Pulsed light generating device and pulsed light generating method

Abstract

A desired number of pulsed lights are generated by modulation using the soliton self-frequency shift. [Solution] A pulsed light generating device 100 includes an oscillator 1 that oscillates pulsed light L, a compressor 4 that is arranged downstream of the oscillator 1 in the optical path of the pulsed light L and controls the time width of the pulsed light L, and a soliton shifted fiber 5 that is arranged downstream of the compressor 4 in the optical path of the pulsed light L and modulates the wavelength of the pulsed light L using soliton self-frequency shift to form one or multiple pulsed lights L with different wavelengths. The compressor 4 controls the time width of the pulsed light L so that the number of pulsed lights L formed in the soliton shifted fiber 5 is a predetermined number.

Description

[Technical Field]

[0001] The present disclosure relates to a pulsed light generating device and a pulsed light generating method. [Background technology]

[0002] A pulsed light generating device is known that includes an oscillator for generating pulsed light and a modulator for modulating the wavelength of the pulsed light generated by the oscillator using soliton self-frequency shift. In such a pulsed light generating device, the intensity of the pulsed light before modulation by the modulator is increased, and the pulsed light is split by the modulation, forming multiple pulsed lights with different wavelengths (multicolored solitons are output) (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2004-527001 Summary of the Invention [Problem to be solved by the invention]

[0004] In a pulsed light generating device, it is sometimes desirable to generate a desired number of pulsed lights by modulation using a modulation unit. However, the above-described techniques have low stability of the generated pulsed lights and make it difficult to control the number of pulsed lights, so there is a risk that the desired number of pulsed lights may not be generated. Therefore, an object of the present disclosure is to provide a pulsed light generating device and a pulsed light generating method that can generate a desired number of pulsed lights by modulation using soliton self-frequency shift. [Means for solving the problem]

[0005] The pulsed light generating device of the present disclosure is [1] "a pulsed light generating device comprising: an oscillator that oscillates pulsed light; a controller that is arranged downstream of the oscillator in the optical path of the pulsed light and controls the time width of the pulsed light; and a modulator that is arranged downstream of the controller in the optical path of the pulsed light and modulates the wavelength of the pulsed light by utilizing soliton self-frequency shift to form one or more pulsed lights with different wavelengths, wherein the controller controls the time width of the pulsed light so that the number of pulsed lights formed by the modulator is a predetermined number."

[0006] As a result of extensive research, the present inventors have found that there is a correlation between the residual dispersion of pulsed light before modulation using soliton self-frequency shift and the number of pulsed light formed by the modulation. Therefore, in the present disclosure, a control unit controls the time width of pulsed light so that the number of pulsed light formed by the modulation unit is a predetermined number. This makes it possible to control the number of pulsed light while performing dispersion compensation for pulsed light to enhance stability. In other words, it is possible to form a desired number of pulsed light by modulation using soliton self-frequency shift.

[0007] The pulsed light generating device of the present disclosure may be [2] "the pulsed light generating device according to [1], wherein the control unit has a pair of diffraction gratings, and the distance between the pair of diffraction gratings is set to a distance such that the number of pulsed lights formed by the modulation unit is a predetermined number." In this case, the number of one or more pulsed lights formed by modulation using soliton self-frequency shift can be controlled by the distance between the pair of diffraction gratings in the control unit.

[0008] The pulsed light generating device of the present disclosure may be [3] "the pulsed light generating device according to [2], wherein the pair of diffraction gratings are fixed with the distance therebetween set to the set distance." In this case, the number of one or more pulsed lights formed by modulation using soliton self-frequency shift can be set to a desired fixed value.

[0009] The pulsed light generating device of the present disclosure may be [4] "the pulsed light generating device according to [2]," in which the pair of diffraction gratings are configured so that the distance therebetween is adjustable. In this case, it is possible to adjust the number of one or more pulsed lights formed by modulation using soliton self-frequency shift.

[0010] The pulsed light generating device of the present disclosure may be [5] "the pulsed light generating device according to any one of [1] to [4], wherein the control unit controls the time width of the pulsed light so that a value related to the wavelength of the one or more pulsed lights formed by the modulation unit becomes a predetermined value." As a result of extensive research, the present inventors have found that there is a correlation between the residual dispersion of the pulsed light before modulation using soliton self-frequency shift and the wavelength of the pulsed light formed by the modulation. Therefore, in the present disclosure, the control unit controls the time width of the pulsed light so that a value related to the wavelength of the pulsed light formed by the modulation unit becomes a predetermined value. This makes it possible for the control unit to control the wavelength of the one or more pulsed lights after modulation using soliton self-frequency shift.

[0011] The pulsed light generating device of the present disclosure may be [6] "the pulsed light generating device according to any one of [1] to [5], including: a branching unit arranged downstream of the modulating unit in the optical path of the pulsed light and branching the plurality of pulsed light beams; an amplifying unit arranged on at least one of the optical paths of the plurality of pulsed light beams branched by the branching unit and amplifying the pulsed light beams; and a sum frequency generating unit that combines some or all of the plurality of pulsed light beams branched by the branching unit, at least some of which have been amplified by the amplifying unit, and emits sum frequency light by sum frequency generation." In this case, it is possible to obtain sum frequency light from the plurality of pulsed light beams formed by the modulating unit.

[0012] The pulsed light generating device of the present disclosure may be [7] "the pulsed light generating device according to any one of [1] to [6], including a light intensity control unit arranged between the oscillator and the modulator in the optical path of the pulsed light, and controlling the intensity of the pulsed light for each pulse." In this case, the wavelength of one or more pulsed lights modulated using soliton self-frequency shift can be varied for each pulse by the light intensity control unit.

[0013] The pulsed light generation method of the present disclosure is [8] "a pulsed light generation method comprising: an oscillation step of oscillating pulsed light; a control step of controlling the time width of the pulsed light oscillated in the oscillation step; and a modulation step of modulating the wavelength of the pulsed light after control in the control step by utilizing soliton self-frequency shift to form one or a plurality of pulsed lights with different wavelengths, wherein in the control step, the time width of the pulsed light is controlled so that the number of pulsed lights formed in the modulation step is a predetermined number."

[0014] In the pulsed light generation method of the present disclosure, the control step controls the time width of the pulsed light so that the number of pulsed lights formed in the modulation step is a predetermined number. This makes it possible to control the number of pulsed lights while enhancing stability by performing dispersion compensation on the pulsed light, similar to the pulsed light generation device described above. That is, it is possible to form a desired number of pulsed lights by modulation utilizing soliton self-frequency shift. [Effects of the Invention]

[0015] According to the present disclosure, it is possible to provide an optical pulse generating device and an optical pulse generating method that are capable of generating a desired number of optical pulses by modulation using soliton self-frequency shift. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a block diagram showing a pulsed light generating device according to the first embodiment. [Figure 2]FIG. 2 is a graph showing the spectral waveform of the pulsed light output from the soliton-shifted fiber of FIG. [Figure 3] FIG. 3 is a graph showing an example of the configuration of the compressor of FIG. [Figure 4] FIG. 4 is a graph showing the correlation between the group delay dispersion of each wavelength remaining in the pulse light, the number of pulse lights, and the central wavelength of the first soliton. [Figure 5] FIG. 5 is a flowchart showing the pulsed light generating method according to the first embodiment. [Figure 6] FIG. 6 is a block diagram showing a pulsed light generating device according to the second embodiment. [Figure 7] FIG. 7 is a diagram illustrating an example of the configuration of the wavelength conversion unit in FIG. [Figure 8] FIG. 8 is a block diagram showing a pulsed light generating device according to the third embodiment. [Figure 9] FIG. 9 is a block diagram showing a pulsed light generating device according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, the embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted.

[0018] [First embodiment] As shown in FIG. 1, the pulsed light generating device 100 according to the first embodiment generates output light LK, which is an ultrashort pulsed light, by utilizing soliton self-frequency shift (Raman soliton shift). The pulsed light generating device 100 can be used as a light source for optical measurement devices or optical inspection devices, such as microscopes, particularly two-photon microscopes. A two-photon microscope is a type of laser scanning fluorescence microscope that excites fluorescent dyes in a sample by irradiating the sample with ultrashort pulsed laser light in the near-infrared region, and then detects signals (fluorescence) from the sample to perform image analysis. The pulsed light generating device 100 constitutes a wavelength-tunable light source in which the wavelength can be tuned for each pulse.

[0019] The pulsed light generating device 100 includes an oscillator (oscillating unit) 1, a fiber amplifier 2, an acousto-optic modulator (light intensity control unit) 3, a compressor (control unit) 4, a soliton shift fiber (modulation unit) 5, and a filter (filter unit) 6.

[0020] The oscillator 1 generates pulsed light L. As the oscillator 1, various oscillators capable of generating ultrashort pulsed light having a time width of, for example, picoseconds to femtoseconds as the pulsed light L can be used. The oscillator 1 generates an ultrashort pulse train in which the pulsed light L is arranged on the time axis at predetermined time intervals. The pulsed light L generated by the oscillator 1 has a repetition rate in the MHz to GHz range.

[0021] The fiber amplifier 2 amplifies the pulsed light L oscillated by the oscillator 1. The fiber amplifier 2 is arranged downstream of the oscillator 1 in the optical path of the pulsed light L. In this embodiment, the fiber amplifier 2 is arranged between the oscillator 1 and the acousto-optic modulator 3 in the optical path of the pulsed light L. The fiber amplifier 2 is configured to include, for example, a fiber amplifier. The fiber amplifier of the fiber amplifier 2 is a normal dispersion fiber, for example, a thulium-doped fiber. The laser medium doped in the fiber of the fiber amplifier 2 is not particularly limited and may be a rare earth element such as ytterbium, erbium, or neodymium, or may be Bi or the like. The fiber amplifier 2 has a gain band corresponding to the wavelength range of the pulsed light L.

[0022] The acousto-optic modulator 3 enables the intensity of the pulsed light L amplified by the fiber amplifier 2 to be controlled for each pulse. The acousto-optic modulator 3 is a device known as an AOM (Acousto Optic Modulator), and modulates the intensity of the pulsed light L for each pulse by utilizing the force of acoustics (sound waves). The acousto-optic modulator 3 can modulate the intensity in accordance with the repetition of the pulsed light L. The acousto-optic modulator 3 is disposed between the fiber amplifier 2 and the soliton-shifted fiber 5 in the optical path of the pulsed light L. In this embodiment, the acousto-optic modulator 3 is disposed upstream (preceding stage) of the compressor 4 in the optical path of the pulsed light L, between the fiber amplifier 2 and the soliton-shifted fiber 5. The acousto-optic modulator 3 also thins out the pulsed light L included in the ultrashort pulse train to reduce the repetition rate.

[0023] The compressor 4 is a dispersion control section that controls (e.g., compresses) the time width of the pulsed light L whose intensity has been controlled by the acousto-optic modulator 3. In other words, the compressor 4 imparts dispersion in the direction opposite to the influence of dispersion that the pulsed light L has received up to the previous stage, thereby achieving dispersion compensation that narrows the widened time width of the pulsed light L. The compressor 4 is arranged upstream of the soliton-shifted fiber 5 in the optical path of the pulsed light L. In this embodiment, the compressor 4 is arranged between the acousto-optic modulator 3 and the soliton-shifted fiber 5 in the optical path of the pulsed light L.

[0024] Various compressors can be used as the compressor 4, such as a compressor including an anomalous dispersion fiber, a compressor including a prism pair, a compressor including a grism pair, etc. In this embodiment, a diffraction grating type compressor including a pair of diffraction gratings is used as the compressor 4 (details will be described later).

[0025] The soliton shift fiber 5 modulates the wavelength of the pulse light L, the time width of which has been controlled by the compressor 4, by utilizing the soliton self-frequency shift, to form one or more pulse lights L with different wavelengths (hereinafter simply referred to as "one or more pulse lights L"). The soliton shift fiber 5 is arranged downstream (after) the compressor 4 in the optical path of the pulse light L. In this embodiment, the soliton shift fiber 5 is arranged between the compressor 4 and the filter 6 in the optical path of the pulse light L. The soliton shift fiber 5 can be, for example, a single-mode anomalous dispersion fiber that exhibits anomalous dispersion in the wavelength band of the pulse light L.

[0026] When pulsed light L is input to the soliton-shifted fiber 5, the soliton-shifted fiber 5 outputs one or more solitons with different wavelengths. In the example shown in FIG. 2 , the soliton-shifted fiber 5 generates three solitons LS with different wavelengths. The multiple solitons LS generated by modulation of the soliton-shifted fiber 5 are sometimes referred to as multi-solitons or multi-soliton trains. The soliton LS is pulsed light L whose wavelength is modulated by soliton self-frequency shift. The wavelength of the soliton LS can be controlled by the intensity of the pulsed light L input to the soliton-shifted fiber 5. Increasing the intensity of the pulsed light L input to the soliton-shifted fiber 5 shifts the wavelength of the soliton LS to the longer wavelength side, while decreasing the intensity of the pulsed light L input to the soliton-shifted fiber 5 shifts the wavelength of the soliton LS to the shorter wavelength side. In this embodiment, the wavelength of one or more pulsed light beams L generated in the soliton-shifted fiber 5 is controlled by controlling the intensities of the multiple pulsed light beams L using the acousto-optic modulator 3.

[0027] Returning to FIG. 1, the filter 6 removes non-soliton components LX (see FIG. 2) excluding solitons LS from the optical components generated by the soliton-shifted fiber 5. The non-soliton components LX are components that do not become solitons LS due to modulation by the soliton-shifted fiber 5. The filter 6 is disposed downstream of the soliton-shifted fiber 5 in the optical path of the pulsed light L. There are no particular limitations on the filter 6 as long as it can remove or attenuate the non-soliton components LX, but it is preferable to use one with an optical density (OD value) of 3 or more. For example, a wavelength separation filter may be used as the filter 6. The filter 6 may be implemented as a standalone unit or as a wavelength division multiplexing coupler. The non-soliton components LX removed by the filter 6 may be reused. The filter 6 outputs one or more pulsed lights L from which the non-soliton components LX have been removed as output light LK to a subsequent stage.

[0028] 3 , the compressor 4 has a pair of diffraction gratings 41 and 42. In the present embodiment, in the compressor 4, the pulsed light L input from the acousto-optic modulator 3 is diffused by a lens 43, transmitted through a dichroic mirror 44, diffracted by the pair of diffraction gratings 41 and 42, and reflected by a mirror 45. The pulsed light L reflected by the mirror 45 is diffracted by the pair of diffraction gratings 41 and 42, reflected by the dichroic mirror 44, and then collected by a lens 46 and output to the soliton shift fiber 5.

[0029] At this time, since the pulsed light L is composed of light of multiple wavelengths that are mutually phase-matched and superimposed, differences occur in the optical path lengths of the respective wavelengths of the pulsed light when the pulsed light L is diffracted by the pair of diffraction gratings 41 and 42. As a result, the group delay times of the respective wavelengths of the pulsed light L change, and the time width is controlled.

[0030] Here, it has been found that there is a correlation between the control of the residual dispersion of the pulsed light L by the compressor 4 (control of the residual dispersion of the pulsed light L before modulation using the soliton self-frequency shift by the soliton shift fiber 5) and the number of pulsed lights L formed by the soliton shift fiber 5. For example, it has been found that there is a correlation shown in Fig. 4 (see "x" in the figure) between the group delay dispersion (GDD, hereinafter referred to as "GDD") of each wavelength remaining in the pulsed light L and the number of pulsed lights L formed by the soliton shift fiber 5.

[0031] Therefore, in the pulsed light generating device 100 of this embodiment, the compressor 4 controls the time width of the pulsed light so that the number of pulsed light L formed by the soliton-shifted fiber 5 is a predetermined number. Specifically, since the GDD can be determined based on the distance between the pair of diffraction gratings 41 and 42, the distance between the pair of diffraction gratings 41 and 42 of the compressor 4 is set to a set distance that will result in the number of pulsed light L formed by the soliton-shifted fiber 5 being a predetermined number. That is, for example, the GDD that will result in the number of pulsed light L formed by the soliton-shifted fiber 5 being a predetermined number is determined based on the correlation shown in FIG. 4, and the set distance that realizes this GDD is set to the distance between the pair of diffraction gratings 41 and 42. The set number is not particularly limited and may be any number, and in the example shown in FIG. 4, it is any number between 1 and 3. The correlation shown in FIG. 4 can be obtained in advance, for example, by actual measurement, simulation, or the like. The pair of diffraction gratings 41 and 42 are fixed with the distance therebetween set to a set distance.

[0032] It has also been found that there is a correlation between the control of residual dispersion of pulsed light L by the compressor 4 and the wavelength of pulsed light L formed by the soliton-shifted fiber 5. For example, it has been found that there is a correlation shown in FIG. 4 (see "◯" in the figure) between the GDD and the central wavelength (value related to wavelength) of the first soliton formed by the modulation. The first soliton is the pulsed light L with the longest wavelength among one or more pulsed light L formed by the soliton-shifted fiber 5.

[0033] Therefore, in the pulsed light generating apparatus 100 of this embodiment, the compressor 4 controls the time width of the pulsed light L so that a value related to the wavelength of the pulsed light L formed in the soliton-shifted fiber 5 becomes a predetermined value. Specifically, since the GDD can be determined based on the distance between the pair of diffraction gratings 41 and 42, the distance between the pair of diffraction gratings 41 and 42 of the compressor 4 is set to a set distance at which the center wavelength of the first soliton formed in the soliton-shifted fiber 5 becomes a predetermined value. In other words, for example, the GDD at which the center wavelength of the first soliton formed in the soliton-shifted fiber 5 becomes a predetermined value is found based on the correlation in FIG. 4 , and the set distance that realizes this GDD is set to the distance between the pair of diffraction gratings 41 and 42. The predetermined value may be any value within the range of the GDD in which the number of pulsed light L is the predetermined number. In the example of FIG. 4, if the predetermined number is 1, it is any value between 1800 nm and 1910 nm; if the predetermined number is 2, it is any value between 1840 nm and 2100 nm; and if the predetermined number is 3, it is any value between 1950 nm and 1980 nm.

[0034] Next, a pulsed light generating method performed using the pulsed light generating device 100 will be described with reference to the flowchart of FIG.

[0035] As shown in FIG. 5, the pulsed light generation method according to this embodiment includes an oscillation step S01, an amplification step S02, a light intensity control step S03, a time duration control step (control step) S04, and a modulation step S05.

[0036] In the oscillation step S01, an oscillator 1 oscillates pulsed light L. In the amplification step S02, a fiber amplifier 2 amplifies the pulsed light L oscillated in the oscillation step S01. In the light intensity control step S03, an acousto-optic modulator 3 controls the intensity of the pulsed light L amplified in the amplification step S02 for each pulse. In the time width control step S04, a compressor 4 controls the time width of the pulsed light L whose intensity has been controlled in the light intensity control step S03. In particular, in the time width control step S04, the time width of the pulsed light L is controlled so that the number of pulsed light L formed in the subsequent modulation step S05 becomes a predetermined number and the center wavelength of the first soliton of the pulsed light L becomes a predetermined value.

[0037] In the modulation step S05, the wavelength of the pulsed light L whose time width has been controlled in the time width control step S04 is modulated by the soliton shift fiber 5 using the soliton self-frequency shift to form one or more pulsed lights L with different wavelengths. After the modulated one or more pulsed lights L have non-soliton components LX removed by the filter 6, they are output as output light LK.

[0038] As described above, in the pulsed light generating device 100, the compressor 4 controls the time width of the pulsed light L so that the number of pulsed light L formed in the soliton-shifted fiber 5 is a predetermined number. This makes it possible to control the number of pulsed light L while enhancing stability by performing dispersion compensation for the pulsed light L modulated by the soliton-shifted fiber 5. In other words, it becomes possible to form a desired number of pulsed lights L by modulation using the soliton self-frequency shift.

[0039] In the pulsed light generating device 100, the compressor 4 has a pair of diffraction gratings 41 and 42, and the distance between the pair of diffraction gratings 41 and 42 is set to a set distance that allows a predetermined number of pulsed lights L to be formed in the soliton shifted fiber 5. In this case, the number of one or more pulsed lights L formed by the soliton shifted fiber 5 can be controlled by the distance between the pair of diffraction gratings 41 and 42 of the compressor 4.

[0040] In the pulsed light generating device 100, the pair of diffraction gratings 41, 42 are fixed with a set distance between them. In this case, the number of one or more pulsed lights L formed by the soliton shifted fiber 5 can be set to a desired fixed value.

[0041] In the pulsed light generating device 100, the compressor 4 controls the time width of the pulsed light L so that the value related to the wavelength of one or more pulsed lights L formed by the soliton shifted fiber 5 becomes a predetermined value. In this case, the wavelength of the pulsed light L after modulation by the soliton shifted fiber 5 can be controlled by the compressor 4.

[0042] The pulsed light generating device 100 includes an acousto-optic modulator 3 disposed between the oscillator 1 and the soliton-shifted fiber 5 in the optical path of the pulsed light L. In this case, the wavelength of the pulsed light L after modulation by the soliton-shifted fiber 5 can be varied for each pulse by the acousto-optic modulator 3.

[0043] In the pulsed light generation method, in the time width control step S04, the time width of the pulsed light L is controlled so that the number of pulsed light L formed in the modulation step S05 is a predetermined number. This makes it possible to control the number of pulsed light L while performing dispersion compensation for the pulsed light L to improve stability. In other words, it is possible to form a desired number of pulsed light L by modulation using the soliton self-frequency shift. .

[0044] In general, the importance of multicolor two-photon imaging is recognized, for example, in the field of the nervous system. However, there is a concern that it is difficult to balance cost with high-speed observation, since it is necessary to prepare multiple light sources for multiple targets (fluorescent proteins). In this regard, the pulsed light generating device 100 and pulsed light generating method of the present embodiment are an effective device and method that can alleviate this concern.

[0045] In this embodiment, the intensity of the pulsed light L is controlled for each pulse by the acousto-optic modulator 3, but this is not particularly limited, and the intensity of the pulsed light L controlled by the acousto-optic modulator 3 may be fixed to a constant value. In this case, the wavelength of each of the one or more pulsed lights L modulated by the soliton shift fiber 5 can be fixed to a constant wavelength.

[0046] [Second embodiment] Next, a second embodiment will be described. In the description of this embodiment, differences from the first embodiment will be described, and overlapping descriptions will be omitted.

[0047] As shown in FIG. 6, the pulsed light generating device 200 according to the second embodiment differs from the first embodiment in that it includes a stretcher 7, a fiber amplifier 8, a compressor 9, and a wavelength converting unit 10.

[0048] The stretcher 7 collectively stretches the time width of one or more pulsed light beams L after the non-soliton component LX has been removed by the filter 6, thereby reducing the peak power of the pulsed light beams L. This makes it possible to suppress undesirable nonlinear optical effects during amplification by the fiber amplifier 8 in the subsequent stage. The stretcher 7 is disposed downstream of the soliton-shifted fiber 5 in the optical path of the pulsed light beam L. In this embodiment, the stretcher 7 is disposed between the filter 6 and the fiber amplifier 8 in the optical path of the pulsed light beam L. The stretcher 7 may stretch the time width of the pulsed light beams L by transmitting the pulsed light beams L through at least one of a fiber and a medium to impart dispersion to the pulsed light beams L. Alternatively, the stretcher 7 may stretch the time width of the pulsed light beams L by imparting dispersion to the pulsed light beams L using a diffraction grating pair, a prism pair, or the like in a spatial system. The dispersion imparted by the stretcher 7 may be either normal dispersion or anomalous dispersion.

[0049] The fiber amplifier 8 collectively amplifies one or more pulsed light beams L whose time width has been stretched by the stretcher 7. The fiber amplifier 8 is arranged downstream of the soliton shift fiber 5 in the optical path of the pulsed light L. In this embodiment, the fiber amplifier 8 is arranged between the stretcher 7 and the compressor 9 in the optical path of the pulsed light L. The fiber amplifier 8 includes a fiber amplifier. The fiber amplifier of the fiber amplifier 8 is a normal dispersion fiber, for example, a thulium-doped fiber. The laser medium doped in the fiber of the fiber amplifier 8 is not particularly limited and may be a rare earth element such as ytterbium, erbium, or neodymium, or may be Bi or the like.

[0050] The compressor 9 collectively controls the time width of one or more pulsed light beams L amplified by the fiber amplifier 8. The compressor 9 applies dispersion in the opposite direction to the influence of dispersion that the pulsed light L has received up to the previous stage, thereby achieving dispersion compensation that narrows the widened time width of the pulsed light L. The compressor 9 is arranged downstream of the fiber amplifier 8 in the optical path of the pulsed light L. In this embodiment, the compressor 9 is arranged between the fiber amplifier 8 and the wavelength conversion unit 10 in the optical path of the pulsed light L. Various compressors can be used as the compressor 9, such as a compressor including an anomalous dispersion fiber, a compressor including a prism pair, or a compressor including a grism pair.

[0051] The wavelength conversion unit 10 performs wavelength conversion on one or more pulsed light beams L whose time widths have been controlled by the compressor 9, for each pulse. The wavelength conversion unit 10 may convert the wavelength of the pulsed light L, for example, from 1800 nm or more to less than 2000 nm to 900 nm or more to less than 1000 nm, which is usable in two-photon microscopes. The wavelength conversion unit 10 may perform the wavelength conversion by second harmonic generation, which is a phenomenon included in nonlinear effects. Second harmonic generation is a phenomenon in which the original wavelength (fundamental wave) is converted into light (double wave) with half the wavelength. The wavelength conversion unit 10 is disposed downstream of the compressor 9 in the optical path of the pulsed light L. The wavelength conversion unit 10 outputs the wavelength-converted pulsed light L as output light LK.

[0052] The wavelength conversion unit 10 according to this embodiment performs highly efficient wavelength conversion using a relatively thick crystal, and without using a driving system, disperses light for each wavelength band and changes the optical path for each wavelength band, thereby performing broadband wavelength conversion of pulsed light L. A detailed configuration example of the wavelength conversion unit 10 will be described below with reference to FIG.

[0053] As shown in FIG. 7 , the wavelength conversion unit 10 includes a diffraction grating 101, a lens 102, a wavelength conversion element 103, a lens 104, and a diffraction grating 105. The diffraction grating 101 and the lens 102 change the optical path for each wavelength band so that light of the wavelength band to be converted at each incident position on the wavelength conversion element 103 is incident on each incident position on the wavelength conversion element 103. The diffraction grating 101 disperses the pulsed light L output from the compressor 9 for each wavelength band, thereby dispersing the pulsed light L for each wavelength band so that light of the wavelength band to be converted at each incident position on the wavelength conversion element 103 is incident on each incident position on the wavelength conversion element 103. The lens 102 focuses the light from the diffraction grating 101 at the incident position on the wavelength conversion element 103. The distance from the diffraction grating 101 to the lens 102 and the distance from the lens 102 to the wavelength conversion element 103 are both set to match the focal length f of the lens 102, e.g., the focal length f of the lens 102.

[0054] The wavelength conversion element 103 is a crystal that converts different wavelength bands depending on the incident position of light. The wavelength conversion element 103 has a fan-shaped structure so that quasi-phase matching of different wavelength bands can be achieved at each incident position. More specifically, the wavelength conversion element 103 may be a PPLN (Periodically Poled Lithium Niobate) with a fan-shaped structure. That is, the wavelength conversion element 103 may be a so-called fan-out PPLN. The fan-shaped structure of the wavelength conversion element 103 makes it possible to achieve quasi-phase matching of any wavelength band at each incident position of the crystal. That is, the period of the part where the second harmonic waves cancel each other varies depending on the wavelength band, but by using a crystal whose period is inverted according to the fan-shaped structure, it is possible to achieve different wavelength bands for quasi-phase matching at each incident position of the crystal. In such a wavelength conversion element 103, it is possible to specify in advance which wavelength band is quasi-phase matched at each incident position, and therefore, by setting the above-mentioned diffraction grating 101 and lens 102 so that light of the wavelength band to be converted is incident on each incident position, it is possible to appropriately perform wavelength conversion for each of the light of various wavelength bands.

[0055] The lens 104 is a lens that focuses the light wavelength-converted by the wavelength conversion element 103 onto the diffraction grating 101. The distance from the wavelength conversion element 103 to the lens 104 and the distance from the lens 104 to the diffraction grating 105 are both set in accordance with the focal length f of the lenses 102 and 104, and may be set to, for example, the focal length f of the lenses 102 and 104. The diffraction grating 105 outputs the light that has been dispersed into each wavelength band by the diffraction grating 101 and then passed through the lens 102, the wavelength conversion element 103, and the lens 104 as wavelength-converted pulsed light L. The number of grooves in the diffraction grating 105 may be twice the number of grooves in the diffraction grating 101 in order to restore the dispersion of the light after wavelength conversion.

[0056] As described above, the pulsed light generation device 200 and pulsed light generation method according to this embodiment also make it possible to generate a desired number of pulsed lights L by modulation using soliton self-frequency shift. Furthermore, in the pulsed light generation device 200, the wavelength conversion unit 10 can perform wavelength conversion on one or more pulsed lights L for each pulse.

[0057] [Third embodiment] Next, a third embodiment will be described. In the description of this embodiment, differences from the first embodiment will be described, and overlapping descriptions will be omitted.

[0058] 8, a pulsed light generating device 300 according to the third embodiment differs from the first embodiment in that it includes a branching unit 11, a stretcher 12, a fiber amplifier (amplifying unit) 13, a multiplexing unit 14, a compressor 15, and a wavelength converting unit 16. In the pulsed light generating device 300, an acousto-optic modulator 3 fixes the intensity of pulsed light L to a constant value, and a compressor 4 controls the time width of pulsed light L so that the number of pulsed light L formed in the soliton-shifted fiber 5 becomes N (N=an integer equal to or greater than 2), thereby forming N pulsed light L (multi-solitons) in the soliton-shifted fiber 5.

[0059] The branching unit 11 branches the N pulsed light L after the non-soliton components LX have been removed by the filter 6. Specifically, the branching unit 11 branches the N pulsed light L having different wavelengths into N pulsed light L1 to LN so that the N pulsed light L is separated into each wavelength based on the wavelength of the pulsed light L. The branching unit 11 is arranged downstream of the filter 6 in the optical path of the pulsed light L. As the branching unit 11, for example, a wavelength division filter such as a dichroic filter, a wavelength division multiplexing coupler, and a space division multiplexing optical system or optical element are used.

[0060] The stretcher 12 stretches the time width of one pulse light L1 (any one pulse light L) branched by the branching unit 11, thereby reducing the peak power of the one pulse light L1. This makes it possible to suppress the occurrence of undesirable nonlinear optical effects during amplification by the fiber amplifier 13 in the subsequent stage. The stretcher 12 is disposed in the optical path of the one pulse light L1. The stretcher 12 may stretch the time width of the one pulse light L1 by transmitting the one pulse light L1 through at least one of a fiber and a medium to impart dispersion to the one pulse light L1. Alternatively, the stretcher 7 may stretch the time width of the one pulse light L1 by imparting dispersion to the one pulse light L1 using a diffraction grating pair, a prism pair, or the like in a spatial system. The dispersion may be either normal dispersion or anomalous dispersion.

[0061] The fiber amplifier 13 amplifies the one pulse light L1 whose time width has been stretched by the stretcher 12. The fiber amplifier 13 is arranged downstream of the stretcher 12 in the optical path of the one pulse light L1. The fiber amplifier 13 includes a fiber amplifier. The fiber amplifier of the fiber amplifier 13 is a normal dispersion fiber, for example, a thulium-doped fiber. The laser medium doped in the fiber of the fiber amplifier 13 is not particularly limited and may be a rare earth element such as ytterbium, erbium, or neodymium, or may be Bi or the like. The fiber amplifier 13 may have a gain band corresponding to the wavelength range of the one pulse light L1.

[0062] The multiplexing unit 14 multiplexes, on the same optical axis, the N pulsed light beams L branched by the branching unit 11. The multiplexing unit 14 includes, for example, a mirror and a dichroic mirror. The multiplexing unit 14 is disposed upstream of the compressor 15 in the optical path of the pulsed light L.

[0063] The compressor 15 collectively controls the time widths of the N pulsed light beams L combined in the combining unit 14. The compressor 15 applies dispersion in the opposite direction to the effect of dispersion that the N pulsed light beams L received up to the previous stage, thereby achieving dispersion compensation that narrows the widened time widths of the N pulsed light beams L. The compressor 15 is disposed downstream of the combining unit 14 in the optical path of the pulsed light beams L. Various compressors can be used as the compressor 15, such as a compressor including an anomalous dispersion fiber, a compressor including a prism pair, or a compressor including a grism pair.

[0064] The wavelength conversion unit 16 performs sum frequency generation using the N pulsed light beams L combined in the multiplexing unit 14, and emits sum frequency light as output light LK. The wavelength conversion unit 16 causes the N pulsed light beams L combined in the multiplexing unit 14 to be incident on a wavelength conversion crystal, and causes sum frequency generation to cause sum frequency light LW to be emitted from the wavelength conversion crystal. The wavelength conversion unit 16 is disposed downstream of the compressor 15 in the optical path of the pulsed light L. The sum frequency light LW has a wavelength in the wavelength range of, for example, 800 nm or more and 900 nm or less. The multiplexing unit 14 and the wavelength conversion unit 16 constitute a sum frequency generation unit.

[0065] As described above, the pulsed light generating apparatus 300 and pulsed light generating method according to this embodiment also make it possible to generate a desired number of pulsed lights L by modulation using soliton self-frequency shift.

[0066] The pulsed light generating device 300 includes a branching unit 11 that branches multiple pulsed light L based on the wavelengths of the pulsed light L, a fiber amplifier 13 arranged in the optical path of one pulsed light L1 branched by the branching unit 11, and a multiplexing unit 14 and wavelength conversion unit 16 that multiplex the multiple pulsed light L (including the one pulsed light L1 amplified by the fiber amplifier 13) branched by the branching unit and emit sum-frequency light (output light LK) by sum-frequency generation. In this case, it is possible to obtain sum-frequency light from the multiple pulsed light L formed by the soliton-shifted fiber 5.

[0067] In this embodiment, the optical path lengths of the N pulsed light beams L are configured to be the same, and for example, the arrival times of the N pulsed light beams L1 at the wavelength conversion crystal of the wavelength converting unit 16 are synchronized. In this embodiment, the combining unit 14 may combine all of the plurality of pulsed light beams L branched by the branching unit 11, or may combine any part of the plurality of pulsed light beams L branched by the branching unit 11. This makes it possible to obtain any number of sum frequencies. In this embodiment, the stretcher 12 and the fiber amplifier 13 are arranged in the optical path of one pulsed light beam L1 branched by the branching unit 11, but they may be arranged in at least any of the optical paths of the N pulsed light beams L.

[0068] [Fourth embodiment] Next, a fourth embodiment will be described. In the description of this embodiment, differences from the third embodiment will be described, and overlapping descriptions will be omitted.

[0069] As shown in Fig. 9, the pulsed light generation device 400 according to the fourth embodiment differs from the third embodiment in that it further includes another stretcher 22. The other stretcher 22 further stretches the temporal width of the one pulsed light L1 whose temporal width has been stretched by the stretcher 12. The other stretcher 22 is arranged between the stretcher 12 and the fiber amplifier 13 on the optical path of the one pulsed light L1. This makes it possible to reliably overlap the pulse of the one pulsed light L1 with the pulse of at least one of the other pulsed light L2 to LN in time in the wavelength conversion unit 16. Note that the pulsed light generation device 400 may include, instead of or in addition to the other stretcher 22, a stretcher arranged on at least one of the optical paths of the pulsed light L2 to LN to stretch at least one of the pulsed light L2 to LN.

[0070] As described above, the pulsed light generating apparatus 400 and pulsed light generating method according to this embodiment also make it possible to generate a desired number of pulsed lights L by modulation using soliton self-frequency shift.

[0071] [Variations] As described above, one aspect of the present disclosure is not limited to the above embodiment.

[0072] In the above embodiment, the acousto-optic modulator 3 is used as the light intensity control section, but this is not limiting, and for example, an electro-optic modulator (EOM) may be used as the light intensity control section. In the above embodiment, a plurality of acousto-optic modulators 3 may be arranged.

[0073] In the above embodiment, the pair of diffraction gratings 41, 42 of the compressor 4 are fixed with a set distance between them, but this is not limited to this. The pair of diffraction gratings 41, 42 may be configured so that the distance between them is adjustable. The configuration for making the distance adjustable is not particularly limited, and various known configurations can be used. Adjusting the distance between the diffraction gratings 41, 42 adjusts the GDD, and makes it possible to adjust the number of pulsed beams L formed by the soliton shift fiber 5.

[0074] In the above embodiment, a fiber amplifier of a double-clad normal dispersion fiber is used as the fiber amplifier 2, but instead, a fiber amplifier of a single-clad normal dispersion fiber (e.g., erbium-doped) may be used. Even in this case, it is possible to at least broaden the spectrum of the pulsed light L.

[0075] The respective components in the above-described embodiment and modified examples are not limited to the materials and shapes described above, and various materials and shapes can be applied. Furthermore, the respective components in the above-described embodiment and modified examples can be arbitrarily applied to the respective components in other embodiments or modified examples. [Explanation of symbols]

[0076] 1...oscillator (oscillating section), 3...acousto-optic modulator (light intensity control section), 4...compressor (control section), 5...soliton shift fiber (modulation section), 11...branching section, 13...fiber amplifier (amplification section), 14...combining section (sum frequency generation section), 16...wavelength conversion section (sum frequency generation section), 41, 42...diffraction grating, 100, 200, 300, 400...pulse light generating device, L, L1 to LN...pulse light, LK...output light.

Claims

1. an oscillator that oscillates pulsed light; a control unit that is arranged downstream of the oscillation unit in the optical path of the pulsed light and that controls a time width of the pulsed light; a modulation unit that is arranged downstream of the control unit in the optical path of the pulsed light, and that modulates the wavelength of the pulsed light by utilizing a soliton self-frequency shift to form one or a plurality of pulsed lights with different wavelengths, The control unit controls the time width of the pulsed light so that the number of the pulsed light formed by the modulation unit is a predetermined number.

2. the control unit has a pair of diffraction gratings, 2. The pulsed light generating device according to claim 1, wherein the distance between the pair of diffraction gratings is set to a set distance such that the number of pulsed lights formed by the modulation section is a predetermined number.

3. 3. The pulsed light generating device according to claim 2, wherein the pair of diffraction gratings are fixed with the distance therebetween set to the set distance.

4. The pulsed light generating device according to claim 2 , wherein the pair of diffraction gratings are configured so that the distance therebetween is adjustable.

5. The pulsed light generating device according to claim 1 , wherein the control unit controls a time width of the pulsed light so that a value related to the wavelength of the pulsed light formed by the modulation unit becomes a predetermined value.

6. a branching unit that is arranged downstream of the modulation unit in an optical path of the pulsed light and branches the pulsed light into a plurality of beams; an amplifier unit disposed on at least one of the optical paths of the plurality of pulsed beams branched by the branch unit, and amplifying the pulsed beam; 3. The pulsed light generating device according to claim 1, further comprising: a sum frequency generating unit that combines some or all of the plurality of pulsed light beams branched by the branching unit, at least any of which has been amplified by the amplifying unit, and emits sum frequency light by sum frequency generation.

7. 3. The pulsed light generating device according to claim 1, further comprising a light intensity control unit disposed between the oscillator and the modulator in an optical path of the pulsed light, the light intensity control unit controlling the intensity of the pulsed light for each pulse.

8. an oscillation step of oscillating pulsed light; a control step of controlling a time width of the pulsed light oscillated in the oscillation step; a modulation step of modulating the wavelength of the pulsed light after the control step by utilizing a soliton self-frequency shift to form one or a plurality of pulsed lights with different wavelengths, In the control step, a time width of the pulsed light is controlled so that the number of the pulsed light formed in the modulating step is a predetermined number.

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