JP6533171B2 - Optical comb generator - Google Patents

Description

  The present invention relates to an optical comb generator used in an optical communication system and an optical measurement system.

  In current optical communication systems, wavelength division multiplexing (WDM) technology is widely used, in which channels are defined at fixed frequency intervals and optical signals are mounted, as the amount of communication information increases. Furthermore, in recent years, in order to increase frequency utilization efficiency, a multi-level modulation optical signal represented by quadrature phase shift keying (QPSK) or quadrature phase amplitude modulation (QAM) is used, so the signal-to-noise ratio (S / N ratio) High optical signal generation is required.

  In the wavelength division multiplexing system, it is necessary to use a wider signal band in order to transmit a larger capacity optical signal, and a multi-wavelength light source having a larger number of wavelengths is required. For this reason, wavelength division multiplexing requires a very large number of light sources. For example, in order to place signals at 100 GHz intervals in a generally used C band (about 30 nm), 38 light sources will be required.

  Further, as capacity utilization is increased by frequency utilization efficiency, a method called Nyquist WDM or a super channel, in which the frequency intervals of signals are closely packed, is considered promising. For example, in order to arrange signals at 25 GHz intervals, 150 light sources, which are four times the 100 GHz intervals, are required.

  Furthermore, if the frequency intervals are closely packed, the accuracy with respect to the frequency between the signals becomes severe. This is because when there is a frequency fluctuation, the signals overlap with one another, making it difficult to identify the signals. Therefore, a highly accurate multi-wavelength light source is required.

  For this reason, in recent years, it is possible to simultaneously generate a plurality of optical carriers, that is, to generate an optical carrier (optical comb) having a narrow spectral line width arranged at a constant frequency interval. It is expected to use an optical comb source of precision. In this specification, each light wave constituting an optical comb is also referred to as a comb.

As a conventional method of generating an optical comb, for example, a method of generating a side band by driving a high-speed phase or intensity modulator (optical modulator) represented by a LiNbO ₃ modulator with a sine wave (conventional method 1: For example, a method using a third-order nonlinear optical medium such as non-patent document 1) or highly non-linear fiber is known (conventional method 2: see, for example, non-patent document 2).

Kazuhiro Imai, Motonobu Kosho "Precision distance measurement using modulated optical comb", Laser Research Vol. 42, No. 9 (2014) K. Imai, M. Kourogi, B. Widiyatmoko and M. Ohtsu, "12 THz frequency difference measurement and noise analysis of an optical frequency combination in optical fiber", IEEE. J. Quantum Electronics, Vol 35, NO: 4, April 1999

  However, the above-described conventional methods 1 and 2 have the following problems.

[Problem of Conventional Method 1]
In the conventional method 1 in which the optical modulator is driven with a sine wave, it is difficult to create an optical comb with a wide frequency interval of signals because the electrical band is limited (20 to 30 GHz). In addition, there is a problem that the number of combs is small because the power of the electric amplifier that drives the optical modulator is limited. It has been difficult to generate an optical carrier wave of 100 waves or more, typically with about 10 to 30 waves.

  If an optical modulator is made into a resonator (cavity), a wide band comb can be generated, but the comb interval is determined by the electrical band. Furthermore, since the resonator is used, the resonator length needs to be precisely controlled, and the configuration becomes complicated.

Also, usually, a LiNbO ₃ modulator with a Ti diffused waveguide is used as an optical modulator, and the power tolerance is low, and only a few tens of mW can be input, resulting in a few mW output. there were.

  Although the bulk crystal modulator can be used for power, it is not suitable for comb generation with a frequency interval of 10 GHz or more because high speed modulation becomes difficult. If a 150-wave comb is output at 1.5 mW, the power of each lightwave will be 0.01 mW (-20 dBm). This power is insufficient as a light source used for WDM transmission.

  In fact, when using as an optical carrier group in a WDM transmission system, it is necessary to amplify the comb signal with an optical amplifier such as EDFA (erbium-doped fiber optical amplifier), but in an optical amplifier, the signal may be weak. As the S / N ratio of the output deteriorates to such an extent, there is a problem that it is difficult to secure the S / N ratio in the transmitter as compared with the case of using an independent light source.

[Problems of Conventional Method 2]
Conventional method 2 using a third-order nonlinear optical medium such as highly nonlinear fiber can generate a comb of 100 waves or more because there is a wide phase matching band when four-wave mixing in the third-order nonlinear optical medium is used .

  However, there is a problem that power can not be input by stimulated Brillouin scattering (SBS) in an optical fiber. For this reason, the output power is lowered, and there is a problem that deterioration of the signal quality of the optical comb can not be avoided as in the conventional method 1 of driving the above-described optical modulator with a sine wave.

  That is, in the conventional method of generating an optical comb, there is a problem that it is difficult to form a wide-band, high-power optical comb.

  The present invention has been made to solve such problems, and the object of the present invention is to provide an S / N ratio comparable to that of an independent light source with a simple configuration, and collectively 100 wave classes. An object of the present invention is to provide an optical comb generator capable of generating an optical carrier (optical comb).

In order to achieve such an object, according to the present invention, a light source (1) generating continuous wave light of frequency ω ₀ and a frequency ω ₀ of the continuous wave light generated by the light source (1) are central frequency ω _The optical modulator (2) generates an optical wave group having a frequency ω ₀ ± n × Δω (n is an integer and Δω is an arbitrary frequency width) including _0, and the optical wave group generated by the optical modulator (2) is amplified And a second-order nonlinear optical element (5) for amplifying the light waves in the input optical comb signal, using the optical amplifier (4) and the lightwave group amplified by the optical amplifier (4) as the input optical comb signal. It features.

In the present invention, an optical modulator (2), the frequency omega ₀ of the continuous wave light source (1) is generated as the center frequency, to generate optical waves set frequency ω ₀ ± n × Δω including the center frequency omega ₀ . The generated light waves are amplified by the optical amplifier (4) and sent to the second-order nonlinear optical element (5). The second-order nonlinear optical element (5) takes the lightwave group amplified by the optical amplifier (4) as an input optical comb signal, and propagates the lightwave in the input optical comb signal. Thus, in the present invention, the lightwave group generated by the light modulator (2) is amplified, the lightwave in the amplified lightwave group is amplified, and the lightwave is output as an optical comb (optical comb output signal) It becomes.

  In the above description, as an example, constituent elements on the drawing corresponding to constituent elements of the invention are indicated by reference numerals in parentheses.

According to the present invention, with the frequency ω ₀ of the continuous wave light generated by the light source as the central frequency, a light wave group of the frequency ω ₀ ± n × Δω including the central frequency ω ₀ is generated, and the generated light wave group is amplified. After that, the light waves in this amplified light wave group are propagated, so with a simple configuration, it has an S / N ratio equal to that of an independent light source, and collectively an optical carrier (optical comb) of 100 wave class. It is possible to generate.

FIG. 1 is a diagram showing the configuration of the main part of the optical comb generator according to the first embodiment of the present invention. FIG. 2 is a conceptual view of the wavelength arrangement of two quasi phase matching wavelengths and a light wave group (input light comb signal) consisting of five light waves. FIG. 3 is a diagram for explaining the propagation process of light waves in the input optical comb signal in the second-order nonlinear optical element. FIG. 4 is a diagram showing the configuration of the main part of the optical comb generator according to Embodiment 2 of the present invention. FIG. 5 is a diagram showing how a light wave group from the light modulator is separated into two light wave groups by the wavelength selective switch. FIG. 6 is a diagram showing the configuration of the main part of the optical comb generator according to Embodiment 3 of the present invention. FIG. 7 is a diagram showing the configuration of the main part of the optical comb generator according to the fourth embodiment of the present invention. FIG. 8 is a diagram showing the configuration of the main part of an optical comb generation apparatus according to Embodiment 5 of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

First Embodiment
FIG. 1 shows the configuration of the main part of the optical comb generator 100 according to the first embodiment of the present invention. In the figure, 1 is a light source generating continuous wave light of frequency ω ₀ , 2 is a frequency ω ₀ ± n × Δω including the central frequency ω ₀ with the frequency ω ₀ of the continuous wave light generated by the light source 1 as a central frequency. n is an integer and Δω is an arbitrary frequency width) An optical modulator that generates an optical wave group 3 is a sine wave generator that drives the optical modulator 2 4 is an optical wave group generated by the optical modulator 2 An optical amplifier (EDFA), 5 is a second-order non-linear optical element for propagating the lightwave in the lightwave group amplified by the EDFA 4.

  In this optical comb generator 100, several light waves (light wave group) are generated using ordinary light comb generation means (light source 1, light modulator 2, sine wave generator 3). After the light wave is amplified by the EDFA 4, the light wave is input to the second-order nonlinear optical element 5 as an input light comb signal. Then, by using the nonlinear optical process in the second-order nonlinear optical element 5 to propagate (expand) the light waves in the input optical comb signal, an optical comb (output optical comb signal) of several tens to several hundreds of waves is generated. Generate

In the optical comb generator 100, the light source 1 generates continuous wave light (CW) of frequency ω ₀ , and the continuous wave light (CW) of frequency ω ₀ is input to the optical modulator 2. Optical modulator 2, the center frequency of omega ₀ of the continuous wave light source 1 is generated (CW), it generates a lightwave group frequencies ω ₀ ± n × Δω including the center frequency omega _0.

  In the present embodiment, a lithium niobate modulator is used as the light modulator 2. The lithium niobate modulator 2 is driven by the 25 GHz sine wave generated by the sine wave generator 3, and Δω = 25 GHz interval The light wave group consisting of five light waves is to be generated. Then, the light wave group consisting of the five light waves is amplified to 2 W using the EDFA 4 and input to the second order nonlinear optical element 5 as an input light comb signal.

  In the optical comb generator 100, a PPLN waveguide (lithium niobate waveguide) having two quasi phase matching wavelengths at a frequency interval of 100 GHz in a 1.55 μm band is manufactured in the second-order nonlinear optical element 5 . The method of producing the PPLN waveguide is exemplified below.

First, on the Zn-doped LiNbO ₃ , a periodic electrode having a periodic phase modulation with a period of 17 μm and a phase modulation period of about 10 mm was formed. Next, a polarization inversion grating corresponding to the above electrode pattern was formed in Zn: LiNbO3 by an electric field application method. Then, Zn has the periodically poled: LiNbO3 (Z-cut Zn: LiNbO3 substrate) was subjected to bonding directly on LiTaO ₃ as a clad, and firmly bonding the two substrates by heat treatment at 500 ° C.. Next, the core layer was thinned to about 5 μm by polishing, and a ridge-type optical waveguide was formed using a dry etching process. The temperature of the waveguide can be adjusted by a Peltier element, and the length of the waveguide is 50 mm. The waveguide (PPLN waveguide) formed in this manner is a module capable of inputting and outputting light with a polarization maintaining fiber of 1.55 μm band.

  Here, the wavelength arrangement of the two quasi-phase matching wavelengths of the second-order nonlinear optical element 5 and the light wave group consisting of five light waves will be described. FIG. 2 is a conceptual view of the wavelength arrangement of the light wave group (input light comb signal) consisting of two quasi phase matching wavelengths and five light waves in the light comb generator 100. As shown in FIG.

A light wave group generated by the light modulator 2 consists of five light waves S ₀ , S _-1 , S _-2 , S ₊₁ , and S _{+2 at} intervals of Δω = 25 GHz. The frequency difference between the highest frequency light wave S ₊₂ and the lowest frequency light wave S _-2 among the five light waves S ₀ , S _-1 , S _-2 , S ₊₁ , S ₊₂ is just 100 GHz. It has become.

On the other hand, the second-order nonlinear optical element 5 has two quasi phase matching wavelengths λ1 and λ2 at 100 GHz intervals. In the present embodiment, among the two pseudo phase matching wavelengths λ1 and λ2, the pseudo phase matching wavelength λ1 and the wavelength of the lightwave S _{+ 2} having the highest frequency in the lightwave group generated by the optical modulator 2 are the same. Thus, the wavelengths are arranged such that the quasi phase matching wavelength λ2 and the wavelength of the lowest frequency lightwave S _{-2 in} the lightwave group generated by the light modulator 2 are the same.

  The two quasi phase matching wavelengths λ1 and λ2 mentioned here refer to the phase matching wavelengths for the second harmonic generation (SHG) or sum frequency generation (SFG) process by the second order nonlinear optical element 5. That is, for the 1.56 μm band input, this is for a wavelength conversion process in which the converted light is in the 0.78 μm band. Here, for convenience, the quasi phase matching wavelength for the SHG will be described.

  The quasi phase matching wavelengths λ1 and λ2 for SHG have two peaks at 100 GHz intervals, and the half width of each is about 0.1 nm. In the second-order nonlinear optical element 5, conversion by a difference frequency generation (DFG) process occurs in addition to the second harmonic generation (SHG) or sum frequency generation (SFG) process. This is caused by light generated by the second harmonic generation (SHG) or sum frequency generation (SFG) process as excitation light. The quasi phase matching wavelength for this DFG process will be described as the quasi phase matching wavelength for DFG. The band of the quasi phase matching wavelength for DFG can be wider than the band of the quasi phase matching wavelength for SHG by using the Z-cut PPLN waveguide as shown in the present embodiment, and in the present embodiment, The fabricated device has a band of about 60 nm.

Next, the process of propagating light waves in the input optical comb signal in the second-order nonlinear optical element 5 will be described with reference to FIG. A lightwave group consisting of five lightwaves S ₀ , S _-1 , S _-2 , S ₊₁ , and S ₊₂ from the optical modulator 2 is amplified by the EDFA 4 and then quasi phase-matched wavelength λ1 for two SHG processes. , Λ 2 as an input optical comb signal (FIG. 3A).

Here, the frequency of the light wave S ₀ is the center frequency ω ₀ , the frequency of the light wave S _-1 is ω _-1 = ω ₀ -Δω, the frequency of the light wave S _-2 is ω ₂ = _{2 0} -ω ₂ -Δω, the light wave S ₊₁ of frequency ω ₊₁ = ω ₀ + Δω, the frequency of the light wave S ₊₂ and ω ₊₂ = ω ₀ + 2Δω. Further, the frequency of the pseudo phase matching wavelength λ1 is ω ₁ , and the frequency of the pseudo phase matching wavelength λ ₂ is ω ₂ . Here, Δω corresponds to 25 GHz. In addition, about the frequency (omega), the word a frequency may be abbreviate | omitted and it may only be described with (omega).

In this wavelength arrangement, the wavelength of the light wave S ₊₂ of ω ₊₂ coincides with the first quasi phase matching wavelength λ 1 (ω ₁ ) for SHG, and the second harmonic generates a light wave of 2ω ₊₂ second-order It is generated in the non-linear element 5. Furthermore, in the second-order non-linear element 5, 2ω _{+ 2} −ω ₁ , 2ω _{+ 2} − ω ₀ , 2ω _{+ 2} due to difference frequency generation of the optical comb signal using the generated 2ω _{+ 2} light wave as excitation light. A light wave of -ω _-1 , 2ω ₊₂ -ω _-2 is generated. As a result, a new light wave is generated in the direction of high frequency in the form of being folded around the frequency ω ₊₂ (FIG. 3 (b)).

Also, the wavelength of the lightwave of ω _-2 matches the second quasi phase matching wavelength λ ₂ (ω ₂ ) for SHG, and the lightwave of 2ω- ₂ is generated in the second-order nonlinear element 5 by the second harmonic generation. Be done. Furthermore, in the second-order nonlinear element 5, the difference frequency generation of the optical comb signal using the generated 2ω _-2 light wave as excitation light generates 2ω _-2 -ω _-1 , 2ω _-2 -ω ₀ , 2ω _-2 A light wave of -ω ₊₁ , 2ω _-2 -ω ₊₂ is generated. As a result, a new light wave is generated in the direction of lower frequency in a form of being folded around the frequency ω- ₂ (FIG. 3 (b)).

Furthermore, in the second-order nonlinear element 5, new light waves are generated one after another from the generated light waves. That is, by generating a difference frequency by using the light wave of 2ω ₊₂ −ω ₊₁ , 2ω ₊₂ −ω ₀ , 2ω ₊₂ −ω ₁ , 2ω ₊₂ −ω ₋₂ and the light wave of 2ω ₋₂ as excitation light _{, 2ω -2 - (2ω +2 -ω} +1), 2ω -2 - (2ω +2 -ω 0), 2ω -2 - (2ω +2 -ω -1), 2ω -2 - (2ω +2 A light wave of −ω ₋₂ ) is generated (FIG. 3 (c)). Similarly, the difference frequency with the light of 2ω _-2 -ω _-1 , 2ω _-2 -ω ₀ , 2ω _-2 -ω ₊₁ , 2ω _-2 -ω ₊₂ and the light of 2ω ₊₂ as excitation light Depending on the generation, 2ω ₊ 2-(2ω- _2- ω- ₁ ), 2ω ₊ 2-(2ω- _2- ω ₀ ), 2ω ₊ 2-(2ω- _2- ω _{+ 1} ), 2ω ₊ 2-(2ω A light wave of ₋₂ −ω ₊₂ ) is generated (FIG. 3 (c)).

  Similarly, in the second-order nonlinear element 5, a difference frequency generation process occurs one after another for the two excitation lights, and the light wave in the optical comb signal is propagated. Considering the above-mentioned two conversions (Fig. 3 (c)), the light waves in the optical comb signal increase to 21 waves, and in the third conversion (Fig. 3 (d)), 29 waves and the fourth conversion (Fig. 3) In (e), the number of wavelengths is expanded to 37 waves. As the number of conversions is taken into consideration, the number of wavelengths is further expanded.

  This process has been described in order for the purpose of explanation, but in the actual second-order nonlinear optical element 5, nonlinear processes occur in succession, and light waves in the optical comb signal are proliferated (wavelength conversion is followed by pendulum) The light waves in the light comb signal will increase as it happens). Note that when an optical comb signal of about 40 waves whose phase and frequency are synchronized is generated from an optical comb signal of about 5 waves, an output of 1 W is obtained for an input of 2 W, and 1 in the optical comb signal A high-intensity light output of 25 mW was obtained per wave.

Further, in the above, the light wave of ω ₊₂ is converted to the light wave of 2ω ₊₂ by the second harmonic generation, and the light wave of ω ₋₂ is converted to the light wave of 2ω ₋₂ by the second harmonic generation. In fact, conversion to excitation light is also performed by a process of sum frequency generation (SFG) of generated light waves.

For example, at the same time by the difference frequency generation between the excitation light and the omega ₊₁ lightwave of 2 [omega _+2, although light waves 2 [omega ₊₂ - [omega] ₊₁ occurs when light waves 2 [omega ₊₂ - [omega] ₊₁ occurs, 2 [omega ₊ The sum frequency generation between the ₂ −ω ₁ light wave and the ω _{1 1} light wave also causes conversion to 2ω ₊₂ excitation light. Transfer of energy from the pump light generates a new light wave, but the pump light power does not decrease monotonically, and there is also a transfer process of energy from the new light wave to the pump light, and the light wave It will contribute to the growth of new light waves.

  It can be seen that, in the light wave propagation process, eight waves are proliferated in consideration of one conversion process. That is, as the number of lightwaves in the first optical comb signal (input optical comb signal) increases, it is possible to easily increase the number of wavelengths, using nine waves of input optical comb signals with 25 GHz intervals and a 200 GHz band. Assuming that the first quasi phase matching wavelength λ1 and the second quasi phase matching wavelength λ2 have the same wavelength as the wavelength of the highest frequency lightwave and the wavelength of the lowest frequency lightwave in the input optical comb signal. Even if you think only the 4th conversion, it is propagated (expanded) to 73 waves. In fact, it was possible to generate an optical comb signal of 100 waves or more by the occurrence of more conversions. At this time, a high-intensity light output of 10 mW or more per wave of the optical comb signal is obtained.

  Thus, in the optical comb generating apparatus 100 according to the first embodiment, an optical carrier (optical comb) of 100 wave class is generated collectively with an S / N ratio comparable to that of an independent light source with a simple configuration. It is possible to

  In the first embodiment, the first quasi phase matching wavelength λ1 and the second quasi phase matching wavelength λ2 are the wavelength of the highest frequency lightwave and the wavelength of the lowest frequency lightwave in the input optical comb signal. Although the wavelength arrangement is the same, the first quasi phase matching wavelength λ1 and the second quasi phase matching wavelength λ2 may be matched with the wavelength of any two light waves in the input optical comb signal. .

For optical comb generator of the first embodiment (100), Conceptually speaking, the light source (1) for generating a continuous wave light frequency omega _0, as center frequency of omega ₀ of the continuous wave light source is generated An optical modulator (2) that generates an optical wave group having a frequency ω ₀ ± n × Δω (where n is an integer and Δω is an arbitrary frequency width) including the central frequency ω _0, and the optical wave group generated by the optical modulator an optical amplifier (4) for amplifying and a quasi-phase matching conditions for second harmonic generation between the light waves of the optical wave and 2 [omega ₁ frequency omega _1, the light wave and omega ₁ - [delta light wave of frequency omega ₁ + [delta] A _first quasi-phase matching condition satisfying either or both quasi-phase matching conditions, where (δ is an arbitrary frequency width) and quasi-phase matching condition for sum frequency generation between light waves of 2ω1; for the second harmonic generation between the frequency omega ₂ of the light waves and 2 [omega ₂ of the lightwave A phase matching condition similar, the quasi phase matching conditions with respect to the sum frequency generation between the light wave and omega ₂ - [delta light waves ([delta] is an arbitrary frequency width) and light waves of 2 [omega ₂ frequency omega ₂ + [delta], or on the other hand, or with both quasi-phase matching condition is satisfied second pseudo phase matching conditions, quasi-phase matching for difference frequency generation between the light waves of the optical wave and 2 [omega ₁ - [omega] _X lightwave frequency omega _X frequency 2 [omega ₁ A second-order nonlinear optical element (5) satisfying the conditions and the quasi-phase matching condition for the difference frequency generation between the light wave of 2ω _2, the light wave of frequency ω _{Y and} the light wave of ₂ ω ₂ -ω _Y , matching omega ₁ and omega ₂ and is one of the two quasi-phase matching conditions frequency of the first and second optical wave frequency omega ₀ in lightwave group consisting of light wave ± n × [Delta] [omega containing omega ₀ Or the frequency of any four lightwaves is the first and second quasi-phase matching condition ω ₁ + At least one of or both of δ and ω ₁ −δ, ω ₂ + δ and ω ₂ −δ is satisfied, and the frequencies of the respective light waves on the ω ₁ side and ω ₂ side centering on ω ₀ are ω It can be said that this is an optical comb generator that propagates the light waves in the optical comb signal input by the generation of the difference frequency as _{X 1} , ω _Y.

Second Embodiment
FIG. 4 shows the configuration of the main part of the optical comb generator 200 according to the second embodiment of the present invention. In the optical comb generator 100 (FIG. 1) of the first embodiment, the optical comb generated by the optical modulator 2 is amplified to watt class by the EDFA 4 and then enters the second-order nonlinear optical element 5 as an input optical comb signal. There is a problem in that spontaneous emission noise (ASE noise) from the EDFA 4 is mixed. Therefore, in the optical comb generating apparatus 200 according to the second embodiment, mixing of spontaneous emission noise from the EDFA 4 is suppressed, and an optical comb (output optical comb signal) having a high S / N ratio is generated.

In FIG. 4, the same reference numerals as those in FIG. 1 denote the same or similar components as the components described with reference to FIG. 1, and the description thereof will be omitted. In the optical comb generator 200 of the second embodiment, a light wave composed of five light waves (light waves of frequencies ω ₀ , ω ₋₁ , ω ₋₂ , ω ₊₁ , ω ₊₂ ) generated by the light modulator 2 Wavelength selective switch (WSS) that splits a group into a first lightwave group (lightwaves of frequency ω _-2 , ω ₊₂ ) and a second lightwave group (light waves of frequency ω ₀ , ω _-1 , ω _{+ 1} ) 6 is provided. Further, a first second-order nonlinear optical element 5 (5-1) and a second second-order nonlinear optical element 5 (5-2) are provided as second-order nonlinear optical elements, and First light wave group (light waves of frequency ω ₋₂ , ω ₊₂ ) to the first second-order nonlinear optical element 5 (5-1) through the EDFA 4 and the band pass filter (BPF) 7, and The third lightwave group (lightwaves with frequencies 2ω _-2 and 2ω ₊₂ ) generated by the second-order nonlinear optical element 5 (5-1) as excitation light to the second second-order nonlinear optical element 5 (5-2) I am trying to give it. In addition, the second light wave group (light waves of frequencies ω ₀ , ω ₋₁ , ω ₊₁ ) separated by the wavelength selective switch 6 is input to the second second-order nonlinear optical element 5 (5-2). It is made to input as.

In the optical comb generator 200, the first second-order nonlinear optical element 5 (5-1) and the second second-order nonlinear optical element 5 (5-2) are the second-order nonlinear optical elements 5 in the first embodiment. Similarly, it has a PPLN ridge waveguide formed using the direct bonding method, and has two quasi phase matching wavelengths λ1 and λ2 for the same SHG. The two quasi phase matching wavelengths λ1 and λ2 for this SHG are arranged in the same wavelength as the light waves of frequencies ω ₋₂ and ω ₊₂ .

In this optical comb generator 200, the five light waves (ω ₀ , ω ₋₁ , ω ₋₂ , ω ₊₁ , ω ₊₂₎ that constitute the light wave group generated by the optical modulator 2 by the wavelength selective switch 6 are Among the lightwaves, only the lightwaves of ω _-2 and ω ₊₂ whose wavelengths coincide with the two quasi phase matching wavelengths λ 1 and λ 2 for SHG are taken out as the first lightwave group (see FIG. 5), and the EDFA 4 After being amplified, the signal is input to the first second-order nonlinear optical element 5 (5-1) through the band pass filter 7.

The first second-order nonlinear optical element 5 (5-1) is the second harmonic generation, 2 [omega _-2, to generate a light wave 2 [omega _+2, dichroic the dichroic mirror omega _-2, omega ₊₂ light and 2 [omega The light waves of _-2 and 2ω ₊₂ are separated, and only the light waves of 2ω _-2 and 2ω ₊₂ are taken out as a third light wave group. The third light wave group (2ω _-2 , 2ω ₊₂ light waves) extracted from the first second-order nonlinear optical element 5 (5-1) is the second second-order nonlinear optical element 5 (5-2) Is input as excitation light.

On the other hand, of the five light waves (light waves of ω ₀ , ω ₋₁ , ω ₋₂ , ω ₊₁ , ω ₊₂ ) that constitute the light wave group generated by the light modulator 2 by the wavelength selective switch 6, ω The light waves of ₀ , ω _-1 , and ω ₊₁ are extracted as a second light wave group (see FIG. 5) and input to the second second-order nonlinear optical element 5 (5-2) as an input optical comb signal. In the second second-order nonlinear optical element 5 (5-2), after the light waves of 2ω _-2 and 2ω _{+2 and} the light waves of ω ₀ , ω _-1 , and ω ₊₁ are combined by the dichroic mirror, It is incident on the PPLN waveguide.

  In the second second-order nonlinear optical element 5 (5-2), wavelength conversion is induced one after another due to the generation of the difference frequency, and the number of wavelengths of the optical comb increases. In this configuration, since the input optical comb signal to the second second-order nonlinear optical element 5 (5-2) is not directly amplified by the EDFA 4, an optical comb (output optical comb signal) having a higher S / N ratio is generated. It becomes possible.

Further, in the optical comb generating apparatus 200 of the second embodiment, excitation light is generated using a second-order nonlinear optical element 5 (5-1) different from the second-order nonlinear optical element 5 (5-2) that propagates light waves. By generating the light waves of 2ω ₋₂ and 2ω ₊₂ , it is possible to perform conversion with higher efficiency, and it is possible to increase the number of wavelengths by 1.25 times compared to the first embodiment.

This optical comb generator of the second embodiment (200), Conceptually speaking, the light source (1) for generating a continuous wave light frequency omega _0, as center frequency of omega ₀ of the continuous wave light source is generated An optical modulator (2) that generates an optical wave group having a frequency ω ₀ ± n × Δω (where n is an integer and Δω is an arbitrary frequency width) including the central frequency ω _0, and the optical wave group generated by the optical modulator the wavelength selection switch that separates (6) into a first optical wave group and the second light wave group, and an optical amplifier (4) for amplifying the first optical wave group separated by the wavelength selective switch, the frequency omega ₁ of Quasi-phase-matching conditions for the second harmonic generation between the lightwave and the lightwave of 2ω _1, the lightwave of frequency ω ₁ + δ, the lightwave of ω ₁ −δ (δ is an arbitrary frequency width) and the lightwave of 2ω ₁ Either one or both of the quasi-phase matching conditions for sum frequency generation between A quasi-phase matching condition is satisfied first quasi-phase matching conditions, a quasi-phase matching conditions for second harmonic generation between the frequency omega ₂ of the light waves and 2 [omega ₂ of the light waves, the light waves of frequency omega ₂ + [delta] omega _{A second} pseudo light meeting a pseudo phase matching condition for one or both of the light wave of ₂ −δ (where δ is an arbitrary frequency width) and the quasi phase matching condition for sum frequency generation between the light wave of 2ω ₂ Phase matching condition, quasi phase matching condition for difference frequency generation between light wave of frequency 2ω ₁ and light wave of frequency ω _X and light wave of 2ω ₁ -ω _X , light wave of 2ω ₂ and light wave of frequency ω _Y A center frequency ω ₀ is provided with first and second second-order nonlinear optical elements (5-1, 5-2) that satisfy the quasi phase matching condition for the difference frequency generation with the light wave of 2ω ₂ −ω _Y one of two light waves in the composed light wave group at light wave frequencies ω ₀ ± n × Δω including Or frequency matches the omega ₁ and omega ₂ and a first and second quasi-phase matching condition, and omega ₁ + [delta] is any of the four quasi-phase matching conditions frequency of the first and second light wave Whether one or both of ω ₁ −δ, ω ₂ + δ, and ω ₂ −δ are met, and the wavelength selective switch matches light waves from the optical modulator to ω ₁ and ω ₂ It divides into the lightwave group (1st lightwave group) which corresponds to ω ₁ + δ, ω ₁ -δ, ω ₂ + δ and ω ₂ -δ, and the other lightwave group (second lightwave group), Second harmonic light obtained by amplifying light waves of ₁ and ω ₂ or ω ₁ + δ and ω ₁ −δ and ω ₂ −δ and ω ₂ + δ and ω ₂ −δ by means of an optical amplifier and then inputting them to a first second-order nonlinear optical element or the sum frequency light entered as excitation light to a second second-order nonlinear optical element, respectively the frequencies of the light waves in the omega ₁ side and omega ₂ side centering on the omega ₀ omega _X, was omega _Y It can be said to be optical comb generator for growing light wave in the optical comb signal inputted by the frequency generation.

Third Embodiment
FIG. 6 shows the configuration of the main part of the optical comb generator 300 according to the third embodiment of the present invention. In the optical comb generator 100 (FIG. 1) of the first embodiment, the light wave in the optical comb signal is propagated by the nonlinear optical process during one pass through the second-order nonlinear optical element 5, so that the configuration is simple. There is a limit to the number of wavelengths that can be expanded (expanded). The same applies to the optical comb generator 200 (FIG. 4) of the second embodiment. Therefore, in the optical comb generator 300 of the third embodiment, an optical comb (output optical comb signal) having a larger number of wavelengths can be generated.

  6, the same reference numerals as those in FIG. 1 denote the same or similar components as the components described with reference to FIG. 1, and the description thereof will be omitted. In the optical comb generator 300 according to the third embodiment, the optical multiplexer 8 is provided at the front stage of the EDFA 4, the optical demultiplexer 9 is provided at the rear stage of the second-order nonlinear optical element 5, and the second-order nonlinear optical element 5 is passed. Thus, a part of the lightwave group thus proliferated is demultiplexed to be combined with the lightwave group from the light modulator 2 to the EDFA 4.

In the optical comb generator 300, the second-order nonlinear optical element 5 has two quasi phase matching wavelengths λ1 and λ2 for the SHG as in the first embodiment, and the quasi phase matching wavelengths λ1 and λ2 for the SHG. Is arranged at the same wavelength as the light wave of frequency ω ₋₂ and ω ₊₂ . In addition, it is also possible that the light wave group from the light modulator 2 to the EDFA 4 is composed of five light waves (light waves with frequencies ω ₀ , ω ₋₁ , ω ₋₂ , ω ₊₁ , ω ₊₂ ). It is the same as Form 1.

  The second-order nonlinear optical element 5 includes a PPLN ridge waveguide formed by using the same direct bonding method as that of the first embodiment. Further, the output from the second-order nonlinear optical element 5 is branched into two by the optical demultiplexer 9, one of which is used as an output (output optical comb signal) and the other is input to the optical multiplexer 8 disposed in the previous stage of the EDFA 4. However, the branching ratio and the combining ratio are both 10% and 90%. Needless to say, other branching ratios and multiplexing ratios may be used.

  In the optical comb generator 300, a new light wave generated by the second-order nonlinear optical element 5 can be incident on the second-order nonlinear optical element 5 again. Furthermore, since the light can be amplified by the EDFA 4 before re-incident light, the number of wavelengths can be expanded without loss of light intensity.

  In the optical comb generator 300, the phase of light incident on the second-order nonlinear optical element 5 is adjusted to be in phase with the input light. Specifically, the optical fiber length is extended and contracted by using a piezo element (PZT) 10 to provide a mechanism for adjusting the optical path length from the optical splitter 9 to the optical multiplexer 8 and monitor a part of the output light By applying feedback to PZT so as to maximize the light intensity, stabilization was performed so that the phase is always the same.

  With such a configuration, in the optical comb generation device 300 of the third embodiment, the optical comb is generated over the entire quasi phase matching wavelength range for the DFG of the second-order nonlinear optical element 5 of 60 nm or more. It has become possible. At 25 GHz intervals, optical combs of 300 waves or more can be output.

For optical comb generator of the third embodiment (300), Conceptually speaking, the light source (1) for generating a continuous wave light frequency omega _0, as center frequency of omega ₀ of the continuous wave light source is generated An optical modulator (2) for generating an optical wave group having a frequency ω ₀ ± n × Δω (where n is an integer and Δω is an arbitrary frequency width) including the central frequency ω ₀ , an optical multiplexer (8), An optical amplifier (4) for amplifying the output from the wave device, quasi phase matching conditions for second harmonic generation between the light wave of frequency ω _{1 and} the light wave of 2ω ₁ , the light wave of frequency ω ₁ + δ and ω _{A first} pseudo condition satisfying one or both quasi phase matching conditions of a _1- δ light wave (where δ is an arbitrary frequency width) and a quasi phase matching condition for sum frequency generation between 2ω ₁ light waves a phase matching condition, versus the second harmonic generation between the frequency omega ₂ of the light waves and 2 [omega ₂ of the lightwave Of the quasi phase matching conditions, a quasi-phase matching conditions for sum frequency generation between the light wave and omega ₂ - [delta light waves of frequency ω ₂ + δ (δ is an arbitrary frequency width) and the lightwave of 2 [omega ₂ that, either one or with both quasi-phase matching condition is satisfied second quasi-phase matching condition or pseudo for the difference frequency generation between the light waves of the optical wave and 2 [omega ₁ - [omega] _X lightwave frequency omega _X frequency 2 [omega ₁ phase and matching condition, the second-order nonlinear optical element that satisfies the quasi phase matching conditions with respect to the difference frequency generation between the light waves of the optical wave and 2 [omega ₂ - [omega] _Y of the light wave of 2 [omega ₂ and the frequency omega _Y (5), the light fraction The frequency of any two light waves in the light wave group including the wave unit (8) and the optical path adjusting mechanism (10) and including the light waves of the frequency ω ₀ ± n × Δω including the center frequency ω ₀ 1 and a second quasi-phase matching condition a is omega ₁ and omega ₂ and to match either one of the four optical wave Wavenumber meet either one or both or matching the first and second quasi-phase matching condition a is omega ₁ + [delta] and omega ₁ - [delta and omega ₂ + [delta] and omega ₂ - [delta, and about the omega ₀ The light waves in the optical comb signal input are propagated by the difference frequency generation where the frequencies of the respective light waves on the ω ₁ side and the ω ₂ side are ω _X and ω _Y respectively, and the light waves are partially amplified. Are separated by the optical demultiplexer, multiplexed with the output from the optical modulator by the optical multiplexer, and then re-input to the second-order nonlinear optical element, and the output from the optical modulator is It can be said that this is an optical comb generating device in which the resonator length is adjusted so that the phase of the light wave group fed back from the light splitter matches at the input to the second order nonlinear optical element.

Fourth Embodiment
FIG. 7 shows the configuration of the main part of an optical comb generator 400 according to the fourth embodiment of the present invention. In the first embodiment (FIG. 1), the second embodiment (FIG. 4) and the third embodiment (FIG. 6), the second-order nonlinear optical element 5 performs the first quasi phase matching and the second quasi phase matching. It was constructed using a PPLN waveguide with a periodically poled structure that fills simultaneously.

  On the other hand, in the fourth embodiment, two second-order nonlinear optical elements 5 '(5-1', 5-2 ') configured using a PPLN waveguide having a single period polarization inversion structure are used. . The difference between the periodically poled structure and the single-period poled structure is simply that the pitch (period) of the periodically poled structure is one type (one pseudo phase matching) or plural types (two types). Basically, it means that there are two quasi-phase matchings.

  7, the same reference numerals as those in FIG. 6 indicate the same or similar components as the components described with reference to FIG. 6, and the description thereof will be omitted. In the optical comb generator 400 of the fourth embodiment, the first second-order nonlinear optical element 5 'having the first quasi phase matching wavelength λ1 between the optical multiplexer 8 and the optical demultiplexer 9 (5 -1 ') and a second second-order nonlinear optical element 5' (5-2 ') having a second quasi phase matching wavelength λ2 are connected in series tandem. Further, the optical amplifier 4 (4-1) is provided at the front stage of the first second-order nonlinear optical element 5 '(5-1'), and the front stage of the second second-order nonlinear optical element 5 '(5-2') And an optical amplifier 4 (4-2).

  In the optical comb generator 400 according to the fourth embodiment, when the input optical comb signal passes through the first second-order nonlinear optical element 5 '(5-1'), the first quasi phase matching wavelength λ1 is centered. When wavelength conversion occurs in a folded form and the input optical comb signal passes through the second second-order nonlinear optical element 5 '(5-2'), it is folded around the second quasi phase matching wavelength λ 2 The wavelength conversion occurs in the shape of a circle, and the light waves in the optical comb signal proliferate.

  However, in this configuration, only once passing through the first second-order nonlinear optical element 5 '(5-1') and the second second-order nonlinear optical element 5 '(5-2') Since only wavelength conversion takes place, large optical comb signals can not be generated.

  Therefore, in the optical comb generating apparatus 400 of the fourth embodiment, as in the third embodiment, the first second-order nonlinear optical element 5 '(5-1') and the second second-order nonlinear optical element 5 ' A part of the lightwave group proliferated by passing (5-2 ') is branched to be combined with the lightwave group from the light modulator 2 to the EDFA 4 (4-1). Thus, multistage wavelength conversion can be induced to generate a large-scale optical comb signal.

For optical comb generator of the fourth embodiment (400), Conceptually speaking, the light source (1) for generating a continuous wave light frequency omega _0, as center frequency of omega ₀ of the continuous wave light source is generated An optical modulator (2) for generating an optical wave group having a frequency ω ₀ ± n × Δω (where n is an integer and Δω is an arbitrary frequency width) including the central frequency ω ₀ , an optical multiplexer (8), Optical amplifier (4-1) for amplifying the output from the wave device, quasi phase matching condition for second harmonic generation between the light wave of frequency ω _{1 and} the light wave of 2ω ₁ , light wave of frequency ω ₁ + δ And a quasi phase matching condition for sum frequency generation between the light wave of ω ₁ −δ (δ is an arbitrary frequency width) and a light wave of 2ω ₁ , or both of the quasi phase matching conditions quasi-phase matching conditions, the light wave of the light wave and 2ω ₁ -ω _X of the light wave and the frequency ω _X of frequency 2ω ₁ of Of the first second-order nonlinear optical element (5-1 ′) satisfying the quasi-phase matching condition for differential frequency generation between the first and second optical elements, and an optical amplifier (4- and 2), second and quasi-phase matching conditions for harmonic generation, optical waves and omega ₂ - [delta frequency omega ₂ + [delta] light waves ([delta] is any frequency between the frequency omega ₂ of the light waves and 2 [omega ₂ of the lightwave a quasi-phase matching condition, either or both of the quasi-phase matching condition is satisfied second pseudo phase matching conditions for sum frequency generation between the width) and the lightwave of 2 [omega _2, of 2 [omega ₂ light waves and the frequency A second second-order nonlinear optical element (5-2 ′) satisfying a quasi phase matching condition for generation of a difference frequency between the light wave of ω _{Y and} the light wave of ₂ ω ₂ −ω _Y , and an optical demultiplexer (9 ) and, an optical path adjusting mechanism (10), is composed of a light wave frequencies ω ₀ ± n × Δω including the center frequency omega ₀ That either of the two frequencies of the light waves of the light wave in the group is equal to omega ₁ and omega ₂ and a first and second quasi-phase matching condition, either the frequency of the four light waves first and And one or both of ω ₁ + δ, ω ₁ −δ, ω ₂ + δ, and ω ₂ −δ, which are quasi-phase matching conditions of ₂ , satisfying ω ₁ side and ω centered on ω _{0 The} light waves in the optical comb signal input are propagated by the difference frequency generation where the frequency of each light wave on the _two sides is ω _X and ω _Y respectively, and a part of the light wave group in which this light wave is grown is It has a resonator structure that can be separated and combined with the output from the optical modulator by the optical multiplexer and then re-input to the first second-order nonlinear optical element, and the output from the optical modulator and the optical demultiplexing The resonator length is adjusted so that the phase of the lightwave group fed back from the resonator matches at the input to the first second-order nonlinear optical element Can be said to be an optical comb generator.

Fifth Embodiment
FIG. 8 shows the configuration of the main part of the optical comb generator 500 according to the fifth embodiment of the present invention. The optical comb generating device 500 of the fifth embodiment is a combination of the second embodiment (FIG. 4) and the fourth embodiment (FIG. 7), and is a PPLN waveguide having a single period polarization inversion structure. Configuration using two second-order nonlinear optical elements 5 '(5-1', 5 '2') configured using the wavelength selective switch 6 and two second-order nonlinear optical elements 5 (5-1, 5 By combining this with the configuration using −2), an output having a higher S / N ratio can be obtained.

  In FIG. 8, the same reference numerals as in FIGS. 4 and 7 denote the same or equivalent components as the components described with reference to FIGS. 4 and 7, and the description thereof will be omitted. In the optical comb generator 500 according to the fifth embodiment, a third second-order nonlinear optical element 5 'having a first quasi phase matching wavelength λ1 between the optical multiplexer 8 and the optical demultiplexer 9 (5 -1 ') and a fourth second-order nonlinear optical element 5' (5-2 ') having a second quasi phase matching wavelength λ2 are connected in series tandem.

In addition, a light wave group consisting of five light waves (light waves with frequencies ω ₀ , ω ₋₁ , ω ₋₂ , ω ₊₁ , ω ₊₂ ) generated by the light modulator 2 is referred to as a first light wave group (frequency ω _{− 2} of the light wave) and a second light wave groups (frequency omega ₊₂ of the light wave) and the third light wave groups (frequency ω _0, ω _-1, a wavelength selective switch for separating the omega ₊₁ of the light wave) (WSS) 6 And the first light wave group (light wave of frequency ω _-2 ) separated by the wavelength selective switch 6 through the EDFA 4 (4-1) and the BPF 7 (7-1) as a first second-order nonlinear optical element 5 The second light wave group (the light wave of frequency ω ₊₂ ) separated by the wavelength selective switch 6 is input to (5-1) through the EDFA 4 (4-2) and the BPF 7 (7-2). It is made to input into 2nd 2nd-order nonlinear optical element 5 (5-2).

Further, the light wave (fourth light wave group) of frequency 2ω _-2 generated by the first second-order nonlinear optical element 5 (5-1) from the light wave of frequency ω _-2 is converted to the third second-order nonlinear optical element 5 ' A light wave of a frequency 2ω ₊₂ (fifth light wave group generated by the second second-order nonlinear optical element 5 (5-2) from the light wave of frequency ω ₊₂ as excitation light is given to (5-1 ′) ) As excitation light to the fourth second-order nonlinear optical element 5 '(5-2'). In addition, the third light wave group (light waves of frequencies ω ₀ , ω ₋₁ , ω ₊₁ ) separated by the wavelength selective switch 6 is passed through the multiplexer 8 to a third second-order nonlinear optical element 5 ′ (5-1 It is made to input to ').

In this example, the first light wave group is a light wave of frequency ω _-2 , the second light wave group is a light wave of frequency ω ₊₂ , and the fourth light wave group is a light wave of frequency 2ω _-2 . The lightwave group of the lightwave group is a lightwave of frequency 2.omega. _{+ 2} , that is, although there is only one lightwave in the lightwave group, the lightwave group in the present invention also refers to a configuration in which there is only one such light wave. Shall be included in the concept of That is, in the invention according to claim 5 corresponding to the fifth embodiment, the first light wave group, the second light wave group, the fourth light wave group, and the fifth light wave group are formed of one light wave. It may also be composed of a plurality of light waves.

In this optical comb generator 500, a light wave composed of five light waves (light waves of ω ₀ , ω ₋₁ , ω ₋₂ , ω ₊₁ , ω ₊₂ ) generated by the light modulator 2 by the wavelength selective switch 6 From the group, light waves of ω _-2 and 2ω ₊₂ whose wavelengths coincide with two quasi phase matching wavelengths λ 1 and λ 2 for SHG are taken out as a first light wave group and a second light wave group, and a first wavelength After the lightwaves of the group (lightwaves of frequency ω ₂ ) are amplified by the EDFA 4 (4-1), the first second-order nonlinear optical element 5 (5-1) is passed through the band pass filter 7 (7-1). Is input to). In addition, after the lightwave of the second wavelength group (lightwave of frequency ω _{+ 2} ) is amplified by the EDFA 4 (4-2), the second second-order nonlinear optics is conducted via the band pass filter 7 (7-2) It is input to the element 5 (5-2).

The first second-order nonlinear optical element 5 (5-1) generates a light wave of 2ω _-2 by second harmonic generation, and separates the light of ω _{-2 and} the light wave of 2ω _-2 by a dichroic mirror, Only the light wave of 2ω _-2 is extracted as the light wave of the fourth wavelength group. The lightwave of the fourth wavelength group (lightwave of frequency 2ω _-2 ) extracted from the first second-order nonlinear optical element 5 (5-1) is the third second-order nonlinear optical element 5 '(5-1') ) As excitation light.

The second second-order nonlinear optical element 5 (5-2) generates a 2ω ₊₂ light wave by the second harmonic generation, and separates the ω ₊₂ light and the 2ω ₊₂ light wave by a dichroic mirror, Only the 2ω _{+ 2} lightwave is extracted as the lightwave of the fifth wavelength group. The lightwave of the fifth wavelength group (lightwave of frequency 2.omega. ₊ 2) extracted from the second second-order nonlinear optical element 5 (5-2) is the fourth second-order nonlinear optical element 5 '(5-2') ) As excitation light.

On the other hand, of the five light waves (light waves of ω ₀ , ω ₋₁ , ω ₋₂ , ω ₊₁ , ω ₊₂ ) that constitute the light wave group generated by the light modulator 2 by the wavelength selective switch 6, ω A light wave of ₀ , ω _-1 , ω ₊₁ is extracted as a third light wave group, and input to the third second-order nonlinear optical element 5 '(5-1') through the optical multiplexer 8 Is entered as

  In the optical comb generator 500 of the fifth embodiment, when the input optical comb signal passes through the third second-order nonlinear optical element 5 '(5-1'), the first quasi phase matching wavelength λ1 is centered. When wavelength conversion occurs in a folded form and the input optical comb signal passes through the fourth second-order nonlinear optical element 5 '(5-2'), it is folded around the second quasi phase matching wavelength λ 2 The wavelength conversion occurs in the shape of a circle, and the light waves in the optical comb signal proliferate.

  However, in this configuration, only once passing through the third second-order nonlinear optical element 5 '(5-1') and the fourth second-order nonlinear optical element 5 '(5-2') can be performed once. Since only wavelength conversion takes place, large optical comb signals can not be generated.

  Therefore, in the optical comb generating device 500 of the fifth embodiment, as in the fourth embodiment, the third second-order nonlinear optical element 5 '(5-1') and the fourth second-order nonlinear optical element 5 ' The third group from the wavelength selective switch 6 to the third second-order nonlinear optical element 5 '(5-1') is branched by branching a portion of the lightwave group propagated by passing (5-2 ') It is made to combine to the light wave group of. Thus, multistage wavelength conversion can be induced to generate a large-scale optical comb signal.

For optical comb generator of the fifth embodiment (500), Conceptually speaking, the light source (1) for generating a continuous wave light frequency omega _0, as center frequency of omega ₀ of the continuous wave light source is generated An optical modulator (2) that generates an optical wave group having a frequency ω ₀ ± n × Δω (where n is an integer and Δω is an arbitrary frequency width) including the central frequency ω _0, and the optical wave group generated by the optical modulator Wavelength-selective switch (6) for separating the first lightwave group into the first lightwave group, the second lightwave group, and the third lightwave group, and the first lightwave group for amplifying the lightwaves in the first lightwave group separated by the wavelength selection switch. Optical amplifier (4-1), a second optical amplifier (4-2) for amplifying light waves in the second light wave group separated by the wavelength selective switch, an optical multiplexer (8), and a frequency ω a quasi-phase matching conditions for second harmonic generation in between the _first optical wave and 2 [omega ₁ of the light wave, One or both quasi-phases of quasi-phase matching conditions for sum frequency generation between a light wave of frequency ω ₁ + δ, a light wave of ω ₁ -δ (δ is an arbitrary frequency width) and a light wave of 2ω ₁ the matching condition is satisfied first quasi-phase matching condition is satisfied first second-order nonlinear optical element (5-1), the pseudo for the second harmonic generation between the frequency omega ₂ of the light waves and 2 [omega ₂ of the lightwave One of the phase matching condition and the quasi phase matching condition for sum frequency generation between the light wave of frequency ω ₂ + δ and the light wave of ω ₂ -δ (where δ is an arbitrary frequency width) and the light wave of 2ω ₂ And a second second-order nonlinear optical element (5-2) satisfying the second quasi-phase matching condition satisfying both quasi-phase matching conditions, the light wave of frequency 2ω _{1 and} the light wave of frequency ω _X and 2ω ₁ -ω third secondary satisfying the quasi-phase matching conditions for the difference frequency generation between the _X light wave Linear optical element (5-1 '), quasi-phase matching condition is satisfied fourth second-order nonlinear for difference frequency generation between the light waves of the optical wave and 2 [omega ₂ - [omega] _Y of the light wave of 2 [omega ₂ and the frequency omega _Y An optical element (5-2 '), an optical demultiplexer (9), and an optical path length adjusting mechanism (10), and a wavelength selective switch, an optical wave of frequency ω ₀ ± n × Δω including center frequency ω ₀ in in configured lightwave group omega ₁ to match or omega ₁ + [delta] and omega ₁ - [delta and the matching lightwave group (first lightwave group), or coincides with ω ₂ ω ₂ + δ and omega ₂ - It divides into the lightwave group (the second lightwave group) which agrees with δ and the other lightwave group (the third lightwave group), and the light wave group of ω ₁ or ω ₁ + δ and ω ₁ −δ is after amplified by the optical amplifier and input to the first second-order nonlinear optical element, the second harmonic light or sum frequency light obtained input as excitation light to the third next non-linear optical element, the omega ₀ Were grown lightwave omega ₁ side in the optical comb signal inputted mind that omega ₁ side and omega ₂ side of the frequency of each light wave, respectively omega _X, by a difference frequency generation and ω _Y, ω ₂ or omega ₂ A light wave group of + δ and ω ₂ −δ is amplified by the second optical amplifier and then input to the second second-order nonlinear optical element, and the obtained second harmonic light or sum frequency light is used as the excitation light to generate the fourth two type next nonlinear optical element, omega respective frequencies of the light waves omega ₀ a centered omega ₁ side and omega ₂ side _X, omega ₂ side in the optical comb signal input by the difference frequency generation and omega _Y The light wave is amplified, and a part of the light wave group in which the light waves on the ω ₁ side and the ω ₂ side are amplified is separated by the optical splitter and combined with the output from the optical modulator by the optical multiplexer. It has a resonator structure that can be re-input to the third second-order nonlinear optical element, and the output from the optical modulator and the light wave fed back from the optical demultiplexer It can be said that it is an optical comb generating device in which the resonator length is adjusted so that the phase of the group coincides with the input to the third second-order nonlinear optical element.

The material which comprises the ridge waveguide used in the above embodiment is only an example. That is, the ridge waveguide is made of LiNbO ₃ , KNbO ₃ , LiTaO ₃ , LiNb _(x) Ta _(1-x) O ₃ (0 ≦ x ≦ 1) or KTiOPO ₄ , or Mg, Zn, Sc, In And at least one selected from the group consisting of

[Extension of the embodiment]
Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the technical idea of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... light source, 2 ... light modulator, 3 ... sine wave generator, 4 ... optical amplifier (EDFA), 5 (5-1, 5- 2), 5 '(5-1', 5- 2 ') ... Second-order nonlinear optical element, 6: wavelength selective switch (WSS), 7: band pass filter (BPF), 8: optical multiplexer, 9: optical demultiplexer, 10: piezo element (PZT), 100 to 500: optical Comb generator.

Claims (4)

A light source generating continuous wave light of frequency ω ₀ ,
Optical modulation that generates a light wave group having a frequency ω ₀ ± n × Δω (n is an integer, Δω is an arbitrary frequency width) including the center frequency ω ₀ with the frequency ω ₀ of continuous wave light generated by the light source as the center frequency And the
A wavelength selective switch that separates a lightwave group generated by the light modulator into a first lightwave group and a second lightwave group;
An optical amplifier for amplifying a first light wave group separated by the wavelength selective switch;
A first second-order nonlinear optical element generating a third lightwave group from the first lightwave group amplified by the optical amplifier;
The third lightwave group generated by the first second-order nonlinear optical element is input as excitation light, and the second lightwave group separated by the wavelength selective switch is input as an input optical comb signal, and this input optical comb A second second-order nonlinear optical element for propagating light waves in the signal ;
The first and second second-order nonlinear optical elements are
A quasi-phase matching conditions for second harmonic generation between the frequency omega ₁ of the optical wave and 2 [omega ₁ of the light wave, the optical wave and omega ₁ - [delta frequency omega ₁ + [delta] lightwave ([delta] is an arbitrary frequency width) and 2 [omega the sum of the quasi-phase matching condition for frequency generation, either or with both quasi-phase matching condition is satisfied first for quasi-phase matching conditions, the frequency omega ₂ of the light waves and light waves of 2 [omega ₂ between the _first optical wave And the quasi-phase matching condition for the second harmonic generation , and the sum frequency between the lightwave of frequency ω ₂ + δ and the lightwave of ω ₂ −δ (δ is an arbitrary frequency width) and the lightwave of 2ω ₂ the quasi-phase matching conditions for the generation, and either or both quasi-phase matching condition is satisfied second quasi-phase matching condition, the light wave and omega _X frequency 2 [omega ₁ lightwave and 2 [omega ₁ - [omega] _X with optical wave a quasi-phase matching condition for difference frequency generation between, the frequency 2 [omega ₂ lightwave and omega _Y lightwave Meet the quasi-phase matching condition for difference frequency generation between the light waves of 2ω ₂ -ω _Y,
The frequency of any two lightwaves in the lightwave group matches the first and second quasi phase matching conditions ω ₁ and ω ₂ or any four lightwaves in the lightwave group The frequency of the first and second quasi phase matching conditions satisfy one or both of the first and second quasi phase matching conditions ω ₁ + δ, ω ₁ −δ, ω ₂ + δ, and ω ₂ −δ,
The wavelength selective switch
The light waves from the light modulator are the light waves of frequencies ω ₁ and ω ₂ or the light waves of frequencies ω ₁ + δ, ω ₁ −δ, ω ₂ + δ, and ω ₂ −δ as the first light wave group. Separating light waves other than the first light wave group as the second light wave group,
The first second-order nonlinear optical element generates second harmonic light or sum frequency light as the third light wave group,
The second second-order nonlinear optical element is an optical comb signal input by the difference frequency generation where the frequencies of the light waves on the ω ₁ side and the ω ₂ side centering on the frequency ω ₀ are ω _X and ω _Y respectively An optical comb generator characterized by proliferating a light wave . A light source generating continuous wave light of frequency ω ₀ ,
Optical modulation that generates a light wave group having a frequency ω ₀ ± n × Δω (n is an integer, Δω is an arbitrary frequency width) including the center frequency ω ₀ with the frequency ω ₀ of continuous wave light generated by the light source as the center frequency And the
A first optical amplifier for amplifying a group of light waves generated by the light modulator;
A first second-order nonlinear system which inputs the lightwave group amplified by the first optical amplifier as an input optical comb signal, and propagates the lightwave on one side centering on the center frequency ω ₀ in the input optical comb signal An optical element,
A second optical amplifier for amplifying a lightwave group in which a lightwave on one side centered on the center frequency ω ₀ is amplified by the first second-order nonlinear optical element;
A lightwave group in which a lightwave on one side centered on the center frequency ω ₀ is amplified by the second optical amplifier is input as an input light comb signal, and the center frequency ω ₀ in the input light comb signal is centered A second second-order nonlinear optical element that propagates the lightwave on the other side,
A light splitter that splits part of a group of light waves in which light waves on one side and the other side centering on the center frequency ω ₀ by passing through the first and second second-order nonlinear optical elements When,
An optical multiplexer that combines the lightwave group demultiplexed by the optical demultiplexer into the lightwave group from the optical modulator to the first optical amplifier ;
The first second-order nonlinear optical element is
A quasi-phase matching conditions for second harmonic generation between the frequency omega ₁ of the optical wave and 2 [omega ₁ of the light wave, the optical wave and omega ₁ - [delta frequency omega ₁ + [delta] lightwave ([delta] is an arbitrary frequency width) and 2 [omega the quasi phase matching conditions with respect to the sum frequency generation between the _first light wave, either one or the both quasi-phase matching condition is satisfied first for quasi-phase matching condition, the light wave of the light wave and omega _X frequency 2 [omega ₁ And the quasi-phase-matching condition for the difference frequency generation between the light waves of 2ω ₁ -ω _X and
The second second-order nonlinear optical element is
A quasi-phase matching conditions for second harmonic generation between the frequency omega ₂ of the light waves and 2 [omega ₂ of the light waves, the light waves and omega ₂ - [delta frequency omega ₂ + [delta] light waves ([delta] is an arbitrary frequency width) and 2 [omega the quasi phase matching conditions with respect to the sum frequency generation between the _two light waves, either or with both quasi-phase matching condition is satisfied second pseudo phase matching conditions, the light wave of the light wave and omega _Y frequency 2 [omega ₂ And the quasi-phase matching condition for the difference frequency generation between the light waves of 2ω ₂ −ω _Y and
The frequency of any two lightwaves in the lightwave group matches the first and second quasi phase matching conditions ω ₁ and ω ₂ or any four lightwaves in the lightwave group The frequency of the first and second quasi phase matching conditions satisfy one or both of the first and second quasi phase matching conditions ω ₁ + δ, ω ₁ −δ, ω ₂ + δ, and ω ₂ −δ,
A light characterized by proliferating the light wave in the optical comb signal input by the difference frequency generation where the frequencies of the light waves on the ω ₁ side and the ω ₂ side centering on the frequency ω ₀ are ω _X and ω _Y respectively. Comb generator. A light source generating continuous wave light of frequency ω ₀ ,
Optical modulation that generates a light wave group having a frequency ω ₀ ± n × Δω (n is an integer, Δω is an arbitrary frequency width) including the center frequency ω ₀ with the frequency ω ₀ of continuous wave light generated by the light source as the center frequency And the
A wavelength selective switch that separates a lightwave group generated by the light modulator into a first lightwave group, a second lightwave group, and a third lightwave group;
A first optical amplifier for amplifying a first light wave group separated by the wavelength selective switch;
A second optical amplifier for amplifying a second light wave group separated by the wavelength selective switch;
A first second-order nonlinear optical element generating a fourth lightwave group from the first lightwave group amplified by the first optical amplifier;
A second second-order nonlinear optical element generating a fifth lightwave group from the second lightwave group amplified by the second optical amplifier;
The fourth lightwave group generated by the first second-order nonlinear optical element is input as excitation light, and the third lightwave group separated by the wavelength selective switch is input as an input optical comb signal, and this input optical comb A third second-order nonlinear optical element for propagating a light wave on one side centered on the central frequency ω ₀ in the signal;
The fifth lightwave group generated by the second second-order nonlinear optical element is input as excitation light, and the third second-order nonlinear optical element amplifies a lightwave on one side centered on the center frequency ω ₀ A fourth second-order non-linear optical element which receives the lightwave group as an input light comb signal and propagates the lightwave on the other side centered on the center frequency ω ₀ in the input light comb signal;
A light splitter that splits part of a group of light waves in which light waves on one side and the other side centering on the center frequency ω ₀ by passing through the third and fourth second-order nonlinear optical elements When,
And an optical multiplexer for multiplexing the demultiplexed light waves groups by the optical demultiplexer to the third light wave groups from the wavelength selective switch to the third second-order nonlinear optical element,
The first second-order nonlinear optical element is
A quasi-phase matching conditions for second harmonic generation between the frequency omega ₁ of the optical wave and 2 [omega ₁ of the light wave, the optical wave and omega ₁ - [delta frequency omega ₁ + [delta] lightwave ([delta] is an arbitrary frequency width) and 2 [omega Satisfy a _first quasi phase matching condition satisfying either or both quasi phase matching conditions with a quasi phase matching condition for sum frequency generation with _one light wave,
The second second-order nonlinear optical element is
A quasi-phase matching conditions for second harmonic generation between the frequency omega ₂ of the light waves and 2 [omega ₂ of the light waves, the light waves and omega ₂ - [delta frequency omega ₂ + [delta] light waves ([delta] is an arbitrary frequency width) and 2 [omega Satisfying a quasi-phase matching condition for sum frequency generation between _two light waves and a _second quasi-phase matching condition satisfying one or both quasi-phase matching conditions;
The third second-order nonlinear optical element is
Satisfy the quasi-phase matching condition for the difference frequency generation between the lightwave of frequency 2ω _1, the lightwave of ω _{X and} the lightwave of 2ω ₁ −ω _X ,
The fourth second-order nonlinear optical element is
Satisfy the quasi-phase matching condition for the difference frequency generation between the lightwave of frequency 2ω _2, the lightwave of ω _{Y and} the lightwave of 2ω ₂ −ω _Y ,
The wavelength selective switch
The lightwave group from the optical modulator, the frequency omega ₁ of the optical or light waves of a frequency omega ₁ + [delta] and omega ₁ - [delta as the first light wave group, the frequency omega ₂ of the light wave or frequency omega ₂ + [delta] and omega, The light waves other than the first and second light wave groups are separated as the third light wave group, with the light wave of _{2 −} δ as the second light wave group,
The first second-order nonlinear optical element generates second harmonic light or sum frequency light as the fourth light wave group,
The second second-order nonlinear optical element generates second harmonic light or sum frequency light as the fifth light wave group,
A light characterized by proliferating the light wave in the optical comb signal input by the difference frequency generation where the frequencies of the light waves on the ω ₁ side and the ω ₂ side centering on the frequency ω ₀ are ω _X and ω _Y respectively. Comb generator. In the optical comb generator according to claim 3 ,
The wavelength selective switch
One of two light waves in the light wave group at the frequency ω ₀ ± n × Δω including the central frequency ω ₀ is used as the first light wave group, the other is used as the second light wave group, and the rest is used as the second light wave group. Separated as a third lightwave group,
The first second-order nonlinear optical element is
If the frequency of the light wave separated by the wavelength selective switch as the first light wave group is ω ₋₂ , a light wave having a frequency of 2ω ₋₂ is generated as the fourth light wave group,
The second second-order nonlinear optical element is
When the wavelength of the light wave separated as the second light wave group is ω ₊₂ , the wavelength selective switch generates a light wave of 2ω ₊₂ frequency as the fifth light wave group apparatus.

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