JP2005278024A - Optical space transmission method and system - Google Patents

Abstract

【Task】
Eliminate the effects of temporary light path interruptions with optical space transmission.
[Solution]
An electrical / optical (E / O) converter 14 converts the data signal into a linearly polarized optical signal. The polarization separator 16 separates the output signal light from the E / O converter 14 into a P wave and an S wave with equal optical power. The optical delay device 18 delays the S wave by a predetermined time Td. The polarization beam combiner 20 combines the S wave from the optical delay device 18 and the P wave from the polarization separator 16 with orthogonal polarization. The projection lens 22 projects the output signal light from the polarization beam combiner 20 onto the spatial transmission path. The signal light beam projected onto the spatial transmission path enters the polarization separator 34 via the condenser lens 32. The polarization separator 34 separates incident light into P waves and S waves. The optical delay device 36 delays the P wave by Td. The polarization beam combiner 38 combines the P wave from the optical delay device 36 and the S wave from the polarization separator 34. The optical / electrical (O / E) converter 40 converts the output signal light of the polarization multiplexer 38 into an electrical signal.
[Selection]
FIG.

Description

  The present invention relates to an optical space transmission method and system for spatially propagating an optical signal.

  2. Description of the Related Art Conventionally, an optical space transmission system that performs communication by propagating an optical signal in free space is widely known. In the optical space transmission system, light path shielding due to rain, fog, smoke, birds and the like causes signal errors. As a method for preventing such a decrease in reception level due to light path shielding, conventionally, a diversity method using a plurality of light paths and a plurality of light sources and a plurality of light receivers and a method of extending the transmission beam diameter according to the distance have been proposed. Has been.

  However, in the former method, when a plurality of light sources and a plurality of light receivers are used, the size of the transmission / reception device increases, leading to an increase in cost. If a plurality of optical paths are blocked at the same time, transmission errors are inevitable. In the latter method, the effect of blocking the beam by birds is small at a position close to the receiving device, but the beam diameter is small at a position close to the transmitting device, so the influence of blocking by the birds cannot be ignored, resulting in a transmission error. Will occur.

  Even if an error correction device is introduced, there is a limit in correcting a burst error due to beam interruption.

  It is an object of the present invention to provide an optical space transmission method and system that can reduce the adverse effects of beam blocking with a simple configuration.

  The optical space transmission method according to the present invention generates a first signal light that carries data and a second signal light that carries the data delayed by a predetermined time (Td) from the first signal light. A generation step, a projection step of projecting the first and second signal lights onto the spatial transmission path, and a delay of the first signal carried by the first signal light from the spatial transmission path for the predetermined time. A delay step, a second signal carried by the second signal light from the spatial transmission path, a synthesis step of synthesizing the delayed second signal to generate a synthesized signal, and the synthesis And a restoration step of restoring the data from the signal.

  The optical space transmission system according to the present invention generates a first signal light that carries data and a second signal light that carries the data delayed by a predetermined time (Td) from the first signal light. A generation device, a projection optical system that projects the first and second signal lights onto a spatial transmission path, and a light receiving optical system that receives light including the first and second signal lights from the spatial transmission path A delay device that delays the first signal carried by the first signal light from the spatial transmission path for the predetermined time, and a second carrier carried by the second signal light from the spatial transmission path. 2, a combiner that combines the delayed second signal and generates a combined signal, and a restoration device that recovers the data from the combined signal.

  According to the present invention, even if an optical path is temporarily interrupted by a bird or the like, data can be transmitted without hindrance.

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

  FIG. 1 shows a schematic block diagram of a first embodiment of the present invention. The optical transmitter 10 transmits the signal light beam to the optical receiver 30 via a spatial transmission path.

  In the optical transmission apparatus 10, the error correction encoding apparatus 12 performs error correction encoding on the transmission data. An electrical / optical (E / O) converter 14 converts the data output from the error correction encoding device 12 into a linearly polarized optical signal. The output signal light from the E / O converter 14 is incident on the polarization separator 16 in a polarization direction inclined by 45 degrees with respect to the main axis of the polarization separator 16. The polarization separator 16 separates the output signal light from the E / O converter 14 into a P wave having substantially the same optical power and an S wave orthogonal to the P wave. The S wave separated by the polarization separator 16 enters the polarization combiner 20 via the optical delay device 18 having a delay time of a predetermined time Td, and the P wave separated by the polarization separator 16 is Directly enters the polarization beam combiner 20. The delay time Td is set to be longer than the optical path blocking time for birds or the like. The polarization beam combiner 20 combines and outputs the incident S wave and P wave in an orthogonal state. The projection lens 22 which is a transmission optical system projects the output signal light of the polarization beam combiner 20 onto the spatial transmission path.

  A condensing lens 32 that is a receiving optical system of the optical receiver 30 condenses the signal light beam projected from the optical transmitter 10 onto the spatial transmission path and enters the polarization separator 34. The polarization separator 34 converts the signal light beam from the condenser lens 32 into the same polarization direction component (P wave) as the P wave separated by the polarization separator 16 and a polarization component component (S) orthogonal thereto. Wave). The P wave separated by the polarization separator 34 enters the polarization synthesizer 38 via the optical delay device 36 having the same delay time Td as the optical delay device 18. The separated S wave is directly incident on the polarization beam combiner 38. The polarization beam combiner 38 synthesizes and outputs the incident S wave and P wave in an orthogonal state. The optical / electrical (O / E) converter 40 converts the output signal light of the polarization multiplexer 38 into an electric signal without polarization dependency. The discriminator 42 discriminates the output electric signal of the O / E converter 40 according to a predetermined threshold value. The error correction device 44 corrects a transmission error included in the digital signal discriminated by the discriminator 42 by using the error correction code by the error correction encoding device 12.

  FIG. 2 shows an example of a timing chart of the present embodiment. With reference to FIG. 2, the characteristic operation of the present embodiment will be described. A waveform 50 shows a P wave separated by the polarization separator 16, and a waveform 52 shows an S wave separated by the polarization separator 16. Since the waveforms 50 and 52 carry the same data, they have exactly the same waveform. A waveform 54 shows an S wave delayed by the time Td by the optical delay device 18. The P wave indicated by the waveform 52 and the S wave indicated by the waveform 54 are orthogonally polarized and transmitted from the optical transmitter 10 to the optical receiver 30. However, the S wave carries exactly the same data as the P wave with a delay of time Td.

  A waveform 56 indicates a P wave separated by the polarization separator 34, and a waveform 58 indicates an S wave separated by the polarization separator 34. Assume that a bird or the like interrupts the spatial transmission path during the period indicated by t1 to t2 in FIG. As a result, the light intensity of the P wave (waveform 56) and the S wave (waveform 58) separated by the polarization separator 34 becomes zero at the shaded portion corresponding to t1 to t2. A waveform 60 shows a P wave delayed by the time Td by the optical delay device 36. The polarization beam combiner 38 combines the S wave indicated by the waveform 58 and the P wave indicated by the waveform 60. A waveform 62 represents the combined light output from the polarization beam combiner 38.

  Since the delay time Td is set to be longer than the optical path cutoff time due to birds or the like, in the waveform 58 and the waveform 60, the positions affected by the optical path cutoff do not overlap on the time axis. Further, since the transmitting device 10 delays the S wave by Td and the receiving device 30 delays the P wave by Td, the P wave and the S wave input to the polarization multiplexer 38 are excluded except where the optical path is interrupted. Are exactly the same time waveform. The waveform 62 of the synthesized light by the polarization beam combiner 38 is a waveform obtained by synthesizing the S wave (waveform 58) and the delayed P wave (waveform 60) with orthogonal polarization at a place where the optical path is not affected. On the other hand, since the light intensity of the S wave (waveform 58) or the delayed P wave (waveform 60) is zero at the place where the optical path is affected, the light intensity of the synthesized light is half that of the other places. Become.

  Normally, the discrimination threshold of the discriminator 42 is set to about half of the pulse peak, but in this embodiment, it is set to about 1/4 of the pulse peak. Thereby, the signal of the location where the light intensity becomes half of the normal due to the influence of the light path interruption can be correctly distinguished.

  In the present embodiment, the same data is transmitted back and forth on the time axis on the same optical path, thereby providing redundancy and strengthening the optical path failure. Since the signal light carrying the same data is transmitted on the same optical path with mutually orthogonal polarizations, the optical axis adjustment between the optical transmission device 10 and the optical reception device 30 becomes easy, and these signals are transmitted by the optical reception device. It becomes easier to separate the light. In the receiving device 30, the signal lights having orthogonal polarizations are combined while eliminating the time lag, and the combined light is converted into an electric signal, so that the electric processing system is simplified. The optical delay units 18 and 36 having the same delay time can be easily realized by using optical fibers having the same length, for example.

  The optical system of the embodiment shown in FIG. 1, that is, the optical system from the polarization separator 16 to the polarization beam combiner 38 can be used bidirectionally. Therefore, it is easy to extend the embodiment shown in FIG. 1 to bidirectional optical transmission. FIG. 3 shows a schematic block diagram of the second embodiment extended in both directions.

  Data transmission from the optical transceiver 110A to the optical transceiver 110B will be described.

  The error correction encoding device 112A of the optical transmission / reception device 110A performs error correction encoding on the transmission data D1. The electrical / optical (E / O) converter 114A converts the data output from the error correction coding device 112A into a linearly polarized optical signal. The output signal light from the E / O converter 114A enters the polarization beam splitter 116 via the ports A and B of the optical circulator 115 with a polarization direction inclined by 45 degrees with respect to the main axis of the polarization beam splitter (PBS) 116. To do. The optical circulator 115 is an optical element that outputs the input light of the port A from the port B and outputs the input light of the port B from the port C. Here, the polarization beam splitter 116, the optical delay device 118, the polarization beam splitter 120, and the projection / condensing lens 122 are respectively the polarization separator 16, the optical delay device 18, the polarization combiner 20, and the projection shown in FIG. Performs the same function as the lens 22. The projection / condensing lens 122 projects the output signal light of the polarization beam splitter 120 onto the spatial transmission path.

  In the optical transmission / reception device 110 </ b> B, the projection / condensing lens 132 condenses the signal light beam projected from the optical transmission / reception device 110 </ b> A onto the spatial transmission path and enters the polarization beam splitter 134. The polarization beam splitter 134, the optical delay device 136, and the polarization beam splitter 138 perform the same functions as the polarization separator 134, the optical delay device 36, and the polarization combiner 38 of the embodiment shown in FIG.

  The combined signal light output from the polarization beam splitter 138 is input to the optical / electrical (O / E) converter 140B via the ports B and C of the optical circulator 139. The O / E converter 140B converts the combined signal light from the polarization beam splitter 138 into an electric signal without polarization dependency. The discriminator 142B discriminates the output electric signal of the O / E converter 140B according to a predetermined threshold value. The error correction device 144B corrects the transmission error included in the digital signal discriminated by the discriminator 142B by using the error correction code by the error correction coding device 112A, and outputs received data D1.

  Next, data transmission from the optical transceiver 110B to the optical transceiver 110A will be described.

  The error correction encoding device 112B of the optical transmission / reception device 110B performs error correction encoding on the transmission data D2. The electrical / optical (E / O) converter 114B converts the data output from the error correction coding device 112B into a linearly polarized optical signal. The output signal light from the E / O converter 114B is incident on the polarization beam splitter 138 through the ports A and B of the optical circulator 139 in a polarization direction inclined by 45 degrees with respect to the main axis of the polarization beam splitter (PBS) 138. To do. The polarization beam splitter 138, the optical delay device 136, and the polarization beam splitter 1134 separate the output signal light of the E / O converter 114B into P wave and S wave orthogonal to each other, delay the P wave by Td, The delayed P wave is synthesized. The projection / condensing lens 132 projects the output signal light of the polarization beam splitter 134 onto the spatial transmission path.

  In the optical transmission / reception device 110 </ b> A, the projection / condensing lens 122 condenses the signal light beam projected from the optical transmission / reception device 110 </ b> B onto the spatial transmission path and enters the polarization beam splitter 120. The polarization beam splitter 120, the optical delay device 118, and the polarization beam splitter 116 separate the signal light from the projection / condensing lens 122 into P wave and S wave orthogonal to each other, delay the S wave by Td, The delayed S wave is synthesized.

  The combined signal light output from the polarization beam splitter 116 is input to the optical / electrical (O / E) converter 140A via the ports B and C of the optical circulator 115. The O / E converter 140A converts the combined signal light from the polarization beam splitter 116 into an electric signal without polarization dependency. The discriminator 142A discriminates the output electric signal of the O / E converter 140A according to a predetermined threshold value. The error correction device 144A corrects the transmission error included in the digital signal discriminated by the discriminator 142A using the error correction code by the error correction coding device 112B, and outputs received data D2.

  As described above, in this embodiment, bidirectional data transmission can be realized by bidirectionally using the optical systems arranged before and after the spatial transmission path. In both data transmission from the optical transmission / reception device 110A to the optical transmission / reception device 110B and vice versa, data can be transmitted without any problem when an optical path is interrupted.

  FIG. 4 shows a schematic block diagram of a third embodiment of the present invention. In the embodiment shown in FIG. 1, signals transmitted with polarized waves orthogonal to each other are optically combined, but may be combined after being converted into an electric signal. In the embodiment shown in FIG. 4, in the optical receiver 30A, the signal lights having mutually orthogonal polarizations are individually converted into electric signals and then combined. The same components as those in FIG. 1 are denoted by the same reference numerals. The configuration and operation of the changed part will be mainly described.

  In the optical receiver 30 </ b> A, the condensing lens 70 condenses the signal light beam projected from the optical transmitter 10 to the spatial transmission path and enters the polarization separator 72. The polarization separator 72 converts the signal light beam from the condenser lens 70 into the same polarization direction component (P wave) as the P wave separated by the polarization separator 16 and a polarization direction component orthogonal thereto. The former is supplied to an optical / electrical (O / E) converter 74P, and the latter is supplied to an optical / electrical (O / E) converter 74S.

  The O / E converter 74P converts the P-wave signal light separated by the polarization separator 72 into an electric signal, and the discriminator 76P discriminates the output electric signal of the O / E converter 74P with a predetermined threshold. . The electric delay device 78 delays the output electric signal of the discriminator 76P by the same time as the delay time Td of the optical delay device 18. On the other hand, the O / E converter 74S converts the S-wave signal light separated by the polarization separator 72 into an electric signal, and the discriminator 76S converts the output electric signal of the O / E converter 74S with a predetermined threshold. Discriminate. The OR circuit 80 takes a logical sum (OR operation) between the output electric signal of the electric delay device 78 and the output electric signal of the discriminator 76S, and outputs the result to the error correction device 82. The OR operation of the OR circuit 80 corresponds to the polarization synthesis by the polarization beam combiner 38 of the embodiment shown in FIG. The error correction device 82 corrects a transmission error included in the output signal of the OR circuit 80 using the error correction code added by the error correction coding device 12 of the optical transmission device 10.

  Instead of the electrical delay 78, an optical delay may be disposed between the polarization separator 72 and the optical / electrical converter 74P.

  Instead of the discriminators 76P and 74S, a discriminator may be arranged between the OR circuit 80 and the error correction device 82. Further, after correcting a transmission error of data transmitted by each polarization, the data may be synthesized by returning to the same timing. In this case, an error correction device is inserted into the outputs of the discriminators 76P and 76S.

  FIG. 5 shows a schematic block diagram of a fourth embodiment of the present invention. In each of the first to third embodiments, the same data signal is transmitted while being shifted in time with mutually orthogonal polarizations on the same beam. Thereby, the optical axis adjustment between the optical transmitter and the optical receiver is facilitated. On the other hand, in the fourth embodiment, since two systems of light beams with different spatial positions are used without using orthogonal polarized waves, the effort of adjusting the optical axis is increased, but the separation and synthesis of polarized waves are increased. Therefore, the optical element can be omitted.

  In the optical transmission device 210, the error correction encoding device 212 performs error correction encoding on the transmission data D. The electrical delay unit 214 delays the output data of the error correction coding device 212 by Td and applies the delayed output data to the electrical / optical (E / O) converter 216. The E / O converter 216 converts the data signal from the delay unit 214 into an optical signal. The output signal light from the E / O converter 216 is projected toward the receiving device 240 by the projection lens 218. That is, the light beam 230 projected by the projection lens 218 is input to the light receiving device 240. The E / O converter 220 converts the output data signal of the error correction coding device 212 into an optical signal. The output signal light of the E / O converter 220 is projected toward the receiving device 240 by the projection lens 222. That is, the light beam 232 projected by the projection lens 222 is input to the light receiving device 240.

  The condenser lens 242 of the optical receiver 240 condenses the signal light beam 230 projected by the projection lens 218 of the optical transmitter 210 and enters the optical / electrical (O / E) converter 244. The O / E converter 244 converts the optical signal from the condenser lens 242 into an electrical signal. The discriminator 246 discriminates the electric signal output from the O / E converter 244 according to a predetermined threshold value. The condensing lens 248 condenses the signal light beam 232 projected by the projection lens 222 of the optical transmission device 210 and enters the optical / electrical (O / E) converter 250. The O / E converter 250 converts the optical signal from the condenser lens 248 into an electric signal. The discriminator 252 discriminates the output electric signal of the O / E converter 250 according to a predetermined threshold value. The delay unit 254 delays the output data of the discriminator 252 by the same time as the delay time Td of the delay unit 214.

  The OR circuit 256 takes the logical sum of the output data of the discriminator 246 and the output data of the delay unit 254 and applies the result to the error correction device 258. The error correction device 258 corrects a transmission error included in the digital signal output from the OR circuit 256 using the error correction code by the error correction coding device 212.

  For example, if one or both of the light beams 230 and 232 are instantaneously interrupted by a bird or the like, the output signals of the discriminators 246 and 252 become zero level during the interruption period. However, since the data carried by the light beam 230 by the delay device 214 is delayed in advance from the data carried by the light beam 232 at the time of transmission, an error caused by beam interruption is transmitted between the light beam 230 and the light beam 232. It exists at a completely different timing on the data. That is, even if there is an error due to beam interruption in the output data of the optical discriminator 246, there is no error due to beam interruption in the output data of the delay unit 254 at the same time. The reverse is also true. This operation is the same as in the first to third embodiments. The OR circuit 256 takes the logical sum of the output of the discriminator 246 and the output of the delay unit 254, so that an error due to beam interruption can be replaced with normal data that has not undergone beam interruption.

  Instead of the discriminators 246 and 252, a discriminator may be arranged between the OR circuit 256 and the error correction device 258. Further, after error correction is performed on the output data of the discriminators 246 and 252, one of the data may be delayed to synthesize both data.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

It is a schematic block diagram of the first embodiment of the present invention. It is an example of the timing chart of the Example shown in FIG. It is a schematic block diagram of the second embodiment of the present invention. It is a schematic block diagram of the third embodiment of the present invention. It is a schematic block diagram of the fourth embodiment of the present invention.

Explanation of symbols

10: Optical transmission device 12: Error correction coding device 14: Electric / optical (E / O) converter 16: Polarization separator 18: Optical delay device 20: Polarization synthesizer 22: Projection lenses 30, 30A: Light Receiver 32: Condenser lens 34: Polarization separator 36: Optical delay device 38: Polarization synthesizer 40: Optical / electrical (O / E) converter 42: Discriminator 44: Error correction device 70: Condenser lens 72: Polarization separators 74P, 74S: Optical / electrical (O / E) converters 76P, 76S: Discriminator 78: Delay device 80: OR circuit 82: Error correction devices 110A, 110B: Optical transmission / reception devices 112A, 112B: Error correction encoders 114A and 114B: Electric / optical (E / O) converter 115: Optical circulator 116: Polarization beam splitter (PBS)
118: Optical delay device 120: Polarization beam splitter 122: Projection / condensing lens 132: Projection / condensing lens 134: Polarization beam splitter 136: Optical delay device 138: Polarization beam splitter 139: Optical circulators 140A, 140B: Optical / electrical (O / E) converters 142A, 142B: discriminators 144A, 144B: error correction device 210: optical transmission device 212: error correction coding device 214: delay device 216: electrical / optical (E / O) converter 218: Projection lens 220: Electric / optical (E / O) converter 222: Projection lens 230, 232: Light beam 240: Light receiving device 242: Condensing lens 244: Optical / electrical (O / E) converter 246: Discriminator 248: condenser lens 250: optical / electrical (O / E) converter 252: discriminator 254: delay unit 256: OR circuit 258: error correction device

Claims (14)

A signal light generation step for generating a first signal light for carrying data, and a second signal light for carrying the data delayed by a predetermined time (Td) from the first signal light;
A projection step of projecting the first and second signal lights onto a spatial transmission path;
A delay step for delaying the first signal carried by the first signal light from the spatial transmission path for the predetermined time;
A combining step of combining the second signal carried by the second signal light from the spatial transmission path and the delayed second signal to generate a combined signal;
And a restoration step of restoring the data from the combined signal.   2. The optical space transmission method according to claim 1, wherein the first and second signal lights are polarization signals orthogonal to each other and propagate through the space transmission path as the same light beam. The signal light generation step includes
An electrical / optical conversion step for converting the data into a linearly polarized optical signal;
A polarization separation step of separating the optical signal into two optical components of polarization orthogonal to each other, and outputting one of the optical components as the first signal light;
3. The optical space transmission according to claim 2, further comprising a step of delaying the other polarization component separated in the polarization separation step for the predetermined time and outputting the second polarization component as the second signal light. Method. The delay step is a step of delaying the first signal light from the spatial transmission path for the predetermined time,
The combining step includes a polarization combining step of combining the first signal light delayed in the delay step and the second signal light from the spatial transmission path with polarizations orthogonal to each other. The optical space transmission method according to claim 1, wherein the method is an optical space transmission method. The delay step includes a first conversion step for converting the first signal light from the spatial transmission path into a first electric signal, and an electric delay step for delaying the first electric signal for the predetermined time. Comprising
The combining step includes a second conversion step for converting the second signal light from the spatial transmission path into a second electric signal, and the second electric signal delayed by the electric delay step. An optical space transmission method according to any one of claims 1 to 3, further comprising an electrical synthesis step of combining with one signal light. A signal light generating device (14, 16, 18; 214) that generates a first signal light that carries data and a second signal light that carries the data delayed by a predetermined time (Td) from the first signal light. , 216, 220),
A projection optical system (20, 22; 218, 222) for projecting the first and second signal lights onto the spatial transmission path;
A light receiving optical system (32, 34; 70, 72; 242, 248) for receiving light including the first and second signal lights from the spatial transmission path;
A delay device (36, 78, 254) for delaying the first signal carried by the first signal light from the spatial transmission path for the predetermined time;
A combiner (38, 80, 256) for generating a combined signal by combining the second signal carried by the second signal light from the spatial transmission path and the delayed second signal;
Restoration device (40, 42, 44; 82; 258) for restoring the data from the synthesized signal
An optical space transmission system comprising:   The projection optical system synthesizes the first and second signal lights with polarization orthogonal to each other, and a projection for projecting the output light of the polarization synthesizer onto the spatial transmission path The optical space transmission system according to claim 6, further comprising a lens (22). The signal light generation device is
An electrical / optical converter (14) for converting the data into a linearly polarized optical signal;
A polarization separator (16) that separates the optical signal into two optical components of polarization orthogonal to each other, and outputs one of the optical components as the first signal light;
An optical delay (18) that delays the other polarization component separated by the polarization separator (16) for the predetermined time and outputs it as the second signal light
The optical space transmission system according to claim 6 or 7, further comprising:   The light receiving optical system includes a signal light separation device (34, 72) for separating the first signal light and the second signal light from light input from the spatial transmission path. The optical space transmission system according to any one of 6 to 8.   The optical space transmission system according to claim 9, wherein the signal light separation device (34) comprises a polarization separation device.   11. The optical delay device according to claim 6, wherein the delay device is an optical delay device that delays the first signal light from the spatial transmission path for the predetermined time. Optical space transmission system.   The combiner is a polarization combiner (38) that combines the output signal light of the optical delay device (36) and the second signal light from the spatial transmission path with mutually orthogonal polarizations. The optical space transmission system according to claim 11. Furthermore, it comprises first and second optical / electrical converters (74P, 74S) for converting the first and second signal lights from the spatial transmission path into first and second electrical signals, respectively.
The delay device is an electrical delay device (78) for delaying the first electrical signal from the first optical / electrical converter (74P) for the predetermined time;
The electrical combiner combines the second signal from the output signal of the second optical / electrical converter (74S) with the first signal delayed by the electrical delay device (78). The optical space transmission system according to any one of claims 6 to 10, wherein the optical space transmission system is an optical device (80). The signal light generation device is
An electrical delay (214) for delaying the data for the predetermined time;
A first electrical / optical converter (216) for converting the output electrical signal of the electrical delay device (214) into the first optical signal;
Second electrical / optical converter (220) for converting the data into the second optical signal
And
The light according to claim 6, wherein the projection optical system includes an optical system (218, 222) that projects the first signal light and the second signal light onto the spatial transmission path as separate light beams. Spatial transmission system.

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