to each other, and a correlated photon pair having a polarization direction orthogonal to the polarization components that have undergone polarization separation is output. A polarization beam splitter that is input to the second and third ports, and is combined and output to the fourth port.
A 90-degree polarization rotator that rotates the polarization of input light by 90 degrees,
The second nonlinear optical device and the 90-degree polarization rotator are arranged in a loop path connecting the second port and the third port of the polarization beam splitter;
The polarization rotator is connected to a first port of the optical multiplexer / demultiplexer;
A first port of the polarization beam splitter is connected to a second port of the optical multiplexer / demultiplexer;
The first optical rejection filter is connected to a third port of the optical multiplexer / demultiplexer;
The second optical rejection filter is connected to a fourth port of the polarizing beam splitter;
After the output light from the light source device passes through the optical high-pass filter and the polarization rotator, the light passes through the first port and the second port of the optical multiplexer / demultiplexer, and passes through the first port and the second port as 45-degree polarized light. Input to port 1,
First and second SFG lights propagating clockwise and counterclockwise through the loop path output from the second port and the third port of the polarization beam splitter are bidirectionally transmitted to the second nonlinear optical device. The first and second correlated photon pairs propagating clockwise and counterclockwise in the loop path, which are input and composed of signal light and idler light by parametric fluorescence, are generated in both directions,
Correlated photon pairs generated in both directions are polarized and separated into signal light component and idler light component in the polarization beam splitter, respectively, and output to the first port and the fourth port, respectively.
2. A polarization entangled photon pair generating apparatus, wherein quantum entangled photon pairs are output from the first optical rejection filter and the second optical rejection filter. Let c be the speed of light in vacuum, and f _{0 represents} the optical frequency of the converted light when phase matching for sum frequency generation (hereinafter abbreviated as SFG) is achieved and converted light of maximum intensity is obtained. SFG light from incoherent light is generated with a phase matching wavelength or pseudo phase matching wavelength of λ _PMW (= 2c / f ₀ ), and natural parametric down conversion (hereinafter referred to as SPDC) is performed. A generated second-order nonlinear optical device;
And incoherent light source for outputting incoherent light including a light frequency f _0/2 near the frequency components,
An optical bandpass filter for transmitting only the optical frequency f _0/2 near the light components of the incoherent light,
An optical low-pass filter to remove the optical frequency f ₀ near the optical components, which transmit light components including the optical frequency f _0/2 near the wavelength components of the SPDC photon pairs,
A light rejection filter which transmits only the wavelength components of the SPDC photon pair to remove the optical frequency f _0/2 near the incoherent light component,
It is equipped with an optical separation circuit that spatially separates and outputs correlated photon pairs consisting of signal photons generated by SPDC and idler photons,
The output light from the incoherent light source is input to the second-order nonlinear optical device after being band-limited to an optical frequency f _0/2 near the optical component by the optical bandpass filter,
In the second-order nonlinear optical device, SFG light is generated using the input incoherent light component as excitation light, SPDC is expressed using the SFG light as excitation light, and a correlated photon pair consisting of signal photons and idler photons is generated. Generate
A correlated photon pair generation apparatus, wherein unnecessary wavelength components other than correlated photon pair wavelength components in output light from the second-order nonlinear optical device are removed by the optical low-pass filter and the optical rejection filter. Let c be the speed of light in vacuum, and f _{0 represents} the optical frequency of the converted light when phase matching for sum frequency generation (hereinafter abbreviated as SFG) is achieved and converted light of maximum intensity is obtained. SFG light from incoherent light is generated with a phase matching wavelength or pseudo phase matching wavelength of λ _PMW (= 2c / f ₀ ), and natural parametric down conversion (hereinafter referred to as SPDC) is performed. A generated second-order nonlinear optical device;
An optical low-pass filter to remove the optical frequency f ₀ near the optical components, which transmit light components including the optical frequency f _0/2 near the wavelength components of the SPDC photon pairs,
And incoherent light source for outputting incoherent light including a light frequency f _0/2 near the frequency components,
An optical bandpass filter for transmitting only the optical frequency f _0/2 near the light components of the incoherent light,
A first optical high-pass filter that selectively transmits light on a higher frequency side than the transmission incoherent optical band determined by the optical band-pass filter and reflects other light components;
A second optical high pass filter that selectively reflects light on a lower frequency side than the transmission incoherent optical band determined by the optical band pass filter;
The reflected light of the first optical high pass filter is input to the second optical high pass filter,
A correlated photon pair generating apparatus, wherein a signal light component is output from a transmission output of the first optical high-pass filter and an idler light component is output from a reflection output of the second optical high-pass filter after being spatially separated. Let c be the speed of light in vacuum, and f _{0 represents} the optical frequency of the converted light when phase matching for sum frequency generation (hereinafter abbreviated as SFG) is achieved and converted light of maximum intensity is obtained. Type-I type second-order nonlinear optics that generates SFG light from incoherent light and generates natural parametric down-conversion with λ _PMW (= 2c / f ₀ ) as the phase-matching wavelength or quasi-phase-matching wavelength The device,
And incoherent light source for outputting incoherent light including a light frequency f _0/2 near the frequency components,
An optical bandpass filter that transmits a wavelength component near the optical frequency f _0/2 ,
An optical low-pass filter that removes SFG light having a wavelength component near the optical frequency f ₀ ,
An optical rejection filter that removes incoherent light components that pass through the optical bandpass filter;
A light separation circuit that spatially separates and outputs a correlated photon pair composed of a signal light component and an idler light component generated by the second-order nonlinear optical device into a signal light component and an idler light component;
A polarizer,
A polarization rotator that rotates the polarization of the incoherent light component transmitted through the polarizer by 45 degrees;
The incoherent light component input from the first port is output to the second port, and the correlated photon pair component composed of the signal light component and the idler light component input from the second port is output to the third port. A duplexer,
The light input from the first port is separated and output to the second and third ports into polarization components that are orthogonal to each other, and the light having the same polarization direction as the polarization-separated polarization components is respectively output to the second and second ports. A polarization beam splitter that is input to the port of 3 and is combined with and polarized to the first port; and
A 90-degree polarization rotator that rotates the polarization of input light by 90 degrees,
The second-order nonlinear optical device and the 90-degree polarization rotator are arranged in a loop path connecting the second port and the third port of the polarization beam splitter,
The optical bandpass filter, the polarizer, and the polarization rotator are connected between the first port of the optical multiplexer / demultiplexer and the incoherent light source,
A first port of the polarization beam splitter is connected to a second port of the optical multiplexer / demultiplexer;
The optical low-pass filter, the optical rejection filter, and the optical separation circuit are connected in this order to a third port of the optical multiplexer / demultiplexer,
The output light from the incoherent light source passes through the optical bandpass filter, the polarizer, and the polarization rotator, and then passes through the first port and the second port of the optical multiplexer / demultiplexer as the 45-degree polarized light. Input to the first port of the polarizing beam splitter,
The incoherent light component propagating clockwise and counterclockwise through the loop path output from the second port and the third port of the polarization beam splitter is input bidirectionally to the second-order nonlinear optical device, and First and second SFG light for the incoherent light component is generated in the second-order nonlinear optical device, and both first and second correlated photon pairs consisting of signal light and idler light are generated by parametric down-conversion to the SFG light. Occur
The first and second correlated photon pairs generated in both directions are combined in the polarization beam splitter and output to the first port,
The correlated photon pair synthesized by polarization is output as the entangled photon pair after passing through the second port, the third port, the optical low-pass filter, the optical rejection filter, and the optical separation circuit of the optical multiplexer / demultiplexer. Polarized quantum entangled photon pair generator characterized in that The polarization quantum entangled photon pair generation device according to claim 14 or 15 is further overlapped with a method of distributing a plurality of photons present in a time slot to a photon pair, In order to form a correlated photon pair having a quantum correlation at the time position, a mode converter that generates a relative delay time difference between the optical paths between two photons whose polarization planes are orthogonal to each other,
The incoherent light source is an incoherent light source that generates optical pulse-shaped incoherent light,
In the mode converter, the relative delay time difference is set to be sufficiently larger than the pulse width of the incoherent light, and the time converter is connected to the front stage or the rear stage of the optical rejection filter. Quantum entangled photon pair generator. The polarization entangled photon pair generation device according to claim 16, further comprising a method of distributing a plurality of photons present in the photon pair in time slots, and a time position between the photon pairs. A mode converter that generates a relative delay time difference between optical paths between two photons whose planes of polarization are orthogonal to each other,
The incoherent light source is an incoherent light source that generates optical pulse-shaped incoherent light,
In the mode converter, the relative delay time difference is set to be sufficiently larger than the pulse width of the incoherent light, the front stage or the rear stage of the first optical rejection filter, or the second optical rejection filter. A time-positioned entangled photon pair generator characterized by being connected to the preceding stage or the subsequent stage. The polarization entangled photon pair generator according to claim 19,
Furthermore, in order to form a correlated photon pair having a quantum correlation at the time position between the photon pairs in a state where the distribution method of each of the plurality of photons existing in the photon pair is superimposed on the time slot, Comprises a mode converter that generates a relative delay time difference between optical paths between two photons orthogonal to each other,
The incoherent light source is an incoherent light source that generates optical pulse-shaped incoherent light,
The mode converter is characterized in that the relative delay time difference is set to be sufficiently larger than the pulse width of the incoherent light, and is connected to a front stage or a rear stage of the optical low-pass filter. Tangle photon pair generator. The mode converter is
A second polarization beam splitter that separates and outputs the correlated photon pair input from the first port into polarization components orthogonal to each other to the second and third ports;
A second 90 degree polarization rotator that rotates the polarization of the correlated photon pair by 90 degrees;
A half branching the correlated photon pair input from the first port equally to the second and fourth ports and equally branching the correlated photon pair input from the third port to the second and fourth ports With a mirror,
A third port of the second polarizing beam splitter and a first port of the half mirror are connected;
The second port of the second polarization beam splitter, the second 90-degree polarization rotator, and the third port of the half mirror are connected in this order,
An optical delay time generated in an optical path between the third port of the second polarizing beam splitter and the first port of the half mirror;
23. The optical delay time generated in the optical path between the second port of the second polarizing beam splitter and the third port of the half mirror is different. Time-entangled entangled photon pair generator.

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