JPH07226713A - Optical communication system - Google Patents

Abstract

PURPOSE:To realize stable large capacity optical communication with high accuracy by realizing a modulation and demodulation characteristic with a high efficiency. CONSTITUTION:A modulator 10 modulates directly an incident light based on a spread spectrum modulation signal, and the modulated transmission light is sent from a sender side by an optical antenna 12 through space propagation, the transmission light propagate through space is received by a receiver optical antenna 13, and the light is synthesized with a local light, a photodetector 16 applies heterodyne detection to the synthesized light to generate an RF signal, and a conjugation filter 17 compresses and demodulates a spread spectrum modulation signal based on the RF signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system constructed in, for example, outer space and performing optical communication by utilizing space propagation.

[0002]

2. Description of the Related Art Generally, in an optical communication system, a method is adopted in which communication stations are connected by an optical fiber cable, and the optical fiber cable is used as a transmission line to perform optical communication between them. In such an optical communication system, it is possible to dramatically increase the communication capacity as compared with conventional RF communication.

By the way, in the recent field of space development, communications such as inter-satellite communications are diversified, and an increase in communications capacity is required. Therefore, in the field of space development, there is a concept of constructing an optical communication system in outer space to increase the communication capacity.

However, the optical communication system using the optical fiber cable has a problem that it is difficult to construct it in outer space because the optical fiber cable must be laid between the communication stations.

Therefore, as an optical communication system constructed in outer space, without laying an optical fiber cable,
A method of transmitting light to a partner station to perform optical communication by utilizing spatial propagation has been considered and studied. Such an optical communication system is called a coherent optical communication system, and it is possible to dramatically increase the communication capacity as compared with a system using an optical fiber cable, but demodulate the modulated transmission light. Since the loss is relatively large, it is an urgent task to reduce modulation / demodulation loss in practice.

[0006]

As described above, the conventional optical communication system has a problem that it is difficult to construct it in outer space. The present invention has been made in view of the above circumstances, and realizes highly efficient modulation / demodulation characteristics,
An object of the present invention is to provide an optical communication system that realizes highly accurate and stable large-capacity optical communication.

[0007]

SUMMARY OF THE INVENTION According to the present invention, modulating means for modulating incident light on the basis of a spread spectrum modulation signal to generate transmitted light, and transmitting light generated by this modulating means is radiated into space to generate a space. An optical transmission means for propagating and transmitting
Optical receiving means for receiving the transmitted light radiated into the space by the optical transmitting means and propagating in the space, and the transmitted light received by the optical receiving means are combined with the local light for heterodyne detection, and R
An optical communication system is configured to include a detection unit that generates an F signal and a conjugate filter that compresses and demodulates the spread spectrum modulation signal based on the RF signal generated by the detection unit.

[0008]

According to the above construction, the incident light is directly modulated on the basis of the spread spectrum modulation signal, the modulated transmission light is transmitted by using the spatial propagation, and the transmission light propagated in the space is received. Then, the transmitted light is heterodyne detected and R
An F signal is generated, and the spread spectrum modulation signal is compressed and demodulated based on this RF signal. This enables highly efficient optical communication with little loss of modulation / demodulation characteristics.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an optical communication system according to an embodiment of the present invention, in which a modulator 10 is arranged on the side of a first spacecraft. An oscillator 11 is connected to the modulator 10, and an optical antenna 12 is connected to the output end thereof. When the incident light is input, the modulator 10 modulates the incident light based on the spread spectrum modulation signal from the oscillator 11 to generate the transmission light λ1 and outputs the transmission light λ1 to the optical antenna 12. To do. The optical antenna 12 is
The transmitted light λ 1 that is input and is directed to the optical antenna 13 installed on the second spacecraft side of the communication partner is converted into parallel light, and this parallel light is radiated to outer space and propagated through the space. 2 to the optical antenna 13 on the side of the spacecraft.

One input end of a beam splitter 14 is connected to the optical antenna 13 on the side of the second spacecraft,
The output end of the local optical oscillator 15 is connected to the other input end of the beam splitter 14. An optical detector 16 is connected to the output end of the beam splitter 14, and the input transmission light λ1 and the local light λ2 from the local optical oscillator 15 are combined to generate an intermediate frequency signal fIF, and the optical detector 16 is supplied. Output.

The photodetector 16 is formed of, for example, a diode, and the output end thereof is connected with a conjugate filter 17 formed of a compression filter such as an elastic surface filter. The optical detector 16 receives the input intermediate frequency signal fIF | (1 / λ1
)-(1 / .lambda.2) | is heterodyne-detected to generate an RF signal, which is output to the conjugate filter 17 connected to its output end. A threshold value judgment circuit 18 is connected to the output end of the conjugate filter 17, and the spread spectrum modulation signal is compressed and demodulated based on the input RF signal and output to the threshold value judgment circuit 18. The threshold value determination circuit 18 determines the input signal based on a predetermined threshold value and generates a demodulated signal.

As described above, in the optical communication system, the modulator 10 directly modulates the incident light based on the spread spectrum modulation signal, and the modulated transmission light is modulated by the optical antenna 1.
At 2, the light is transmitted from the transmitting side using space propagation, and the transmitted light propagating in this space is received by the optical antenna 13 on the receiving side,
After being multiplexed with the local light, the photodetector 16 performs heterodyne detection to generate an RF signal, and the conjugate filter 17 compresses and demodulates the spread spectrum modulation signal based on the RF signal.

According to this, a highly efficient modulation / demodulation characteristic with almost no loss is realized, and the construction of a large communication capacity coherent optical communication for radiating the transmitted light to outer space and propagating in outer space for transmission is realized. To be done.

In the above embodiment, the case where the device is mounted on a spacecraft and provided for optical communication in outer space has been described. However, the present invention is not limited to this, and it can be transmitted in a space where the transmitted light can propagate in space. Is also applicable.

In the above embodiment, the conjugate filter 17 is used.
In the above description, the threshold value determination circuit 18 determines the signal demodulated in step 1 by a predetermined threshold value to generate a demodulated signal. However, the present invention is not limited to this. You may comprise so that it may extract as a demodulation signal. Therefore, it is needless to say that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

[0016]

As described in detail above, according to the present invention, it is possible to provide an optical communication system which realizes highly efficient modulation / demodulation characteristics and realizes highly accurate and stable large capacity optical communication. .

[Brief description of drawings]

FIG. 1 is a diagram showing an optical communication system according to an embodiment of the present invention.

[Explanation of symbols]

 10 ... Modulator. 11 ... Oscillator. 12, 13 ... Optical antenna. 14 ... Beam splitter. 15 ... Local optical oscillator. 16 ... Photodetector. 17 ... Conjugate filter. 18 ... Threshold value judging circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H04B 10/152 10/142 10/04 10/06 H04J 13/00 H04J 13/00 A

Claims (2)

[Claims] 1. A modulation means for modulating incident light on the basis of a spread spectrum modulation signal to generate a transmission light, and an optical transmission for radiating the transmission light generated by the modulation means into a space and propagating the space for transmission. Means, an optical receiving means for receiving the transmitted light radiated into the space by the optical transmitting means and propagated in the space, and a heterodyne detection by combining the transmitted light received by the optical receiving means with the local light to obtain an RF signal. An optical communication system comprising: a detection unit that generates the signal and a conjugate filter that compresses and demodulates the spread spectrum modulation signal based on the RF signal generated by the detection unit. 2. The optical communication system according to claim 1, further comprising threshold value determining means for determining a threshold value of the demodulated signal demodulated by the conjugate filter and extracting the demodulated signal.