JP6320136B2 - Optical frequency control device - Google Patents

Description

  The present invention relates to an optical frequency control apparatus that performs phase synchronization of signal light.

  As a method for realizing a high-power laser system, there is known coherent beam combination (CBC) in which a single laser beam is used as seed light for optical amplification and optical amplification is performed after branching and then synthesis is performed (for example, a patent) Reference 1). In a CBC-based high-power laser, a beam with high output and high brightness can be output by aligning the phase of each optical path and outputting the beam.

JP 2000-323774 A JP 2011-507035 A

However, the conventional high-power laser system disclosed in Patent Document 1 uses the DC component of the optical phase modulator for optical phase control, and the dynamic range of phase control is limited to the operating range of the phase modulator. There was a problem.
In addition, in order to reduce the size of the reception system for phase synchronization and pointing angle error detection when the number of signals increases, a configuration is shown in which reception is performed using a single photodetector and the SPGD method. However, the above method has a problem that the control band is limited by the number of signals when the number of signals increases.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an optical frequency control device capable of realizing phase synchronization in a wide control band.

  An optical frequency control device according to the present invention is driven according to an input signal and performs phase modulation of input local light, local light that is phase-modulated by the optical phase modulator, and input signal light A photodetector for detecting a beat signal of the signal, an RF reference signal source for generating an RF signal serving as a reference for phase synchronization, and an RF signal generated by the RF reference signal source for the beat signal detected by the photodetector A phase error detection circuit that detects a phase difference signal indicating a phase difference between the phase error signal and a phase control circuit that generates a sawtooth signal whose period is adjusted based on the phase difference signal detected by the phase error detection circuit as an input signal It is provided.

  The optical frequency control device according to the present invention includes a reference light source that generates reference light, an optical branching splitter that branches the reference light generated by the reference light source into local light and a plurality of signal lights, and an input signal. A plurality of optical phase modulators that drive and perform phase modulation of the corresponding signal light branched by the optical branching splitter, the signal light phase-modulated by the corresponding optical phase modulator, and a station branched by the optical branching splitter A plurality of photodetectors for detecting beat signals with light emission, an RF reference signal source for generating an RF signal serving as a reference for phase synchronization, and an RF reference signal source for beat signals detected by the corresponding photodetectors A plurality of phase error detection circuits that detect a phase difference signal indicating a phase difference from the RF signal generated by the first and second, and a period is adjusted based on the phase difference signal detected by the corresponding phase error detection circuit. Those having a plurality of phase control circuit for generating a sawtooth signal as a corresponding input signal of the optical phase modulator.

  The optical frequency control device according to the present invention includes a reference light source that generates reference light, an optical branching splitter that branches the reference light generated by the reference light source into local light and a plurality of signal lights, and an input signal. A plurality of optical phase modulators that drive and phase-modulate the corresponding signal light branched by the optical branching splitter, the signal light phase-modulated by each optical phase modulator, and the local light branched by the optical branching splitter A single photodetector that detects the beat signal and a sine wave signal of a different frequency for each optical phase modulator, and the beat signal detected by the photodetector for each component of the frequency An RF reference signal source separates a frequency discriminating circuit to be separated, an RF reference signal source that generates an RF signal as a reference for phase synchronization, and a corresponding beat signal separated by the frequency discriminating circuit. A plurality of phase error detection circuits for detecting a phase difference signal indicating a phase difference from the generated RF signal, and a sawtooth signal whose period is adjusted based on the phase difference signal detected by the corresponding phase error detection circuit A plurality of phase control circuits, a corresponding sine wave signal generated by the frequency discriminating circuit and a sawtooth signal generated by the corresponding phase control circuit to obtain a corresponding optical phase modulator input signal. And an adder circuit.

  The optical frequency control device according to the present invention includes a reference light source that generates reference light, an optical branching splitter that branches the reference light generated by the reference light source into local light and a plurality of signal lights, and an input signal. A plurality of optical phase modulators for driving and phase-modulating the corresponding signal light branched by the optical splitter, and for the signal light phase-modulated by the corresponding optical phase modulator, according to the input control signal A plurality of directivity angle control devices that control the directivity angle, and a split light receiving element that receives the signal light whose directivity angle is controlled by each directivity angle control device and the local light that is branched by the optical branching splitter. A split type photodetector that outputs a current signal corresponding to the received light power for each element, and a sine wave signal with a different frequency for each optical phase modulator, and a split type photodetector A frequency discriminating circuit that separates the output current signal for each component of the frequency, an RF reference signal source that generates an RF signal serving as a reference for phase synchronization, and a corresponding current signal separated by the frequency discriminating circuit , A plurality of phase error detection circuits for detecting a phase difference signal indicating a phase difference from the RF signal generated by the RF reference signal source, and a period is adjusted based on the phase difference signal detected by the corresponding phase error detection circuit A plurality of phase control circuits for generating a sawtooth signal, a corresponding sine wave signal generated by a frequency discriminating circuit, and a sawtooth signal generated by a corresponding phase control circuit, and corresponding optical phase modulator And a plurality of second frequency discriminating circuits for separating the frequency component of the corresponding sine wave signal from the power signal output by the split photodetector The directional angle of each signal light is determined based on the plurality of centroid calculating circuits that detect the directional angle from the current signal separated by the corresponding second frequency discriminating circuit and the directional angle detected by the corresponding centroid calculating circuit. A plurality of directivity angle control circuits that generate control signals for the corresponding directivity angle control devices are provided so as to be constant.

  According to the present invention, since it is configured as described above, phase synchronization in a wide control band can be realized.

It is a figure which shows the structure of the optical frequency control apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the optical frequency control apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining operation | movement of the optical phase modulator in Embodiment 1 of this invention, (a) It is a figure which shows the sawtooth signal input, (b) It is a figure which shows the spectrum of an output signal. It is a figure explaining operation | movement of the optical phase modulator in Embodiment 1 of this invention, (a) It is a figure which shows the sawtooth signal input, (b) It is a figure which shows the spectrum of an output signal. It is a figure which shows the structure of the optical frequency control apparatus which concerns on Embodiment 2 of this invention. It is a flowchart which shows operation | movement of the optical frequency control apparatus which concerns on Embodiment 2 of this invention. It is a figure which shows the structure of the optical frequency control apparatus which concerns on Embodiment 3 of this invention. It is a figure which shows the structural example of the frequency discrimination circuit in Embodiment 3 of this invention. It is a figure explaining the input signal to the optical phase modulator in Embodiment 3 of this invention, (a) It is a figure which shows the output signal (sine wave signal) of a frequency discrimination circuit, (b) Of a phase control circuit It is a figure which shows an output signal, (c) It is a figure which shows the output signal of an addition circuit. It is a figure which shows the spectrum of the received signal by the single photodetector in Embodiment 3 of this invention. It is a figure which shows the operation | movement of the frequency discrimination circuit in Embodiment 3 of this invention, (a) It is a figure which shows the output signal of a photodetector, (b) It is a figure which shows the unnecessary wave suppression by a band pass filter, (C) It is a figure which shows the down conversion by a frequency mixer. It is a figure which shows the structure of the optical frequency control apparatus which concerns on Embodiment 4 of this invention. It is a figure explaining the input signal to the optical phase modulator in Embodiment 4 of this invention, (a) It is a figure which shows the output signal (sine wave signal) of a frequency discrimination circuit, (b) Of a phase control circuit It is a figure which shows an output signal, (c) It is a figure which shows the output signal of an offset phase control signal output circuit, (d) It is a figure which shows the output signal of an addition circuit. It is a figure which shows the structure of the optical frequency control apparatus which concerns on Embodiment 5 of this invention. It is a figure which shows the reception image of the division | segmentation type | mold photodetector in Embodiment 5 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of an optical frequency control apparatus according to Embodiment 1 of the present invention.
As shown in FIG. 1, the optical frequency control device includes an optical phase modulator 1, an optical coupler 2, a photodetector 3, an RF reference signal source 4, a phase error detection circuit 5, and a phase control circuit 6.

  The optical phase modulator 1 is driven according to an input signal and performs phase modulation of the input local light. The local light that has been phase-modulated by the optical phase modulator 1 is output to the optical coupler 2.

  The optical coupler 2 combines the local light from the optical phase modulator 1 and the input signal light. The local light and signal light combined by the optical coupler 2 are output to the photodetector 3.

  The photodetector 3 detects a beat signal of the local light and signal light combined by the optical coupler 2. The beat signal detected by the photodetector 3 is output to the phase error detection circuit 5.

  The RF reference signal source 4 generates an RF (Radio Frequency) signal that is a reference for phase synchronization. The RF signal generated by the RF reference signal source 4 is output to the phase error detection circuit 5.

  The phase error detection circuit 5 detects a phase difference signal indicating a phase difference between the beat signal from the photodetector 3 and the RF signal from the RF reference signal source 4. The phase difference signal detected by the phase error detection circuit 5 is output to the phase control circuit 6.

  The phase control circuit 6 generates a sawtooth signal whose period is adjusted based on the phase difference signal from the phase error detection circuit 5 as an input signal of the optical phase modulator 1. The sawtooth signal generated by the phase control circuit 6 is output to the optical phase modulator 1.

Next, the operation of the optical frequency control apparatus configured as described above will be described with reference to FIG.
In the operation of the optical frequency control device, as shown in FIG. 2, first, the optical phase modulator 1 is driven in accordance with an input signal and performs phase modulation of the input local light (step ST201). The local light that has been phase-modulated by the optical phase modulator 1 is output to the optical coupler 2.

  Next, the optical coupler 2 combines the local light from the optical phase modulator 1 and the input signal light (step ST202). The local light and signal light combined by the optical coupler 2 are output to the photodetector 3.

  Next, the photodetector 3 detects the beat signal of the local light and the signal light combined by the optical coupler 2 (step ST203). The beat signal detected by the photodetector 3 is output to the phase error detection circuit 5.

  Next, the RF reference signal source 4 generates an RF signal that is a reference for phase synchronization (step ST204). The RF signal generated by the RF reference signal source 4 is output to the phase error detection circuit 5.

  Next, the phase error detection circuit 5 detects a phase difference signal indicating a phase difference between the beat signal from the photodetector 3 and the RF signal from the RF reference signal source 4 (step ST205). The phase difference signal detected by the phase error detection circuit 5 is output to the phase control circuit 6.

  Next, the phase control circuit 6 generates a sawtooth signal whose period is adjusted based on the phase difference signal from the phase error detection circuit 5 as an input signal of the optical phase modulator 1 (step ST206). The sawtooth signal generated by the phase control circuit 6 is output to the optical phase modulator 1. Thus, by feeding back the phase difference signal to the optical phase modulator 1 via the phase control circuit 6, the phase difference between the signal light and the local light can be synchronized with the RF signal.

Here, the operation of the optical phase modulator 1 will be described with reference to FIGS.
When the optical phase modulator 1 is driven by a sawtooth signal having a drive frequency f and a phase width of ± π (FIG. 3A), the output signal of the optical phase modulator 1 is as shown in FIG. The frequency is shifted by 1 / T with respect to the input signal (f0) of the optical phase modulator 1. Then, by changing the period of the sawtooth signal input to the optical phase modulator 1 (FIG. 4A), the optical phase modulator 1 is operated as an optical frequency shifter (VCO: Voltage Control Oscillator). (FIG. 4B).

  On the other hand, in the conventional configuration, frequency control of local light is performed using an optical frequency shifter. However, the operating band of the optical frequency shifter is generally as low as 100 [kHz], and high-speed (> 1 [MHz]) frequency control cannot be performed. On the other hand, the optical phase modulator 1 used in the present embodiment can respond at a high speed of GHz or higher, and can perform high-speed frequency control and phase control.

  In the above description, the case where unmodulated signal light is used and the optical coupler 2 is used for multiplexing the signal light and the local light is shown. However, the present invention is not limited to this. For example, a modulated signal light such as BPSK (Binary Phase Shift Keying) may be used, and the modulated signal light may be combined with the local light using an optical 90-degree hybrid. Alternatively, pulse signal light may be used.

  As described above, according to the first embodiment, the optical phase modulator 1 is driven by adjusting the period of the sawtooth signal based on the phase difference from the RF signal. 1 can be operated as an optical frequency shifter, and phase synchronization with a high speed and a wide control band can be realized.

Embodiment 2. FIG.
In the first embodiment, phase synchronization of one signal light has been described. In the second embodiment, a configuration in which the present invention is applied to a phased array laser using a plurality of signal lights will be described. FIG. 5 is a diagram showing a configuration of an optical frequency control apparatus according to Embodiment 2 of the present invention.
As shown in FIG. 5, the optical frequency control apparatus includes a reference light source 11, an optical branching splitter 12, an optical phase modulator 13, first and second optical collimators 14, 15, a beam splitter 16, a photodetector 17, an RF reference. The signal source 18, the RF branch splitter 19, the phase error detection circuit 20, and the phase control circuit 21 are included. Here, a plurality (N) of optical phase modulators 13, first optical collimators 14, photodetectors 17, phase error detection circuits 20, and phase control circuits 21 are provided.

  The reference light source 11 generates reference light. The reference light generated by the reference light source 11 is output to the optical branching splitter 12.

  The optical branching splitter 12 branches the reference light from the reference light source 11 into local light and a plurality of signal lights. The local light branched by the optical branching splitter 12 is output to the second optical collimator 15, and the signal light is output to the corresponding optical phase modulator 13.

  The optical phase modulator 13 is driven according to an input signal and performs phase modulation of the corresponding signal light from the optical branching splitter 12. The signal light phase-modulated by the optical phase modulator 13 is output to the corresponding first optical collimator 14.

The first optical collimator 14 spatially outputs the signal light from the corresponding optical phase modulator 13.
The second optical collimator 15 spatially outputs the local light from the optical branching splitter 12.

  The beam splitter 16 multiplexes the signal light spatially output by each first optical collimator 14 and the local light output spatially output by the second optical collimator 15. Each signal light and local light combined by the beam splitter 16 is output to the corresponding photodetector 17. The signal light transmitted through the beam splitter 16 is used as output light.

  The photodetector 17 detects a beat signal of the corresponding signal light combined with the beam splitter 16 and the local light. The beat signal detected by the photodetector 17 is output to the corresponding phase error detection circuit 20.

  The RF reference signal source 18 generates an RF signal serving as a phase synchronization reference. The RF signal generated by the RF reference signal source 18 is output to the RF branch splitter 19.

  The RF branching splitter 19 branches the RF signal from the RF reference signal source 18. The RF signal branched by the RF branch splitter 19 is output to the corresponding phase error detection circuit 20.

  The phase error detection circuit 20 detects a phase difference signal indicating a phase difference between the beat signal from the corresponding photodetector 17 and the corresponding RF signal from the RF branching splitter 19. The phase difference signal detected by the phase error detection circuit 20 is output to the corresponding phase control circuit 21.

  The phase control circuit 21 generates a sawtooth signal whose period is adjusted based on the phase difference signal from the corresponding phase error detection circuit 20 as an input signal of the corresponding optical phase modulator 13. The sawtooth signal generated by the phase control circuit 21 is output to the corresponding optical phase modulator 13.

Next, the operation of the optical frequency control apparatus configured as described above will be described with reference to FIG.
In the operation of the optical frequency control device, as shown in FIG. 6, first, the reference light source 11 generates reference light (step ST601). The reference light generated by the reference light source 11 is output to the optical branching splitter 12.

  Next, the optical branching splitter 12 branches the reference light from the reference light source 11 into a local light and a plurality of signal lights (step ST602). The local light branched by the optical branching splitter 12 is output to the second optical collimator 15, and the signal light is output to the corresponding optical phase modulator 13.

  Next, the optical phase modulator 13 is driven according to the input signal, and performs phase modulation of the corresponding signal light from the optical branching splitter 12 (step ST603). Here, the optical phase modulator 13 is driven by a sawtooth signal (period T) having an amplitude of ± Vπ. The output light from the optical phase modulator 13 becomes light that is phase-modulated with a period T of ± π, and the center frequency is shifted by the frequency 1 / T as shown in FIG. The signal light phase-modulated by the optical phase modulator 13 is output to the first optical collimator 14.

  Next, the first optical collimator 14 spatially outputs the signal light from the corresponding optical phase modulator 13, and the second optical collimator 15 spatially outputs the local light from the optical branching splitter 12 (step). ST604).

  Next, the beam splitter 16 combines the signal light from each first optical collimator 14 and the local light from the second optical collimator 15 (step ST605). Each signal light and local light combined by the beam splitter 16 is output to the corresponding photodetector 17. The signal light transmitted through the beam splitter 16 is used as output light.

  Next, the photodetector 17 detects the beat signal of the corresponding signal light combined with the beam splitter 16 and the local light (step ST606). Here, the signal detected by the photodetector 17 is a beat signal having a frequency (f = 1 / T). The beat signal detected by the photodetector 17 is output to the corresponding phase error detection circuit 20.

  Next, the RF reference signal source 18 generates an RF signal serving as a phase synchronization reference (step ST607). The RF signal generated by the RF reference signal source 18 is output to the RF branch splitter 19.

  Next, the RF branch splitter 19 branches the RF signal from the RF reference signal source 18 (step ST608). The RF signal branched by the RF branch splitter 19 is output to the corresponding phase error detection circuit 20.

  Next, the phase error detection circuit 20 detects a phase difference signal indicating a phase difference between the corresponding beat signal from the photodetector 17 and the corresponding RF signal from the RF branch splitter 19 (step ST609). The phase difference signal detected by the phase error detection circuit 20 is output to the corresponding phase control circuit 21.

  Next, the phase control circuit 21 generates a sawtooth signal whose period is adjusted based on the phase difference signal from the corresponding phase error detection circuit 20 as an input signal of the corresponding optical phase modulator 13 (step ST610). The sawtooth signal generated by the phase control circuit 21 is output to the corresponding optical phase modulator 13.

  Here, by setting the period T of the sawtooth signal to T + ΔT, the optical phase modulator 13 can be operated as an optical frequency shifter. In this way, the phase control circuit 21 can feed back the signal for compensating the phase difference signal to the optical phase modulator 13, thereby establishing phase synchronization between the signal lights.

  As described above, according to the second embodiment, in the phased array laser using a plurality of signal lights, the optical phase modulator 13 is adjusted by adjusting the period of the sawtooth signal based on the phase difference from the RF signal. Since it is configured to be driven, the optical phase modulator 13 can be operated as an optical frequency shifter, and phase synchronization with a high speed and a wide control band can be realized without depending on the number of signals.

In the above description, the output light of the optical phase modulator 13 is spatially output as it is for each signal light. However, the output light of the optical phase modulator 13 is amplified by an optical amplifier and output spatially. Good.
In the above description, the amplitude of the sawtooth signal to the optical phase modulator 13 is ± π as an example. However, the present invention is not limited to this, and the amplitude of the sawtooth signal may be ± nπ (n is a natural number).

Embodiment 3 FIG.
In the second embodiment, the configuration using a plurality of photodetectors 17 for a plurality of signal lights has been described. On the other hand, in the third embodiment, reception is performed by a single photodetector 17 by superimposing phase-modulated signals of different frequencies on a plurality of signal lights, and the received signals are separated in the frequency domain. A configuration for detecting phase difference signals of a plurality of signal lights will be described.
FIG. 7 is a diagram showing a configuration of an optical frequency control apparatus according to Embodiment 3 of the present invention. The optical frequency control device according to the third embodiment shown in FIG. 7 has a single photodetector 17 of the optical frequency control device according to the second embodiment shown in FIG. 5, and includes a frequency discrimination circuit 22 and an addition circuit 23. It is added. A plurality (N) of adder circuits 23 are provided. Other configurations are the same, and only the different parts are described with the same reference numerals.

  The frequency discriminating circuit 22 generates sine wave signals (frequency discrimination signals) having different frequencies for the respective optical phase modulators 13, and separates the beat signal from the photodetector 17 for each component of the frequency. is there. Details of the frequency discrimination circuit 22 will be described later. The sine wave signal generated by the frequency discrimination circuit 22 is output to the corresponding adder circuit 23, and the beat signal separated for each frequency component is output to the corresponding phase error detection circuit 20.

  The adder circuit 23 adds the corresponding sine wave signal from the frequency discriminating circuit 22 and the sawtooth signal from the corresponding phase control circuit 21 to obtain the input signal of the corresponding optical phase modulator 13. The signal obtained by the adder circuit 23 is output to the corresponding optical phase modulator 13.

  The phase error detection circuit 20 detects a phase difference signal indicating a phase difference between the corresponding beat signal from the frequency discrimination circuit 22 and the corresponding RF signal from the RF branch splitter 19.

Next, a configuration example of the frequency discrimination circuit 22 will be described with reference to FIG.
As shown in FIG. 8, the frequency discrimination circuit 22 includes an RF branch splitter 221, a band pass filter 222, an RF oscillator 223, and a frequency mixer 224. A plurality (N) of band-pass filters 222, RF oscillators 223, and frequency mixers 224 are provided.

  The RF branching splitter 221 branches the beat signal from the photodetector 17. The beat signal branched by the RF branch splitter 221 is output to the corresponding bandpass filter 222.

  The band pass filter 222 suppresses unnecessary waves with respect to the corresponding beat signal from the RF branching splitter 221. Each band pass filter 222 is set to a different center frequency. The beat signal whose unnecessary wave is suppressed by the band pass filter 222 is output to the corresponding frequency mixer 224.

  The RF oscillator 223 oscillates sinusoidal signals having different frequencies. The sine wave signal oscillated by the RF oscillator 223 is output to the corresponding frequency mixer 224. A part of the sine wave signal oscillated by the RF oscillator 223 is output to the corresponding adder circuit 23 as a frequency discrimination signal.

  The frequency mixer 224 combines the beat signal in which the unnecessary wave is suppressed by the corresponding bandpass filter 222 and the corresponding sine wave signal from the corresponding RF oscillator 223, and downconverts the beat signal. The signal down-converted by the frequency mixer 224 is output to the corresponding phase error detection circuit 20.

Next, the operation of the optical frequency control apparatus configured as described above will be described.
The configuration of the third embodiment is different from that of the second embodiment in that a photodetector 17 is provided by inputting a frequency discrimination signal (sine wave signal) and a phase control signal (saw wave signal) to the optical phase modulator 13. Is a single point.
FIG. 9 shows an image of an input signal to each optical phase modulator 13 in the second embodiment. The frequency discriminating circuit 22 outputs a sine wave signal having a different frequency (FIG. 9A), and the phase control circuit 21 outputs a sawtooth wave signal (FIG. 9B). These two signals are added by the adder circuit 23 (FIG. 9C), and then output to the corresponding optical phase modulator 13.

  FIG. 10 shows an image of the spectrum of the received signal by the single photodetector 17. The frequency discrimination signal is a sine wave signal having a frequency of f1 to fN for each input signal light. In this case, a carrier signal is generated at a frequency (f0 + 1 / T) and a side carrier signal for frequency discrimination is generated at f0 + 1 / T + f1 to fN. Then, in the frequency discriminating circuit 22, as shown in FIG. 11, the desired frequency is separated in the frequency domain, converted into the same frequency as the RF reference signal source 18, and then phase comparison is performed.

Next, the operation of the frequency discrimination circuit 22 will be described with reference to FIG.
In the operation of the frequency discrimination circuit 22, first, the RF branch splitter 221 branches the beat signal (see FIG. 11A) from the photodetector 17. Next, unnecessary waves are suppressed from the beat signal by the band pass filters 222 having different center frequencies (1 / T + fi) (see FIG. 11B). Next, a sine wave signal having a frequency fi is oscillated by the RF oscillator 223. Next, the frequency mixer 224 combines the corresponding beat signal in which the unnecessary wave is suppressed and the corresponding sine wave signal, and down-converts (see FIG. 11C). Here, the down-converted signal has the same frequency of 1 / T. The beat signal down-converted by the frequency mixer 224 is output to the corresponding phase error detection circuit 20. A part of the sine wave signal oscillated by the RF oscillator 223 is output to the corresponding adder circuit 23 as a frequency discrimination signal.

  As described above, according to the third embodiment, since the optical phase modulator 13 is driven using the sawtooth signal and the frequency discrimination signal, in addition to the effects of the second embodiment, the photodetector 17 can be single. In addition, since the optical phase modulator 13 applies the optical phase synchronization and the frequency discrimination signal, it is not necessary to prepare a phase synchronization modulator and a frequency discrimination modulator, and the size can be reduced.

In the above description, the output light of the optical phase modulator 13 is spatially output as it is for each signal light. However, the output light of the optical phase modulator 13 is amplified by an optical amplifier and output spatially. Good.
In the above description, the amplitude of the sawtooth signal to the optical phase modulator 13 is ± π as an example. However, the present invention is not limited to this, and the amplitude of the sawtooth signal may be ± nπ (n is a natural number). Further, by installing a plurality of this configuration, it is possible to cope with an increase in the number of signals.

Embodiment 4 FIG.
In the fourth embodiment, a configuration in which offset phases of a plurality of signal lights of a phased array laser can be controlled by controlling a DC component of an input signal of the optical phase modulator 13 will be described.
FIG. 12 is a diagram showing a configuration of an optical frequency control apparatus according to Embodiment 4 of the present invention. The optical frequency control apparatus according to the fourth embodiment shown in FIG. 12 is obtained by adding an offset phase control signal output circuit 24 to the optical frequency control apparatus according to the third embodiment shown in FIG. Other configurations are the same, and only the different parts are described with the same reference numerals.

The offset phase control signal output circuit 24 generates an offset phase control signal (DC signal). The offset phase control signal generated by the offset phase control signal output circuit 24 is output to the corresponding adder circuit 23.
The adder circuit 23 also adds the corresponding offset phase control signal from the offset phase control signal output circuit 24 to obtain the input signal of the corresponding optical phase modulator 13.

  The difference from the third embodiment is that the offset phase after phase synchronization is established can be adjusted by adjusting the DC component of the input signal of the optical phase modulator 13. In the third embodiment, the offset phase at the time of phase synchronization can be adjusted by changing the phase of the RF signal input to the phase error detection circuit 20. However, the adjustable phase range and control band are limited depending on the band and operation range of the offset phase control circuit (for example, RF phase shifter) used at that time. On the other hand, in the fourth embodiment, since the signal applied to the optical phase modulator 13 is changed, offset phase control is possible within the band of the optical phase modulator 13.

  FIG. 13 shows an image of an input signal to the optical phase modulator 13 in the fourth embodiment. In the fourth embodiment, a sine wave signal (FIG. 13 (a)) from the frequency discriminating circuit 22 having a different frequency for each signal light, a sawtooth wave signal (FIG. 13 (b)) from the phase control circuit 21, and an offset phase. A signal (FIG. 13 (d)) obtained by adding the offset phase control signal (FIG. 13 (c)) from the control signal output circuit 24 is output to the optical phase modulator 13. As a result, phase fluctuation control in the signal optical path, discrimination of a plurality of signal lights, and offset phase control in establishing phase synchronization can be realized by a single optical phase modulator 13.

Embodiment 5. FIG.
In the fifth embodiment, description will be given of a configuration in which the directivity angle detection and the position error detection of the signal light are simultaneously performed by using the split photodetector 26 instead of the photodetector 17.
FIG. 14 is a diagram showing a configuration of an optical frequency control apparatus according to Embodiment 5 of the present invention. In the optical frequency control apparatus according to the fifth embodiment shown in FIG. 14, the photodetector 17 of the optical frequency control apparatus according to the fourth embodiment shown in FIG. A device 25, an RF branching splitter 27, an RF combiner 28, a second frequency discriminating circuit 29, a center-of-gravity calculation circuit 30, and a directivity angle control circuit 31 are added. Other configurations are the same, and only the different parts are described with the same reference numerals. Note that a plurality of (N) directivity angle control devices 25, second frequency discrimination circuits 29, center-of-gravity calculation circuits 30, and directivity angle control circuits 31 are provided.

The directivity angle control device 25 controls the directivity angle according to the control signal from the directivity angle control circuit 31 with respect to the signal light from the corresponding first optical collimator 14. The directivity angle control device 25 is composed of, for example, an adaptive mirror. The signal light whose directivity angle is controlled by the directivity angle control device 25 is output to the beam splitter 16.
The beam splitter 16 multiplexes the signal light from each directivity angle control device 25 and the local light from the second optical collimator 15. Each signal light and local light combined by the beam splitter 16 is output to the split photodetector 26. The signal light transmitted through the beam splitter 16 is used as output light.

  The split-type photodetector 26 has a split light-receiving element that receives each signal light and local light combined by the beam splitter 16, and outputs a current signal corresponding to the received light power for each split light-receiving element. is there. As the split photodetector 26, for example, a four-split photodetector as shown in FIG. 15 can be used. The current signal obtained by the split photodetector 26 is output to the RF branch splitter 27.

  The RF branch splitter 27 branches the current signal from the split photodetector 26 into two. One of the current signals branched by the RF branch splitter 27 is output to the RF combiner 28 for phase error detection, and the other is output to the second frequency discrimination circuit 29 for detection of the directivity angle.

The RF combiner 28 combines the current signals from the RF branch splitter 27. As this RF combiner 28, for example, one that combines four signals is used. The electrical signal combined by the RF combiner 28 is output to the frequency discrimination circuit 22.
The frequency discriminating circuit 22 generates sinusoidal signals (frequency discrimination signals) having different frequencies for the respective optical phase modulators 13 and separates the electric signal from the RF combiner 28 for each component of the frequency.

  The second frequency discrimination circuit 29 separates the frequency component of the corresponding frequency discrimination signal from the current signal from the RF branch splitter 27. The electric signal separated by the second frequency discriminating circuit 29 is output to the corresponding centroid calculating circuit 30.

  The center-of-gravity calculation circuit 30 detects the directivity angle from the electrical signal from the corresponding second frequency discrimination circuit 29. A signal indicating the directivity angle detected by the center-of-gravity calculation circuit 30 is output to the corresponding directivity angle control circuit 31.

  The directivity angle control circuit 31 generates a control signal for the corresponding directivity angle control device 25 based on the directivity angle detected by the corresponding center-of-gravity calculation circuit 30 so that the directivity angle of each signal light is constant. It is. The control signal generated by the directivity angle control circuit 31 is output to the directivity angle control device 25.

Next, the operation of the optical frequency control apparatus configured as described above will be described.
In the optical frequency control device according to the fifth embodiment, the signal light from the first optical collimator 14 is subjected to directivity angle control by the directivity angle control device 25 and then received by the split photodetector 26. A current signal corresponding to the received light power is output from the split photodetector 26 for each split light receiving element.

Here, the reception image of the split photodetector 26 is shown in FIG. 15 by taking a four split photodetector as an example. Note that the local light is condensed as a size larger than all the light receiving elements, and the signal light (first and second signal lights in FIG. 15) is set to be smaller than the whole light receiving elements.
In FIG. 15, the first signal light shows a case where it is input to the center of the divided light receiving element, and the second signal light shows a case where the directivity angle is shifted. Thereby, the signal level (Ia-Id) output for every division | segmentation light receiving element changes with directivity angles.

  Thereafter, the output signal of the split-type photodetector 26 is branched into two for phase error detection and directivity angle detection by the RF branch splitter 27. After two branches, the phase error detection signals are combined by the RF combiner 28. The combined signal is used for phase error detection of the corresponding signal light via the frequency discrimination circuit 22 and the phase error detection circuit 20.

On the other hand, the signal for directivity angle detection is input to the center-of-gravity calculation circuit 30 after the frequency component corresponding to the signal light is separated by the second frequency discrimination circuit 29. Then, the center-of-gravity calculation circuit 30 detects the directivity angles of the X and Y components using the following equation (1). Then, a directivity angle control circuit 31 generates a control signal based on the detected directivity angle, and the control signal is applied to the directivity angle control device 25 to make the directivity angles of the plurality of signal lights constant.

  As described above, the directivity angle control circuit 31 can change the directivity angle of other signal light to a specific signal light (for example, the first signal light) based on the output signal difference of the gravity center arithmetic circuit 30 caused by the signal level difference. By controlling the directivity angle control device 25 so as to be the same, it becomes possible to output signal light having the same optical phase and directivity angle.

  In the above description, the case where the CW signal light is used as the signal light has been described. However, the present invention is not limited to this. For example, the case where the pulse signal light is used can be realized.

  As described above, according to the fifth embodiment, the split light detector 26 is used in place of the light detector 17, and the directivity angle detection and the position error detection of the signal light are performed simultaneously. In addition to the effects of the fourth embodiment, high-speed phase synchronization and directivity control can be performed without depending on the number of signals. In addition, since reception is performed by the single split-type photodetector 26 and the phase error signal and the directivity angle error signal are calculated, the number of detectors can be reduced and the size can be reduced.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  DESCRIPTION OF SYMBOLS 1 Optical phase modulator, 2 Optical coupler, 3 Optical detector, 4 RF reference signal source, 5 Phase error detection circuit, 6 Phase control circuit, 11 Reference light source, 12 Optical branch splitter, 13 Optical phase modulator, 14 1st Optical collimator, 15 second optical collimator, 16 beam splitter, 17 photodetector, 18 RF reference signal source, 19 RF branch splitter, 20 phase error detection circuit, 21 phase control circuit, 22 frequency discrimination circuit, 23 addition circuit , 24 offset phase control signal output circuit, 25 directivity angle control device, 26 split type photodetector, 27 RF branch splitter, 28 RF combiner, 29 second frequency discrimination circuit, 30 center of gravity arithmetic circuit, 31 directivity angle control circuit, 221 RF splitter splitter, 222 band pass filter, 223 RF oscillator, 224 frequency mixer .

Claims (7)

An optical phase modulator that is driven according to an input signal and performs phase modulation of the input local light;
A photodetector for detecting a beat signal between the local light phase-modulated by the optical phase modulator and the input signal light;
An RF reference signal source for generating an RF signal which is a reference for phase synchronization;
A phase error detection circuit for detecting a phase difference signal indicating a phase difference between the beat signal detected by the photodetector and the RF signal generated by the RF reference signal source;
An optical frequency control device comprising: a phase control circuit that generates, as the input signal, a sawtooth signal whose period is adjusted based on a phase difference signal detected by the phase error detection circuit. A reference light source for generating reference light;
An optical branching splitter for branching the reference light generated by the reference light source into local light and a plurality of signal lights;
A plurality of optical phase modulators that drive according to an input signal and perform phase modulation of the corresponding signal light branched by the optical branching splitter;
A plurality of photodetectors for detecting beat signals of the signal light phase-modulated by the corresponding optical phase modulator and the local light branched by the optical branching splitter;
An RF reference signal source for generating an RF signal which is a reference for phase synchronization;
A plurality of phase error detection circuits for detecting a phase difference signal indicating a phase difference between the beat signal detected by the corresponding photodetector and the RF signal generated by the RF reference signal source;
A plurality of phase control circuits that generate a sawtooth signal whose period is adjusted based on the phase difference signal detected by the corresponding phase error detection circuit as the input signal of the corresponding optical phase modulator. Control device. A reference light source for generating reference light;
An optical branching splitter for branching the reference light generated by the reference light source into local light and a plurality of signal lights;
A plurality of optical phase modulators that drive according to an input signal and perform phase modulation of the corresponding signal light branched by the optical branching splitter;
A single photodetector for detecting a beat signal of the signal light phase-modulated by each optical phase modulator and the local light branched by the optical branching splitter;
A frequency discriminating circuit that generates sinusoidal signals of different frequencies for each of the optical phase modulators, and separates the beat signal detected by the photodetector for each component of the frequency;
An RF reference signal source for generating an RF signal which is a reference for phase synchronization;
A plurality of phase error detection circuits for detecting a phase difference signal indicating a phase difference between the corresponding beat signal separated by the frequency discrimination circuit and the RF signal generated by the RF reference signal source;
A plurality of phase control circuits for generating a sawtooth signal whose period is adjusted based on the phase difference signal detected by the corresponding phase error detection circuit;
A plurality of adder circuits that add the corresponding sine wave signal generated by the frequency discriminating circuit and the corresponding sawtooth signal generated by the phase control circuit to obtain the input signal of the corresponding optical phase modulator; An optical frequency control device comprising: An offset phase control signal output circuit for generating an offset phase control signal;
The optical frequency control apparatus according to claim 3, wherein the adding circuit also adds the offset phase control signal generated by the offset phase control signal output circuit to obtain the input signal. A reference light source for generating reference light;
An optical branching splitter for branching the reference light generated by the reference light source into local light and a plurality of signal lights;
A plurality of optical phase modulators that drive according to an input signal and perform phase modulation of the corresponding signal light branched by the optical branching splitter;
A plurality of directivity angle control devices for controlling directivity angles in accordance with an input control signal with respect to the signal light phase-modulated by the corresponding optical phase modulator;
A split light-receiving element that receives the signal light whose directivity angle is controlled by each of the directivity-angle control devices and the local light branched by the optical branching splitter, and a current signal corresponding to the received light power for each of the split light-receiving elements A split-type photodetector for output;
A frequency discriminating circuit that generates sinusoidal signals of different frequencies for each of the optical phase modulators, and separates the current signal output by the split photodetector for each component of the frequency;
An RF reference signal source for generating an RF signal which is a reference for phase synchronization;
A plurality of phase error detection circuits for detecting a phase difference signal indicating a phase difference between the corresponding current signal separated by the frequency discrimination circuit and the RF signal generated by the RF reference signal source;
A plurality of phase control circuits for generating a sawtooth signal whose period is adjusted based on the phase difference signal detected by the corresponding phase error detection circuit;
A plurality of adder circuits that add the corresponding sine wave signal generated by the frequency discriminating circuit and the corresponding sawtooth signal generated by the phase control circuit to obtain the input signal of the corresponding optical phase modulator; ,
A plurality of second frequency discriminating circuits for separating the corresponding frequency component of the sine wave signal from the power signal output by the split photodetector;
A plurality of center-of-gravity calculation circuits for detecting a directivity angle from the current signal separated by the corresponding second frequency discrimination circuit;
A plurality of directivity angle control circuits that generate the control signals of the corresponding directivity angle control devices so that the directivity angles of the signal lights are constant based on the directivity angles detected by the corresponding gravity center calculation circuits. And an optical frequency control device. The optical frequency control device according to any one of claims 1 to 5, wherein the signal light is modulated signal light. The optical frequency control device according to any one of claims 1 to 5, wherein the signal light is pulse signal light.

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