JP6541925B1 - Optical space communication device - Google Patents

Abstract

  When the initial capture is completed, the signal processing unit (101e) controls the light variable attenuator (10-4) and the control signal generation unit (10-5) to attenuate the optical power of the initial capture light.

Description

  The present invention relates to an optical space communication apparatus for communicating by propagating laser light to space.

In optical space communication, it is necessary to control the directivity angle of transmission light by detecting the propagation direction of an incoming wave and capturing the incoming wave.
For example, in the optical space communication apparatus described in Patent Document 1, the light beam for initial capture and the light beam for communication are spatially multiplexed, and the beam spread angle of the light beam for initial capture is a light beam for communication. It's bigger than that. This enhances the certainty of the initial capture of the communication partner.

JP 2001-326608 A

  However, in the optical space communication apparatus described in Patent Document 1, even if communication is established and initial capture is completed, it is necessary to continue to emit the light beam for initial capture with the same optical power as at initial capture, There is a problem that the efficiency of initial capture and optical communication is poor.

  This invention solves the said subject, and it aims at obtaining the optical space communication apparatus which can implement | achieve an efficient and stable initial capture and optical communication.

  An optical space communication apparatus according to the present invention includes a first light source unit, a second light source unit, an optical conversion unit for capture, a multiplexing unit, an optical amplifier, and a signal processing unit. The first light source unit outputs an initial capturing light which is a single wavelength and a continuous wave. The second light source unit outputs communication light having a wavelength different from that of the initial capture light and being a continuous wave. The capture light conversion unit converts the initial capture light into pulsed light, and adjusts the light power of the initial capture light. The combining unit combines the light for initial capture and the light for communication. The optical amplifier amplifies the light multiplexed by the multiplexer and outputs the amplified light as transmission light. When the initial capture is completed, the signal processing unit controls the capture light conversion unit to attenuate the light power of the initial capture light.

  According to the present invention, the optical power of the initial capture light is maintained until the initial capture is completed, and after the initial capture is completed, the optical power of the initial capture light is attenuated to transmit the communication light in the transmission light Relatively increase the light power of As a result, it is possible to secure both the optical power necessary for the completion of the initial acquisition and the optical power necessary for the optical communication, so that it is possible to realize the efficient initial acquisition and the optical communication stably.

It is a block diagram which shows the structure of the optical space communication apparatus concerning Embodiment 1 of this invention. FIG. 5 is a diagram showing spectral images of transmission light and reception light in the first embodiment. 5 is a flowchart showing an operation of the optical space communication apparatus according to Embodiment 1. FIG. 7 is a diagram showing temporal changes in optical power of the initial capture light and the communication light in Embodiment 1. It is a block diagram which shows the structure of the optical space communication apparatus concerning Embodiment 2 of this invention. FIG. 16 is a diagram showing temporal changes in optical power of a semiconductor optical amplifier (SOA) drive signal, an initial capturing light, and a communication light in Embodiment 2. It is a block diagram which shows the structure of the optical space communication apparatus concerning Embodiment 3 of this invention. It is a block diagram which shows the structure of the optical space communication apparatus concerning Embodiment 4 of this invention. It is a graph which shows the time waveform of a sawtooth wave signal, frequency shift amount, and a frequency shift compensation signal. FIG. 17 is a diagram showing time change of optical power of the initial capturing light and the communication light in the fourth embodiment.

Hereinafter, in order to explain the present invention in more detail, embodiments for carrying out the present invention will be described according to the attached drawings.
Embodiment 1
FIG. 1 is a block diagram showing a configuration of an optical space communication apparatus 100 according to Embodiment 1 of the present invention. The optical space communication apparatus 100 is an optical communication apparatus that propagates laser light in space to perform communication, and includes an optical transmission unit 101, an optical reception unit 102, a wavelength separation filter 103, an adaptive mirror 104, an optical antenna 105, and a beam separation unit. And 106, a pointing angle detection unit 107 and a control signal generation unit 108. The optical transmission unit 101 includes an initial acquisition unit 101a, an optical communication unit 101b, a wavelength division multiplexing (WDM) coupler 101c, an optical amplifier 101d, and a signal processing unit 101e.

  The transmission light output from the optical transmission unit 101 is separated into a transmission optical path by the wavelength separation filter 103, passes through the adaptive mirror 104, and is then output to space as transmission light by the optical antenna 105. The received light received by the optical antenna 105 passes through the adaptive mirror 104, is separated from the transmitted light by the wavelength separation filter 103, and is output to the receiving optical path.

The beam separation unit 106 outputs the received light output to the reception light path by the wavelength separation filter 103 to the light reception unit 102 and the directivity angle detection unit 107. The light receiving unit 102 extracts data from the optical space communication apparatus 100 of the communication partner from the received light.
The directivity angle detection unit 107 is a component that detects the directivity angle (arrival angle) of the received light, and is realized by, for example, a four quadrant PD (photodiode).

The directivity angle detected by the directivity angle detection unit 107 is output to the control signal generation unit 108. The control signal generation unit 108 generates a control signal having a constant value of the directivity angle input from the directivity angle detection unit 107 and feeds it back to the adaptive mirror 104.
The adaptive mirror 104 functions as a directivity angle control unit that controls the directivity angle in accordance with the control signal input from the control signal generation unit 108.
For example, when the angle of the adaptive mirror 104 is changed using a drive mechanism, the pointing angle is changed.

In the initial capture period, the adaptive mirror 104 controls the directivity angle of the initial capture light, which is the transmission light, until the error between the directivity angle of the reception light and the constant value falls within the threshold.
Also in the optical space communication apparatus 100 of the communication partner, the adaptive mirror controls the pointing angle of the light for initial capture in the same manner as described above. Thereby, initial capture and establishment of optical communication following this are performed between the optical space communication devices 100 and 100.

The initial capture unit 101 a in the light transmission unit 101 is a first light source unit that outputs the initial capture light.
The initial acquisition unit 101a includes a transmission light source 10-1, an optical intensity modulator 10-2, a pulse signal generator 10-3, an optical variable attenuator 10-4, and a control signal generation unit 10-5. The transmission light source 10-1 generates laser light of a single wavelength, continuous oscillation and constant polarization as light for initial capture.

The light intensity modulator 10-2 converts the light output from the transmission light source 10-1 into pulse light based on the pulse signal generated by the pulse signal generator 10-3.
The signal processing unit 101e controls pulse signal generation by the pulse signal generator 10-3. For example, the signal processing unit 101e instructs the pulse signal generator 10-3 to stop the generation of the pulse signal, thereby returning the initial capture light of pulse light to a continuous wave.

The light variable attenuator 10-4 attenuates the light power of the initial capturing light output from the light intensity modulator 10-2 in accordance with the control signal generated by the control signal generation unit 10-5.
The signal processing unit 101e controls the generation of the control signal by the control signal generation unit 10-5.
The control signal generation unit 10-5 generates, for example, a control signal for setting the light variable attenuator 10-4 to 0 dB according to the control of the signal processing unit 101e. The variable light attenuator 10-4 attenuates the light power of the initial capture light to the light power indicated by the control signal input from the control signal generation unit 10-5.
As described above, the light intensity modulator 10-2 and the variable light attenuator 10-4 function as a capture light conversion unit that converts the initial capture light into pulse light and adjusts the light power of the initial capture light. .

The optical communication unit 101b is a second light source unit that outputs communication light.
The optical communication unit 101b includes a transmission light source 11-1, an optical phase modulator 11-2, and a data signal generation unit 11-3. The transmission light source 11-1 generates, as communication light, laser light having a wavelength different from that of the initial capture light, continuous oscillation, and constant polarization.

The optical phase modulator 11-2 optically modulates the laser light output from the transmission light source 11-1 with a modulation signal including a data signal, and superimposes the data signal on the laser light.
As a modulation signal containing a data signal, for example, there is a BPSK (Binary Phase Shift Keying) modulation signal, but it may be a QPSK (Quadrature Phase Shift Keying) modulation signal or a QAM (Quadrature Amplitude Modulation) modulation signal.
The data signal generation unit 11-3 generates a modulation signal including the data signal and outputs the modulation signal to the optical phase modulator 11-2.

The WDM coupler 101c is a multiplexing unit that combines the initial capturing light output from the initial capturing unit 101a and the communication light output from the optical communication unit 101b.
The optical amplifier 101d amplifies light of a plurality of wavelengths multiplexed by the WDM coupler 101c and outputs the amplified light as transmission light. The optical power of the light output from the optical amplifier 101d is determined by the average power ratio of the optical powers of the input light of a plurality of wavelengths.
Therefore, in the light output from the optical amplifier 101d, when the light power of the initial capture light is attenuated, the light power of the communication light is increased accordingly.

FIG. 2 is a diagram showing spectral images of transmission light and reception light in the first embodiment. 2, a ₁ wavelength lambda initial acquisition light output from the transmitting light source 10-1, the wavelength of the initial acquisition for the light received as a received light from the optical space communication apparatus 100 of the communicating party is lambda ₃ There shall be. Wavelength of output from the transmission light sources 11-1-light communication is that lambda _2, the wavelength of light for communications sent to the communication partner from the optical space communication apparatus 100 is assumed to be lambda _4.
The optical power of the initial capturing light (λ ₁ , λ ₃ ) is set to be higher than that of the communication light (λ ₂ , λ ₄ ) in the optical space communication device 100 and the communication partner optical space communication device 100 Ru.

Next, the operation will be described.
FIG. 3 is a flowchart showing the operation of the optical space communication apparatus 100.
FIG. 4 is a diagram showing time change of optical power of the initial capturing light and the communication light in the first embodiment.
First, initial capture is started (step ST1).
Here, the initial capture unit 101a may output an initial capture light is a pulse beam having a wavelength lambda _1, the optical communication unit 101b outputs the communication light is a continuous wave of a wavelength lambda _2.
WDM coupler 101c is output to the optical amplifier 101d multiplexes the communication light of the initial capture light and the wavelength lambda ₂ wavelength lambda _1. The optical amplifier 101d amplifies the optical power of the transmission light multiplexed by the WDM coupler 101c, and outputs the amplified light as transmission light.

  The transmission light output from the optical transmission unit 101 is output to the transmission optical path by the wavelength separation filter 103, passes through the adaptive mirror 104, and is then output to space as transmission light by the optical antenna 105. Thus, the space optical communication apparatus 100 transmits the light for initial capture, and similarly, the space optical communication apparatus 100 of the other party of communication transmits the light for initial capture.

Next, adaptive mirror scan is performed (step ST2).
The control signal generation unit 108 generates a control signal in which the directivity angle of the received light received by the directivity angle detection unit 107 has a constant value, and feeds it back to the adaptive mirror 104.
The adaptive mirror 104 controls the pointing angle of the initial capturing light until the error between the pointing angle of the received light and the above-mentioned constant value is within the threshold according to the control signal input from the control signal generation unit 108 (step ST3) .

If the error of the pointing angle is larger than the threshold (step ST3; NO), the process returns to step ST2 and the adaptive mirror scan is continued.
If the error of the pointing angle falls within the threshold (less than the threshold) (step ST3; YES), the adaptive mirror 104 stops controlling the pointing angle of the initial capture light. Thus, initial capture is completed (step ST4).

Initial in acquisition period, as shown in FIG. 4, the transmission light comprising the wavelength lambda ₁ of the pulsed light initial capture light and wavelength lambda ₂ of the continuous wave communication light is transmitted to the communication partner.
When the initial acquisition is completed and the optical communication period starts, the signal processing unit 101e stops the generation of the pulse signal by the pulse signal generator 10-3 (step ST5).
The initial capture light output from the light intensity modulator 10-2 returns from pulse light to a continuous wave.

Next, the signal processing unit 101e instructs the control signal generation unit 10-5 to generate a control signal that makes the light power of the initial capture light lower than the average power P _{Ave of the} light input to the optical amplifier 101d. Let The variable optical attenuator 10-4 attenuates the optical power of the initial capture light as indicated by the downward arrow in FIG. 4 according to the control signal input from the control signal generation unit 10-5 (step ST6).

After this, optical communication is started between the optical space communication apparatus 100 and the optical space communication apparatus 100 of the communication counterpart (step ST7). The optical amplifier 101 d is driven by a constant drive current, and amplifies light of wavelengths λ ₁ and λ ₂ . At this time, the optical power of the light output from the optical amplifier 101 d is determined by the average power ratio of the optical powers of the input light of the wavelengths λ ₁ and λ ₂ . Therefore, when attenuating the optical power of the initial acquisition optical, optical power of the wavelength lambda ₂ of the communication light in transmitted light as indicated by the upward arrow in FIG. 4 increases relatively. This makes it possible to achieve both the optical power required for initial capture and the optical power required for optical communication.

  As described above, in the optical space communication apparatus 100 according to the first embodiment, when the initial capture is completed, the signal processing unit 101 e controls the variable optical attenuator 10-4 to attenuate the optical power of the initial capture light. . As a result, it is possible to secure both the optical power necessary for the completion of the initial acquisition and the optical power necessary for the optical communication, so that it is possible to realize the stable initial acquisition and the optical communication efficiently.

Second Embodiment
In the first embodiment, the conversion of the initial capture light into pulse light and the adjustment of the light power are performed by the light intensity modulator and the variable light attenuator.
In the second embodiment, the semiconductor optical amplifier executes conversion of the initial capture light into pulse light and adjustment of the light power. As a result, in comparison with the configuration shown in the first embodiment, the optical space communication apparatus can be miniaturized and the output can be increased.

FIG. 5 is a block diagram showing a configuration of an optical space communication apparatus 100A according to Embodiment 2 of the present invention. In FIG. 5, the same components as in FIG.
The optical space communication apparatus 100A includes an optical transmission unit 101A, an optical reception unit 102, a wavelength separation filter 103, an adaptive mirror 104, an optical antenna 105, a beam separation unit 106, a directivity angle detection unit 107, and a control signal generation unit 108. . The optical transmission unit 101A includes an initial acquisition unit 101a-1, an optical communication unit 101b, a WDM coupler 101c, an optical amplifier 101d, and a signal processing unit 101e-1.

The initial acquisition unit 101a-1 includes a transmission light source 10-1, a semiconductor optical amplifier 10-6, and an arbitrary waveform generation circuit 10-7.
The semiconductor optical amplifier 10-6 switches the waveform of the initial capture light output from the transmission light source 10-1 based on an arbitrary waveform signal generated by the arbitrary waveform generation circuit 10-7.
Here, an arbitrary waveform signal is referred to as an SOA drive signal. The semiconductor optical amplifier 10-6 adjusts the light power of the light output from the transmission light source 10-1.
As described above, the semiconductor optical amplifier 10-6 functions in the same manner as the trapping light conversion unit described in the first embodiment.

  The signal processing unit 101e-1 controls the generation of the SOA drive signal by the arbitrary waveform generation circuit 10-7. The arbitrary waveform generation circuit 10-7 outputs the SOA drive signal of the waveform instructed from the signal processing unit 101e to the semiconductor optical amplifier 10-6. For example, the semiconductor optical amplifier 10-6 converts the initial capture light into pulse light based on the SOA drive signal of the pulse signal.

FIG. 6 is a diagram showing temporal changes in optical power of the SOA drive signal, the initial capture light, and the communication light in the second embodiment. In the initial capture period, the signal processing unit 101e-1 instructs the arbitrary waveform generation circuit 10-7 to output the SOA drive signal of the pulse signal shown in FIG. 6 to the semiconductor optical amplifier 10-6. Semiconductor optical amplifiers 10-6, in response to the SOA driving signal of the pulse signal, has been the initial acquisition for light of the wavelength lambda ₁ outputted from the transmission light source 10-1 is switched to the pulsed light.

When the initial capture is completed and the optical communication period starts, the signal processing unit 101e-1 instructs the arbitrary waveform generation circuit 10-7 to transmit, for example, the SOA drive signal of a 0 V DC signal to the semiconductor optical amplifier 10-6. Make it output. Semiconductor optical amplifiers 10-6, when the SOA driving signal is applied, as indicated by the downward arrow in FIG. 6, and stops the output of the initial acquisition for the light having a wavelength of lambda _1.

The optical amplifier 101 d is driven by a constant drive current, and amplifies light of wavelengths λ ₁ and λ ₂ . The optical power of the light output from the optical amplifier 101d is determined by the average power ratio of the optical power of the input light of the wavelengths λ ₁ and λ ₂ .
Therefore, when attenuating the optical power of the initial acquisition light, as indicated by the upward arrow in FIG. 6, in the transmission light, the optical power of the communication optical wavelength lambda ₂ is relatively increased. This makes it possible to achieve both the optical power required for initial capture and the optical power required for optical communication.

As described above, in the optical space communication apparatus 100A according to the second embodiment, the semiconductor optical amplifier 10-6 converts the initial capture light into pulse light and adjusts the optical power of the initial capture light.
That is, the optical space communication apparatus 100A realizes the functions of the light intensity modulator 10-2 and the optical variable attenuator 10-4 in the optical space communication apparatus 100 according to the first embodiment by using the semiconductor optical amplifier 10-6. There is.
Thus, the optical space communication device 100A can be smaller than the optical space communication device 100.
Also, the semiconductor optical amplifier 10-6 can achieve higher output of the initial capturing light than the light intensity modulator 10-2.

Third Embodiment
In the first embodiment and the second embodiment, the configuration to control the directivity angle of the transmission light using the adaptive mirror 104 is shown, but in the third embodiment, the transmission light is distributed in multiples and each phase control is performed. An optical space communication apparatus that functions as an active phased array laser will be described.

  FIG. 7 is a block diagram showing a configuration of an optical space communication apparatus 100B in accordance with Embodiment 3 of the present invention. 7, the same components as in FIG. 1 and FIG. 5 are assigned the same reference numerals and explanation thereof is omitted. An optical space communication apparatus 100B includes an optical splitter 12, optical frequency shifters 13-1 to 13-N, optical amplifiers 14-1 to 14-N, and beam splitters (hereinafter referred to as BS) 15-1 to 15-N. , Optical receivers 16-1 to 16-N, optical phase synchronization circuits 17-1 to 17-N, control signal generation circuits 18-1 to 18-N, optical communication unit 101b, signal processing unit 101e-2, optical A reception unit 102, a wavelength separation filter 103, an optical antenna 105, a beam separation unit 106, and a directivity angle detection unit 107 are provided.

  The optical communication unit 101b in the third embodiment is a third light source unit that outputs communication light. The optical communication unit 101b includes a transmission light source 11-1, an optical phase modulator 11-2, and a data signal generator 11-3. The transmission light source 11-1 generates, as communication light, laser light of a single wavelength, continuous oscillation, and constant polarization.

  The optical phase modulator 11-2 optically modulates the laser light output from the transmission light source 11-1 with a modulation signal including a data signal, and superimposes the data signal on the laser light. The data signal generation unit 11-3 generates a modulation signal including the data signal and outputs the modulation signal to the optical phase modulator 11-2.

  The optical distributor 12 is a distribution unit that divides the light output from the optical communication unit 101b into local light emission to one optical path and signal light to the N (N> 1) optical path. The optical frequency shifters 13-1 to 13 -N are provided corresponding to the signal lights of the N optical paths distributed by the optical distributor 12, shift the frequency of the signal lights and output. The optical amplifiers 14-1 to 14-N are provided corresponding to the optical frequency shifters 13-1 to 13-N, respectively, and amplify the light output from each of the optical frequency shifters 13-1 to 13-N. .

The BSs 15-1 to 15-N output the signal light output from each of the optical amplifiers 14-1 to 14-N to the wavelength separation filter 103, and the local light and the optical amplifiers 14-1 to 14-N, respectively. Functions as a multiplexing unit that multiplexes the signal light output from the optical receiver 16-1 to the optical receivers 16-1 to 16-N.
The optical receivers 16-1 to 16-N, based on the output lights of the BSs 15-1 to 15-N, are optical phases between the signal lights in the signal lights outputted from the respective optical amplifiers 14-1 to 14-N. It is a phase error detection unit that detects an error. For example, the optical receivers 16-1 to 16-N perform heterodyne detection.

  The optical phase synchronization circuits 17-1 to 17-N respectively select the optical frequency shifters 13-1 to 13-N based on the optical phase error between the signal lights detected by the optical receivers 16-1 to 16-N. And an optical phase synchronization unit that synchronizes the optical phases of the signal lights in the plurality of signal lights. For example, the optical phase synchronization circuits 17-1 to 17-N are configured to transmit the relative phases of a plurality of signal lights detected by the optical receivers 16-1 to 16-N, respectively, to the optical frequency shifters 13-1 to 13-N. By performing feedback to each of the above as the instantaneous frequency, phase synchronization of each relative phase of a plurality of signal lights is performed.

The control signal generation circuits 18-1 to 18-N output the offset phase to each of the optical phase synchronization circuits 17-1 to 17-N under the control of the signal processing unit 101e-2.
The signal processing unit 101 e-2 controls the light phase synchronization circuits 17-1 to 17 -N in the initial capture period to turn the light phases of the plurality of signal lights into transmission light 19 having beam spread. Set to phase. When the initial capture is completed and the optical communication period starts, the signal processing unit 101e-2 controls the optical phase synchronization circuits 17-1 to 17-N to make the optical phases of the plurality of signal lights the same phase. The transmission light 20 is collimated by setting.

Next, the operation will be described.
The communication light output from the optical communication unit 101 b is distributed by the optical distributor 12 into local light of one optical path and signal light of N optical paths.
The optical frequency shifters 13-1 to 13-N shift the respective frequencies of the signal light in the N optical paths, and the optical amplifiers 14-1 to 14-N output from the respective optical frequency shifters 13-1 to 13-N. Amplified signal light.

The BSs 15-1 to 15-N output the signal lights output from the optical amplifiers 14-1 to 14-N to the wavelength separation filter 103. The BSs 15-1 to 15-N multiplex the local light and the signal light output from each of the optical amplifiers 14-1 to 14-N, and output the multiplexed light to each of the optical receivers 16-1 to 16-N. . The signal light output from each of the BSs 15-1 to 15-N is transmitted to the optical space communication apparatus 100B of the opposite communication partner via the wavelength separation filter 103 and the optical antenna 105. Transmitting light to the optical space communication apparatus 100B of the communication partner, for example, as in the first embodiment, the initial acquisition light or wavelength of the wavelength lambda ₁ is communication light lambda _2.

On the other hand, as for the received light received by the optical antenna 105, only the received light is output by the wavelength separation filter 103 to the beam separation unit 106. The received light is, for example, an initial capturing light of wavelength λ ₃ or a communication light of wavelength λ ₄ as in the first embodiment.
The beam separation unit 106 separates the received light and outputs the light to the light receiving unit 102 and the directivity angle detection unit 107. The light receiving unit 102 extracts data from the communication partner optical space communication apparatus 100B from the received light. The directivity angle detection unit 107 detects the directivity angle (arrival angle) of the received light.

The signal processing unit 101 e-2 controls the phase amount of the signal light distributed to each of the optical frequency shifters 13-1 to 13 -N in order to make the optical space communication device 100 B function as a phased array laser. It calculates according to the arrival angle detected by.
The control signal generation circuits 18-1 to 18-N generate control signals for setting the offset phases of the respective signal lights based on the phase amounts calculated by the signal processing unit 101e-2, and perform optical phase synchronization. It outputs to the circuits 17-1 to 17-N.

The optical phase synchronization circuits 17-1 to 17-N set the offset phase corresponding to the signal light by controlling the optical frequency shifters 13-1 to 13-N according to the control signal.
As a result, the optical space communication apparatus 100B can perform non-mechanical drive beam tracking by electronic control of the phase of the signal light without using an adaptive mirror that requires a mechanical drive mechanism.

  The signal processing unit 101 e-2 controls the optical phase synchronization circuits 17-1 to 17 -N in the initial capture period to control the plurality of signal lights distributed to the optical frequency shifters 13-1 to 13 -N, respectively. The light phase is set to a phase to be the transmission light 19 having a beam spread (defocus setting). As a result, the transmission light 19 has a beam spread as shown in FIG. 7, so the dynamic range of the initial capture is expanded.

  When the initial capture is completed and the optical communication period starts, the signal processing unit 101e-2 controls the optical phase synchronization circuits 17-1 to 17-N to the optical frequency shifters 13-1 to 13-N. The optical phases of a plurality of distributed signal lights are set to the same phase. As a result, the transmission light 20 becomes collimated light as shown in FIG. 7, so the light power of the transmission light in optical communication increases.

  As described above, in the optical space communication apparatus 100B according to the third embodiment, the signal processing unit 101e-2 controls the optical phase synchronization circuits 17-1 to 17-N in the initial capture period to obtain a plurality of signals. Each light phase of the light is set to a phase to be the transmission light 19 having a beam spread. When the initial capture is completed and the optical communication period starts, the signal processing unit 101e-2 controls the optical phase synchronization circuits 17-1 to 17-N to make the optical phases of the plurality of signal lights the same phase. Make it set. As a result, the dynamic range in the initial capture can be expanded, and the optical power of transmission light in optical communication can be increased.

  In the optical space communication apparatus 100B according to the third embodiment, the optical phase synchronization circuits 17-1 to 17-N perform electronic control of the beam propagation direction of transmission light by actively controlling the optical phases of a plurality of signal lights. . Thus, the optical space communication apparatus 100B functions as a phased array laser without using an adaptive mirror that requires a mechanical drive mechanism, and performs non-mechanical drive beam tracking by electronic control of the phase of signal light. It becomes possible.

Fourth Embodiment
The optical space communication apparatus 100B according to the third embodiment performs phase control of each of the multiple distributed light to electronically control the directivity angle.
An optical space communication apparatus 100C according to the fourth embodiment is an optical space communication apparatus that functions as an active phased array laser that handles light of multiple wavelengths, and is a light source that outputs communication light as a light source that outputs light for initial capture. To control the light power of the light for initial capture.

  FIG. 8 is a block diagram showing a configuration of an optical space communication apparatus 100C according to Embodiment 4 of the present invention. In FIG. 8, the same components as in FIG. 1, FIG. 5 and FIG. 7 will be assigned the same reference numerals and descriptions thereof will be omitted. The optical space communication apparatus 100C includes an optical splitter 12, optical frequency shifters 13-1 to 13-N, optical amplifiers 14-1 to 14-N, BSs 15-1 to 15-N, and optical receivers 16-1 to 16-. N, optical phase synchronization circuits 17-1 to 17-N, control signal generation circuits 18-1 to 18-N, wavelength separation filter 21, unit for initial capture 101a-2, unit for optical communication 101b, WDM coupler 101c, signal The processing unit 101 e-3, the light reception unit 102, the wavelength separation filter 103, the light antenna 105, the beam separation unit 106, and the directivity angle detection unit 107 are provided.

The initial capture unit 101a-2 is a fourth light source unit that outputs initial capture light having a single wavelength and a continuous wave, and includes the transmission light source 10-1, the semiconductor optical amplifier 10-6, and the arbitrary waveform generation. A circuit 10-7, an optical phase modulator 10-8 and a sawtooth wave generation circuit 10-9 are provided.
The optical phase modulator 10-8 phase modulates the output light of the transmission light source 10-1 based on the modulation signal of the sawtooth wave generated by the sawtooth wave generation circuit 10-9, and the frequency generated by the semiconductor optical amplifier 10-6 Apply the inverse characteristic of the shift. Thereby, it is possible to generate light for initial capture of pulse light whose frequency shift has been compensated. The phase modulation is, for example, serrodyne modulation.

The optical communication unit 101b in the fourth embodiment is a fifth light source unit that outputs communication light. The optical communication unit 101b includes a transmission light source 11-1, an optical phase modulator 11-2, and a data signal generator 11-3. The transmission light source 11-1 generates, as communication light, laser light of a single wavelength, continuous oscillation, and constant polarization.
Transmitting light to the optical space communication apparatus 100C of the communicating party, as in the first embodiment, the initial acquisition light or wavelength of the wavelength lambda ₁ is communication light lambda _2.
Receiving light from the optical space communication apparatus 100C is, similarly to the first embodiment, the initial acquisition light or wavelength of the wavelength transmitted from the optical space communication apparatus 100C of the communication partner lambda ₃ is a communication light lambda ₄ .

The WDM coupler 101c in the fourth embodiment is a multiplexing unit that multiplexes the initial capture light output from the initial capture unit 101a-2 and the communication light output from the optical communication unit 101b.
The wavelength separation filter 21 is a wavelength separation unit which is provided in the optical path for local light emission and transmits only the transmission light of the wavelength λ ₂ among the light distributed to the optical path for local light emission by the light distributor 12.
The light transmitted by the wavelength separation filter 21 is output as local light to the BSs 15-1 to 15-N.

The BSs 15-1 to 15-N in the fourth embodiment output the signal lights output from the optical amplifiers 14-1 to 14-N to the wavelength separation filter 103.
Also, BSs 15-1 to 15-N combine the local light of wavelength λ ₂ separated by the wavelength separation filter 21 with the signal light output from each of the optical amplifiers 14-1 to 14-N. It functions as a multiplexing unit for outputting to each of the optical receivers 16-1 to 16-N.

Next, the operation will be described.
After the transmission light output from the transmission light source 10-1 of the initial capture unit 101a-2 and the transmission light output from the transmission light source 11-1 of the optical communication unit 101b are multiplexed by the WDM coupler 101c, The optical distributor 12 distributes the local light of one optical path and the signal light of the N optical path. The wavelength separation filter 21 extracts the component of the wavelength λ ₂ from the local light distributed by the light distributor 12 and outputs the component as the final local light to the BSs 15-1 to 15-N.

The optical frequency shifters 13-1 to 13-N shift the respective frequencies of the signal light of the N optical paths distributed by the optical distributor 12, and the optical amplifiers 14-1 to 14-N transmit the optical frequency shifter 13-1. The signal light output from each of 13 to 13 N is amplified.
The BSs 15-1 to 15-N output the signal lights output from the optical amplifiers 14-1 to 14-N to the wavelength separation filter 103.

Also, BSs 15-1 to 15-N combine the local light output from the wavelength separation filter 21 with the signal light output from each of the optical amplifiers 14-1 to 14-N, and Output to each of 16-1 to 16-N.
The signal light output from each of the BSs 15-1 to 15-N is transmitted to the optical space communication apparatus 100C of the opposite communication counterpart via the wavelength separation filter 103 and the optical antenna 105.

As for the received light received by the optical antenna 105, only the received light is output to the beam separation unit 106 by the wavelength separation filter 103.
The beam separation unit 106 separates the received light and outputs the light to the light receiving unit 102 and the directivity angle detection unit 107. The light receiving unit 102 extracts, from the received light, data transmitted from the communication partner optical space communication apparatus 100C. The directivity angle detection unit 107 detects the directivity angle (arrival angle) of the received light.

The signal processing unit 101 e-2 is a pointing angle detection unit for measuring the phase amount of each signal light distributed to the optical frequency shifters 13-1 to 13 -N in order to make the optical space communication device 100 C function as a phased array laser. It is calculated according to the arrival angle detected by 107.
The control signal generation circuits 18-1 to 18-N generate control signals for setting the offset phases of the respective signal lights based on the phase amounts calculated by the signal processing unit 101e-3, and perform optical phase synchronization. It outputs to the circuits 17-1 to 17-N.

The optical phase synchronization circuits 17-1 to 17-N set the offset phase corresponding to the signal light by controlling the optical frequency shifters 13-1 to 13-N according to the control signal.
Thus, the optical space communication apparatus 100C can perform non-mechanical drive beam tracking by electronic control of the phase of signal light without using an adaptive mirror that requires a mechanical drive mechanism.

  Furthermore, the signal processing unit 101 e-3 controls the optical phase synchronization circuits 17-1 to 17 -N in the initial capture period, and the plurality of signals distributed to each of the optical frequency shifters 13-1 to 13 -N The light phase of the light is set to be the phase to be the transmission light 19 having beam spread (defocus setting). As a result, the transmission light 19 has a beam spread as shown in FIG. 8, so the dynamic range of the initial capture is expanded.

  When the initial capture is completed and the optical communication period starts, the signal processing unit 101e-3 controls the optical phase synchronization circuits 17-1 to 17-N to transmit the optical frequency shifters 13-1 to 13-N. The optical phases of a plurality of distributed signal lights are set to the same phase. As a result, the transmission light 20 becomes collimated light as shown in FIG. 8, so the optical power of the transmission light in optical communication increases.

  In the optical medium of the semiconductor optical amplifier 10-6, when the pulse light propagates, the refractive index changes according to the light power. With this change in refractive index, frequency shift occurs in the pulsed light of the initial capture light. When the pulse light having such a frequency shift is divided into a plurality and output as a phased array laser, the respective lights can not be in the same phase, which causes a decrease in the optical power of the output light.

Therefore, in the fourth embodiment, the reverse characteristic of the frequency shift is applied by serrodyne modulating the light output from the transmission light source 10-1 with a sawtooth signal. Thereby, it is possible to generate pulsed light of the initial capture light whose frequency shift has been compensated.
FIG. 9 is a graph showing time waveforms of a sawtooth signal, a frequency shift amount, and a frequency shift compensation signal. The sawtooth signal generated by the sawtooth wave generation circuit 10-9 is a signal with a period Tm, as shown in the upper graph of FIG.

The optical phase modulator 10-8 applies the modulation signal, which is the sawtooth signal, to the light output from the transmission light source 10-1. When the phase value of light changes from 0 to 2π, the optical frequency shifts by 1 / Tm due to the period Tm of the sawtooth wave.
In the fourth embodiment, the frequency shift amount is compensated by making the amount of frequency shift the inverse characteristic of the frequency shift generated in the transmission light by the semiconductor optical amplifier 10-6.

The frequency shift amount c shown in the lower graph of FIG. 9 is a frequency shift amount generated in one pulse of the initial capture light. The frequency shift compensation signal d has an inverse characteristic of the frequency shift amount c as shown in FIG. Therefore, by applying a frequency shift compensation signal d to the transmission light, it is possible to the optical frequency of the initial acquisition for the light to the optical frequency f ₀ of the reference.

The light electric field when the light output from each of the transmission light source 10-1 and the transmission light source 11-1 is output as a phased array laser and the optical electric field when the local light is output are represented by the following formulas (1) to (3) Can be represented by In Formula (1) ~ (3), f 1 is the optical frequency of the output from the transmission light source 10-1 light, _{f 2} is the optical frequency of the light output from the transmission light sources 11-1 . φ _{Si —} λ ₁ indicates the phase variation at the wavelength λ ₁ of the ith element (the ith optical path), and φ _{Si —} λ ₂ indicates the phase variation at the wavelength λ ₂ of the ith element (the ith optical path) There is. δφ _i (t) is a phase amount feedback-controlled by the optical frequency shifter 13-i, and f _AOM is a frequency shift amount of light shifted by the optical frequency shifter. φ _L (t) indicates the amount of phase change in the optical path of local light.
E _{Si λ 1} (t)
= E in _{_ 1} x exp [i {2 π (f ₁ + f _AOM ) t + _{Si Si _ 1} (t) + _{δ i i} (t)}] (1)
E _{Si λ 2} (t)
= E in _{λ 2} × exp [i { ₂ π (f ₂ + f _AOM ) t + _{Si Si λ 2} (t) + _{δ i i} (t)}]
E _L (t) = E _L × exp [i {2πf ₂ t + φ _L (t)}] (3)

For the local light, only the wavelength component of λ ₂ is transmitted by the wavelength separation filter 21. Therefore, signals detected in the reception frequency band of the optical receiver 16-1 to 16-N is a heterodyne detection signal of only the wavelength lambda _2. At this time, the signal of wavelength λ ₁ can be ignored, and the heterodyne detection signal is expressed by the following formulas (4) to (6).
| E _S1λ2 (t) −E _L (t) | ²
= 2 E in _λ 2 × E _L sin (2πf _AOM t + _{S S} 1 _{_ λ 2- L L} ) (4)
| E _S2λ2 (t) −E _L (t) | ²
= 2E _{in_λ} 2 × E _L sin (2πf _AOM t + φ _S 2 _{_ λ 2-} φ _L + _δ φ _l-2 (t)) (5)
δφ _l−i (t) = φ _{S1_λ2} −φ _{Si_λ2} (6)

The optical electric field when phase synchronization is performed with respect to the element of i = 1 can be expressed by the following equations (7) and (8), and the phase errors of different wavelengths propagating in the same optical path (element) are It can be expressed by equation (9).
The phase error shown in the following equation (9) is “0” when light propagating in the same optical path is an object, and the influence of the chromatic dispersion is ignored. In an optical frequency shifter such as AOM, the shift amount does not change even when the input light wavelength changes, so in the configuration using the optical frequency shifter, the following equation (9) is "0".
Therefore, by controlling and detecting a phase error of the wavelength lambda ₂ of light, the phase synchronization for the signal light of multiple wavelengths becomes possible.
E _{Si λ 1} (t)
= E in _{_ 1} x exp [i {2 π (f ₁ + f _AOM ) t + _{Si Si _ 1} (t) + _δ φ _l-i (t)}]
= E in _{λ 1} × exp [i {2 π (f ₁ + f _AOM ) t + Δφ _λi + φ _{S 1} _ _{λ 2} (t)}]
... (7)
E _{Si λ 2} (t)
= E in _{λ 2} × exp [i { ₂ ((f ₂ + f _AOM ) t + φ _{Si λ 2} (t) + _{δ l l-i} (t)}]
= E in _{λ 2} × exp [i { ₂ π (f ₂ + f _AOM ) t + _{S S 1} _ _{λ 2} }]
... (8)
Δφ _λi = φ _{Si_λ2} −φ _{Si_λ1} = 0 (9)

  Next, FIG. 10 is a diagram showing temporal changes in optical power of the initial capture light and the communication light. As shown in FIG. 10, the optical power per pulse of the initial capture light is from the optical space communication device 100 of one element (one optical path) shown in FIG. 1 by the phased array output of N elements (N optical paths). Will also grow.

Further, when the initial capture is completed and the optical communication period starts, the signal processing unit 101e-3 instructs the arbitrary waveform generation circuit 10-7 to generate an SOA drive signal for reducing the optical power of the initial capture light. Output to the optical amplifier 10-6. The semiconductor optical amplifier 10-6, the the SOA driving signal is applied, reducing the light power of the wavelength lambda ₁ of the initial acquisition light as indicated by the downward arrow in FIG. 10.

Each of the optical amplifiers 14-1 to 14-N is driven by a constant drive current as in the optical amplifier 101d in the first embodiment, and amplifies light of wavelengths λ ₁ and λ ₂ .
At this time, the optical power of the light output from each of the optical amplifiers 14-1 to 14-N is determined by the average power ratio of the optical power of the input light of the wavelengths λ ₁ and λ ₂ . Therefore, when attenuating the optical power of the initial acquisition optical, optical power of the wavelength lambda ₂ of the communication light in transmitted light as indicated by the upward arrow in FIG. 10 is relatively increased. This makes it possible to achieve both the optical power required for initial capture and the optical power required for optical communication.

  Although the optical space communication apparatus 100C according to the fourth embodiment includes the initial capturing unit 101a-2 including the semiconductor optical amplifier 10-6 as the initial capturing unit, the capturing light conversion unit Similarly to the first embodiment, the light intensity modulator 10-2 and the variable light attenuator 10-4 may be used.

  As described above, in the optical space communication apparatus 100C according to the fourth embodiment, the wavelength separation filter 103 generates and outputs local light of the wavelength component of the communication light. The optical receivers 16-1 to 16-N are based on light obtained by combining the local light output from the wavelength separation filter 103 and the output light of the plurality of optical amplifiers 14-1 to 14-N. The optical phase error between the signal light in the signal light output from each of the (-1) to (14) -N is detected. The optical phase synchronization circuits 17-1 to 17-N respectively operate the optical frequency shifters 13-1 to 13-N based on the optical phase error between the signal lights detected by the optical receivers 16-1 to 16-N. Are controlled to synchronize the optical phase between the signal lights in the plurality of signal lights. With this configuration, phase synchronization can be achieved with respect to multi-wavelength signal light.

  In the optical space communication apparatus 100C according to the fourth embodiment, the signal processing unit 101e-3 controls the optical phase synchronization circuits 17-1 to 17-N in initial capture to control the optical phases of the plurality of signal lights. Is set to the phase to be the transmission light having beam spread, and when the initial capture is completed, the optical phase synchronization circuits 17-1 to 17-N are controlled to make the respective optical phases of the plurality of signal light the same phase. Make it set. As a result, the dynamic range in the initial capture can be expanded, and the optical power of transmission light in optical communication can be increased.

  In the optical space communication apparatus 100C according to the fourth embodiment, when the initial capture is completed, the signal processing unit 101e-3 controls the semiconductor optical amplifier 10-6 to attenuate the optical power. As a result, it is possible to secure both the optical power necessary for the completion of the initial acquisition and the optical power necessary for the optical communication, so that it is possible to realize the efficient initial acquisition and the optical communication stably.

In the optical space communication apparatus 100C according to the fourth embodiment, the optical phase synchronization circuits 17-1 to 17-N control the optical frequency shifters 13-1 to 13-N to control the semiconductor optical amplifier 10-6. The frequency of each of the plurality of signal lights is shifted by a frequency shift amount that is reverse to the frequency shift that occurs when the initial capture light is made into pulsed light.
With this configuration, it is possible to prevent the decrease in the light power of the initial capture light due to the frequency shift of the pulse light of the initial capture light.

  In the first embodiment, the third embodiment and the fourth embodiment, the optical space communication apparatus handles two wavelengths of light for initial capture and light for communication, but the present invention is not limited to this. is not. For example, in the optical space communication apparatus according to the first to fourth embodiments, the optical communication unit may output multi-wavelength light as communication light.

As a method of realizing optical phase synchronization, although the method of controlling the optical frequency shifter with reference to the phase of a certain element (i = 1) using the result of heterodyne detection has been shown, the method is not limited to this. Absent.
For example, phase errors may be detected with a single photodetector using a dithering signal.
Further, the relative phase of each of the plurality of signal light may be fed back to the optical phase modulator to perform phase synchronization.
Also, an external signal source may be used as a signal source of a signal to be a reference.

  The present invention is not limited to the above embodiment, and within the scope of the present invention, variations or embodiments of respective free combinations of the embodiments or respective optional components of the embodiments. An optional component can be omitted in each of the above.

  Since the optical space communication device according to the present invention can efficiently and stably realize initial acquisition and optical communication, it can be used in various optical communication fields.

  10-1, 11-1 transmission light source, 10-2 light intensity modulator, 10-3 pulse signal generator, 10-4 light variable attenuator, 10-5, 108 control signal generator, 10-6 semiconductor optical amplifier, 10-7 Arbitrary Waveform Generation Circuit, 10-8, 11-2 Optical Phase Modulator, 10-9 Sawtooth Generation Circuit, 11-3 Data Signal Generator, 12 Optical Divider, 13-1 to 13-N Optical Frequency Shifter, 14-1 to 14-N, 101d optical amplifier, 15-1 to 15-N BS, 16-1 to 16-N optical receiver, 17-1 to 17-N optical phase synchronization circuit, 18-1 18-N control signal generation circuit, 19 transmission light, 20 transmission light, 21, 103 wavelength separation filter, 100, 100A to 100C optical space communication device, 101, 101A light transmitter, 101a, 101a-1, 101a-2 initial Acquisition unit, 101b Optical communication unit, 101c WDM coupler, 101e, 101e-1 to 101e-3 Signal processing unit, 102 Optical receiving unit, 104 Adaptive mirror, 105 Optical antenna, 106 Beam separation unit, 107 Directional angle detection unit .

Claims (7)

A first light source unit that outputs light for initial capture that is a single wavelength and a continuous wave;
A second light source unit that outputs communication light having a wavelength different from that of the initial capture light and being a continuous wave;
A capture light conversion unit that converts the initial capture light into pulsed light and adjusts the light power of the initial capture light;
A multiplexing unit that multiplexes the initial capture light and the communication light;
An optical amplifier that amplifies the light multiplexed by the multiplexing unit and outputs the amplified light as transmission light;
An optical space communication apparatus, comprising: a signal processing unit that controls the capture light conversion unit to attenuate the light power of the initial capture light when the initial capture is completed. The optical space communication apparatus according to claim 1, wherein the optical conversion unit for capture is a semiconductor optical amplifier. The optical space communication apparatus according to claim 1, wherein the second light source unit outputs multi-wavelength light as the communication light. A fourth light source unit that outputs an initial capturing light having a single wavelength and a continuous wave;
A fifth light source unit that outputs communication light having a wavelength different from that of the initial capturing light and being a continuous wave;
A capture light conversion unit that converts the initial capture light into pulsed light and adjusts the light power of the initial capture light;
A multiplexing unit that multiplexes the initial capture light and the communication light;
A distribution unit for dividing the light combined by the combining unit into a plurality of signal lights;
A plurality of optical amplifiers for amplifying and outputting each of the plurality of signal lights;
A phase error detector configured to detect an optical phase error between the signal lights of the plurality of signal lights;
An optical phase synchronization unit that synchronizes the optical phase between the signal lights of the plurality of signal lights based on the optical phase error between the signal lights detected by the phase error detection unit;
In the initial acquisition, the optical phase synchronization unit is controlled to set the optical phase of each of the plurality of signal lights to an optical phase to be transmission light having beam spread, and when the initial acquisition is completed, the optical phase synchronization unit An optical space communication apparatus comprising: a signal processing unit configured to control an optical phase of each of the plurality of signal lights to be set to the same phase. The optical space communication apparatus according to claim 4 , wherein the signal processing unit controls the capturing light conversion unit to attenuate the light power of the initial capturing light when the initial capturing is completed. The capture optical conversion unit is a semiconductor optical amplifier,
The optical phase synchronization unit is configured to shift the frequency shifts of the plurality of signal lights by a frequency shift amount having a reverse characteristic to the frequency shift that occurs when the initial capturing light is converted into pulse light by the semiconductor optical amplifier. The optical space communication apparatus according to claim 4 or 5, wherein the compensation is performed. The optical space communication apparatus according to any one of claims 4 to 6 , wherein the fifth light source unit outputs multi-wavelength light as the communication light.

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