JPH0654896B2 - Heterodyne detection type optical signal receiver for space propagation communication - Google Patents

Description

The present invention relates to a heterodyne detection type optical signal receiving device for spatial propagation communication.

[Prior Art] An optical receiver of a space propagation type between satellites receives not only signal light to be received but also unnecessary background light such as sunlight existing in the space and frequency range of the photodetector. To do. Since the received background light is processed together with the necessary signal light, the transmission characteristics are greatly deteriorated with respect to the baseband signal detected by the optical receiver. When the spectral luminance function of this background noise light source is N (f), the background light power Pb [W] received in the bandwidth B [Hz] centered on the frequency f [Hz] is expressed by the following equation.

(1) As shown in FIG. 11 (A), the solid angle Ωfv of the field of view of the receiver
When [steradian] is included in the solid angle Ωs [steradian] of the noise source when viewed from the receiver and Ωfv <Ωs, Pb = N (f) BArΩfv (1), and (2) 11th As shown in Fig. (B), when the solid angle Ωs [steradian] of the noise source when viewed from the receiver is included in the solid angle Ωfv [steradian] of the field of view of the receiver and Ωfv ≤ Ωs, Pb = N (f) BArΩs… (2). Where Ar is the area [m ² ] of the receiving antenna,
For example, the light source of background light that is a particular problem in optical inter-satellite communication is the sun, and the background light power received at that time is
It becomes formula (1).

FIG. 12 is a block diagram of a conventional FSK heterodyne detection type optical receiver. Here, the signal light is 650 [M
It is a signal that is FSK-modulated at ± 200 [MHz] centering on [Hz].

In FIG. 12, the received signal light is input to the optical multiplexer 2 via the optical receiving antenna 1 formed of, for example, a Cassegrain antenna, and is multiplexed with the local oscillation light output from the local oscillator 10, It is input to the photodetector 3. The optical detector 3 converts an input optical signal into an electrical signal (hereinafter referred to as “O”).
It is called / E conversion. ), And outputs the electric signal to an intermediate frequency filter (hereinafter referred to as an IF filter) 4. The IF filter 4 extracts only the signal in the band from 300 MHz to 1 GHz and outputs it to the frequency discriminator 6 via an intermediate frequency amplifier (hereinafter referred to as IF amplifier) 5 having an intermediate frequency of 650 MHz. The frequency discriminator 6 converts a change in the frequency of the signal centered on the intermediate frequency into a change in the voltage, outputs an electric signal indicating the change in the voltage to the local oscillator 10, and via the baseband filter 7. Signal processing circuit 8
Output to. Here, the electric signal is an FSK-demodulated digital signal, and the digital signal is subjected to known processing such as waveform shaping in the signal processing circuit 8 and then output to the output terminal as a digital signal.

On the other hand, the local oscillator 10 responds to the input electric signal by controlling the frequency of the local oscillation light so that the average frequency of the signal output from the photodetector 3 becomes 650 MHz which is the intermediate frequency, The local oscillation light is output to the optical multiplexer 2.

The FSK heterodyne detection type optical receiver configured as described above is stable and has a high gain, as well known, as compared with a direct detection type optical receiver that does not include the local oscillator 10. It has the advantage that the signal to noise ratio of the received signal is large.

[Problems to be Solved by the Invention] When the background light is input to the optical receiving antenna 1 of the optical receiver shown in FIG. 12, there is a problem that the signal-to-noise ratio of the signal light is significantly reduced. It was

As described above, the received background light power when the background light is the sun is given by the above formula (1). Therefore, in order to reduce the background light power from the sun, the bandwidth B, the area Ar of the receiving antenna, or the solid angle Ωfv of the field of view of the receiver may be reduced, but if these parameters are reduced, the signal is reduced. There was a problem of causing deterioration of light.

An object of the present invention is to solve the above problems, reduce the background light noise without degrading the signal light, and improve the signal-to-noise ratio of the signal light as compared with the conventional example. An object is to provide an optical signal receiving device for space propagation communication.

[Means for Solving Problems] An optical signal receiving device for spatial propagation communication of a heterodyne detection system according to the present invention receives the signal light transmitted from a partner station during the spatial propagation communication, and then receives the received signal. In a heterodyne detection type optical signal receiving device for spatial propagation communication that multiplexes light and local oscillation light and converts it into an electric signal of a predetermined frequency for demodulation, detects the level of background light received together with the signal light. Then, the detection means for outputting a detection signal proportional to the level of the background light, and the beam diameter of the locally oscillated light is reduced as the detection signal output from the detection means becomes larger to receive the optical signal receiving device. And a control means for reducing the field of view.

[Operation] With the above configuration, the detection means detects the level of the background light received together with the signal light and outputs the detection signal proportional to the level of the background light, and the control means is As the detection signal output from the detection means increases, the beam diameter of the local oscillation light is reduced to reduce the reception field of view of the optical signal receiving device. This makes it possible to reduce the background light according to the level of the background light without degrading the signal light.

[Embodiment] First Embodiment FIG. 1 is a block diagram of an optical receiver of the FSK heterodyne detection system according to the first embodiment of the present invention. In FIG. The same reference numerals are attached.

This optical receiver is different from the conventional optical receiver shown in FIG. 12 in that in addition to the optical receiver shown in FIG.
IF amplifier 12, detector 13, controller 14, drive device 1
5 and the deflector 16 are provided, and the beam diameter of the local oscillation light output from the local oscillator 10 is controlled by the deflector 16 according to the power level of the background light noise received by the photodetector 3. As a result, the photodetector 3 for the local oscillation light
It is characterized by reducing the background light by controlling the area above and equivalently controlling the field of view of the receiver. Hereinafter, the difference will be described in detail. In addition, the signal light is ± 20 around 650 [MHz] as in the conventional example.
The signal is FSK-modulated at 0 [MHz].

In FIG. 1, the received signal light is input to the optical multiplexer 2 via the optical receiving antenna 1, is multiplexed with the local oscillation light output from the local oscillator 10, and is input to the optical detector 3. It The optical detector 3 O / E converts the input optical signal, outputs the electrical signal to the IF filter 11, and outputs the electrical signal to the frequency discriminator 6 via the IF filter 4 and the IF amplifier 5. The frequency discriminator 6 converts a change in the frequency of the signal centered on the intermediate frequency into a voltage, outputs an electric signal indicating the change in the voltage to the local oscillator 10, and performs signal processing via the baseband film 7. Output to the circuit 8. Here, the electric signal is an FSK demodulated digital signal, and the signal is subjected to known processing such as waveform shaping in the signal processing circuit 8 and then output to the output terminal as a digital signal.

On the other hand, the local oscillator 10 responds to the input electric signal by controlling the frequency of the local oscillation light so that the average frequency of the signal output from the photodetector 3 becomes 650 MHz which is the intermediate frequency, The local oscillation light is output to the optical multiplexer 2 via the deflector 16. Here, the local oscillator 10 is
The FSK signal is configured so as not to follow the change in the electric signal due to the change in the frequency.

Further, the IF filter 11 uses the input electric signal to
As shown in FIG. 7, a band component from 1.2 GHz to 1.5 GHz is extracted, and the band component is sent to a detector 13 via an IF amplifier 12 which is a band amplifier for amplifying a signal in the band from 1.2 GHz to 1.5 GHz. Output. Here, FIG. 7 is a diagram showing the spectrum of the output signal of the photodetector 3, and the output of the photodetector 3 is a signal light having an average frequency of 650 MHz and a band from about 300 MHz to about 1 GHz. 60 and shot noise 62 having a frequency component that is substantially flat and generated when the local oscillation light is input to the photodetector 3. Further, when background light is input to the optical receiving antenna 1, the output of the photodetector 3 has background optical noise 61 having a substantially flat frequency component in addition to the above. Therefore, the background light noise 61, the shot noise 62, and the IF amplifier 12 are included in the detector 13.
The thermal noise generated at will be input. Here, the shot noise 62 and the thermal noise are at substantially constant levels, but the background optical noise 61 changes according to the amount of background light input to the optical receiving antenna 1, and therefore the detector 13 The detected power level changes according to the amount of background light.

The detector 13 detects the power level of the input band component and outputs a detection signal proportional to the power level to the controller 14. In response to this, the controller 14 drives the driving device 15 according to the input detection signal, and changes the beam diameter of the deflector 16 that allows the local oscillation light output from the local oscillator 10 to pass therethrough. Here, the beam diameter of the deflector 16 is controlled so as to decrease as the power level detected by the detector 13 increases, provided that the beam diameter of the signal light on the photodetector 3 is controlled. It is controlled not to become smaller than.

For example, the solid angle Ωfv of the field of view of a direct detection optical receiver.
As shown in FIG. 8, [Stellasian] means that the focal length of the photodetector 3 is fc [m] and the light receiving area of the photodetector 3 is Ad.
[m ² ] can be represented by the following formula as is well known.

Ωfv≈Ad / fc ² (3) On the other hand, the solid angle Ωfv [steradian] of the field of view of the optical receiver of the heterodyne detection system of the present embodiment is the local oscillation on the photodetector 3 as shown in FIG. Assuming that the light receiving area of light is Ac [m ² ], it can be expressed by the following equation as is well known.

Ωfv ≈ Ac / fc ² (4) Therefore, in the direct detection type optical receiver, the solid angle Ωfv of the field of view of the receiver is equivalently controlled by controlling the light receiving area Ad of the optical detector 3. can do. On the other hand, in the heterodyne detection type optical receiver of the present embodiment,
By controlling the area Ac of the locally oscillated light on the photodetector 3, the solid angle Ωfv of the field of view of the receiver can be equivalently controlled. By controlling the solid angle Ωfv of the field of view of the receiver, the received background light power Pb can be changed as shown in the above equation (1).

In the optical receiver of FIG. 1, the change in the power level of the background light noise is detected as described above, and as the power level detected by the detector 13 becomes higher, that is, the power level of the background light noise becomes higher. Accordingly, the beam diameter of the deflector 16 is controlled to be small.

That is, when the background light is not received, FIG.
As shown in (A), the beam diameter of the local oscillation light is increased so that the area 42 of the local oscillation light on the photodetector 3 is slightly smaller than the detection area 40 of the photodetector 3 and Control to be included in 40 to widen the field of view of the receiver. This makes it possible to reduce the tracking accuracy of the tracking device that tracks the signal light 41. In general,
Since the time for receiving the sun as the background light is relatively short, there is an advantage that the tracking accuracy of the tracking device can be reduced for a long time.

On the other hand, when the background light is being received, as shown in FIG. 10 (B), since the background light 43 is incident on almost the entire detection area 40 of the photodetector 3, the beam diameter of the local oscillation light is changed. The area 42 of the locally oscillated light on the photodetector 3 is controlled to be slightly smaller than the area 41 of the signal light so that the area 41 of the signal light is included in the area 42 of the locally oscillated light. , Reduce the field of view of the receiver and narrow it down. This reduces the background light noise by reducing the space matching area between the background light and the local oscillation light on the photodetector 3. At this time, it is necessary to increase the tracking accuracy of the tracking device that tracks the signal light 41.

As described above, in this optical receiver, as the power level of background optical noise increases, the optical detector 3
The field of view of the optical receiver can be narrowed by reducing the light receiving area Ac of the upper locally oscillated light, thereby reducing the background light noise without degrading the signal light. As a result, the signal-to-noise ratio of the demodulated signal light can be improved, and the bit error rate of the demodulated digital signal can be significantly reduced.

Second Embodiment FIG. 2 is a block diagram of an FSK heterodyne detection type optical receiver according to a second embodiment of the present invention. In FIG. 2, the same parts as those in the above-mentioned drawings are designated by the same reference numerals. Attached.

This optical receiver differs from the optical receiver of the first embodiment shown in FIG. 1 in that the driving device 15 and the deflector 16 shown in FIG. 1 are replaced by the driving device 21 and the spatial filter 20, respectively. The other configurations are the same. Hereinafter, the difference will be described in detail.

The control 14 drives the driving device 21 according to the detection signal input from the detector 13 to change the hole diameter of the pin fall of the spatial filter 20 to change the beam diameter of the local oscillation light output from the local oscillator 10. Change. Here, the beam diameter of the locally oscillated light is controlled so as to decrease as the power level detected by the detector 13 increases, provided that the beam diameter of the signal light on the photodetector 3 is controlled. It is controlled not to become smaller than.

The optical receiver of FIG. 2 configured as described above operates in the same manner as the first embodiment of FIG. 1 and has the same operation and effect as the optical receiver of the first embodiment.

Third Embodiment FIG. 3 is a block diagram of an FSK heterodyne detection type optical receiver according to a third embodiment of the present invention. In FIG. 3, the same parts as those in the above-mentioned drawings are designated by the same reference numerals. Attached.

This optical receiver is different from the optical receiver of the first embodiment of FIG. 1 in that the driving device 15 and the deflector 16 of FIG. 1 are respectively a driving device 25 and a collimating lens 22 for local oscillation light. Condensing lens 23 for local oscillation light, and the lens 2
The position control device 24 for moving the position No. 3 in the optical axis direction is replaced, and other configurations are the same. Hereinafter, the difference will be described in detail.

The local oscillation light output from the local oscillator 10 is a collimating lens 22 for local oscillation light and a condenser lens 2 for local oscillation light.
It is output to the optical multiplexer 2 via 3. On the other hand, the controller 14
Drives the driving device 25 in accordance with the detection signal input from the detector 13 to move the position of the local oscillation light condensing lens 23 in the optical axis direction by the position control device 24, whereby the optical detection is performed. The beam diameter of the locally oscillated light on the container 3 is changed. Here, the beam diameter of the locally oscillated light on the photodetector 3 is controlled so as to decrease as the power level detected by the detector 13 increases, provided that the beam diameter on the photodetector 3 decreases. It is controlled so as not to become smaller than the beam diameter of the signal light. The optical receiver of FIG. 3 configured as described above operates similarly to the first embodiment of FIG.
It has the same operation and effect as the optical receiver of the first embodiment.

Fourth Embodiment FIG. 4 is a block diagram of an FSK heterodyne detection type optical receiver according to a fourth embodiment of the present invention. In FIG. 4, the same parts as those in the above-mentioned drawings are designated by the same reference numerals. Attached.

This optical receiver differs from the optical receiver of the first embodiment shown in FIG. 1 in that the IF filter 11, the IF amplifier 12 shown in FIG.
And the detector 13 are not provided, but the amplifier 30, the detector 31, and the calculator 32 are provided, and other configurations are the same. Hereinafter, the difference will be described in detail.

In FIG. 4, the output of the photodetector 3 is the IF filter 4
Is output to the detector 31 via the amplifier 30 that performs wide band amplification up to about 1.5 GHz. The detector 31 detects the power level of each spectrum of the input band component, outputs a detection signal proportional to the power level to the calculator 32, and in response thereto, the calculator 32 receives the input detection signal. The average power level in all bands is calculated from the signal, and a level signal proportional to the average power level is output to the controller 14. In response to this, the controller 14 drives the driving device 15 according to the input detection signal to change the beam diameter of the deflector 16 as in the first embodiment.

The optical receiver of FIG. 4 configured as described above operates similarly to the first embodiment of FIG. 1 and has the same operation and effect as the optical receiver of the first embodiment.

Fifth Embodiment FIG. 5 is a block diagram of an FSK heterodyne detection type optical receiver according to a fifth embodiment of the present invention. In FIG. 5, the same parts as those in the above-mentioned drawings are designated by the same reference numerals. Attached.

This optical receiver differs from the optical receiver of the second embodiment of FIG. 2 in that the IF filter 11, the IF amplifier 12, and the detector 13 of FIG. 2 are the same as those of the fourth embodiment. The amplifier 30, the detector 31, and the calculator 32 are not provided, but the other configurations are the same.

The optical receiver of FIG. 5 configured as described above operates similarly to the second embodiment of FIG. 2 and has the same operation and effect as the optical receiver of the second embodiment.

Sixth Embodiment FIG. 6 is a block diagram of an FSK heterodyne detection type optical receiver according to a sixth embodiment of the present invention. In FIG. 6, the same parts as those in the above-mentioned drawings are designated by the same reference numerals. Attached.

This optical receiver differs from the optical receiver of the third embodiment shown in FIG. 3 in that the IF of FIG. 3 is the same as in the fourth and fifth embodiments.
The filter 11, the IF amplifier 12, and the detector 13 are not provided, but the amplifier 30, the detector 31, and the calculator 32 are provided, and other configurations are the same.

The optical receiver of FIG. 6 configured as described above operates similarly to the third embodiment of FIG. 3, and has the same operation and effect as the optical receiver of the third embodiment.

Other Embodiments In the above embodiments, the heterodyne detection type optical receiver for receiving the FSK signal is described, but the present invention is not limited to this, and the present invention is not limited to the heterodyne detection type optical receiver. It can be easily applied to an optical receiver.

In the above embodiments, as the power level of the background optical noise increases, the light receiving area Ac of the locally oscillated light on the photodetector 3 is reduced to narrow the visual field of the optical receiver and reduce the background optical noise. However, not limited to this, a threshold value for detecting the power level of the background light noise is provided, and it is detected whether or not the power level of the received background light noise exceeds the above threshold value. When the presence or absence of background light is detected and the background light is not received, the light receiving area Ac of the locally oscillated light on the photodetector 3 is set to be relatively large as shown in FIG. 10 (A). 10 and the background light is being received, the light receiving area Ac of the locally oscillated light on the photodetector 3 is shown in FIG.
As shown in (B), the above-mentioned device may be controlled so as to be relatively small.

In the above fourth to sixth embodiments, the input of the amplifier 30 is obtained from the output of the photodetector 3, but not limited to this, it may be obtained from the output of the IF filter 4 or the IF amplifier 5. . When the input of the amplifier 30 is obtained from the output of the IF filter 4, the amplifier 30 is configured to have an amplification band similar to that of the IF amplifier 5, while when the input of the amplifier 30 is obtained from the output of the IF amplifier 5, the amplifier 30 is obtained. May be omitted.

The optical receiver of the heterodyne detection method described in the above embodiments removes light other than the signal band by the heterodyne detection method, and operates as a frequency filter, on the other hand, by controlling the field of view to the receiver, especially the reception background. It reduces optical power and operates equivalently as a spatial filter. Therefore, the optical receiver of the present invention operates as the two frequency filters and the spatial filter, and has an advantage that the signal-to-noise ratio of the signal light can be significantly improved as compared with the conventional example.

As described above in detail, according to the present invention, in the optical signal receiving device for spatial propagation communication of the heterodyne detection system, the level of background light received together with the signal light is detected, and the detected background light is detected. Since the beam diameter of the local oscillation light is made smaller as the level of becomes higher to reduce the field of view for receiving the signal light and the local oscillation light, the background light of the background light is not deteriorated without degrading the signal light. Background light can be reduced according to the level. Therefore, it is possible to improve the signal-to-noise ratio of the demodulated signal light, and
This has the advantage that the bit error rate of the demodulated digital signal can be significantly reduced.

[Brief description of drawings]

1 to 6 show the first to sixth embodiments of F.
FIG. 7 is a block diagram of an optical receiver of the SK heterodyne detection system, FIG. 7 is a diagram showing the spectrum of the output of the optical detector 3 of FIGS. 1 to 6, and FIG. 8 is a focal length of the optical receiver of the direct detection system. And FIG. 9 are diagrams showing the solid angle of the visual field, FIG. 9 is a diagram showing the focal length and the solid angle of the visual field of the optical receiver of the heterodyne detection system, and FIGS. 10 (A) and (B) are FIGS. Photodetector 3
11A and 11B are plan views showing signal light, local oscillation light, and background light in the light receiving area of FIG. FIG. 12 is a block diagram of a conventional FSK heterodyne detection type optical receiver. 1 ... Optical receiving antenna, 2 ... Optical multiplexer, 3 ... Optical detector, 4, 11 ... Intermediate frequency filter (IF filter), 5, 12 ... Intermediate frequency amplifier (IF amplifier), 6 ... Frequency discriminator, 7 ... Baseband filter, 8 ... Signal processing circuit, 10 ... Local oscillator, 13, 31 ... Detector, 14 ... Controller, 15, 21, 25 ... Driving device, 16 ... Deflection device, 20 ... Spatial filter, 22 ... Collimating lens for local oscillation light, 23 ... Condensing lens for local oscillation light, 24 ... Position control device, 30 ... Amplifier, 32 ... Operation unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kanshiro Kashiki 5 Seiji-cho, Seika-cho, Soraku-gun, Kyoto Pref. 5 Hiratani, Arai Optical Communications Research Laboratory, Inc. (56) Reference JP-A-59- 165536 (JP, A)

Claims (1)

[Claims] 1. After receiving a signal light transmitted from a partner station during space propagation communication, the received signal light and a local oscillation light are combined and converted into an electric signal of a predetermined frequency for demodulation. In the optical signal receiving device for spatial propagation communication of the heterodyne detection method, detecting means for detecting the level of background light received together with the signal light and outputting a detection signal proportional to the level of the background light, and output from the detecting means And a control means for reducing the beam diameter of the local oscillation light to reduce the reception field of view of the optical signal receiving device as the detected signal increases. Optical signal receiver.