JP2024162571A - Optical transceiver for free space optical communications - Google Patents

Abstract

To provide an optical communication apparatus which simplifies the constitution of an optical system remarkably and allows for stable operation in the space with accurate point ahead, a high transfer rate, and low latency.SOLUTION: An optical communication apparatus comprising a transmission and reception antenna for receiving reception light from a satellite 401 on a communication opposite party side for performing data communication using light of circular polarization in a free space and transmitting transmission light for data to the communication opposite party, a guide mechanism (a gimbal mechanism 402, a biaxial steering mirror 409) for tracking the satellite on the communication opposite party side using the reception light, an angle detector for detecting an angle of the reception light, and a tracking controller for controlling the guide mechanism using an output from the angle detector and tracking the satellite on the communication opposite party side comprises a spatial optical phase modulator 411 which both the transmission light and reception light pass through and subjects the transmission light to spatial optical phase modulation in general.SELECTED DRAWING: Figure 4-4

Description

This disclosure relates to the technical field of optical transceivers used in optical communication devices that realize mutual optical communication in free space.

In wireless communication, the available radio frequency bands are already in use by many communication methods, and the newly available radio frequency bands are depleted, which is causing major problems such as being unable to respond to improvements in communication speeds and an increase in the number of communication terminals. In order to solve this problem of depletion of radio frequency bands, optical communication methods using light as a transmission carrier are currently being actively researched. Radio wave communication has an advantage over optical communication on the ground, as communication is easily blocked by obstacles and weather. However, in space, the good straightness of light offers great advantages such as reduced transmission power and high-speed communication, and various efforts are being made to put it into practical use. Optical communication technology is mainly composed of four elements of technology: "beam steering technology," "high-speed tracking technology," "transmitting and receiving polarization separation technology," and "adaptive optics technology." By improving each of these technologies, efforts are being made to put it into practical use as a faster and more reliable communication technology. Below, these four main elemental technologies are explained with examples of the past.

"Beam steering technology" is a technology that improves the directivity of optical communication terminals and enables signals to be transmitted and received while following the movement of satellites. Page 1060 of Non-Patent Document 1 discloses a steering technology of a transmitted optical beam that takes into account the relative speed between satellites moving at high speed, and this technology will be explained using Figure 1. In Figure 1, 101 is a satellite 1 in optical communication, 102 is a receiving optical antenna mounted on 101, 103 is a transmitting optical antenna mounted on 101, 104 is a transmitted light from satellite 105, 105 is a satellite 2 that communicates with satellite 1, 106 is a transmitting optical antenna mounted on 102, 107 is a receiving optical antenna mounted on 102, and 108 is a transmitted light emitted from satellite 1 101. Figure 1 shows a case where two satellites 101 and 105 that communicate with each other are moving at a relative speed of 8 km/s. The optical communication antennas (102, 103, 106, 107) for transmitting and receiving mounted on each satellite have an aperture diameter of 9 cm, and the optical wavelength used for communication is 1550 nm for communication from satellite 1 (101) to satellite 2 (105), and 1570 nm for communication from satellite 2 (105) to satellite 1 (101). These parameters are general values when optical communication is performed between satellites in outer space. For example, as shown in FIG. 1, if the direction of the receiving antenna 102 can be correctly controlled by relying on the transmitted light 104 emitted from satellite 2 (105), the transmitted light 104 from satellite 2 (105) can be received, and data reception from satellite 2 (105) is established. This is also true when satellite 2 (105) receives data from satellite 1 (101). On the other hand, when transmitting data from satellite 1 and satellite 2, optical beam steering control is required taking into account the relative speeds of each satellite. 1 shows the situation when the satellite 1, 101, emits a transmission light 108 to the satellite 2, 105. The satellite 1, 101, receives the transmission light 104 from the satellite 2, 105, and controls the direction of the receiving optical antenna 102 with high precision, but even if the transmitting optical antenna 103 is aimed in the same direction and transmits light, it will not reach the satellite 2, 105. This is because, in the example of FIG. 1, the satellite 1, 101, and the satellite 2, 105, move at a relative speed of 8 km/s, and the positional relationship between the satellites 101 and 102 changes during the time from when the satellite 2, 105, emits light and reaches the satellite 1, 101, to when the satellite 2, 101, irradiates light toward the satellite 2, 105, and the light reaches the satellite 2, 105. In order to irradiate the transmission light to the satellite 102, the satellite 1, 101, needs to accurately control the direction taking into consideration the change in the positional relationship between the two satellites moving in the direction of the transmitted light beam 108. FIG. 1 shows an example of transmitting parallel light to a satellite 2000 km away using a transmitting antenna with an aperture diameter of 8 cm. In this case, the spread angle of the transmitted light is 0.00126°. This is smaller than the angle difference of 0.00305° that occurs due to the relative positional relationship between the satellites, which changes depending on the arrival time of the light, meaning that communication cannot be performed unless the angle of the transmitting antenna 103 is controlled taking into account the positional relationship between the two satellites. This control of the transmitting antenna 103 taking into account the positional relationship is called point-ahead control, and has been introduced between many optical communication terminals between satellites. This point-ahead control is disclosed in Patent Documents 1 and 2. The technology disclosed in Patent Documents 1 and 2 realizes an optical communication terminal by using "high-speed tracking technology" and "transmitting and receiving polarization separation technology" in addition to point-ahead technology, and these technologies will be described using FIG. 2 based on the disclosures of Patent Documents 1 and 2.

In FIG. 2, 201 is a satellite with which optical communication is performed, 202 is a gimbal mechanism on which the optical system part of the optical communication terminal is mounted, 203 is a data signal processing and control processing block that controls the mechanism of the optical communication terminal and processes the transmission and reception of communication data, 204 is an optical antenna barrel, 205 is a gimbal mechanism that rotates the optical antenna barrel 204 in the tilt direction, 206 is a gimbal mechanism that rotates the optical antenna barrel 204 in a plane, 207 is a focusing mirror that focuses the communication light, 208 is a convex mirror that reflects the light from the focusing mirror 207 as parallel light, and 209 is a two-axis steering wheel that changes the beam angle of the optical communication light. 215 is an optical fiber, 216 is a receiving optical amplifier that amplifies the light intensity of the received light, 217 is an optical fiber, 218 is an InGaAs photodiode for receiving data, and 219 is a pair of optical fibers that further couple the light reflected by the beam splitter 212 to an optical fiber. 220 is a condenser lens that reduces the size of the light beam reflected by the beam splitter 219. 221 is a coarse angle detection sensor composed of a four-segment InGaAs photodiode that detects the rough angle of the communication light from the position of the light condensed by 220. 222 is a condenser lens that reduces the beam size of the transmitted light split by 219. 223 is a fine angle detection sensor composed of a four-segment InGaAs photodiode that detects the high-precision angle of the communication light from the position of the light condensed by 222. 224 is an output from the data signal processing and control processing block 203. The transmitting laser turns on and off the output according to the transmitted data, 225 is an optical fiber, 226 is a transmitting optical amplifier that amplifies the output of the transmitting laser 224, 227 is an optical fiber, 228 is an optical fiber connector, 228 is a condenser lens that converts the output of the optical fiber connector 228 into parallel light, 230 is a two-axis point-ahead mirror that realizes the above-mentioned point-ahead control, 231 is a calibration laser that calibrates the angle of the two-axis point-ahead mirror, 232 is an optical fiber, 233 is a quarter-wave plate, and 234 is a retroreflector that reflects the adjustment light in the same direction as it was incident. The optical fiber 226 and the optical fiber 231 are fused and connected, and the light emitted from the laser 223 and the laser 230 is combined at this fusion part and emitted from the same optical fiber connector 227.

First, the path of the light transmitted when transmitting data from the optical communication terminal to the satellite 201 will be described with reference to FIG. 2. The communication light emitted to the satellite 201 is transmitted data output from the data signal processing and control processing block 203, which is input to the transmission laser 224, which is turned on and off according to the input transmission data, and is input to the optical amplifier 226 through the optical fiber 225, where it is amplified by about 100 times and up to an output of 5 watts. The light output from the optical amplifier 226 is coupled to the optical fiber connector 228 arranged at the focal position of the focusing lens 229 through the optical fiber 227, where it is converted into parallel light, and enters the two-axis point-ahead mirror 230. The two-axis point-ahead mirror 230 determines the relative speed based on the orbit information exchanged in advance between the communicating satellites, and sets an angle corresponding to that speed, thereby performing the beam-ahead control of the angle of the transmitted light as described above. The transmitted light, angle-controlled at 230, is P-polarized and passes through the polarizing beam splitter at 211, then passes through the quarter-wave plate at 210 to become circularly polarized light, which is then precisely controlled in the direction of the satellite by the steering mirror at 209, and is irradiated as parallel light toward the satellite 201 via the convex mirror at 208 and the focusing mirror at 207.

On the other hand, the circularly polarized light emitted from the satellite 201 passes through the lens barrel of the optical antenna 204 as the received light, is collected by the collecting mirror 207, and is converted into parallel light by the convex mirror 208. The parallel light is further reflected by the steering mirror 209, passes through the quarter-wave plate 210 and is converted into S-polarized light, so it is reflected by the polarizing beam splitter 211 and enters the beam splitter 212. 70% of the light that enters the beam splitter 212 is reflected by the beam splitter 212 and used as a signal to demodulate the received data. This reflected light is led through the collecting lens 213 to the optical fiber connector 214 and the optical fiber 215 to the optical amplifier 216, where it is amplified 100 times, and then converted into an electrical signal by the InGaAs photodiode 218, and the communication data is demodulated in the data signal processing and control processing block 203. The light that passes through the beam splitter 212 is further split 1:1 by the beam splitter 219 into reflected light and transmitted light. The reflected light is collected by the collecting lens 220 and enters an InGaAs photodiode 221 whose sensor portion is divided into four parts. The transmitted light also passes through the collecting lens 222 and enters an InGaAs photodiode 223 whose sensor portion is divided into four parts. The collecting lenses 220 and 222 have different focal lengths, and generally, an optical configuration is used in which the rough angle detection sensor 221 can detect the direction of the received light in a relatively wide angle range of about ±0.2 degrees, and the precise angle detection sensor 223 can detect the direction of the received light with high sensitivity of ±0.006 degrees. In order to realize stable optical communication, it is necessary to stably guide the receiving light to the receiving fiber 215, and the necessary control angle precision is required to be about ±0.0001 degrees, while when the satellites start communication, there is an error in the position information of each satellite, and an angle error of about ±0.2 degrees occurs in the communication light, so that control is possible even for an angle deviation of about ±0.2 degrees, and the control precision must be realized to be ±0.0001 degrees. For this reason, the optical communication terminal generally uses a method in which, using the coarse angle detection sensor 221 and the precise angle sensor 223, which have a relatively large error detection range, when controlling the angle when the error is large, the information of the coarse angle detection sensor 221 is used during angle control, and after the error is reduced to a certain extent by control and falls within the detection range of the precise adjustment angle detection sensor 223, the information of the precise adjustment angle detection sensor 223 is used for control. These controls can be realized by switching the angle error signals of 221 and 223 depending on the amount of light input to the coarse angle detection sensor 221 and the precise angle detection sensor 221, respectively. It can also be realized by adding the angle error signals 221 and 223 at an appropriate ratio to perform control. The data signal processing and control processing block 203 performs these controls. The control block 203 is connected to the gimbal mechanism 202 and the two-axis steering mirror 209, and appropriately controls the gimbal mechanism 202 and the two-axis steering mirror 209 according to the frequency band and the control angle range to stably couple the received light to the optical fiber 215. Since the core system of a single mode optical fiber is about 10 μm, the control angle precision of the received light required to stably collect the received light with the collecting lens 213 and stably couple it to the optical fiber 215 is about ±0.0001 degrees. In general, the lens barrel 204 of the optical antenna is heavy, and the control band of the gimbal mechanisms 204 and 205 that move it is about 10 to 30 Hz. However, in order to track a satellite moving at high speed and correct the angular deviation of the received light caused by the vibrations inside the satellite to within ±0.0001 degrees, a control system with a control band of 300 Hz or more is generally required. The technology to achieve this is the "high-speed tracking technology." In the conventional example of FIG. 2, a two-axis steering mirror 209 is provided to achieve this "high-speed tracking technology." The two-axis steering mirror 209 can control the angle of the communication light within an angle range of about ±2 degrees, but since the weight of the mirror, which is the moving part, is light, it can control up to a high bandwidth. The control block 203 divides the band of the angle error signals 221 and 223, and controls the gimbal mechanism 202 for control that requires a low-speed response but a wide movable range, and controls the steering mirror 209 for the angle fluctuation elements of the high-speed communication light, thereby achieving a wide response range and a wide control frequency characteristic. "High-speed tracking technology" uses a wideband steering mirror 209 to achieve control characteristics with a high gain crossover point of 300 Hz, approximately 10 times higher than the conventional 30 Hz, thereby improving control accuracy.

"Transmitting and receiving polarization separation technology" is a technology that uses the polarization properties of light to separate the optical paths of the transmitted light and the received light in order to perform the point ahead mentioned above. In the optical communication terminal of FIG. 2, which is a conventional embodiment, the optical fiber connector 228, which is the emission point of the transmitted light, and the optical fiber connector 214, which is the reception point of the received light, are spatially separated into different locations, and only the transmitted light passes through the point ahead mirror 230 and is combined into the same optical path by the polarized beam splitter 211. This configuration that separates the optical paths of the transmitted light and the received light makes it possible to change the direction of the transmitted communication light and the angle of the received light, and this is achieved by "transmitting and receiving polarization separation technology". In order to perform stable communication, the point ahead mirror 230 needs to be accurately controlled with an accuracy of about ±0.0002 degrees.

However, since a typical point-ahead mirror 230 has a mechanism for tilting the mirror with a voice coil or the like, it is very difficult to achieve an accuracy of ±0.0002 degrees with feed-forward control, and a process is required to measure the relationship between the amount of driving the point-ahead mirror 230 and the amount of tilt of the mirror actually, and perform calibration. An optical system for performing this process is installed in the conventional optical communication terminal of FIG. 2. The operation of this calibration system will be explained below with reference to FIG. 2. The calibration laser 231 has a polarization plane arranged in the same S-polarized direction as the received light 224, and the calibration laser 231 is coupled to the optical fiber 232, then merged with the optical fiber 227 for light transmission, and emitted from the optical fiber connector 228, converted into parallel light by the focusing lens 229, reflected by the point-ahead mirror 230, and enters the polarizing beam splitter 211. Since the calibration laser is S-polarized, it is reflected by the beam splitter 221, enters the quarter-wave plate 233, and becomes circularly polarized. It is then reflected by the retroreflector at the same angle as the incident direction, passes through the quarter-wave plate again, becomes P-polarized, and passes through the polarizing beam splitter 211. The transmitted calibration laser light is detected by the coarse angle detection sensor 221 and the fine angle sensor 223 as with the received light. By successively measuring the angle of the optical axis of this calibration laser while changing the drive amount of the beam ahead mirror 230, the relationship between the drive amount of the beam ahead mirror 230 and the angle of the optical axis can be obtained. Conventional optical communication terminals achieve accurate beam ahead control while being feedforward by performing this calibration process.

Finally, the "adaptive optical system" will be explained with reference to FIG. 3. The "adaptive optical system" is a technology used for performing optical communication in the atmosphere with high accuracy, for example, between a satellite and a satellite ground station. It is a technology to correct the deterioration of optical communication signals caused by atmospheric turbulence. The optical communication terminal in FIG. 3 is a conventional optical communication terminal explained in FIG. 2, to which a transmitting light phase modulator 301 composed of a liquid crystal element that modulates the phase correction of the transmitting light and a receiving light phase modulator 302 composed of the same liquid crystal element are added, and it is possible to control the spatial optical phase of the transmitting light and the receiving light from the control block 203. For example, Patent Document 3 discloses a technology to maximize the receiving light by controlling the phase of the light by arranging an adaptive optical mirror at a place where both the transmitting light and the receiving light pass. In the conventional example in FIG. 3, the optical spatial phase of the receiving light disturbed by atmospheric turbulence is controlled and flattened by the receiving light modulator 302 using a method similar to that of Patent Document 3, thereby maximizing the receiving light. In the conventional example of Figure 3, the spatial optical phase of the transmitted light can be controlled by the transmitted light phase modulator 301, and when two satellites start optical communication, the spread angle of the transmitted light can be controlled by the transmitted light phase modulator 301, making it possible to control the start of communication stably by widening the beam width of the transmitted light to start communication. In this way, "adaptive optical technology," which adaptively controls the optical phase of the transmitted light and received light, is a technology that makes it possible to prevent attenuation of the communication light due to stability at the start of communication and atmospheric turbulence that occurs during communication.

Japanese Patent Application Laid-Open No. 01-025218 JP 2000-082996 A JP 2000-068934 A

Springer Handbook of Optical Networks

Optical communication terminals are mainly composed of four elements of technology: "beam steering technology," "high-speed tracking technology," "transmitting and receiving polarization separation technology," and "adaptive optical technology." In order to realize beam steering, as shown in Figure 2, it was necessary to spatially separate the optical fiber connector 228 at the end of the optical fiber 227, which is the light emitting point of the transmitted light, and the optical fiber connector 214 at the end of the optical fiber 215, which is the light receiving point of the received light, using "transmitting and receiving polarization separation technology." When communicating between moving objects such as satellites moving at high speed, a beam ahead is required to change the transmission angle of the transmitted light relative to the direction of emission of the received light. For this purpose, a technology was used in which the optical paths of the transmitted light and the received light are separated, and only the transmitted light passes through a device that changes the angle of the light beam, such as a beam ahead mirror 230, to change the angle of the light beam relative to the received light. However, the conventional optical configuration had a major problem in ensuring the reliability of communication terminals not only in harsh environments such as space but also for long-term use. As shown in FIG. 2, the optical system of the conventional optical communication terminal uses a polarized light separation element such as a polarized beam splitter 212 to separate the received light from the transmitted light. The angle of the reflecting surface of this polarized beam splitter is usually set to 45 degrees, but if the angle of this reflecting surface changes, it will cause an angular deviation between the received light and the transmitted light. In the "beam steering technology", an angle difference is set between the received light and the transmitted light by feedforward control of the beam ahead mirror, but the setting accuracy required for this angle difference is ±0.0002 degrees. Since the fluctuation of the angle of the reflecting surface of the polarized beam splitter 212 becomes the angle difference between the transmitted light and the received light, even if the received light is detected by the precision angle sensor 223 and controlled so that the received light is incident on the optical antenna in parallel with high accuracy, if the angle of the reflecting surface of the polarized beam splitter 212 fluctuates, the angular difference of the transmitted light cannot be accurately maintained. Furthermore, the angular difference between the transmitted light and the received light also fluctuates depending on the angle of the reflecting surface of the beam splitter 219, so the behavior of the angular difference between the transmitted light and the received light becomes even more complicated. In addition, the light for receiving data must be reflected by the reflecting surface of the beam splitter 212 and efficiently coupled to the optical fiber 215, and fluctuations in the reflecting surface of the beam splitter 212 also affect the performance of the optical communication terminal. It is very difficult to maintain the angle of the reflecting surface of the beam splitters 211, 212, and 219 fixed by adhesive or the like with an accuracy of ±0.0002 degrees or less for a long period of time, and this is particularly difficult to achieve in an environment with drastic temperature changes such as outer space, which has been a major obstacle to the widespread use of optical communication as a low-cost, highly reliable technology, such as increased costs and reduced lifespans of optical communication terminals. To achieve high reliability, optical components must be precisely positioned on a high-strength optical base, which increases the weight of the optical communication terminal and makes it difficult to put optical communication into practical use in small satellite terminals that are expected to become more widespread in the future. If the optical system configuration of the optical communication terminal can be simplified to achieve small size and weight reduction, it is predicted that this will be a very significant technological innovation for free space communication, where radio wave bandwidth is insufficient.

The optical communication device of the present invention has been developed in consideration of the above problems, and has a transmitting/receiving antenna that receives received light from the communication partner and transmits transmitted light for data to the communication partner in order to perform data communication using circularly polarized light in free space, a guide mechanism for tracking the communication partner's satellite using the received light, an angle detector that detects the angle of the received light, and a tracking controller that uses the output of the angle detector to control the guide mechanism and track the communication partner, and is characterized by having a spatial phase modulator that is equipped with spatial phase modulation through which both the transmitted light and the received light pass, and in which spatial phase modulation is mainly performed on the transmitted light. In addition, by having the above characteristics, it is possible to realize an optical communication device that is characterized by having an optical path from which the received light and the transmitted light are emitted or incident from approximately the same point in space. One of the characteristics of the spatial light phase modulator, which is the point of this invention, is that it is a spatial light phase modulator that has different phase modulation amounts depending on the difference in the polarization direction of the incident light, and another characteristic is that the spatial light phase modulator uses LCOS, a device in which the spatial phase modulation amount varies depending on the difference in the polarization direction. In addition, the same effect can be achieved by using a spatial phase modulator in which the phase modulation amount varies depending on the difference in the wavelength of the incident light. The change of the pattern of the spatial phase modulator can be easily realized by providing a control processing block that holds or generates a pattern for performing spatial light phase modulation and sets the spatial phase modulation pattern, so that the angle of the transmitted light relative to the received light can be freely changed. As a characteristic of the transmitted light and the received light, it is desirable that the aperture of the transmitted light relative to the transmitting and receiving antennas for the transmitted light and the received light is smaller, and this configuration makes it possible to improve the power efficiency of transmission. In addition, the controller that performs tracking control controls a coarse adjustment mechanism with a wide angle range for changing the direction of light and a fine adjustment mechanism with a narrow range for changing the direction of light as control objects, and the fine adjustment mechanism is configured with an optical element that operates in the direction of two or three axes, making it possible to perform control at a higher speed than in the past, and a condenser lens or a condenser mirror can be used as a specific optical element. In order to realize an optical path in which the received light and the transmitted light are emitted or incident from almost the same spatial point, which is a feature of the present invention, it is necessary to couple the optical paths of the transmitted light and the received light. As a connection form, the input of the transmitted light and the received light is configured as an optical fiber input, and the input received light and the transmitted light are combined with an optical circulator, which makes it possible to efficiently form almost the same spatial point while preventing optical crosstalk between the transmitted light and the received light, thereby realizing an optical communication device with better performance. In addition, the optical communication device of the present invention can also connect the transmitted light and the received light with one optical fiber by coupling the optical fiber to almost the same spatial point. Even if a device with low modulation resolution of the spatial light phase modulator is used, it is possible to realize performance equivalent to that of a spatial light modulator with high resolution by holding two or more patterns for the control processing block to perform spatial light phase modulation and switching between the two or more patterns at a speed faster than the response speed of the spatial light modulator. In addition, due to the feature of the present invention that the transmitted light and the received light are at almost the same point in space, it is also possible to detect the angle of the received light from the light at the periphery of the received light, and because the optical element can be placed near the light focusing point, an optically stable angle detector can be realized, resulting in a high-performance optical communications terminal.

In addition, by applying the above-mentioned selective spatial light phase modulator to the modulation of the received light, it is possible to realize excellent characteristics that could not be realized by conventional optical communication devices. Specifically, in order to perform data communication using circularly polarized light in free space, an optical communication device having a transmitting/receiving antenna that receives received light from the communication partner and transmits transmitted light for data to the communication partner, a guide mechanism for tracking the satellite of the communication partner using the received light, an angle detector that detects the angle of the received light, and a tracking controller that uses the output of the angle detector to control the guide mechanism and track the communication partner, is provided with a spatial light phase modulator through which both the transmitted light and the received light pass and in which the received light is generally spatially modulated. In addition, an optical communication terminal equipped with a spatial light phase modulator that generally modulates the received light can be provided with an optical path in which the received light and the transmitted light are emitted from or incident on approximately the same point in space, thereby realizing stable reception performance. In addition, the optical communication device of the present invention is equipped with a control processing block that holds or generates a pattern for performing spatial light phase modulation on the received light and sets the spatial phase modulation pattern in the spatial light control processor, making it possible to easily change the characteristics during reception. Specifically, the state of the optical communication device is input to the control processing block, and multiple spatial light phase modulation patterns are switched according to this input to configure an optimal receiving optical system according to the communication state. Specifically, by setting a pattern in which the amount of light for control is greater than the amount of light for communication when the state of the optical communication device is in the acquisition phase, and setting a pattern in which the amount of light for control is smaller than the amount of light for communication when the state of the optical communication device is in the tracking phase, high-speed acquisition and communication at a high transfer rate can be achieved at the same time. In addition, by setting a spatial modulation pattern in which the light irradiated to the center of the spatial phase modulator is not spatially phase modulated, and the light irradiated to other than the center has an optical axis tilted toward the center, it is possible to realize an angle error detector with a wide detection range for angle errors and high detection accuracy for angle errors, and a high-performance, low-cost optical communication device can be realized.

The optical communications terminal realized by the above-mentioned configuration not only has a significantly simpler optical system configuration than conventional optical communications terminals, but also has higher point-ahead accuracy than conventional optical communications devices, which require extremely precise angle control, due to the feature that the optical paths of the received light and transmitted light are shared. Furthermore, since it can be realized with a simple optical system, this invention makes it possible to realize an optical communications device that can be operated stably in outer space, where low cost, maintenance-free, and long-term use are required. In addition, since the optical characteristics can be changed according to the state of the optical communications device for the received light, the present invention realizes an optical communications device with high transfer rate and low latency.

FIG. 2 is a diagram for explaining the communication state of optical communication between satellites. FIG. 1 is a diagram for explaining a conventional optical communication terminal technology. FIG. 1 is a diagram for explaining the technology of a conventional optical communication terminal equipped with a spatial phase modulator. FIG. 1 is a diagram for explaining a satellite system according to an embodiment. FIG. 1 is a diagram for explaining a communication control system according to an embodiment. FIG. 2 is a schematic block diagram of a computer that functions as a communication control device. 1 is a diagram for explaining a first embodiment of an optical communication terminal of the present invention; 1A and 1B are diagrams for explaining an angle detection sensor and a coupling state of received and transmitted light to an optical fiber in the optical communication terminal according to the first embodiment of the present invention. 5A to 5C are diagrams for explaining the operation of a spatial phase modulator in the optical communication terminal according to the first embodiment of the present invention. 5A to 5C are diagrams for explaining the operation of a spatial phase modulator in the optical communication terminal according to the first embodiment of the present invention. FIG. 11 is a diagram for explaining a second embodiment of the optical communication terminal of the present invention. 11A and 11B are diagrams for explaining an angle detection sensor and a coupling state of received and transmitted light to an optical fiber in an optical communication terminal according to a second embodiment of the present invention. 13A to 13C are diagrams for explaining the operation of a spatial phase modulator in the optical communication terminal according to the third embodiment of the present invention. FIG. 13 is a diagram for explaining a fourth embodiment of the optical communication terminal of the present invention. 13A and 13B are diagrams for explaining a focus position detection sensor, an angle detection sensor, and a coupling state of received and transmitted light to an optical fiber in an optical communication terminal according to a fourth embodiment of the present invention. 13A and 13B are diagrams for explaining a focus position detection sensor, an angle detection sensor, and a coupling state of received and transmitted light to an optical fiber in an optical communication terminal according to a fourth embodiment of the present invention. 13A and 13B are diagrams for explaining a focus position detection sensor, an angle detection sensor, and a coupling state of received and transmitted light to an optical fiber in an optical communication terminal according to a fourth embodiment of the present invention. FIG. 13 is a diagram for explaining a fifth embodiment of the optical communication terminal of the present invention. 13A to 13C are diagrams for explaining an acquisition operation in the optical communication terminal according to the fifth embodiment of the present invention. 13A to 13C are diagrams for explaining the operation of a spatial phase modulator in an operation mode in the optical communication terminal according to the fifth embodiment of the present invention. 13A to 13C are diagrams for explaining the operation of a spatial phase modulator in an operation mode in the optical communication terminal according to the fifth embodiment of the present invention.

The following describes in detail an embodiment of the optical communication terminal of the present invention with reference to the drawings.

Figure 4-1 is a diagram showing a satellite system 1 of this embodiment. As shown in Figure 4-1, the satellite system 1 of this embodiment includes a relay satellite 2, other satellites 3A, 3B, and 3C (hereinafter also simply referred to as "user satellites") that are different from the relay satellite 2, and a ground station 4, which is a radio station on Earth. The relay satellite 2 and the user satellites 3A, 3B, and 3C are artificial satellites. The ground station 4 installed on the ground is an example of an earth station that performs wireless communication or optical communication, and when multiple ground stations 4 are installed, it may be a collective term for them.

Each of the user satellites 3A, 3B, and 3C orbits in a first orbit in outer space. The relay satellite 2 orbits in a second orbit in outer space. The altitudes of the first and second orbits from the Earth's surface are lower than the altitude of a geosynchronous orbit from the Earth's surface (altitude of about 36,000 km). A geostationary orbit (GEO) is an example of a geosynchronous orbit. Furthermore, the altitude of the second orbit from the Earth's surface is higher than the altitude of the first orbit from the Earth's surface. The first orbit is, for example, a low Earth orbit (LEO). The altitude of the apogee of the low Earth orbit from the Earth's surface is, for example, 20 km to 2,000 km from the Earth's surface. The second orbit is, for example, a medium Earth orbit (MEO). The altitude of the apogee of a medium earth orbit above the Earth's surface is, for example, between 1,000 km and approximately 36,0000 km above the Earth's surface.

Each of the multiple user satellites 3A, 3B, and 3C performs wireless communication with the relay satellite 2 and performs data communication with the ground station 4 via the relay satellite 2. The relay satellite 2 performs data communication with the multiple user satellites 3A, 3B, and 3C, and at the same time performs data communication with the ground station 4 in parallel, thereby relaying data communication between the multiple user satellites 3A, 3B, and 3C and the ground station 4 in real time. The ground station 4 and the server 6 are connected by a network 5 such as the Internet, and the server 6 receives data acquired by the user satellites 3A, 3B, and 3C via the ground station 4. As a result, the server 6 can obtain data acquired by the user satellites 3A, 3B, and 3C while remaining on the ground, and has the functions necessary to operate the satellite system of FIG. 4-1. Note that when referring to any one of the multiple user satellites 3A, 3B, and 3C, it is simply referred to as "user satellite 3."

Figure 4-2 is a diagram showing a detailed configuration example of the communication control system 12 of the embodiment. As shown in Figure 4-2, the communication control system 12 includes multiple optical communication devices 14A, 14B, and 14C, a communication control device 16, a signal switching circuit 18, a data multiplexing circuit 19A, a multiplexed data separation circuit 19B, and a high-frequency radio device 20. The communication control system 12 is mounted on a relay satellite 2. When referring to any one of the multiple optical communication devices 14A, 14B, and 14C, it is simply referred to as an "optical communication device 14". The number of user satellites 3 is not limited to three as shown in Figure 4-2, and may be more than three. Furthermore, the number of user satellites 3 does not need to be the same as the number of optical communication devices 14, and may exceed the number of optical communication devices 14. The user satellite 3 may be part of a satellite constellation in which multiple satellites are linked to achieve a single function or service.

(Optical communication device)
Each of the optical communication devices 14A, 14B, and 14C includes an optical telescope 22A, an optical receiver 24A, and an optical transmitter 26A, as shown in the optical communication device 14A in Fig. 4-2. The configurations of the optical communication devices 14B and 14C shown in Fig. 4-2 are similar to that of the optical communication device 14A. Therefore, only the configuration of the optical communication device 14A will be described below.

The optical telescope 22A transmits and receives laser light between the user satellites 3A, 3B, and 3C. Note that the user satellite with which the optical communication device 14A optically communicates is not limited to the user satellite 3A. The optical communication device 14A can also optically communicate with the user satellites 3B and 3C. The optical telescope 22A has a window (not shown) that serves as an entrance and exit for the laser light. The optical telescope 22A also has a beam steering mirror (not shown). The beam steering mirror adjusts the optical path.

The optical telescope 22A outputs the laser light received from other satellites to the optical receiver 24A (described later) via a beam steering mirror. The optical telescope 22A also outputs the laser light output from the optical transmitter 26A (described later) to other satellites via a beam steering mirror.

The optical receiver 24A optically demodulates the laser light output from the optical telescope 22A to obtain a digital electrical signal corresponding to the laser light received by the optical telescope 22A. The optical receiver 24A then outputs the digital electrical signal to the high-frequency radio 20, which will be described later.

The optical transmitter 26A obtains laser light corresponding to the digital electrical signal by optically modulating the digital electrical signal output from the high-frequency radio device 20 described below. The optical transmitter 26A then outputs the laser light to the optical telescope 22A.

(Communication control device)
4B, the communication control device 16 includes a setting unit 28 and a control unit 30. The setting unit 28 sets various information required for optical communication. The control unit 30 controls each device in the communication control system 1.

(Signal switching circuit)
The signal switching circuit 18 switches the signal paths between the multiple optical communication devices 14A, 14B, 14C and the signal paths between the multiple optical communication devices 14A, 14B, 14C and the high-frequency radio device 20 described later in response to a control signal output from the communication control device 16.

(Data multiplexing circuit and multiplexed data separation circuit)
The data multiplexing circuit 19A multiplexes data so that optical communication can be performed by a plurality of optical communication devices. The multiplexed data demultiplexing circuit 19B demultiplexes the multiplexed data so that optical communication can be performed by a plurality of optical communication devices.

(High frequency radio)
The high frequency radio device 20 is an example of a relay communication device for the relay satellite 2 to communicate with the ground station 4 and the like. The high frequency radio device 20 includes a high frequency modulation circuit 32, a high frequency transmission antenna 33, a high frequency transmitter 34, a high frequency receiving antenna 35, a high frequency receiver 204, and a high frequency demodulation circuit 37. The high frequency radio device 20 modulates data acquired by the multiple optical communication devices 14A, 14B, and 14C and transmits the data to the ground station 4. The high frequency radio device 20 also demodulates data transmitted from the ground station 4 and passes it to the multiple optical communication devices 14A, 14B, and 14C.

The high frequency modulation circuit 32 modulates the digital electrical signal output from the optical communication device 14 and outputs it to the high frequency transmitter 34.

The high-frequency transmitter 34 converts the signal modulated by the high-frequency modulation circuit 32 into a high-frequency signal and amplifies the signal.

The high-frequency transmission antenna 33 radiates the high-frequency signal output from the high-frequency transmitter 34 toward the ground station 4.

The high frequency receiving antenna 35 receives high frequency waves transmitted from the ground station 4.

The high frequency receiver 204 extracts a modulated signal from the high frequency received by the high frequency receiving antenna 35 and outputs the modulated signal.

The high frequency demodulation circuit 37 demodulates the modulated signal output from the high frequency receiver 204 and converts it into a digital electrical signal.

The communication control device 16 of the communication control system 12 can be realized, for example, by a computer 70 shown in FIG. 4-3. The computer 70 includes a Central Processing Unit (CPU) 71, a memory 72 as a temporary storage area, and a non-volatile storage unit 73. The computer 70 also includes an input/output interface (I/F) 74 to which an input/output device (not shown) is connected, and a read/write (R/W) unit 75 that controls reading and writing of data to a recording medium. The computer 70 also includes a network interface (I/F) 76 that allows the communication control system 12 to connect to a terrestrial communication system such as the Internet. The CPU 71, memory 72, storage unit 73, input/output I/F 74, R/W unit 75, and network I/F 76 are connected to each other via a bus 77.

The storage unit 73 can be realized by a hard disk drive (HDD), a solid state drive (SSD), a flash memory, or the like. The storage unit 73 as a storage medium stores a program for causing the computer 70 to function. The CPU 71 reads the program from the storage unit 73, expands it into the memory 72, and sequentially executes the processes contained in the program.

The functions realized by the program can also be realized, for example, by a semiconductor integrated circuit, or more specifically, an Application Specific Integrated Circuit (ASIC).

In addition, each device included in the communication control system 12 may also be realized by a computer 70 shown in Figure 4-3.

For configurations not described above, please refer to Japanese Patent No. 6987420. The contents disclosed in Japanese Patent No. 6987420 are incorporated by reference into this specification to the same extent as if the contents were specifically and individually set forth in this specification.

The optical communication terminal in each of the following embodiments is an example of an optical communication device, and may correspond to the optical communication device of the above-mentioned satellite system 1. The angle detection sensor in each of the following embodiments is an example of an angle detector. The data signal processing/control processing block in each of the following embodiments is an example of a tracking controller. The data signal processing/control processing block may be realized by the communication control device 16 of the above-mentioned satellite system 1. In each of the following embodiments, the gimbal mechanism (mechanism that changes the angle of the light beam by a large amount) and the steering mirror or steering lens (mechanism that changes the angle of the light beam by a small amount) are examples of guide mechanisms for tracking the other satellite.

<Optical communication terminal of the first embodiment>
Fig. 4-4 shows an example of the first embodiment of the optical communication terminal of the present invention. In Fig. 4-4, 401 is a satellite on the other side of the optical communication, 402 is a gimbal mechanism on which the optical system part of the optical communication terminal is mounted, 403 is a data signal processing and control processing block that performs mechanical control of the optical communication terminal and processing for transmitting and receiving communication data, 404 is an optical antenna barrel, 405 is a gimbal mechanism that rotates the optical antenna barrel 404 in the tilt direction, 406 is a gimbal mechanism that rotates the optical antenna barrel 404 in a plane, 407 is a focusing mirror that focuses communication light, 408 is a convex mirror that reflects the light from the focusing mirror 407 as parallel light, 409 is a two-axis steering mirror that changes the beam angle of the optical communication light, 410 is a 1/4 λ plate, and 411 is an LCOS (Liquid Crystal on Silicon) that modulates the optical phase of the P-polarized component. The optical fiber 416 for receiving light and the optical fiber 420 for transmitting light are connected by an optical circulator 415, and the optical fiber 420 for transmitting light are connected by an optical circulator 415, and the optical fiber 420 for transmitting light is ... In order to perform beam-ahead control to advance the angle of the transmitted light from the received light, a beam-ahead mirror (230 in FIG. 1) or the like is arranged to separate the optical paths of the transmitted light and the received light. In the optical communication terminal of the present invention, the transmitted light and the received light are spatially at the same light-emitting point or light-receiving point, and the transmitted light and the received light share the same optical path, realizing the beam-ahead function of advancing the angle of the transmitted light relative to the angle of the received light.

First, the optical path of the received light shown by the dotted line in Figure 4-4 will be explained. The light emitted from the satellite 401 with which communication is being performed is incident as received light on the optical communication terminal in Figure 4-4. In Figure 4-4, the received light is shown by the dotted line. The received light incident on the optical antenna lens tube 404 is collected by the collecting mirror 407, becomes parallel light by the convex mirror 408, is reflected by the two-axis steering mirror 409, and becomes linearly polarized S-polarized light by the 1/4 λ plate 410. It is reflected by the spatial light phase modulator 411, but since the spatial light phase modulator 411 does not perform phase modulation on S-polarized light, the received light is reflected without being spatial phase modulated and is collected by the collecting lens 412. The collected received light is received by the angle detection sensor 413, which receives the light from the outer periphery of the collected light, and the angle of the received light is detected. Details of the angle detection sensor 413 are shown in Figure 5. FIG. 5 shows a state where the received light is irradiated onto the angle detection sensor. The received light 501 shows a state where the received light is collected by the collecting lens 412 at the center of the optical fiber 415/420 and is coupled to the optical fiber. The received light 502 is the received light that has an angle deviation and is not coupled to the optical fiber. The light incident surface of the angle detection sensor 413 has a hole at its center through which the received light can pass, and when the received light is in the center, the received light passes through the hole and is coupled to the optical fiber 415 of the received light. When there is an angle deviation of the received light, the received light moves to a position different from the center as shown by 502 in FIG. 5, and cannot be coupled to the optical fiber 415 of the received light. If the steering mirror 409 can be controlled so that the received light is at the position 501 according to the amount of deviation of the received light at this time, the received light can be stably coupled to the optical fiber 415. In this embodiment, sensors divided into four are arranged around a hole 503 through which the received light passes, and a part or all of the received light is incident on one of the four divided sensors 504/505/506/507 depending on the angle of the received light. The amount of deviation from the center of the light beam can be detected by performing the following calculation on the output of these four divided sensors 504/505/506/507. If the horizontal direction of the light incident surface in FIG. 5 is the X-axis, the vertical direction is the Y-axis, the output of sensor 504 is A, the output of sensor 505 is B, the output of sensor 506 is C, the output of sensor 507 is D, the deviation in the X-axis direction is Ex, and the deviation in the Y-axis direction is Ey, Ex and Ey can be calculated by Ex=(A-B-C+D)/(A+B+C+D) and Ey=(A+B-C-d)/(A+B+C+D). If the angle of the fine steering mirror is controlled in the X-axis and Y-axis directions so that both Ex and Ey are zero, the received light is controlled to the position 501, and the received light can be stably coupled to the optical fiber. Ex and Ey are divided by A+B+C+D, which is the total amount of light input to the angle detection sensor 413, and this is a measure to prevent the control gain of the control system from changing when the amount of received light changes. Since the fine steering mirror 409 responds quickly, it can be controlled up to high frequencies, but the operating range is often narrow, about ±0.2 degrees. In order to capture and track satellites over an even wider angle range, the optical communication terminal of the first embodiment uses the low-frequency components of the angle detection sensor 413 to feedback control the gimbal mechanism 405 that rotates the optical antenna barrel in the tilt direction and the gimbal mechanism 406 that rotates it within a plane from the data signal processing and control processing block 403. The central portion of the received light guided to the center of the angle detection sensor 413 by this feedback control passes through an optical fiber connector 414 and is introduced into an optical circulator 415, where only the received light is coupled to an optical fiber 416 and amplified 100 times by an optical amplifier 417. The amplified received light passes through an optical fiber 418 and is received by an InGaAs photodiode 419 for data reception, where the light intensity is converted into the intensity of an electrical signal, and then demodulated as received data by the data signal processing and control processing block 403.

Next, the optical path of the transmitted light shown by the dashed line in Figure 4-4 will be explained. The signal pre-modulated with the communication data output from the data signal processing/control processing block 403 is on-off keyed by the transmitted light laser 423, coupled to the optical fiber 422, amplified 300 times by the optical amplifier 421 to become a 3W laser light, which is input to the optical circulator 415 through the optical fiber 420 and emitted as P-polarized light from the fiber connected to the optical fiber connector 414. The optical circulator 415 is a device that limits the direction of light travel, and the light input from the optical connector 414 is introduced into the optical fiber 416, and the light from the optical fiber 420 side is introduced into the fiber on the optical connector side of 415, so that it functions to separate the received light from the transmitted light. The light emitted from the optical connector 415 passes through the hole 503 provided in the center of the angle detection sensor 413, is converted into parallel light by the condenser lens 412, and enters the spatial light phase modulator 411. By using a spatial phase modulator 411 having polarization selectivity that modulates the phase of light for P-polarized light and does not modulate the phase of light for S-polarized light, an optical communication terminal is realized in which the transmission angle of the transmitted light can be freely changed with respect to the angle of the received light, even though the light emission point of the transmitted light and the light reception point of the received light are at the same spatial point. The operation of the spatial phase modulator 411 that changes the transmission angle of the transmitted light with respect to the angle of the received light will be described with reference to FIG. 6. In the first embodiment of the present invention, an LCOS is used as the spatial phase modulator. An LCOS is a device that controls the phase difference of light by applying a voltage to liquid crystal. The LCOS used in the first embodiment has a size of 16 mm×13 mm and is divided into 1280×1024 pixels as shown in FIG. 6-1, and the phase of light irradiated to each pixel can be controlled in 256 gradations from 0 to 1λ. For example, if it is desired to change the reflection angle of light in the X direction using an LCOS, the reflection angle can be changed by linearly changing the phase of each pixel in the X direction as shown in FIG. 6-2. For example, when a pattern is set on the LCOS in which the optical phase between 1280 pixels is changed from 0 to 1 λ using light of the wavelength of 1.55 μm in the first embodiment as shown in FIG. 6-2, the reflected light can be tilted by about 0.0056 degrees. Since the resolution of each pixel performing phase modulation is 1/256 λ and a very small optical phase can be controlled, it is possible to control the reflection angle of light very finely and with high precision. Specifically, the phase setting value V(x, y) of each pixel of the LCOS when tilting the transmitted light by Ax degrees in the X direction and Ay degrees in the Y direction in FIG. 6 is expressed by the following (Equation 1), where Lx is the size of the LCOS in the X direction, Ly is the size in the Y direction, Px is the number of pixels in the X direction, Py is the number of pixels in the Y direction, x, y are the pixel coordinates, and λ is the wavelength of the transmitted light. In the optical communication terminal of the present invention, it is possible to set the phase of the LCOS pixels according to (Equation 1) based on the beam-ahead angles Ax and Ay of the transmitted light, and it is possible to control the spatial phase of the transmitted light with a resolution of 1/256 of the wavelength of light, and to change the angle of the transmitted light relative to the received light with extremely high precision.

In conventional optical communication terminals, beam ahead is performed by adjusting the angle of the mirror, and it is very difficult to achieve high accuracy such as 1/1000 degrees, and a complicated procedure is required, such as calibrating the angle of the beam ahead mirror (230) in advance using an adjustment laser (231). Not only is it difficult to realize a high-precision optical communication terminal, but it is also vulnerable to deformation of optical components due to temperature changes, etc., and this has been a major obstacle to improving the transfer rate of optical communication terminals and realizing low-cost optical communication terminals. In contrast, the optical communication terminal of the present invention uses a spatial phase modulator 411 that can selectively add spatial phase modulation to the polarization direction of light, making it possible to add spatial phase modulation only to the transmitted light that is P polarized, and has a major feature in that the spatial phase modulation is not performed by 411 on the received light that is S polarized transmitted from the other satellite passing through the same optical path, and by controlling the two-axis steering mirror 409 using the received light, the direction of the other satellite can be captured with high accuracy, and by adding spatial phase modulation to the transmitted light based on this received light, it is possible to change the angle of the transmitted light with respect to the received light with very high accuracy. The generation and transfer of the pattern of (Equation 1) to the spatial phase modulator 411 according to the beam ahead angle is performed by the data signal processing and control processing block 403. By operating the optical communication terminal according to the first embodiment thus realized, it was confirmed that the angular resolution of the beam ahead of the transmitted light can be controlled with an accuracy of about 5×10 ⁻⁵ degrees. This is sufficient performance for use in the beam ahead of an optical communication terminal. In addition, in this embodiment, it was also confirmed that the angle control of the received light can be performed with a control accuracy of about 0.3 μrad by setting the gain crossover point of the control system of the received light to 300 Hz and using PID control to control the fine steering mirror 409 in the data signal processing and control processing block 403. The error rate at that time was also confirmed to be 10 ⁻¹² , which is sufficient characteristics for an optical communication terminal.

The spatial phase modulator with polarization selectivity used in the first embodiment is ideally 0% sensitive to S-polarized light and 100% sensitive to P-polarized light, but if the sensitivity to P-polarized light is generally 70% or more, 70% of the transmitted light can be used for communication light, and communication can be performed without problems. In this case, the sensitivity to S-polarized light is a maximum of 30%, which means that 30% of the received light is lost, but it is possible to obtain a sufficient amount of light to function as an optical communication terminal. Therefore, the use of a spatial light modulator with a phase modulation sensitivity to S-polarized light of 30% or less and a phase modulation sensitivity to P-polarized light of 70% or more is the desired characteristic of the spatial light modulator when implementing the present invention. In the first embodiment, even if a spatial light modulator with a modulation characteristic of 70% for P-polarized light and a modulation characteristic of 30% for S-polarized light is used as the spatial phase modulator, the tracking characteristic and error rate were confirmed to be equivalent to that of a spatial light modulator with a modulation characteristic of almost 100% for P-polarized light and a modulation characteristic of almost 0% for S-polarized light. In the first embodiment, LCOS is used as a phase modulator with polarization selection characteristics for spatial phase modulation, but if a spatial phase modulator with polarization selectivity in phase modulation characteristics is used, the same performance as in the first embodiment can be achieved. For example, similar characteristics can be obtained by using a spatial phase modulator with wavelength selectivity by changing the wavelengths of the transmitted and received light, or a spatial phase modulator using birefringence characteristics due to the Kerr effect. In addition, if there is no need to change the amount of beam ahead, a spatial phase modulator using a crystal with birefringence characteristics may be used. In addition, in the first embodiment, an optical amplifier 417 for amplifying the transmitted light and an optical amplifier 421 for amplifying the received light are used, but this is to realize long-distance communication, and these optical amplifiers are not necessarily required because the function of the present invention can be similarly exerted even without them.

Optical communication terminal of second embodiment
Fig. 7 shows an example of the second embodiment of the optical communication terminal of the present invention. In Fig. 7, 701 is a satellite on the other side of the optical communication, 702 is a gimbal mechanism on which the optical system of the optical communication terminal is mounted, 703 is a data signal processing and control processing block that performs mechanical control of the optical communication terminal and processing for transmitting and receiving communication data, 704 is an optical antenna barrel, 705 is a gimbal mechanism that rotates the optical antenna barrel 704 in the tilt direction, 706 is a gimbal mechanism that rotates the optical antenna barrel 704 in a plane, 707 is a collecting mirror that collects communication light, 708 is a convex mirror that reflects the light from the collecting mirror 707 as parallel light, 709 is a two-axis steering mirror that changes the beam angle of the optical communication light, 710 is a 1/4 λ plate, and 711 is an LCOS (Liquid Crystal on Silicon) that modulates the optical phase of the P-polarized component. The reference numeral 715 denotes an optical circulator for separating received light from transmitted light, 716 denotes an optical fiber for received light, 717 denotes an optical amplifier for received light, 718 denotes an optical fiber, 719 denotes an InGaAs photodiode for receiving data, 720 denotes an optical fiber for transmitted light, 721 denotes an optical amplifier for amplifying transmitted light, 722 denotes an optical fiber, and 723 denotes a laser for generating transmitted light. The optical fiber for received light 716 and the optical fiber for transmitted light 720 are connected by an optical circulator 715, and the received light and transmitted light are emitted or input from the same optical fiber connector 714. The second embodiment has a similar configuration to the first embodiment, but is characterized in that the receiving light aperture size, which is the range of receiving light, is larger than the transmitting light aperture size, which is the range of receiving light into the collecting mirror 707. In Fig. 7, the receiving light is shown by a dotted line and the transmitting light is shown by a dashed line, and the range of the transmitting light shown by the dashed line is narrower than the range of the receiving light incident on the collecting mirror 707 shown by the dotted line, and this feature allows the second embodiment to improve the transmission efficiency of the transmitting light compared to the first embodiment. In the second embodiment, the aperture size of the transmitting light is made smaller than the aperture size of the receiving light, so that the design parameters of the optical components and the like that calibrate the optical communication terminal are different from those of the first embodiment, but the functions are the same, so a detailed description of the optical paths of the transmitting light and the receiving light is omitted, and the feature of the second embodiment, which is the improvement of the transmission efficiency of the transmitting light, is described in detail below.

Figure 8 is an enlarged view showing the state of the received light and the transmitted light on the angle detection sensor 713, and shows the state in which the angle of the received light is controlled by the two-axis steering mirror 709 from the data signal processing and control processing block 703 based on the angle information of the received light 801 detected by the angle detection sensor 713, and the received light is controlled to the center of the angle detection sensor 713. In the first and second embodiments, the optical design is such that in this state, about 20% of the outer peripheral part of the received light is incident on the four-part optical sensor light receiving parts 804/805/806/807 of the angle detection sensor 713. In the first embodiment, in which the aperture size of the received light and the transmitted light are designed to be the same, as shown in Figure 5, the outer peripheral part of the transmitted light output from the optical fiber 415 connected to the optical connector 414 cannot pass through the hole, so about 20% is not used as transmitted light, resulting in a decrease in the power efficiency of transmission. The second embodiment is made to solve the problem of the decrease in the power efficiency of the transmitted light in the first embodiment, and can increase the efficiency of the laser emission of the transmitted light to a value close to about 100%. The second embodiment is characterized in that the aperture size of the received light is made larger than the aperture size of the transmitted light. By making the aperture size of the transmitted light smaller than the aperture size of the received light, it becomes possible for most of the transmitted light 802 emitted from the optical fiber 715 to pass through the hole 803 as shown in FIG. 8, and the power efficiency of the transmitted light can be increased to about 95%. In the second embodiment, the aperture size of the transmitted light is set to be 20% smaller than the aperture size of the received light, but if the aperture size of the transmitted light is made smaller than the aperture size of the received light, the power efficiency of the transmitted light is increased and the same effect as in the second embodiment can be obtained. How much of the outer periphery of the received light should be used as an angle control signal and the remainder as light for data communication is a design issue that requires a trade-off between the control precision required for an optical communications terminal and the transmission and reception transfer rates, but in general it is desirable to use about 50% to 10% of the light as a control signal, and in this case it is desirable to set the aperture size of the transmitted light to about 50% to 10% of the aperture size of the received light as well.

<Optical communication terminal of the third embodiment>
An optical communication terminal of the third embodiment capable of further improving the beam-ahead accuracy of the optical communication terminal will be described with reference to FIG. 9. In FIG. 9, 903 is a data signal processing and control processing block that holds a plurality of patterns to be set in the spatial phase modulator 711 and sets the modulation pattern. In the optical communication terminal of the third embodiment, the pattern to be set in the spatial light phase modulator composed of the LCOS 711 is changed, thereby improving the resolution of the beam-ahead angle and further improving the beam-ahead accuracy, compared to the optical communication terminal of the second embodiment. FIG. 9 shows the control part of the LCOS, which is the difference between the second embodiment and the third embodiment. As shown in FIG. 9, the optical communication terminal of the third embodiment generates an angle difference with the received light by setting a phase modulation pattern by the data signal processing and control processing block 903 according to the angle at which the beam-ahead is performed, but generally, the pattern that can be set in a spatial phase modulator such as an LCOS is a digital setting value, so that it is a digital value such as pattern A or pattern B in FIG. 9. In order to further improve the accuracy of the beam-ahead, it is necessary to increase the resolution of the phase value that can be set in the LCOS so that an intermediate state between A and B can be set. However, increasing the resolution of the LCOS leads to problems such as increased costs and complicated interfaces for setting patterns, which have become obstacles to further improving the accuracy of beam ahead. The third embodiment is an invention made to solve this problem, and makes it possible to control the phase of the spatial modulator with an accuracy equal to or lower than the resolution of the spatial modulator. The data signal processing/control processing block 903 of the optical communication terminal of the third embodiment has a function of, for example, phase modulating the patterns A and B for predetermined times T1 and T2, respectively. The pattern of T1+T2 is a time during which it repeatedly changes, and by making this time faster than the modulation response speed of the spatial modulator 711, it is possible to set the phase modulation pattern shown in FIG. 9, which is an intermediate value between the patterns A and B, according to the time ratio of T1 and T2. This is done by setting T1+T2 to a predetermined value but a period faster than the response time of the spatial phase modulator, and by switching between the patterns A and B, the spatial phase modulator 711 becomes an intermediate value determined by the ratio of T1 and T2. By performing such control, the resolution that can be set by the spatial phase modulator 711 can be greatly improved. For example, even if each pixel of the spatial phase modulator has only a 1-bit resolution of ON and OFF, it is possible to perform spatial phase modulation with a set resolution of the ratio of T1 and T2. By introducing such spatial phase modulator control into the data signal processing and control processing block 903, the third embodiment can improve the beam ahead resolution by about 20 times compared to the second embodiment.

Optical communication terminal of the fourth embodiment
Fig. 10 shows an example of the fourth embodiment of the optical communication terminal of the present invention. In Fig. 10, 1001 is a satellite on the other side of the optical communication, 1002 is a gimbal mechanism on which the optical system part of the optical communication terminal is mounted, 1003 is a data signal processing and control processing block that performs mechanical control of the optical communication terminal and processing for transmitting and receiving communication data, 1004 is an optical antenna lens, 1005 is a gimbal mechanism that rotates the optical antenna lens barrel 1004 in the tilt direction, 1006 is a gimbal mechanism that rotates the optical antenna lens barrel 704 in a plane, 1007 is a focusing lens that focuses the communication light, 1008 is a three-axis steering lens that changes the beam angle of the optical communication light, 1009 is a mirror that reflects the communication light, 1010 is a 1/4 λ plate, 1011 is a spatial light phase modulator made of LCOS (Liquid Crystal on Silicon) that modulates the optical phase of the P-polarized light component, and 1012 is a spatial light phase modulator made of LCOS (Liquid Crystal on Silicon) that modulates the optical phase of the S-polarized light component. The spatial light phase modulator is made of a silicon (Si), 1013 is a condenser lens, 1014 is a front light angle detection sensor made of a four-part InGaAs photodiode, 1015 is a rear light angle detection sensor made of a four-part InGaAs photodiode, 1016 is an optical fiber connector, 1017 is an optical circulator that separates the received light from the transmitted light, 1018 is an optical fiber for the received light, 1019 is an optical amplifier for the received light, 1020 is an optical fiber, 1021 is an InGaAs photodiode for data reception, 1022 is an optical fiber for the transmitted light, 1023 is an optical amplifier for amplifying the transmitted light, 1024 is an optical fiber, and 1025 is a laser that generates the transmitted light. The optical fiber for the received light 1018 and the optical fiber for the transmitted light 1022 are connected by the optical circulator 1017, and the received light and the transmitted light are emitted or input from the same optical fiber connector 1016. The fourth embodiment has a similar configuration to the second embodiment, but uses a condenser lens 1007 to condense the received light and the transmitted light, and instead of the two-axis steering mirror used in the first embodiment, the steering lens 1008 has a moving axis in two axial directions in a plane perpendicular to the transmitted and received light beams and one axis parallel to the transmitted and received light beams, changing the angle of the transmitted light or the received light. In the first, second and third embodiments, it is necessary to couple the received light to the optical fiber of the optical circulator (415/715) with high efficiency, and the coupling is performed by condensing the light to 10 μm or less using the condenser lens (412/712). However, since the condensed state changes due to vibrations and temperature changes in the satellite, in order to maintain a high coupling state, it is necessary to fix the condenser lens (412/712) and the optical fiber connector (414/714) to a base with high rigidity and little temperature change, which has caused problems in reducing the cost and improving the reliability of the optical communication terminal. The optical communication terminal of the fourth embodiment has been made to solve this problem, and is characterized in that the focusing state of the received light focused on the optical fiber 1017 is controlled by using a three-axis steering lens 1008 that operates in the focus direction. As a result, stable optical communication is maintained by performing feedback control even when the state of the focused beam coupled to the optical fiber 1017 of the optical circulator changes due to vibrations in the satellite, aging fluctuations of the optical system, temperature fluctuations, etc. In order to realize this feedback control, it is necessary to detect the focus position, which is the focusing state of the focusing lens 1013. The method of detecting this focus position will be described below with reference to FIG. 11. FIG. 11-1 is an example of an optical configuration for detecting the focus position, and 1101 and 1102 are first-order diffracted lights of the received light reflected from the spatial light phase modulator 1102. The spatial light phase modulator 1012 is composed of an LCOS element that performs spatial phase modulation only on the S-polarized component, and only the received light incident with S-polarized light undergoes spatial phase modulation. A spatial phase modulation pattern of a grating 1120 as shown in FIG. 11-2 is transferred to the spatial phase modulator 1012 from the data signal processing/control processing block 1003, and the received light, which is S-polarized light, is split by this grating pattern 1120 into a straight-traveling zeroth-order light 1103 and diffracted first-order light 1101 and 1102, and the zeroth-order light is coupled to an optical circulator 1017 via an optical fiber connector 1106. The first-order light diffracted by the spatial phase modulator 1012 is detected by a front light angle detection sensor 1014 and a rear light angle detection sensor 1105, which are provided to detect the focus position and the angle of the received light. The transmitted light is also incident on the spatial phase modulator 1012, but the transmitted light, which is P-polarized light, is reflected by 1102 without undergoing phase modulation and is not diffracted, and almost 100% of the light is used as the transmitted light. In the fourth embodiment, in order to set the ratio of the first-order diffracted light used for control to the zeroth-order light used for demodulating the received data to 0.2:0.8, the interval of the grating pattern 1120 shown in Fig. 11-2 is set to 2.54 μm, and the phase difference of the grating part modulated by the spatial phase modulator is set to 1/12 λ (λ: optical wavelength of the received light used in optical communication). In a state where the zeroth-order light is focused and coupled to the optical fiber of the optical circulator 1017, the front light angle detection sensor 1014 is disposed in front of the focal position of the first-order light, and the back light angle detection sensor 1105 is disposed behind the focal position of the first-order light, and in this state, the positional relationship is set such that the beam spot sizes on the front light angle detection sensor 1014 and the back light angle detection sensor 1105 are equal. When the focal position of the zeroth order light is shifted forward, the beam spot on the front light angle detection sensor 1014 becomes larger and the beam size on the back light angle detection sensor 1105 becomes smaller, so that if the difference in the light beam size on the sensors 1014 and 1015 is detected, a focus position signal reflecting the focal position of the zeroth order light is detected. Since it is necessary to simultaneously detect the angle of the received light from the sensors 1014 and 1015, the sensors 1014 and 1015 are divided as shown in Fig. 11-3 to simultaneously detect the light beam size and position on the sensors. In Fig. 11-3, 1101 denotes the back focal light spot of the first order light diffracted by the spatial phase modulator, 1102 denotes the front focal light spot of the first order light diffracted by the spatial phase modulator, 1103 denotes the zeroth order light coupled to the optical fiber of the optical circulator 1107 connected to the optical fiber connector 1016, and 1104 to 1110 denote photodetectors formed on the angle detection sensors 1014 and 1015.

Below, we will explain the means for calculating the signals obtained from sensors 1014 and 1015 to calculate the focus position detection signal and the received light angle detection signal. If the output from each sensor is SXXXX when the symbol number shown in Figure 11-3 is XXXX, the focus position detection signal FE and the received light angle detection signals PX, PY can be obtained by performing the following calculations.

FE = {(S1104+S1107+S1108+S1111) - (S1112+S1115+S1116+S1119) - (S1105+S1106+S1109+S1110) - (S1113+S1114+S1117+S1118)} / (S1104+S1105+S1106+S1107+S1108+S1109+S1110+S1111)

PX = {(S1104+S1105+S1111+S1110) - (S1106+S1107+S1108+S1109) + (S1112+S1113+S1119+S1118) - (S1114+S1115+S1116+S1117)} / (S1104+S1105+S1106+S1107+S1108+S1109+S1110+S1111)

PY = {(S1104+S1105+S1106+S1107) - (S1108+S1109+S1110+S1111) + (S1112+S1113+S1114+S1115) - (S1116+S1117+S1118+S1119)} / (S1104+S1105+S1106+S1107+S1108+S1109+S1110+S1111)

By using the angle detection signals PX and PY of the received light, the data signal processing/control processing block 1003 controls the steering lens 1008 in two axes, X and Y, in a plane perpendicular to the optical axis, so that the received light can be controlled to the center of the optical fiber of the optical circulator 1017. After that, the data signal processing/control processing block 1003 controls the steering lens 1008 in a direction parallel to the optical axis so that the focus position detection signal FE becomes zero or a desired value, so that the focal position of the condenser lens 1103 is stabilized and the received zero-order diffracted light reflected by the spatial phase modulator 1012 can be stably coupled to the optical circulator 1017. The focus position detection signal FE is preferably detected when the light beam is positioned approximately in the center of the angle detection sensors 1014 and 1015, so that the correct beam size can be detected. Therefore, it is desirable to perform focus position control after angle control of the received light. The optical communication terminal of the fourth embodiment controls the condensed state of the received light coupled to the optical circulator 1017, thereby enabling a more stable optical communication link than in the past, and the error rate of communication data can be improved by one to two orders of magnitude compared to the optical communication terminals of the first and second embodiments. In the fourth embodiment, a detection method using the spot size difference before and after the focal position is used as one means for detecting the focus position, but this detection method is not necessarily limited to this detection method, and it is also possible to use focus position detection by the astigmatism method by adding astigmatism characteristics to the condenser lens 1014 as a method for detecting the focus position. In addition, it is also possible to change the diffraction direction of the light beam by changing the pattern of the spatial phase modulator that modulates the phase of the received light, thereby obtaining a detection signal for focus. In the fourth embodiment, a spatial phase modulator is used simultaneously to beam ahead the transmission light of 1011, but if the relative speed between the optical communication terminals is slow, a spatial phase modulator that phase modulates the transmission light to beam ahead the transmission light of 1011 is not necessary, and the effect obtained in the fourth embodiment can be obtained only with the spatial modulator 1012 for the received light. The fourth embodiment is characterized by using a spatial phase modulator 1012 that modulates only the received light, which produces a great effect not seen in the past, that is, the received light can be divided to obtain the necessary control signal without affecting the transmitted light at all. This makes it possible to realize an optical communication terminal configured with transmitted light emitted from the same spatial point and received light incident on the same point, making it possible to realize very stable and reliable optical communication.

Optical communication terminal of the fifth embodiment
FIG. 10 shows an example of the fifth embodiment of the optical communication terminal of the present invention. The fifth embodiment is made to improve communication latency by performing acquisition at high speed when starting communication between optical communication terminals and shortening the time before starting communication. When starting optical communication between satellites, communication is started by emitting an optical beam in the direction of the other party based on each other's orbit position information and tracking the other party's optical beam. However, since there is an error in each other's orbit information, even if an optical beam is emitted in the direction determined from the orbit information, the optical beam does not reach the other party's satellite and communication cannot start. A communication start sequence for starting communication with the other party's satellite at the beginning is determined and is outlined in FIG. 13. In FIG. 13, 1301 is the other party's satellite with which communication is performed, 1302 is the own satellite with which communication is performed, 1303 is the optical communication light of the own satellite, and 1304 is the optical communication light of the other party's satellite. The sequence up to starting communication shown in FIG. 13 is scheduled in advance, and the scheduled time is used as a trigger to execute the following five steps to link the optical communication channel between the satellites, that is, to start tracking between the satellites. In the first step, the satellite 1302 performs a spiral scan with a light beam centered on the position of the satellite 1301 calculated from the orbit information, and the satellite 1301 attempts to detect communication light from the satellite 1302. When the communication light 1303 of the satellite 1302, which is scanning in a spiral shape, is irradiated to the satellite 1301, the satellite 1301 detects the direction of the satellite 1302 based on the detection value of the internal receiving light angle detection sensor, and performs an operation to point the satellite in that direction. This is acquisition phase 1. Next, the satellite 1301 performs a spiral scan with communication light centered on the direction of the satellite 1302 detected in the previous step, and the satellite 1302 attempts to detect the direction of the satellite 1301. When the communication light of the satellite 1301 is irradiated to the satellite 1302, the satellite 1302 detects the direction of the satellite 1301 based on the detection value of the internal receiving light angle detection sensor, and performs an operation to point the satellite in that direction. This is acquisition phase 2. In the next fine acquisition phase, the satellites 1301 and 1302 perform a spiral scan again to more accurately determine the directions of both satellites from the values of the internal receiving light angle detection sensors and correct each other's directions, and then move to the tracking phase in which the tracking control of both satellites is performed using the transmitted light of both satellites as a guide. The above-mentioned first to fourth embodiments have described the operation after the tracking phase and the start of communication. The optical communication terminal of the fifth embodiment has a similar configuration to the fourth terminal, but can exhibit unprecedentedly excellent characteristics even in the communication start sequence by using a spatial phase modulator that performs spatial phase modulation only on P-polarized or S-polarized light. The specific operation in this communication start sequence will be described with reference to Figures 12 and 14.

The fifth embodiment of the present invention shown in FIG. 12 is configured by replacing the already described fourth embodiment with a data signal processing/control processing block 1201 that performs mechanical control of the optical communication terminal and processing for transmitting and receiving communication data, a two-axis steering lens 1202 that changes the beam angle of the optical communication light, and a focus adjustment lens 1203 that has a mechanism for moving the condenser lens in the optical axis direction to adjust the focus position. The other components are the same as those in the fourth embodiment, so the same reference numerals are used. The components that are the same as those in the fourth embodiment have already been described, so their description is omitted and the modified components 1201, 1202, and 1203 will be described below. In acquisition phases 1 and 2, the optical communication terminal only detects the angle of the communication light of the other party, and communication light required for demodulating data is not required in this phase. In conventional optical communication terminals, the optical path of the received light and the ratio of the control signal light and the communication signal light were determined by the characteristics of predetermined optical elements such as beam splitters and could not be changed. In particular, in the acquisition phase, the communication light of the other satellite is a Gaussian beam, and angle detection must be performed from the communication light that is reduced to 1/2 to 1/3 at the periphery of the beam, and there is a trade between the angle detection accuracy and the scan speed of acquisition phases 1 and 2, which causes a problem that the performance cannot shorten the link time. Since the optical communication terminal of the present invention can add spatial phase modulation only to the reception light that is S-polarized and enters the spatial phase modulator 1012, it has an excellent characteristic that can change the light intensity ratio of the angle detection signal by the 1st order diffracted light and the data reception light by the 0th order light, and by this characteristic, in the acquisition phases 1 and 2 and the fine acquisition phase, a pattern in which the intensity of the 1st order diffracted light is almost 100% is set in the spatial phase modulator 1012, and in the tracking phase, the pattern is changed to that of the fourth embodiment, which can greatly improve the pull-in performance of the acquisition phases 1 and 2 and the fine acquisition phase compared to the conventional one. A specific setting example of the spatial phase modulator 1012 is shown in FIG. 14-1. 1401 is a grating pattern during the acquisition phase and fine acquisition phase, and by setting the spacing of the grating pattern 1401 to 2.54 μm and the phase difference of the grating portion 1401 modulated by the spatial phase modulator to λ (λ: optical wavelength of the received light used in optical communication), the intensity ratio of the 0th order diffracted light, which is the received data light, to the 1st order diffracted light, which is the control signal light, can be made approximately 100:0. In the tracking phase, by setting the phase difference of the grating portion 1402, which is the same as in the fourth embodiment, to 1/12λ, the intensity ratio of the 0th order diffracted light to the 1st order diffracted light, which is the control signal light, can be dynamically changed to approximately 0.8:0.2 depending on the operating state, enabling optimal signal distribution for each operating mode.

The fifth embodiment of the present invention can also provide a function that dynamically changes the angle detection sensitivity of 1014 and 1015 in the acquisition phase and tracking phase by changing the spatial modulation pattern of the phase modulator 1012. In the conventional optical communication terminal, as shown in FIG. 2, sensors with two types of sensitivity, a rough angle detector 221 and a fine angle detector 223, are used, and since it is necessary to split the control signal at a ratio determined by the characteristics of the optical components by the beam splitter 219, the signal amount of the control signal decreases, making it difficult to improve the control performance, and preventing an improvement in the data communication speed. The fifth embodiment of the present invention can also dynamically change the detection sensitivity of the receiving light angle detector in the acquisition phases 1 and 2, the fine acquisition phase, and the tracking phase. In the acquisition phases 1 and 2 and the fine acquisition phase, it is required to detect the angle of the receiving light over a wide range, and if the detection range can be widened, the spiral scan pitch can be set wide, so the acquisition time can be shortened. In the tracking phase, it is necessary to improve the detection accuracy of the control signal, so the detection angle range is narrow, but it is necessary to improve the detection sensitivity. Generally, the angular detection sensitivity of the received light requires a detection range of about ±0.2 degrees in acquisition phases 1 and 2 and the fine acquisition phase, and is designed to have a detection range of about ±0.006 degrees in the tracking phase. It would be ideal if detection sensitivities that differ by about 30 times could be achieved with the same optical system, but conventionally, control was performed by splitting the received light and using a detection system with two types of detection sensitivity.

In the fifth embodiment of the present invention, the spatial modulation pattern of the spatial phase modulator 1012 is changed to dynamically change the angle detection sensitivity of 1014 and 1015 in the acquisition phase and tracking phase. A specific implementation method will be described below with reference to FIG. 14-2. FIG. 14-2 is a diagram showing a relationship between the modulation pattern of the spatial phase modulator of the present invention and the angle detection sensitivity of the received light. 1403 is the optical axis center when the received light is not tilted, 1404 is the optical axis center when the optical axis of the received light is tilted to the positive side, 1405 is the optical axis center when the optical axis of the received light is tilted to the negative side, 1406 is a schematic diagram of the spatial modulation pattern of the present invention, 1407 is the light spot on the angle detection sensor 1015 when the optical axis of the received light is not tilted, 1408 is the light spot on the angle detection sensor 1015 when the optical axis of the received light is tilted to the positive side, and 1409 is the light spot on the angle detection sensor 1015 when the optical axis of the received light is tilted to the positive side. 1406 is set so that the phase periodic pattern becomes denser the further away from the center, and by performing such phase modulation, the optical axis can be changed toward the center as it passes through the outer periphery of 1406. When the optical axis of the received light is tilted, the spot of the received light moves to a position shifted from the center of the spatial phase modulator 1012. However, by adding a phase pattern such as 1406 in FIG. 14-2, which tilts the traveling direction of the light toward the center according to the amount of this shift, to the spatial phase modulator 1012, the beam spot on the angle detection sensor is moved closer to the center when the tilt angle of the received light increases, so that the light spot does not deviate from the detector of the angle detection sensor, and the angle detection range can be expanded. In this way, by changing the spatial modulation pattern of the phase modulator 1012, it is possible to dynamically change the angle detection sensitivity of 1014 and 1015 in the acquisition phase and tracking phase. Compared to the conventional method, it is no longer necessary to divide the received light and detect it with multiple sensors with different tilt angle detection sensitivities, making it possible to increase the amount of received light, and to realize an optical communication terminal with a higher transfer rate and higher stability.

The present invention is not limited to the above-described embodiment, and various modifications and applications are possible without departing from the spirit of the invention.

For example, although the present specification has described an embodiment in which the program is pre-installed in the storage unit 73 of the computer 70, the program can also be provided by storing it in a computer-readable recording medium. For example, the program may be provided in a form stored in a non-transitory storage medium such as a CD-ROM (Compact Disk Read Only Memory), a DVD-ROM (Digital Versatile Disk Read Only Memory), or a USB (Universal Serial Bus) memory. The program may also be provided in a form in which it is downloaded from an external device via a network.

In the above embodiment, the processing executed by the CPU after reading the software (program) may be executed by various processors other than the CPU. In this case, examples of the processor include a PLD (Programmable Logic Device) such as an FPGA (Field-Programmable Gate Array) whose circuit configuration can be changed after manufacture, and an ASIC (Application Specific Integrated Circuit) which is a dedicated electric circuit that is a processor having a circuit configuration designed specifically to execute a specific process. Alternatively, a GPGPU (General-purpose graphics processing unit) may be used as the processor. Each process may be executed by one of these various processors, or by a combination of two or more processors of the same or different types (for example, multiple FPGAs, or a combination of a CPU and an FPGA). The hardware structure of these various processors is, more specifically, an electric circuit that combines circuit elements such as semiconductor elements.

In addition, each process of this embodiment may be implemented by a computer or server equipped with a general-purpose processor and storage device, and each process may be executed by a program. This program is stored in a storage device, and can be recorded on a recording medium such as a magnetic disk, optical disk, or semiconductor memory, or can be provided via a network. Of course, any other components do not have to be implemented by a single computer or server, and may be distributed across multiple computers connected by a network.

All publications, patent applications, and technical standards mentioned in this specification are incorporated by reference into this specification to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Please note that in the above embodiment, unless there is a statement such as "based only on XX", "depending only on XX", or "in the case of XX only", it is assumed in this specification that additional information may be taken into consideration. As an example, the statement "do b if a" does not necessarily mean "always do b if a" unless expressly stated.

Furthermore, even if there is an aspect of a method, program, terminal, device, server, or system (hereinafter, "method, etc.") that performs an operation different from that described in this specification, each aspect of the disclosed technology is directed to an operation identical to any of the operations described in this specification, and the existence of an operation different from that described in this specification does not make the method, etc. outside the scope of each aspect of the disclosed technology.

The following additional information is provided below.

(Appendix 1)
An optical communication device having a transmit/receive antenna that receives received light from a communication partner and sends transmitted light for data to the communication partner in order to communicate data in free space using circularly polarized light, a guide mechanism for tracking the communication partner's satellite using the received light, an angle detector that detects the angle of the received light, and a tracking controller that controls the guide mechanism using the output of the angle detector to track the communication partner, characterized in that the optical communication device further comprises a spatial light phase modulator through which both the transmitted light and the received light pass and which performs spatial phase modulation on the transmitted light.

(Appendix 2)
2. The optical communication device according to claim 1, further comprising an optical path in which the received light and the transmitted light are emitted from or incident on approximately the same spatial point.

(Appendix 3)
2. The optical communication device according to claim 1, wherein the spatial light phase modulator is a spatial light phase modulator in which an amount of phase modulation varies depending on a polarization direction of incident light.

(Appendix 4)
4. The optical communication device according to claim 3, wherein the spatial light phase modulator is implemented using LCOS.

(Appendix 5)
2. The optical communication device according to claim 1, further comprising a spatial phase modulator having a phase modulation amount that varies depending on the wavelength of incident light.

(Appendix 6)
2. The optical communication device according to claim 1, further comprising a control processing block that holds or generates a pattern for performing spatial optical phase modulation on the transmitted light and sets the spatial phase modulation pattern in the spatial phase modulator.

(Appendix 7)
2. The optical communication device according to claim 1, wherein an aperture for the transmitting/receiving antenna for the transmitting light is smaller than that for the receiving light.

(Appendix 8)
In the optical communication device described in Appendix 1, the tracking controller controls a coarse adjustment mechanism having a wide angular range for changing the direction of light and a fine adjustment mechanism having a narrow range for changing the direction of light, and the fine adjustment mechanism is composed of an optical element that operates in a two-axis or three-axis direction.

(Appendix 9)
9. The optical communication terminal according to claim 8, wherein the optical element of the precision adjustment mechanism is a focusing lens.

(Appendix 10)
3. The optical communication device according to claim 2, wherein the input of the transmitting light and the receiving light is configured as an optical fiber input, and the input receiving light and the transmitting light are combined by an optical circulator to form the substantially same spatial point.

(Appendix 11)
3. The optical communication device according to claim 2, wherein the optical communication device is coupled to the substantially same spatial point by an optical fiber.

(Appendix 12)
7. The optical communication device according to claim 6, wherein the control processing block holds two or more patterns for performing spatial light phase modulation, and switches between the two or more patterns at a speed faster than a response speed of the spatial light modulator.

(Appendix 13)
8. The optical communication device according to claim 7, further comprising an angle detector for detecting an angle of the received light from peripheral light of the received light.

(Appendix 14)
An optical communication device having a transmit/receive antenna that receives received light from a communication partner and sends transmitted light for data to the communication partner in order to communicate data in free space using circularly polarized light, a guide mechanism for tracking the communication partner's satellite using the received light, an angle detector that detects the angle of the received light, and a tracking controller that controls the guide mechanism using the output of the angle detector to track the communication partner, characterized in that the optical communication device further comprises a spatial light phase modulator through which both the transmitted light and the received light pass and which performs spatial phase modulation on the received light.

(Appendix 15)
15. The optical communication device according to claim 14, further comprising an optical path in which the received light and the transmitted light are emitted from or incident on approximately the same spatial point.

(Appendix 16)
15. The optical communication device according to claim 14, wherein the spatial light phase modulator is a spatial light phase modulator in which an amount of phase modulation varies depending on a difference in a polarization direction of incident light.

(Appendix 17)
17. The optical communication device according to claim 16, wherein the spatial light phase modulator is implemented using LCOS.

(Appendix 18)
15. The optical communication device according to claim 14, further comprising a spatial phase modulator having a phase modulation amount that varies depending on the wavelength of incident light.

(Appendix 19)
15. The optical communication device according to claim 14, further comprising a control processing block that holds or generates a pattern for performing spatial light phase modulation on the received light and sets the spatial phase modulation pattern in the spatial phase modulator.

(Appendix 20)
15. The optical communication device according to claim 14, wherein an aperture for the transmitting/receiving antenna for the transmitting light is smaller than that for the receiving light.

(Appendix 21)
In the optical communication device described in Appendix 14, the tracking controller controls a coarse adjustment mechanism having a wide angular range for changing the direction of light and a fine adjustment mechanism having a narrow range for changing the direction of light, and the fine adjustment mechanism is configured with an optical element that operates in a two-axis or three-axis direction.

(Appendix 22)
22. The optical communication terminal according to claim 21, wherein the optical element of the precision adjustment mechanism is a focusing lens.

(Appendix 23)
16. The optical communication device according to claim 15, wherein the input of the transmitting light and the receiving light is configured as an optical fiber input, and the input receiving light and the transmitting light are combined by an optical circulator to form the substantially same spatial point.

(Appendix 24)
16. The optical communication device according to claim 15, wherein the optical communication device is coupled to the substantially same spatial point by an optical fiber.

(Appendix 25)
20. The optical communication device according to claim 19, wherein the control processing block holds two or more patterns for performing spatial light phase modulation, and switches between the two or more patterns at a speed faster than a response speed of the spatial light modulator.

(Appendix 26)
21. The optical communication device according to claim 20, further comprising an angle detector for detecting an angle of the received light from peripheral light of the received light.

(Appendix 27)
20. The optical communication device according to claim 19, wherein the control processing block receives a state of the optical communication device as an input and switches between a plurality of patterns in response to the input.

(Appendix 28)
28. The optical communication device according to claim 27, further comprising a control block for setting a pattern in which the amount of light for control is greater than the amount of light for communication in an acquisition phase, and for setting a pattern in which the amount of light for control is smaller than the amount of light for communication in a tracking phase.

(Appendix 29)
28. The optical communication device according to claim 27, further comprising a control block that sets a spatial modulation pattern in which, when the state of the optical communication device is in an acquisition phase, light irradiated to a center of the spatial phase modulator is not spatially phase modulated, and light irradiated other than the center has an optical axis tilted toward the center.

101 Satellite 1
102: Receiving optical antenna mounted on satellite 1; 103: Transmitting optical antenna mounted on satellite 1; 104: Transmitted light from satellite 1; 105: Satellite 2
106: Satellite 2's transmitting optical antenna 107: Satellite 2's receiving optical antenna 108: Transmitted light from satellite 1 201: Partner satellite with which optical communication is performed 202: Gimbal mechanism 203: Data signal processing/control processing block 204: Optical antenna lens barrel 205: Tilt direction rotation gimbal mechanism 206: In-plane rotation gimbal mechanism 207: Collecting mirror 208: Convex mirror 209: Two-axis steering mirror 210: 1/4 λ plate 211: Polarizing beam splitter 212: Beam splitter 213: Collecting lens 214: Fiber connector for fixing optical fiber 215: Optical fiber 216: Optical amplifier 217: Optical fiber 218: InGaAs photodiode 219: Beam splitter 220: Lens 221: Coarse angle detection sensor 222: Collecting lens 223: Fine angle detection sensor 224: Transmitting laser 225: Optical fiber 226: Transmitting optical amplifier 227: Optical fiber 228 Optical fiber connector 229 Condenser lens 230 Two-axis point-ahead mirror 231 Calibration laser 232 Optical fiber 233 1/4 wavelength plate 234 Retroreflector 301 Transmitting light optical phase modulator 302 Received light optical phase modulator 401 Partner satellite 402 for optical communication Gimbal mechanism 403 Data signal processing/control processing block 404 Optical antenna barrel 405 Tilt direction gimbal mechanism 406 Rotation gimbal mechanism 407 Condenser mirror 408 Convex mirror 409 Two-axis steering mirror 410 1/4 λ plate 411 Spatial light phase modulator 412 Condenser lens 413 Angle detection sensor 414 Optical fiber connector 415 Optical circulator 416 Optical fiber for received light 417 Optical amplifier for received light 418 Optical fiber 419 InGaAs photodiode 420 Optical fiber 421 Optical amplifier 422 Optical fiber 423 Transmitting light laser 501 Received light 502 with no angular deviation Received light 503 with angular deviation Holes 504, 505, 506, 507 through which the received light passes Four-part sensor 701 Partner satellite 702 for optical communication Gimbal mechanism 703 Data signal processing/control processing block 704 Optical antenna lens barrel 705 Tilt direction gimbal mechanism 706 In-plane rotation gimbal mechanism 707 Condenser mirror 708 for concentrating communication light Convex mirror 709 Two-axis steering mirror 710 1/4 λ plate 711 Spatial light phase modulator 712 Condenser lens 713 Angle detection sensor 714 Optical fiber connector 715 Optical circulator 716 Optical fiber 717 Optical amplifier 718 Optical fiber 719 InGaAs photodiode 720 Optical fiber 721 Optical amplifier 722 Optical fiber 723 Transmitting light laser 801 Received light 802 Transmitted light 803 Holes 804, 805, 806, 807 Optical sensor light receiving unit 903 Data signal processing/control processing block 1001 Partner satellite 1002 for optical communication Gimbal mechanism 1003 Data signal processing/control processing block 1004 Optical antenna lens barrel 1005 Tilt direction rotation gimbal mechanism 1006 In-plane rotation gimbal mechanism 1007 Condenser lens 1008 3-axis steering lens 1009 Reflecting mirror 1010 1/4 λ plate 1011 Spatial light phase modulator 1012 Spatial light phase modulator 1013 Condenser lens 1014 Front light angle detection sensor 1015 Rear light angle detection sensor 1016 Optical fiber connector 1017 Optical circulator 1018 for separating received light and transmitted light Optical fiber 1019 Optical amplifier 1020 Optical fiber 1021 InGaAs photodiode 1022 Optical fiber 1023 Optical amplifier 1024 Optical fiber 1025 Transmitted light laser 1101 1st order diffracted light 1102 1st order diffracted light 1103 0th order diffracted light 1104 to 1119 Photodetector sensor section 1120 Grating 1201 Data signal processing/control processing block 1202 Two-axis steering lens 1203 Focus adjustment lens 1301 Partner satellite with which to communicate 1302 Self-satellite with which to communicate 1303 Optical communication light from self-satellite 1304 Optical communication light from partner satellite 1401 Grating on spatial phase modulator 1402 Grating on spatial phase modulator 1403 Optical axis center when received light is not tilted 1404 Optical axis center when the optical axis of received light is tilted to the positive side 1405 Optical axis center when the optical axis of received light is tilted to the negative side 1406 Schematic diagram of spatial modulation pattern 1407 Light spot 1408 when the optical axis of the received light is not tilted Light spot 1409 when the optical axis of the received light is tilted to the plus side Light spot 1409 when the optical axis of the received light is tilted to the plus side

Claims (29)

In an optical communication device having a transmitting/receiving antenna that receives incoming light from a communication partner and transmits outgoing light for data communication to the communication partner in free space using circularly polarized light, a guide mechanism for tracking the partner's satellite using the received light, an angle detector that detects the angle of the received light, and a tracking controller that uses the output of the angle detector to control the guide mechanism and track the communication partner, the optical communication device is characterized by having a spatial light phase modulator through which both the transmitted light and the received light pass and which generally performs spatial phase modulation on the transmitted light. The optical communication device according to claim 1, characterized in that it is provided with an optical path in which the received light and the transmitted light are emitted from or incident on approximately the same spatial point. The optical communication device according to claim 1, characterized in that the spatial light phase modulator has a different phase modulation amount depending on the polarization direction of the light incident on the spatial light phase modulator. The optical communication device according to claim 3, characterized in that the spatial light phase modulator is implemented using LCOS. The optical communication device according to claim 1, characterized in that the spatial phase modulator has a different amount of phase modulation depending on the wavelength of the incident light. The optical communication device according to claim 1, further comprising a control processing block that holds or generates a pattern for performing spatial optical phase modulation on the transmitted light and sets the spatial phase modulation pattern in the spatial phase modulator. The optical communication device according to claim 1, characterized in that the aperture of the transmitting and receiving antennas for the transmitting light and the receiving light is smaller for the transmitting light. In the optical communication device described in claim 1, the tracking controller controls a coarse adjustment mechanism that changes the direction of light over a wide angular range and a fine adjustment mechanism that changes the direction of light over a narrow range, and the fine adjustment mechanism is configured with an optical element that operates in the direction of two or three axes. An optical communication terminal characterized by the above. The optical communication terminal according to claim 8, wherein the optical element of the precision adjustment mechanism is a focusing lens. The optical communication device according to claim 2, characterized in that the input of the transmitted light and the received light is configured as an optical fiber input, and the input received light and the transmitted light are combined by an optical circulator to form the spatially almost identical point. The optical communication device according to claim 2, wherein the optical communication device is coupled to the substantially same spatial point by an optical fiber. The optical communication device according to claim 6, characterized in that the control processing block holds two or more patterns for performing spatial light phase modulation, and switches between the two or more patterns at a speed faster than the response speed of the spatial phase modulator. The optical communication device according to claim 7, further comprising an angle detector that detects the angle of the received light from the peripheral light of the received light. In order to perform data communication in free space using circularly polarized light, an optical communication device having a transmitting/receiving antenna that receives incoming light from a communication partner and sends out outgoing light for data to the communication partner, a guide mechanism for tracking the partner's satellite using the received light, an angle detector that detects the angle of the received light, and a tracking controller that uses the output of the angle detector to control the guide mechanism and track the communication partner, is characterized in that the optical communication device is equipped with a spatial light phase modulator through which both the transmitted light and the received light pass and which performs spatial phase modulation on the received light. The optical communication device according to claim 14, characterized in that it is provided with an optical path in which the received light and the transmitted light are emitted from or incident on approximately the same spatial point. The optical communication device according to claim 14, characterized in that the spatial light phase modulator is a spatial light phase modulator in which the amount of phase modulation differs depending on the polarization direction of the light incident thereon. The optical communication device according to claim 16, characterized in that the spatial light phase modulator is implemented using LCOS. The optical communication device according to claim 14, characterized in that the spatial phase modulator has a different amount of phase modulation depending on the wavelength of the incident light. The optical communication device according to claim 14, further comprising a control processing block that holds or generates a pattern for performing spatial optical phase modulation on the received light and sets the spatial phase modulation pattern in the spatial phase modulator. The optical communication device according to claim 14, characterized in that the aperture of the transmitting and receiving antennas for the transmitting light and the receiving light is smaller for the transmitting light. In the optical communication device described in claim 14, the tracking controller controls a coarse adjustment mechanism that changes the direction of light over a wide angular range and a fine adjustment mechanism that changes the direction of light over a narrow range, and the fine adjustment mechanism is configured with an optical element that operates in two or three axial directions. An optical communication terminal characterized by the above. The optical communication terminal according to claim 21, wherein the optical element of the precision adjustment mechanism is a focusing lens. The optical communication device according to claim 15, characterized in that the input of the transmitted light and the received light is configured as an optical fiber input, and the input received light and the transmitted light are combined by an optical circulator to form the spatially almost identical point. The optical communication device according to claim 15, wherein the optical communication device is coupled to the substantially same spatial point by an optical fiber. The optical communication device according to claim 19, characterized in that the control processing block holds two or more patterns for performing spatial light phase modulation, and switches between the two or more patterns at a speed faster than the response speed of the spatial phase modulator. The optical communication device according to claim 20, further comprising an angle detector that detects the angle of the received light from the peripheral light of the received light. The optical communication device according to claim 19, wherein the control processing block receives the state of the optical communication device as an input and switches between a plurality of patterns in response to the input. The optical communication device according to claim 27, characterized in that it is provided with a control block that sets a pattern in which the amount of light for control is greater than the amount of light for communication during the acquisition phase, and sets a pattern in which the amount of light for control is smaller than the amount of light for communication during the tracking phase. The optical communication device according to claim 27, characterized in that the optical communication device is provided with a control block that sets a spatial modulation pattern in which, when the state of the optical communication device is in the acquisition phase, the light irradiated to the center of the spatial phase modulator is not spatially phase modulated, and the light irradiated to areas other than the center has its optical axis tilted toward the center.