JPH0879184A - Optical communication equipment - Google Patents

Abstract

PURPOSE: To make an optical communication equipment small and light by leading the detection signal of each photo diode of a four-quadrant photodetector to an operational amplifier part and calculating the deviation of the incidence direction or laser light to each light reception part and using a part of photo diodes as a light reception element for communication. CONSTITUTION: In the four-quadrant photodetector, laser light received by light reception parts 1 to 4 is led to optical amplifiers 9 to 12 through optical fibers 5 to 8 and is amplified in the stage of light. Amplified signal light is led to photo diodes 13 to 16 and is converted to electric signals, and they are processed in an operation processing part 17, and deviation detection signals of laser light made incident on light reception parts 1 to 4 are outputted. A direction control mirror not shown in Fig. is driven by these deviation signals to correct the deviation of incident laser light, and thus, acquisition and tracking operation are performed. An optical signal for communication is detected in the photo diode 16 and is converted to an electric signal and is amplified by an amplifier and is demodulated by a demodulator and is received.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication device using laser light used for cooperative communication between spacecraft such as artificial satellites.

[0002]

2. Description of the Related Art In various spacecraft such as artificial satellites and space stations, it is important to cooperate with each other in terms of operation. Therefore, in terms of communication as well, cooperative communication between these spacecraft is required. Has been done. Conventionally,
Such cooperative communication between spacecraft is performed using radio waves. However, as the activities in space such as earth observation satellites and space stations increase, the amount of information to be transmitted between spacecraft also increases dramatically, and the data signal rate is required to be about 1 to 10 Gbps. However, the conventional radio-wave communication system has already reached a practical limit due to the problem of frequency allocation for preventing interference, the antenna aperture, the transmission output limit, and the like. Therefore, an optical communication system using laser light has been attracting attention, and an optical communication system between spacecrafts is regarded as promising especially in outer space that is not affected by the atmosphere. By the way, when this optical communication system using laser light is used for coordinated communication between spacecraft, the beam width of the laser light is very narrow, about 10 ^-12 to 10 ^-15 deg. It is necessary to perform a capturing operation for capturing the laser beam from the other party and a tracking operation for continuously capturing the laser beam from the other party according to the movement of the other party after setting the communication line.

In such an optical communication apparatus accompanied by the capturing / tracking operation, high-precision beam control on the order of μrad is required for transmitting / receiving a laser beam to / from a communication partner at a long distance of tens of thousands of kilometers. As a sensor used for this beam control, a four-division photodiode (QD) 101 as shown in FIG. 3 which is a light-receiving element having a light-receiving surface divided into four in the past, or a four-division photodiode as shown in FIG. An avalanche photodiode (QAPD) 111 is known. The four-divided photodiode 101 does not have an amplifying action, but the four-divided avalanche photodiode 111 has an electric amplification function by the avalanche effect, like the normal avalanche photodiode.
As shown in FIG. 4, each divided light receiving element 112 of this four-divided avalanche photodiode is divided into four divided light-receiving elements 102 of the four-divided photodiode shown in FIG. 3 for noise reduction.
The distance between them is wider than that. And tens of thousands of km
Although the optical signal propagated over a long distance is diffused and becomes extremely weak, the incident direction of the laser beam is detected from the difference in the amount of light received by each of the four divided light receiving elements by using the above four divided light receiving elements to direct the light. The control mirror and the like are controlled to perform a capturing / tracking operation.

[0004]

By the way, the above-mentioned four-division photodiode (QD) is obtained by dividing a light-receiving surface of a photodiode, which is a general light-receiving element, into four, and is small in size like a general photodiode. It is easy to handle, but since it has no amplification effect, it has the drawback of poor sensitivity. On the other hand, a 4-division avalanche photodiode (QAPD), unlike the 4-division photodiode, has sufficient sensitivity because it has an amplifying function in the element itself, but is strongly affected by shot noise because it has an amplifying function. Further, there is a problem that the size and weight become large due to the electric system required for amplification.

The present invention has been made to solve the above-mentioned problems of the four-division photodiode or the four-division avalanche photodiode used in the conventional optical communication device, and is a general photoreception system which is easy to handle. It is an object of the present invention to provide an optical communication device equipped with a four-quadrant photodetector that can obtain sensitivity equivalent to that of a four-divided avalanche photodiode by using a diode.

[0006]

In order to solve the above problems, the present invention is mounted on spacecraft such as artificial satellites, and optical communication by laser light for performing cooperative communication between the spacecrafts. In the device, four light-receiving sections each including an optical system arranged in close proximity, an optical amplifier for amplifying each laser beam received by each light-receiving section, and four for detecting each amplified optical signal. A four-quadrant photodetector for tracking / capturing, which is composed of two photodiodes, is configured so that a part of the four photodiodes constituting the four-quadrant photodetector for tracking / capturing can also be used as a light receiving element for communication. To do.

In the optical communication device configured as described above, each laser beam received by each light receiving section is amplified by an optical amplifier and then detected by an individual photodiode. Then, it is used as a control signal for tracking / capturing, and a part of the photodiode is also used as a light receiving element for communication to detect a communication signal. Therefore, it is possible to obtain an amplified detection signal for tracking / capturing similar to the case of using the quadrant avalanche photodiode by using the photodiode which is easy to handle. Also, because a part of the photodiode is used as a light receiving element for communication, there is no need for a separate optical element such as a light receiving element for communication or a beam splitter, and the number of parts used is reduced to simplify the configuration and facilitate optical design. It is possible to reduce the size and weight of the entire device.

[0008]

EXAMPLES Next, examples will be described. FIG. 1 is a schematic diagram showing a configuration of a four-quadrant photodetector portion in an embodiment of an optical communication device according to the present invention. 1 to 4 in FIG.
Are light-receiving portions made of, for example, an optical lens system having a diameter of about 0.5 mm, and are arranged extremely close to each other, for example, at intervals of 0.1 mm or less. 5 to 8 are optical fibers,
One end is connected to each of the light receiving units 1 to 4 and the other end is connected to the optical amplifiers 9 to 12, respectively. As the optical amplifiers 9 to 12, semiconductor optical amplifiers (elements having a structure similar to that of a semiconductor laser, which does not oscillate by itself but optically amplifies the optical signal when input) are used. Reference numerals 13 to 16 are photodiodes for converting the optical signals amplified by the optical amplifiers 9 to 12 into electric signals, and 17 is an arithmetic processing unit, which is photoelectrically converted from the photodiodes 13 to 16. Receiving the detection signal, performing arithmetic processing, detecting the deviation of the incident direction of the incident laser light to the light receiving units 1 to 4, and sending a control signal to a driving device for driving a directional control mirror (not shown). Is.

Of the photodiodes 13 to 16, for example, the photodiode 16 is used as a light receiving element for communication, and the optical signal guided to the photodiode 16 is used as an optical signal for communication, and the photodiode 16 converts it into an electrical signal. After conversion, as shown in Fig. 2, it is led to the amplifier 18 for amplification and demodulation.
It is configured to demodulate at 19 and receive.

In the four-quadrant photodetector of the embodiment thus constructed, the laser light received by the light receiving sections 1 to 4 is
It is guided to the optical amplifiers 9 to 12 through the optical fibers 5 to 8 and is amplified at the stage of light. The amplified signal light is guided to the photodiodes 13 to 16 and converted into an electric signal, and arithmetic processing is performed by the arithmetic processing unit 17, and the deviation detection signal of the incident laser light to the light receiving units 1 to 4 is output. It A directivity control mirror (not shown) is driven by the shift detection signal, and the shift in the incident direction of the incident laser light is corrected, whereby the capture / tracking operation is performed.

In the photodiode 16, a communication optical signal is further detected, converted into an electric signal, amplified by an amplifier 18, demodulated by a demodulator 19 and received.

[0012]

As described above on the basis of the embodiments,
According to the present invention, a low noise optical amplifier and a photodiode are combined to form a four-quadrant photodetector.
Since noise is small, an amplified detection output similar to that of a 4-division avalanche photodiode can be obtained, and part of the photodiodes is used as a light-receiving element for communication. The overall size and weight can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a 4-quadrant photodetector portion of an embodiment of an optical communication device according to the present invention.

2 is a diagram showing a communication signal processing system connected to the four-quadrant photodetector shown in FIG.

FIG. 3 is a diagram showing a configuration example of a conventional four-division photodiode.

FIG. 4 is a diagram showing a configuration example of a conventional 4-division avalanche photodiode.

[Explanation of symbols]

 1 to 4 light receiving unit 5 to 8 optical fiber 9 to 12 optical amplifier 13 to 16 photodiode 17 arithmetic processing unit 18 amplifier 19 demodulator

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Claims (1)

[Claims] 1. An optical communication device using a laser beam, which is mounted on a spacecraft such as an artificial satellite and performs cooperative communication between the spacecraft, and comprises an optical system arranged close to each other.
Four quadrant light for tracking / capturing, which is composed of one light receiving section, an optical amplifier for amplifying each laser beam received by each light receiving section, and four photodiodes for detecting each amplified optical signal. An optical communication device comprising a detector, wherein a part of four photodiodes constituting the tracking / capturing four-quadrant photodetector is also used as a communication light receiving element.