JP2017097294A - Wavelength conversion device, light source device using the same, and information acquisition device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength conversion device capable of generating an optical pulse with high peak strength with less distortion in spectral shape while suppressing the energy of optical pulse.SOLUTION: The wavelength conversion device includes: a nonlinear waveguide that converts the wavelength of a first optical pulse into an optical parametric; a feedback part that feeds back a part of the optical pulse, the wavelength of which has been converted, as a resonant optical pulse; and a pulse compression part that compresses the time width of the resonant optical pulse in the nonlinear waveguide by giving a group delay dispersion with a sign opposite to a sign of a group delay dispersion which is a resonant optical pulse given by a resonator to a resonant optical pulse.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical pulse wavelength converter, and more particularly, to an optical pulse wavelength conversion technique using a nonlinear waveguide.

  In recent molecular imaging, development of a technique for observing without staining by using short pulse light as excitation light has been advanced. In particular, research is being actively conducted in which imaging is performed by selecting molecular species by irradiating an observation target with short pulse light and detecting the intensity of light scattered by the short pulse light. In these molecular imaging, for example, observation is performed by detecting coherent anti-Stokes Raman scattering (CARS) light. Alternatively, observation is performed by detecting stimulated Raman scattering (SRS) light. At this time, two light pulses having different optical frequencies corresponding to the natural frequency of the observation object are used as the excitation light irradiated to the observation object.

  Two optical pulses having different frequencies can be obtained by wavelength conversion using a nonlinear effect generated when the optical pulse propagates in the nonlinear waveguide. For example, Non-Patent Document 1 discloses a wavelength conversion technique for obtaining a high-power optical pulse with a narrow spectral line width. In Non-Patent Document 1, a fiber optical parametric oscillator (FOPO) using four-wave mixing in a nonlinear fiber is used as a wavelength converter.

  In wavelength conversion by four-wave mixing, an idler light pulse having a longer wavelength and a signal light pulse having a shorter wavelength than the seed light pulse are generated simultaneously. In FOPO, one of the optical pulses is taken out as an output pulse. Then, the idler light pulse and the signal light pulse that have not been taken out are fed back to the nonlinear waveguide, and are again introduced into the nonlinear waveguide in synchronization with the seed light pulse. This optical pulse synchronized with the seed light pulse is hereinafter referred to as “resonant light pulse”.

  In order to improve the S / N ratio in such nonlinear imaging, it is necessary to increase the peak intensity of an optical pulse used as a light source. However, increasing the pulse energy to increase the peak intensity of the light pulse increases the damage to the subject. Therefore, in order to generate an optical pulse with a high peak intensity while suppressing the energy of the optical pulse, it is necessary to shorten the time width of the optical pulse to be used.

Optics Express, Vol. 22, no. 18, pp. 21921-21928, 3 September 2014

  As a general property of a wave including an optical pulse, it is known that the time width Δt and the spectral width Δω are inversely proportional to each other and cannot be reduced at the same time. For this reason, in order to obtain an output pulse with a short time width from FOPO, it is necessary to widen the spectral line width of the resonant light pulse that resonates within FOPO. However, when the spectral line width of the resonant light pulse is wide, the time width of the resonant light pulse is extended due to group velocity dispersion of the medium constituting the FOPO. As a result, there is a problem that the spectral shape of the resonant light pulse is distorted and the spectral shape of the output pulse is distorted due to cross-phase modulation (XPM) by the seed light pulse electric field. The present invention is intended to solve such a problem, and an object of the present invention is to obtain a wavelength converter that can generate an optical pulse with a high peak intensity with less distortion in the spectrum shape while suppressing the energy of the optical pulse. .

A wavelength conversion device according to the present invention includes a multiplexing unit that introduces a first optical pulse having a first wavelength, and a nonlinear waveguide that converts the wavelength of the first optical pulse introduced from the multiplexing unit by optical parametrics. A waveguide, an extraction unit that extracts a part of the wavelength-converted optical pulse, a feedback unit that feeds back the wavelength-converted optical pulse that was not extracted by the extraction unit to the multiplexing unit as a resonant optical pulse, and a resonant optical pulse And a pulse compression unit that compresses the time width of the resonant optical pulse by compensating at least a part of the group delay dispersion of the first optical pulse, the time width of the first optical pulse is Δt _p , and the resonant optical pulse the spectral width [Delta] [omega _r, the sum of D _o of the group delay dispersion resonator has on the resonant optical _pulses, the group delay dispersion pulse compressor has on the resonant optical pulse D _c, the first resonant optical pulse When the walk-off amount to the light pulse and t _wo, as equation (2) is satisfied will be described later, it is characterized by compressing the time width of the resonant optical pulses.

  By using the wavelength conversion device according to the present invention, it is possible to generate an optical pulse having a high peak intensity with little distortion in the spectrum shape.

It is a schematic diagram which shows the optical frequency change of the resonant light pulse by XPM (cross phase modulation). It is a schematic diagram explaining that the influence of XPM is reduced by pulse compression. It is a schematic diagram which shows the structure of the wavelength converter which concerns on the 1st Embodiment of this invention. It is a simulation result which shows that the influence of XPM is reduced by the pulse compression part in the wavelength converter which concerns on the 1st Embodiment of this invention. It is a schematic diagram which shows the structure of the wavelength converter which concerns on the 2nd Embodiment of this invention. It is a schematic diagram which shows the structure of the pulse compression part in the wavelength converter which concerns on the 5th Embodiment of this invention. It is a schematic diagram which shows the structure of the wavelength converter which concerns on the 8th Embodiment of this invention. It is a schematic diagram which shows the structure of the light source device which concerns on the 11th Embodiment of this invention. It is a schematic diagram which shows the structure of the information acquisition apparatus which concerns on the 12th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment, In the range which does not deviate from the summary, it can change suitably. In the drawings described below, components having the same function are denoted by the same reference numerals, and the description thereof may be omitted or simplified.

(First embodiment)
First, an outline of technical features of the present invention will be described with reference to FIGS. 1 and 2. The present invention includes a pulse compression unit that compensates part or all of the group delay dispersion of a resonant optical pulse resonating in a resonator such as FOPO (hereinafter simply referred to as “resonator”). It is a feature. As will be described later, the pulse compression unit includes, for example, a fiber that gives negative dispersion to the resonant light pulse in a resonator having positive dispersion to the resonant light pulse, a compressor using a diffraction grating, and a chirped fiber. It is obtained by inserting a Bragg grating (CFBG) or the like. Thus, the time width of the resonant light pulse in the nonlinear waveguide in the resonator can be compressed by the pulse compression unit compensating part or all of the group delay dispersion of the resonant light pulse. In the case where the resonator gives negative dispersion to the resonant light pulse, the same effect can be obtained by using a pulse compression section that gives positive dispersion.

を満たす場合において、下式（２）で表されるパルス圧縮条件、

を満たすような、Ｄ_ｏとは逆符号の群遅延分散Ｄ_ｃを、パルス圧縮部によって与える。ここで、Δｔ_ｐは、シード光パルスの非線形導波路中での時間幅である。また、ウォークオフｔ_ｗｏは、非線形導波路中でのシード光パルスと共振光パルスの群速度の違いを起因として非線形導波路の光入力端から光出射端までの間に共振光パルスに生じる、シード光パルスに対する共振光パルスのタイミングの変化量である。ウォークオフｔ_ｗｏは、非線形導波路の長さＬ、非線形導波路内でのシード光パルスの群屈折率ｎ_ｐおよび共振光パルスの群屈折率ｎ_ｒ、真空中の光速度ｃを用いて、

で表される。 In this embodiment, in particular, the relationship between the spectral width Δω _r of the resonant light pulse at the optical input end of the nonlinear waveguide and the total group delay dispersion D _o given to the resonant light pulse by the resonator is _expressed by the following equation (1).

In the case of satisfying, the pulse compression condition represented by the following formula (2),

That satisfies, and D _o the group delay dispersion D _c of opposite sign, provided by pulse compressor. Here, Delta] t _p is the time width in the nonlinear waveguide of the seed light pulse. Further, the walk-off t _wo is generated in the resonant light pulse between the light input end and the light output end of the nonlinear waveguide due to the difference in the group velocity between the seed light pulse and the resonant light pulse in the nonlinear waveguide. This is the amount of change in the timing of the resonant light pulse relative to the seed light pulse. The walk-off t _wo uses the length L of the nonlinear waveguide, the group refractive index n _p of the seed light pulse in the nonlinear waveguide, the group refractive index n _r of the resonant light pulse, and the light velocity c in vacuum,

It is represented by

In the nonlinear waveguide, the fed back resonant light pulse and the seed light pulse propagate synchronously. At this time, the optical frequency change of the resonant light pulse occurs by XPM due to the electric field E _p (t) of the seed light pulse. FIG. 1 is a schematic diagram showing a change in optical frequency of a resonant light pulse by XPM. The horizontal axis in FIG. 1 represents time. The frequency change amount δω _r (t) of the resonant light by XPM is proportional to the time change of the seed light pulse intensity | E _p (t) | ² as shown in the following equation (4).

That is, as the time variation of the seed light pulse intensity increases, the frequency variation δω _r (t) of the resonant light pulse increases. When the time waveform of the seed light pulse is a single peak as shown in FIG. 1, the amount of change in frequency δω _r (t) of the resonant light is a positive value in the first half of the seed light pulse (t> 0), and the latter half. The portion (t <0) has a negative value. The absolute value of the frequency change amount δω _r (t) of the resonant light is maximized around time t _0.5 when | E _p (t) | ² becomes half the peak value. FIG. 1 shows the half-value point t _0.5 ⁻ of the rising edge of the pulse existing in the first half of the optical pulse and the half-value point t _0.5 ⁺ of the falling edge of the pulse existing in the second half of the optical pulse. . Since the resonant light pulse has a temporal spread, the amount of frequency change δω _r (t) at each time of the time width of the resonant light pulse is not uniform, and the spectrum of the resonant light pulse is distorted and spread.

となる。また、上式（２）のパルス圧縮条件を満たさない従来のパルス圧縮部を挿入した場合には、非線形導波路の光入力端における共振光パルスの時間幅Δｔ_ｒは、

となる。いずれの場合においても、図２（ａ）に示すように、非線形導波路の光入力端における共振光パルスの時間幅Δｔ_ｒは、シード光パルスの時間幅Δｔ_ｐとウォークオフｔ_ｗｏの差Δｔ_ｐ−ｔ_ｗｏより大きくなる。このような場合、ｔ_０．５ ⁻、ｔ_０．５ ^＋、に共振光パルスが重なるため、共振光パルスのスペクトルの歪みが大きくなってしまう。 FIG. 2 is a schematic diagram for explaining that the influence of XPM is reduced by pulse compression. Under the conditions satisfying the above formula (1), when pulse compression unit is not, the time width (FWHM) Delta] t _r of the resonant optical pulses fed back to the light input end of the nonlinear waveguide, as shown in FIG. 2 (a) to, the variance of the sum D _o the resonator has,

It becomes. Further, when inserting the conventional pulse compressor which does not satisfy the pulse compression condition of the above equation (2) it is the time width Delta] t _r of the resonant light pulse in the light input end of the nonlinear waveguide,

It becomes. In any case, as shown in FIG. 2 (a), the time width Delta] t _r of the resonant light pulse in the light input end of the nonlinear waveguide, the difference in time width Delta] t _p and walk-off t _wo of the seed light pulse Delta] t It becomes larger than the _p -t _wo. In such a case, since the resonance light pulse overlaps t _0.5 ⁻ and t _0.5 ⁺ , the spectrum distortion of the resonance light pulse becomes large.

  Since the idler light pulse and the signal light pulse are obtained by amplification of the resonant light pulse in the nonlinear waveguide or wavelength conversion from the resonant light pulse and the seed light pulse, the spectral distortion of the resonant light pulse remains as it is in the spectrum of the output pulse. It becomes distortion.

となる。このため、図２（ｂ）に示すように、非線形導波路中でｔ_０．５ ⁻、ｔ_０．５ ^＋に共振光パルスが重なることが無くなる。その結果ＸＰＭが低減され、共振光スペクトルの歪みが低減される。 On the other hand, in this embodiment, so as to satisfy the pulse compression conditions shown in D _c is the above equation (2), since it has a pulse compressor that gives group delay dispersion in the resonant optical pulses,

It becomes. For this reason, as shown in FIG. 2B, resonance light pulses do not overlap with t _0.5 ⁻ and t _0.5 ⁺ in the nonlinear waveguide. As a result, XPM is reduced, and distortion of the resonant light spectrum is reduced.

  As described above, in this embodiment, by inserting a pulse compression unit that gives dispersion satisfying the pulse compression condition of the above equation (2) in the resonator, a nonlinear waveguide can be obtained even for a resonant optical pulse having a wide spectral width. Spectral distortion due to XPM can be reduced. As a result, it is possible to generate an output light pulse having a wide spectrum width and a small distortion in the spectrum shape, and an optical pulse having a high peak intensity can be obtained by compressing the output light pulse.

  Hereinafter, although the structural example of the wavelength converter in the 1st Embodiment of this invention is demonstrated using FIG. 3 and FIG. 4, this invention is not limited at all by the structure of embodiment etc. which are demonstrated below. Absent.

  FIG. 3 is a schematic diagram showing the configuration of the wavelength conversion device according to the first embodiment of the present invention. A wavelength conversion device 300 illustrated in FIG. 3 includes a nonlinear waveguide 302, a first optical waveguide 303, an extraction unit 304, a feedback unit 305, a multiplexing unit 306, a second optical waveguide 307, and a third optical waveguide 309. Here, the nonlinear waveguide 302, the first optical waveguide 303, the extraction unit 304, the feedback unit 305, the multiplexing unit 306, and the second optical waveguide 307 are connected in this order to form an optical resonator. The introduction unit 301 introduces the seed light pulse into the optical resonator. A pulse compression unit 308 is inserted in the optical resonator.

  The seed light pulse introduced from the introduction part 301 passes through the multiplexing part 306 and is guided to the nonlinear waveguide 302 by the second optical waveguide 307. The seed light pulse causes an optical parametric process inside the nonlinear waveguide 302 and is wavelength-converted into an idler light pulse and a signal light pulse. The seed light pulse only needs to be wavelength-converted inside the nonlinear waveguide 302 as described above, and the wavelength, spectrum distribution, and the like are not particularly limited. The generated idler light pulse and the signal light pulse are guided to the extraction unit 304 by the first optical waveguide 303, and one or both of the idler light pulse and the signal light pulse are extracted to the outside of the resonator by the extraction unit 304. . Then, it propagates through the third optical waveguide 309 and is output. After the third optical waveguide 309, the seed light pulse and the resonant light pulse are output to a space or separated by using a wavelength filter or a WDM coupler so as not to generate XPM. On the other hand, the idler light pulse and the signal light pulse that are not extracted to the outside are guided to the multiplexing unit 306 by the feedback unit 305 as a resonance light pulse. The resonance light pulse is superimposed in synchronism with the seed light pulse by the multiplexing unit 306, and is guided again to the nonlinear waveguide 302 by the second optical waveguide 307.

  The resonant light pulse is dispersed in the first optical waveguide 303, the feedback unit 305, the second optical waveguide 307, and the third optical waveguide 309 in the course of such a waveguide. The pulse compression unit 308 inserted in the middle compresses (shortens) the time width of the resonant optical pulse at the optical input end of the nonlinear waveguide 302 by compensating for all or part of this dispersion.

  Next, the function of each component of the wavelength conversion device 300 of the present embodiment will be described more specifically. In addition, the numerical value given below shows an example and this embodiment is not limited to these numerical values. The introduction unit 301 is made of a single mode fiber or the like, and introduces an optical pulse having a wavelength of 1035 nm as a seed light pulse, a repetition frequency of 10 MHz, a pulse energy of 2 nJ, and a pulse time width of 3.3 ps into the multiplexing unit 306. . The introduction of the seed light pulse into the wavelength conversion device 300 is performed by fusing the output fiber of the seed light source and the introduction unit 301. When the seed light pulse propagates through the space system, it may be coupled to the introduction unit 301 using a lens. Further, by introducing a seed light pulse directly from the spatial system to the multiplexing unit 306 using an optical system such as a mirror, a nonlinear process caused when an optical fiber is used for the introducing unit 301 may be reduced. In this case, the optical system such as the mirror serves as the introduction unit 301. Alternatively, the introduction unit 301 may be included in the multiplexing unit 306. In the present invention, the time width of the light pulse from the seed light source is preferably 0.8 ps or more and 20 ps or less, and more preferably 1 ps or more and 15 ps or less.

An optical fiber having a high nonlinear coefficient is used for the nonlinear waveguide 302. In this embodiment, the zero dispersion wavelength is 1054 nm, the second order dispersion constant is 1.64 × 10 ⁻³ ps ² / m, the third order dispersion constant is 6.55 × 10 ⁻⁵ ps ³ / m, and the fourth order dispersion constant is −9.40 × 10 ⁻⁸ ps ⁴ / m 20 cm photonic crystal fiber is used. This fiber realizes an optical parametric gain having a center wavelength of 824 nm and a bandwidth of 6 nm with respect to the seed light pulse. The fiber also provides a 1.4 ps walk-off between an optical pulse with a wavelength of 1035 nm and an optical pulse with a wavelength of 824 nm.

  The first optical waveguide 303 guides the signal light pulse output from the nonlinear waveguide 302 to the extraction unit 304 with a wavelength of 800 nm to 900 nm. In the present embodiment, a 10 cm single-mode fiber is used as the first optical waveguide 303, but the present invention is not limited to this, and the first optical waveguide 303 may be a waveguide that guides a resonant optical pulse. If a nonlinear process that occurs when an optical fiber is used for the first optical waveguide 303 becomes a problem, the first optical waveguide 303 may be guided by a spatial system from the nonlinear waveguide 302 to the extraction unit 304. In this case, the space portion where the resonant light pulse propagates becomes the first optical waveguide 303.

  The extraction unit 304 uses a fiber coupler that splits light having a wavelength of 800 nm or more and 900 nm or less into two, and guides a part of the signal light pulse to the feedback unit 305 as a resonance light pulse. The extraction unit 304 may be a spatial optical system such as a beam splitter. It is also possible to take out idler light pulses by WDM or a dichroic mirror and to guide the signal light to the feedback unit 305.

The feedback unit 305 uses an optical fiber whose length is adjusted so that the repetition frequency of the FOPO matches the repetition frequency of the seed light pulse. In this embodiment, a 10 m single mode fiber is used. A delay line may be inserted in the feedback unit 305 for fine adjustment of the repetition frequency. If the polarization of the resonant light pulse at the multiplexing unit 306 does not match the polarization of the seed light pulse, an element for controlling the polarization is inserted into the feedback unit 305 so that the polarization of the resonant light pulse and the seed light pulse are matched. Also good. The dispersion parameter for light with a wavelength of 800 nm to 900 nm of the single mode fiber used for the feedback unit 305 is about −100 ps / nm / km, which is about 35 ps ² / km in terms of group velocity dispersion. Therefore, in this embodiment using a 10 m single mode fiber, the feedback unit 305 gives a group delay dispersion of about 0.35 ps ² to the resonant light pulse. The resonant light pulse has a bandwidth of 6 nm (17 THz), and this resonator configuration satisfies the above equation (1). As a result, the time width of the resonant light pulse is expanded to about 6 ps due to dispersion of the feedback unit 305, and becomes larger than a value obtained by subtracting 1.4 ps of walk-off from the time width 3.3 ps of the seed light pulse.

FIG. 4 is a simulation result showing that the influence of XPM is reduced by the pulse compression unit in the wavelength converter according to the first embodiment of the present invention. FIG. 4A shows the spectrum of a resonant light pulse at the optical input end (entrance) of the nonlinear waveguide 302. If there is no pulse compression unit, as shown in broken lines f ₀ in FIG. 4 (b), distortion occurs in the spectrum of the resonant optical pulses at the output of the nonlinear waveguide 302 (exit). In this embodiment, since the output pulse is extracted from the resonant light by the optical coupler, this spectral distortion becomes the spectral distortion of the output pulse as it is. In the configuration of the present embodiment, for simplicity of explanation, the amount of dispersion given to the resonance light by the first optical waveguide 303 and the second optical waveguide 307 is small, compared with the amount of dispersion given by the feedback unit 305 to the resonance light. Can be ignored. Further, in the present embodiment, XPM generated in the first optical waveguide 303, the second optical waveguide 307, and the third optical waveguide 309 is negligible compared to XPM generated in the nonlinear waveguide 302. However, it is not limited to this.

  The multiplexing unit 306 synchronizes the resonant light pulse with a wavelength of 800 nm to 900 nm and the seed light pulse with a wavelength of 1035 nm introduced from the introducing unit 301. In this embodiment, WDM is used, but a dichroic mirror may be used for coupling in a spatial system.

  The second optical waveguide 307 guides the optical pulse combined by the combining unit 306 to the nonlinear waveguide 302. In this embodiment, a 10-cm single mode fiber is used as the second optical waveguide 307, but the present invention is not limited to this, and the second optical waveguide 307 may be a waveguide that guides a resonant light pulse and a seed light pulse. That's fine. Further, the light may be guided from the multiplexing unit 306 to the nonlinear waveguide 302 by a spatial system. In this case, the space part in which the seed light pulse and the resonant light pulse propagate and the element such as a lens that introduces the seed light pulse and the resonant light pulse into the nonlinear waveguide 302 are the second optical waveguide 307. By inserting an element for controlling the polarization into the second optical waveguide 307, the polarization of the laser pulse may be matched with the polarization in which the wavelength conversion in the nonlinear waveguide 302 occurs most efficiently.

The pulse compression unit 308 is a part that gives the group delay dispersion of the opposite sign to the group delay dispersion given by the feedback unit 305 to the resonance optical pulse. The pulse compression unit 308 may be inserted into any of the first optical waveguide 303, the feedback unit 305, and the second optical waveguide 307, or between the nonlinear waveguide 302 and the first optical waveguide 303, or the second optical waveguide. You may insert between 307 and the nonlinear waveguide 302. FIG. From the above equation (2), when the amount of dispersion to be given by the pulse compression unit 308 in the present embodiment is obtained, it is −0.46 ps ² or more and −0.24 ps or less. In this embodiment, by inserting a 10 m hollow fiber that gives a dispersion of 100 ps / nm / km to an optical pulse with a wavelength of 800 nm or more and 900 nm or less into the feedback unit 305, the resonant optical pulse has about −0.35 ps ² . Gives group delay dispersion. As a result, the sum of the dispersion amounts given to the resonant light pulse by the feedback unit 305 and the pulse compression unit 308 is 0 ps ² , and the time width of the resonant light pulse at the optical input end of the nonlinear waveguide 302 is the time width of the Fourier transform limit ( 0.13 ps). Time width Delta] t _r of the resonant optical pulse is smaller than the value obtained by subtracting the 1.4ps walk-off _{t wo} from 3.3ps duration Delta] t _p of the seed light pulse, the solid line _{f 1} shown in FIG. 4 (b) As shown, spectral distortion due to XPM is reduced.

  Thus, the time width of the resonant light pulse at the optical input end of the nonlinear waveguide 302 can be compressed by inserting the pulse compression unit 308. As a result, it is possible to perform wavelength conversion from the seed light pulse to the signal light pulse having a spectral width of 6 nm while suppressing the spectral distortion of the resonant light pulse caused by XPM. Also, by using an optical fiber that gives negative dispersion to the resonant light pulse as the pulse compression unit 308, the amount of dispersion given by adjusting the length of the fiber can be easily adjusted, and at the same time a compact configuration that does not use a spatial system It becomes possible.

As described above, in the present embodiment, the resonator includes the pulse compression unit that compresses the time width of the resonant light pulse at the optical input end of the nonlinear waveguide by applying group delay dispersion to the resonant light pulse. As a result, it is possible to obtain a wavelength converter that can generate a high-peak-intensity optical pulse with less distortion in the spectrum shape while suppressing the energy of the optical pulse.
In the present embodiment, it is desirable that the above expression (2) is satisfied, but the present invention is not necessarily limited to this. In this embodiment, as long as a part or all of the group delay dispersion of the resonant optical pulse is compensated so that the time width of the resonant optical pulse at the optical input end of the nonlinear waveguide is further compressed, the resonant optical pulse The distortion of the spectrum shape can be further suppressed.

(Second Embodiment)
A wavelength converter according to the second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a schematic diagram showing a configuration of a wavelength conversion device according to the second embodiment of the present invention.

  This embodiment is different from the first embodiment in that the feedback unit 305 includes a wavelength filter 501 that limits the transmission wavelength. Others are the same as those in the first embodiment, and thus the description thereof is omitted.

The wavelength filter 501 shown in FIG. 5 is for limiting the transmission wavelength in the feedback unit 305 in order to obtain an output pulse having a narrower spectral width (for example, 4 nm) than the optical parametric gain band. Due to the wavelength selection by the wavelength filter 501, the spectral width of the resonant light pulse at the optical input end of the nonlinear waveguide 302 is also 4 nm. At this time, the time width of the resonant light pulse by dispersion of 0.35 ps ^{2 provided} by the feedback unit 305 is about 4 ps, which is longer than the time width of the seed light pulse. Even in this case, the time width at the optical input end of the nonlinear waveguide 302 becomes about the Fourier transform limit pulse width (0.20 ps) by inserting the same pulse compression unit 308 as in the first embodiment, and the resonance light by XPM Can be suppressed.

  As described above, in the present embodiment, the feedback unit has the wavelength filter that limits the wavelength of the resonant light pulse. As a result, the spectral line width of the output pulse determined in the optical parametric gain band in the first embodiment can be controlled to an arbitrary spectral line width.

(Third embodiment)
A wavelength conversion device according to the third embodiment of the present invention will be described. The configuration of this embodiment is the same as that of the first embodiment shown in FIG. This embodiment is different from the first embodiment in that the pulse compression unit 308 includes an optical fiber that gives positive group velocity dispersion to the resonant light pulse. Others are the same as those in the first embodiment, and thus the description thereof is omitted.

  In this embodiment, the length of the feedback unit 305 is adjusted, and the idler light pulse having a wavelength of 1350 nm or more and 1450 nm or less is synchronized with the seed light pulse by the multiplexing unit 306, thereby making the idler light pulse a resonant light pulse. It is also possible to use a WDM or dichroic mirror instead of the optical coupler as the extraction unit 304, extract a signal light pulse having a wavelength of 800 nm to 900 nm as an output, and introduce only the idler light pulse into the feedback unit 305. In this case, the generated signal light pulse can be extracted without energy loss.

A single mode fiber that propagates a resonant light pulse is used as the feedback unit 305. These fibers generally impart negative dispersion to light pulses having a wavelength of 1350 nm to 1450 nm. In this case, a fiber that gives positive dispersion to an optical pulse with a wavelength of 1350 nm or more and 1450 nm or less, such as a dispersion compensating fiber, is used as the pulse compression unit 308 with its length adjusted. As a result, it is possible to time width Delta] t _r of the resonant light pulse in the light input end of the nonlinear waveguide 302 compresses the resonant optical pulse so as to satisfy the above equation (7).

  As described above, in this embodiment, the pulse compression unit includes an optical fiber that gives positive group velocity dispersion to the resonant light pulse. Thereby, an optical pulse having a wavelength that receives negative group delay dispersion from the resonator can be used as the resonant optical pulse. Note that this embodiment can also be implemented in combination with the first and second embodiments.

(Fourth embodiment)
The wavelength converter in the 4th Embodiment of this invention is demonstrated. The configuration of this embodiment is the same as that of the first embodiment shown in FIG. This embodiment is different from the first embodiment in that the pulse compression unit 308 includes an optical system using a chirp mirror. Others are the same as those in the first embodiment, and thus the description thereof is omitted.

In this embodiment, as a seed light pulse, an optical pulse having the same wavelength, energy, and pulse time width as that of the first embodiment and having a repetition frequency higher than that of the first embodiment, for example, 25 MHz, is supplied to the multiplexing unit 306. Introduce. As the feedback unit 305, a single mode fiber having a length of about 6 m is used. The dispersion that this fiber gives to the resonant light pulse is about 35 ps ² / km in terms of group velocity dispersion. Therefore, in this embodiment, the feedback unit 305 gives a group delay dispersion of about 0.21 ps ² to the resonant optical pulse, and the time width of the resonant optical pulse at the optical input end of the nonlinear waveguide 302 is 3.5 ps. It becomes.

As the pulse compression unit 308, instead of the fiber that gives the negative dispersion used in the first embodiment to the resonant light pulse, the resonant light pulse is once emitted into the spatial system and reflected by the chirped mirror, thereby generating the resonant light pulse. Give negative dispersion. From the above equation (2), the dispersion amount to be given by the pulse compression unit 308 in the present embodiment is −0.32 ps ² or more and −0.10 ps ² or less. In the present embodiment, a chirped mirror which gives the dispersion of 175 fs ² at one reflection as chirped mirror, imparting dispersion -0.14Ps ² by reflection gauge 80 times. As a result, the pulse width of the resonant light pulse at the optical input end of the nonlinear waveguide 302 is compressed to about 1.2 ps. The time width Delta] t _r of the resonant optical pulse is smaller than the value obtained by subtracting the 1.4ps walk-off _{t wo} from 3.3ps duration Delta] t _p of the seed light pulse, the spectral distortion due to XPM is reduced.

  As described above, in this embodiment, the pulse compression unit includes an optical system using a chirp mirror. Thereby, the dispersion amount which can be provided can be easily adjusted by changing the number of reflections of the chirp mirror. In addition, the design of the chirp mirror makes it possible to control not only group delay dispersion but also higher-order dispersion. Furthermore, the FOPO repetition frequency can be easily adjusted by changing the optical path length of the spatial system. Note that this embodiment can also be implemented in combination with the first to third embodiments.

(Fifth embodiment)
A wavelength converter according to a fifth embodiment of the present invention will be described with reference to FIG. FIG. 6 is a schematic diagram showing a configuration of a pulse compression unit in the wavelength conversion device according to the fifth embodiment of the present invention. The configuration of this embodiment is the same as that of the first embodiment shown in FIG. This embodiment is different from the first embodiment in that the pulse compression unit 308 includes an optical system using a diffraction grating. Others are the same as those in the first embodiment, and thus the description thereof is omitted.

In the present embodiment, the pulse compression unit 308 uses a diffraction grating 601 as shown in FIG. 6 in place of the fiber that gives the negative dispersion used in the first embodiment to the resonant light pulse, so that the resonant light can be used. Give negative dispersion. Using a diffraction grating of the number of grooves 1200 / mm as a diffraction grating 601, the incident angle 71 degrees to the first sheet of the diffraction grating, by the spacing of the diffraction grating pair and 7.3 cm, distribution of -0.21Ps ² To the resonant light. As a result, the time width of the resonant light pulse at the optical input end of the nonlinear waveguide 302 is compressed to 130 fs. The time width Delta] t _r of the resonant optical pulse is smaller than the value obtained by subtracting the 1.4ps walk-off _{t wo} from 3.3ps duration Delta] t _p of the seed light pulse, the spectral distortion due to XPM is reduced.

  As described above, in this embodiment, the pulse compression unit includes an optical system using a diffraction grating. Here, the pulse compression unit may have a configuration using a pair of diffraction grating pairs and a folding mirror. Thereby, the dispersion amount which can be provided by changing the distance between the diffraction grating pairs can be easily adjusted. Further, the FOPO repetition frequency can be easily adjusted by changing the distance between the diffraction grating pair and the folding mirror. Note that this embodiment can be implemented in combination with the first to fourth embodiments.

(Sixth embodiment)
A wavelength converter according to the sixth embodiment of the present invention will be described. The configuration of this embodiment is the same as that of the first embodiment shown in FIG. This embodiment is different from the first embodiment in that the pulse compression unit 308 includes a fiber Bragg grating. Others are the same as those in the first embodiment, and thus the description thereof is omitted.

  In the present embodiment, the feedback unit 305 uses a single mode fiber having a length of about 19 m. As the pulse compression unit 308, instead of the fiber that gives the negative dispersion used in the first embodiment to the resonant optical pulse, a circulator and a chirped fiber Bragg grating (CFBG) are used to apply negative group delay dispersion to the resonant optical pulse. Give.

  As described above, in the present embodiment, the pulse compression unit includes the fiber Bragg grating. Thus, by adjusting the design of the fiber Bragg grating, not only the group delay dispersion but also the higher-order phase dispersion of the resonant light pulse can be controlled without using a spatial system. This embodiment can also be implemented in combination with the first to fifth embodiments.

(Seventh embodiment)
A wavelength conversion device according to a seventh embodiment of the present invention will be described with reference to FIG. In the first embodiment, the method for suppressing XPM generated in the nonlinear waveguide 302 has been mainly described. In the present embodiment, a method for suppressing XPM generated in waveguides other than the nonlinear waveguide 302 will be described. The configuration of this embodiment is the same as that of the first embodiment.

In the first embodiment, the XPM for the resonant light pulse is mainly generated in the nonlinear waveguide 302. The pulse compression conditions of the above equations (2) and (3) are defined so that the time width of the resonant light pulse is compressed in the nonlinear waveguide 302. However, in a waveguide where XPM other than the nonlinear waveguide 302 cannot be ignored, if the time width of the resonant light pulse is widened, the spectrum of the resonant light pulse is distorted. Therefore, in the present embodiment, the pulse compression condition is defined so that the time width of the resonant light pulse is also compressed in waveguides other than the nonlinear waveguide 302. Specifically, instead of the walk-off t _{wo in} the above equation (3), for example, the following equation including a walk-off term for the seed light pulse of the resonant light pulse in the first optical waveguide 303 and the third optical waveguide 309 is used. (8) is used.

That is, when the seed light pulse and the resonant light pulse overlap and propagate from the optical input end of the nonlinear waveguide 302 to the optical output end of the third optical waveguide 309, the walk-off amount t _wo is expressed by the above equation (8). Given in. Here, the subscripts “NL”, “1”, and “3” indicate constants related to the nonlinear waveguide 302, the first optical waveguide 303, and the third optical waveguide 309, respectively. Since the length of the extraction unit 304 is sufficiently short, the walk-off in the extraction unit 304 is included in the first optical waveguide 303. The pulse compression unit 308 of this embodiment gives group delay dispersion to the resonant optical pulse so that the pulse compression condition using the above equation (8) is satisfied at the optical input end of the nonlinear waveguide 302. Thereby, the time width of the resonant light pulse from the optical input end of the nonlinear waveguide 302 to the optical output end of the third optical waveguide 309 can be compressed, and the spectral distortion of the resonant optical pulse due to XPM can be suppressed.

Alternatively, the following equation (9) including a walk-off term in the second optical waveguide 307 may be used instead of the above equation (8). In this case, the pulse compression unit 308 performs group delay on the resonant optical pulse so that the pulse compression condition using the above equation (9) is satisfied at the multiplexing unit 306 (or the optical input end of the second optical waveguide 307). Give dispersion.

That is, when the seed light pulse and the resonance light pulse overlap and propagate from the multiplexing unit 306 to the light output end of the third optical waveguide 309, the walk-off amount t _wo is given by the above equation (9). Here, the subscript “2” indicates a constant related to the second optical waveguide 307. Since the length of the multiplexing unit 306 is sufficiently short, the walk-off in the multiplexing unit 306 is included in the second optical waveguide 307. Thereby, the time width of the resonant light pulse from the multiplexing unit 306 to the light output end of the third optical waveguide 309 can be compressed, and the spectral distortion of the resonant light pulse due to XPM can be suppressed.

An example when the pulse compression condition satisfies the above equation (9) is shown below. Assume that an optical pulse having a wavelength of 1035 nm, a repetition frequency of 10 MHz, a pulse energy of 4 nJ, and a pulse time width of 6.6 ps is used as the seed light pulse. Assume that XPM occurs in the first optical waveguide 303, the second optical waveguide 307, and the third optical waveguide 309. Note that the extraction unit 304 extracts the seed light pulse and the resonance light pulse, so that the light intensity of the optical pulse to be fed back becomes sufficiently small. Therefore, the XPM in the feedback unit 305 is negligibly small. As the first optical waveguide 303, the second optical waveguide 307, and the third optical waveguide 309, single-mode fibers (Corning, HI-1060) each having a length of 10 cm are used as in the first embodiment. Further, it is assumed that the dispersion value of the single mode fiber is −53 ps / nm / km at 980 nm. At this time, the 10 cm single-mode fiber provides a walk-off t _wo of approximately 1.12 ps between the seed light pulse having a wavelength of 1035 nm and the resonant light pulse having a wavelength of 824 nm. Also, as described in the first embodiment, the 20 cm nonlinear waveguide 302 provides a walk-off of approximately 1.40 ps. Therefore, the total amount of walk-off t _wo from the multiplexing unit 306 to the optical output end of the third optical waveguide 309 is 4.76 (= 1.40 + 3 × 1.12) ps.

On the other hand, the pulse compression unit 308 of the present embodiment compresses the time width of the resonant light pulse in the multiplexing unit 306 to about the time width of the Fourier transform limit (0.13 ps), as in the first embodiment. . Accordingly, the time width Delta] t _r of the resonant light pulse becomes smaller than a value obtained by subtracting the total amount 4.76ps walk-off _{t wo} from 6.6ps duration Delta] t _p of the seed light pulse, Fig. 4 (b) as shown by the solid line _{f 1,} the spectral distortion due to XPM is reduced. Similarly, even when the pulse compression condition satisfies the above equation (8), the spectral distortion due to XPM is reduced.

  As described above, in the present embodiment, the resonant optical pulse of the resonant optical pulse is further satisfied so that the pulse compression condition further including the walk-off term in the first optical waveguide and the third optical waveguide is further satisfied at the optical input end of the nonlinear waveguide. Compress time span. Thereby, the time width of the resonant light pulse from the optical input end of the nonlinear waveguide to the optical output end of the third optical waveguide can be compressed, and the spectral distortion of the resonant optical pulse due to XPM can be suppressed.

  Alternatively, the time width of the resonant optical pulse is compressed so that the pulse compression condition that further includes the walk-off term in the second optical waveguide is further satisfied at the multiplexing portion (or the optical input end of the second optical waveguide). Thereby, the time width of the resonant light pulse from the multiplexing part to the light output end of the third optical waveguide can be compressed, and the spectral distortion of the resonant light pulse due to XPM can be suppressed. This embodiment can also be implemented in combination with the first to sixth embodiments.

(Eighth embodiment)
A wavelength converter according to an eighth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a schematic diagram showing a configuration of a wavelength conversion device 300b according to the eighth embodiment of the present invention. The wavelength conversion device 300b illustrated in FIG. 7 amplifies the seed light pulse between the first optical waveguide 303 and the nonlinear waveguide 302, as compared with the wavelength conversion device 300 according to the first embodiment illustrated in FIG. The difference is that an optical amplifier 700 is provided. Others are the same as those in the first embodiment, and thus the description thereof is omitted. An optical amplifier 700 shown in FIG. 7 includes a laser diode 702, a pump optical waveguide 703, a pump combiner 704, a fourth optical waveguide 705, and an optical amplification fiber 706.

  The optical amplification fiber 706 amplifies the 1035 nm seed light pulse. As the optical amplification fiber 706, for example, YbDF (ytterbium-doped fiber) can be used. Alternatively, different types of rare earth-doped fibers such as ErDF (erbium-doped fiber) may be used instead of the optical amplification fiber 706 depending on the wavelength band. A semiconductor optical amplifier or the like may be used. The laser diode 702 generates pump light for exciting the optical amplification fiber 706. The pump optical waveguide 703 guides the pump light to the pump combiner 704. The pump combiner 704 combines the pump light, the seed light pulse, and the resonance light pulse. The fourth optical waveguide 705 guides the combined pump light, seed light pulse, and resonant light pulse to the nonlinear waveguide 302. In the present embodiment, the length of the optical amplification fiber 706 is 80 cm, and the length of the fourth optical waveguide 705 is 10 cm.

  In the present embodiment, since the optical amplifier 700 is provided in this way, the energy of the seed light pulse introduced by the introducing unit 301 can be reduced as compared with the first embodiment. For example, an optical pulse having a wavelength of 1035 nm, a repetition frequency of 10 MHz, a pulse energy of 0.5 nJ, and a pulse time width of 6.6 ps is introduced as a seed light pulse. Since the pulse energy of the seed light pulse is thus small, XPM generated between the seed light pulse and the resonance light pulse is negligibly small from the multiplexing unit 306 to the light output end of the fourth optical waveguide 705. In the optical amplifying fiber 706, the seed light pulse is amplified and the pulse energy becomes as large as 4 nJ. However, since the core diameter of the optical amplifying fiber 706 is as large as 10 μm, XPM generated in the optical amplifying fiber 706 can be similarly ignored. Small enough. The seed light pulse and the resonant light pulse guided to the nonlinear waveguide 302 undergo energy transition from the seed light pulse to the resonant light pulse due to the parametric gain generated in the nonlinear waveguide 302.

As described above, in the present embodiment, XPM in the second optical waveguide 307 and the optical amplifier 700 can be ignored, and therefore, for example, the above equation (8) can be used. The time width of the resonant light pulse from the multiplexing unit 306 to the light output end of the third optical waveguide 309 can be compressed. The first optical waveguide 303, the second optical waveguide 307, and the third optical waveguide 309 are assumed to be the same as those in the first embodiment. Also, as described in the first embodiment, the 20 cm nonlinear waveguide 302 provides a walk-off of approximately 1.40 ps. At this time, the total amount of the walk-off t _wo given from the multiplexing unit 306 to the output end of the third optical waveguide 309 is 3.64 (= 1.40 + 2 × 1.12) ps.

On the other hand, the pulse compression unit 308 of the present embodiment compresses the time width of the resonant light pulse in the multiplexing unit 306 to about the time width of the Fourier transform limit (0.13 ps), as in the first embodiment. . Accordingly, the time width Delta] t _r of the resonant light pulse becomes smaller than a value obtained by subtracting the total amount 3.64ps walk-off _{t wo} from 6.6ps duration Delta] t _p of the seed light pulse, Fig. 4 (b) as shown by the solid line _{f 1,} the spectral distortion due to XPM is reduced.

  As described above, this embodiment further includes an optical amplifier that is connected between the second optical waveguide and the nonlinear waveguide and amplifies the first optical pulse. Thereby, since XPM in the second optical waveguide 307 can be ignored, the time width of the resonant light pulse from the multiplexing portion (or the optical input end of the second optical waveguide) to the optical output end of the third optical waveguide is compressed, Spectral distortion of the resonant light pulse due to XPM can be suppressed. Note that this embodiment can also be implemented in combination with the first to seventh embodiments.

(Ninth embodiment)
A wavelength converter according to the ninth embodiment of the present invention will be described with reference to FIG. In the eighth embodiment, the case where the pulse energy of the seed light pulse is small and XPM in the second optical waveguide 307 and the optical amplifier 700 can be ignored has been described. On the other hand, in the present embodiment, a case where the pulse energy of the seed light pulse is large and XPM in the second optical waveguide 307 and the optical amplifier 700 cannot be ignored will be described. The configuration of this embodiment is the same as that of the eighth embodiment.

In this embodiment, an optical pulse having a wavelength of 1035 nm, a repetition frequency of 10 MHz, a pulse energy of 4 nJ, and a pulse time width of 16 ps is introduced as a seed light pulse. When the pulse energy of the seed light pulse is thus large, the influence of XPM generated in the second optical waveguide 307 and the optical amplifier 700 cannot be ignored. Therefore, in this embodiment, the pulse compression condition is defined so that the time width of the resonant light pulse is also compressed in the second optical waveguide 307 and the optical amplifier 700. Specifically, instead of the walk-off t _{wo in} the above equation (8), the following equation (10) further including a walk-off term in the second optical waveguide 307 and the optical amplifier 700 is used.

That is, when the seed light pulse and the resonant light pulse are propagated through the optical amplifier 700, the walk-off amount t _wo is given by the above equation (10). Here, subscripts “4” and “A” indicate constants relating to the fourth optical waveguide 705 and the optical amplification fiber 706, respectively. The pulse compression unit 308 of this embodiment gives group delay dispersion to the resonant optical pulse so that the pulse compression condition using the above equation (10) is satisfied in the multiplexing unit 306. Thereby, the time width of the resonant light pulse from the multiplexing unit 306 to the light output end of the third optical waveguide 309 can be compressed, and the spectral distortion of the resonant light pulse due to XPM can be suppressed.

For example, suppose that the same thing as 1st Embodiment is used as the 1st optical waveguide 303, the 2nd optical waveguide 307, and the 3rd optical waveguide 309. FIG. The dispersion value of the fourth optical waveguide 705 and the optical amplification fiber 706 is assumed to be −50 ps / nm / km at 980 nm. A 10 cm fourth optical waveguide 705 and an 80 cm optical amplification fiber 706 provide a walk-off of approximately 10 ps. Also, as described in the first embodiment, the 20 cm nonlinear waveguide 302 provides a walk-off of approximately 1.40 ps. Therefore, the total amount of walk-off t _wo from the multiplexing unit 306 to the optical output end of the third optical waveguide 309 is 14.76 (= 1.40 + 3 × 1.12 + 10.00) ps.

On the other hand, the pulse compression unit 308 of the present embodiment compresses the time width of the resonant light pulse in the multiplexing unit 306 to about the time width of the Fourier transform limit (0.13 ps), as in the first embodiment. . Accordingly, the time width Delta] t _r of the resonant light pulse becomes smaller than a value obtained by subtracting the total amount 14.76ps walk-off _{t wo} from 16ps duration Delta] t _p of the seed light pulse, a solid line f shown in FIG. 4 (b) _As shown in FIG. ₁ , the spectral distortion due to XPM is reduced.

  As described above, in the present embodiment, the time width of the resonant optical pulse is compressed so that the pulse compression condition that further includes the walk-off term in the multiplexing unit 306 is further satisfied in the multiplexing unit 306. Thereby, the time width of the resonant light pulse from the multiplexing unit 306 to the optical output end of the third optical waveguide can be compressed, and the spectral distortion of the resonant light pulse due to XPM can be suppressed.

(Tenth embodiment)
A wavelength converter according to the tenth embodiment of the present invention will be described with reference to FIG. In the eighth embodiment, the case where XPM in the optical amplifier 700 is negligible has been described. On the other hand, in the ninth embodiment, the case where XPM in the optical amplifier 700 cannot be ignored has been described. On the other hand, in this embodiment, a case where XPM in the optical amplifier 700 can be partially ignored will be described. The configuration of this embodiment is the same as that of the eighth embodiment.

In this embodiment, an optical pulse having a wavelength of 1035 nm, a repetition frequency of 10 MHz, a pulse energy of 0.5 nJ, and a pulse time width of 12 ps is introduced as a seed light pulse. In this embodiment, the pulse energy of the seed light pulse is thus small. However, as the seed light pulse is amplified on the optical output end side of the optical amplification fiber 706 constituting the optical amplifier 700, the seed light pulse and the resonant light are amplified. The XPM during the pulse becomes large. Therefore, in the present embodiment, the pulse compression condition is defined so as to include the XPM term partially generated on the light output end side of the optical amplification fiber 706. Specifically, instead of the walk-off t _{wo in} the above equation (8), the following equation (11) including the walk-off term Δt _wo in the optical amplification fiber 706 is used.

That is, when the seed light pulse and the resonance light pulse are propagated through the optical amplification fiber 706 of the optical amplifier 700, the walk-off amount t _wo is given by the above equation (11). Here, in the optical amplifier, the group refractive index for the first optical pulse of the optical amplification fiber that amplifies the first optical pulse is n _pA , the group refractive index for the resonant optical pulse is n _rA , the length is L _A , and the vacuum The light speed inside was set to c. The walk-off term Δt _wo in the optical amplifying fiber 706 becomes the maximum value L _A | n _rA −n _pA | when XPM occurs in the entire length from the input end to the output end of the optical amplifying fiber 706, and XPM does not occur. In this case, the minimum value is 0. The pulse compression unit 308 gives group delay dispersion to the resonant optical pulse so that the pulse compression condition using the above equation (11) is satisfied in the optical amplification fiber 706 in the optical amplification unit. Thereby, the time width of the resonant light pulse from the optical amplification fiber 706 to the optical output end of the third optical waveguide 309 can be compressed, and the spectral distortion of the resonant light pulse due to XPM can be suppressed.

For example, suppose that the same thing as 1st Embodiment is used as the 1st optical waveguide 303, the 2nd optical waveguide 307, and the 3rd optical waveguide 309. FIG. The dispersion value of the optical amplification fiber 706 is assumed to be −50 ps / nm / km at 980 nm. Then, at 20 cm from the input end side of the 80 cm optical amplifying fiber 706, the seed light pulse is not sufficiently amplified and XPM is negligibly small, while the remaining 60 cm has a walk-off of about 6.5 ps. Suppose you give. Also, as described in the first embodiment, the 20 cm nonlinear waveguide 302 provides a walk-off of approximately 1.40 ps. Therefore, the total amount of the walk-off t _wo from the multiplexing unit 306 to the optical output end of the third optical waveguide 309 is 10.14 (= 1.40 + 2 × 1.12 + 6.5) ps.

On the other hand, the pulse compression unit 308 of the present embodiment compresses the time width of the resonant light pulse in the optical amplifying fiber 706 to the time width of the Fourier transform limit (0.13 ps) as in the first embodiment. . Accordingly, the time width Delta] t _r of the resonant light pulse becomes smaller than a value obtained by subtracting the total amount 10.14ps walk-off _{t wo} from 12ps duration Delta] t _p of the seed light pulse, a solid line f shown in FIG. 4 (b) _As shown in FIG. ₁ , the spectral distortion due to XPM is reduced.

As described above, in this embodiment, the walk-off t _wo further includes a partial walk-off Δt _wo in the optical amplification fiber that amplifies the first optical pulse in the optical amplification fiber. Thereby, the time width of the resonant light pulse from the optical input end of the optical amplification fiber to the optical output end of the third optical waveguide can be compressed, and the spectral distortion of the resonant optical pulse due to XPM can be suppressed.

(Eleventh embodiment)
A light source device according to an eleventh embodiment of the present invention will be described with reference to FIG. FIG. 8 is a schematic diagram showing a configuration of a light source device 800 according to the eleventh embodiment of the present invention. The light source device 800 of this embodiment shown in FIG. 8 further includes a laser 801, a demultiplexing unit 802, a second pulse compression unit 803, and a second combination with respect to the wavelength conversion device 300 or 300b of the first to tenth embodiments. A wave unit 804 is provided.

  The laser 801 outputs an optical pulse having a first wavelength. As the laser 801, for example, a Yb fiber mode-locked laser that outputs an optical pulse of 1035 nm as the first wavelength can be used. An output pulse from the laser 801 is branched into two optical pulses by a demultiplexing unit 802 using an optical coupler or the like. Each branched optical pulse is amplified by a Yb-doped fiber that is excited by an LD (Laser Diode) or the like. One of the amplified light pulses is input to the wavelength conversion device 300 as a seed light pulse. The wavelength conversion device 300 converts the wavelength of the 1035 nm seed light pulse into a signal light pulse having a center wavelength of 750 nm to 900 nm. As a result, a signal light pulse having a high peak intensity with little distortion of the spectrum shape can be obtained. Furthermore, by compensating the phase dispersion of the signal light pulse by the second pulse compression unit 803, it is possible to obtain a short pulse output having a time width of 130 fs. If the time width of the signal light pulse output from the wavelength conversion device 300 is sufficiently short, the second pulse compression unit 803 may be omitted. This signal light pulse is multiplexed in synchronism with the other optical pulse having a wavelength of 1035 nm separated by the demultiplexing unit 802 and the second multiplexing unit 804 such as WDM. In this manner, a two-wavelength pulsed light synchronized light source used for molecular imaging becomes possible.

  As described above, the light source device of the present embodiment includes the wavelength conversion devices of the first to tenth embodiments. Then, the optical pulse obtained by converting the wavelength of the optical pulse having the first wavelength using the wavelength conversion device and the optical pulse having the first wavelength are output in synchronization. For example, a signal light pulse having a center wavelength of 750 nm to 900 nm is generated from the light pulse having the first wavelength of 1035 nm. At this time, since the repetition frequencies of the two optical pulses are completely the same, a two-wavelength pulse-synchronized light source can be realized without requiring a device for controlling the repetition frequency. Although the two-wavelength pulse-synchronized light source is taken as an example here, the wavelength converters described in the first to tenth embodiments can also be used for three or more optical pulse-synchronized light sources.

(Twelfth embodiment)
An information acquisition apparatus according to the twelfth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a schematic diagram showing a configuration of an information acquisition apparatus 900 according to the twelfth embodiment of the present invention. The information acquisition apparatus 900 of this embodiment shown in FIG. 9 is a two-photon microscope system configured to further include a photodetector 908 with respect to the wavelength conversion apparatus 300 or 300b of the first to tenth embodiments. The photodetector 908 detects light that is output from the wavelength conversion device 300 or 300b and propagates through the subject.

  For example, an output pulse having a wavelength of 1035 nm from a Yb fiber mode-locked laser is introduced into the wavelength converter 300 or 300b described in the first to tenth embodiments. Then, a signal light pulse output having a high peak intensity with a center wavelength of 750 nm or more and 900 nm or less, a spectrum width of 6 nm and little distortion of the spectrum shape is obtained.

  The obtained signal light pulse passes through the beam collimator 901, the X scan mirror 902, and the Y scan mirror 903, and is condensed and irradiated onto the subject 907 fixed to the stage 906 by the dichroic mirror 904 and the objective lens 905. In the subject 907, fluorescence due to two-photon absorption occurs in the portion where the light pulse is condensed and irradiated. This fluorescence is captured by the objective lens 905, passes through the dichroic mirror 904, and is detected by the photodetector 908.

  At this time, when the X scan mirror 902 is driven, the condensing point can scan the inside of the subject 907 in the X direction, and when the Y scan mirror 903 is driven, the condensing point is perpendicular to the X direction in the subject 907. Can be scanned in the Y direction. Accordingly, a two-dimensional image can be acquired by scanning the focal point on the subject 907 with the X scan mirror 902 and the Y scan mirror 903.

  Further, after the end of one two-dimensional scan, the stage 906 is moved to move the focal point by a predetermined distance in the optical axis direction, and a similar two-dimensional scan is repeated to obtain a three-dimensional image of the subject 907. Is possible. In addition, it is also possible to use the light source device 800 of the eleventh embodiment instead of the wavelength conversion device 300 or 300b of the first to tenth embodiments.

  As described above, in the information acquisition apparatus according to the present embodiment, the output from the wavelength conversion apparatus according to the first to tenth embodiments or the output from the light source apparatus according to the eleventh embodiment is used as a light source. A light detector that detects light output from the wavelength conversion device or the light source device and propagating through the subject is provided. This makes it possible to obtain a two-photon microscope that can increase the peak intensity by narrowing the pulse width and can acquire information with a high SN ratio.

  In the present embodiment, a two-photon microscope is used as an information acquisition device that irradiates a subject with a light pulse, detects at least one of light reflected, transmitted, or emitted from the subject and acquires information about the subject. Was described as an example. However, the present invention is not limited to this, and the wavelength conversion described in any one of the first to tenth embodiments is also applied to information acquisition apparatuses such as a stimulated Raman scattering microscope and an endoscope, as in this embodiment. The light source device described in the eleventh embodiment can be used.

(Other embodiments)
The present invention is not limited to the above embodiment, and various modifications can be made. For example, the configuration described in the above embodiment is an example, and the wavelength conversion device, the light source device, and the information acquisition device to which the present invention can be applied are limited to the diagrams used in the description of the above embodiment. It is not something. The configurations described in the above embodiments can be implemented in combination. The present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

  In the present invention, it is desirable that the above expression (2) is satisfied, but the present invention is not necessarily limited to this. In the present invention, as long as a part or all of the group delay dispersion of the resonant optical pulse is compensated so that the time width of the resonant optical pulse is further compressed, distortion of the spectral shape of the resonant optical pulse is further suppressed. be able to.

301 Introduction unit 302 Non-linear waveguide 303 First optical waveguide 304 Extraction unit 305 Feedback unit 306 Multiplexing unit 307 Second optical waveguide 308 Pulse compression unit 501 Wavelength filter 601 Diffraction grating 700 Optical amplifier 800 Light source device 801 Laser 802 Demultiplexing unit 803 Second pulse compression unit 804 Second multiplexing unit 900 Information acquisition device 901 Beam collimator 902 X scan mirror 903 Y scan mirror 904 Dichroic mirror 905 Objective lens 906 Stage 907 Subject 909 Photo detector

Claims (19)

A multiplexing section for introducing a first optical pulse having a first wavelength;
A nonlinear waveguide for wavelength-converting the first optical pulse introduced from the multiplexing unit by optical parametric;
A take-out part for taking out a part of the wavelength-converted optical pulse;
A feedback unit that feeds back the wavelength-converted optical pulse that was not extracted by the extraction unit to the multiplexing unit as a resonant optical pulse;
A pulse compression unit that compresses the time width of the resonant light pulse by compensating at least part of the group delay dispersion of the resonant light pulse;
The pulse compression unit sets the time width of the first optical pulse to Δt _p , the spectral width of the resonant optical pulse to Δω _r , the sum of group delay dispersion given by the resonator to the resonant optical pulse, D _o , When the group delay dispersion given to the resonant optical pulse by the compression unit is D _c and the walk-off of the resonant optical pulse in the nonlinear waveguide with respect to the first optical pulse is t _wo , the following pulse compression condition

The wavelength conversion device is characterized in that the time width of the resonant light pulse is compressed so that In the wavelength converter of Claim 1,
A first optical waveguide connecting the extraction portion and the nonlinear waveguide;
A second optical waveguide connecting the multiplexing unit and the nonlinear waveguide; and
The pulse compression unit includes a group delay dispersion having a sign opposite to a sum of group delay dispersions given to the resonance optical pulse by a resonator including the nonlinear waveguide, the feedback unit, the first optical waveguide, and the second optical waveguide. A wavelength conversion device characterized by compressing the time width of the resonant light pulse in the nonlinear waveguide by applying to the resonant light pulse. In the wavelength converter of Claim 1,
A first optical waveguide connecting the extraction portion and the nonlinear waveguide;
A second optical waveguide connecting the multiplexing unit and the nonlinear waveguide; and
The pulse compression unit includes a group delay dispersion having a sign opposite to a sum of group delay dispersions given to the resonance optical pulse by a resonator including the nonlinear waveguide, the feedback unit, the first optical waveguide, and the second optical waveguide. Is applied to the resonant light pulse to compress the time width of the resonant light pulse in the multiplexing unit. In the wavelength converter of Claim 1,
A first optical waveguide connecting the extraction portion and the nonlinear waveguide;
An optical amplifying unit for amplifying the first optical pulse and connecting to the nonlinear waveguide;
A second optical waveguide connecting the multiplexing unit and the optical amplification unit,
The pulse compression unit includes a group delay dispersion having a sign opposite to a sum of group delay dispersions given to the resonance optical pulse by a resonator including the feedback unit, the first optical waveguide, the second optical waveguide, and the optical amplification unit. To the resonant light pulse, the time width of the resonant light pulse at the optical input end of the nonlinear waveguide is compressed. In the wavelength converter of Claim 1,
A first optical waveguide connecting the extraction portion and the nonlinear waveguide;
An optical amplifying unit for amplifying the first optical pulse and connecting to the nonlinear waveguide;
A second optical waveguide connecting the multiplexing unit and the optical amplification unit,
The pulse compression unit includes a group delay dispersion having a sign opposite to a sum of group delay dispersions given to the resonance optical pulse by a resonator including the feedback unit, the first optical waveguide, the second optical waveguide, and the optical amplification unit. The wavelength conversion device is characterized in that the time width of the resonant light pulse is compressed in the optical amplifying unit by applying to the resonant light pulse. A multiplexing section for introducing a first optical pulse having a first wavelength;
A nonlinear waveguide for wavelength-converting the first optical pulse introduced from the multiplexing unit by optical parametric;
A take-out part for taking out a part of the wavelength-converted optical pulse;
A feedback unit that feeds back the wavelength-converted optical pulse that was not extracted by the extraction unit to the multiplexing unit as a resonant optical pulse;
A pulse compression unit that compresses the time width of the resonant light pulse by compensating at least part of the group delay dispersion of the resonant light pulse;
The pulse compression unit sets the time width of the first optical pulse to Δt _p , the spectral width of the resonant optical pulse to Δω _r , the sum of group delay dispersion given by the resonator to the resonant optical pulse, D _o , The group delay dispersion given to the resonance light pulse by the compression unit is D _c , and the walk-off of the resonance light pulse with respect to the first light pulse at the portion where the first light pulse and the resonance light pulse propagate in an overlapping manner. _{Where two} is the pulse compression condition of the following equation

The wavelength conversion device is characterized in that the time width of the resonant light pulse is compressed so that The wavelength converter according to claim 6,
A first optical waveguide connecting the extraction portion and the nonlinear waveguide;
An optical amplifying unit for amplifying the first optical pulse and connecting to the nonlinear waveguide;
A second optical waveguide connecting the multiplexing unit and the optical amplification unit;
A third optical waveguide forming an output end from the take-out part,
The portion in which the first optical pulse and the resonant optical pulse are overlapped and propagates is the multiplexing unit, the first optical waveguide, the second optical waveguide, the optical amplification unit, the nonlinear waveguide, and the extraction unit. And the third optical waveguide. The wavelength converter according to claim 6,
A first optical waveguide connecting the extraction portion and the nonlinear waveguide;
A second optical waveguide connecting the multiplexing unit and the nonlinear waveguide;
A third optical waveguide forming an output end from the take-out part,
The portions where the first optical pulse and the resonant optical pulse are overlapped and propagated are the multiplexing portion, the first optical waveguide, the second optical waveguide, the nonlinear waveguide, the extraction portion, and the third optical light. A wavelength converter characterized by being a waveguide. The wavelength converter according to claim 6,
The wavelength converter according to claim 1, wherein the first optical pulse and the resonant optical pulse are overlapped and propagated at least in the multiplexing unit, the nonlinear waveguide, and the extraction unit. In the wavelength converter of any one of Claim 1 to 9,
The wavelength conversion device, wherein the pulse compression unit is inserted into the feedback unit. In the wavelength converter of any one of Claim 1 to 10,
The wavelength converter according to claim 1, wherein the feedback unit includes a wavelength filter that limits a wavelength of the resonant light pulse. The wavelength converter according to any one of claims 1 to 11,
The wavelength converter according to claim 1, wherein the pulse compression unit includes an optical fiber that gives negative group velocity dispersion to the resonant light pulse. The wavelength converter according to any one of claims 1 to 11,
The wavelength converter according to claim 1, wherein the pulse compression unit includes an optical fiber that gives positive group velocity dispersion to the resonant light pulse. The wavelength converter according to any one of claims 1 to 13,
The wavelength conversion device, wherein the pulse compression unit includes an optical system using a chirp mirror. The wavelength converter according to any one of claims 1 to 14,
The wavelength converter according to claim 1, wherein the pulse compression unit includes an optical system using a diffraction grating. The wavelength converter according to any one of claims 1 to 15,
The wavelength conversion device, wherein the pulse compression unit includes a fiber Bragg grating.   17. A light source device comprising: the wavelength conversion device according to claim 1; and a laser that outputs the first optical pulse having the first wavelength.   An information device comprising: the wavelength conversion device according to any one of claims 1 to 16; and a photodetector that detects light output from the wavelength conversion device and propagating through the subject. Acquisition device.   An information acquisition apparatus comprising: the light source device according to claim 17; and a photodetector that detects light output from the light source device and propagating through the subject.

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