Light source device and method for controlling shape of light spectrum

Abstract

A light source device (100) comprises: a light source (1) that outputs seed light having a prescribed peak frequency; a first modulator (3) that generates first modulated light by phase modulation of the seed light by a first modulation signal having a first frequency; a second modulator (4) that generates second modulated light by phase modulation of the first modulated light by a second modulation signal having a second frequency; and a control unit (7c) that can change the relative phase between the first modulation signal and the second modulation signal and the amplitude of the first modulation signal and / or the amplitude of the second modulation signal.

Description

Light source device and method for controlling the shape of an optical spectrum

[0001] The present invention relates to a light source device and a method for controlling the shape of an optical spectrum.

[0002] For example, in order to suppress stimulated Brillouin scattering (SBS) that occurs in an optical fiber when transmitting laser light with a narrow linewidth through the optical fiber, the light is modulated with a white noise signal and further modulated with a sine wave signal to widen the spectral width of the light and suppress the peak power. A technique is known (Non-Patent Document 1).

[0003] Further, in order to realize laser light having higher power and a narrower linewidth, a technique of modulating with a pseudo-random bit sequence (PRBS) signal which is a kind of white noise signal or pseudo-random signal and further modulating with a sine wave signal is known (Patent Document 1).

[0004] Japanese Patent Publication No. 2017-527124

[0005] Roopa Prakash et al., "Enhancing the Efficacy of Noise Modulation for SBS Suppression in High Power, Narrow Linewidth Fiber Lasers by the Incorporation of Sinusoidal Modulation" IEEE PHOTONICS JOURNAL, VOL. 13, NO. 5, OCTOBER 2021

[0006] Regarding the shape of the optical spectrum, various shapes are required depending on the use of the light. Therefore, it is preferable that the degree of freedom in controlling the shape of the optical spectrum is high.

[0007] The present invention has been made in view of the above, and an object thereof is to provide a light source device and a method for controlling the shape of an optical spectrum with a high degree of freedom in controlling the shape of the optical spectrum.

[0008] To solve the above-mentioned problems and achieve the objective, one aspect of the present invention is a light source device comprising: a light source that outputs seed light having a predetermined peak frequency; a first modulator that generates first modulated light by phase modulating the seed light with a first modulated signal having a first frequency; a second modulator that generates second modulated light by phase modulating the first modulated light with a second modulated signal having a second frequency; and a control unit that can change the relative phase between the first modulated signal and the second modulated signal, and at least one of the amplitude of the first modulated signal and the amplitude of the second modulated signal.

[0009] The first modulated signal may also be a pseudo-random signal.

[0010] The light source device includes a low-pass filter, and the first modulated signal may be a pseudo-random signal after passing through the low-pass filter.

[0011] The second modulated signal may also be a sine wave signal.

[0012] The first frequency and the second frequency may be equal.

[0013] A common signal generator that outputs the first modulated signal and the second modulated signal may be provided.

[0014] The first modulated light and the second modulated light may include a plurality of frequency-discrete peak components.

[0015] The light source device includes an optical fiber for transmitting the second modulated light, and the peak frequencies of the plurality of peak components may be shifted from the peak frequency of the Brillouin gain band generated in the optical fiber due to the second modulated light.

[0016] The frequency of the main peak component in the second modulated light, which has a power that stands out from the surrounding peak components, may be equal to the peak frequency of the seed light.

[0017] The light source device may include a first brancher that branches a reference light from the seed light, a second brancher that branches the second modulated light into a plurality of second modulated lights, and a phase matching unit that matches the phase of each of the plurality of second modulated lights with the phase of the reference light.

[0018] Each of the plurality of second modulated lights contains a plurality of frequency-discrete peak components, and the principal peak component among the plurality of peak components that has a power that stands out from the surrounding peak components is equal to the peak frequency of the seed light. In this state, the phase matching unit may match the phase of each of the principal peak components of the plurality of second modulated lights with the phase of the reference light.

[0019] One aspect of the present invention is a method for controlling the shape of an optical spectrum, which involves generating a first modulated light by phase modulating a seed light having a predetermined peak frequency with a first modulated signal having a first frequency, generating a second modulated light by phase modulating the first modulated light with a second modulated signal having a second frequency, and changing the relative phase between the first modulated signal and the second modulated signal, as well as changing at least one of the amplitude of the first modulated signal and the amplitude of the second modulated signal, thereby changing the shape of the optical spectrum of the second modulated light.

[0020] According to the present invention, it is possible to control the shape of the optical spectrum with a high degree of freedom.

[0021] Figure 1 is a schematic configuration diagram of a light source device according to Embodiment 1. Figure 2A is a diagram showing an example of the spectrum of the modulated light in Embodiment 1. Figure 2B is a diagram showing an example of the spectrum of the modulated light in Embodiment 1. Figure 2C is a diagram showing an example of the spectrum of the modulated light in Embodiment 1. Figure 3A is a diagram showing an example of the simulation results of controlling the shape of the spectrum of the second modulated light in Embodiment 1. Figure 3B is a diagram showing an example of the simulation results of controlling the shape of the spectrum of the second modulated light in Embodiment 1. Figure 3C is a diagram showing an example of the simulation results of controlling the shape of the spectrum of the second modulated light in Embodiment 1. Figure 4A is a diagram showing an example of the experimental results of controlling the shape of the spectrum of the second modulated light in Embodiment 1. Figure 4B is a diagram showing an example of the experimental results of controlling the shape of the spectrum of the second modulated light in Embodiment 1. Figure 4C is a diagram showing an example of the experimental results of controlling the shape of the spectrum of the second modulated light in Embodiment 1. Figure 5 is a schematic configuration diagram of a light source device according to Embodiment 2. Figure 6 is a diagram showing an example of the simulation results of the spectrum of the second modulated light in Embodiment 2. Figure 7 is a diagram illustrating another example of the SBS suppression method. Figure 8 is a schematic configuration diagram of a light source device according to Embodiment 3. Figure 9 is a diagram illustrating the phase matching in Embodiment 3.

[0022] Embodiments will be described below with reference to the drawings. However, this embodiment does not limit the present invention. Furthermore, in the drawings, the same or corresponding elements are denoted by the same reference numerals as appropriate, and redundant explanations are omitted as appropriate. It should also be noted that the drawings are schematic, and the dimensional relationships and ratios of each element may differ from reality. Even between drawings, there may be parts where the dimensional relationships and ratios differ.

[0023] (Embodiment 1) Figure 1 is a schematic diagram of a light source device according to Embodiment 1. This light source device 100 includes a seed light source 1, an optical isolator 2, a first modulator 3, a second modulator 4, an optical amplifier 5, an end cap 6, a signal generator 7, and an optical fiber transmission line 8. The light source device 100 is a light source used, for example, in coherent beam coupling (CBC).

[0024] The seed light source 1 outputs seed light having a single peak frequency. Seed light is light with a relatively narrow linewidth and relatively high coherence. In this embodiment, the linewidth of the seed light is 15 kHz or less. However, the linewidth of the seed light is not limited to 15 kHz or less; for example, it may be 100 kHz or less, or 1 MHz or less. Also, the wavelength and power of the seed light are not particularly limited, but in this embodiment they are 1064 nm and 10 mW, respectively. The seed light source 1 that outputs such seed light can be constructed using, for example, a semiconductor laser or a ytterbium fiber laser.

[0025] Optical isolator 2 is connected downstream of seed light source 1 via optical fiber. Optical isolator 2 allows seed light from seed light source 1 to pass through, while blocking light transmitted from the opposite side of seed light source 1.

[0026] The first modulator 3 is connected downstream of the optical isolator 2 via an optical fiber. The first modulator 3 generates and outputs the first modulated light by phase-modulating the seed light with the first modulated signal. The first modulator 3 can be configured, for example, using an electro-optic modulator.

[0027] The second modulator 4 is connected downstream of the first modulator 3 via an optical fiber. The second modulator 4 generates and outputs the second modulated light by phase-modulating the first modulated light with the second modulated signal. The second modulator 4 can also be configured using, for example, an electro-optic modulator.

[0028] The optical amplifier 5 is connected downstream of the second modulator 4 via an optical fiber. The optical amplifier 5 optically amplifies the second modulated light and outputs it. In this embodiment, the optical amplifier 5 can be configured using, for example, a ytterbium optical fiber amplifier. Alternatively, the optical amplifier 5 may have a multi-stage configuration, such as a four-stage configuration.

[0029] The end cap 6 is connected to the downstream stage of the optical amplifier 5 via an optical fiber. The end cap 6 outputs the second modulated light, which has been optically amplified by the optical amplifier 5, as output light L1. The end cap 6 also has known functions such as expanding the beam of the second modulated light to suppress power per unit area and suppressing end-face reflection of the second modulated light.

[0030] The signal generator 7 comprises a first modulated signal output unit 7a, a second modulated signal output unit 7b, and a control unit 7c.

[0031] The first modulation signal output unit 7a outputs the first modulation signal S1 to the first modulator 3. The first modulation signal S1 is a modulation signal having a first frequency, and in this embodiment, it is a PRBS signal. The first frequency is, for example, 10 GHz. The pattern length of the PRBS signal is 2 ｎ It is -1, and n is, for example, around 7 to 9.

[0032] The second modulation signal output unit 7b outputs the second modulation signal S2 to the second modulator 4. The second modulation signal S2 is a modulation signal having a second frequency, and in this embodiment, it is a sine wave signal. In this embodiment, the second frequency is 10 GHz, which is the same as the first frequency.

[0033] The control unit 7c is configured to change the relative phase between the first modulated signal S1 and the second modulated signal S2. Furthermore, the control unit 7c is configured to change at least one of the amplitudes of the first modulated signal S1 and the second modulated signal S2.

[0034] Such a signal generator 7 can be configured using a known pulse pattern generator (PPG). In this case, the first modulated signal S1 is output from the signal output of the PPG. The second modulated signal S2 can be generated and output using the clock frequency output of the PPG. The signal generator 7 is an example of a common signal generator that outputs a first modulated signal and a second modulated signal.

[0035] The optical fiber transmission line 8 is, for example, a silica glass optical fiber that transmits the second modulated light from the output side of the second modulator 4 to the end cap 6. The optical fiber transmission line 8 consists of optical fibers connecting the elements of the second modulator 4, the optical amplifier 5, and the end cap 6, and optical fibers that transmit the second modulated light within each element.

[0036] Figures 2A to 2C show an example of the spectrum of the modulated light in Embodiment 1. Figure 2A is the spectrum of the first modulated light output by the first modulator 3. Figure 2B is a magnified view of a part of the spectrum in Figure 2A. In Figure 2A, the horizontal axis is frequency with respect to the peak frequency of the seed light, and the vertical axis is power. As shown in Figure 2A, the spectrum of the first modulated light has a gentle peak shape spread to a width of about 10 GHz centered on 0 GHz. However, as shown in Figure 2B, this spectrum is composed of multiple frequency-discrete sharp peak components, and the gentle peak shape is the envelope of the multiple peak components. The frequency interval of the multiple peak components is f ＣＬＫ / (2 ｎ -1) Here, f ＣＬＫ This is the clock frequency of the PPG, and corresponds to the first frequency.

[0037] Furthermore, as shown in Figure 2A, the spectrum contains a principal peak component that has a power that stands out from the surrounding peak components among the multiple peak components. In this embodiment, the frequencies of the principal peak components are -20 GHz, -10 GHz, +10 GHz, and 20 GHz, and the positions of these peaks are the frequencies corresponding to the first frequency (i.e., f ＣＬＫis an integer multiple of (). However, in this embodiment, since the first modulation signal is a PRBS signal, there are no peak components or main peak components at 0 GHz corresponding to the carrier band frequency. Although the cause of the main peak component is not necessarily clear, it is considered, for example, that the high-frequency components of the PRBS signal are attenuated due to the characteristics of the signal generator 7 and the first modulator 3.

[0038] FIG. 2C is a spectrum of the second modulated light output from the second modulator 4. The spectrum of the second modulated light is obtained by overlapping the spectra of a plurality of first modulated lights with their center frequencies shifted from each other, and further has a shape affected by interference.

[0039] The influence of the interference described above changes according to the relative phase between the first modulation signal and the second modulation signal. Therefore, if the relative phase between the first modulation signal and the second modulation signal is changed, the shape of the spectrum of the second modulated light can also be changed. Similarly, the influence of the interference changes according to at least one of the amplitude of the first modulation signal and the amplitude of the second modulation signal. Therefore, if at least one of the amplitude of the first modulation signal and the amplitude of the second modulation signal is changed, the shape of the spectrum of the second modulated light can also be changed. In this case, for example, the amplitude and phase of the second modulation signal may be changed while the amplitude and phase of the first modulation signal are fixed.

[0040] In the light source device 100 configured as described above, by changing the relative phase between the first modulation signal S1 and the second modulation signal S2, and at least one of the amplitude of the first modulation signal S1 and the amplitude of the second modulation signal S2, an effect can be obtained in which highly flexible control of the shape of the optical spectrum with respect to the second modulated light can be realized.

[0041] Also, in the light source device 100, since the signal generator 7 is a common signal generator that outputs the first modulation signal and the second modulation signal, it is easy to synchronize the first modulation signal and the second modulation signal, and the device configuration is simplified.

[0042] Hereinafter, an example of the spectrum of the second modulated light will be described using computer simulation results and experimental results. In the following, the relative phase between the first modulation signal S1 and the second modulation signal S2 may be simply referred to as the relative phase. Also, the amplitude of the first modulation signal S1 may be referred to as the first amplitude, and the amplitude of the second modulation signal S2 may be referred to as the second amplitude.

[0043] FIGS. 3A to 3C are diagrams showing an example of the simulation results of controlling the shape of the spectrum of the second modulated light in Embodiment 1. FIG. 3A shows the result when the relative phase, the first amplitude, and the second amplitude are set to certain values. In the case of FIG. 3A, an optical spectrum close to a flat-top shape having gentle peaks around 0 GHz and ±10 GHz is obtained. Such a spectrum shape is suitable for suppressing SBS in the optical fiber transmission line 8. Also, in the case of FIG. 3A, it has five main peak components corresponding to the positions of -20 GHz, -10 GHz, 0 GHz, +10 GHz, and +20 GHz.

[0044] In FIG. 3A, there is a main peak component that does not exist in the first modulated light at the position of 0 GHz (the position of the peak frequency of the seed light). This main peak component is considered to be a peak generated by the interference between the +10 GHz main peak component and the -10 GHz main peak component when the spectra shown in FIG. 2A are overlapped three times. This main peak component is an example of a main peak component whose frequency is equal to the peak frequency of the seed light.

[0045] Also, when the second amplitude is increased by 1.6 times from the state of FIG. 3A, the shape of the spectrum of the second modulated light can be controlled as shown in FIG. 3B.

[0046] Also, when the relative phase is changed by 0.45π from the state of FIG. 3A, the shape of the spectrum of the second modulated light can be controlled as shown in FIG. 3B.

[0047] FIGS. 4A to 4C are diagrams showing an example of the experimental results of controlling the shape of the spectrum of the second modulated light in Embodiment 1. The experimental results shown in FIGS. 4A, 4B, and 4C were obtained under experimental conditions corresponding to the simulation conditions of FIGS. 3A, 3B, and 3C, respectively, and it can be seen that the experimental results are substantially consistent with the simulation results.

[0048] (Embodiment 2) Figure 5 is a schematic diagram of the light source device according to Embodiment 2. This light source device 100A has a configuration in which a low-pass filter 9 is added to the light source device 100 shown in Figure 1. In the light source device 100A, the first modulated signal S1 is the PRBS signal after passing through the low-pass filter 9. Even with this configuration, the effect of being able to control the shape of the optical spectrum with a high degree of freedom with respect to the second modulated light can be obtained.

[0049] For example, Figure 6 shows an example of the simulation results of the spectrum of the second modulated light in the light source device 100A according to Embodiment 2. A low-pass filter with a cutoff wavelength of 2.5 GHz was used. Both the first and second frequencies were set to 5 GHz. As shown in Figure 6, the light source device 100A can achieve a spectral shape with a flatter top and suppressed side lobes.

[0050] Furthermore, the spectrum shown in Figure 6 is also effective in suppressing SBS. Specifically, SBS is a phenomenon in which light (amplified light) with a frequency shifted to a lower frequency side by the Brillouin shift frequency from the seed light frequency in an optical fiber is amplified by stimulated Brillouin scattering. The Brillouin shift frequency is approximately 16 GHz in a quartz glass optical fiber when the wavelength of the seed light is 1064 nm. In the spectrum shown in Figure 6, the power of the second modulated light at a position shifted to a lower frequency side by 16 GHz from the seed light frequency f0 is sufficiently low. As a result, even if a portion of the second modulated light is reflected at a reflection point in the optical fiber transmission line 8 or at the end face of the end cap 6 and propagates in the optical fiber transmission line 8 in the opposite direction to the second modulated light, SBS can be effectively suppressed.

[0051] (Another example of an SBS suppression method) Here, another example of a method for suppressing SBS in the light source devices 100 and 100A according to Embodiments 1 and 2 will be described. Figure 7 is a diagram illustrating another example of an SBS suppression method.

[0052] In Figure 7, the signal light is the second modulated light transmitted through the optical fiber transmission line 8, and its direction of propagation is from the second modulator 4 toward the end cap 6. The single arrows indicate multiple frequency-discrete peak components, and the dashed line indicates the envelope.

[0053] On the other hand, the reflected component is the component in which a portion of the second modulated light is reflected at reflection points or end caps 6 in the optical fiber transmission path 8 and propagates in the opposite direction to the signal light.

[0054] For example, at a frequency shifted to a lower frequency side by a Brillouin shift frequency (16 GHz in this case) from the peak frequency of a certain peak component P1 in the signal light, a Brillouin gain band originating from the signal light is generated. Therefore, if the frequency of the peak component in the reflected component overlaps with the peak frequency of this Brillouin gain band, that peak component is Brillouin amplified, resulting in SBS, which is undesirable.

[0055] Therefore, in the method shown in Figure 7, the position of the peak component is adjusted so that the peak frequency of the peak component in the second modulated light is shifted from the peak frequency of the Brillouin gain band. This makes it possible to suppress SBS. Such adjustment can be achieved, for example, by adjusting the first frequency of the first modulated signal. In light source devices 100 and 100A, since the second modulated light contains multiple frequency-discrete peak components, this SBS suppression method can be realized. In particular, for all peak components, Δf = f is set so that there are no peak components at a frequency 16 GHz lower than their peak frequency. ＣＬＫ / (2 ｎ -1) is preferable.

[0056] Furthermore, if we denote the frequency difference between a peak component shifted to a lower frequency by a Brillouin shift frequency (16 GHz in this case) from its peak frequency and the peak component closest to this position as δ, and the full width at half maximum of the Brillouin gain band as Γ, then it is preferable to adjust the position of the peak component such that |δ / (Γ / 2)| ≥ 0.5, and it is even more preferable to adjust the position of the peak component such that |δ / (Γ / 2)| >> 0.5.

[0057] (Embodiment 3) Figure 8 is a schematic diagram of the light source device according to Embodiment 3. This light source device 100B is configured as a CBC system. The light source device 100B has a configuration in which the optical amplifier 5 and end cap 6 are removed from the light source device 100 according to Embodiment 1 shown in Figure 1, and a plurality of branchers 11, 12, 13, 14, a plurality of phase adjusters 16, a plurality of optical amplifiers 17, a plurality of branchers 18, a coherent combiner 19, and a phase control unit 20 are added.

[0058] The brancher 11 is positioned between the optical isolator 2 and the first modulator 3, and branches the reference light L2 from the seed light output from the seed light source 1. The brancher 11 is, for example, a % optical coupler with a 1-10% bias. The brancher 11 is an example of a first brancher.

[0059] Multiple branchers 12 to 14 are sequentially connected to the second modulator 4 via optical fibers. One brancher 12 splits the second modulated light input from the second modulator 4 into two outputs. Two branchers 13 (only one is shown in the figure) each split each of the second modulated light input from brancher 12 into two outputs. Four branchers 14 (only two are shown in the figure) each split each of the second modulated light input from brancher 13 into four outputs in terms of power. Branchers 12 to 14 are examples of second branchers.

[0060] The sixteen phase adjusters 16 (eight of which are shown in the figure) are each connected to the downstream of each brancher 14 via optical fiber and have the function of adjusting the phase of each branched second modulated optical fiber. The phase adjusters 16 can be constructed, for example, using acousto-optic modulators.

[0061] The sixteen optical amplifiers 17 (eight of which are shown in the figure) are each connected to the downstream of each phase adjuster 16 via optical fiber. Each optical amplifier 17 optically amplifies and outputs each second modulated light whose phase has been adjusted. The optical amplifiers 17 in this embodiment can be constructed using, for example, ytterbium optical fiber amplifiers, similar to the optical amplifier 5, or they can be configured in a multi-stage configuration, such as a four-stage configuration.

[0062] The sixteen branchers 18 (eight of which are shown in the diagram) are optically connected to the downstream stage of each optical amplifier 17. Each brancher 18 branches a portion of the optically amplified second modulated light and outputs it to the phase control unit 20, while outputting the remainder of each second modulated light to the coherent combiner 19. The branchers 18 are, for example, beam splitters of about 1 to 10%.

[0063] The coherent combiner 19 combines the remaining portion of the input second modulated light and outputs it as an optical beam L3. The coherent combiner 19 may be, for example, a lens system that combines light in space. As a modification of the light source device 100B, the coherent combiner 19 may be removed, and a configuration may be adopted in which multiple second modulated light beams output into space are combined at a distance by Fraunhofer diffraction.

[0064] The phase control unit 20 detects the phase difference between the reference light L2 input from the brancher 11 and each second modulated light input from the brancher 18, for example using the heterodyne method, and controls each phase adjuster 16 to bring each phase difference closer to zero. In other words, the phase adjuster 16, brancher 18, and phase control unit 20 constitute a phase matching unit 21 that matches the phase of each of the multiple second modulated lights with the phase of the reference light.

[0065] The light source device 100B according to this embodiment provides the advantage of being able to obtain a second modulated light as high-power coherent light, as well as to achieve highly flexible control over the shape of the optical spectrum.

[0066] Furthermore, in the light source device 100B, the first modulated signal S1 and the second modulated signal S2 are periodic. Therefore, even if there is a difference in optical path length ΔL in each fiber transmission line, the phases of each second modulated light can be matched as long as the difference in optical path length ΔL satisfies the relationship ΔL = ncT = nc / Δf. Here, n is an integer, c is the speed of light in the optical fiber transmission line, T is the period of the modulated signal, and Δf is the frequency interval of the peaks that constitute the modulated light spectrum. Therefore, the light source device 100B also has the effect of making phase matching easier.

[0067] In addition, in the light source device 100B, the control unit 7c may adjust the second modulated light to a state in which a main peak component whose frequency is equal to the peak frequency of the seed light exists, as shown in Figure 3A, and in that state, the phase matching unit 21 may match the phase of the main peak component of each second modulated light with the phase of the reference light.

[0068] The following provides a detailed explanation. Figure 9 illustrates the phase matching in Embodiment 3. The frequency of the reference light L2 is equal to the frequency f0, which is the peak frequency of the seed light. On the other hand, the main peak component P2 is a main peak component equal to the peak frequency of the seed light, but after being output from the phase adjuster 16 for heterodyne detection, the frequency becomes f ＿ Only the shift is being shifted.

[0069] When the second modulated light is adjusted to a state where such a main peak component P2 exists, the main peak component P2 becomes a relatively high peak power, so when performing phase matching with the reference light L2, phase matching control can be performed with relatively high SNR and with good accuracy.

[0070] In the above embodiment, the first modulated signal is a PBRS signal, but it may be any other pseudo-random signal, or even a modulated signal of another periodic waveform, such as a sine wave signal, a square wave signal, or a triangular wave signal. Similarly, the second modulated signal may also be a modulated signal of another periodic waveform, such as a square wave signal or a triangular wave signal. For example, the first modulated signal may be a sine wave and the second modulated signal may be a PBRS signal. That is, if the first modulated signal and the second modulated signal are periodic waveform signals, the shape of the optical spectrum of the output second modulated light can be controlled by changing their relative phase, as well as at least one of the amplitudes of the first modulated signal and the second modulated signal. In the above embodiment, the first frequency of the first modulated signal and the second frequency of the second modulated signal are equal, but they may be different. In the above embodiment, a common signal generator outputs the first modulated signal and the second modulated signal, but they may be configured to output each modulated signal using separate signal generators.

[0071] Furthermore, the present invention is not limited by the embodiments described above. Configurations that appropriately combine the above-described components are also included in the present invention. Moreover, further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the embodiments described above, and various modifications are possible.

[0072] This invention can be used as a light source.

[0073] 1: Seed light source 2: Optical isolator 3: First modulator 4: Second modulator 5, 17: Optical amplifier 6: End cap 7: Signal generator 7a: First modulated signal output section 7b: Second modulated signal output section 7c: Control section 8: Optical fiber transmission line 9: Low-pass filter 11, 12, 13, 14, 18: Splitter 16: Phase adjuster 19: Coherent combiner 20: Phase control section 21: Phase matching section 100, 100A, 100B: Light source device L1: Output light L2: Reference light L3: Optical beam P1: Peak component P2: Main peak component S1: First modulated signal S2: Second modulated signal

Claims

1. A light source device comprising: a light source that outputs seed light having a predetermined peak frequency; a first modulator that generates first modulated light by phase modulating the seed light with a first modulated signal having a first frequency; a second modulator that generates second modulated light by phase modulating the first modulated light with a second modulated signal having a second frequency; and a control unit that can change the relative phase between the first modulated signal and the second modulated signal, and at least one of the amplitude of the first modulated signal and the amplitude of the second modulated signal.

2. The light source device according to claim 1, wherein the first modulated signal is a pseudo-random signal.

3. The light source device according to claim 1, comprising a low-pass filter, wherein the first modulated signal is a pseudo-random signal after passing through the low-pass filter.

4. The light source device according to claim 1, wherein the second modulated signal is a sinusoidal signal.

5. The light source device according to claim 1, wherein the first frequency and the second frequency are equal.

6. The light source device according to claim 1, further comprising a common signal generator that outputs the first modulated signal and the second modulated signal.

7. The light source device according to claim 1, wherein the first modulated light and the second modulated light include a plurality of frequency-discrete peak components.

8. The light source device according to claim 7, comprising an optical fiber for transmitting the second modulated light, wherein the peak frequencies of the plurality of peak components are shifted from the peak frequency of the Brillouin gain band generated in the optical fiber due to the second modulated light.

9. The light source device according to claim 7, wherein the frequency of the principal peak component having a power that stands out from the surrounding peak components among the plurality of peak components in the second modulated light is equal to the peak frequency of the seed light.

10. The light source device according to claim 1, comprising: a first branching device for branching a reference light from the seed light; a second branching device for branching the second modulated light into a plurality of second modulated lights; and a phase matching unit for matching the phase of each of the plurality of second modulated lights with the phase of the reference light.

11. The light source device according to claim 10, wherein each of the plurality of second modulated lights includes a plurality of frequency-discrete peak components, and the principal peak component among the plurality of peak components having a power that stands out relative to the surrounding peak components is equal to the peak frequency of the seed light, and the phase matching unit matches the phase of each of the principal peak components of the plurality of second modulated lights with the phase of the reference light in the state described above.

12. A method for controlling the shape of an optical spectrum, comprising: generating a first modulated light by phase modulating a seed light having a predetermined peak frequency with a first modulated signal having a first frequency; generating a second modulated light by phase modulating the first modulated light with a second modulated signal having a second frequency; and changing the relative phase between the first modulated signal and the second modulated signal, as well as changing at least one of the amplitude of the first modulated signal and the amplitude of the second modulated signal to change the shape of the optical spectrum of the second modulated light.

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