Pulse light generation device and pulse light generation method

Abstract

To provide a pulse light generation device and a pulse light generation method that can suppress a plurality of pulse lights from being generated through modulation utilizing a soliton self-frequency shift.SOLUTION: A pulse light generation device comprises an oscillation part which oscillates a pulse light, an amplification part which expands the bandwidth of the spectrum of the pulse light oscillated by the oscillation part, and a modulation part which modulates the wavelength of the pulse light having the spectrum expanded in bandwidth by the amplification part by utilizing a soliton self-frequency shift.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] There is known 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. In such a pulse light generation device, by increasing the intensity of the pulse light before modulation by the modulation unit, it is intended to split the pulse light into a plurality of pulse lights having different wavelengths (output multi-colored solitons) by the modulation (see, for example, Patent Literature 1).

Prior Art Documents

Patent Literatures

[0003]

Patent Literature 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described pulse light generation device, as described above, when the intensity of the pulse light before modulation by the modulation unit is increased, the pulse light is split by the modulation to form a plurality of pulse lights (hereinafter also referred to as “multi-soliton conversion”). However, it is very difficult to set all of the plurality of pulse lights to a desired wavelength. Further, since applications in which all of the plurality of pulse lights are simultaneously used as a desired wavelength range are very rare, it is necessary to remove unnecessary pulse lights. From a practical point of view, such multi-soliton conversion is often not preferable. Therefore, when performing wavelength conversion, it is desirable to suppress multi-soliton conversion.

[0005] Therefore, an object of the present disclosure is to provide a pulse light generation device and a pulse light generation method that can suppress the formation of a plurality of pulse lights by modulation using soliton self-frequency shift. [Means for Solving the Problems]

[0006] The pulsed light generation device of the present disclosure is a "pulsed light generation device including [1] an oscillation unit that oscillates pulsed light, an amplification unit that broadens the spectrum of the pulsed light oscillated by the oscillation unit, and a modulation unit that modulates the wavelength of the pulsed light whose spectrum has been broadened by the amplification unit using soliton self-frequency shift".

[0007] As a result of intensive studies, the present inventors have obtained the knowledge that multi-soliton formation can be suppressed by broadening the spectrum of the pulsed light before modulation using soliton self-frequency shift. Therefore, in the pulsed light generation device of the present disclosure, the spectrum of the pulsed light is broadened, and the wavelength of the broadened pulsed light is modulated using soliton self-frequency shift. Thereby, for example, even when the intensity of the pulsed light before modulation is increased, it becomes possible to suppress multi-soliton formation.

[0008] The pulsed light generation device of the present disclosure may be a "pulsed light generation device according to [1], wherein the amplification unit broadens the spectrum of the pulsed light by similiton amplification". In this case, in the amplification unit, stretching of the pulse can be suppressed. Thereby, modulation using soliton self-frequency shift can be effectively realized.

[0009] The pulsed light generation device of the present disclosure may be a "pulsed light generation device according to [1] or [2], wherein the amplification unit includes a normal dispersion fiber". In this case, broadening of the spectrum of the pulsed light by the amplification unit can be specifically realized.

[0010] The pulsed light generation device of the present disclosure may be a "pulsed light generation device according to any one of [1] to [3], wherein the amplification unit includes a double-clad fiber". In this case, for example, a double-clad fiber co-doped with erbium and ytterbium can be used in the amplification unit, and thereby, it becomes possible to effectively increase the output power of the pulsed light before modulation.

[0011] The pulsed light generation device of the present disclosure may be the one described in any of [1] to [4] where "[5] the amplification unit is configured to set the spectral width of the pulsed light to 100 nm or more". In this case, it is possible to reliably suppress multi-soliton formation.

[0012] The pulsed light generation device of the present disclosure may be the one described in any of [1] to [5] where "[6] an optical intensity control unit is disposed between the amplification unit and the modulation unit in the optical path of the pulsed light, and the optical intensity control unit is configured to control the intensity of the pulsed light for each pulse". In this case, it is possible to vary the wavelength of the generated pulsed light for each pulse by means of the optical intensity control unit.

[0013] The pulsed light generation device of the present disclosure may be the one described in any of [1] to [6] where "[7] a pulse compression unit is disposed between the amplification unit and the modulation unit in the optical path of the pulsed light, and the pulse compression unit is configured to compress the pulse time width of the pulsed light". In this case, modulation utilizing soliton self-frequency shift can be effectively realized.

[0014] The pulsed light generation method of the present disclosure is the one described in [8] "a pulsed light generation method comprising an oscillation step of oscillating pulsed light, an amplification step of broadening the spectrum of the pulsed light oscillated in the oscillation step, and a modulation step of modulating the wavelength of the pulsed light whose spectrum has been broadened in the amplification step by utilizing soliton self-frequency shift".

[0015] In the pulsed light generation method of the present disclosure as well, since the wavelength of the broadened pulsed light is modulated by utilizing soliton self-frequency shift, it is possible to suppress multi-soliton formation even when, for example, the output of the pulsed light before modulation is increased.

Advantages of the Invention

[0016] According to the present disclosure, it is possible to provide a pulsed light generation device and a pulsed light generation method that can suppress the formation of a plurality of pulsed lights by modulation using soliton self-frequency shift.

Brief Description of Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments will be described in detail with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0019] As shown in Fig. 1, the pulsed light generating device 1 of this embodiment generates ultrashort pulsed light (pulsed light) L with a long wavelength by utilizing a soliton self-frequency shift (Raman soliton shift). The pulsed light generating device 1 includes an oscillator 2, a fiber amplifier 3, an acousto-optic modulator 4, a compressor 5, a soliton shift fiber 6, and a filter 7.

[0020] The oscillator 2 constitutes an oscillation unit that oscillates ultrashort pulsed light L. As shown in Fig. 2(a), the oscillator 2 generates an ultrashort pulse train with a predetermined period F1. Here, the oscillator 2 oscillates ultrashort pulsed light L having a spectrum with a first spectral width H1 and a first intensity K1 as shown in Fig. 2(b). The oscillator 2 is not particularly limited, and various oscillators can be used.

[0021] The fiber amplifier 3 constitutes an amplification unit that broadens the spectrum of the ultrashort pulsed light L oscillated by the oscillator 2. The fiber amplifier 3 broadens the spectrum of the ultrashort pulsed light L by similariton amplification and increases the output power of the ultrashort pulsed light L. The fiber amplifier 3 is disposed between the oscillator 2 and the soliton shift fiber 6 in the optical path of the ultrashort pulsed light L.

[0022] The fiber amplifier 3 includes a fiber amplifier. The fiber amplifier of the fiber amplifier 3 is a normal dispersion fiber, which is a double-clad fiber co-doped with erbium and ytterbium. That is, the fiber amplifier 3 performs amplification while causing a non-linear effect by means of a normal dispersion double-clad fiber so as not to stretch, and obtains the ultrashort pulse light L as broadband amplified light. The normal dispersion fiber is a fiber in a state where the dispersion parameter D (ps / nm / km) is negative. The additive used in the fiber amplifier 3 is not particularly limited, and various additives may be adopted.

[0023] As shown in FIGS. 2(c) and 2(d), the fiber amplifier 3 broadens the spectral width of the ultrashort pulse light L to a second spectral width H2 wider than the first spectral width H1. The fiber amplifier 3 increases the intensity of the ultrashort pulse light L to a second intensity K2 higher than the first intensity K1. Specifically, as shown in FIG. 3, the fiber amplifier 3 sets the spectral width of the ultrashort pulse light L to 100 nm or more. In FIG. 3, the horizontal axis represents the wavelength of the ultrashort pulse light L, and the vertical axis represents the relative value based on a predetermined intensity with respect to the intensity of the ultrashort pulse light L.

[0024] The acousto-optic modulator 4 constitutes an optical intensity control unit that controls the intensity of the ultrashort pulsed light L for each pulse. The acousto-optic modulator 4 is a device that modulates the ultrashort pulsed light L by utilizing the force of sound (acoustic wave), and is called an AOM (Acousto Optic Modulator). In the present embodiment, the acousto-optic modulator 4 is disposed between the fiber amplifier 3 and the soliton shift fiber 6 in the optical path of the ultrashort pulsed light L. Note that the acousto-optic modulator 4 may be disposed at any position as long as it is between the oscillator 2 and the soliton shift fiber 6. As shown in FIGS. 4(a) and 4(b), the acousto-optic modulator 4 controls the intensity of the ultrashort pulsed light L to vary for each pulse. For example, as shown in FIG. 4(a), when intensity modulations M1 and M2 are given, ultrashort pulsed lights LM1 and LM2 corresponding to the intensities given by M1 and M2 are generated as shown in FIG. 4(b). The intensity modulation range and accuracy of the ultrashort pulsed light L (LM1, LM2) depend on the performance of the acousto-optic modulator 4. The intensity of each pulsed light in the pulse train of the ultrashort pulsed light L can be arbitrarily modulated by the acousto-optic modulator 4. Note that the optical intensity control unit is not particularly limited to the acousto-optic modulator 4, and for example, an electro-optic modulator (Electro-optic modulator: EOM) may be used.

[0025] The compressor 5 constitutes a pulse compression unit that compresses the pulse time width of the ultrashort pulsed light L. In the present embodiment, the compressor 5 is disposed between the acousto-optic modulator 4 and the soliton shift fiber 6 in the optical path of the ultrashort pulsed light L. Note that the compressor 5 may be disposed at any position as long as it is between the fiber amplifier 3 and the soliton shift fiber 6. The compressor 5 outputs the ultrashort pulsed light L with a time width of less than a certain spread (less than 1 picosecond), by compressing the time width of the ultrashort pulsed light L even when the ultrashort pulsed light L is stretched (e.g., stretched by several picoseconds) by the fiber amplifier 3, for example. The compressor 5 is not particularly limited, and various compressors can be used.

[0026] The soliton shift fiber 6 constitutes a modulation unit that modulates the wavelength of the ultrashort pulsed light L with increased output while broadening the spectrum by the fiber amplifier 3, by utilizing the soliton self-frequency shift. The soliton shift fiber 6 is arranged on the downstream side of the fiber amplifier 3 in the optical path of the ultrashort pulsed light L. As shown in FIGS. 5(a) and 5(b), the soliton shift fiber 6 increases the wavelength of the ultrashort pulsed light L and generates a soliton S1. The soliton shift fiber 6 can use, for example, a single-mode dispersion-decreasing fiber that exhibits anomalous dispersion in the wavelength band of the ultrashort pulsed light L generated by the fiber amplifier 3. In addition, by controlling the acousto-optic modulator 4, solitons with wavelengths different from that of the soliton S1 can also be generated. When intensity modulations M1 and M2 are applied to the wavelength of the soliton S as shown in, for example, FIG. 5(c), the soliton S shifts to a wavelength corresponding to the intensity applied by M1 and M2 as shown in FIG. 5(d) (solitons S1 and S2). The shift wavelength range and accuracy of the soliton S depend on the performance of the acousto-optic modulator 4. The shift wavelength of each soliton S in the soliton train generated from the pulse train of the ultrashort pulsed light L can be arbitrarily changed by applying intensity modulation to the pulse train with the acousto-optic modulator 4. In the illustrated example, the ultrashort pulsed light L modulated by the soliton self-frequency shift includes a non-soliton component S0 (a component that did not become the soliton S1 or S2).

[0027] The filter 7 filters the ultrashort pulsed light L whose wavelength is modulated by the soliton shift fiber 6. The filter 7 is arranged on the downstream side of the soliton shift fiber 6 in the optical path of the ultrashort pulsed light L. In the illustrated example, the filter 7 cuts the non-soliton component S0 of the ultrashort pulsed light L as shown in FIGS. 5(b) and 5(d). It is desirable that the OD value of the filter 7 be 3 or more. The filter 7 is not particularly limited, and various filters can be used.

[0028] Next, a pulse light generation method implemented using the pulse light generation device 1 will be described with reference to the flowchart of FIG. 6.

[0029] First, an ultrashort pulse light L is oscillated in the oscillator 2 to generate an ultrashort pulse train with a predetermined period (oscillation step: step S1). The fiber amplifier 3 increases the output power of the ultrashort pulse light L and broadens the spectrum of the ultrashort pulse light L (amplification step: step S2). The acousto-optic modulator 4 controls the intensity of the ultrashort pulse light L for each pulse according to, for example, the specifications or conditions required by the pulse light generation device 1 (step S3).

[0030] Subsequently, the compressor 5 compresses the time width of the ultrashort pulse light L (step S4). The soliton shift fiber 6 modulates the wavelength of the ultrashort pulse light L with a broadened spectrum by utilizing the soliton self-frequency shift to make it longer in wavelength (modulation step: step S5). The filter 7 filters the ultrashort pulse light L with a longer wavelength and cuts its non-soliton component S0 (step S6).

[0031] Here, as a result of intensive studies by the present inventors, as shown in FIG. 7(a), it has been found that when the intensity of the ultrashort pulse light L input to the soliton shift fiber 6 is increased, the wavelength of the soliton generated by the soliton self-frequency shift becomes longer. In this case, it has been found that the variable range of the wavelength of the ultrashort pulse light L generated by the pulse light generation device 1 is widened. On the other hand, it has been found that when the intensity of the ultrashort pulse light L input to the soliton shift fiber 6 is too high, a phenomenon called multi-soliton occurs and the number of solitons becomes plural. From the practical point of view, for example, multi-soliton is preferably suppressed.

[0032] Therefore, the present inventors have further conducted intensive studies. As shown in FIG. 7(b), it has been found that multi-soliton can be suppressed by widening the spectral width of the ultrashort pulse light L input to the soliton shift fiber 6, that is, by broadening the spectrum of the ultrashort pulse light L before performing the modulation using the soliton self-frequency shift.

[0033] Therefore, in the pulse light generation device 1 and the pulse light generation method, the spectrum of the ultrashort pulse light L is broadened by the fiber amplifier 3, and the wavelength of the broadened ultrashort pulse light L is modulated using the soliton self-frequency shift. As a result, the intensity of the ultrashort pulse light L input to the soliton shift fiber 6 is increased to efficiently increase the wavelength of the soliton, and it becomes possible to suppress multi-soliton formation while expanding the wavelength variable range.

[0034] In the pulse light generation device 1 and the pulse light generation method, the fiber amplifier 3 broadens the spectrum of the ultrashort pulse light L by similariton amplification. In this case, the fiber amplifier 3 can suppress pulse stretching, and thereby effectively realize modulation using the soliton self-frequency shift.

[0035] In the pulse light generation device 1 and the pulse light generation method, the fiber amplifier 3 includes a normal dispersion fiber. In this case, the spectrum broadening of the ultrashort pulse light L by the fiber amplifier 3 can be specifically realized.

[0036] In the pulse light generation device 1 and the pulse light generation method, the fiber amplifier 3 includes a double-clad fiber. In this case, for example, a double-clad fiber co-doped with erbium and ytterbium can be used as the fiber amplifier 3, and thereby it becomes possible to effectively increase the output power of the ultrashort pulse light L before modulation.

[0037] In the pulse light generation device 1 and the pulse light generation method, the fiber amplifier 3 sets the spectrum width of the ultrashort pulse light L to 100 nm or more. In this case, it becomes possible to reliably suppress multi-soliton formation.

[0038] In the pulsed light generation device 1 and the pulsed light generation method, by modulating the intensity of the ultrashort pulsed light L input to the soliton shift fiber 6 by the acousto-optic modulator 4 at high speed for each pulse, the wavelength of the generated ultrashort pulsed light L can be variably adjusted at high speed for each pulse. Although there is a concern that the intensity of the ultrashort pulsed light L may significantly decrease when using the acousto-optic modulator 4, since the fiber amplifier 3 provides high output, such a concern can be suppressed.

[0039] The acousto-optic modulator 4 can modulate the intensity of the ultrashort pulsed light L input to the soliton shift fiber 6 to an intensity that does not generate a soliton self-frequency shift. In that case, it is possible to selectively thin out a pulse train with a desired repetition frequency in combination with the filter 7, and the repetition frequency can be modulated. In this case, while modulating the wavelength of the ultrashort pulsed light L at high speed for each pulse, it is possible to simultaneously modulate its repetition frequency.

[0040] The pulsed light generation device 1 and the pulsed light generation method compress the pulse time width of the ultrashort pulsed light L input to the soliton shift fiber 6 by the compressor 5. In this case, modulation utilizing the soliton self-frequency shift can be effectively realized.

[0041] In the pulsed light generation device 1 and the pulsed light generation method, since a fiber laser is used, maintenance-free operation can be realized compared to the case of using a titanium sapphire laser. In the pulsed light generation device 1 and the pulsed light generation method, by adjusting the intensity (output) of the ultrashort pulsed light L input to the soliton shift fiber 6, an ultrashort pulsed light L with a long wavelength can be freely generated. Also, since a configuration that requires a physical moving part when converting the wavelength is not used, the wavelength can be switched at high speed compared to, for example, the case of using a titanium sapphire laser.

[0042] Incidentally, in the technique of modulating the wavelength of the ultrashort pulsed light L using soliton self-frequency shift by a modulation unit, there may be a case where wavelength conversion is performed by increasing the intensity of the ultrashort pulsed light L before modulation to split the ultrashort pulsed light L into a plurality of pulsed lights with different wavelengths (multi-soliton formation). However, in this case, the above-mentioned problems caused by multi-soliton formation occur. Furthermore, since the modulation speed is, for example, on the order of several hundred kHz, which is much slower than the repetition frequency of general ultrashort pulsed light L (on the order of MHz), it is difficult to perform high-speed wavelength modulation such as wavelength conversion for each pulse on the ultrashort pulsed light L.

[0043] Also, in the technique of modulating the wavelength of the ultrashort pulsed light L using soliton self-frequency shift by a modulation unit, there may be a case where a soliton having a longer center wavelength is generated by increasing the fiber length in the modulation unit to extend the interaction length of soliton self-frequency shift. However, in this case, even if the longer wavelength is realized, its center wavelength remains, for example, at 2.03 μm, and the upper limit value of the center wavelength when the wavelength is increased is small. In addition, even if the longer wavelength is realized, the obtained light becomes multi-soliton, and the above-mentioned problems caused by multi-soliton formation occur.

[0044] In this regard, in the present embodiment, the ultrashort pulse light L from the fiber amplifier 3 that broadens the spectrum is modulated by the soliton shift fiber 6. That is, at the stage before the soliton shift fiber 6 that modulates using the soliton self-frequency shift, while broadening the ultrashort pulse light L, by performing dispersion compensation on the broadened ultrashort pulse light L, it is possible to achieve both suppressing multi-soliton formation and enhancing the effect of the soliton self-frequency shift. As a result, it is possible to realize the generation of solitons with a variable central wavelength up to a long wavelength (for example, 2.2 μm). Furthermore, since multi-soliton formation is suppressed, the modulation of the intensity of the ultrashort pulse light L and the central wavelength of the soliton can be made to correspond one-to-one. As a result, at the stage before the soliton shift fiber 6, by modulating the intensity of the ultrashort pulse light L at high speed by the light intensity control unit (such as an AOM or EOM), it is possible to wavelength-convert the ultrashort pulse light L for each pulse on the order of MHz to GHz, enabling high-speed wavelength modulation.

[0045] As described above, one aspect of the present disclosure is not limited to the above-described embodiment.

[0046] In the above embodiment, as the fiber amplifier 3, a fiber amplifier with a normal dispersion fiber and a double-clad fiber was used, but instead, a fiber amplifier with a normal dispersion fiber and a single-clad fiber (for example, erbium-doped) may be used. Even in this case, at least broadening of the spectrum of the ultrashort pulse light L is possible.

[0047] Each configuration in the above embodiment and the above modification is not limited to the materials and shapes described above, and various materials and shapes can be applied. Also, each configuration in the above-described embodiment and modification can be arbitrarily applied to each configuration in other embodiments or modifications.

Explanation of Reference Numerals

[0048] 1... Pulse light generation device, 2... Oscillator (oscillation unit), 3... Fiber amplifier (amplification unit), 4... Acousto-optic modulator (light intensity control unit), 5... Compressor (pulse compression unit), 6... Soliton shift fiber (modulation unit), 7... Filter, L, LM1, LM2... Ultra-short pulse light (pulse light).

Claims

1. an oscillator for emitting pulsed light; an amplifier that broadens the spectrum of the pulsed light oscillated by the oscillator; a modulation section that modulates the wavelength of the pulsed light, the spectrum of which has been broadened by the amplification section, by utilizing a soliton self-frequency shift.

2. The pulsed light generating device according to claim 1 , wherein the amplifying section broadens the spectrum of the pulsed light by similariton amplification.

3. The pulsed light generating device according to claim 1 , wherein the amplifying section includes a normal dispersion fiber.

4. The pulsed light generating device according to claim 1 , wherein the amplifying section includes a double-clad fiber.

5. The pulsed light generating device according to claim 1 , wherein the amplifier unit sets a spectral width of the pulsed light to 100 nm or more.

6. 3. The pulsed light generating device according to claim 1, further comprising a light intensity control section disposed between the amplifying section and the modulating section in an optical path of the pulsed light, the light intensity control section controlling an intensity of the pulsed light for each pulse.

7. 3. The pulsed light generating device according to claim 1, further comprising a pulse compressor arranged between the amplifier and the modulator in an optical path of the pulsed light, the pulse compressor compressing a time width of the pulse of the pulsed light.

8. an oscillation step of oscillating pulsed light; an amplifying 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, the spectrum of which has been broadened in the amplification step, by utilizing a soliton self-frequency shift.

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