Pulsed light generation apparatus and pulsed light generation method

Abstract

The present invention provides a pulsed light generation apparatus and a pulsed light generation method capable of generating pulsed light with high wavelength controllability. [Solution] The pulse light generation device 1A comprises an oscillator (oscillator) 2 that oscillates pulse light as seed light L0, a fiber amplifier (broadbanding unit) 3 that broadens the spectrum of the seed light L0 oscillated by the oscillator 2, a soliton shift fiber (wavelength modulation unit) 6 that modulates the wavelength of the seed light L0 whose spectrum has been broadened by the fiber amplifier 3 using soliton self-frequency shift to generate soliton waves LS and dispersed waves LD originating from the seed light L0, and a fiber amplifier (dispersed wave amplification unit) 9 that amplifies the dispersed waves LD generated by the soliton shift fiber 6.

Description

Technical Field

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

Background Art

[0002] There is known a pulsed light generating device including an oscillation unit that oscillates pulsed light, and a modulation unit that modulates the wavelength of the pulsed light oscillated by the oscillation unit using soliton self-frequency shift (see, for example, Patent Document 1 and Non-Patent Document 1). In such a pulsed light generating device, by amplifying the pulsed light before inputting it to the modulation unit, in the modulation unit, the input pulsed light can be split into a plurality of pulsed lights having different wavelengths (multi-colored soliton waves).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The pulsed light generator described above can be applied, for example, to a light source for a two-photon microscope. 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 the signal (fluorescence) from the sample to perform image analysis. When considering its application as a light source to such a device, the conventional pulsed light generator described above generates multi-solitonized pulsed light through modulation using soliton self-frequency shift, but it is difficult to control so that all of the multi-solitonized pulsed light is at the desired wavelength. If pulsed light of unwanted wavelengths is included, crosstalk may occur in the signal from the sample.

[0006] This disclosure was made to solve the above-mentioned problems and aims to provide a pulsed light generation apparatus and a pulsed light generation method that can generate pulsed light with high wavelength controllability. [Means for solving the problem]

[0007] The gist of this disclosure is as follows:

[0008] [1] A pulse light generation device comprising: an oscillator that oscillates pulse light as seed light; a broadbanding unit that broadens the spectrum of the seed light oscillated by the oscillator; a wavelength modulation unit that modulates the wavelength of the seed light whose spectrum has been broadened by the broadbanding unit using soliton self-frequency shift to generate soliton waves and dispersion waves originating from the seed light; and a dispersion wave amplification unit that amplifies the dispersion waves generated by the wavelength modulation unit.

[0009] This pulsed light generator broadens the spectrum of the seed light and modulates the wavelength of the broadened seed light using soliton self-frequency shifting, thereby converting the soliton wave originating from the seed light into a single soliton. When generating the soliton wave originating from the seed light, a dispersion wave is also generated. The wavelength of the dispersion wave varies depending on the wavelength of the soliton wave, but by converting the soliton wave originating from the seed light into a single soliton, a one-to-one correspondence can be established between the wavelength of the soliton wave and the wavelength of the dispersion wave. Since the wavelength of the soliton wave can be controlled by the intensity of the seed light modulated by soliton self-frequency shifting, the wavelength of the dispersion wave can also be controlled by the intensity of the seed light modulated by soliton self-frequency shifting. Therefore, this pulsed light generator can generate a dispersion wave with a wavelength determined by the intensity of the seed light, and by amplifying this dispersion wave, it can generate pulsed light with high wavelength controllability.

[0010] [2] The pulsed light generation apparatus according to [1], further comprising an intensity modulation unit that modulates the intensity of the seed light whose spectrum has been broadened by the broadband unit for each pulse. In this case, by modulating the intensity of the seed light for each pulse, it is possible to make the wavelength of the dispersed wave variable for each pulse.

[0011] [3] The pulse light generation apparatus according to [1] or [2], further comprising a time width compression unit for compressing the time width of the seed light whose spectrum has been broadened in the broadband unit. In this case, the broadening of the time width of the seed light due to the broadbanding of the spectrum in the broadband unit can be corrected.

[0012] [4] A pulsed light generation apparatus according to any one of [1] to [3], further comprising a filter that attenuates non-soliton components other than the soliton wave and the dispersion wave among the optical components generated in the wavelength modulation section. In this case, unwanted components can be attenuated from the generated pulsed light.

[0013] [5] A pulse light generation apparatus according to any one of [1] to [4], further comprising a time width extension unit and a time width compression unit that amplify the dispersed wave in the dispersed wave amplification unit using chirp pulse amplification. In this case, damage to the amplification medium when amplifying the dispersed wave can be avoided. In addition, undesirable nonlinear optical effects can be suppressed during amplification.

[0014] [6] A pulse light generation apparatus according to any one of [1] to [5], further comprising a wavelength conversion unit for converting the wavelength of the dispersed wave amplified by the dispersed wave amplification unit. In this case, the wavelength of the dispersed light can be controlled in a wavelength range different from the wavelength determined by the intensity of the seed light.

[0015] [7] A pulsed light generator according to any one of [1] to [6], further comprising a branching section that separates the optical path into the dispersed wave and the soliton wave. In this case, the applications of the pulsed light generator can be expanded by outputting both the dispersed wave and the soliton wave.

[0016] [8] The pulsed light generation apparatus according to [7], wherein a dispersion wave amplifier for amplifying the dispersion wave is arranged in the dispersion wave optical path branched at the branching section, and a soliton wave amplifier for amplifying the soliton wave is arranged in the soliton wave optical path branched at the branching section. In this case, by amplifying the dispersion wave and the soliton wave separately, efficient amplification according to each wavelength becomes possible.

[0017] [9] A pulse light generation method comprising: an oscillation step of oscillating pulse light as seed light; a broadbanding step of broadening the spectrum of the seed light oscillated in the oscillation step; a wavelength modulation step of modulating the wavelength of the seed light whose spectrum has been broadened in the broadbanding step using soliton self-frequency shift to generate a soliton wave and a dispersion wave caused by the seed light; and a dispersion wave amplification step of amplifying the dispersion wave generated in the wavelength modulation step.

[0018] In this pulse light generation method, the spectrum of the seed light is broadened, and the wavelength of the broadened seed light is modulated using soliton self-frequency shift, so that the soliton wave caused by the seed light can be single-solitonized. When generating the soliton wave caused by the seed light, a dispersive wave is also generated. The wavelength of the dispersive wave varies according to the wavelength of the soliton wave. However, by single-solitonizing the soliton wave caused by the seed light, the wavelength of the soliton wave and the wavelength of the dispersive wave can be associated one-to-one. Since the wavelength of the soliton wave can be controlled by the intensity of the seed light modulated by soliton self-frequency shift, as a result, the wavelength of the dispersive wave can also be controlled by the intensity of the seed light modulated by soliton self-frequency shift. Therefore, in this pulse light generation method, a dispersive wave having a wavelength determined by the intensity of the seed light is generated, and by amplifying the dispersive wave, pulse light with high wavelength controllability can be generated.

Advantages of the Invention

[0019] According to the present disclosure, pulse light with high wavelength controllability can be generated.

Brief Description of the Drawings

[0020] [Figure 1] It is a block diagram showing a pulse light generation device according to an embodiment of the present disclosure. [Figure 2] (a) is a schematic diagram showing the time waveform of an ultrashort pulse train (seed light) output from an oscillator, (b) is a schematic diagram showing the spectrum of the ultrashort pulse light constituting the ultrashort pulse train in (a), (c) is a schematic diagram showing the time waveform of an ultrashort pulse train (seed light) output from a fiber amplifier, and (d) is a schematic diagram showing the spectrum of the ultrashort pulse light constituting the ultrashort pulse train in (c). [Figure 3] It is a graph showing an example of the spectrum of the broadened seed light. [Figure 4] (a) is a schematic diagram showing the time waveform of an ultrashort pulse train (seed light) output from an acousto-optic modulator, and (b) is a schematic diagram showing the spectrum of the ultrashort pulse light constituting the ultrashort pulse train in (a). [Figure 5](a) is a schematic diagram showing the spectra of soliton waves and dispersion waves output from a soliton shift fiber, (b) is a graph showing an example thereof, and (c) is a schematic diagram showing how the wavelength of the dispersion wave for each pulse is controlled. [Figure 6] It is a schematic diagram showing the spectra of soliton waves and dispersion waves output from a fiber amplifier. [Figure 7] It is a flowchart showing a pulse light generation method according to an embodiment of the present disclosure. [Figure 8] It is a block diagram showing a pulse light generation measure according to a modification of the present disclosure.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, with reference to the drawings, preferred embodiments of a pulse light generation device and a pulse light generation method according to one aspect of the present disclosure will be described in detail.

[0022] FIG. 1 is a block diagram showing a pulse light generation device according to an embodiment of the present disclosure. The pulse light generation device 1A shown in FIG. 1 is a device that generates ultrashort pulsed light as output light LK using soliton self-frequency shift (Raman soliton shift). The pulse light generation device 1A of the present embodiment can be applied as a light source for an optical measurement device or an optical inspection device, for example, a microscope, particularly a two-photon microscope. A two-photon microscope is a type of laser scanning fluorescence microscope that excites a fluorescent dye in a sample by irradiating the sample with ultrashort pulsed laser light in the near-infrared region, and detects a signal (fluorescence) from the sample to perform image analysis.

[0023] As shown in Figure 1, the pulsed light generator 1A comprises an oscillator (oscillator) 2, a fiber amplifier (broadband amplifier) ​​3, an acousto-optic modulator (intensity modulation amplifier) ​​4, a compressor (time-width compression amplifier) ​​5, a soliton-shift fiber (wavelength modulation amplifier) ​​6, a filter 7, a stretcher (time-width extension amplifier) ​​8, a fiber amplifier (dispersive wave amplification amplifier) ​​9, and a compressor (time-width compression amplifier) ​​10. Each of these components is optically connected to the others by an optical fiber F. An example of an optical fiber F is a polarization-maintaining fiber.

[0024] Oscillator 2 is an oscillator that oscillates using pulsed light as seed light L0. Various oscillators capable of generating ultrashort pulse light LP having a time width of picoseconds to femtoseconds can be used as oscillator 2. As shown in Figure 2(a), oscillator 2 generates an ultrashort pulse train LT as seed light L0, in which ultrashort pulse light LP is arranged on the time axis at a predetermined time interval F1. Each of the ultrashort pulse light LP included in seed light L0 has a first spectral width H1 and a first intensity K1, as shown in Figure 2(b).

[0025] The fiber amplifier 3 is a broadbanding unit that broadens the spectrum of the seed light L0 oscillated by the oscillator 2. The fiber amplifier 3 is positioned at any position between the oscillator 2 and the soliton-shift fiber 6. In this embodiment, the fiber amplifier 3 is positioned between the oscillator 2 and the acousto-optic modulator 4. The fiber amplifier 3 broadens the spectrum of the ultrashort pulse light LP, which is the seed light L0, by, for example, similariton amplification, and also amplifies the ultrashort pulse light LP.

[0026] The fiber amplifier 3 is composed of, for example, a fiber amplifier. For the fiber amplifier, for example, an erbium-doped single-clad normal dispersion fiber can be used. A normal dispersion fiber is a fiber in which the dispersion parameter D (ps / nm / km) is negative. There are no particular restrictions on the additives used in the fiber, and various additives can be used. The fiber amplifier 3 performs amplification while generating a nonlinear effect using the above-mentioned single-clad normal dispersion fiber, and generates ultrashort pulse light LP as broadband amplifier light.

[0027] As shown in Figures 2(c) and 2(d), the fiber amplifier 3 broadens the spectral width of the ultrashort pulse light LP to a second spectral width H2, which is wider than the first spectral width H1. The fiber amplifier 3 also amplifies the intensity of the ultrashort pulse light LP to a second intensity K2, which is higher than the first intensity K1. Figure 3 is a graph showing an example of the spectrum of the broadened seed light. In Figure 3, the horizontal axis shows wavelength (nm) and the vertical axis shows intensity (arbitrary units). In the example in Figure 3, the spectral width of the seed light L0 in the 1550 nm wavelength band is broadened to more than 100 nm.

[0028] The acousto-optic modulator 4 is an intensity modulation unit that modulates the intensity of the seed light L0, whose spectrum has been broadened by the fiber amplifier 3, pulse by pulse. The acousto-optic modulator 4 is a device called an AOM (Acousto Optic Modulator) that modulates the intensity of the seed light L0 pulse by pulse using the power of sound (sound waves). The acousto-optic modulator 4 can be placed at any position between the oscillator 2 and the soliton-shift fiber 6. In this embodiment, the acousto-optic modulator 4 is placed before the compressor 5, between the fiber amplifier 3 and the soliton-shift fiber 6.

[0029] As shown in Figures 4(a) and 4(b), the acousto-optic modulator 4 modulates the intensity of the ultrashort pulse light LP included in the ultrashort pulse train LT pulse by pulse. In the example shown in Figures 4(a) and 4(b), the ultrashort pulse light LP included in the ultrashort pulse train LT is alternately given two different intensities M1 and M2. As a result, in the ultrashort pulse train LT, ultrashort pulse light LP1 with a relatively low intensity M1 and ultrashort pulse light LP2 with a relatively high intensity M2 are alternately arranged in time.

[0030] The compressor 5 is a time-width compression unit that compresses the time width of the seed light L0 whose spectrum has been broadened by the fiber amplifier 3. The compressor 5 is positioned at any position between the fiber amplifier 3 and the soliton shift fiber 6. In this embodiment, the compressor 5 is positioned between the acousto-optic modulator 4 and the soliton shift fiber 6. The compressor 5 corrects the broadening of the time width of the seed light L0 that occurs when the spectrum is broadened by the fiber amplifier 3. For example, even if the time width of the ultrashort pulse light LP is broadened to several picoseconds by the fiber amplifier 3, the compressor 5 can compress the time width of the ultrashort pulse light LP to less than 1 picosecond. Various types of compressors, such as chirp mirrors and prism types, can be used as the compressor 5, but in this embodiment, a diffraction grating type compressor including a pair of diffraction gratings is used.

[0031] The soliton shift fiber 6 is a wavelength modulation unit that modulates the wavelength of the seed light L0, whose spectrum has been broadened by the fiber amplifier 3, using soliton self-frequency shifting. The soliton shift fiber 6 can be positioned anywhere on the downstream side of the fiber amplifier 3. In this embodiment, the soliton shift fiber 6 is positioned downstream of the compressor 5. For example, a single-mode anomalous dispersion fiber that exhibits anomalous dispersion in the wavelength band of the seed light L0 can be used for the soliton shift fiber 6.

[0032] When an ultrashort pulse light LP, which is the seed light L0, is input to the soliton shift fiber 6, a soliton wave LS is generated by stimulated Raman scattering, as shown in Figure 5(a). Simultaneously with the generation of the soliton wave LS, a dispersion wave LD is also generated. The dispersion wave LD is a type of soliton wave LS generated by Cherenkov radiation in a highly nonlinear fiber. The soliton wave LS is generated at a wavelength longer than the wavelength of the seed light L0 due to soliton self-frequency shifting. The dispersion wave LD is generated at a wavelength shorter than the wavelength of the seed light L0. The wavelength of the dispersion wave LD corresponds one-to-one with the wavelength of the soliton wave LS.

[0033] Figure 5(b) is a graph showing an example of the spectra of soliton waves and dispersion waves output from a soliton-shift fiber. In Figure 5(b), the horizontal axis shows wavelength (nm) and the vertical axis shows intensity (arbitrary units). In the example in Figure 5(b), a soliton wave LS with a peak around 2050 nm is generated by the soliton self-frequency shift of the seed light L0 after broadbanding to the 1550 nm wavelength band. In addition, in the example in Figure 5(b), secondary diffraction light of the dispersion wave with a peak around 1900 nm can be observed. This indicates that a dispersion wave LD with a peak around 950 nm is generated.

[0034] The wavelength of the soliton wave LS can be controlled by the intensity of the seed light L0 input to the soliton shift fiber 6. Increasing the intensity of the seed light L0 input to the soliton shift fiber 6 shifts the wavelength of the soliton wave LS to the longer wavelength side, and decreasing the intensity of the seed light L0 input to the soliton shift fiber 6 shifts the wavelength of the soliton wave LS to the shorter wavelength side. However, if the intensity of the seed light L0 input to the soliton shift fiber 6 becomes excessive, multi-solitonization may occur, and multiple soliton waves LS may be generated for a single ultrashort pulse light LP.

[0035] In contrast, in this embodiment, the spectral width of the seed light L0 input to the soliton shift fiber 6 is pre-broadened by the fiber amplifier 3. As a result, even when the intensity of the seed light L0 input to the soliton shift fiber 6 is increased, it is possible to lengthen the wavelength of the soliton wave LS, that is, to expand the wavelength tuning range of the soliton wave LS, while suppressing multi-solitonization.

[0036] The wavelength shift of the dispersion wave LD occurs in the opposite direction to the wavelength shift of the soliton wave LS. When the wavelength of the soliton wave LS shifts to the longer wavelength side, the wavelength of the dispersion wave LD shifts to the shorter wavelength side. When the wavelength of the soliton wave LS shifts to the shorter wavelength side, the wavelength of the dispersion wave LD shifts to the longer wavelength side. As described above, the wavelength of the dispersion wave LD corresponds one-to-one with the wavelength of the soliton wave LS. Therefore, in this embodiment, the wavelength of the dispersion wave LD can be controlled by the intensity of the seed light L0 modulated by the soliton self-frequency shift.

[0037] In this embodiment, the acousto-optic modulator 4 can modulate the intensity of the ultrashort pulse light LP included in the ultrashort pulse train LT on a pulse-by-pulse basis. In other words, in this embodiment, by modulating the intensity of the ultrashort pulse light LP on a pulse-by-pulse basis, the wavelength of the soliton wave LS generated in the soliton shift fiber 6 can be modulated on a pulse-by-pulse basis, and as a result, the wavelength of the dispersed wave LD generated in the soliton shift fiber 6 can be modulated on a pulse-by-pulse basis.

[0038] As shown in Figures 4(a) and 4(b), when ultrashort pulse light LP included in the ultrashort pulse train LT is alternately supplied with different intensities M1 and M2, the soliton shift fiber 6 is alternately input with ultrashort pulse light LP1 having a relatively low intensity M1 and ultrashort pulse light LP2 having a relatively high intensity M2. In this case, as shown in Figure 5(c), the soliton shift fiber 6 alternately generates a short-wavelength soliton wave LS1 corresponding to the ultrashort pulse light LP1 and a long-wavelength soliton wave LS2 corresponding to the ultrashort pulse light LP2 in time. In addition, a long-wavelength dispersive wave LD1, which is generated simultaneously with the short-wavelength soliton wave LS1, and a short-wavelength dispersive wave LD2, which is generated simultaneously with the long-wavelength soliton wave LS2, are alternately generated in time.

[0039] Furthermore, as shown in Figure 5(c), the optical components output from the soliton-shift fiber 6 may include not only soliton waves LS and dispersed waves LD, but also non-soliton components LZ consisting of components other than soliton waves LS and dispersed waves LD. The non-soliton components LZ include components of the seed light L0 that were not modulated by soliton self-frequency shift and did not become soliton waves LS and dispersed waves LD, soliton waves and dispersed waves other than soliton waves LS and dispersed waves LD, and other noise components.

[0040] Returning to Figure 1, filter 7 is the part that attenuates the non-soliton component LZ from the optical component generated by the soliton shift fiber 6, excluding the soliton wave LS and dispersion wave LD. Filter 7 is positioned at any position downstream of the soliton shift fiber 6. In this embodiment, filter 7 is positioned between the soliton shift fiber 6 and the stretcher 8. There are no particular restrictions on filter 7 as long as it can attenuate the non-soliton component LZ, but it is preferable to use one with an optical density (OD value) of 3 or more.

[0041] The fiber amplifier 9 is a dispersion wave amplifier that amplifies the dispersion wave LD generated by the soliton shift fiber 6. The fiber amplifier 9 is positioned at any location downstream of the soliton shift fiber 6. In this embodiment, the fiber amplifier 9 is positioned downstream of the filter 7, between the stretcher 8 and the compressor 10. The fiber amplifier 9 is composed of, for example, a fiber amplifier. For the fiber amplifier, for example, a ytterbium-doped single-clad or double-clad fiber can be used. The fiber amplifier 9 amplifies the intensity of the dispersion wave LD (LD1, LD2) to a level higher than the intensity of the soliton wave LS (LS1, LS2), as shown in Figure 6, for example.

[0042] The stretcher 8 and compressor 10 are time-width extension and time-width compression units that convert the amplification of the dispersed wave LD in the fiber amplifier 9 to chirp pulse amplification. The stretcher 8 extends the time width of the dispersed wave LD before it is amplified by the fiber amplifier 9, reducing the peak power of the dispersed wave LD. This avoids damage to the amplification medium when amplifying the dispersed wave LD. It also suppresses the occurrence of undesirable nonlinear optical effects during amplification. The compressor 10 compresses the time width of the dispersed wave LD after it has been amplified by the fiber amplifier 9, converting the dispersed wave LD back into ultrashort pulse light.

[0043] The dispersed wave LD amplified by the fiber amplifier 9 is output to the outside of the pulsed light generator 1A as output light LK. When using the dispersed wave LD as output light LK, a filter to cut out the soliton wave LS may be placed downstream of the soliton shift fiber 6. If the stretcher 8 before the fiber amplifier 9 or the compressor 10 after the fiber amplifier 9 is a diffraction grating type compressor containing a pair of diffraction gratings, wavelength separation can be performed by the diffraction gratings, allowing only the dispersed wave LD to be output as output light without the need for additional filters.

[0044] Figure 7 is a flowchart showing a pulsed light generation method according to one embodiment of the present disclosure. As shown in Figure 7, the pulsed light generation method according to this embodiment comprises an oscillation step S01, a broadband step S02, an intensity modulation step S03, a time width compression step S04, a wavelength modulation step S05, a dispersive wave amplification step S06, and an output step S07. The pulsed light generation method according to this embodiment is carried out using the pulsed light generation apparatus 1A described above.

[0045] Oscillation step S01 is a step in which an ultrashort pulse light LP is used as seed light L0 for oscillation. In oscillation step S01, an ultrashort pulse train LT, in which ultrashort pulse light LP having a first spectral width H1 and a first intensity K1 is arranged on the time axis at a predetermined time interval F1, is output from oscillator 2 as seed light.

[0046] The broadbanding step S02 is a step in which the spectrum of the seed light L0 oscillated in the oscillation step S01 is broadened. In the broadbanding step S02, the spectrum of the ultrashort pulse light LP, which is the seed light L0, is broadened to a second spectral width H2 that is wider than the first spectral width H1 by simirariton amplification in the fiber amplifier 3, and the intensity of the ultrashort pulse light LP is amplified to a second intensity K2 that is higher than the first intensity K1.

[0047] The intensity modulation step S03 is a step in which the intensity of the seed light L0, whose spectrum has been broadened in the broadbanding step S02, is modulated pulse by pulse. In the intensity modulation step S03, the acousto-optic modulator 4 modulates the intensity of the ultrashort pulse light LP included in the ultrashort pulse train LT pulse by pulse. Here, for example, different intensities M1 and M2 are assigned to the ultrashort pulse light LP included in the ultrashort pulse train LT so that ultrashort pulse light LP1 with a relatively low intensity M1 and ultrashort pulse light LP2 with a relatively high intensity M2 are arranged alternately in time.

[0048] The time width compression step S04 is a step in which the time width of the seed light L0, whose spectrum has been broadened in the broadbanding step S02, is compressed. In the time width compression step S04, the compressor 5 corrects the broadening of the time width of the seed light L0 that occurs due to the broadbanding of the spectrum in the fiber amplifier 3.

[0049] The wavelength modulation step S05 is a step in which the wavelength of the seed light L0, whose spectrum was broadened in the broadbanding step S02, is modulated using soliton self-frequency shifting to generate soliton waves LS and dispersion waves LD originating from the seed light L0. In the wavelength modulation step S05, the broadbanded seed light L0 is input to the soliton shift fiber 6 to generate soliton waves LS and dispersion waves LD by stimulated Raman scattering.

[0050] In this embodiment, an ultrashort pulse light LP1 having a relatively low intensity M1 and an ultrashort pulse light LP2 having a relatively high intensity M2 are alternately input to the soliton shift fiber 6. Therefore, a short-wavelength soliton wave LS1 corresponding to the ultrashort pulse light LP1 and a long-wavelength soliton wave LS2 corresponding to the ultrashort pulse light LP1 are generated alternately in time. Consequently, a long-wavelength dispersive wave LD1 generated simultaneously with the short-wavelength soliton wave LS1 and a short-wavelength dispersive wave LD2 generated simultaneously with the long-wavelength soliton wave LS2 are generated alternately in time.

[0051] The dispersive wave amplification step S06 is a step in which the dispersive wave LD generated in the wavelength modulation step S05 is amplified. In the dispersive wave amplification step S06, the dispersive wave LD(LD1,LD2) is amplified to a level higher than the intensity of the soliton wave LS(LS1,LS2), for example, by chirp pulse amplification using the stretcher 8, fiber amplifier 9, and compressor 10, while suppressing the occurrence of undesirable nonlinear optical effects.

[0052] The output step S07 is a step in which the dispersed wave LD amplified in the dispersed wave amplification step S06 is output as output optical light LK. In this embodiment, the output optical light LK is output with the soliton wave LS and the non-soliton component LZ removed by the filter 7. By using a diffraction grating type stretcher 8 including a pair of diffraction gratings or a diffraction grating type compressor 10 including a pair of diffraction gratings, it is possible to output output optical light LK containing only the dispersed wave LD by wavelength separation at the diffraction grating.

[0053] As explained above, the pulsed light generator 1A broadens the spectrum of the seed light L0 and modulates the wavelength of the broadened seed light L0 using soliton self-frequency shifting, thereby converting the soliton wave LS originating from the seed light L0 into a single soliton. Furthermore, even if multiple soliton waves are generated, since the wavelength ranges of each soliton wave are sufficiently far apart, it is possible to convert them into a single soliton in the wavelength range longer than the cut wavelength by using a short-wavelength cut filter or the like. When generating the soliton wave LS originating from the seed light L0, a dispersion wave LD is also generated. The wavelength of the dispersion wave LD varies according to the wavelength of the soliton wave LS, but by converting the soliton wave LS originating from the seed light L0 into a single soliton, a one-to-one correspondence can be established between the wavelength of the soliton wave LS and the wavelength of the dispersion wave LD. Since the wavelength of the soliton wave LS can be controlled by the intensity of the seed light L0 modulated by soliton self-frequency shifting, the wavelength of the dispersion wave LD can also be controlled by the intensity of the seed light L0 modulated by soliton self-frequency shifting. Therefore, the pulsed light generator 1A generates a dispersed wave LD with a wavelength determined by the intensity of the seed light L0, and by amplifying the dispersed wave LD, it is possible to generate pulsed light with high wavelength controllability.

[0054] The pulsed light generator 1A further includes an acousto-optic modulator 4 that modulates the intensity of the seed light L0, whose spectrum has been broadened by the fiber amplifier 3, for each pulse. This makes it possible to vary the wavelength of the dispersed wave LD for each pulse by modulating the intensity of the seed light L0 for each pulse.

[0055] The pulsed light generator 1A is further equipped with a compressor 5 that compresses the time width of the seed light L0 whose spectrum has been broadened by the fiber amplifier 3. This makes it possible to compensate for the broadening of the time width of the seed light L0 that occurs when the spectrum is broadened by the fiber amplifier 3.

[0056] The pulsed light generator 1A further includes a filter 7 that attenuates non-soliton components LZ other than soliton waves LS and dispersed waves LD from the optical components generated by the soliton shift fiber 6. This allows unwanted components to be attenuated from the generated pulsed light.

[0057] The pulsed light generator 1A further includes a stretcher 8 and a compressor 10 that perform chirp pulse amplification of the dispersed wave LD in the fiber amplifier 9. This avoids damage to the amplification medium when amplifying the dispersed wave LD. It also suppresses the occurrence of undesirable nonlinear optical effects during amplification.

[0058] Figure 8 is a block diagram showing a modified pulsed light generation device according to the present disclosure. As shown in Figure 8, the modified pulsed light generation device 1B differs from the pulsed light generation device 1A described above in that it includes a branching section 21 that separates the dispersed wave LD and the soliton wave LS. The configuration from the oscillator 2 to the soliton shift fiber 6 is the same as that of the pulsed light generation device 1A.

[0059] The branching section 21 is composed of an optical fiber coupler capable of separating light of different wavelengths. In the example shown in Figure 8, the branching section 21 is located downstream of the soliton shift fiber 6 and branches the dispersed wave LD and soliton wave LS generated by the soliton shift fiber 6 into a dispersed wave optical path RD and a soliton wave optical path RS.

[0060] The dispersive wave optical path RD includes, for example, a filter 7, a stretcher 8, a fiber amplifier 9, a compressor 10, and a nonlinear optical crystal (wavelength conversion section) 22. Each of these components is optically connected to the others by optical fibers F, just as in the section preceding the branching section 21. An example of an optical fiber F is a polarization-maintaining fiber. The configuration of the filter 7, stretcher 8, fiber amplifier 9, and compressor 10 is the same as that of the pulsed light generation device 1A.

[0061] The nonlinear optical crystal 22 is a wavelength conversion unit that converts the wavelength of the dispersed wave LD amplified by the fiber amplifier 9. Here, the dispersed wave LD output from the compressor 10 is focused by a lens or the like and incident on the nonlinear optical crystal to generate the harmonic LDk of the dispersed wave LD. The dispersed wave LD and its harmonic LDk are output to the outside of the pulsed light generator 1B as output light LK1.

[0062] The optical path RS for soliton waves includes a stretcher 23, a fiber amplifier (soliton wave amplification unit) 24, and a compressor 25. The fiber amplifier 24 is composed of, for example, a fiber amplifier. The fiber amplifier can use, for example, a thulium-doped single-clad or double-clad fiber, or a thulium and holonium co-doped double-clad fiber. The fiber amplifier 24 amplifies the intensity of the soliton wave LS generated in the soliton-shift fiber 6 to an even higher level.

[0063] The stretcher 23 and compressor 25 are time-width extension and time-width compression units, respectively, that convert the amplification of the soliton wave LS in the fiber amplifier 24 into chirp pulse amplification. The stretcher 23 extends the time width of the soliton wave LS before amplification in the fiber amplifier 24, reducing the peak power of the soliton wave LS. This avoids damage to the amplification medium when amplifying the soliton wave LS. It also suppresses the occurrence of undesirable nonlinear optical effects during amplification. The compressor 25 compresses the time width of the soliton wave LS after amplification in the fiber amplifier 24, converting the dispersed wave LD back into ultrashort pulse light. The soliton wave LS after amplification by the fiber amplifier 24 is output as output light LK2 outside the pulse light generator 1B.

[0064] In the pulsed light generator 1B having the above configuration, the same effects as the pulsed light generator 1A are achieved, generating a dispersed wave LD with a wavelength determined by the intensity of the seed light L0, and by amplifying the dispersed wave LD, pulsed light with high wavelength controllability can be generated.

[0065] The pulsed light generator 1B includes a nonlinear optical crystal 22 that converts the wavelength of the dispersed wave LD amplified by the fiber amplifier 9. This allows the wavelength of the dispersed wave LD to be controlled within a wavelength range different from the wavelength determined by the intensity of the seed light L0. In the pulsed light generator 1A, such a nonlinear optical crystal 22 may be placed, for example, after the compressor 10.

[0066] The pulsed light generator 1B is equipped with a branching section 21 that separates the optical path into a dispersed wave LD and a soliton wave LS. This configuration allows for the output of both output light LK1, which includes a dispersed wave LD, and output light LK2, which includes a soliton wave LS, thereby expanding the applications of the pulsed light generator 1B.

[0067] In the pulsed light generator 1B, a fiber amplifier 9 for amplifying the dispersed wave LD is located in the dispersed wave optical path RD branched at the branching section 21, and a fiber amplifier 24 for amplifying the soliton wave LS is located in the soliton wave optical path RS branched at the branching section 21. With this configuration, by amplifying the dispersed wave LD and the soliton wave LS separately, efficient amplification according to each wavelength becomes possible.

[0068] This disclosure is not limited to the embodiments described above. For example, in each of the embodiments described above, an erbium-doped single-clad normal dispersion fiber was exemplified as the fiber amplifier constituting the fiber amplifier 3, but instead, a double-clad normal dispersion fiber co-doped with erbium and ytterbium may be used. In such a configuration as well, the spectrum of the ultrashort pulse light L can be broadened. Furthermore, in each of the embodiments described above, the arrangement of the acousto-optic modulator 4 can be omitted. Even in this case, a dispersed wave LD with a wavelength determined by the intensity of the seed light L0 can be generated, and by amplifying the dispersed wave LD, pulse light with high wavelength controllability can be generated.

[0069] In the pulsed light generator 1B, the arrangement of the nonlinear optical crystal 22 may be omitted depending on the wavelength required for the output light LK1. Alternatively, in the pulsed light generator 1B, a filter 7 may also be placed in the soliton wave optical path RS. In this case, the non-soliton component LZ can be attenuated in the output light LK2 output from the soliton wave optical path RS. In the pulsed light generator 1B, a branching section 21 that divides the intensity of the seed light L0 may be placed after the compressor 5, and soliton shift fibers 6 may be placed in the dispersive wave optical path RD and the soliton wave optical path RS, respectively, which are branched by the branching section 21. With such a configuration, efficient amplification according to each wavelength becomes possible by amplifying the dispersive wave LD and the soliton wave LS separately. [Explanation of Symbols]

[0070] 1A, 1B...Pulsed light generator, 2...Oscillator (oscillating unit), 3...Fiber amplifier (broadband conversion unit), 4...Acousto-optic modulator (intensity modulation unit), 5...Compressor (time width compression unit), 6...Soliton shift fiber (wavelength modulation unit), 7...Filter, 8...Stretcher (time width extension unit), 9...Fiber amplifier (dispersive wave amplification unit), 10...Compressor (time width compression unit), 21...Branching unit, 22...Nonlinear optical crystal (wavelength conversion unit), 24...Fiber amplifier (soliton wave amplification unit), L0...Seed light, LP...Ultrashort pulse light (pulsed light), LS...Soliton wave, LD...Dispersive wave, LZ...Non-soliton component, RD...Optical path for dispersed wave, RS...Optical path for soliton wave.

Claims

1. An oscillator that uses pulsed light as a seed light, A broadbanding unit that broadens the spectrum of the seed light oscillated by the oscillation unit, A wavelength modulation unit modulates the wavelength of the seed light whose spectrum has been broadened in the broadband unit using soliton self-frequency shift to generate soliton waves and dispersion waves originating from the seed light. A pulsed light generation device comprising a dispersion wave amplification unit for amplifying the dispersion wave generated in the wavelength modulation unit.

2. The pulsed light generation apparatus according to claim 1, further comprising an intensity modulation unit that modulates the intensity of the seed light whose spectrum has been broadened in the broadband unit for each pulse.

3. The pulse light generation apparatus according to claim 1, further comprising a time width compression unit for compressing the time width of the seed light whose spectrum has been broadened in the broadband unit.

4. The pulsed light generation apparatus according to claim 1, further comprising a filter that attenuates non-soliton components from the light components generated in the wavelength modulation section, excluding the soliton waves and the dispersion waves.

5. The pulse light generation apparatus according to claim 1, further comprising a time width extension unit and a time width compression unit that perform chirp pulse amplification in the dispersed wave amplification unit.

6. The pulsed light generation apparatus according to claim 1, further comprising a wavelength conversion unit for converting the wavelength of the dispersed wave amplified by the dispersed wave amplification unit.

7. The pulsed light generation apparatus according to any one of claims 1 to 6, further comprising a branching section that separates the optical path into the dispersed wave and the soliton wave.

8. The dispersive wave amplification unit is arranged in the dispersive wave optical path branched at the aforementioned branching section, The pulsed light generation apparatus according to claim 7, wherein a soliton wave amplification unit for amplifying the soliton wave is arranged in the soliton wave optical path branched at the branching unit.

9. An oscillation step in which pulsed light is used as seed light, A broadbanding step which broadens the spectrum of the seed light oscillated in the oscillation step, A wavelength modulation step is performed to modulate the wavelength of the seed light whose spectrum has been broadened in the broadband step using soliton self-frequency shift, thereby generating soliton waves and dispersion waves originating from the seed light. A pulsed light generation method comprising a dispersion wave amplification step for amplifying the dispersion wave generated in the wavelength modulation step.

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