Phase-locked laser device

Abstract

This phase-locked laser device is provided with: an optical circulator (2) that receives laser light, supplies the laser light to a feed optical path, and outputs return light received from a return optical path; an optical splitter (3) that branches the laser light received from the optical circulator via the feed optical path into reference light and signal light; element circuits (4), each element circuit including a phase compensator that outputs signal light obtained by performing phase control of the branched signal light; a partial optical reflector (5) that receives the reference light or phase-controlled signal light as incident light, reflects a part of the incident light as reflected light, and transmits the remainder of the incident light; and a photoelectric converter (6) that receives the return light and photoelectrically converts the return light, the return light received by the photoelectric converter (6) being laser light in which the reflected light is multiplexed by the optical splitter, wherein each element circuit performs frequency conversion on the output of the photoelectric converter (6) to detect a phase error of an electric signal having a frequency component corresponding to each element circuit, and each phase compensator compensates for the detected phase error.

Description

Phase-locked laser device

[0001] The present disclosure relates to phase-locked laser devices.

[0002] A technique called coherent beam combining (CBC) is known as a method for realizing a high-power laser system. Coherent beam combining is a technique that uses a single laser beam as seed light for optical amplification, branches the laser beam into multiple laser beams (signal light), optically amplifies each of the branched laser beams, and combines the optically amplified laser beams (see, for example, Figure 1 of Patent Document 1). A high-power laser device using CBC outputs a single beam with high power and high brightness by aligning the phases of each optical path and combining multiple beams.

[0003] Japanese Patent Application Laid-Open No. 2000-323774

[0004] The high-power laser system described in Patent Document 1 has a problem in that as the number of signal lights increases, larger optical components are required to multiplex the local light and the multiple signal lights.

[0005] The present disclosure has been made to solve such problems, and aims to provide a phase-locked laser device that can be made smaller even when the number of signals increases.

[0006] A phase-locked laser device according to an embodiment of the present disclosure includes an optical circulator that receives laser light emitted from a reference light source through a first port and supplies it to a sending optical path, and outputs return light received from a return optical path through a second port; an optical splitter that splits the laser light received from the optical circulator through the sending optical path into reference light and a plurality of signal lights; and a plurality of element circuits, each of which includes a phase compensator that performs phase control on the plurality of signal lights split by the optical splitter and outputs a plurality of phase-controlled signal lights. The optical fiber includes a plurality of optical partial reflecting mirrors that receive phase-controlled signal light as incident light, reflect a portion of the incident light as reflected light, and transmit the remainder of the incident light, and an opto-electrical converter that receives the returned light, performs opto-electrical conversion, and outputs an electrical signal after opto-electrical conversion, wherein the returned light is laser light obtained by multiplexing the plurality of reflected light beams by the optical splitter, and each element circuit performs frequency conversion on the electrical signal output by the opto-electrical converter to detect a phase error of the electrical signal having a frequency component corresponding to each element circuit, and each phase compensator compensates for the detected phase error.

[0007] According to the phase-locked laser device according to the embodiment of the present disclosure, even if the number of signals increases, it can be made smaller than conventional devices.

[0008] FIG. 11 is a diagram showing an example of the configuration of a phase-locked laser device according to a first embodiment. FIG. 12 is a diagram showing an example of the configuration of an element circuit of a phase-locked laser device according to the first embodiment. FIG. 3A is a conceptual diagram of the spectrum of a received signal received by a photodiode. FIG. 3B is a conceptual diagram of the spectrum of a received signal after frequency division by a 1 / 2 frequency divider. FIG. 3C is a conceptual diagram of the spectrum of a received signal after band limitation by a band-limiting filter. FIG. 12 is a diagram showing an example of the configuration of an element circuit of a phase-locked laser device according to a second embodiment. FIG. 13 is a diagram showing an example of the configuration of an element circuit of a phase-locked laser device according to a third embodiment. FIG. 14 is a diagram showing an example of the configuration of an element circuit of a phase-locked laser device according to the third embodiment. FIG. 15 is a diagram showing an example of an output beam pattern when the number of subarrays is three. FIG. 16 is a diagram showing an example of the configuration of an element circuit for local light of a phase-locked laser device according to the fourth embodiment. FIG. 17 is a diagram showing an example of the configuration of an element circuit for signal light of a phase-locked laser device according to the fourth embodiment. FIG. 18 is a diagram showing an example of the configuration of an element circuit for signal light of a phase-locked laser device according to the fourth embodiment. FIG. 19 is a diagram showing an example of the spectrum of a received signal of a local light beam portion. FIG. 19 is a diagram showing an example of the spectrum of a received signal after frequency division by a 1 / 2 frequency divider. FIG. 19 is a diagram showing an example of the spectrum of an optical signal of subarray #1. 11D is a conceptual diagram of the spectrum of the received signal of subarray #1. FIG. 11E is a conceptual diagram of the spectrum of the received signal of subarray #1 after band limitation by the band limiting filter. FIG. 11D is a conceptual diagram of the spectrum of the received signal of subarray #1 after band limitation by the band limiting filter. FIG. 11E is a diagram showing an example of the configuration of a phase-locked laser device according to a fifth embodiment.

[0009] Various embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Components with the same or similar reference numerals in the drawings have the same or similar configurations or functions, and redundant descriptions of such components will be omitted. Furthermore, in this disclosure, the term "or" means an inclusive logical OR unless otherwise specified.

[0010] First Embodiment <Configuration> A phase-locked laser device CL1 according to a first embodiment of the present disclosure will be described with reference to Fig. 1. As shown in Fig. 1, the phase-locked laser device CL1 includes, as an example, a reference light source 1, an optical circulator 2, an optical splitter 3, element circuits 4 (4-1 to 4-N), collimators 5 (5-1 to 5-N; optical partial reflectors), a photodiode 6, and a distributor 7.

[0011] More specifically, the phase-locked laser device CL1 includes an optical circulator 2 that receives laser light emitted from a reference light source 1 at a first port and supplies it to a sending optical path, and outputs return light received from a return optical path from a second port; an optical splitter 3 that splits the laser light received from the optical circulator via the sending optical path into reference light and a plurality of signal lights; and a plurality of element circuits 4, each of which includes a phase compensator that performs phase control on the plurality of signal lights split by the optical splitter and outputs a plurality of phase-controlled signal lights; The phase-locked laser device CL1 includes a plurality of collimators 5 that receive phase-controlled signal light as incident light, reflect a portion of the incident light as reflected light, and transmit the remainder of the incident light, and a photodiode 6 that receives the returned light, performs photoelectric conversion, and outputs a photoelectrically converted electrical signal, the returned light being a laser beam obtained by combining the plurality of reflected light beams via the optical splitter, and each element circuit performs frequency conversion on the electrical signal output by the photoelectric converter to detect a phase error of the electrical signal having a frequency component corresponding to that element circuit, and each phase compensator compensates for the detected phase error. The components of the phase-locked laser device CL1 will be described in more detail below.

[0012] (Reference Light Source) The reference light source 1 is, for example, a narrow linewidth laser light source that oscillates in a single mode. The reference light source 1 is connected to the optical circulator 2 via an optical fiber. The reference light source 1 supplies the oscillated laser light to the optical circulator 2 via the optical fiber.

[0013] (Optical Circulator) The optical circulator 2 has three ports and separates the optical paths of outgoing light and returning light. For example, the optical circulator 2 receives laser light from the reference light source 1 via port A (first port) as outgoing light, outputs the received outgoing light from port B, and outputs the returning light received from port B from port C (second port).

[0014] The optical circulator 2 is connected to the optical splitter 3 via an optical fiber. The optical circulator 2 receives the light from the reference light source 1 and supplies it to the optical splitter 3 via the optical fiber.

[0015] The optical circulator 2 is also connected to the photodiode 6 via an optical fiber. The optical circulator 2 supplies the return light received from the optical splitter 3 to the photodiode 6 via the optical fiber.

[0016] (Optical Splitter; Optical Coupler) The optical splitter 3 splits the outgoing light supplied from the optical circulator 2 into N signal light beams and one reference light beam. N is any positive integer. The optical splitter 3 is connected to N element circuits 4 (4-1 to 4-N) via optical fibers. The optical paths between the optical splitter 3 and the N element circuits 4 are indicated by optical path 1, ..., optical path N in Figure 1. The optical splitter 3 supplies each signal light beam to one element circuit 4 via one optical path. For example, the optical splitter 3 supplies one signal light beam to element circuit 4-1 via optical path 1, and another signal light beam to element circuit 4-N via optical path N.

[0017] The optical splitter 3 is also connected to a collimator 5-N+1 (collimator R) via an optical fiber. The optical path between the optical splitter 3 and the collimator 5-N+1 (collimator R) is indicated by an optical path R in Fig. 1. The optical splitter 3 supplies reference light (local light) to the collimator 5-N+1 (collimator R) via the optical path R.

[0018] In addition, an optical splitter may be referred to as an optical coupler in this disclosure. An optical splitter and an optical coupler are the same thing. Depending on the functional difference between being used as a splitter for splitting a single light into multiple lights and being used as a coupler for coupling multiple lights into a single light, the terms optical splitter and optical coupler may be distinguished.

[0019] (Element Circuit) The element circuit 4 is a circuit that controls the optical phase of the signal light. The element circuits 4-1 to 4-N have the same configuration and perform phase modulation (phase control) on the signal light input from the optical paths 1 to N to generate N phase-modulated optical signals (phase-controlled optical signals). The element circuits 4-1 to 4-N supply the generated phase-modulated optical signals to the collimators 5-1 to 5-N (collimator 1 to collimator 5-N). A more detailed configuration of the element circuit 4 will be described later.

[0020] (Collimator) The collimator 5 outputs the received signal light into space. When the signal light is output into space, return light occurs due to Fresnel reflection. In this disclosure, the collimator is an example of a partially reflecting mirror.

[0021] (Photodiode) The photodiode 6 photoelectrically converts the received return light and supplies the photoelectrically converted electrical signal to the distributor 7. Note that the photodiode is an example of a photoelectric converter in the present disclosure.

[0022] (Distributor) The distributor 7 distributes the received signal, which is an electrical signal received from the photodiode, to each of the element circuits 4 (4-1 to 4-N).

[0023] (Element Circuit; Details) Next, a detailed configuration of the element circuit 4 will be described with reference to Fig. 2. As shown in Fig. 2, the element circuit 4 includes a modulation signal source 10, an optical phase modulator 8, an optical frequency shifter 9, a 1 / 2 frequency divider 11, a mixer 12, a band-limiting filter 17, a reference signal source 13, a phase comparator 14, a loop filter 15, and a VCO 16.

[0024] (Modulation Signal Source) The modulation signal source 10 is a signal source that outputs a modulation signal (dithering signal) with a different frequency for each element in order to identify each signal light.

[0025] (Optical Phase Modulator) The optical phase modulator 8 is driven by a modulation signal output from a modulation signal source 10 and modulates the phase of the signal light. Different modulation signals are supplied to the N element circuits 4 (4-1 to 4-N), and the different modulation signals are superimposed on the phases of the N signal lights.

[0026] (Optical Frequency Shifter; Phase Compensator) The optical frequency shifter 9 compensates for the phase of the optical signal output from the optical phase modulator 8. The optical frequency shifter 9 compensates for the phase of the optical signal output from the optical phase modulator 8 by shifting the frequency by the frequency of the frequency-modulated signal output from the VCO 16. Since the phase is represented by the time integral of the frequency, in other words, the frequency is represented by the time differential of the phase, phase control (phase compensation) can be performed by frequency control. The optical frequency shifter 9 outputs the optical signal after phase compensation. Note that the optical frequency shifter 9 is an example of a phase compensator in this disclosure.

[0027] (1 / 2 Frequency Divider) The 1 / 2 frequency divider 11 divides the frequency of the received signal received by the photodiode 6 and distributed by the distributor 7 by 1 / 2, and outputs the divided signal. By dividing the frequency, the phase of the return path of the returned light is removed.

[0028] (Mixer) The mixer 12 mixes the signal output by the 1 / 2 frequency divider 11 with a modulated signal (dithering signal), and outputs the mixed signal.

[0029] (Band Limiting Filter) The band limiting filter 17 extracts a signal in a desired band from the signals output from the mixer 12 .

[0030] (Reference Signal Source) The reference signal source 13 generates a reference signal that serves as a phase reference, and outputs the generated reference signal.

[0031] (Phase Comparator) The phase comparator 14 compares the phase of the reference signal received from the reference signal source 13 with the phase of the received signal received via the band-limiting filter 17, and outputs a phase error signal that is the result of the comparison.

[0032] (Loop Filter) Loop filter 15 calculates a control signal from the phase error signal received from phase comparator 14, and outputs the calculated control signal.

[0033] (VCO; Voltage-Controlled Oscillator) The VCO 16 oscillates a frequency-modulated signal at a frequency that follows the control signal output from the loop filter 15, and outputs the oscillated frequency-modulated signal.

[0034] <Operation> Next, the overall operation of the phase-locked laser device CL1 will be described. Laser light output from reference light source 1 is propagated to the sending optical path by optical circulator 2. The laser light from reference light source 1 propagates along the sending optical path and is split by optical splitter 3 into laser light as reference light (local light) for optical path R and laser light as signal light for optical paths (signal optical paths) 1 to N. After splitting, the signal light is output into space from collimators 5-1 to 5-N via element circuits 4 (4-1 to 4-N), and the local light is output into space from collimator 5-N+1.

[0035] When the signal is output to space, return light (reflected light) is generated due to Fresnel reflection. The return light of the signal light is input to the optical splitter 3 via the element circuit 4, while the return light (reflected light) of the local light is input directly, i.e., without passing through the element circuit 4. The optical splitter 3 multiplexes (couples) the return light of the multiple signal lights with the return light of the local light to generate multiplexed light. The multiplexed light output from the optical splitter 3 is propagated to the return light path by the optical circulator 2. The multiplexed light is then received by the photodiode 6 and photoelectrically converted by the photodiode 6. The received signal output as an electrical signal from the photodiode 6 is split by the splitter 7 according to the number of signal lights and input to each element circuit 4.

[0036] The laser light input to the element circuit 4 is phase-modulated by an optical phase modulator 8 driven by a weak modulation signal from a modulation signal source 10. The laser light output from the optical phase modulator 8 is frequency-shifted by an optical frequency shifter 9 to which a phase control signal is fed back, and the frequency-shifted laser light is output.

[0037] 3A shows a spectrum image of the signal received by the photodiode 6. Since the laser light passes through the element circuit 4 twice, as a transmitted light and a returned light, the frequency shift amount of the optical frequency shifter 9 is f ＡＯＭ , the modulation frequency of the modulation signal source 10 in the i-th element circuit 4-i is f ｉ Then, the carrier signal is 2f ＡＯＭ The frequency of the side carrier generated by phase modulation is 2(f ＡＯＭ ±f ｉ ) by dividing the frequency by 1 / 2 frequency divider 11, each frequency is halved as shown in FIG. 3B. Then, by performing frequency conversion using the output signal from modulation signal source 10, the frequency of the signal output from mixer 12 (mixer output signal) becomes f ＡＯＭ The mixer output signal is ＡＯＭ After the unnecessary signal is suppressed by the central band-limiting filter 17, the signal output from the band-limiting filter 17 and the frequency (f ＡＯＭ 3C is a conceptual diagram of the spectrum of the received signal after band-limiting by the band-limiting filter 17 when i=1.

[0038] (Establishment of phase synchronization) The amount of phase change of the local light in one direction on the optical path R is φ Ｒ , the amount of phase change in one direction of the signal light in the optical path i (i is an integer from 1 to N) is φ ｉ The phase control amount in the optical frequency shifter 9 in the element circuit 4 is φ ＡＯＭ The beat signal of the signal received by the photodiode 6 on the optical path i and the optical path R is approximately expressed by the following equation:

[0039] Looking at the phase term of the Cos function, the signal phase after 1 / 2 division is φ Ｒ -φ ｉ -φ ＡＯＭ This becomes:

[0040] The phase of the reference signal source 13 is φ ｒ Then, when phase synchronization is established, the relationship of the following equation (2) holds.

[0041] By modifying equation (2), the following equation (3) is obtained.

[0042] The phase of the signal light i outputted in space is expressed by the following equation (4).

[0043] Therefore, according to the phase-locked laser device CL1 of the first embodiment, the signal light i outputted in space is subjected to a phase fluctuation (φ ｉ ) is not dependent on

[0044] As described above, in a configuration in which the signal light makes a double pass through the signal light path, by using the Fresnel-reflected light from the signal light collimator to divide the received signal and then establish phase synchronization, it is possible to coherently combine multiple light beams without being affected by phase fluctuations in the signal light path. Because this configuration can be constructed using only a fiber system, alignment or optical systems for phase error detection are not required, and the system can be made smaller even when the number of signals is increased. In addition, the configuration of the component circuits after the mixer is the same for all elements, making adjustments easy.

[0045] In the above explanation, an example has been given in which the optical frequency shifter 9 is used for phase synchronization, but instead of the optical frequency shifter 9, a configuration using a fiber stretcher or bias control of an optical phase modulator may also be used.

[0046] Embodiment 2. A phase-locked laser device CL2 according to embodiment 2 will now be described with reference to Fig. 4. The overall configuration of the phase-locked laser device CL2 according to embodiment 2 is the same as that of the phase-locked laser device CL1 according to embodiment 1, and therefore the description will not be repeated. Fig. 4 is a diagram showing the configuration of the component circuits of the phase-locked laser device CL2 according to embodiment 2, and in Fig. 4, components that are the same as or similar to those in embodiment 1 are given the same reference numerals and will not be described again.

[0047] The second embodiment differs from the first embodiment in that a semiconductor optical amplifier 18 that does not have an isolator at the input / output end is added to the output of the optical frequency shifter 9. By adding the semiconductor optical amplifier 18, not only the output optical power but also the level of the returned light is increased, thereby improving the received signal-to-noise ratio (SNR) and enabling highly accurate optical phase synchronization.

[0048] The gain of the semiconductor optical amplifier 18 is G ＳＯＡ In this case, the output light level is G ＳＯＡ Similarly, the return light due to Fresnel reflection is also amplified by G ＳＯＡ The Fresnel reflection loss is increased by I Ｆ Then, the feedback light level in the first embodiment is P ＡＯＭ In this case, P ＡＯＭ -I Ｆ When the configuration of FIG. 4 is used, the reception level is P ＡＯＭ +G ＳＯＡ -I Ｆ +G ＳＯＡ And 2G ＳＯＡ The reception level will be increased accordingly.

[0049] As described above, by using this embodiment, it is possible to establish optical phase synchronization with high precision by increasing not only the output light level but also the return light level. In a phase error detection system using Fresnel reflection, the reception level is weak, so there is a problem that the precision of phase synchronization is degraded compared to conventional configurations. By using this embodiment, the reception SNR is improved, enabling highly precise phase synchronization.

[0050] Third Embodiment A phase-locked laser device CL3 according to a third embodiment will now be described with reference to FIGS. 5 to 7. FIG. 5 is a diagram showing an example of the overall configuration of the phase-locked laser device CL3. FIG. 6 is a diagram showing an example of the configuration of the component circuits of the phase-locked laser device CL3. FIG. 7 is a diagram showing an example of an output beam pattern when the number of subarrays is three (N=3). In FIGS. 5 and 6, components that are the same as or similar to those in the first embodiment are given the same reference numerals, and descriptions thereof will not be repeated.

[0051] The phase-locked laser device CL3 according to the third embodiment has a configuration suitable for use in a case where a high-power optical amplifier 30 that does not allow reverse input, such as a fiber amplifier or a waveguide-type optical amplifier, is used in the signal optical path. More specifically, the phase-locked laser device CL3 has a local light control unit 28 that sub-arrays the configuration of the first or second embodiment to supply multiple local light beams, and the inclusion of such a local light control unit 28 makes it possible to sub-array the signal light.

[0052] A high-power optical amplifier 30, such as a fiber amplifier, capable of generating high optical power cannot perform reverse input from the output side as described in the second embodiment. Therefore, in a phase-locked laser device CL3 equipped with a high-power optical amplifier 30, it is possible to increase the number of elements by subarraying the signal light as shown in FIG. 7 . However, when subarraying, if a configuration in which the phase of the signal light is synchronized with a single local light is used, increasing the number of elements makes it difficult to increase the signal light because the beam diameter increases. Therefore, it is possible to prepare multiple phase-synchronized local light. Therefore, in this embodiment, the local light control unit 28, which does not include a high-power optical amplifier, performs phase synchronization using Fresnel reflection as described in the first embodiment to prepare multiple phase-synchronized local light. This makes it possible to supply multiple phase-synchronized local light, so the phase-locked laser device CL3 equipped with a high-power optical amplifier 30 can accommodate an increase in the number of elements (an increase in the number of signal light). In other words, the configuration of the phase-locked laser device CL3 enables the number of subarrays to be increased in a scalable manner.

[0053] 5, the phase-locked laser device CL3 according to the third embodiment includes a reference light source 1, an optical splitter 19 that splits the laser light output from the reference light source 1 into a laser light to be directed to a local light path 20 and a laser light to be directed to a signal light path 21, a local light control unit 28 that receives the laser light from the local light path 20 and generates a plurality of local lights for which phase synchronization has been established, an optical splitter 22 that splits the laser light from the signal light path 21 into a plurality of signal lights, and a signal light control unit 29 that receives the plurality of signal lights split by the optical splitter 22 and controls the signal lights. The signal light control unit 29 includes a plurality of signal light subarrays formed by subarraying a plurality of signal lights obtained from the laser light emitted from the reference light source 1. The local light control unit 28 supplies a plurality of phase-locked local lights to the plurality of signal light subarrays.

[0054] The local light control unit 28 has the configuration described in accordance with embodiment 1. In the example shown in Fig. 5, the local light control unit 28 generates N local light beams in which phase synchronization has been established, where N represents the number of subarrays.

[0055] More specifically, the local light control unit 28 includes an optical circulator 2 that receives the laser light from a first port and supplies it to a sending optical path, and outputs return light received from a return optical path from a second port; an optical splitter 3 that splits the laser light received from the optical circulator 2 via the sending optical path into reference light and a plurality of local lights; a plurality of element circuits 4, each of which includes an optical frequency shifter 9 (phase compensator) that performs phase control on the plurality of local lights split by the optical splitter and outputs a plurality of phase-controlled local lights; and a light source 100 that receives the reference light or the plurality of phase-controlled local lights as incident light. The optical frequency converter 20 includes a plurality of collimators 5 that reflect a portion of the incident light as reflected light and transmit the remainder of the incident light, and a photodiode 6 (first photoelectric converter) that receives the returned light, performs photoelectric conversion, and outputs an electrical signal after photoelectric conversion, the returned light being a laser beam obtained by multiplexing the plurality of reflected light beams by the optical splitter 3, each element circuit 4 (first element circuit) performs frequency conversion on the electrical signal output by the photodiode 6 and detects a phase error of the electrical signal having a frequency component corresponding to each element circuit 4, and each optical frequency shifter 9 (phase compensator) compensates for the detected phase error. Note that although the collimators 5-1 to 5-N are illustrated in FIG. 5 as components of the signal light control unit 29, as described above, the local light control unit 28 may also include the collimators 5-1 to 5-N.

[0056] 5, the signal light control unit 29 includes N signal light subarrays 23 (23-1 to 23-N). Each signal light subarray 23 has N signal light subarrays. Ｓ Minute element circuits 24 (24-N-1 to 24-N-N Ｓ ; second element circuit) and element circuits 24 (24-N-1 to 24-N-N Ｓ N for collimating the signal light output from the element circuit, corresponding to Ｓ Collimators 50 (50-N-1 to 50-N-N Ｓ ) and N Ｓ Collimators 50 (50-N-1 to 50-N-N Ｓa beam splitter 25-N (SN) that receives signal light output from the collimator 5 (5-N) and local light output from the collimator 5 (5-N), generates multiplexed light, outputs a portion of the generated multiplexed light as signal light for output, and outputs a portion of the generated multiplexed light as signal light for phase error detection, a photodiode 26-N (second photoelectric converter) that photoelectrically converts the signal light for phase error detection output from the beam splitter 25-N, and a distributor 27-N that distributes the electrical signal output from the photodiode 26-N to a plurality of element circuits 24.

[0057] Next, the overall operation of the phase-locked laser device CL3 will be described. The laser light output from the reference light source 1 is split by the optical splitter 19 into a laser light to be sent to the local light path 20 and a laser light to be sent to the signal light path 21.

[0058] In the local light path 20, the local light control unit 28 realizes phase synchronization with the output end of the collimator as a reference.

[0059] In the signal light path 21, the laser light from the optical splitter 19 is split into multiple (N x Ns) signal lights by the optical splitter 22. As mentioned above, Ns represents the number of signal lights in a subarray, and N represents the number of subarrays. For example, if Ns is 7 and N is 3, the total number of elements is 21. The number of local oscillator lights required is 3, as it corresponds to the number of subarrays. An example of the output pattern in this case is shown in FIG. 7.

[0060] The signal light split by the optical splitter 22 is grouped into Ns beams to form one signal light subarray 23. In each signal light subarray, the signal light split by the optical splitter 22 is amplified by element circuits 24 (24-N-1 to 24-N-Ns), and then passed through collimators 50 (50-N-1 to 50-N-Ns). Ｓ ) and output into space. The signal light (transmitted light) output into space is split by a beam splitter 25-N (SN) into a signal light for phase error detection and a signal light for output. The signal light for phase error detection is multiplexed (photomixed) with the local light input from the reverse port of the beam splitter 25-N (SN), and the mixed light generated by the multiplexing (mixing) is received by a photodiode 26-N. The received signal is distributed to each element circuit by a distributor 27-N.

[0061] In the element circuits 24 (24-1-1 to 24-N-Ns), the signal light phase-controlled by the phase-control optical frequency shifter 9 is amplified by the high-power optical amplifier 30, and the amplified signal light is output.

[0062] According to the phase-locked laser device CL3 as described above, it is possible to perform in-line optical phase synchronization between a plurality of local oscillation lights, thereby realizing scalability with a reduced number of alignments.

[0063] Embodiment 4. A phase-locked laser device CL4 according to embodiment 4 will now be described with reference to FIGS. 8 to 11. FIG. 8 is a diagram showing an example of the overall configuration of the phase-locked laser device CL4. FIG. 9 is a diagram showing an example of the configuration of element circuits for local light of the phase-locked laser device CL4. FIG. 10 is a diagram showing an example of the configuration of element circuits for signal light of the phase-locked laser device CL4. In FIGS. 8, 9, and 10, elements that are the same as or similar to those in embodiment 1, embodiment 2, or embodiment 3 are given the same reference numerals, and descriptions thereof will not be repeated.

[0064] The difference between the fourth embodiment and the third embodiment is that the optical frequency shifters of the local light are all shifted to different frequencies (f ＡＯＭ＿ｉ ) in the third embodiment. In the third embodiment, phase-modulated light of different frequencies is used to identify a plurality of local oscillation lights, but in the fourth embodiment, the frequency shift amounts are individually set to identify the plurality of local oscillation lights. In other words, in the third embodiment, the modulated signal source 10, the optical phase modulator 8, and the mixer 12 are used to identify the local oscillation lights, but in the fourth embodiment, these components are not used. On the other hand, in the signal light path, in order to coherently combine the combined outputs, the frequency shift amounts superimposed by the optical frequency shifter 9 are all the same frequency shift amount (f ＡＯＭ )

[0065] Next, the overall operation will be described. A laser beam from the reference light source 1 is split into multiple beams, resulting in multiple local oscillation lights. The multiple local oscillation lights are given different frequency shifts by the element circuits 31-i (i=1 to N). As shown in FIG. 9, the reference signal source 33-i outputs a certain frequency fＡＯＭ＿ｉ and outputs a reference signal of frequency f ＡＯＭ＿ｉ are different from one another, with i=1 to N. The optical frequency shifters 35-i are tuned to the corresponding center frequencies.

[0066] In the element circuits 24 (24-1-1 to 24-N-Ns) of the signal light, a side carrier beat signal generated by heterodyne detection of the local light and the phase-modulated signal light is detected by f ＡＯＭ_ｓ -f ＡＯＭ_ｉ Convert to the center frequency f ＡＯＭ_ｓ -f ＡＯＭ_ｉ After the unnecessary signal is suppressed by the band limiting filter 17, the phase of the signal output from the band limiting filter 17 and the reference signal (f ＡＯＭ_ｓ -f ＡＯＭ_ｉ ) by the phase comparator 14, thereby establishing phase synchronization.

[0067] 11A and 11B show the spectrum of the signal at each stage. Fig. 11A is a conceptual diagram of the spectrum of the signal received by the local oscillator. Fig. 11B is a conceptual diagram of the spectrum of the signal received after frequency division by the 1 / 2 frequency divider 11.

[0068] Fig. 11C is a conceptual diagram of the spectrum of the optical signal of subarray #1. Fig. 11D is a conceptual diagram of the spectrum of the received signal of subarray #1. Fig. 11E is a conceptual diagram of the spectrum of the received signal of subarray #1 after band limitation by the band limiting filter 17.

[0069] As in embodiment 4, it is possible to eliminate unnecessary frequency components in the local light by individually setting the frequencies of a plurality of local light beams, thereby reducing the side carrier signal generated by phase modulation during heterodyne detection of the signal light and the local light beam, and realizing phase synchronization with a simple configuration.

[0070] Fifth Embodiment A phase-locked laser device CL5 according to a fifth embodiment of the present disclosure will now be described with reference to Fig. 12. Fig. 12 is a diagram showing an example of the overall configuration of the phase-locked laser device CL5. In Fig. 12, elements that are the same as or similar to those in the first, second, third, or fourth embodiment are designated by the same reference numerals, and description thereof will not be repeated.

[0071] The difference between the fifth embodiment and the fourth embodiment is that the fifth embodiment includes a light source modulator 36 that modulates the reference light source 1. In the fourth embodiment, the reference light source 1 emits a narrow linewidth laser beam. In this case, the output of the high-power optical amplifier 30 is limited by the nonlinear optical effect. By superimposing frequency modulation or phase modulation on the reference light source 1 as in the present embodiment, the linewidth of the reference light source 1 can be broadened in a pseudo manner, thereby enabling even higher output power.

[0072] It is possible to combine the embodiments, and to modify or omit each embodiment as appropriate.

[0073] The phase-locked laser device of the present disclosure can be used, for example, as a laser device for laser processing.

[0074] 1 Reference light source, 2 Optical circulator, 3 Optical splitter, 4 (4-1 to 4-N) Element circuit, 5 (5-1 to 5-N+1) Collimator, 6 Photodiode, 7 Distributor, 8 Optical phase modulator, 9 Optical frequency shifter, 10 Modulation signal source, 11 ½ frequency divider, 12 Mixer, 13 Reference signal source, 14 Phase comparator, 15 Loop filter, 17 Band-limiting filter, 18 Semiconductor optical amplifier, 19 Optical splitter, 20 Local light path, 21 Signal light path, 22 Optical splitter, 23 Signal light subarray, 24 (24-1-1 to 24-N-N Ｓ ) element circuit (first element circuit), 25 beam splitter, 26 photodiode, 27 distributor, 28 local light control unit, 29 signal light control unit, 30 high-power optical amplifier, 31 (31-1 to 31-N) element circuit (first element circuit), 33-i reference signal source, 35-i optical frequency shifter, 36 light source modulator, CL (CL1 to CL5) phase-locked laser device, 50 (50-1-1 to 50-N-N Ｓ ) Collimator.

Claims

1. An optical circulator that receives laser light emitted from a reference light source from a first port, supplies it to an outgoing optical path, and outputs return light received from the return optical path from a second port; An optical splitter that splits the laser light received from the optical circulator via the outgoing optical path into a reference light and a plurality of signal lights; A plurality of element circuits, each element circuit comprising a phase compensator that performs phase control on the plurality of signal lights split by the optical splitter and outputs a plurality of phase-controlled signal lights; A plurality of optical partial reflectors into which the reference light or the plurality of phase-controlled signal lights are incident as incident light, a part of the incident light is reflected as reflected light, and the rest of the incident light is transmitted; A photoelectric converter that receives the return light, performs photoelectric conversion, and outputs an electrical signal after photoelectric conversion, wherein the return light is a laser light in which the plurality of reflected lights are combined by the optical splitter, Each element circuit performs frequency conversion on the electrical signal output by the photoelectric converter to detect a phase error of an electrical signal having a frequency component corresponding to each element circuit, Each phase compensator compensates for the detected phase error, A phase synchronization laser device.

2. The phase synchronization laser device according to claim 1, wherein each element circuit includes a semiconductor optical amplifier having no isolator at an input / output end at a subsequent stage of each phase compensator.

3. A phase synchronization laser device comprising: a signal light control unit including a plurality of signal light sub-arrays in which a plurality of signal lights obtained from laser light emitted from a reference light source are sub-arrayed; and a local light emission control unit that supplies a plurality of local light emissions phase-synchronized with the plurality of signal light sub-arrays. The local light emission control unit includes: an optical circulator that receives the laser light from a first port and supplies it to a transmission optical path, and outputs the return light received from the return optical path from a second port; an optical splitter that branches the laser light received from the optical circulator via the transmission optical path into a reference light and a plurality of local light emissions; a plurality of first element circuits, each of which includes a phase compensator that performs phase control on the plurality of local light emissions branched by the optical splitter and outputs a plurality of phase-controlled local light emissions; a plurality of optical partial reflectors in which the reference light or the plurality of phase-controlled local light emissions are incident as incident light, a part of the incident light is reflected as reflected light, and the rest of the incident light is transmitted; and a first photoelectric converter that receives the return light, performs photoelectric conversion, and outputs an electrical signal after photoelectric conversion, where the return light is a laser light in which the plurality of reflected lights are combined by the optical splitter. Each first element circuit performs frequency conversion on the electrical signal output by the first photoelectric converter and detects a phase error of an electrical signal having a frequency component corresponding to each first element circuit. Each phase compensator compensates for the detected phase error. Phase synchronization laser device.

4. Each signal light sub-array includes: a beam splitter that photomixes a part of the transmission light and local light emission to generate mixed light; a second photoelectric converter that performs photoelectric conversion on the mixed light and outputs an electrical signal after photoelectric conversion; and a second element circuit that compensates for a phase error of one of the plurality of signal lights using the electrical signal output from the second photoelectric converter. The phase synchronization laser device according to claim 3.

5. The plurality of local light emissions are distinguished from each other by phase modulation. The phase synchronization laser device according to claim 4.

6. The local light emission control unit includes an optical frequency shifter that superimposes different frequency shift amounts on each other to identify the plurality of local light emissions, and the signal light control unit includes an optical frequency shifter that superimposes the same frequency shift amount. The phase synchronization laser device according to claim 4.

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