JP3075909B2 - Spatial coherent optical transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial coherent optical transmission device used in the field of optical communication and the like.

[0002]

2. Description of the Related Art A conventional spatial light transmission device using coherent light detection will be described below. FIG. 14 is a configuration diagram of a beat signal detection device in a conventional wireless optical communication system. In FIG. 14, a signal light 1 is incident from an entrance window 2 provided with a condenser lens, passes through an optical multiplexer / demultiplexer 3, and is incident on one light receiving element 4a in a light receiving element array 4. On the other hand, the local oscillation light is generated by the semiconductor laser 5, collimated by the collimating lens 6, and then diffused by the diffusion optical element 7 to become a diffusion local oscillation light 8 which is a diffusion plane wave. After changing, the signal light 1
And enters the light receiving element array 4. here,
A selfoc lens array (lens spacing 1 mm, aperture 0.2) was used as the diffusion optical element 7. Due to the diffusing optical element 7, a plane wave component of the diffused local oscillation light 8a is present on the light receiving element array 4 at intervals of 0.05 degrees. The existence angle range is determined by the aperture of the diffusion optical element 7 which is a selfoc lens array, and is ± 11.5 degrees. If the angle range is extended beyond this range, the individual plane wave components become weak and cannot be applied to actual communication. Here, if the deviation of the incident direction of the signal light 1 is within ± 11.5 degrees, the beat signal can be detected by the diffusion local oscillation light 8a. 3 is rotated by an actuator to detect a beat signal.

[0003] To explain this actuator,
The optical multiplexer / demultiplexer 3 is a rotating stage 10 on which a magnet 9 is mounted.
It is installed above. The center of the rotary stage 10 is bonded to a rod with a soft resin adhesive (not shown). Further, coils 11 and 12 for generating a magnetic field in a direction perpendicular to the plane of FIG. 14 and in the horizontal direction are provided, and the rotation stage 10 and the optical multiplexer / demultiplexer 3 can be rotated by interaction with the magnet 9.

A signal detected by the light receiving element array 4 is processed by a control circuit 13 to optimize a current flowing through current sources 14 and 15. Thereby, the signal light 1 and the local oscillation light 8a
And coherent detection can be performed (wavefront tuning). The detected beat signal is processed by the beat signal frequency control circuit 16 to control the wavelengths of the signal light 1 and the local oscillation light 8a while maintaining a constant relationship. Is controlled by the temperature controller 17 (wavelength tuning).

[0005]

In the above-mentioned conventional configuration,
Normally, there is an advantage that high-speed data transmission can be performed, but there are the following problems 1 to 3.

[0006] 1. When a beat signal is not detected, for example, when a communication is established, it takes time to realize wavelength tuning by scanning a temperature or the like, which hinders an increase in communication speed.

[0007] 2. Similarly, when the communication is opened or the wavefront or wavelength is out of tune during data transmission and the beat signal cannot be detected, it is impossible to determine which of the wavelength tuning and the wavefront tuning is out of sync, and the tuning is performed again. Requires a lot of time. In particular, there is always a possibility that the wavefront is shifted when the mobile phone is installed and used on a moving body, and this is a serious problem.

[0008] 3. If the wavefront and wavelength shift during data transmission, or if an obstacle occurs on the optical path, there is a problem that data is lost during that time. Besides that,
The transmitting side could not detect the situation on the receiving side, and it was impossible at all to perform data transmission timing, confirm data reception, and verify transmitted data.

The present invention solves the above-mentioned conventional problem. By exchanging information on a data transmission / reception state between a transmitting side and a receiving side, high-speed communication can be performed even when a beat signal is not detected or cannot be detected. It is another object of the present invention to provide a spatially coherent optical transmission device that can perform data transmission and prevent data loss.

[0010]

According to the present invention, there is provided a spatially coherent optical transmission apparatus which emits a data signal as a first coherent light, generates a second coherent light, and generates a second coherent light. And a light receiving means for multiplexing and receiving the first coherent light and coherently detecting the data signal, wherein the light receiving means includes the first coherent light and Wavefront tuning means for tuning the wavefront of the second coherent light is provided , and both the light transmitting means and the light receiving means provide coherent light transmission conditions and beat signal strength.
A detection unit that detects at least one of a coherent optical detection situation including detection of a degree and a beat signal frequency ,
A control signal transmitting unit for transmitting a control signal corresponding to the situation information detected by the detecting unit, a control signal receiving unit for receiving the control signal, and a photocurrent received by the control signal receiving unit for transmitting the data signal A control unit is provided for controlling at least one of the wavelength of the light, the operation of continuation, suspension, and retransmission of the transmission, and the wavelength of the second coherent light , thereby achieving the above object.

Also, the spatial coherent light transmission device of the present invention generates an optical transmitter for emitting a data signal as a first coherent light, generates a second coherent light, and outputs the second coherent light and the first coherent light. the coherent light received by the multiplexing of the data signal to a spatial coherent optical transmission device having a light receiving means for coherent detection, to the light receiving means, the beat signal strength and the beat signal
A detecting unit for detecting a coherent photodetection situation including frequency detection, and a detecting unit based on the coherent photodetection situation.
Of the wavefronts of the first coherent light and the second coherent light
A wavefront tuning unit for performing tuning; and a control signal transmitting unit for transmitting a control signal according to the situation information detected by the detecting unit, wherein the optical transmitting unit includes a control signal receiving unit for receiving the control signal. And a control unit that controls at least one of the wavelength of the light of the data signal and the continuation, suspension, and retransmission operations of the light of the data signal by a photocurrent received by the control signal light receiving unit, Thereby, the above object is achieved.

Further, the spatial coherent optical transmission device of the present invention generates an optical transmitter for emitting a data signal as first coherent light, and generates second coherent light.
The second coherent light and the first coherent light received by the multiplexing, the data signal a spatial coherent optical transmission device having a light receiving means for coherent detection, to the light receiving means, the beat Signal strength and beat signal
A detection unit that detects a coherent optical detection situation including detection of a signal frequency, a control signal transmission unit that transmits a control signal according to the situation information detected by the detection unit, and a detection signal that is detected by the detection unit. A wavelength tuning unit for controlling the wavelength of the second coherent light so as to tune the wavelength based on the obtained situation information; and the detection unit.
The first coherent based on the situation information detected in
Wavefront tuning for tuning the wavefront of light and the second coherent light
Regulating means and is provided, on the light transmitting unit, and a control signal receiving unit for receiving the control signal, the continuation of the wavelength and transmission of light of the data signal by the light current received by the control signal receiving unit, discontinued and A control unit for controlling at least one of the retransmission operations, whereby the object is achieved.

Further, the spatial coherent optical transmission device of the present invention generates an optical transmission means for emitting a data signal as first coherent light, and generates second coherent light.
A spatial coherent optical transmission device comprising: a second coherent light and a first coherent light that are combined and received, and a light receiving unit that performs coherent detection of the data signal. A first detection unit that detects an optical transmission state, and a signal transmission unit that transmits a control signal corresponding to the status information detected by the first detection unit as an optical signal is provided . a signal receiving unit for receiving the optical signal, control of the received optical signal by the signal receiving section
The second detection for detecting the coherent optical transmission status from the control signal
An output unit, and a data signal of the optical signal received by the signal receiving unit.
Signal strength and beat signal frequency
A third detection unit for detecting a coherent detection state including :
A wavelength tuning unit for controlling the wavelength of the second coherent light so as to tune the wavelength based on the situation information detected by the second and third detection units, the first coherent light and the second
Wavefront tuning means for tuning the wavefront of coherent light is provided.
This achieves the above object.

Further, the spatial coherent optical transmission device of the present invention generates an optical transmitter for emitting a data signal as a first coherent light, and a second coherent light,
A spatial coherent optical transmission device comprising: a second coherent light and a first coherent light that are combined and received, and a light receiving unit that performs coherent detection of the data signal. A first detection unit for detecting an optical transmission situation, a signal transmission unit for transmitting a first control signal corresponding to the situation information detected by the first detection unit as the optical signal, and receiving a second control signal A control signal light receiving unit, and a control unit that controls at least one of the wavelength of the data signal light and the operation of continuation, suspension, and retransmission of the data signal light by a photocurrent received by the control signal light reception unit; the light receiving means, a signal receiving unit for receiving the optical signal, a second detector for detecting the first control signal or al coherent light transmission state of the received optical signal at the signal receiver, the signal Receiving
Beat signal strength from the data signal of the optical signal received by the section
Coherent optical detection, including detection of beat and beat signal frequencies
A third detection unit that detects a wave condition, a wavelength tuning unit that controls the wavelength of the second coherent light so as to tune the wavelength based on the situation information detected by the second and third detection units,
Based on the situation information detected by the third detection unit, the first
Of the wavefronts of the coherent light beam and the second coherent light beam.
A wavefront tuning means for performing tuning, and a control signal transmitting section for transmitting as a second control signal according to the situation information detected by the third detecting section . You.

Further, preferably, the coherent optical detection state detected by the detection unit in the spatial coherent optical transmission device of the present invention includes detection of a noise current intensity, thereby achieving the above object.

Still preferably, in a spatial coherent optical transmission apparatus according to the present invention, a temperature and an oscillation wavelength are detected as a coherent optical transmission state detected by a detection unit, thereby achieving the above object. More specific
Specifically, the detection section has a wavelength filter, and the wavelength filter
A structure that detects the oscillation wavelength from the transmittance of light that has passed through the filter
Can be achieved. Also, the detection unit may be an optical diffraction grating.
From the diffraction angle of the light incident on the optical diffraction grating.
A configuration for detecting the vibration wavelength may be adopted.

Also, the spatial coherent light transmission device of the present invention generates an optical transmitter for emitting a data signal as first coherent light, generates second coherent light, and generates the second coherent light and the first coherent light. A spatially coherent optical transmission device having optical receiving means for multiplexing and receiving the coherent light beams and coherently detecting the data signal , provided in the optical receiving means, wherein the first coherent light beam and the second A wavefront tuning means for tuning the wavefront of the second coherent light; and a wavelength tuning means provided in at least one of the light transmitting means and the light receiving means for tuning the wavelengths of the first coherent light and the second coherent light. And a wavelength tuning means for performing the above, whereby the above object is achieved.
Further, the spatial coherent optical transmission device of the present invention is a spatial coherent optical transmission device that receives a first coherent light transmitted as a data signal by combining a second coherent light with the second coherent light, and coherently detects the data signal. Wavefront tuning means for tuning the wavefronts of the first coherent light and the second coherent light, and wavelength tuning means for tuning the wavelengths of the first coherent light and the second coherent light And coherent optical transmission status , beat signal strength
The detection unit detects at least one of the coherent optical detection states including the detection of the degree and the beat signal frequency , and a control signal corresponding to the detection of the wavelength of the light of the data signal and the operation of the continuation, stop, and retransmission of the data signal. A control unit that controls at least one of the first and second coherent lights,
An optical transmitter for generating the second coherent light and the control signal from a common light emitting unit and transmitting the first coherent light and the control signal; and an optical transmitter transmitted from another spatial coherent optical transmission device. A light receiving unit for receiving and receiving the first coherent light, the control signal, and the second coherent light generated by the light emitting unit with a common light receiving unit, and performing bidirectional communication. As a result, the above object is achieved. The wavefront tuning means,
An envelope detection circuit for detecting the amplitude of the beat signal, a determination circuit for determining the state of the wavefront tuning based on the amplitude of the beat signal detected by the envelope detection circuit, and a control signal corresponding to the determined information on the wavefront tuning And a control signal transmitting unit that transmits the control signal.

[0018] Still preferably, in the spatial coherent optical transmission system of the present invention, the light receiving unit, a filter unit for separating the received signal into the control signal and the beat signal, the control signal separated by the filter unit And a beat signal detector for coherently detecting the beat signal separated by the filter unit, thereby achieving the above object. Previous
The control signal is light whose intensity is modulated with respect to the data signal.
It can be configured as a signal.

[0019]

According to the first aspect of the present invention, data transmission is performed while confirming the coherent detection status by the optical receiving means at the time of establishing communication or the like, and the coherent detection status is such that a beat signal is not detected by the detection unit. In addition, since the information is transmitted from the control signal transmitting unit to the control signal light receiving unit of the optical transmitting unit and the control unit controls the transmission of the data optical signal, even if the beat signal is not detected, the same data signal is transmitted. If retransmitted, data loss when the beat signal is not detected is eliminated. At this time, the wavelength tuning unit controls the wavelength of the second coherent light so that the wavelength is tuned based on the detection status information detected by the detection unit. The wavelength can be easily tuned and higher-speed data communication becomes possible.

Further, according to the configuration of the second aspect, even if the beat signal cannot be detected only by changing the wavelength of the receiving side depending on the usage state of the receiving side, the receiving side detects the beat signal detecting state and transmits the information to the transmitting side. Therefore, if a semiconductor laser is used for each of the transmission side and the reception side, a beat signal within the operating temperature range of the semiconductor laser can be detected.

Further, according to the third aspect of the present invention, the receiving section detects the beat signal detection state and controls the oscillation wavelength of itself, thereby detecting the beat signal without changing the wavelength on the transmitting side. A number of receivers can be installed for one transmitter, and applications such as a local area network are also possible.

Furthermore, according to the configuration of claim 4, when the receiving unit attempts to tune the wavelength only by looking at the beat signal, if a laser is used on each of the transmitting side and the receiving side, for example, the beat signal frequency, that is, the two lasers are used. If it is not possible to detect the wavelength shift and there is a wavelength shift, there is no guideline on whether to increase or decrease the wavelength of the local oscillation light, but if the transmitter transmits data on its own wavelength, The wavelength tuning of the receiving unit is further simplified.

Further, according to the configuration of the fifth aspect, the transmission side and the reception side monitor each other's situation, so that retransmission of data, laser failure, and the like are determined, and each can be optimally controlled. In particular, when the wavefront and the wavelength are not tuned, it is impossible to monitor the two-way coherent optical transmission devices with each other, but it becomes possible only by using the light intensity modulation and the direct detection system together.

Furthermore, according to the configuration of claim 11 , it is possible to inform the user whether communication is possible by knowing the noise current intensity and the like, so that the user can accurately grasp the cause of the communication failure. Becomes

Further, according to the structure of the twelfth aspect , the receiving side can accurately detect the temperature and the oscillation wavelength of the oscillation side,
If the beat signal cannot be detected, it is known that the wavefront tuning has been lost, and the guidelines for wavelength tuning and wavefront tuning can be understood.

Further, according to the configuration of claim 7 , the optical transmitter
The stage comprises a first coherent light, a second coherent light,
And a control signal are generated from a common light emitting unit,
The optical receiver and the control signal, and
The first core transmitted from the spatial coherent optical transmission device of
Generates the coherent light, the control signal, and the light emitting unit
Receiving and receiving the second coherent light
Communication, it is possible to perform bidirectional communication. I
Since the light emitting portion and the light receiving portion are shared, for example, if a semiconductor laser is used for the light emitting portion, the number of semiconductor lasers used can be reduced, and the cost can be reduced.

Furthermore, by making the coherent optical signal receiving section and the control signal receiving section common, the circuit configuration is simplified and the size and weight of the apparatus can be reduced.

[0028]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 is a block diagram of a spatially coherent optical transmission apparatus showing a first embodiment of the present invention. In FIG. 1, a data source 21, which is a generator of data to be transmitted, is connected to a data storage 22,
Data from the signal source 21 is temporarily stored in the data storage 22. The LD driver 23 to which the data storage 22 is connected is connected to the transmitting LD 24 and controls the driving of the transmitting LD 24 to emit an optical signal corresponding to the data from the data storage 22. Further, the light receiving element 25 for the control optical signal is connected to the data storage 22, and is connected to the data storage 22 via the control circuit 26.
And receives and demodulates a control optical signal emitted from the receiving side, and outputs the demodulated signal to the data storage 22. The transmission unit is configured as described above. On the other hand, the basic configuration of the receiving unit is as follows. That is, the optical filter 28 and the optical multiplexer / demultiplexer 29 serving as a beam splitter are provided at a predetermined interval, and an optical signal from the transmission-side LD 24 is input to the optical multiplexer / demultiplexer 29 via the optical filter 28. For this optical multiplexer / demultiplexer 29,
A local oscillation LD 30, which generates local oscillation light, a collimating lens 31, an optical multiplexer / demultiplexer 32, which is a beam splitter, and a diffusion micro lens 33, which is a light diffusing element, are provided. Further, the light passes through an optical multiplexer / demultiplexer 32 and is diffused by a diffusion microlens 33 to produce a diffuse plane wave, which is input to an optical multiplexer / demultiplexer 29. A light receiving element 35 is provided via a condenser lens 34a so as to face the optical multiplexer / demultiplexer 29. The optical multiplexer / demultiplexer 29 multiplexes the signal light and the diffusion plane wave, and passes through the condenser lens 34a. The light is incident on the light receiving element 35. A current-voltage conversion circuit (hereinafter referred to as an IV circuit) 36 to which the light receiving element 35 is connected is connected to a high-pass filter 37 which is a high-frequency transmission filter, and a band which is an intermediate frequency transmission filter to which the high-pass filter 37 is connected. The pass filter 38 includes a frequency-voltage conversion circuit (hereinafter referred to as an fV circuit) 39a and a comparator 40a.
Is connected to a beat signal demodulation circuit 42 to which an output terminal 41 is connected. A beat signal detection circuit 43 is configured by the IV circuit 36, the high pass filter 37, the band pass filter 38, the fV circuit 39a, the comparator 40a, and the beat signal demodulation circuit 42, and detects a beat signal.

A mark rate detection circuit 44 to which the beat signal demodulation circuit 42 is connected detects a mark rate from the detected beat signal. The fV circuit 39b to which the output terminal of the high-pass filter 37 is connected is connected to the comparator 40.
b is connected to one input terminal and the other input terminal
The output terminal of the mark ratio detection circuit 44 is connected. The fV circuit 39b and the comparator 40b form a wavelength tuning circuit 45, which tunes the wavelength from the beat signal.

Further, the envelope detection circuit 46 to which the output terminal of the band pass filter 38 is connected is provided with a comparator 40c.
And the comparator 40c and the fV circuit 39
The output terminal of the local oscillation LD3 is connected to the discrimination circuit 48.
A light emission intensity of 0, a beat signal intensity, and a beat signal frequency are determined. The output terminals of the temperature controller 47 and the determination circuit 48 to which the output terminal of the comparator 40b is connected are connected to the local oscillation LD 30. The discriminating circuit 48 is connected to an optical shutter 50 using a liquid crystal plate via a control circuit 49, and outputs a control signal from the control circuit 49 according to the output of the discriminating circuit 48. The optical shutter 50 is controlled by the control signal. ON / OFF control.

The actual data transmission according to the above configuration will be described below. First, on the transmitting side, the data source 21
As shown in FIG. 2A, a pulse group (corresponding to 80 K bits) having a time width of 0.4 msec is generated every 0.5 msec, and the data is stored in the data storage 22 and at the same time, passed through the LD driver 23. Driving the transmitting LD 24 which is a laser. At this time, the transmission side LD 24
Is changed corresponding to the data 1 and 0, and as shown in FIG. 2B, the oscillation frequency ν of the light is changed according to the data.
Oscillate at 1, ν2.

Next, on the receiving side, the wavelength λ3 (λ3 is the wavelength of the oscillation frequency ν3,
A beat signal is excited in the light receiving element 35 by superimposition with a diffuse plane wave having a wavelength of λ1, λ2, and the like (which has the same relationship as that of the wavelength of λ3). The frequencies are | ν3-ν1 | and | ν3-ν2 |. In this embodiment, as shown in FIG. 3A, | ν3−ν1 | = 400M
Hz, | ν3−ν2 | = 200 MHz.

Here, the wavelength tuning will be described. A signal generated in the light receiving element 35 is converted from a current component to a voltage component by an IV circuit 36, and then only a beat signal component is extracted by a high-pass filter 37. . The average frequency of the output is converted to a voltage by the fV circuit 39b. The comparator 40b compares the output from the fV circuit 39b with a predetermined voltage (a voltage corresponding to an average frequency based on the mark ratio obtained from the mark ratio detection circuit 44) to control the temperature controller 47. Then, the frequency of the local oscillation LD 30 is controlled so that the wavelength is tuned by the output of the temperature controller 47.

The demodulation of the beat signal will be described. The other output of the high-pass filter 37 is used to cut the noise component by the band-pass filter 38 that transmits only the beat signal, and then the frequency is reduced by the fV circuit 39a. And the comparator 40a demodulates 1 or 0 of the data from the voltage by the comparator 40a.
On the other hand, the amplitude of the output that has passed through the band-pass filter 38 is detected by the envelope detection circuit 46, and further subjected to threshold processing by the comparator 40c. The result signal is input to the determination circuit 48.

Further, the beat signal demodulation circuit 42
When K bits (0.4 msec) of data are received,
The optical shutter 50 is controlled by a control signal corresponding to the end of data group reception.
Is transmitted to the transmission unit 26 side. The transmitting section 26 receives this optical signal with the light receiving element 25 and transmits the next data.

At this time, if a wavelength shift or a wavefront shift occurs suddenly, data during the shift is lost. When the beat signal intensity does not satisfy a certain C / N ratio due to a situation such as a wavelength shift due to a temperature change or the like during transmission of a certain data group, an optical shutter 50 is provided by a control circuit 49 as a control signal generation circuit through a determination circuit 48. On and off. The on / off signal as the control signal is the local oscillation laser 3
The light intensity from 0 is varied as shown in FIG. 3b. At this time, the information to be transmitted has been encoded. The transmitting side receiving this optical signal can know information on the transmitting side (in this case, data loss due to wavelength shift) by demodulating the encoded signal with a demodulation circuit (not shown).
Further, the control circuit 26 controls the transmission of the optical signal based on the information. For example, in this embodiment, the information to be transmitted can be known by monitoring the local oscillation light intensity (eg, monitoring the current of a light receiving element (not shown) attached to the local oscillation laser 30 which is a semiconductor laser element). Possible), beat signal frequency discrimination status, beat signal amplitude detection status, and the like. According to this embodiment, even when a beat signal of a predetermined frequency is not detected by the demodulation circuit 42, a beat signal current of several GHz is detected by the fV circuit 39b if the wavelength is tuned by about 0.1 nm. Therefore, in this case, it can be seen that the wavefront tuning is performed but the wavelength tuning is not performed.
If the wavelength tuning is deviated, the wavelength of the temperature controller 47 is scanned to control the frequency, thereby performing the wavelength tuning again. The thermal response speed of the semiconductor laser we used in this example was 100 KHz, and the above operation could be performed within 0.05 msec. Thereafter, the data group that could not be received is retransmitted from the data storage 22.
When the retransmission of this data group is completed, the stored data is cleared and the next data is transmitted. In this way, information transmission from the receiving side to the transmitting side is performed once every 0.5 msec, and the pulse width can be made sufficiently wider than that of normal data transmission. Therefore, the direct detection method is sufficient. Actually, a baseband modulation method of 1 Mbps was used. Also,
By including the parity of the transmission data in the data, the data can be retransmitted when a bit error occurs.

As described above, in the present embodiment, data transmission at 160 Mbps can be performed without any data loss.
80 Mbps when data loss occurs at a rate of 1/2
Data transmission.

(Embodiment 2) FIG. 4 is a block diagram of a spatially coherent optical transmission apparatus according to a second embodiment of the present invention. In FIG. 4, an IV circuit 36a to which the light receiving element 25 is connected includes a bandpass filter 38a and an fV circuit 3
9c, a comparator 40d and a data storage 22 via a control circuit 61.

The band pass filter 38b to which the IV circuit 36b is connected includes an automatic gain circuit (hereinafter referred to as an AGC circuit) 62a, an fV circuit 39d, and a comparator 4
0e is further connected to the demodulation circuit 42a to monitor the control signal. The high-pass filter 37a to which the IV circuit 36b is connected includes a band-pass filter 38c, an AG
The C signal is connected to the C circuit 62b, the phase detector 63, the comparator 40f, and the demodulation circuit 42b, and the beat signal is coherently detected. Further, the low pass filter 64 to which the IV circuit 36b is connected, the fV circuit 39e to which the high pass filter 37a is connected, and the discriminating circuit 48a to which the comparator 40h is connected,
The control circuit 65 is connected to an optical modulator 66 interposed between the collimator lens 31 and the optical multiplexer / demultiplexer 32 and modulates the light from the local oscillation LD 30 based on the output of the discrimination circuit 48a. The local oscillation LD 30 includes a comparator 40g.
Is connected to a temperature controller 47 to which an output terminal of the local oscillation LD 30 is connected, an APC circuit 68 to which a DC power supply 67 for supplying a DC current to the local oscillation LD 30 is connected,
The local oscillation LD 30 is controlled by each output signal.

With the above configuration, first, on the transmission side, the LD driver 23 is driven while the signal from the data source 21 is stored in the data storage 22, and an optical signal is output from the transmission side LD 24. At this time, the oscillation wavelength is λ1, and phase modulation is performed by a phase modulator (not shown) in accordance with data 1 and 0.

Next, on the receiving side, the local oscillation LD 30 emits light at the wavelength λ3, and its amplitude is modulated by the optical modulator 66 into a sine wave. In other words, the situation on the receiving side is modulated by modulating the frequency of the sine wave and transmitted to the transmitting side. The local oscillation light is multiplexed with the signal light by the optical multiplexer / demultiplexer 29 and enters the light receiving element 35. The total current I excited by the light receiving element 35 is calculated by using the frequency ω of the frequency modulation of the local oscillation light by the optical modulator 66 as an external modulator and the beat signal frequency fb, and I = Asin (ωt + φ1) cos ( fb + φ2) + DC current. Here, as shown in FIG. 5A, the beat signal frequency fb was set to 200 MHz, and the frequency ω of the frequency modulation by the optical modulator 66 was set to 2 to 10 MHz. This signal is subjected to current-voltage conversion by the IV circuit 36b, and then guided to the band-pass filter 38b and the high-pass filter 37a. The transmission frequency band of the high-pass filter 37a is 100 MHz or more. The transmission frequency band of the band-pass filter 38b is 100 KHz to 20 MHz.
Which is sufficient to separate the two frequency signals. The signal passed through the band-pass filter 38b is AGC
After passing through the circuit 62a, the signal is demodulated by the fV circuit 39d and the comparator 40e into the original frequency modulation signal by the optical modulator 66 in the demodulation circuit 42a, and the state of the signal can be monitored.

On the other hand, the signal passes through the IV circuit 36b and the high-pass filter 37a, and passes through the band-pass filter 38c (the transmission band 1).
The signal transmitted through (00 to 300 MHz) is only a beat signal component. This signal, as shown in FIG.
A beat signal having a constant strength is obtained by the circuit 62b. Thereafter, phase detection is performed by the phase detector 63, and the original digital data is demodulated through the comparator 40f and the demodulation circuit 42b.

Further, in the wavelength tuning, the mark ratio is detected by the mark ratio detection circuit 44 in the same manner as in the first embodiment.
The expected average beat frequency is compared with the output of the frequency discrimination circuit by the comparator 40g, and the temperature controller 47 performs the comparison with the local oscillation LD 30 based on the comparison output. At this time, the luminous efficiency of the local oscillation LD 30 changes depending on the temperature. In this case, the DC power supply is controlled by the APC circuit 68 so that the optical power becomes constant from the current value of the light receiving element (not shown) attached to the local oscillation LD 30. The injection current injected from 67 is controlled.

The strength of the beat signal is determined by detecting the amplitude of the beat signal by the envelope detection circuit 46 after the band-pass filter 38c. As a result, the determination circuit 4
8a drives the control circuit 65 which is a control signal generation circuit. Here, the light is modulated by an optical modulator 66 via the control circuit 65.

Further, in this embodiment, the local oscillation LD 30 which is a semiconductor laser is formed by using the APC circuit 68.
As a result, the DC current component excited by the light receiving element 35 could be kept substantially constant. When this unit is used under strong background light (sunlight, illumination light, etc.), the magnitude of the background light is reduced by lowering the AC component of the output of the IV circuit 36b with a low-pass filter 64. Can be monitored. Of course, if the background light becomes large, a sufficient C / N ratio cannot be obtained, so that the discrimination circuit 48a transmits the fact to the transmitting side. The data transmitted to the transmitting side is a beat signal detection intensity status (wavefront tuning, wavefront tuning status), a beat signal frequency status (wavelength tuning information), a status of the local oscillation LD 30, and a background light intensity. As shown in (1), the frequency of the frequency modulation signal by the optical modulator 66 is changed according to those situations. On the transmission side, an optical signal (here, an optical modulator 66) extracted from the optical multiplexer / demultiplexer 32, which is a beam splitter, by the local oscillation LD 30.
1) is received by the light receiving element 25, and is converted from current to voltage by the IV circuit 36a, and then is subjected to the signal by the band-pass filter 38a having the same characteristics as the band-pass filter 38b. Only the component is detected, and the frequency is converted to a voltage by the fV circuit 39c, and the voltage is demodulated by comparing the voltage with a predetermined voltage by the comparator 40d. Based on the demodulated signal, the control circuit 61 determines optical signal transmission control such as data transmission, retransmission, and transmission stop.

As described above, according to the present embodiment, the receiving side can always inform the transmitting side of the state, and data can be transmitted during that time.

(Embodiment 3) FIG. 7 is a block diagram of a spatial coherent optical transmission apparatus according to a third embodiment of the present invention. This configuration is an optical transmission / reception unit, in which a transmitter and a receiver are integrated. Has become. In FIG. 7, a data storage 22a is connected to a semiconductor LD via an LD driver 23a.
30a. This semiconductor LD 30a is used as a transmission side LD and also as a local oscillation LD. Also, the f-V to which the high-pass filter 37a is connected
The circuit 39e is connected to the temperature controller 47 via the comparator 40g, and is connected to the band-pass filter 38c.
Is connected to the comparator 40.
h is connected to the discrimination circuit 48b. These temperature controller 47 and determination circuit 48b are semiconductor LDs.
30a. Further, the determination circuit 48b
Is connected to the collimating lens 31.
And the optical modulator 66a interposed between the optical multiplexer / demultiplexer 32.

First, a description will be given of a time of data transmission with the above configuration. Data transmission is performed by the Manchester method. That is, when the signal of the data source is 1, it changes from the high level to the low level, and when the signal of the data source is 0, it changes from the low level to the high level. Semiconductor LD
30a has an LD driver 23a such that its oscillation wavelength becomes λ1 and λ2 according to the high level and the low level.
More current is injected. At this time, the optical modulator 66a
Does nothing, and the light of the wavelengths λ1 and λ2 is radiated and transmitted at a certain solid angle via the optical multiplexer / demultiplexer 32.

Next, the reception time will be described. Semiconductor L
D30a oscillates at a wavelength λ3 slightly different from the signal light wavelengths λ1 and λ2, is multiplexed by the optical multiplexer / demultiplexer 29 with the signal light arriving from the transmission side, and is received by the light receiving element 35. As in the second embodiment, the semiconductor LD 30 is controlled by the optical modulator 66a.
The local oscillation light from a is frequency-modulated. Here, in the same manner as in the second embodiment, the beat signal is demodulated by the demodulation circuit 42b, and its own control signal by the optical modulator 66a is demodulated by the demodulation circuit 42a.

Further, the wavelength tuning will be described. In this embodiment, since the Manchester system is adopted, the average frequency of the beat signal is always constant without depending on the mark rate, and (| ν3−ν1 | + | ν3−ν2 |) / 2, so that the mark ratio detection circuit 44 in the first and second embodiments becomes unnecessary.

Here, the transmitting side will be described again.
On the transmitting side, the control light of the wavelength λ3, which has been subjected to external modulation and emitted by the local oscillation LD 30a on the receiving side, is received by the light receiving element 35 via the optical filter 28 and the optical multiplexer / demultiplexer 29. The beat signal of the light of the wavelengths λ1 and λ2 emitted by itself and the received control light of λ3, and the control signal on the light receiving side provided by the light modulator 66a on the light receiving side are detected as the light receiving current. Of these, only the control signal is selected by the band-pass filter 38b and demodulated by the method described in the second embodiment, so that the transmission side can monitor the light receiving side. Since there is no need to tune the wavelength on the transmitting side, the wavelength tuning circuit may be turned off to save power. As described above, according to this embodiment, transmission and reception can be performed by one device.

(Embodiment 4) FIG. 8 is a block diagram of a spatial coherent optical transmission apparatus showing a fourth embodiment of the present invention, and this configuration is an optical transmission / reception apparatus. 8, the fV circuit 39e to which the output terminal of the high-pass filter 37a is connected is connected to a control circuit 65b via a comparator 40g. The envelope detection circuit 46b to which the output terminal of the band-pass filter 38c is connected is connected to the comparator 40h. The output terminals of the fV circuit 39e and the comparator 40h, and the semiconductor LD 30a are connected to the discrimination circuit 48c. Signal detection status and semiconductor L
D30a is monitored. These control circuits 65b
The discrimination circuit 48c is connected to the local oscillation LD 30a. The discrimination circuit 48c is connected to the control signal LED69 via the light modulator 66b. Further, a light receiving element 35a, an IV circuit 36a, a high-pass filter 37
a, a light receiving unit provided opposite to the optical filter 28b separately from a series circuit for coherent detection of a beat signal, which is composed of a band-pass filter 38c, an AGC circuit 62b, an envelope detection circuit 46a, a comparator 40f, and a demodulation circuit 42b. A series circuit including an element 35b, an IV circuit 36b, a band-pass filter 38b, an fV circuit 39d, a comparator 40e, and a demodulation circuit 42a is configured, and a control signal is monitored.

The operation at the time of data reception with the above configuration will be described. The transmitting side (not shown) transmits the data by a method of changing the emission intensity with the oscillation wavelength λ1 according to 1 or 0 of the data to be transmitted. On the receiving side, the received signal light and a diffuse plane wave of wavelength λ3 generated by itself are multiplexed by an optical multiplexer / demultiplexer 29 which is a beam splitter, and received by a light receiving element 35a. When the data is 1, the current flowing through the light receiving element 35a is A1cos (2π (ν1−ν3) t + φ), and when the data is 0, the current is A2cos (2π (ν1).
−ν3) t + φ) (where A1> A2). This current is converted from a current to a voltage by an IV circuit 36a, and then converted to a high-pass filter 37a and a band-pass filter 38.
The signal is guided to the AGC circuit 62b via c. Thereafter, envelope detection is performed by the envelope detection circuit 46a, threshold processing is performed by the comparator 40f, and the original digital data is demodulated by the demodulation circuit 42b.

Next, wavelength tuning will be described. In the present embodiment, a two-electrode DFB laser (tunable wavelength laser) is used as the semiconductor LD 30a, and a wavelength can be largely changed only by an injection current without using a controller unlike the first embodiment (approximately). 4 nm). More specifically, the beat frequency of the beat signal is converted into a voltage by the fV circuit 39e, and the voltage is converted into a voltage by the comparator 40e.
g and is compared with a predetermined voltage (corresponding to | ν3-ν1 |). The semiconductor LD 30a may be controlled by changing the drive current by the control circuit 65b according to the output.

On the other hand, the output detected by the envelope detection circuit 46b by the envelope detection circuit 46b is compared with a predetermined voltage by the comparator 40h, and then sent to the discrimination circuit 48c. The discrimination circuit 48c monitors the semiconductor LD 30a, and also receives the output from the fV circuit 39e and monitors the beat frequency. This determination circuit 48c
Is a control signal LED6 using the optical modulator 66b as a driver.
9 (center wavelengths λ4 ≠ λ3, λ4 ≠ λ1).
This signal is based on frequency modulation using a modulation frequency of 1 MHz (subcarrier method). The transmitting side receives this signal, performs current-voltage conversion and frequency discrimination, and then demodulates it as a control signal.

If the wavelength cannot be tuned by controlling the semiconductor laser 30a, the fact can be transmitted to the transmitting side by a control signal. On the transmitting side receiving this signal, the oscillation wavelength can be changed by controlling the injection current of the semiconductor laser 30a, which is a tunable laser. Thereby, the temperature range in which wavelength tuning can be realized can be widened.

Further, when this unit is used as a receiving side, it is used to receive and demodulate control symbols (for example, data including a transmission wavelength and a failure state of the LD on the transmitting side) transmitted from the transmitting side. (The other examples in which the transmission side issues a control signal will be described in the following fifth, sixth, and seventh embodiments). The optical filter 28b is designed to transmit the wavelength (center wavelength λ4) of the control signal emitted from the transmission side. On the other hand, the optical filter 28a is designed to cut off the light having the wavelength λ4. The wavelength of the control signal LED 69 is λ
By setting the relations 4 ≠ λ3 and λ4 ≠ λ1,
The light having the wavelength λ4 can be prevented from interfering with the local oscillation light or the signal light. Further, by modulating the light of the semiconductor LD 30a and extracting the light from the optical multiplexer / demultiplexer 32, which is a beam splitter, the light can be used as a transmitter. In this case, the light receiving element 35b receives the control signal issued from the receiving side. As a result, data transmission and reception by coherent detection can be performed in this unit with time separated, and during that time, it is also possible to continuously monitor each other's situation. In addition, the use of the wavelength tunable laser allows a system configuration that does not require a temperature controller.

(Embodiment 5) FIG. 9 is a block diagram of a spatially coherent optical transmission apparatus according to a fifth embodiment of the present invention. The configuration of the present embodiment aims at transmitting the wavelength information of the transmitting side to the receiving side and performing the wavelength tuning at a higher speed. In FIG. 9, the signal source 21a to which the light receiving element 25 is connected is an LD to which the temperature monitor 70 is connected.
It is connected to the transmission LD 24 via the driver 23b. On the other hand, an optical filter 28, an optical multiplexer / demultiplexer 29, and a condenser lens 34 are arranged in series, and a light receiving element 35c is provided to face the condenser lens 34. The light receiving element 35c includes a pulse demodulation circuit 71 and a beat signal demodulation circuit 7
2 are connected. The pulse demodulation circuit 71 is connected to the temperature controller 47a, and the beat signal demodulation circuit 72
Is a temperature controller 47 via a wavelength information demodulation circuit 73.
a. This temperature controller 47a is connected to the local oscillation LD 30b.

The operation of the above configuration will be described below.

FIG. 10 is a time chart when data transmission is performed using the spatial coherent optical transmission device of FIG.

First, the transmitting side monitors the temperature with the temperature monitor 70, and sends the result to the LD driver 23b.
After encoding into a digital signal, the transmission LD 24 is driven. At this time, the optical signal from the transmission LD 24 is
As shown in FIG. 0, it has a header portion at the beginning to inform the receiving side that temperature information is to be transmitted. Subsequently, a pulse train representing the temperature as a digital signal is repeatedly transmitted. On the other hand, the receiving side receives the pulse train, and demodulates the temperature information by the pulse demodulation circuit 71.
The temperature of the local oscillation LD 30b is made the same as that of the transmission side LD 24 by a. At this time, the local oscillation LD 30b is not driven yet. In this embodiment, a DFB laser is used for both the LD on the transmission side and the LD on the reception side, and the variation of the oscillation wavelength between the elements at the same temperature is suppressed to about 1 nm. Therefore, it is possible to oscillate at substantially the same wavelength by keeping both temperatures substantially the same. At time t1, when the receiving side detects the temperature of the transmitting side and can control the temperature of its own LD,
The local oscillation LD 30b is oscillated, and its light is extracted from the optical multiplexer / demultiplexer 32, which is a beam splitter, to inform the transmitting side of a signal waiting state. After receiving this pulse by the light receiving element 25, the transmitting side emits light for a certain time (about 0.01 msec) in order to perform wavelength tuning on the receiving side. This wavelength tuning is performed so that the wavelength difference between the signal light and the local oscillation light has a fixed relationship, not shown, as in the first embodiment. Thereafter, desired data is transmitted from the data source 21a. FIG. 10 shows the state of data transmission at that time.

Further, on the receiving side, the local oscillation light is multiplexed with the signal light by using the optical multiplexer / demultiplexer 29. A beat signal having a frequency corresponding to a slight wavelength difference between the two multiplexed lights is excited by the light receiving element 35c, and is transmitted to the beat signal demodulating circuit 7c.
Demodulate at 2. Furthermore, in order to prevent the wavelength from being out of synchronization during communication, the wavelength information demodulation circuit 73, which is a wavelength tuning circuit, controls the temperature controller 47a so as to always detect a beat signal of a constant frequency, thereby controlling the local oscillation LD 30b. Therefore, wavelength tuning at the time of communication between places having relatively different temperatures can be realized at higher speed.

(Embodiment 6) FIG. 11 is a block diagram of an optical transmission unit in a spatially coherent optical transmission apparatus according to a sixth embodiment of the present invention, and shows only one configuration on the transmission side. In FIG. 11, a transmission side LD2 which is a semiconductor laser
The collimating lens 31 is opposed to the back surface side of 4a.
The optical multiplexer / demultiplexer 32a and the optical filter 81 are arranged in series via a, and the light receiving element 35c is arranged to face the optical filter 81. Further, the collimating lens 31a, the optical multiplexer / demultiplexer 32a, and the optical filter 81 are arranged in a direction perpendicular to the
The light receiving element 35d is arranged so as to oppose a.
The division circuit 82 to which the light receiving elements 35c and 35d are connected is connected to the control signal LED69a.

With the above configuration, the transmitting side transmits the oscillation wavelength as it is. Light emitted from the back side of the transmission light emission surface A of the transmission side LD 24a is vertically split 1: 1 by an optical multiplexer / demultiplexer 32a which is a beam splitter. afterwards,
One light in the optical multiplexer / demultiplexer 32a is incident on an optical filter 81 having transmission characteristics as shown in FIG. 12, and the emitted light is received by a light receiving element 35c. The optical multiplexer / demultiplexer 32
The other light at a is received by the light receiving element 35d as it is. The photocurrents excited by the light receiving elements 35c and 35d are converted into voltages by an IV circuit (not shown), and then guided to a division circuit 82, and a digital signal corresponding to the result is transmitted through a control signal LED69a. You. Of course, an optical signal as a data signal is emitted from the transmitting light emitting surface A of the transmitting LD 24a.

On the receiving side, the receiving unit shown in FIG. 8 is used.
The light emission of the control signal LED 69a is transmitted to the light receiving element 35b of FIG.
To receive light. On the other hand, the signal light emitted from the A-side of the transmitting LD 24a is demodulated by coherent detection on the receiving side. Also in this embodiment, a DFB laser having a wavelength of 780 nm is used as a semiconductor laser of the transmission-side LD 24a. The oscillation wavelength of this DFB laser is about 0.06 nm with temperature.
/ ° C., so that the transmission characteristics of the optical filter 81 are set so that the wavelength can be tuned in a temperature range of 0 to 60 ° C. Actually, it was produced by coating a dielectric thin film on a glass substrate in multiple layers.

(Embodiment 7) FIG. 13 is a block diagram of a spatially coherent optical transmission apparatus according to a seventh embodiment of the present invention. In FIG. 13, the transmitting LD 24b to which the LD driver 23d is connected emits signal light from the front and back sides. A collimator lens 31b is arranged so as to face the back side of the transmitting LD 24b, and a diffraction grating plate 83 on which parallel light from the collimator lens 31b is incident is arranged at a predetermined angle. A light receiving element array 84 is disposed via a condenser lens 34b that collects the reflected light from the diffraction grating plate 83. The output end of this light receiving element array 84 is LD
It is connected to the driver 23d.

A method for knowing the wavelength on the transmitting side with the above configuration will be described. After shaping the light emitted from the back surface of the transmitting side LD 24b into parallel light by the collimating lens 31b,
The light is incident on the diffraction grating plate 83 having the pitch Λ at an incident angle θi.
At this time, the diffracted light of the order m is given by
Diffraction is performed while satisfying the relationship of (sin θm + sin θi) = mλ. For example, wavelength λ = 780 nm, pitch Λ =
It is shown that the diffraction angle of the first-order diffracted light at 460 nm and θi = 45 ° is θm = 81 °. The wavelength dependence of the diffraction angle θm is given by △ θm = m · Δλ / Λ / cosθ
It is represented by m. That is, when the wavelength λ changes by ± 0.1 nm, it becomes {θm = 0.084}. In the present embodiment, the first-order diffracted light is condensed by the condenser lens 34b.
Focus on 4 Here, when the point B of the center of the light of the diffraction plate is the focal length of the condenser lens 34b and the distance is 15 mm, the change in the position corresponding to {θm = 0.084} is represented by Δx = 22 μm. Therefore, in this embodiment, the pitch of the arrayed light receiving elements is set to 20 μm, and the detection of the oscillation wavelength of the laser,
It is possible with an accuracy of about nm. By using such a light receiving element, the electric capacity of each light receiving element can be greatly reduced,
A response speed of about 10 GHz can be realized. The detected wavelength is converted into a digital signal by the LD driver 23d and transmitted to the receiving side as wavelength information. Although a specific transmission method is not particularly described, it can be easily realized from the above embodiment.

As described above, according to the present embodiment, the wavelength is
It was possible to match with an accuracy of 0.1 nm. If coherent detection is performed in this situation, when the wavefront is not tuned, no beat signal current is detected. At this time, first, the wavefront is tuned. Since the beat signal current is detected when the wavefront is tuned, the wavelength is tuned by controlling the local oscillation light LD so as to keep the frequency constant. Thus, the guideline for tuning the wavefront and wavelength can be determined.

Therefore, the spatial coherent optical transmission device according to the above embodiment is a conventional spatial coherent optical transmission device having a transmitting side having a function of emitting coherent light and a receiving side having a local oscillation light source and performing coherent detection. In addition, the following respective configurations are added.

That is, a temperature sensor or a wavelength detector for detecting its own oscillation wavelength and a light emitting device for varying the intensity are provided on the transmitting side, and the detected wavelength information is emitted into space by modulating the light intensity. The receiving side is provided with a configuration for receiving and demodulating the intensity-modulated light.

Further, the receiving side is provided with a configuration for detecting the frequency and intensity of the coherently detected electric signal or a direct current generated in the entire light receiving element, a light emitting device for varying the intensity, and an optical device for detecting the detected situation. A configuration is provided in which the intensity is modulated and emitted to space, and a configuration is provided on the transmitting side for receiving and demodulating the intensity-modulated light.

According to the configuration of the above embodiment, the following effects 1 to 4 can be obtained.

1. Since the transmitting side monitors the receiving side, data transmission can be performed by confirming the coherent detection state on the receiving side when communication is established. Further, it is possible to know the loss of data during data transmission, and it is possible to retransmit data.

Alternatively, when the receiving side monitors the transmitting side, the coherent detection cannot be performed when the receiving side cannot tune the wavelength. Therefore, it is impossible to know whether the transmitting side is transmitting data. Signals can be easily known by transmitting them at the same time, the temperature of the local oscillation light is scanned, the frequency of the generated beat signal is detected by a frequency discrimination circuit, and the wavelength is controlled by controlling the frequency to be constant. Tuning can be performed.

2. In particular, the receiving side knows the temperature and the oscillation wavelength of the transmitting side, so that the wavelength tuning on the receiving side can be performed at higher speed. That is, the transmitting side transmits the information on the wavelength, so that the receiving side can realize high-speed wavelength tuning. In particular, it is effective in communication in a place where the temperature difference is large. Further, since the transmitting side accurately detects the wavelength (about ± 0.1 nm), the receiving side can instantaneously determine which of the wavelength and the wavefront is out of synchronization.

3. When the receiving side detects a beat signal strength and a beat signal frequency, it serves as a guideline for wavefront tuning and wavelength tuning. That is, by continuously detecting the beat signal frequency and the beat signal amplitude, the receiving side can judge whether the wavefront tuning or the wavelength tuning has deviated, and realize the coherent detection state more quickly and easily. it can. In addition, the transmission side and the reception side monitor each other's situation, so that data retransmission, laser failure, and the like can be determined, and each can be optimally controlled. In particular, when the wavefront and the wavelength are not tuned, it is impossible to monitor the two-way coherent optical transmission devices with each other, but it becomes possible only by using the light intensity modulation and the direct detection system together. By monitoring the received light current, the background light intensity can be known, and it is possible to request the transmission side to stop, retransmit, or continue data transmission.

4. By sharing some light emitting elements or light receiving elements by utilizing the fact that optical coherent detection and light intensity modulation do not interfere with direct detection, that is, generation of coherent signal light or local oscillation light By using the same device as the device and the device for generating the intensity-modulated light as a control signal, or by using a light-receiving device for coherent detection and a light-receiving device for direct detection of the control signal, the beat signal is filtered by a filter. By separating the signal and the intensity modulation signal, a compact and simple device configuration can be obtained.

[0079]

As described above, according to the first aspect of the present invention, when the beat signal is not detected by the detection unit as the coherent detection situation, the information is transmitted from the control signal transmission unit to the optical transmission unit. Since the control signal is transmitted to the control signal light receiving unit and the control unit controls transmission of the data optical signal, even if the beat signal is not detected, retransmission of the same data signal can prevent data loss. At this time, the wavelength tuning unit controls the wavelength of the second coherent light so that the wavelength is tuned based on the detection status information detected by the detection unit. The wavelength can be tuned and higher-speed data communication can be performed.

According to the second aspect, even when the beat signal cannot be detected only by changing the wavelength of the receiving side depending on the usage state of the receiving side, the receiving side detects the beat signal detecting state and transmits the information to the transmitting side. In order to control the wavelength on the transmission side by notifying the user, if a semiconductor laser is used for each of the transmission side and the reception side, a beat signal within the operating temperature range of the semiconductor laser can be detected.

Further, according to the third aspect, since the receiving section detects the beat signal detection state and controls its own oscillation wavelength, it can detect the beat signal without changing the wavelength on the transmitting side. There can be several receivers per side, for example applications such as local area networks.

Further, according to the fourth aspect, if the receiving section attempts to tune the wavelength only by looking at the beat signal, if a laser is used on each of the transmitting side and the receiving side, for example, the beat signal frequency, that is, the two lasers are used. If the wavelength shift cannot be detected and there is a wavelength shift, there is no guideline on whether to increase or decrease the wavelength of the local oscillation light, but when the transmitting unit transmits data on its own wavelength, The wavelength tuning of the receiving unit can be performed more easily.

Further, according to the fifth aspect, the transmission side and the reception side monitor each other's situation, thereby making it possible to judge retransmission of data, laser failure, etc., and to control each of them optimally. In particular, when the wavefront and the wavelength are not tuned, it is impossible to monitor the two-way coherent optical transmission devices with each other, but it becomes possible only by using the light intensity modulation and the direct detection system together.

Further, according to the eleventh aspect , it is possible to inform the user whether communication is possible by knowing the noise current intensity or the like, so that the user can accurately grasp the cause of the impossibility of communication. Can be.

Further, according to the twelfth aspect , the receiving side can accurately detect the temperature and the oscillation wavelength on the oscillation side,
Thereby, when the beat signal cannot be detected, it is known that the wavefront tuning has been lost, and it is possible to know the guidelines for the wavelength tuning and the wavefront tuning.

Further, according to claim 7 , the optical transmission means
Are the first coherent light, the second coherent light, and
And a control signal are generated from a common light-emitting unit,
Transmitting the optical signal and the control signal, and
The first coffee transmitted from the spatial coherent optical transmission device
Light, control signals, and the
The second coherent light received by the common light receiving unit and received
Therefore, bidirectional communication can be performed. Moreover,
Because the light emitting unit and the light receiving unit are shared, for example,
If a semiconductor laser is used for the light emitting portion, the number of semiconductor lasers used can be reduced, and the cost can be reduced.

Further, according to the ninth aspect, since the coherent optical signal receiving section and the control signal receiving section are shared, the circuit configuration can be simplified, and the size and weight of the apparatus can be reduced. .

[Brief description of the drawings]

FIG. 1 is a block diagram of a spatially coherent optical transmission device according to a first embodiment of the present invention.

FIGS. 2A and 2B are signal waveform diagrams of respective main parts of FIG. 1, where a indicates a data pulse, and b indicates a signal light oscillation frequency corresponding to data 1 and 0. FIG.

FIG. 3 is a signal waveform diagram of each main part of FIG. 1, where a indicates a wavelength, a beat signal due to synchronization and non-synchronization of a wavefront, and b indicates a light intensity of a control signal.

FIG. 4 is a block diagram of a spatially coherent optical transmission device according to a second embodiment of the present invention.

5 is a signal waveform diagram of each main part of FIG. 4, where a is a current excited by the light receiving element 35, and b is an AGC circuit 62a.
Shows the beat signal immediately after.

FIG. 6 is a waveform chart of a control signal (light intensity modulated by an external modulator 23) in FIG.

FIG. 7 is a block diagram of a spatial coherent optical transmission device according to a third embodiment of the present invention.

FIG. 8 is a block diagram of a spatially coherent optical transmission device according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram of a spatially coherent optical transmission device according to a fifth embodiment of the present invention.

10 is a time chart of transmission data when data transmission is performed using the spatial coherent optical transmission device of FIG. 9;

FIG. 11 is a block diagram of an optical transmission unit in a spatially coherent optical transmission device according to a sixth embodiment of the present invention.

12 is a transmission characteristic diagram of an optical filter in the spatial coherent optical transmission device of FIG.

FIG. 13 is a block diagram of an optical transmission unit in a spatially coherent optical transmission device according to a seventh embodiment of the present invention.

FIG. 14 is a configuration diagram of a beat signal detection device in a conventional wireless optical communication system.

[Explanation of symbols]

21, 21a Data source 22 Data storage 23, 23a, 23b, 23c, 23d LD driver 24, 24a, 24b Transmitting LD 25 Control optical signal light receiving element 26 Control circuit 28, 28a, 28b Optical filter 29, 32, 32a Waveguide 30, 30b Local oscillation LD 30a Semiconductor LD 31, 31a, 31b Collimating lens 33 Light diffusing element 34a, 34b Condensing lens 35, 35a, 35b, 35c, 35d Signal receiving element 36, 36a, 36b Current-voltage conversion circuit ( IV circuit) 37, 37a High frequency transmission filter (high pass filter) 38, 38a, 38b Intermediate frequency transmission filter (band pass filter) 39a, 39b, 39c, 39d, 39e Frequency voltage conversion circuit (fV circuit) 40a, 40b, 40c, 40d, 4 e, 40f, 4
0g Comparator 42, 42a, 42b Demodulation circuit 43 Beat signal detection circuit 44 Mark rate detection circuit 45 Wavelength tuning circuit 46, 46a, 46b Envelope detection circuit 47, 47a Temperature controller 48, 48a, 48b, 48c Discrimination circuit 49 Control circuit 50 Optical shutter 61 Control circuit 62a, 62b Automatic gain circuit (AGC circuit) 63 Phase detector 64 Low frequency transmission filter (low pass filter) 65, 65a, 65b Control circuit 66, 66a Optical modulator 67 DC power supply 68 APC circuit 69, 69a Control signal LED 70 Temperature monitor 71 Pulse demodulation circuit 72 Beat signal demodulation circuit 73 Wavelength information demodulation circuit 81 Optical filter 82 Division circuit 83 Diffraction grating 84 Light receiving element array

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H04B 10/14 10/142 10/22 (72) Inventor Hidenori Kasai 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (56) References JP-A-2-249327 (JP, A) JP-A-3-46839 (JP, A) JP-A-63-221726 (JP, A) JP-A-63-198426 (JP, A) JP-A-63 -224426 (JP, A) JP-A-1-34029 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08

Claims (14)

(57) [Claims] An optical transmitter for emitting a data signal as a first coherent light, a second coherent light is generated, and the second coherent light and the first coherent light are combined and received. A spatial coherent optical transmission device comprising: a light receiving means for coherently detecting the data signal, wherein the light receiving means tunes the wavefronts of the first coherent light and the second coherent light. means is provided, et al.
The coherent optical transmission status , the beat signal strength, and the
A detection unit that detects at least one of coherent optical detection situations including detection of a beat signal frequency; a control signal transmission unit that transmits a control signal corresponding to situation information detected by the detection unit; A control signal light receiving unit for receiving light, a wavelength of light of the data signal and an operation of continuation, stop, and retransmission of the data signal by a photocurrent received by the control signal light receiving unit ;
A control unit for controlling at least one of the two coherent light wavelengths . 2. A light transmitting means for radiating a data signal as a first coherent light, a second coherent light being generated, the second coherent light and the first coherent light being multiplexed and received. a spatial coherent optical transmission device having a light receiving means for coherent detection of the data signal, to the light receiving means, the beat signal strength and the beat signal frequency
A detecting unit for detecting a coherent photodetection situation including detection of a number, and the first unit based on the coherent photodetection situation.
Tuning the wavefronts of the coherent light and the second coherent light
And a control signal transmitting unit for transmitting a control signal corresponding to the situation information detected by the detecting unit, wherein the optical transmitting unit includes a control signal receiving unit for receiving the control signal, A spatial coherent optical transmission device comprising: a control unit that controls at least one of the wavelength of the light of the data signal and the continuation, suspension, and retransmission operations of the light of the data signal by a photocurrent received by the control signal light receiving unit. 3. An optical transmitter for emitting a data signal as a first coherent light, generating a second coherent light, multiplexing the second coherent light and the first coherent light, and receiving the combined light. a spatial coherent optical transmission device having a light receiving means for coherent detection of the data signal, to the light receiving means, the beat signal strength and the beat signal frequency
A detection unit for detecting a coherent photodetection situation including detection of a number, a control signal transmission unit for transmitting a control signal according to the situation information detected by the detection unit, and a control unit based on the situation information detected by the detection unit. a wavelength tuning unit for controlling the wavelength of the second coherent light to wavelength tuning Te, detected by the detection unit
The first coherent light and the
Wavefront tuning means for tuning the wavefront of the second coherent light
Provided in the optical transmitting means, a control signal light receiving unit for receiving the control signal, and a wavelength of the light of the data signal and continuation, stop, and retransmission of the data signal by a photocurrent received by the control signal light receiving unit. A spatial coherent optical transmission device, comprising: a control unit that controls at least one of the operations. 4. An optical transmitter for emitting a data signal as a first coherent light, a second coherent light is generated, and the second coherent light and the first coherent light are multiplexed and received. A spatial coherent optical transmission device having an optical receiving unit for coherently detecting the data signal, wherein the optical transmitting unit includes a first detecting unit for detecting a coherent optical transmission state; and a signal transmitting unit for transmitting a control signal corresponding to the detected status information as an optical signal
Provided, on the light receiving means, a signal receiving unit for receiving the optical signal, the
The control signal of the optical signal received by the signal
A second detection unit for detecting a rent light transmission state;
Beat signal from the data signal of the optical signal received by the transmitter
A third detecting section for detecting a coherent detection state including detection of an intensity and a beat signal frequency; and the second coherent light so as to tune a wavelength based on the state information detected by the second and third detecting sections. Wavelength tuning unit for controlling the wavelength of the first coherent light and the second coherent light
A spatial coherent optical transmission device provided with a wavefront tuning means for tuning the wavefront . 5. An optical transmitter for emitting a data signal as a first coherent light, generating a second coherent light, multiplexing the second coherent light and the first coherent light, and receiving the combined light. A spatial coherent optical transmission device having an optical receiving unit for coherently detecting the data signal, wherein the optical transmitting unit includes a first detecting unit for detecting a coherent optical transmission state; A signal transmitting unit for transmitting a first control signal corresponding to the detected situation information as the optical signal, a control signal receiving unit for receiving the second control signal, and the data signal based on a photocurrent received by the control signal receiving unit A control unit that controls at least one of a signal light wavelength and an operation of continuation, suspension, and retransmission of transmission; a signal reception unit that receives the optical signal; and the signal reception unit; Received by A second detector for detecting the first control signal or al coherent light transmission state of the optical signal, the signal
Beat signal from optical signal data signal received by receiver
Coherent including intensity and beat signal frequency detection
A third detection unit for detecting a light detection situation, and a wavelength tuning unit for controlling the wavelength of the second coherent light so as to tune the wavelength based on the situation information detected by the second and third detection units. , Based on the situation information detected by the third detection unit.
Wavefronts of the first coherent light and the second coherent light
A spatially coherent optical transmission device comprising: a wavefront tuning means for performing the tuning described above; and a control signal transmitting section for transmitting as a second control signal according to the situation information detected by the third detecting section. 6. A light transmitting means for emitting a data signal as a first coherent light, generating a second coherent light, multiplexing the second coherent light and the first coherent light, and receiving the combined light. A spatial coherent optical transmission device having optical receiving means for coherently detecting the data signal , provided in the optical receiving means, for tuning the wavefronts of the first coherent light and the second coherent light. A space provided with a wavefront tuning means, and a wavelength tuning means provided in at least one of the light transmitting means and the light receiving means for tuning the wavelengths of the first coherent light and the second coherent light; Coherent optical transmission device. 7. A spatial coherent optical transmission device for receiving a first coherent light transmitted as a data signal by combining a second coherent light with the first coherent light, and coherently detecting the data signal. Wavefront tuning means for tuning the wavefronts of the coherent light and the second coherent light, wavelength tuning means for tuning the wavelengths of the first coherent light and the second coherent light, , Beat signal strength and
The detection unit detects at least one of the coherent optical detection states including the detection of the beat signal frequency , and by a control signal corresponding thereto, the wavelength of the light of the data signal and the continuation of transmission, the operation of the stop and the retransmission. A control unit that controls at least one of: generating the first coherent light, the second coherent light, and the control signal from a common light emitting unit, and transmitting the first coherent light and the control signal Optical transmitting means; and the first transmitted from another spatially coherent optical transmission device.
Spatial coherent light transmission for performing bidirectional communication, comprising: a coherent light, the control signal, and light receiving means for receiving and receiving the second coherent light generated by the light emitting unit with a common light receiving unit. apparatus. 8. An envelope detection circuit for detecting the amplitude of a beat signal, wherein the wavefront tuning means determines a wavefront tuning state based on the amplitude of the beat signal detected by the envelope detection circuit. The spatial coherent optical transmission device according to any one of claims 1 to 7, further comprising: a control signal transmitting unit configured to transmit a control signal according to the information of the wavefront tuning performed. 9. A filter unit, wherein the optical receiving unit separates a received signal into the control signal and a beat signal; a control signal detector, which directly detects the control signal separated by the filter unit; And a beat signal detector for coherently detecting the beat signal separated by the step (c).
Or the spatial coherent optical transmission device according to 8. 10. The spatial coherent optical transmission device according to claim 1, wherein the control signal is an optical signal obtained by intensity-modulating the data signal. 11. The spatial coherent optical transmission device according to claim 1, wherein the coherent optical detection state detected by the detection unit includes detection of a noise current intensity . 12. A temperature and an oscillation wavelength are detected as a coherent light transmission state detected by the detection unit.
10. The spatial coherent optical transmission device according to 4, 5, 7, 8, or 9. 13. The detection unit has a wavelength filter,
13. The spatial coherent optical transmission device according to claim 12, wherein an oscillation wavelength is detected from a transmittance of the light passing through the wavelength filter. 14. The spatial coherent optical transmission device according to claim 12, wherein the detection unit has an optical diffraction grating, and detects an oscillation wavelength from a diffraction angle of light incident on the optical diffraction grating.