JPH04256234A - Optical space transmission system - Google Patents

Abstract

PURPOSE:To hold transmission quality while burden for light sources is reduced by detecting the level of a received optical signal, feeding back the detected result to a transmission-side, and permitting the transmission-side to control the level of an input current for the light sources to an irreducible minimum. CONSTITUTION:An auxiliary carrier 2 is previously modulated in a modulator 3 based on the input signal, 1, is branched into n-number in a branching unit 4. The signals are amplified in the appropriate levels in respective amplifiers 5a-5n, are converted into the optical signals in E/O converters 6a-6n and are transmitted to an open space. The optical signals transmitting the space are converged in a lens system 8, are converted into electric signals in an O/E converter 9 and are branched in a branching unit 10. Then, the reception levels of the optical signals are detected in an optical signal reception level detector 12 and they are noticed to a control part 7 on the transmission-side by a feedback means 13. The control part 7 controls the input current level to the irreducible minimum so that the reception optical level becomes optimum based on the optical signal reception level information.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical space communication system in which information to be transmitted is transmitted and received in the form of optical signals using an open space as a transmission path.

0002

[Prior Art] Conventionally, in optical space communication, due to the characteristics of the transmission path in open space, subcarriers are used in input signals, taking into account the effects of fluctuations in the level of optical signals due to fluctuations in the atmosphere and attenuation of the optical signals themselves. By modulating the intensity of the light source with the modulated signal and converting it into an optical signal, the signal is transmitted and received through an open space as a transmission path. The transmission method is one-to-one, in which the optical signal is sent to and received from the target location as parallel light using a lens system.
It can be broadly divided into communication and 1-to-N communication, in which optical signals are diffused by a lens system and sent to and received from multiple locations.

0003

[Means for solving the problem] However, in the conventional 1-to-1 and 1-to-N optical space communications, the received light level decreases due to attenuation and diffusion of the optical signal in the atmosphere, making it difficult to accurately transmit information. The transmission distance over which data can be sent and received was limited, and there were problems with reliability.

[0004] Therefore, one possible solution to the above problem is to increase the transmission optical power on the transmitting side. However, the peak current that can be input to the light source is
There is always a maximum rating, and if you input a level that exceeds that, the light source will be damaged or destroyed. Furthermore, a light source with a maximum rating that allows for a large input peak current is expensive and difficult to obtain. Furthermore, if the effects of secondary distortion, intermodulation distortion, etc. caused by nonlinearity in the power current characteristics of the light source cannot be ignored, additional limitations on the degree of modulation will occur.

[0005] Due to the above-mentioned constraints, it is currently difficult to solve the above-mentioned problems. A method has also been proposed in which the input signal is split into multiple parts, the intensity modulation is performed on multiple light sources, the resulting optical signals are combined, and each optical signal is transmitted using a common transmission path. However, if the received light level on the receiving side is higher than necessary, it is useless.

The present invention was made to solve the above problem, and the level of the received optical signal is detected, the detection result is fed back to the transmitting side, and the transmitting side adjusts the input current to each light source. The object of the present invention is to provide an optical space transmission system that can reduce the burden on a light source while maintaining transmission quality by controlling the level to the minimum necessary level.

[0007]

Means for Solving the Problems In order to achieve the above object, the optical space transmission system of the present invention has the following configuration. In other words, in optical space communication, which splits an input signal into multiple signals and modulates the intensity of each light source with each signal, it is transmitted and received by the receiving side in an open space as a transmission path. a detection means for detecting an optical signal level; a feedback means for feeding back the detection result of the detection means to a transmitting side; and a control for controlling intensity modulation of the light source on the transmitting side based on the detection result of the feedback means. means.

[0008]

[Operation] In the above configuration, the input signal is split into multiple signals, each signal is used to modulate the intensity of each light source, the resulting optical signal is optically transmitted to an open space as a transmission path, and the receiving side The received optical signal level is detected and the detection result is fed back to the transmitting side. Then, on the transmitting side, it operates to control the intensity modulation of the light source based on the feedback received optical signal level.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of the optical space transmission apparatus in this embodiment. In FIG. 1, a subcarrier 2 is premodulated by a modulator 3 based on an input signal 1, and the modulated wave is split into n pieces by a splitter 4. Next, each of the demultiplexed modulated waves is transmitted to each of the amplifiers 5a to 5.
n, and is amplified to an appropriate level within the maximum rating of a light emitting element such as a laser diode (hereinafter referred to as LD) or a light emitting diode (hereinafter referred to as LED) in the corresponding E/O converter 6a to 6n. And each E/O converter 6a to 6
n is converted into an optical signal and sent out into open space.

On the other hand, the optical signal transmitted through the space is focused by a lens system 8, and is focused by a Pin photodiode (hereinafter referred to as a Pin photodiode).
PD) and avalanche photodiode (APD)
) is converted into an electrical signal by an O/E converter 9 including a light receiving element such as a light receiving element. Here, the converted signal is demultiplexed by a demultiplexer 10 and inputted to a detector 11 and an optical signal reception level detector 12, respectively. Then, the signal is regenerated into the original signal by the wave detector 11, and the optical signal reception level is detected by the optical signal reception level detector 12. This detected reception level is fed back to the control unit 7 on the transmitting side by the feedback means 13. and,
Based on the optical signal reception level information, the control unit 7 controls each light source (E/O
The amplification degree of each amplifier 5a-5n, which determines the input current level to the converters 6a-6n), is controlled to the necessary minimum.

[0012] As the above-mentioned feedback means 13, for example, the signal may be returned to the transmitting side again in the form of an optical signal, or a telephone line or the like may be used.

As explained above, according to this embodiment,
If the optical signal is greatly attenuated in the atmosphere due to weather conditions, etc., the transmission margin can be increased by increasing the input current level to the light source and increasing the optical output containing effective information. In addition, when the attenuation of optical signals in the atmosphere is small, by reducing the input current level to the light source, it reduces power consumption and the burden on the light source while maintaining transmission quality. be able to.

In this embodiment, premodulation is performed as a means of high-quality optical transmission without relying on the linearity of the light source, but it is also possible to directly modulate the light emitting element by changing the amplitude of the input signal. It's okay. In this case, the device configuration is simple, but since the information corresponds to changes in the amplitude of the light intensity, it is easily affected by nonlinear distortion and noise of the light emitting element, and the light emitting element must have good linearity. becomes.

[0015]

[Other Embodiments] Next, other embodiments according to the present invention will be described below with reference to the drawings.

The control unit 7 in the above-described embodiment controls the level of input current to the light source by controlling the amplification degree of each of the amplifiers 5a to 5n, but as shown in FIG.
Variable attenuators 14a to 14n are provided at the next stage of 5n,
It may be configured to control each attenuator value.

Further, in this embodiment, application to optical space communication in which optical signals are transmitted and received using an open space as a transmission path has been described, but it is also possible to use it for wired transmission using an optical fiber.

Furthermore, as shown in FIG. 3, by combining each optical signal using the optical multiplexer 15 and transmitting it using a common transmission path, it is only necessary to adjust the axis alignment of the transmitted light at one location. It becomes like this.

[0019] Furthermore, in wired transmission, transmission is possible using a single optical fiber. FIG. 4 is a diagram showing a fiber coupler as an example of an optical multiplexer.

According to the embodiment described above, an input signal is demultiplexed into a plurality of signals, the optical signals obtained by intensity modulating a plurality of light sources with each signal are multiplexed, and the optical signals are combined into a common signal. By transmitting using a transmission line, it is possible to increase the size of the optical signal containing effective information even if a cheap and easily available light source with a small maximum input peak current rating is used. The transmission margin becomes larger. Therefore, it becomes possible to extend the transmission distance and improve reliability.

Furthermore, by combining the optical signals and transmitting them using a common transmission path, it becomes easy to adjust the axis of the transmitted light. Furthermore, even if one of the light emitting elements is damaged or destroyed, the transmission system will not be immediately disconnected.

[0022]

[Effects of the Invention] As explained above, according to the present invention,
By detecting the level of the received optical signal and feeding back the detection result to the transmitting side, the transmitting side controls the input current level to each light source to the minimum necessary.
It is possible to reduce the burden on the light source while maintaining transmission quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an optical space transmission device in this embodiment.

FIG. 2 is a block diagram showing the configuration of an optical space transmission device in another embodiment.

FIG. 3 is a diagram showing an optical multiplexer for spatial transmission.

FIG. 4 is a diagram showing an optical multiplexer for wired transmission.

[Explanation of symbols]

1 Input information 2 Subcarrier 3 Modulator 4 Duplexer 5a~5n Amplifier 6a-6n E/O converter 7 Control section 8. Optical system 9 O/E converter 10 Duplexer 11 Detector 12 Optical signal reception level detector 13 Feedback system 14a~14n Variable attenuator 15 Optical multiplexer 16 Optical fiber coupler

Claims (1)

[Claims] Claim 1: An optical signal obtained by splitting an input signal into multiple signals and modulating the intensity of each light source with each signal,
In optical space communication, which transmits and receives data through open space as a transmission path,
The receiving side includes a detection means for detecting the received optical signal level, a feedback means for feeding back the detection result by the detection means to the transmitting side, and a transmitting side for detecting the light source based on the detection result by the feedback means. 1. An optical space transmission system comprising: control means for controlling intensity modulation.