Pulsed light generation device and pulsed light generation method

Abstract

According to the present disclosure, it is possible to provide a pulsed light generation device and a pulsed light generation method, which are able to suppress the occurrence of ASE while also suppressing formation of a plurality of pulsed light beams due to modulation using a soliton self-frequency shift, and to reliably amplify the modulated pulsed light.　A pulsed light generation device (100) comprises: an oscillation unit (1) for oscillating pulsed light; a bandwidth-widening unit (2) that is arranged on the downstream side of the oscillation unit (1) in the optical path of the pulsed light and broadens the spectrum of the pulsed light; a modulation unit (5) that is arranged on the downstream side of the bandwidth-widening unit (2) in the optical path of the pulsed light and uses a soliton self-frequency shift to modulate the wavelength of the pulsed light; a branching unit (8) that is arranged on the downstream side of the bandwidth-widening unit (2) in the optical path of the pulsed light and splits the pulsed light; and amplification units (11, 21) that are arranged on the downstream side of the modulation unit (5) and the branching unit (8) in the optical path of the pulsed light and amplify the pulsed light.

Description

Pulse light generation device and pulse light generation method

[0001] The present disclosure relates to a pulse light generation device and a pulse light generation method.

[0002] A pulse light generation device including an oscillation unit that oscillates pulse light and a modulation unit that modulates the wavelength of the pulse light oscillated by the oscillation unit using soliton self-frequency shift is known. In such a pulse light generation device, by increasing the intensity of the pulse light before modulation by the modulation unit, the pulse light is split by the modulation, and a plurality of pulse lights are formed (output of multi-colored solitons) (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2004-527001

[0004] In the above-described pulse light generation device, as described above, the pulse light is split by the modulation by the modulation unit, and a plurality of pulse lights are formed (hereinafter, also referred to as "multi-soliton formation"). However, since it is very difficult to set all of the plurality of pulse lights thus formed to a desired wavelength, etc., from a practical point of view, multi-soliton formation is often not preferable, and it is desired to suppress multi-soliton formation. Further, in the above-described pulse light generation device, the pulse light after modulation by the modulation unit may be amplified by an amplification unit. In this case, due to the wavelength dependence of the amplification factor, the pulse light of the desired wavelength component cannot be efficiently amplified, so there is a risk that the extra energy to the amplification unit leads to the generation of amplified spontaneous emission (ASE).

[0005] Therefore, an object of the present disclosure is to provide a pulse light generation device and a pulse light generation method capable of suppressing the formation of a plurality of pulse lights by modulation using soliton self-frequency shift, suppressing the generation of ASE, and surely amplifying the pulse light after the modulation.

[0006] The pulsed light generation apparatus of the present disclosure is a pulsed light generation apparatus comprising: [1] an oscillator that oscillates pulsed light; a broadbanding unit disposed downstream of the oscillator in the optical path of the pulsed light and broadening the spectrum of the pulsed light; a modulation unit disposed downstream of the broadbanding unit in the optical path of the pulsed light and modulating the wavelength of the pulsed light using soliton self-frequency shift; a branching unit disposed downstream of the broadbanding unit in the optical path of the pulsed light and branching the pulsed light; and an amplification unit disposed downstream of the modulation unit and the branching unit in the optical path of the pulsed light and amplifying the pulsed light.

[0007] As a result of diligent research, the disclosers have found that multi-solitonization can be suppressed by broadening the spectrum of the pulsed light before modulation using soliton self-frequency shifting. Therefore, in the pulsed light generation device of this disclosure, the spectrum of the pulsed light is broadened, and the wavelength of the broadened pulsed light is modulated using soliton self-frequency shifting. This makes it possible to suppress multi-solitonization even when, for example, the intensity of the pulsed light before modulation is increased. In addition, in the pulsed light generation device of this disclosure, since the pulsed light after modulation by the modulation unit and the pulsed light branched at the branching unit is amplified in the amplification unit, compared to when the pulsed light before branching is amplified, efficient amplification according to the wavelength of the pulsed light after modulation by the modulation unit is possible, and the input of energy to the amplification unit is suppressed, thereby suppressing the occurrence of ASE. Accordingly, the pulsed light generation device of this disclosure makes it possible to suppress the formation of multiple pulsed lights by modulation using soliton self-frequency shifting, suppress the occurrence of ASE, and reliably amplify the modulated pulsed light.

[0008] The pulsed light generation apparatus of the present disclosure may also be [2] "the pulsed light generation apparatus according to [1], which includes: a branching unit that branches a plurality of pulsed light into a first pulsed light and a second pulsed light based on the wavelength of the pulsed light; a modulation unit that is arranged upstream of the branching unit in the optical path of the pulsed light; and an amplification unit that is arranged in the optical path of the first pulsed light and has a gain band corresponding to the wavelength range of the first pulsed light, and amplifies the first pulsed light; and a second amplification unit that is arranged in the optical path of the second pulsed light and has a gain band corresponding to the wavelength range of the second pulsed light, and amplifies the second pulsed light." In this case, since the first pulsed light can be amplified by the first amplification unit that has a gain band corresponding to the wavelength range of the first pulsed light, amplification of the first pulsed light in a region outside its gain band can be suppressed in the first amplification unit. At the same time, since the second pulsed light can be amplified by the second amplification unit that has a gain band corresponding to the wavelength range of the second pulsed light, amplification of the second pulsed light in a region outside its gain band can be suppressed in the second amplification unit. As a result, it becomes possible to suppress the generation of ASE (Autonomous Emission Reduction) when amplifying pulsed light.

[0009] The pulsed light generation apparatus of the present disclosure may also be [3] "the pulsed light generation apparatus according to [1] or [2], which is disposed between the broadband section and the modulation section in the optical path of the pulsed light and comprises an optical intensity control unit that controls the intensity of the pulsed light for each pulse." In this case, the wavelength of the pulsed light modulated by the modulation section can be varied for each pulse by the optical intensity control unit.

[0010] The pulsed light generation apparatus of the present disclosure may also be [4] "the pulsed light generation apparatus according to [1], wherein the branching unit branches the pulsed light into a first pulsed light and a second pulsed light so that the intensity of the pulsed light is divided, the modulation unit is arranged in the optical path of the first pulsed light and modulates the wavelength of the first pulsed light to a predetermined wavelength, and the amplification unit is arranged in the optical path of the first pulsed light and has a gain band corresponding to a wavelength range including the predetermined wavelength and amplifies the first pulsed light." In this case, the first pulsed light can be amplified by the amplification unit having a gain band corresponding to a predetermined wavelength which is the wavelength of the first pulsed light, and amplification of the first pulsed light in a region outside the gain band of the amplification unit can be suppressed. As a result, it is possible to suppress the occurrence of ASE when amplifying the first pulsed light.

[0011] The pulsed light generation apparatus of the present disclosure may also be the pulsed light generation apparatus according to [4], comprising: [5] "another modulation unit arranged in the optical path of the second pulsed light and modulating the wavelength of the second pulsed light using soliton self-frequency shift; and a sum-frequency generation unit that combines the first pulsed light amplified by the amplification unit and the second pulsed light modulated by the other modulation unit and emits sum-frequency light by sum-frequency generation." In this case, sum-frequency light of a desired wavelength can be obtained while suppressing the generation of ASE.

[0012] The pulsed light generation apparatus of the present disclosure may also be [6] "the pulsed light generation apparatus according to [5], which is arranged upstream of the other modulation unit in the optical path of the second pulsed light and comprises an optical intensity control unit that controls the intensity of the second pulsed light pulse by pulse." In this case, the wavelength of the second pulsed light modulated by the other modulation unit can be varied pulse by pulse by the optical intensity control unit.

[0013] The pulsed light generation apparatus of the present disclosure may also be the pulsed light generation apparatus according to [1], which includes: [7] "the branching unit, which branches the pulsed light into a first pulsed light and a second pulsed light so that the intensity of the pulsed light is divided; the modulation unit, which is arranged upstream of the branching unit in the optical path of the pulsed light; and the amplification unit, which includes a first amplification unit arranged in the optical path of the first pulsed light and amplifying the first pulsed light, and a second amplification unit arranged in the optical path of the second pulsed light and amplifying the second pulsed light." In this case, the first pulsed light can be amplified by the first amplification unit, and the second pulsed light can be amplified by the second amplification unit. Therefore, it is possible to suppress the input of energy to the first amplification unit and the second amplification unit to the extent that ASE occurs.

[0014] The pulsed light generation apparatus of the present disclosure may also be [8] "the pulsed light generation apparatus according to [7], which is disposed between the broadband section and the modulation section in the optical path of the pulsed light and comprises an optical intensity control unit that controls the intensity of the pulsed light for each pulse." In this case, the wavelength of the pulsed light modulated by the modulation section can be varied for each pulse by the optical intensity control unit.

[0015] The pulsed light generation apparatus of the present disclosure may also be [9] "a pulsed light generation apparatus according to any one of [1] to [8], which is arranged upstream of the modulation unit in the optical path of the pulsed light and comprises a time width compression unit for compressing the time width of the pulsed light." In this case, modulation using soliton self-frequency shift can be effectively realized in the modulation unit.

[0016] The pulsed light generation apparatus of the present disclosure may also be

[10] "a pulsed light generation apparatus according to any one of [1] to [9], comprising a filter unit arranged downstream of the modulation unit in the optical path of the pulsed light and for removing non-soliton components that were not modulated by the modulation unit." In this case, the filter unit can remove non-soliton components that were not modulated by the modulation unit.

[0017] The pulsed light generation method of the present disclosure is

[11] "a pulsed light generation method comprising: an oscillation step of oscillating pulsed light; a broadbanding step of broadening the spectrum of the pulsed light oscillated in the oscillation step; a modulation step of modulating the wavelength of the pulsed light after broadbanding by the broadbanding step using soliton self-frequency shift; a branching step of branching the pulsed light after broadbanding by the broadbanding step; and an amplification step of amplifying the pulsed light after modulation by the modulation step and after branching by the branching step by an amplification unit."

[0018] In the pulsed light generation method of this disclosure, since the wavelength of the broadbanded pulsed light is modulated using soliton self-frequency shift, it is possible to suppress multi-solitonization even when the intensity of the pulsed light before modulation is high. Furthermore, since the pulsed light after modulation and branching is amplified in the amplification unit, compared to the case where the pulsed light before branching is amplified, efficient amplification according to the wavelength of the pulsed light after modulation is possible, and the input of energy to the amplification unit can be suppressed, thereby suppressing the occurrence of ASE. Therefore, according to the pulsed light generation method of this disclosure, it is possible to suppress multi-solitonization and reliably amplify the pulsed light.

[0019] According to this disclosure, it is possible to provide a pulse light generation device and a pulse light generation method that can suppress the formation of multiple pulse light beams by modulation using soliton self-frequency shift, suppress the occurrence of ASE (Autonomous Emission Error), and reliably amplify the modulated pulse light beams.

[0020] Figure 1 is a block diagram showing a pulsed light generation apparatus according to the first embodiment. Figure 2(a) is a graph showing the time waveform of pulsed light output from the oscillator in Figure 1. Figure 2(b) is a graph showing the spectral waveform of pulsed light output from the oscillator in Figure 1. Figure 2(c) is a graph showing the time waveform of pulsed light output from the fiber amplifier in Figure 1. Figure 2(d) is a graph showing the spectral waveform of pulsed light output from the fiber amplifier in Figure 1. Figure 3 is a graph showing a specific example of the spectral waveform of pulsed light output from the fiber amplifier in Figure 1. Figure 4(a) is a graph showing the time waveform of pulsed light output from the acousto-optic modulator in Figure 1. Figure 4(b) is a graph showing the time waveform of pulsed light output from the compressor in Figure 1. Figure 5(a) is a graph showing the time waveform of pulsed light output from the soliton-shift fiber in Figure 1. Figure 5(b) is a graph showing the spectral waveform of pulsed light output from the soliton-shift fiber in Figure 1. Figure 5(c) is a graph showing the time waveform of the pulsed light output from the stretcher in Figure 1. Figure 6(a) is a graph showing the time waveform of the first pulsed light output from the branching section in Figure 1. Figure 6(b) is a graph showing the time waveform of the second pulsed light output from the branching section in Figure 1. Figure 6(c) is a graph showing the spectral waveform of the first pulsed light output from the branching section in Figure 1. Figure 6(d) is a graph showing the spectral waveform of the second pulsed light output from the branching section in Figure 1. Figure 7(a) is a graph showing the time waveform of the first pulsed light output from the short-wavelength fiber amplifier in Figure 1. Figure 7(b) is a graph showing the time waveform of the second pulsed light output from the long-wavelength fiber amplifier in Figure 1. Figure 7(c) is a graph showing the spectral waveform of the first pulsed light output from the short-wavelength fiber amplifier in Figure 1. Figure 7(d) is a graph showing the spectral waveform of the second pulsed light output from the long-wavelength fiber amplifier in Figure 1. Figure 8(a) is a graph showing the time waveform of the first pulse light output from the compressor in Figure 1. Figure 8(b) is a graph showing the time waveform of the second pulse light output from the compressor in Figure 1. Figure 9(a) is a graph showing the spectral waveform of the first pulse light output from the wavelength conversion unit in Figure 1.Figure 9(b) is a graph showing the spectral waveform of the second pulse light output from the wavelength conversion unit in Figure 1. Figure 10 is a flowchart showing the pulse light generation method according to the first embodiment. Figure 11 is a block diagram showing the pulse light generation apparatus according to the second embodiment. Figure 12(a) is a graph showing the time waveform of the first pulse light output from the branching unit in Figure 11. Figure 12(b) is a graph showing the time waveform of the second pulse light output from the branching unit in Figure 11. Figure 12(c) is a graph showing the spectral waveform of the first pulse light output from the branching unit in Figure 11. Figure 12(d) is a graph showing the spectral waveform of the second pulse light output from the branching unit in Figure 11. Figure 13 is a block diagram showing the pulse light generation apparatus according to the third embodiment.

[0021] The embodiments will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0022] [First Embodiment] As shown in Figure 1, the pulsed light generator 100 according to the first embodiment is a device that generates output light LK, which is an ultrashort pulse light, using soliton self-frequency shift (Raman soliton shift). The pulsed light generator 100 can be applied as a light source for optical measuring devices or optical inspection devices, such as microscopes, and especially two-photon microscopes. A two-photon microscope is a type of laser scanning fluorescence microscope that excites fluorescent dyes in a sample by incidenting ultrashort pulse laser light in the near-infrared region onto the sample, and performs image analysis by detecting a signal (fluorescence) from the sample. The pulsed light generator 100 constitutes a tunable light source in which the wavelength is variable for each pulse.

[0023] The pulsed light generation device 100 includes an oscillator (oscillating unit) 1, a fiber amplifier (broadbanding unit) 2, an acousto-optic modulator (light intensity control unit) 3, a compressor (time width compression unit) 4, a soliton shift fiber (modulation unit) 5, a filter (filter unit) 6, a stretcher 7, a branching unit 8, a short-wavelength fiber amplifier (amplification unit, first amplification unit) 11, a compressor 12, a wavelength conversion unit 13, a long-wavelength fiber amplifier (amplification unit, second amplification unit) 21, a compressor 22, and a wavelength conversion unit 23.

[0024] Oscillator 1 generates pulsed light L. For oscillator 1, various oscillators capable of emitting ultrashort pulses L having a time width of picoseconds to femtoseconds can be used. Oscillator 1 generates an ultrashort pulse train LT in which pulsed light L is arranged on the time axis at predetermined time intervals (see Figure 2(a)). The pulsed light L generated by oscillator 1 has a spectral width H1 and an intensity K1 (see Figure 2(b)). The pulsed light L generated by oscillator 1 has a repetition rate in the MHz to GHz range.

[0025] In Figure 2(a), the horizontal axis represents time and the vertical axis represents intensity (similarly in Figures 2(c), 4(a), 4(b), 5(a), 5(c), 6(a), 6(b), 7(a), 7(b), 8(a), and 8(b)). Figure 2(b) shows the spectral waveform with the horizontal axis representing wavelength and the vertical axis representing intensity (similarly in Figures 2(d), 5(b), 6(c), 6(d), 7(c), 7(d), 9(a), and 9(b)).

[0026] The fiber amplifier 2 amplifies the pulsed light L oscillated by the oscillator 1, for example, by similariton amplification. The fiber amplifier 2 broadens the bandwidth of the spectrum of the pulsed light L oscillated by the oscillator 1 through nonlinear effects (see Figure 2(d)). In addition, the fiber amplifier 2 secondarily widens the time width of the pulsed light L (see Figure 2(c)). The fiber amplifier 2 is located downstream of the oscillator 1 in the optical path of the pulsed light L. In this embodiment, the fiber amplifier 2 is located between the oscillator 1 and the acousto-optic modulator 3 in the optical path of the pulsed light L.

[0027] The fiber amplifier 2 is configured to include, for example, a fiber amplifier. The fiber amplifier can use, for example, an erbium-doped single-clad normal dispersion fiber, or a double-clad normal dispersion fiber co-doped with erbium and ytterbium. A normal dispersion fiber is a fiber in which the dispersion parameter D (ps / nm / km) is negative in the wavelength range in which the fiber is used. There are no particular restrictions on the additives used in the fiber, and various additives can be used. The fiber amplifier 2 amplifies while generating a nonlinear effect using the normal dispersion fiber, and generates pulsed light L as broadband amplifier light.

[0028] The fiber amplifier 2 broadens the spectral width of the pulsed light L to a second spectral width H2, which is wider than the spectral width H1, and amplifies the intensity of the pulsed light L spectrum to an intensity K2, which is higher than the intensity K1 (see Figure 2(d)). Figure 3 is a graph showing an example of the spectrum of the broadened pulsed light L. In Figure 3, the horizontal axis shows wavelength (nm) and the vertical axis shows intensity (arbitrary unit). In the example in Figure 3, the fiber amplifier 2 broadens the spectral width of the pulsed light L in the 1550 nm wavelength band to 100 nm or more.

[0029] Returning to Figure 1, the acousto-optic modulator 3 controls the intensity of the pulsed light L, whose spectrum has been broadened by the fiber amplifier 2, on a pulse-by-pulse basis. The acousto-optic modulator 3 is a device called an AOM (Acousto Optic Modulator) that modulates the intensity of the pulsed light L on a pulse-by pulse basis using the power of sound (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 located between the fiber amplifier 2 and the soliton-shift fiber 5 in the optical path of the pulsed light L. In this embodiment, the acousto-optic modulator 3 is located upstream (before) the compressor 4 in the optical path of the pulsed light L, between the fiber amplifier 2 and the soliton-shift fiber 5.

[0030] The acousto-optic modulator 3 can alternately assign different intensities to the pulsed light L contained in the ultrashort pulse train LT. As a result, in the ultrashort pulse train LT controlled by the acousto-optic modulator 3, for example, pulsed light L with a relatively low intensity M1 and pulsed light L with a relatively high intensity M2 are arranged alternately in time (see Figure 4(a)). The acousto-optic modulator 3 also reduces the repetition rate by thinning out the pulsed light L contained in the ultrashort pulse train LT.

[0031] The compressor 4 compresses the time width of the pulsed light L whose spectrum has been broadened by the fiber amplifier 2 (see Figure 4(b)). In other words, the compressor 4 applies dispersion in the opposite direction to the dispersion effect that the pulsed light L has experienced up to the previous stage, thereby achieving dispersion compensation that narrows the time width of the broadened pulsed light L. The compressor 4 is located upstream of the soliton shift fiber 5 in the optical path of the pulsed light L. In this embodiment, the compressor 4 is located between the acousto-optic modulator 3 and the soliton shift fiber 5 in the optical path of the pulsed light L.

[0032] The compressor 4 can compensate for the broadening of the pulse width L due to the spectrum broadening in the fiber amplifier 2. For example, even if the pulse width L is broadened to several picoseconds by the fiber amplifier 2, the compressor 4 can compress the pulse width L of each pulse to less than 1 picosecond. Various compressors can be used as the compressor 4, such as a compressor containing an anomalous dispersion fiber, a compressor containing a pair of chirp mirrors, a compressor containing a pair of prisms, or a compressor containing a pair of grisms. In this embodiment, a diffraction grating type compressor containing a pair of diffraction gratings is used as the compressor 4.

[0033] The soliton-shift fiber 5 modulates the wavelength of the pulsed light L, whose spectrum has been broadened by the fiber amplifier 2, using soliton self-frequency shifting. The soliton-shift fiber 5 is located downstream of the fiber amplifier 2 in the optical path of the pulsed light L. In this embodiment, the soliton-shift fiber 5 is located downstream (after) of the compressor 4 and upstream of the branching section 8 in the optical path of the pulsed light L. For example, a single-mode anomalous dispersion fiber exhibiting anomalous dispersion in the wavelength band of the pulsed light L can be used as the soliton-shift fiber 5.

[0034] As shown in Figures 5(a) and 5(b), when a pulsed light L is input to the soliton shift fiber 5, it outputs a soliton LS with a wavelength corresponding to the intensity of the input pulsed light L. The soliton shift fiber 5 generates a soliton LS having a wavelength longer than the wavelength of the input pulsed light L. The soliton shift fiber 5 generates an ultrashort pulse train LT in which the soliton LS are aligned on the time axis at predetermined time intervals. For example, the soliton shift fiber 5 outputs a soliton LS having a wavelength in the wavelength range of 1800 nm to 2200 nm.

[0035] A soliton LS is a pulsed light L whose wavelength is modulated by soliton self-frequency shifting. The wavelength of the soliton LS can be controlled by the intensity of the pulsed light L input to the soliton shift fiber 5. Increasing the intensity of the pulsed light L input to the soliton shift 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 shift fiber 5 shifts the wavelength of the soliton LS to the shorter wavelength side. However, if the intensity of the pulsed light L input to the soliton shift fiber 5 becomes excessive, multi-solitonization may occur, and multiple soliton LS may be generated for a single pulsed light L.

[0036] In contrast, in this embodiment, the spectral width of the pulsed light L input to the soliton shift fiber 5 is pre-broadened by the fiber amplifier 2. As a result, even when the intensity of the pulsed light L input to the soliton shift fiber 5 is increased, it is possible to form solitons LS while suppressing multi-solitonization.

[0037] In this embodiment, the acousto-optic modulator 3 controls the intensity of multiple pulsed light L pulse by pulse, thereby controlling the wavelength of multiple solitons LS generated in the soliton shift fiber 5 pulse by pulse. When multiple pulsed light L included in the ultrashort pulse train LT are alternately given different intensities M1 and M2, the soliton shift fiber 5 is alternately input with pulsed light L having a relatively low intensity M1 and pulsed light L having a relatively high intensity M2. In this case, the soliton shift fiber 5 alternately generates a short-wavelength soliton LS1 corresponding to the pulsed light L with low intensity M1 and a long-wavelength soliton LS2 corresponding to the pulsed light L with high intensity M2. The short-wavelength soliton LS1 has a wavelength in the range of 1800 nm to less than 2000 nm, for example. The long-wavelength soliton LS2 has a wavelength in the range of 2000 nm to 2200 nm, for example.

[0038] As shown in Figure 1, filter 6 removes non-soliton components (components that did not become solitons LS) from the optical components generated by the soliton shift fiber 5, excluding the soliton LS. Filter 6 is located downstream of the soliton shift fiber 5 in the optical path of the pulsed light L. In this embodiment, filter 6 is located between the soliton shift fiber 5 and the stretcher 7 in the optical path of the pulsed light L. There are no particular restrictions on filter 6 as long as it can remove or attenuate non-soliton components, but it is preferable to use one with an optical density (OD value) of 3 or more. For example, a wavelength-separated filter may be used as filter 6. Filter 6 may be implemented as a standalone unit or as part of a wavelength-division multiplexing coupler. The non-soliton components removed by filter 6 may be reused.

[0039] The stretcher 7 extends the time width of the pulsed light L (soliton LS) from which the non-soliton component has been removed by the filter 6, thereby reducing the peak power of the pulsed light L (see Figure 5(c)). This suppresses the occurrence of undesirable nonlinear optical effects in the amplification by the subsequent short-wavelength fiber amplifier 11 and long-wavelength fiber amplifier 21. The stretcher 7 is located downstream of the soliton-shift fiber 5 in the optical path of the pulsed light L. In this embodiment, the stretcher 7 is located between the filter 6 and the branching section 8 in the optical path of the pulsed light L.

[0040] The stretcher 7 may extend the time width of the pulsed light L by transmitting the pulsed light L through at least one of the fiber and / or the medium to impart dispersion. Alternatively, the stretcher 7 may extend the time width of the pulsed light L by imparting dispersion to the pulsed light L in a spatial system using a diffraction grating pair or a prism pair, etc. The dispersion may be either normal dispersion or abnormal dispersion.

[0041] The branching section 8 branches the pulsed light L whose time width has been stretched by the stretcher 7. The branching section 8 is located downstream of the fiber amplifier 2 in the optical path of the pulsed light L. In this embodiment, the branching section 8 is located downstream of the stretcher 7 in the optical path of the pulsed light L. The branching section 8 branches a plurality of pulsed light L into a first pulsed light L1 and a second pulsed light L2 based on the wavelength of the pulsed light L. Specifically, the branching section 8 branches a plurality of pulsed light L into a first pulsed light L1 having a wavelength in the first wavelength range and a second pulsed light L2 having a wavelength in the second wavelength range which is longer than the first wavelength range. Here, the branching section 8 branches a plurality of solitons LS such that they are separated into solitons LS1 on the short wavelength side (see Figures 6(a) and 6(c)) and solitons LS2 on the long wavelength side (see Figures 6(b) and 6(d)).

[0042] The first wavelength range, which is in the short wavelength region, is a wavelength range shorter than the reference wavelength, for example, a wavelength range of 1800 nm or more and less than 2000 nm. The second wavelength range, which is in the long wavelength region, is a long wavelength range of the reference wavelength or more, for example, a wavelength range of 2000 nm or more and 2200 nm or less. As the branching section 8, for example, a wavelength division filter such as a dichroic filter, a wavelength division multiplexer, and an optical system or optical element of a space division multiplexing method are used.

[0043] The short wavelength fiber amplifier 11 amplifies the first pulsed light L1 (soliton LS1) that is modulated by the soliton shift fiber 5 and branched by the branching section 8 (see FIGS. 7(a) and 7(c)). The short wavelength fiber amplifier 11 is arranged on the downstream side of the soliton shift fiber 5 and the branching section 8 in the optical path of the pulsed light L. In the present embodiment, the short wavelength fiber amplifier 11 is arranged on the upstream side of the compressor 12 in the optical path of the first pulsed light L1.

[0044] The short wavelength fiber amplifier 11 includes a fiber amplifier. The fiber amplifier of the short wavelength fiber amplifier 11 is an anomalous dispersion fiber, for example, a fiber doped with thulium or a fiber co-doped with thulium and holmium. The laser medium added to the fiber of the short wavelength fiber amplifier 11 is not particularly limited, and may be a rare earth such as ytterbium, erbium, neodymium, or the like, or may be Bi or the like. The short wavelength fiber amplifier 11 has a gain band corresponding to the first wavelength range (for example, 1800 nm or more and less than 2000 nm).

[0045] The compressor 12 compresses the time width of the first pulsed light L1 amplified by the short-wavelength fiber amplifier 11 (see Figure 8(a)). The compressor 12 applies dispersion in the opposite direction to the dispersion effect on the first pulsed light L1 up to the preceding stage, thereby achieving dispersion compensation that narrows the broadened time width of the first pulsed light L1. The compressor 12 is located downstream of the short-wavelength fiber amplifier 11 in the optical path of the first pulsed light L1. In this embodiment, the compressor 12 is located between the short-wavelength fiber amplifier 11 and the wavelength conversion unit 13 in the optical path of the first pulsed light L1. Various compressors can be used as the compressor 12, such as a compressor including an anomalous dispersion fiber, a compressor including a chirp mirror pair, a compressor including a prism pair, or a compressor including a grism pair. In this embodiment, a diffraction grating type compressor including a pair of diffraction gratings is used as the compressor 12.

[0046] The wavelength conversion unit 13 performs wavelength conversion on each pulse of the first pulse light L1, whose time width has been compressed by the compressor 12. The wavelength conversion unit 13 may, for example, convert the wavelength of the first pulse light L1, which is between 1800 nm and less than 2000 nm, to between 900 nm and less than 1000 nm, which is usable for two-photon microscopy. The wavelength conversion unit 13 may perform the above wavelength conversion by second harmonic generation, a phenomenon included in nonlinear effects. Second harmonic generation is a phenomenon in which the original wavelength (fundamental wave) is converted into light with half the wavelength (second harmonic). The wavelength conversion unit 13 is located downstream of the compressor 12 in the optical path of the first pulse light L1. The wavelength conversion unit 13 outputs the first pulse light L1 after wavelength conversion as the first output light LK1 (see Figure 9(a)).

[0047] The long-wavelength fiber amplifier 21 amplifies the second pulsed light L2 (soliton LS2) which is modulated by the soliton-shift fiber 5 and branched at the branching section 8 (see Figures 7(b) and 7(d)). The long-wavelength fiber amplifier 21 is located downstream of the soliton-shift fiber 5 and the branching section 8 in the optical path of the pulsed light L. In this embodiment, the long-wavelength fiber amplifier 21 is located upstream of the compressor 22 in the optical path of the second pulsed light L2.

[0048] The fiber amplifier 21 for long wavelengths includes a fiber amplifier. The fiber amplifier of the fiber amplifier 21 for long wavelengths is an anomalous dispersion fiber, for example, a fiber doped with thulium or a fiber co-doped with thulium and holmium. The laser medium added to the fiber of the fiber amplifier 21 for long wavelengths is not particularly limited, and may be a rare earth such as ytterbium, erbium, neodymium, etc., or may be Bi or the like. The fiber amplifier 21 for long wavelengths has a gain band corresponding to the second wavelength range (for example, 2000 nm or more and 2200 nm or less).

[0049] The compressor 22 compresses the time width of the second pulsed light L2 amplified by the fiber amplifier 21 for long wavelengths (see FIG. 8(b)). The compressor 22 provides dispersion in the opposite direction to the influence of the dispersion received by the second pulsed light L2 up to the previous stage, and realizes dispersion compensation for narrowing the time width of the broadened second pulsed light L2. The compressor 22 is disposed on the downstream side of the fiber amplifier 21 for long wavelengths in the optical path of the second pulsed light L2. In the present embodiment, the compressor 22 is disposed between the fiber amplifier 21 for long wavelengths and the wavelength conversion unit 23 in the optical path of the second pulsed light L2. As the compressor 22, various compressors such as a compressor including an anomalous dispersion fiber, a compressor including a chirped mirror pair, a compressor including a prism pair, a compressor including a grism pair, etc. can be used. In the present embodiment, a diffraction grating type compressor including a pair of diffraction gratings is used as the compressor 22.

[0050] The wavelength conversion unit 23 performs wavelength conversion for each pulse on the second pulsed light L2 whose time width is compressed by the compressor 22. The wavelength conversion unit 23 may convert the wavelength of the second pulsed light L2 of, for example, 2000 nm or more and 2200 nm or less to 1000 nm or more and 1100 nm or less that can be used for a two-photon microscope. The wavelength conversion unit 23 may perform the above wavelength conversion by second harmonic generation which is a phenomenon included in the non-linear effect. The wavelength conversion unit 23 is disposed on the downstream side of the compressor 22 in the optical path of the second pulsed light L2. The wavelength conversion unit 23 outputs the second pulsed light L2 after wavelength conversion as the second output light LK2 (see FIG. 9(b)).

[0051] Next, the pulsed light generation method performed using the pulsed light generation device 100 will be explained with reference to the flowchart in Figure 10.

[0052] As shown in Figure 10, the pulse light generation method according to this embodiment comprises an oscillation step S01, a broadband step S02, a light intensity control step S03, a time width compression step S04, a modulation step S05, a time width extension step S06, a branching step S07, an amplification step S08, a time width compression step S09, and a wavelength conversion step S10.

[0053] In the oscillation step S01, the oscillator 1 generates pulsed light L. In the broadbanding step S02, the fiber amplifier 2 broadens the spectrum of the pulsed light L generated in the oscillation step S01. In the light intensity control step S03, the acousto-optic modulator 3 controls the intensity of the pulsed light L whose spectrum was broadened in the broadbanding step S02, pulse by pulse. In the time width compression step S04, the compressor 4 compresses the time width of the pulsed light L whose intensity was controlled in the light intensity control step S03.

[0054] In the modulation step S05, the wavelength of the pulsed light L, whose time width was compressed in the time width compression step S04, is modulated by the soliton shift fiber 5 using soliton self-frequency shifting. The non-soliton component of the modulated pulsed light L (soliton LS) is removed by the filter 6. In the time width extension step S06, the time width of the pulsed light L, whose wavelength was modulated in the modulation step S05, is extended by the stretcher 7.

[0055] In the branching step S07, the branching unit 8 branches the pulsed light L, whose time width has been extended in the time width extension step S06, into two based on its wavelength. In the amplification step S08, the short-wavelength fiber amplifier 11 amplifies the first pulsed light L1, which is the pulsed light L after modulation in the modulation step S05 and after branching in the branching step S07. Also in the amplification step S08, the long-wavelength fiber amplifier 21 amplifies the second pulsed light L2, which is the pulsed light L after modulation in the modulation step S05 and after branching in the branching step S07.

[0056] In the time width compression step S09, the compressor 12 compresses the time width of the first pulse light L1 amplified in the amplification step S08. Also in the time width compression step S09, the compressor 22 compresses the time width of the second pulse light L2 amplified in the amplification step S08. In the wavelength conversion step S10, the wavelength conversion unit 13 performs wavelength conversion on the first pulse light L1 whose time width was compressed in the time width compression step S09 and outputs it as the first output light LK1. Also in the wavelength conversion step S10, the wavelength conversion unit 23 performs wavelength conversion on the second pulse light L2 whose time width was compressed in the time width compression step S09 and outputs it as the second output light LK2.

[0057] As a result of diligent research, the Disclosers have found that increasing the intensity of the pulsed light L input to the soliton shift fiber 5 causes the wavelength of the solitons generated by soliton self-frequency shift to become longer. In this case, they found that the wavelength tuning range of the pulsed light L generated by the pulsed light generator 100 expands. On the other hand, they found that if the intensity of the pulsed light L input to the soliton shift fiber 5 is too high, a phenomenon called multi-solitonization occurs, resulting in multiple solitons. From a practical standpoint, for example, it is desirable to suppress multi-solitonization. Therefore, the Disclosers have further diligently researched and found that multi-solitonization can be suppressed by broadening the spectral width of the pulsed light L input to the soliton shift fiber 5, that is, by broadening the spectrum of the pulsed light L before modulation using soliton self-frequency shift. In other words, in the pulsed light generation apparatus 100 and pulsed light generation method according to this embodiment, the spectrum of pulsed light L is broadened by the fiber amplifier 2, and the wavelength of the broadened pulsed light L is modulated using soliton self-frequency shifting. This increases the intensity of the pulsed light L input to the soliton shift fiber 5, efficiently lengthening the wavelength of the soliton, and makes it possible to suppress multi-soliton formation while expanding the wavelength tuning range.

[0058] In addition, the pulsed light generation device 100 and pulsed light generation method amplify the pulsed light L, which has been modulated by the soliton shift fiber 5 and branched at the branching section 8, using the short-wavelength fiber amplifier 11 and the long-wavelength fiber amplifier 21. This makes it possible to efficiently amplify the pulsed light L according to its wavelength after modulation by the soliton shift fiber 5, compared to when the pulsed light L is amplified before branching. This suppresses the input of large amounts of energy into the short-wavelength fiber amplifier 11 and the long-wavelength fiber amplifier 21, thereby suppressing the occurrence of ASE (Autonomous Energy Emission).

[0059] Therefore, according to the pulsed light generation apparatus 100 and pulsed light generation method of this embodiment, it is possible to suppress the formation of multiple pulsed light L by modulation using soliton self-frequency shift, suppress the generation of ASE, and reliably amplify the modulated pulsed light L. It becomes unnecessary to attenuate ASE using a gain smoothing filter.

[0060] In the pulsed light generator 100, the branching unit 8 branches the multiple pulsed light L into a first pulsed light L1 and a second pulsed light L2 based on their wavelengths. The short-wavelength fiber amplifier 11, positioned in the optical path of the first pulsed light L1, has a gain band corresponding to the wavelength range of the first pulsed light L1. The long-wavelength fiber amplifier 21, positioned in the optical path of the second pulsed light L2, has a gain band corresponding to the wavelength range of the second pulsed light L2.

[0061] In this case, the first pulsed light L1 can be amplified by a short-wavelength fiber amplifier 11 having a gain band corresponding to the wavelength range of the first pulsed light L1, thus suppressing amplification of the first pulsed light L1 in the region outside the gain band of the short-wavelength fiber amplifier 11. At the same time, the second pulsed light L2 can be amplified by a long-wavelength fiber amplifier 21 having a gain band corresponding to the wavelength range of the second pulsed light L2, thus suppressing amplification of the second pulsed light in the region outside the gain band of the long-wavelength fiber amplifier 21. In other words, by dividing the wavelengths of multiple pulsed light L into two regions and amplifying them using the short-wavelength fiber amplifier 11 and the long-wavelength fiber amplifier 21, which are fiber amplifiers optimized for each wavelength range, amplification of the pulsed light L in the region outside the gain band can be suppressed. As a result, it becomes possible to suppress the generation of ASE when amplifying pulsed light L.

[0062] The pulsed light generator 100 includes an acousto-optic modulator 3 between the fiber amplifier 2 and the soliton-shift fiber 5 in the optical path of the pulsed light L. In this case, the wavelength of the pulsed light L modulated by the soliton-shift fiber 5 can be varied for each pulse by the acousto-optic modulator 3.

[0063] The pulsed light generator 100 includes a compressor 4 upstream of the soliton-shifted fiber 5 in the optical path of the pulsed light L. In this case, modulation using soliton self-frequency shift can be effectively realized in the soliton-shifted fiber 5.

[0064] The pulsed light generator 100 includes a filter 6 downstream of the soliton-shift fiber 5 in the optical path of the pulsed light L. In this case, the filter 6 can remove non-soliton components that were not modulated by the soliton-shift fiber 5.

[0065] [Second Embodiment] Next, a second embodiment will be described. In this description, the differences from the first embodiment will be explained, and redundant explanations will be omitted.

[0066] As shown in Figure 11, the pulse light generation device 200 according to the second embodiment differs from the first embodiment in that, instead of the soliton shift fiber 5, filter 6, stretcher 7, branching unit 8, short-wavelength fiber amplifier 11, compressor 12, wavelength conversion unit 13, long-wavelength fiber amplifier 21, compressor 22, and wavelength conversion unit 23 (see Figure 1), it is equipped with a branching unit 20, soliton shift fiber (modulation unit) 31, filter (filter unit) 32, stretcher 33, fiber amplifier (amplification unit) 34, compressor 35, acousto-optic modulator (light intensity control unit) 41, soliton shift fiber (other modulation unit) 42, filter 43, multiplexing unit 50, and wavelength conversion unit 51.

[0067] The branching section 20 is located downstream of the compressor 4 in the optical path of the pulsed light L. The branching section 20 branches the pulsed light L, whose time width has been compressed by the compressor 4, into a first pulsed light L1 and a second pulsed light L2, so as to divide the intensity of the pulsed light L. Specifically, the branching section 8 branches a single pulsed light L, whose time width has been compressed by the compressor 4, into a first pulsed light L1 having a first intensity and a second pulsed light L2 having a second intensity.

[0068] The branching section 20 here divides the intensity of the pulsed light L into two. That is, the branching section 20 branches the pulsed light L before branching (see Figure 4(b)), which has intensities M1 and M2, into a first pulsed light L1 (see Figure 12(a)) with intensities M3 and M4, which are half the intensities of M1 and M2 respectively, and a second pulsed light L2 (see Figure 12(b)) with intensities M3 and M4. The branching section 8 also branches the pulsed light L before branching (see Figure 2(b)), which has an intensity K2, into a first pulsed light L1 (see Figure 12(c)) with an intensity K3, which is half the intensity of K2, and a second pulsed light L2 (see Figure 12(d)) with an intensity K3.

[0069] As the branching section 20, for example, a fiber coupler or a spatial division multiplexing optical system combining a beam splitter can be used. In this embodiment, the branching section 20 divides the intensity of the pulsed light L into two, and the first intensity of the first pulsed light L1 and the second intensity of the second pulsed light L2 are equal. However, the branching ratio of the intensity by the branching section 20 is not particularly limited, and the first and second intensities may be different from each other.

[0070] The soliton shift fiber 31 modulates the wavelength of the first pulsed light L1, which is branched at the branching section 20, to a predetermined wavelength (for example, 1950 nm) using soliton self-frequency shifting. The soliton shift fiber 31 is positioned in the optical path of the first pulsed light L1. The other configurations of the soliton shift fiber 31 are the same as those of the soliton shift fiber 5 (see Figure 1).

[0071] Filter 32 removes the non-soliton component from the optical components generated by the soliton-shift fiber 31. Filter 32 is located downstream of the soliton-shift fiber 31 in the optical path of the first pulse light L1. The other configurations of filter 32 are the same as those of filter 6 (see Figure 1).

[0072] The stretcher 33 extends the duration of the first pulsed light L1 (soliton LS) from which the non-soliton component has been removed by the filter 32, thereby reducing the peak power of the first pulsed light L1. The stretcher 33 is located downstream of the filter 32 in the optical path of the first pulsed light L1. The other configurations of the stretcher 33 are the same as those of the stretcher 7 (see Figure 1).

[0073] The fiber amplifier 34 amplifies the first pulse light L1 whose time width has been stretched by the stretcher 33. The fiber amplifier 34 is located downstream of the stretcher 33 in the optical path of the first pulse light L1. The fiber amplifier 34 has a gain band corresponding to a wavelength range that includes a predetermined wavelength. The fiber amplifier 34 here has a gain band that can amplify the predetermined wavelength the most. The other configurations of the fiber amplifier 34 are the same as those of the short-wavelength fiber amplifier 11 and the long-wavelength fiber amplifier 21 (see Figure 1).

[0074] The compressor 35 compresses the time width of the first pulse light L1 amplified by the fiber amplifier 34. The compressor 35 is located downstream of the fiber amplifier 34 in the optical path of the first pulse light L1. The rest of the configuration of the compressor 35 is the same as that of the compressor 22 (see Figure 1).

[0075] The acousto-optic modulator 41 controls the intensity of the second pulsed light L2, which is branched at the branching section 20, on a pulse-by-pulse basis. The acousto-optic modulator 3 also reduces the repetition rate by thinning out the second pulsed light L2. The acousto-optic modulator 41 is positioned in the optical path of the second pulsed light L2. The other configurations of the acousto-optic modulator 41 are the same as those of the acousto-optic modulator 3 (see Figure 1).

[0076] The soliton shift fiber 42 modulates the wavelength of the second pulse light L2, whose intensity is controlled by the acousto-optic modulator 41, to a predetermined wavelength range (for example, 1800 nm to 2200 nm) using soliton self-frequency shifting. The soliton shift fiber 42 is located downstream of the acousto-optic modulator 41 in the optical path of the second pulse light L2. The other configurations of the soliton shift fiber 42 are the same as those of the soliton shift fiber 5 (see Figure 1).

[0077] Filter 43 removes the non-soliton component from the optical components generated by the soliton-shift fiber 42. Filter 43 is located downstream of the soliton-shift fiber 42 in the optical path of the second pulse light L2. The other configurations of filter 43 are the same as those of filter 6 (see Figure 1).

[0078] The multiplexing unit 50 combines the first pulse light L1, whose time width has been compressed by the compressor 35, and the second pulse light L2, from which the non-soliton component has been removed by the filter 43, on the same optical axis. The multiplexing unit 50 is composed of, for example, a mirror and a dichroic mirror. The multiplexing unit 50 is located downstream of the compressor 35 and downstream of the filter 43 in the optical path of the pulse light L.

[0079] The wavelength conversion unit 51 emits sum-frequency light LW as output light LK by sum-frequency generation using the first pulse light L1 and second pulse light L2 combined in the wave-combining unit 50. In the wavelength conversion unit 51, the first pulse light L1 and second pulse light L2 combined in the wave-combining unit 50 are incident on the wavelength conversion crystal, and sum-frequency generation causes sum-frequency light LW having a wavelength in a wavelength range shorter than the predetermined wavelength range of the second pulse light L2 to be emitted from the wavelength conversion crystal. The sum-frequency light LW has a wavelength in the wavelength range of, for example, 800 nm to 900 nm. The wave-combining unit 50 and the wavelength conversion unit 51 constitute a sum-frequency generation unit.

[0080] In such a pulsed light generator 200, the first pulsed light L1 with a wavelength of 1950 nm, which can be amplified most effectively by the fiber amplifier 34, is strongly amplified, while the second pulsed light L2 with a wavelength of 1800 nm to 2200 nm is propagated to the next stage without amplification. The strongly amplified first pulsed light L1 and the unamplified second pulsed light L2 are then combined and wavelength conversion is performed by sum frequency generation. In this embodiment, the optical path lengths of the first pulsed light L1 and the second pulsed light L2 are configured to be the same, so that, for example, the arrival timing of the first pulsed light L1 and the second pulsed light L2 at the wavelength conversion crystal of the wavelength conversion unit 51 is synchronized.

[0081] As described above, the pulsed light generation apparatus 200 and pulsed light generation method according to this embodiment also suppress the formation of multiple pulsed light L by modulation using soliton self-frequency shift, suppress the occurrence of ASE, and reliably amplify the modulated pulsed light L.

[0082] Furthermore, in the pulsed light generator 200, the branching section 20 branches the pulsed light L into a first pulsed light L1 and a second pulsed light L2 so that the intensity of the pulsed light L is divided into two. The fiber amplifier 34 is positioned in the optical path of the first pulsed light L1 and has a gain band corresponding to a wavelength range that includes a predetermined wavelength which is the wavelength of the first pulsed light L1. This makes it possible to suppress amplification of the first pulsed light L1 in the region outside the gain band of the fiber amplifier 34. As a result, it is possible to suppress the generation of ASE when amplifying the first pulsed light L1.

[0083] The pulsed light generator 200 combines the first pulsed light L1 amplified by the fiber amplifier 34 and the second pulsed light L2 whose wavelength is modulated by the soliton shift fiber 42, and emits sum-frequency light LW by sum-frequency generation. In this case, sum-frequency light LW of the desired wavelength can be obtained while suppressing the generation of ASE.

[0084] The pulsed light generation device 200 is equipped with an acousto-optic modulator 41 upstream of the soliton-shift fiber 42 in the optical path of the second pulsed light L2. In this case, the wavelength of the second pulsed light L2 modulated by the soliton-shift fiber 42 can be varied for each pulse using the acousto-optic modulator 41.

[0085] [Third Embodiment] Next, a third embodiment will be described. In describing this embodiment, the differences from the first embodiment will be explained, and redundant explanations will be omitted.

[0086] As shown in Figure 13, the pulse light generation device 300 according to the third embodiment differs from the first embodiment in that, instead of the branching unit 8, short-wavelength fiber amplifier 11, compressor 12, and wavelength conversion unit 13, long-wavelength fiber amplifier 21, compressor 22, and wavelength conversion unit 23 (see Figure 1), it is equipped with a branching unit 60, a first fiber amplifier (amplifier, first amplifier) ​​61, a second fiber amplifier (amplifier, second amplifier) ​​62, a multiplexing unit 70, a compressor 71, and a wavelength conversion unit 72.

[0087] The branching section 60 is located downstream of the filter 6 in the optical path of the pulsed light L. The branching section 60 branches the pulsed light L, from which the non-soliton component has been removed by the filter 6, into a first pulsed light L1 and a second pulsed light L2 so that the intensity of the pulsed light L is divided. The other configurations of the branching section 60 are the same as those of the branching section 20 (see Figure 11).

[0088] The first fiber amplifier 61 amplifies the first pulsed light L1 that has been branched at the branching section 60. The first fiber amplifier 61 is positioned in the optical path of the first pulsed light L1. The first fiber amplifier 61 has a gain band corresponding to a wavelength range of, for example, 1800 nm to 2200 nm. The other configurations of the first fiber amplifier 61 are the same as those of the short-wavelength fiber amplifier 11 and the long-wavelength fiber amplifier 21 (see Figure 1).

[0089] The second fiber amplifier 62 amplifies the second pulsed light L2 that was branched at the branching section 60. The second fiber amplifier 62 is positioned in the optical path of the second pulsed light L2. The configuration of the second fiber amplifier 62 is the same as that of the first fiber amplifier 61.

[0090] The multiplexing unit 70 combines the first pulsed light L1 amplified by the first fiber amplifier 61 and the second pulsed light L2 amplified by the second fiber amplifier 62 on the same optical axis to generate a third pulsed light L3. The multiplexing unit 50 is configured to include, for example, a mirror and a dichroic mirror. The multiplexing unit 50 is located downstream of the first fiber amplifier 61 and the second fiber amplifier 62 in the optical path of the pulsed light L.

[0091] The compressor 71 compresses the time width of the third pulse light L3, which is obtained by combining in the multiplexing unit 70. The compressor 71 is located downstream of the multiplexing unit 70 in the optical path of the third pulse light L3. The other configurations of the compressor 71 are the same as those of the compressors 12 and 22 (see Figure 1).

[0092] The wavelength conversion unit 72 performs wavelength conversion on each pulse of the third pulse light L3, whose time width has been compressed by the compressor 71. The wavelength conversion unit 13 outputs the wavelength-converted third pulse light L3 as output light LK. The other configurations of the wavelength conversion unit 72 are the same as those of the wavelength conversion unit 13 (see Figure 1).

[0093] As described above, the pulsed light generation apparatus 300 and pulsed light generation method according to this embodiment also suppress the formation of multiple pulsed light L by modulation using soliton self-frequency shift, suppress the occurrence of ASE, and reliably amplify the modulated pulsed light L.

[0094] Furthermore, in the pulsed light generator 300, the branching section 60 branches the pulsed light L into a first pulsed light L1 and a second pulsed light L2 so that the intensity of the pulsed light L is divided into two. A first fiber amplifier 61 is placed in the optical path of the first pulsed light L1, and a second fiber amplifier 62 is placed in the optical path of the second pulsed light L2. In this case, the first fiber amplifier 61 can amplify the first pulsed light L1, and the second fiber amplifier 62 can amplify the second pulsed light L2. Therefore, it is possible to suppress the input of large amounts of energy to each of the first fiber amplifier 61 and the second fiber amplifier 62, and thus suppress the generation of ASE.

[0095] In this embodiment, the number of pulses L branched by the branching unit 60 is not particularly limited. The branching unit 60 may branch the pulses L into first to nth pulses (where N is an integer of 2 or more). The optical path lengths of the first to nth pulses are configured to be the same, and for example, the arrival timing of the first to nth pulses at the wavelength conversion unit 72 is synchronized.

[0096] [Modifications] The embodiments described above are not limited to the above-described embodiments.

[0097] In the above embodiment, an acousto-optic modulator 3 was used as the light intensity control unit, but the embodiment is not limited to this, and for example, an electro-optic modulator (EOM) may be used as the light intensity control unit. In the above embodiment, there may be multiple acousto-optic modulators 3. In the first and third embodiments, the acousto-optic modulator 3 may be placed at any position between the oscillator 1 and the soliton shift fiber 5.

[0098] In the first embodiment described above, the stretcher 7 is positioned between the filter 6 and the branching section 8 in the optical path of the pulsed light L. However, the stretcher 7 may be positioned upstream of the short-wavelength fiber amplifier 11 in the optical path of the first pulsed light L1 and upstream of the long-wavelength fiber amplifier 21 in the optical path of the second pulsed light L2. In the third embodiment described above, the stretcher 7 is positioned between the filter 6 and the branching section 60 in the optical path of the pulsed light L. However, the stretcher 7 may be positioned upstream of the first fiber amplifier 61 in the optical path of the first pulsed light L1 and upstream of the second fiber amplifier 62 in the optical path of the second pulsed light L2.

[0099] In the above embodiment, a fiber amplifier made of a normally dispersed, double-clad fiber was used as the fiber amplifier 2. However, a fiber amplifier made of a normally dispersed, single-clad fiber (e.g., erbium-doped) may be used instead. In this case as well, it will still be possible to broaden the spectrum of the pulsed light L.

[0100] The components in the above embodiments and modifications are not limited to the materials and shapes described above, and various materials and shapes can be applied. Furthermore, the components in the above embodiments and modifications can be arbitrarily applied to the components in other embodiments or modifications.

[0101] 1...Oscillator (oscillating section), 2...Fiber amplifier (broadband section), 3, 41...Acousto-optic modulator (light intensity control section), 4...Compressor (time width compression section), 5, 31...Soliton shift fiber (modulation section), 6, 32...Filter (filter section), 8, 20, 60...Branching section, 11...Short-wavelength fiber amplifier (amplification section, first amplification section), 21...Long-wavelength fiber amplifier (amplification section, second amplification section), 34...Fiber amplifier (amplification section), 42...So Lyton shift fiber (other modulation section), 50...Multiplying section (sum frequency generation section), 51...Wavelength conversion section (sum frequency generation section), 61...First fiber amplifier (amplification section, first amplification section), 62...Second fiber amplifier (amplification section, second amplification section), 100, 200, 300...Pulse light generation device, L...Pulse light, L1...First pulse light, L2...Second pulse light, L3...Third pulse light, LK...Output light, LK1...First output light, LK2...Second output light, LW...Sum frequency light.

Claims

1. A pulsed light generation device comprising: an oscillator for oscillating pulsed light; a broadbanding unit disposed downstream of the oscillator in the optical path of the pulsed light and broadening the spectrum of the pulsed light; a modulation unit disposed downstream of the broadbanding unit in the optical path of the pulsed light and modulating the wavelength of the pulsed light using soliton self-frequency shifting; a branching unit disposed downstream of the broadbanding unit in the optical path of the pulsed light and branching the pulsed light; and an amplification unit disposed downstream of the modulation unit and the branching unit in the optical path of the pulsed light and amplifying the pulsed light.

2. The pulse light generation apparatus according to claim 1, wherein the branching unit branches a plurality of pulse light into a first pulse light and a second pulse light based on the wavelength of the pulse light, the modulation unit is arranged upstream of the branching unit in the optical path of the pulse light, and the amplification unit includes a first amplification unit arranged in the optical path of the first pulse light and having a gain band corresponding to the wavelength range of the first pulse light, and amplifying the first pulse light, and a second amplification unit arranged in the optical path of the second pulse light and having a gain band corresponding to the wavelength range of the second pulse light, and amplifying the second pulse light.

3. The pulsed light generation apparatus according to claim 1 or 2, further comprising an optical intensity control unit disposed between the broadbanding unit and the modulation unit in the optical path of the pulsed light, which controls the intensity of the pulsed light for each pulse.

4. The pulse light generation apparatus according to claim 1, wherein the branching unit branches the pulse light into a first pulse light and a second pulse light so that the intensity of the pulse light is divided; the modulation unit is arranged in the optical path of the first pulse light and modulates the wavelength of the first pulse light to a predetermined wavelength; and the amplification unit is arranged in the optical path of the first pulse light and has a gain band corresponding to a wavelength range including the predetermined wavelength and amplifies the first pulse light.

5. The pulse light generation apparatus according to claim 4, comprising: another modulation unit arranged in the optical path of the second pulse light and modulating the wavelength of the second pulse light using soliton self-frequency shift; and a sum-frequency generation unit that combines the first pulse light amplified by the amplification unit and the second pulse light modulated by the other modulation unit and emits sum-frequency light by sum-frequency generation.

6. The pulsed light generation apparatus according to claim 5, further comprising an optical intensity control unit positioned upstream of the other modulation unit in the optical path of the second pulsed light, which controls the intensity of the second pulsed light pulse by pulse.

7. The pulse light generation apparatus according to claim 1, wherein the branching section branches the pulse light into a first pulse light having a first intensity and a second pulse light having a second intensity lower than the first intensity; the modulation section is arranged upstream of the branching section in the optical path of the pulse light; and the amplification section includes a first amplification section arranged in the optical path of the first pulse light and amplifying the first pulse light, and a second amplification section arranged in the optical path of the second pulse light and amplifying the second pulse light.

8. The pulsed light generation apparatus according to claim 7, further comprising an optical intensity control unit disposed between the broadbanding unit and the modulation unit in the optical path of the pulsed light, which controls the intensity of the pulsed light for each pulse.

9. A pulse light generation apparatus according to any one of claims 1 to 8, comprising a time width compression unit arranged upstream of the modulation unit in the optical path of the pulse light, for compressing the time width of the pulse light.

10. A pulsed light generation apparatus according to any one of claims 1 to 9, comprising a filter unit disposed downstream of the modulation unit in the optical path of the pulsed light, which removes non-soliton components that were not modulated by the modulation unit.

11. A pulse light generation method comprising: an oscillation step of oscillating pulse light; a broadbanding step of broadening the spectrum of the pulse light oscillated in the oscillation step; a modulation step of modulating the wavelength of the pulse light after broadbanding by the broadbanding step using soliton self-frequency shift; a branching step of branching the pulse light after broadbanding by the broadbanding step; and an amplification step of amplifying the pulse light after modulation by the modulation step and after branching by the branching step using an amplification unit.

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