JPH0479624A - Optical spatial communication equipment - Google Patents

Abstract

PURPOSE:To reduce the occurrence of signal errors by providing a light spreading device which emits an optical beam in a state where the beam is spread to a prescribed angle and a photodetector which receives an incident optical beam and constituting the light spreading device to be provided in front of a semiconductor laser element with a concave lens system. CONSTITUTION:The concave lens 31 of a light spreading device 30 is provided in front of the glass window 20 of a semiconductor laser element 20 in a state where the lens 31 is faced to the window 24 at a short distance. When the laser chip 23 of the element 20 is operated by supplying an electric current to the chip 23, beams B1a and B1b are emitted in a forward/backward direction from the chip 23. The backward beam B1b is made incident on a photodiode 26 where the light quantity of the beam B1b is automatically controlled and the forwarding beam B1a becomes an optical beam B1 after passing through the window 24 and made incident on the lens 31. The optical beam B1 is emitted in a state where the beam B1 is spread to an angle theta1 between lines H1 and H2 in a vertical direction by the radiation characteristic of the lens 31. When the shape of the lens 31 is changed, in addition, the spread state of the light beam can be changed arbitrarily in a three- or two-dimensional space.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical space communication device that emits and enters a light beam from a semiconductor laser element in a long distance space to communicate signals to be transmitted.

2. Description of the Related Art In a conventional optical space communication device, as shown in FIG. 4, an output signal from a signal generator 3 that generates a signal to be transmitted is modulated by a modulator 2 and applied to a laser element 1. Ru. The light beam B emitted from this laser element 1 is also
is incident on the light-receiving element 4 which is separated by a certain distance and is converted into an electrical signal, and this electrical signal is demodulated by the demodulator 5 and taken out as a received signal.

Problems to be Solved by the Invention However, in the conventional optical space communication device described above, since the light intensity modulated is used as the light emitted from the laser element 1, the received light power at the light receiving element 4 is different from that of the laser element. 1
It becomes smaller in inverse proportion to the square of the distance between the light receiving element 4 and the light receiving element 4. Therefore, for example, the minimum light receiving sensitivity -5Q dBm
If this is the case, even a laser light source with an output of 1 mW can only be applied over a distance of several hundred meters, and the communication distance is extremely limited.

Furthermore, in the same optical space communication device, since the laser beam has sharp directivity, if the laser beam deviates from the laser beam, the light will not be received by the light receiving element. Therefore, strict positional accuracy is required for the light receiving element 4 with respect to the laser element 1. Although the illustrated optical space communication device uses direct modulation of a laser element, the same applies to external modulation.

Furthermore, due to the directivity and straightness of the laser beam, if there is a foreign material in the light propagation path, or if the refractive index changes due to local changes in the propagation path, such as temperature or humidity, etc. , causing diffraction, path changes, speed changes, etc. of the optical signal. Therefore, in the transmission of high-speed optical signals, transmission errors may occur, and the signal light may be disturbed by the influence of external light. Effective countermeasures for these problems have not yet been proposed, and rely on methods such as lowering the transmission speed or using cable transmission using optical fibers.

In addition, although it is difficult to receive signals outside the optical propagation path due to the straightness of light, it is possible to intercept optical signals using reflected light, etc., so there are issues such as the secrecy of the signal is not perfect. There is.

In view of these conventional problems, an object of the present invention is to provide a communication system for optical space transmission that can extend the communication distance and reduce transmission errors under various conditions of the optical propagation path. Furthermore, it is an object of the present invention to obtain an optical space communication device that can facilitate signal transmission, improve quality, and reduce cost, ensure signal confidentiality, and simplify system configuration.

Means for Solving the Problem In order to achieve this problem, the present invention provides a coded signal generator that encodes and generates a signal to be transmitted, and a modulator that modulates the coded signal from the coded signal generator. and a semiconductor laser element that emits a light beam according to a modulation signal of the modulator, a light diffusion device that diffuses the light beam at a predetermined angle and emits it, and a light receiving element that receives the incident light beam,
First, the light diffusing device installed in front of the semiconductor laser element is constituted by a concave lens system.

Second, the light diffusing device installed in front of the semiconductor laser element is constituted by a hologram mirror.

Effects According to the configuration of the present invention described above, the coded signal from the coded signal generator is modulated, converted into a light beam by the semiconductor laser element, and then outputted to the light receiving element side in the form of spectrum spread by the light diffusion device. , and optical transmission communication is performed. As a result, even when the light intensity is weak, transmission errors are small, and accordingly, restrictions on the reachable distance are relaxed, and furthermore, the signal light is not disturbed by the influence of external light, and is correctly transmitted. Further, in the case of high-speed optical signal transmission, the signal is transmitted in the same manner, and the confidentiality of the signal can be ensured. A light diffusing device is easily installed in front of the semiconductor laser element, and the emitted light can be diffused to any desired extent.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an optical space communication device according to the present invention, which includes a coded signal generator 13 that codes and generates a signal to be transmitted. The coded signal from the coded signal generator 13 is input to the modulator 12, modulated, and applied to the semiconductor laser element 20. The light beam B1 emitted from this semiconductor laser element 20 is also transmitted to the light diffusing device 3.
0 and is processed to be diffused at a predetermined angle θ and output, and this spectrally spread light beam B! is emitted into the air along the optical propagation path. On the other hand, a light receiving element 15 is located at a distance from the light diffusing device 30, and a light beam B2
is installed so that a part of the light beam B is incident thereon.

The light receiving element 15 converts the light beam B into an electrical signal, and this electrical signal is input to a demodulator 16 to be demodulated and further input to a signal decoder 17. Signal decoding device 1
7 decodes the encoded signal by performing signal processing in the opposite manner to that of the encoded signal generator 13, so that a normal received signal is extracted.

According to the optical space communication device of the illustrated embodiment described above, the light beam B of the encoded signal from the light diffusion device 30.

is emitted while being diffused over a wide area, and this encoded signal is electrically decoded again on the side of the light receiving element 15 and optically transmitted. Therefore, with this type of encoded signal transmission form, the emitted light can be received sufficiently even when the light intensity is weak or over a long distance, and the signal light is not disturbed by various external conditions or the influence of external light. In other words, even if there is a foreign substance in the light propagation path or a change in refractive index occurs due to local changes in temperature, humidity, etc. in the propagation path, the optical signal There will be no changes such as diffraction, course changes, speed changes, etc. Also, the signal will not be disturbed by the influence of external light, thereby eliminating transmission errors and ensuring correct transmission.

On the other hand, as described above, by improving the efficiency of optical transmission, even in the case of high-speed optical signal transmission, high-speed and correct transmission is possible. Signal encoding ensures confidentiality. Furthermore, since the light beam is emitted in a diffused manner, the positional accuracy of the optical system is no longer critical, and good reception is possible within the range of the diffusion angle θ.

Next, an example of optical transmission will be explained below.

First, the optical output of the semiconductor laser element 20 is 1 mw, the emission wavelength is 53 Q nm, and the insertion loss in the light diffusing device 30 is approximately 8 d.
B. When the diffusion angle θ is about 60 degrees, the light receiving power of the light receiving element 15 is about -43 at a distance of about 5 m.
It was dBm. The spreading code in the encoded signal generator 13 was an m-sequence, and a direct spectrum spread method with a frequency band of 800 MHz was used. The signal word length was 8 bits, 255, and a convolution type matched filter was used for demodulation. Of course, an ultrasonic delay line matched filter may also be used. Regarding the spreading method, a frequency hopping method may be used instead of direct spectrum spreading, and the spreading code is m-sequence,
Other sequences such as the G-old sequence may also be used.

In an experiment regarding signal interference due to external light, when approximately 3 mV of white light was mixed, almost no interference occurred. Although a semiconductor laser was used in this experiment, a gas laser, solid-state laser, or semiconductor laser may also be used.

Part 2 is a side view of an embodiment of the semiconductor laser device and light diffusion device portion of the optical space communication device according to the present invention. The can 21 is fixed with adhesive, and an inert gas such as nitrogen gas is filled inside the can 21 .

A glass window 24 is provided in front of the laser chip 23 at an angle of about 8 degrees, and an APC (automatic light control) monitor photodiode 26 is installed inside the base 25 behind the laser chip 23. A pin 27 for supplying current to the laser chip 23 and photodiode 26 is provided on the outside of the pin 25 . A concave lens 31 of a light diffusing device 30 is installed in front of the glass window 24 of this semiconductor laser element 20 so as to face each other in close proximity.

According to the illustrated embodiment described above, when the laser chip 23 of the semiconductor laser device 20 is operated by supplying the current of the encoded signal, the emitted light B, . . .
Bmb comes out. The rear emitted light B1b is the photodiode 2
6, the amount of light is automatically controlled, and the 8 front emitted lights pass through the glass window 24 and become the light beam Bs, which is then turned into the concave lens 3.
1. The light beam B1 is emitted after being diffused at an angle θ1 between H1° (1°) in the vertical direction due to the radiation characteristics of the concave lens 31.

Note that by changing the shape of the concave lens 31, the spread of light can be set arbitrarily three-dimensionally or two-dimensionally.

FIG. 4 shows another embodiment described above, in which the semiconductor laser element 2
0 has the same configuration as that shown in FIG. 3, and a hologram element 32 is installed in front of the glass window 24. Therefore, in this embodiment, the light beam B1 is emitted while being diffused within the angle θ! of direction H,,)(4) due to the radiation characteristics of the hologram element 32. The shape of 32 allows the light diffusion state to be set arbitrarily.

Effects of the Invention As explained above, the optical space communication device according to the present invention has no directivity (no interference caused by external light, and the received signal error is extremely small), making it suitable for high-quality optical communication devices. The utility value as a material is greatly improved.

Since the system configuration is easy to install and is inexpensive, it has industrial value as a key device for information transmission in the future information society. In addition, since the light beam of a semiconductor laser is used, the above-mentioned effects can be fully demonstrated.
Since the light diffusing device is installed in front of the semiconductor laser element, it can be integrated compactly.

[Brief explanation of drawings]

Fig. 1 is a block wiring diagram of the optical space communication device according to the present invention, Fig. 2 is a side view of an embodiment of a semiconductor laser element and a light diffusion device, Fig. 3 is a side view of an embodiment included in the package, and Fig. 4 is a block diagram of a conventional optical space communication device. 20... Semiconductor laser element, 12... Modulator, 13
...Encoded signal generator, 30...Light diffusion device, 1
5... Light receiving element. Name of agent: Patent attorney Shigetaka Awano and one other person Figure 2

Claims (4)

[Claims] (1) A coded signal generator that encodes and generates a signal to be transmitted, a modulator that modulates the coded signal from this coded signal generator, and a semiconductor that emits a light beam based on the modulation signal of this modulator. The light diffusing device includes a laser element, a light diffusing device that diffuses and emits a light beam at a predetermined angle, and a light receiving element that receives the incident light beam, and is installed in front of the semiconductor laser device and is configured with a concave lens system. An optical space communication device characterized by: (2) The coded signal generator has the following coded signal format:
2. The optical space communication device according to claim 1, wherein the optical space communication device uses a spread spectrum method using an m-sequence signal. (3) A coded signal generator that encodes and generates a signal to be transmitted, a modulator that modulates the coded signal from this coded signal generator, and a semiconductor that emits a light beam based on the modulation signal of this modulator. The light diffusing device, which includes a laser element, a light diffusing device that diffuses and emits a light beam at a predetermined angle, and a light receiving element that receives the incident light beam, and is installed in front of the semiconductor laser device, is configured with a hologram mirror. An optical space communication device characterized by: (4) The coded signal generator has the following coded signal format:
4. The optical space communication device according to claim 3, wherein the optical space communication device uses a spread spectrum method using an m-sequence signal.