Multi-channel optical communication system that controls optical reflection for each channel and optical transmitting and receiving apparatus therefor

[0001] [Technical field to which the invention belongs] The present invention uses light as a medium<u style="single">Kotsu</u>Regarding the communication system, in particular, multi-channel using a retroreflective device represented by a corner cube.<u style="single">Kotsu</u>Communication system and optical transmission equipment for it<u style="single">In place</u>Related. [0002] [Conventional technology] Research is being conducted on communication systems using light that are not legally restricted, such as radio wave communication, by replacing communication using radio waves that are subject to various legal restrictions. An example of such an optical communication system is "High-speed light intensity modulation using attenuated total reflection in corner cubes" (Toshihiro Tsumura et al., Shingaku Giho SANE94-91, SAT94-91, pp.111-114). It is disclosed in. [0003] The communication system disclosed here is a bidirectional space optical communication system using a laser, and a laser oscillator is provided on one side and a corner cube is provided on the other side. By modulating the laser light emitted from the laser oscillator with an external signal, the light receiving side can demodulate the signal from the received laser light. [0004] The corner cube reflects this incident light toward the laser oscillator. At this time, as a characteristic of the corner cube, light incident from a certain direction is reflected in the same direction. Therefore, the reflected light always reaches the very vicinity of the laser oscillator. A modulator for modulating the reflected light is provided on one surface of the corner cube depending on whether the reflection on the corner cube surface is total reflection or non-reflection. By driving this modulator with an external signal, information can be placed on the reflected light. A light receiving sensor that receives the reflected light is provided on the laser oscillator side, and a signal transmitted from the corner cube side can be demodulated from the output of the light receiving sensor. [0005] [Problems to be Solved by the Invention] However, although the above-mentioned communication system can perform bidirectional optical communication, there is a problem that only one channel can be assigned to each transmission / reception. Especially when trying to transmit image information by optical communication, the amount of information becomes very large, so if only one channel is used, the signal section per symbol will be shortened, especially in optical communication using a photoelectric conversion element. In some cases, there is a problem that the demodulation becomes difficult. [0006] Further, as a medium for a multi-channel communication system using light, there is a medium using an optical fiber. Optical fiber can be used for efficient optical communication, but there is a problem that the optical fiber must be spread over a wide area and a huge amount of money is required to build the infrastructure. Further, the optical fiber is not effective in the mutual communication with the mobile body and the mutual spatial communication between the mobile body and the mobile body. [0007] Therefore, an object of the present invention is a multi-channel capable of inexpensively performing a large-capacity optical communication.<u style="single">Kotsu</u>Shin system<u style="single">and</u>Optical transmission equipment for that<u style="single">Place</u>To provide. [0008] [Means for solving problems]<u style="single">Book</u>invention<u style="single">First phase of</u>In the multi-channel optical communication system, the retroreflecting means that reflects the incident light in the same direction as the incident direction and the light reflected by the retroreflective means are used.<u style="single">Multi-channel</u>Modulated by the modulation means from an optical transmitter including a modulation means for modulating based on a transmitted signal, a light emitting means that emits light, and light emitted from the light emitting means and reflected by the retroreflecting means.<u style="single">Multi-channel</u>Includes an optical receiver that includes a demodulation means for demodulating the transmitted signal.<u style="single">It is a multi-channel optical communication system.</u>The modulation means is on the reflective surface of the retroreflective means.<u style="single">, Supports multi-channel transmission signals</u>A plurality of total reflection condition control elements that are arranged and capable of independently controlling light reflection, and each of the total reflection condition control elements,<u style="single">Of the multi-channel transmission signals, the channel corresponding to each reflection condition control element</u>A plurality of demodulation means arranged corresponding to an arrangement of a plurality of total reflection condition control elements for receiving reflected light, including a driving means for controlling independently based on a transmission signal. From the light receiving means having the light receiving element and the output of a plurality of light receiving elements<u style="single">Of the multi-channel transmission signals, the channel corresponding to the total reflection condition control element corresponding to each light receiving element</u>Transmission signal<u style="single">Respectively</u>Includes means for rebuilding. [0009] A plurality of total reflection condition control elements can independently control the reflection of light. Therefore, by controlling the reflection of these plurality of total reflection condition control elements with separate information, a signal is generated from the optical transmitter to the optical receiver as a bundle of light beams modulated by different information. Can be transmitted in multiple channels. Since optical communication is performed on multiple channels, the symbol period can be lengthened, and stable photoelectric conversion can be performed by the light receiving means of the optical receiving device. [0014] Claim<u style="single">1</u>The multi-channel optical communication system according to the invention described in 1.<u style="single">Then</u>The total reflection condition control element is arranged on the reflection surface, and the light reflectance in the total reflection condition control element is obtained by moving the opaque magnetic material enclosed in the transparent capsule and the magnetic material in the transparent capsule by magnetic force. Includes a magnetic force generating means for changing the distribution of. [0015] By changing the distribution of the opaque magnetic material with a magnetic force, total reflection and non-reflection on the reflective surface can be controlled. Since total reflection is performed at the time of reflection, stable communication can be performed with little light loss and relatively little risk of transmission error. [0016] Claim<u style="single">2</u>The multi-channel optical communication system according to the invention described in 1.<u style="single">Then</u>The total reflection condition control element is arranged so as to face the total reflection surface of the retroreflection means from the direction opposite to the direction in which the light is incident on the total reflection surface of the retroreflection means, and is irradiated with light of a specific wavelength. In response to, an optical drive element that changes its shape between a first shape that is in close contact with the total reflection surface and a second shape in which a gap is formed between the total reflection surface and the light drive element. The reflection of the total internal reflection surface is controlled by irradiating the light with a specific wavelength. [0017] Since the total reflection condition control element is driven by light, wiring for sending a signal to the total reflection condition control element becomes unnecessary. The configuration of the device is simplified, the total reflection condition control element can be miniaturized, and the density can be increased. Therefore, the number of channels that can be used increases. [0018] The present invention<u style="single">Other aspects</u>The optical transmitter for a multi-channel optical communication system according to the above is a retroreflective means that reflects incident light in the same direction as the incident direction, and a retroreflective means that reflects light reflected by the retroreflective means.<u style="single">Multi-channel</u>An optical transmitter including a modulation means for modulating based on a transmitted signal.<u style="single">And</u>, Modulation means on the reflective surface of the retroreflective means<u style="single">, Supports multi-channel transmission signals</u>A plurality of reflection condition control elements that are arranged and capable of independently controlling light reflection, and each of the reflection condition control elements,<u style="single">Of the multi-channel transmission signals, the channel corresponding to each reflection condition control element</u>Includes a drive means for independent control based on the transmitted signal. [0019] Multiple<u style="single">Anti</u>The emission condition control elements can independently control the reflection of light. Therefore, these plural<u style="single">Anti</u>By controlling the reflection of the emission condition control element with different information, the signal is transmitted from the optical transmitter to the optical receiver as a bundle of light beams modulated by different information in multiple channels. Can be done. Since optical communication is performed on multiple channels, the symbol period can be lengthened, and stable photoelectric conversion can be performed by the light receiving means of the optical receiving device. [0028] Claim<u style="single">3</u>An optical transmitter for a multi-channel optical communication system according to the invention described in 1.<u style="single">Then</u>The reflection condition control element is arranged on the light reflection surface, and the distribution of the light reflectance in the reflection condition control element by moving the opaque magnetic material enclosed in the transparent capsule and the magnetic material in the transparent capsule by magnetic force. Includes a magnetic force generating means for changing the. [0029] By changing the distribution of the opaque magnetic material with a magnetic force, total reflection and non-reflection on the reflective surface can be controlled. Since total reflection is performed at the time of reflection, stable communication can be performed with little light loss and relatively little risk of transmission error. [0030] Claim<u style="single">4</u>An optical transmitter for a multi-channel optical communication system according to the invention described in 1.<u style="single">Then</u>The reflection condition control element is arranged on the back surface of the transparent plate constituting the reflection surface of the retroreflection means, and in response to being irradiated with light of a specific wavelength, the first shape closely adhered to the back surface and the back surface It includes an optical drive element that changes its shape from the second shape in which a gap is formed between the two, and by irradiating the optical drive element with light of a specific wavelength, the reflection on the back surface of the transparent plate is reflected. Be controlled. [0031] By light<u style="single">Anti</u>Because the shooting condition control element is driven<u style="single">, Anti</u>Wiring for sending a signal to the emission condition control element becomes unnecessary. The configuration of the device becomes simple<u style="single">, Anti</u>The shooting condition control element can be miniaturized and the density can be increased. Therefore, the number of channels that can be used increases. [0036] BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment With reference to FIG. 1, the multi-channel optical communication system 20 according to the first embodiment of the present invention includes an optical transmitter 24 and an optical receiver 22. For example, a video camera 25 is connected to the optical transmitter 24. The optical transmitter 24 transmits the signal received from the video camera 25 to the optical receiver 22 using light. The optical receiver 22 reproduces the video signal output by the video camera 25 from this optical signal and gives it to the signal processing circuit 26 and the monitor 28 for display. [0037] The light receiving device 22 is placed on the optical path of the light source 30 and the light source 30 for emitting a slightly spread light beam toward the light transmitting device 24, and branches the light reflected from the light transmitting device 24 side. The beam splitter 32 for the purpose, the CCD (solid-state image sensor) 34 arranged at the position where the light branched by the beam splitter 32 is received, and the beam splitter 32 are reflected by the beam splitter 32 by rotating the beam splitter 32 around the central axis. A stepping motor 31 for guiding the light to the light receiving surface of the CCD 34, a clock reproduction circuit 36 for reproducing a clock component in a signal transmitted from the optical transmission device 24 based on the output of the CCD 34, and a clock. The signal output by the CCD 34 according to the clock reproduced by the reproduction circuit 36 includes an A / D (analog / digital) conversion circuit 38 for analog / digital conversion according to a signal obtained by multiplying the clock signal output by the clock reproduction circuit 36. .. The output of the A / D conversion circuit 38 is given to the signal processing circuit 26 and displayed on the monitor 28. [0038] The optical transmitter 24 controls the corner cube 40 whose one surface is divided into a large number of pixels and the reflection / non-reflection of each pixel on the above-mentioned one surface of the corner cube 40 according to the video signal given from the video camera 25. Including the modulator 42 of. [0039] With reference to FIG. 2, the corner cube 40 has three reflective surfaces 52, 54 and 56 that are vertically combined with each other. Of these reflecting surfaces 52, 54 and 56, for example, the reflection surface 52 is divided into a plurality of pixels 58. The total reflection / non-reflection of each pixel 58 is controlled by the modulation device 42 for each pixel. [0040] With reference to FIG. 4, the modulator 42 shown in FIG. 1 includes a large number of digital micromirror devices 70 arranged to match the arrangement of the large number of pixels 58 shown in FIG. Each digital micromirror device 70 includes a micromirror 74 and a microactuator 72 that changes the direction of the micromirror 74 depending on the applied voltage. For example, when no voltage is applied to the digital micromirror device 70, the micromirror 74 faces the microactuator 72 at a slight angle as shown in FIG. 4, and is determined with respect to the digital micromirror device 70. When the voltage of is applied, the micromirror 74 comes into close contact with the upper surface of the microactuator 72 as shown in FIG. [0041] These digital micromirror devices are described in "Above LCDs? Next Generation Display Favorites" (Nikkei Business, November 15, 1999, pp.60-64). [0042] With reference to FIG. 6, the reflective surface 52 includes a transparent glass plate 76 and a number of digital micromirror devices 70 (see FIG. 4) located on the back surface of the glass plate 76. In each of these digital micromirror devices 70, the reflective surface of the micromirror is in close contact with the back surface of the glass plate 76 when a voltage is applied, and the micromirror 74 is separated from the back surface of the glass plate 76 when no voltage is applied. It is assumed that it is arranged in such a position. If the index of refraction of the micromirror 74 is different from that of the glass plate 76, as shown in FIG. 6, at the position corresponding to the digital micromirror device 70 to which no voltage is applied (micromirrors 74A and 74C), the light 80A And 80C are not reflected, and light 80B is reflected at the position of the reflective surface 74B corresponding to the digital micromirror device to which the voltage is applied. [0043] Therefore, in the corner cube 40 shown in FIG. 2, for each of the plurality of pixels 58, the voltage applied to the corresponding digital micromirror device is changed according to the video signal from the video camera 25 shown in FIG. Total reflection / non-reflection can be controlled. In the device of the present embodiment, the reflection / non-reflection of light in the corner cube 40 is controlled for each pixel in this way, and the light receiving device 22 side receives and demodulates the light for each pixel to obtain a signal for each pixel. Can be demodulated. [0044] Although the digital micromirror device is used in the system of this embodiment, when the reflecting surface 74 is arranged on the back surface of the transparent plate constituting the light reflecting surface as in this example, the reflecting surface 74 is not necessarily light. It does not have to be of a reflective nature. As long as the refractive index of the transparent plate and the reflective surface 74 are different, the light is totally reflected by bringing the reflective surface 74 into close contact with the back surface of the transparent plate, and the light is not reflected if a certain interval is provided. is there. [0045] The optical communication system 20 according to the first embodiment operates as follows. It is assumed that the light source 30 and the corner cube 40 are preliminarily adjusted so that their relative positions are substantially constant, but as will be described later, one or both of the optical receiving device 22 and the optical transmitting device 24 may be used. By adjusting the rotation angle of the beam splitter 32, the CCD 34 can stably receive the reflected light from the optical transmitter 24 even if its relative position shifts as in the case of being on a moving body. .. [0046] First, the light source 30 emits a luminous flux toward the corner cube 40. This light enters the corner cube 40, is reflected, and returns toward the light source 30. At this time, by controlling the reflection / non-reflection of each pixel 58 on one reflecting surface 52 on the corner cube 40 according to the video signal from the video camera 25, the light is reflected at the position corresponding to a certain pixel, and the other Light is not reflected at the position corresponding to the pixel of. [0047] The beam splitter 32 splits the optical path of the light reflected from the corner cube 40 laterally by 90 ° and guides it onto the light receiving surface of the CCD 34. The CCD 34 repeats light reception and output of the light reception signal at a predetermined cycle, but the light reception period is as long as one cycle of the transmission signal sent from the optical transmission device 24 under the control of the clock reproduction circuit 36. Controlled to match. The clock reproduction circuit 36 reproduces a clock signal based on the output of the CCD 34 as described above to control the operation of the CCD 34, and gives a signal obtained by multiplying this clock signal by a predetermined number to the A / D conversion circuit 38. The A / D conversion circuit 38 digitally converts the serial analog signal output from the CCD 34 according to the multiplied clock signal given from the clock reproduction circuit 36, and supplies the serial analog signal to the signal processing circuit 26. The signal given to the signal processing circuit 26 is similar to the digital serial signal output from the video camera 25 as a result. By processing this signal by the signal processing circuit 26 and displaying it on the monitor 28, the image captured by the video camera 25 is reproduced on the monitor 28. [0048] At this time, the optical signal transmitted from the optical transmitting device 24 to the optical receiving device 22 is a multi-channel optical signal arranged in parallel for each pixel. Therefore, the signal period for each channel is much longer than when the video signal is serially transmitted on one channel. Therefore, the light receiving period by the CCD34 can be extended, and stable demodulation can be performed. [0049] In the present embodiment, as shown in FIG. 6, the micromirror 74 is arranged so as to be in close contact with the glass plate 76, thereby controlling the total reflection at the interface (total reflection surface) between the glass plate 76 and the micromirror 74. .. However, the present invention is not limited to such a configuration, and for example, the micromirror 74 may be arranged in a matrix so as to form the reflection surface 52 itself shown in FIG. In this case, the micromirror may correctly reflect the light in the normal position, and when a predetermined voltage is applied, the micromirror may change the position to reflect the light in a direction different from the predetermined direction, and vice versa. It may be configured. An example of this will be described later with reference to FIGS. 15 and 16. [0050] Further, when the micromirror 74 is arranged so as to be in close contact with the glass plate 76 as shown in FIG. 6, if the density of the micromirror 74 is higher than the density of the glass plate 76, it is possible to control the total reflection as described above. Become. The upper surface of the micromirror 74 itself does not have to be reflective. [0051] With reference to FIG. 3, it is assumed that the position of the optical transmitter 24 relative to the optical receiver 22 changes from the state shown in FIG. As described above, the light beam emitted from the light source 30 has a spread. Therefore, even if the position of the light transmitter 24 is displaced, a part of the light beam is reflected by the corner cube 40 and returned. Since this reflected light has the same direction as the incident light on the corner cube 40, the incident angle on the beam splitter 32 changes as compared with the case of FIG. Therefore, if the direction of the beam splitter 32 is left as it is, this reflected light cannot be directed to the light receiving surface of the CCD 34. [0052] In this case, if the angle of the beam splitter 32 is adjusted by the stepping motor 31 to adjust the reflection direction of the incident beam, the reflected light from the corner cube 40 can be guided to the light receiving surface of the CCD 34. [0053] Second embodiment In the optical communication system of the first embodiment described above, the optical communication itself is multi-channel, but the input signal for that purpose and the demodulated signal after transmission are both serial signals. Therefore, as a result, the signal for one channel is transmitted. However, the present invention is not limited to such embodiments. For example, signals of a plurality of channels can be transmitted by optical communication of a large number of channels and demodulated as separate signals on the receiving side. The optical communication system 120 of the second embodiment is such a system. [0054] With reference to FIG. 7, the optical communication system 120 includes an optical receiver 122 and an optical transmitter 124. [0055] The optical transmitter 124 includes a corner cube 140 in which one surface is divided into a plurality of pixels, and a modulator 142 for driving each pixel separately, as in the optical transmitter 24 of the first embodiment. including. [0056] With reference to FIG. 8, the modulation device 142 includes four partial modulation circuits 152A-152D in this embodiment. Then, as shown in FIG. 7, each partial modulation circuit 152A to 152D is driven by a signal from a separate signal source 125A to 125D. In the case of this example, the signals serially input from the respective signal sources 125A to 125D are once held in the storage elements arranged in the shape shown in FIG. 8, and then the held signals are simultaneously stored in the modulator 142. Give to each element part. By doing so, the serially input signals can be transferred in parallel and with a long signal cycle. [0057] The light receiver 122 is based on the light source 30 and the beam splitter 32 arranged as in the first embodiment, the CCD 134 for receiving the light beam branched by the beam splitter 32, and the output of the CCD 134. A clock signal is reproduced to control the light receiving period by the CCD 134, and a clock reproduction circuit 138 for outputting a signal obtained by multiplying this clock signal and a serial signal output from each of the four regions of the CCD 134 are received in parallel to obtain a clock. It includes A / D conversion circuits 136A to 136D for analog / digital conversion according to the multiplied clock signal given from the reproduction circuit 138. The outputs of these A / D conversion circuits 136A to 136D are given to the destinations 126A to 126D corresponding to the signal sources 125A to 125D, respectively. [0058] [0058] The optical communication system 120 of the second embodiment operates as follows. Each of the signal sources 125A to 125D independently gives a signal to the modulator 142. The partial modulation circuits 152A to 152D of the modulator 142 sequentially store these serially applied signals for each pixel and feed them to the corresponding digital micromirror device at a certain timing. As a result, when the light emitted from the light source 30 is reflected by the corner cube 140, its reflection / non-reflection is controlled for each pixel. The light modulated by the original signal is incident on the beam splitter 32 and further incident on the light receiving surface of the CCD 134. The clock reproduction circuit 138 reproduces a clock signal based on the output of the CCD 134 and controls the output cycle of the CCD 134. At the same time, the clock reproduction circuit 138 creates a signal obtained by multiplying this clock signal by a predetermined number and gives it to the A / D conversion circuits 136A to 136D. Each A / D conversion circuit 136A to 136D converts a signal serially output from the corresponding 1/4 surface of the CCD134 into a digital signal and gives it to the corresponding destinations 126A to 126D. In this way, the signals given from the plurality of signal sources 125A to 125D are simultaneously transmitted to the optical receiver 122 via one multi-channel optical communication path, and are independently transmitted to the corresponding transmission destinations 126A to 126D. [0059] In this second embodiment, optical communication can be performed in the form of a collection of serial signals that are not image signals. In this case as well, since the optical communication itself is performed on multiple channels, the symbol period can be lengthened as compared with the case where each signal is communicated serially, and stable optical communication can be performed. [0060] Third Embodiment In the device of the first embodiment, the serial video signal output from the video camera 25 (see FIG. 1) is once given to the modulation device 42, and transmitted as a multi-channel signal by optical communication. However, the present invention is not limited to the form of the first embodiment even when it is used for image transmission. For example, as in the optical communication system 220 of the third embodiment, image signals can be input in parallel. [0061] With reference to FIG. 9, the optical communication system 220 includes an optical transmitter 224 and an optical receiver 222. [0062] The optical transmitter 224 is arranged behind the corner cube 240 and one surface of the corner cube 240, and is a light receiving / modulating device 242 in which a solid-state imaging element and the above-mentioned digital micromirror device are integrally formed, and a light receiving / modulating device. Controls the optical system 246 for forming an optical image of the subject on the imaging surface (light receiving surface) of the CCD of 242, the light receiving period by the light receiving / modulating device 242, and the transfer of charge to the digital micromirror device. Includes driver device 248 and for. [0063] The driver device 248 controls the orientation of each reflecting surface of the digital micromirror device by simultaneously applying the charges generated on the light receiving surface of the light receiving / modulating device 242 to the digital micromirror device during a certain period of time. At the same time, the driver device 248 erases the electric charge on the light receiving surface and repeats the work of receiving light for the next period. [0064] The light receiving device 222 receives and holds in parallel the charges from the light source 30 and the beam splitter 32 described above, the CCD 234 arranged at a position for receiving the light branched by the beam splitter 32, and the light receiving elements of the CCD 234. , The charge transfer element 236 having the same configuration as the solid-state image sensor for serial output, and the clock component included in the transmission signal are reproduced based on the output of the CCD234 to control the operation of the CCD234 and the charge transfer element 236. The clock signal is generated and output, and is output from the charge transfer element 236 according to the clock reproduction circuit 238 for outputting the multiplied signal of this clock signal and the multiplied clock signal given from the clock reproduction circuit 238. It includes an A / D conversion circuit 238 for converting a serial signal into a digital signal. The output of the A / D conversion circuit 238 is given to the signal processing circuit 26 as in the case of the first embodiment, and is further displayed by the monitor 28. [0065] The optical communication system 220 of the third embodiment operates as follows. The driver device 248 erases the charge on the light receiving surface of the light receiving / modulating device 242 and starts receiving light. An optical image of the subject is formed on the light receiving surface by the optical system 246, and each photoelectric conversion element on the light receiving surface accumulates electric charges according to the amount of incident light. The driver device 248 transfers this charge to the corresponding digital micromirror device at a predetermined timing, and erases the charge on the light receiving element of the CCD. Under the control of the driver device 248, the reflective surface of each micromirror device constituting the light receiving / modulating device 242 changes to a total reflection position or a non-reflection position, respectively. [0066] The light emitted from the light source 30 of the light receiving device 222 is reflected by the corner cube 240 and incident on the beam splitter 32. At this time, on one surface of the corner cube 240, the light receiving / modulating device 242 does not reflect light at a position corresponding to a certain pixel, and reflects light at a position corresponding to another pixel. As a result, the light reflected from the corner cube 240 toward the beam splitter 32 is a multi-channel luminous flux in which each reflected light is modulated according to the state of each of these elements. When this luminous flux reflected by the beam splitter 32 is incident on the CCD234, a charge distribution similar to that formed by the optical image of the subject is formed on the CCD234. The clock reproduction circuit 238 accumulates electric charges on the CCD 234 for a period corresponding to one symbol interval, and then transfers each electric charge to the electric charge transfer element 236 in parallel. At the same time, the clock reproduction circuit 238 erases the charge of each photoelectric conversion element on the CCD 234. [0067] The charge transfer element 236 serially outputs the accumulated charge according to the clock signal given from the clock reproduction circuit 238 and gives it to the A / D conversion circuit 238. The A / D conversion circuit 238 converts this signal into a digital signal according to the multiplied clock signal output from the clock reproduction circuit 238 and gives it to the signal processing circuit 26. [0068] In this way, in the optical communication system of the third embodiment, the optical image of the subject formed on the light receiving surface on the optical transmitter side is directly converted into a parallel signal, which is further converted into a parallel optical signal by the optical receiver. Can be transferred to the side. Also in this case, since the symbol section is longer on the receiving side as compared with the case where this video signal is transmitted in parallel using one channel, stable optical communication can be performed. [0069] In the example shown in FIG. 9, the position of the optical system 246 is fixed at a position where an image of the subject is formed on the light receiving surface. However, the present invention is not limited to this. The arrangement of the optical system can be changed in various ways, provided that the optical image of the subject is formed on the light receiving surface. [0070] Fourth Embodiment As is clear from the first to third embodiments, this optical communication system can transmit signals from a plurality of signal sources in parallel. The maximum number of channels for that purpose is each pixel formed on the corner cube (as described below, it has a function of controlling the total reflection condition on the reflection surface, and is hereinafter referred to as "total reflection condition control element". It is the same as the number of.). Of course, it may not be available for the total reflection condition control element existing in the peripheral position of the reflection surface, but even if only the total reflection condition control element provided near the center of the corner cube is used, a considerably large number of channels are used. The optical communication that was used can be performed. The optical communication system of the fourth embodiment can perform independent communication for each channel in this way. [0071] The optical communication system 320 according to the fourth embodiment with reference to FIG. 10 includes an optical transmitter 324 and an optical receiver 322. [0072] The optical transmitter 324 is an integration device 344 for collecting signals from a large number of signal sources, a modulation device 342 including a large number of digital micromirror devices, and a modulation device for each signal integrated by the integration device 344 independently. A connection line 346 for connecting to each digital micromirror device of 342, a driver device 348 for driving the modulator 342, and a corner cube 340 in which the modulator 342 is arranged on the back surface of one of its reflecting surfaces. Including. [0073] The optical receiver 322 reproduces a light source 30, a beam splitter 32, a CCD 334 arranged at a position for receiving a luminous flux branched by the beam splitter 32, and a clock signal for driving the CCD 334 based on the output of the CCD 334. The clock reproduction circuit 338 for this purpose and the branch circuit 336 for receiving the output of each photoelectric conversion element of the CCD 334 in parallel, amplifying it, converting it into a digital signal, branching it, and outputting it are included. [0074] The clock reproduction circuit 338 causes the CCD334 to perform photoelectric conversion for one symbol period, and when one period ends, outputs the signals of each photoelectric conversion element to the branch circuit 336 in parallel. At the same time, the clock reproduction circuit 338 erases the electric charge of each photoelectric conversion element of the CCD 334, and performs a process for preparing for the photoelectric conversion in the next period. [0075] The optical communication system 320 of the fourth embodiment operates as follows. The signals collected from a large number of separate signal sources are integrated by the integration device 344 and given to the modulation circuit 342 by the connection line 346. The modulation circuit 342 takes in the signal given from the connection line 346 every predetermined section and gives it to the corresponding digital micromirror device under the control of the driver device 348. Each digital micromirror device changes the position of its reflective surface according to the values of these signals. [0076] The light emitted from the light source 30 enters the corner cube 340 and is reflected. At this time, reflection / non-reflection is controlled for each element on one reflection surface of the corner cube 340 according to the position of the reflection surface of the digital micromirror device. Therefore, the light reflected from the corner cube 340 toward the beam splitter 32 is a multi-channel optical signal that carries the signal modulated by the modulator 342 for each channel. [0077] This luminous flux reflected by the beam splitter 32 is incident on the CCD334, and a charge corresponding to each element is generated for each element of the CCD334. Under the control of the clock reproduction circuit 338, the output of each photoelectric conversion element is given to the branch circuit 336, converted into a digital signal, and transmitted to each corresponding transmission destination. [0078] In the optical communication system of the fourth embodiment, the number of total reflection condition control elements is equal to the number of total reflection condition control elements by having a one-to-one relationship between a large number of signal sources and the total reflection condition control elements on the corner cube. Optical communication channel can be provided. As a result, it is possible to stably transmit a large number of channel signals in a very compact manner. For example, if the arrangement of the total reflection condition control elements is 1000 × 1000, the number of channels provided is 1000 × 1000 = 1,000,000, and wideband communication using optical communication can be performed. [0079] Other examples of total internal reflection condition control elements In the above description, a corner cube in which a total reflection condition control element is formed by arranging a digital micromirror device on the surface of the light reflecting surface or a digital microactuator on the back surface of a transparent plate constituting the light reflecting surface is used. There is. However, the configuration of the total reflection condition control element is not limited to these. An example is shown in FIG. [0080] [0080] With reference to FIG. 11, a plurality of total reflection condition control elements 402 for controlling the total reflection conditions of the prism are arranged on one reflection surface of the corner cube 400. As shown in FIG. 12, each total internal reflection condition control element 402 is separately divided into a transparent capsule 404, an opaque ferrofluid 410 enclosed in the transparent capsule 404, and each half region of the transparent capsule 404. Includes two electromagnets 420 and 422 that are formed and generate a magnetic field when an electric current is applied. [0081] For example, when an electric current is passed through the electromagnet 420 in FIG. 12, a magnetic field is generated, and the magnetic fluid 410 gathers in the direction of the electromagnet 420. As a result, a transparent portion 412 without the ferrofluid 410 is formed. On the contrary, when an electric current is passed through the electromagnet 422, the magnetic fluid 410 gathers in the direction of the electromagnet 422. As a result, contrary to FIG. 12, the region indicated by reference numeral 410 becomes transparent, and as a result, there is no region in contact with the magnetic fluid on the prism surface, and the prism is in a total reflection state in this region. Further, since the region indicated by reference numeral 412 becomes opaque, the magnetic fluid becomes a portion in contact with the prism surface, and total reflection is hindered. Different reflectance distributions are created depending on whether the light passes through, which makes it possible to modulate and reflect the incident light. [0082] In the example shown in FIG. 12, a magnetic fluid was used. For example, a large number of tiny bar magnets whose directions are fixed in the same direction are enclosed in an elongated tube, and a large number of the tubes are bundled together. It may be used instead of the magnetic fluid. In this case, by placing a magnetic field of S pole at one end of the transparent capsule 404, for example, all these bar magnets move in the same direction by the magnetic force between their own magnetic poles and this S pole, and replace this S pole. If you put the N pole, all these bar magnets will move in the opposite direction. As a result, the distribution of the total reflection portion in the total reflection control element group can be changed as in the case of using the magnetic fluid. [0083] When using such a very small bar magnet, if the same magnetic magnetic poles are placed at both ends of the transparent capsule 404, an attractive force acts on the bar magnet from one magnetic pole and a repulsive force acts from the other magnetic pole. As a result, the bar magnet moves faster when the magnetism of the magnetic pole is changed. Therefore, such a configuration has the effect of improving the response as compared with the case where only one magnetic pole is used. [0084] Yet another example of a total internal reflection condition control element As another example of the total reflection condition control element, a microactuator controlled by light rather than by current can also be used. In particular, an actuator having a high response speed can be realized by using a substance having a property of deforming when exposed to light, such as a polymer compound called polydiacetylene. [0085] FIG. 13 shows a cross-sectional view of the total reflection condition control element 440 including the microactuator controlled by such light. With reference to FIG. 13, this microactuator is arranged on the total internal reflection surface of prism 450 of the corner cube, and is thin and slightly elastic, which is normally arranged so as to be in close contact with the total internal reflection surface of prism 450. The total reflection control body 452 made of a material having a density higher than that of the prism 450, and the above-mentioned polydiacetylene bonded to the surface of the total reflection control body 452 opposite to the surface in close contact with the prism 450. Includes thin film 454. The total reflection control body 452 is adhered to the back surface of the glass surface 450 at the peripheral portion thereof. The total reflection control body 452 can be brought into close contact with the total reflection surface of the prism 450, and when deformed as described later, the gap generated between the total reflection control body 452 and the total reflection surface is large enough to hinder total reflection. Those having elasticity are used. [0086] As shown in FIG. 13, in the first state, the total reflection control body 452 is in close contact with the total reflection surface of the prism 450. Therefore, the light incident on the glass plate 450 is not totally reflected by the total reflection surface of the prism 450, but is transmitted to the total reflection control body 452 side. That is, light is not reflected by the total reflection surface. [0087] It is known that polydiacetylene has the property that its volume increases by about 3% when exposed to light with a wavelength of 450 to 550 nanometers, and returns to its original state when exposed to light having a wavelength of 350 to 400 nanometers. [0088] Therefore, in the state of FIG. 13, light having a wavelength of 450 to 550 nanometers is applied to the total reflection condition control element corresponding to the portion to be totally reflected from the back surface. In this portion, the volume of the polydiacetylene thin film 454 increases, and a gap is created between the polydiacetylene thin film 454 and the total reflection surface of the prism 450 as shown in the center of FIG. Therefore, the light incident on the total reflection condition control element is totally reflected. [0089] On the other hand, the total reflection condition control element corresponding to the portion where total reflection is not performed is exposed to light having a wavelength of 350 to 400 nanometers from the back surface. Then, as shown on the left and right of FIG. 14, the volume of the polydiacetylene thin film 454 decreases, so that the entire total reflection condition control element together with the total reflection control body 452 is in close contact with the glass surface 450 at the center thereof. Transforms into. As a result, the light incident on the total reflection surface of the prism 450 is not totally reflected. [0090] Depending on the substance that has the property of being deformed by light in this way<u style="single">Anti</u>When the shooting condition control element is driven, the response speed is high and the structure is relatively simple. Also<u style="single">, Anti</u>To drive the shooting condition control element with light<u style="single">, Anti</u>There is no need to dispatch a ship to drive the shooting condition control element with a signal. Therefore, the device can be further miniaturized, and high-density multi-channel optical communication can be realized. [0091]<u style="single">Example of reflection condition control element</u>A modified example of the corner cube 40 shown in FIG. 2 is shown in FIGS. 15 and 16. In the example shown in FIG. 15, the corner cube 500 is orthogonal to the reflecting surfaces 54 and 56, which are made of a material that does not reflect light, instead of the reflecting surface 52 in FIG. 2, as compared to the corner cube 40 shown in FIG. The difference is that the substrate 510 provided as described above includes a plurality of micromirror devices 512 arranged in a matrix on the surfaces of the substrate 510 facing the reflection surfaces 54 and 56. The substrate 510 may be a transparent material or an opaque material. It may also be made of a substance that reflects light. [0092] Each of the plurality of micromirror devices 512 has a reflective surface whose direction can be controlled in the first direction and the second direction. The first direction is such that the reflective surface of the digital mirror microdevice is included in the plane orthogonal to the reflective surfaces 54 and 56. The second direction may be any direction other than the direction different from the first direction, that is, the direction in which the reflecting surface of the micromirror device is orthogonal to the reflecting surfaces 54 and 56. [0093] With this corner cube 500, when the reflective surface of a digital microdevice is facing the first direction, the light incident on the reflective surface of the digital microdevice is reflected parallel to the incident direction. When the reflecting surface of the digital microdevice faces the second direction, it is reflected in a direction different from the incident direction. Therefore, as in the case of the first embodiment, the corner cube 500 can be used for multi-channel optical communication. [0094] Also, the corner cube 520 shown in FIG. 16 is shown in FIG.<u style="single">thing</u>The feature is that the substrate 510 is removed, and the reflective surface is composed of a plurality of digital microdevices 522 arranged in a matrix. Also in this case, if the direction of each reflecting surface of the digital microdevice 522 can be controlled to the first direction and the second direction similar to those in FIG. 15, it can be used for multi-channel optical communication. [0095] It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and it is intended to include all modifications within the meaning and scope equivalent to the scope of claims. [Simple explanation of drawings] FIG. 1 is a block diagram of an optical communication system according to the first embodiment of the present invention. FIG. 2 is a diagram showing the appearance of a corner cube. FIG. 3 is a block diagram when the angle of the beam splitter is changed in the optical communication system according to the first embodiment. FIG. 4 is a diagram for explaining the operation of the digital micromirror device. FIG. 5 is a diagram for explaining the operation of the digital micromirror device. [Fig. 6] It is a figure for demonstrating the control of reflection / non-reflection using a digital micromirror device. FIG. 7 is a block diagram of an optical communication system according to a second embodiment of the present invention. FIG. 8 is a diagram showing an arrangement of partial modulation circuits used in the second embodiment. FIG. 9 is a block diagram of an optical communication system according to a third embodiment of the present invention. FIG. 10 is a block diagram of an optical communication system according to a fourth embodiment of the present invention. FIG. 11 is a diagram showing another example of another corner cube surface having a total reflection condition control element. FIG. 12 is a schematic view of a group of total reflection condition control elements used in the example of FIG. FIG. 13 is a cross-sectional view showing still another example of the total reflection condition control element. FIG. 14 is a cross-sectional view showing the operating principle of the total reflection condition control element shown in FIG. FIG. 15 is a perspective view showing a modified example of a corner cube using a digital micromirror device. FIG. 16 is a perspective view showing still another modification of a corner cube using a digital micromirror device. [Explanation of symbols] 20,120,220,320 Optical communication system, 22,122,222,322 Optical receiver, 24,124,224,324 Optical transmitter, 30 light sources, 32 beam splitter, 34,134,234,334 CCD, 40,140,240,340 corner cube, 42,142,342 modulator, 70 digital micromirror device, 242 receiver / modulator.