Spatial optical communication transceiver

Abstract

This spatial optical communication transceiver comprises: a light source (1101) that generates laser light; an optical modulator (1102) that superimposes a communication signal on the laser light generated by the light source (1101); an OHPA (1103) that amplifies the laser light after superimposition by the optical modulator (1102); a collimator (1105) that includes a fiber connector (11051) and a collimator lens (11052), converts the laser light after amplification by the OHPA (1103) into spatial light, and emits transmission light, which is the spatial light; an optical telescope (1108) that expands the beam width of the transmission light emitted by the collimator (1105) and emits the same onto a spatial transmission path; a drive mechanism (1112) capable of adjusting the focal length of the collimator lens (11052); and a drive controller (1113) that determines a drive amount of the drive mechanism (1112) such that the product of a free space loss calculated from the distance between the host device and a communication partner spatial optical communication transceiver (11) and a transmission gain determined by a beam divergence angle of the transmission light is constant.

Description

Free-space optical communication transceiver

[0001] The present disclosure relates to a free-space optical communications transceiver that is mounted on a mobile body and transmits data.

[0002] Free-space optical communication uses a very high carrier frequency of terahertz or higher, ensuring a wide bandwidth. Furthermore, free-space optical communication has high spatial directionality. These advantages make free-space optical communication promising for use in long-distance, high-speed communications.

[0003] On the other hand, in a free-space optical communications transceiver mounted on a mobile object, when maintaining a communication path over a wide range of distance fluctuations from short to long, loss fluctuations that exceed the dynamic range of the photoelectric converter in the optical demodulator or the photoreceiver such as the acquisition and tracking sensor may occur. Note that the dynamic range here refers to the ratio between the minimum received light intensity and the saturation intensity.

[0004] The free space loss in the free space transmission path of optical free space communications varies as the square of the propagation distance. Therefore, for example, if the distance of the free space transmission path varies by 20 dB from 100 km to 10,000 km, a dynamic range of 40 dB or more is required.

[0005] In contrast, for example, in the device disclosed in Patent Document 1, the amount of light incident on the light receiving element is corrected by adjusting the spatial light attenuator on the receiving side, and the light receiving sensitivity of the light receiving element is corrected, and the gain of the amplifier circuit after receiving the light is changed. In this way, this device can correct changes in the amount of incident light over a wide range.

[0006] However, this device increases the number of components on the receiver side, making it more complex. Furthermore, the adjustable range of the light intensity in this device depends on the attenuation rate that the variable attenuator can achieve. Therefore, in long-distance optical communications, this device increases the loss in the internal optical system on the receiver side, deteriorating the line performance.

[0007] Another possible method for dealing with distance variations in the spatial transmission path is to electrically control the gain of the OHPA (Optical High Power Amplifier) ​​of the spatial optical communications transceiver. That is, the drive current or injection current of the OHPA's excitation light is changed by an OHPA controller to control the OHPA's gain. However, with a high-gain OHPA, electrical control near the gain threshold is difficult. Furthermore, gain control toward a high gain induces amplified spontaneous emission (ASE), degrading the noise figure (NF), and causing fluctuations in the S / N ratio of the communication path.

[0008] In contrast, in the devices disclosed in Patent Documents 2 and 3, for example, the coupling efficiency of the spatial light to the fiber is changed by controlling the spacing of the spatial optical system or the position of the focusing lens in the optical axis direction, thereby increasing or decreasing the intensity of the optical signal. As a result, in these devices, the output light intensity of the OHPA can be adjusted without the need for electrical control of the OHPA, particularly the fiber amplifier.

[0009] However, this device is configured to couple the spatial light back into the fiber, so that excess light generated when the output light intensity is adjusted may be locally irradiated outside the fiber core, potentially damaging the fiber.

[0010] JP 2005-195806 JP 2002-221675 JP 06-037719

[0011] As described above, when a variable attenuator on the receiver side is used to extend the communication distance of a free-space optical communication device, the internal optical system loss increases and the line performance deteriorates. Also, when the gain of the optical amplifier of the transmitter is electrically controlled to extend the communication distance of the free-space optical communication device, it is difficult to electrically control the gain near the gain threshold, and the S / N ratio of the communication path fluctuates due to changes in noise characteristics caused by gain changes.

[0012] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a spatial optical communications transceiver that can accommodate variations in the distance of the spatial transmission path without electrical gain variation.

[0013] The spatial optical communications transceiver according to the present disclosure is characterized by comprising a light source that generates laser light, an optical modulator that superimposes a communication signal on the laser light generated by the light source, an optical amplifier that amplifies the laser light superimposed by the optical modulator, a collimator that has a fiber connector and a collimator lens and converts the laser light amplified by the optical amplifier into spatial light and emits transmission light, which is the spatial light, an optical telescope that expands the beam width of the transmission light emitted by the collimator and emits it onto a spatial transmission path, a drive mechanism that can adjust the focal length of the collimator lens, and a drive controller that determines the drive amount of the drive mechanism so that the product of the free space loss calculated from the distance between the transceiver itself and the spatial optical communications transceiver with which it is communicating and the transmission gain determined by the beam divergence angle of the transmission light is constant.

[0014] According to the present disclosure, the above-described configuration makes it possible to accommodate variations in the distance of the spatial transmission path without electrically varying the gain.

[0015] 2A and 2B are diagrams for explaining an overview of varying the beam divergence angle of transmitted light by adjusting the focal length of a collimator lens in the first embodiment, where FIG. 2A is a diagram showing an example of a case where the position of the collimator lens is not adjusted, and FIG. 2B is a diagram showing an example of a case where the position of the collimator lens is adjusted.

[0034] FIG. 2B is a diagram showing an example of a configuration of a collimator in the first embodiment, where the collimator lens is moved.

[0035] FIG. 2C is a diagram showing an example of a configuration of a collimator in the first embodiment, where the end of a fiber connector is moved.

[0036] FIG. 2D is a diagram showing an example of a configuration of a collimator in the first embodiment, where an electro-optic material is used in the collimator lens portion.

[0037] FIG. 2E is a diagram showing an example of a configuration of a free-space optical communication system according to the second embodiment.

[0038] FIG. 2F is a diagram showing an example of a free-space optical communication system according to the third embodiment.

[0039] FIG. 9A to FIG. 9C are diagrams showing an example of spiral scanning of an error range with transmitted light.

[0039] FIG. 9C is a flowchart showing an example of an operation during initial capture by one of the free-space optical communication transceivers in the free-space optical communication system according to the third embodiment. 12A and 12B are flowcharts illustrating an example of an operation at the time of initial capture by the other free-space optical communications transceiver in the free-space optical communications system according to embodiment 3. Fig. 12A and Fig. 12B are diagrams illustrating an example of a hardware configuration of the free-space optical communications transceiver according to embodiments 1 to 3.

[0016] Hereinafter, embodiments will be described in detail with reference to the drawings. Embodiment 1. FIG. 1 is a diagram showing an example of the configuration of a free-space optical communication system according to embodiment 1. As shown in FIG. 1, the free-space optical communication system includes a free-space optical communication device 1-1 and a free-space optical communication device 1-2. In this free-space optical communication system, bidirectional communication is performed between the free-space optical communication device 1-1 and the free-space optical communication device 1-2. Note that here, when it is necessary to distinguish between systems for the free-space optical communication device 1 and the components of the free-space optical communication device 1, suffixes (-1, -2) are added to the reference symbols.

[0017] The free-space optical communications device 1-1 is mounted on a mobile body and communicates with a free-space optical communications device 1-2 as a communication partner. The free-space optical communications device 1-1 according to the first embodiment has a function of maintaining constant the optical intensity of the transmitted light received by the free-space optical communications device 1-2 as a communication partner, even when the distance of the free-space transmission path fluctuates, thereby enabling the establishment of a stable free-space optical communications path. As shown in FIG. 1, this free-space optical communications device 1-1 includes a free-space optical communications transceiver 11-1 and an attitude orbit control computer 12-1.

[0018] As shown in FIG. 1, the spatial optical communication transceiver 11-1 includes a light source 1101-1, an optical modulator 1102-1, an OHPA 1103-1, an OHPA controller 1104-1, a collimator 1105-1, a dichroic mirror 1106-1, a tip-tilt mirror 1107-1, an optical telescope 1108-1, a gimbal 1109-1, a beam splitter 1110-1, an optical demodulator 1111-1, a drive mechanism 1112-1, a drive controller 1113-1, a memory device 1114-1, an acquisition and tracking sensor 1115-1, and an acquisition and tracking controller 1116-1.

[0019] The light source 1101-1 generates a laser beam that is a carrier wave to be propagated through space. The laser beam generated by the light source 1101-1 is output to an optical modulator 1102-1. The light source 1101-1 may be, for example, an LD (Laser Diode).

[0020] The optical modulator 1102-1 superimposes transmission data 101-1 onto the laser light generated by the light source 1101-1. The transmission data 101-1 is a communication signal input from outside the spatial optical communications transceiver 11-1. The laser light after superposition by the optical modulator 1102-1 is output to the OHPA 1103-1. The optical modulation method by the optical modulator 1102-1 can be selected appropriately, for example, OOK (On-Off Keying) using intensity modulation of light, or PSK (Phase Shift Keying) using phase modulation of light, etc.

[0021] The OHPA 1103-1 is an optical amplifier that uses a fiber as an input and output. This OHPA 1103-1 amplifies the optical intensity of the laser light superimposed by the optical modulator 1102-1. The laser light amplified by this OHPA 1103-1 is output to a collimator 1105-1. Examples of this OHPA 1103-1 include a fiber amplifier such as an erbium-doped fiber amplifier (EDFA) or a semiconductor optical amplifier (SOA). A fiber amplifier amplifies signal light by injecting pumping light into the fiber. Furthermore, a semiconductor optical amplifier amplifies signal light by injecting current.

[0022] The OHPA controller 1104-1 is an optical amplifier controller that controls the gain of the OHPA 1103-1. That is, if the OHPA 1103-1 is a fiber amplifier, the OHPA controller 1104-1 controls the gain of the fiber amplifier by controlling the pumping light of the fiber amplifier. Also, if the OHPA 1103-1 is a semiconductor optical amplifier, the OHPA controller 1104-1 controls the gain of the semiconductor optical amplifier by controlling the injection current of the semiconductor optical amplifier.

[0023] The collimator 1105-1 converts the laser light amplified by the OHPA 1103-1 into spatial light close to parallel light and emits the spatial light as transmission light. The transmission light emitted by the collimator 1105-1 is output to the optical telescope 1108-1 via a dichroic mirror 1106-1 and a tip-tilt mirror 1107-1. The collimator 1105-1 is typically composed of a fiber connector 11051-1 and a collimator lens 11052-1. The collimator 1105-1 sets the distance between the end of the fiber connector 11051-1 and the collimator lens 11052-1 to the focal length of the collimator lens 11052-1, so that the output light from the collimator lens 11052-1 becomes parallel light, i.e., collimated light.

[0024] Dichroic mirror 1106-1 separates the wavelengths of the transmitted light emitted by collimator 1105-1 and the received light reflected by tip-tilt mirror 1107-1. That is, dichroic mirror 1106-1 transmits the transmitted light emitted by collimator 1105-1 and reflects the received light reflected by tip-tilt mirror 1107-1. The transmitted light that passes through dichroic mirror 1106-1 is output to tip-tilt mirror 1107-1, and the received light reflected by dichroic mirror 1106-1 is output to beam splitter 1110-1.

[0025] Tip-tilt mirror 1107-1 is a mirror that can adjust the angles in two axial directions of the transmitted light and the received light. Tip-tilt mirror 1107-1 reflects the transmitted light that has passed through dichroic mirror 1106-1 and reflects the received light that has been received by optical telescope 1108-1. The transmitted light reflected by tip-tilt mirror 1107-1 is output to optical telescope 1108-1, and the received light reflected by optical telescope 1108-1 is output to dichroic mirror 1106-1.

[0026] Tip-tilt mirror 1107-1 controls the angles of both the transmitted light and the received light using the same mirror. On the other hand, if the distance between the spatial optical communications transceivers 11 is long, a separate tip-tilt mirror that independently controls the angle of only the transmitted light may be added in addition to tip-tilt mirror 1107-1. If the distance of the spatial transmission path is long, the spatial optical communications device 1-2, which is the communication partner and is mounted on a mobile object, moves while the light propagates through the spatial transmission path. Therefore, if the pointing direction of the communication partner is identified based on the received light from the communication partner and the pointing control of the transmitted light is performed, a pointing error occurs due to the movement of the mobile object during the time the light travels back and forth through the spatial transmission path. This is called optical aberration. To correct this optical aberration, a tip-tilt mirror for correcting optical aberration may be added between the dichroic mirror 1106-1 and the collimator 1105-1.

[0027] The optical telescope 1108-1 expands the beam width of the transmission light reflected by the tip-tilt mirror 1107-1 and radiates it onto the spatial transmission path. The optical telescope 1108-1 also receives, as received light, the transmission light radiated by the optical telescope 1108-2 in the opposing spatial optical communications transceiver 11-2.

[0028] The gimbal 1109-1 is a device that can adjust the direction of the optical axis of the optical telescope 1108-1.

[0029] Beam splitter 1110-1 splits the received light reflected by dichroic mirror 1106-1 into two beams. One of the beams obtained by beam splitter 1110-1 is output to optical demodulator 1111-1, and the other beam is output to acquisition and tracking sensor 1115-1.

[0030] The optical demodulator 1111-1 photoelectrically converts one of the received lights obtained by the beam splitter 1110-1 to demodulate the communication signal, and the communication signal demodulated by the optical demodulator 1111-1 is output to the outside as received data 102-1.

[0031] The driving mechanism 1112-1 drives the collimator lens 11052-1 of the collimator 1105-1. By driving the collimator lens 11052-1, the driving mechanism 1112-1 adjusts the optical axis direction of the collimator lens 11052-1 and adjusts the focal length of the collimator lens 11052-1.

[0032] The drive controller 1113-1 controls the drive of the drive mechanism 1112-1 based on the distance between the moving bodies predicted by the attitude orbit control computer 12-1 and information stored in the storage device 1114-1. At this time, the drive controller 1113-1 determines the drive amount of the drive mechanism 1112-1 based on the distance between the moving bodies predicted by the attitude orbit control computer 12-1 so that the product of the free space loss calculated from the distance and the transmission gain determined by the beam divergence angle of the transmitted light is constant.

[0033] The storage device 1114-1 is a setting table that stores information indicating the relationship between the lens driving amount of the driving mechanism 1112-1 and the beam divergence angle of the transmitted light radiated from the optical telescope 1108-1 to the spatial transmission path.

[0034] Examples of storage device 1114-1 include non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), EEPROM (Electrically EPROM), magnetic disk, flexible disk, optical disk, compact disk, mini disk, or DVD (Digital Versatile Disc).

[0035] 1 shows a case where the storage device 1114-1 is provided inside the free-space optical communications transceiver 11-1, but the present invention is not limited to this, and the storage device 1114-1 may be provided outside the free-space optical communications transceiver 11-1.

[0036] Acquisition and tracking sensor 1115-1 detects the angle of arrival of the other received light based on the other received light obtained by beam splitter 1110-1. Information indicating the angle of arrival of the received light detected by acquisition and tracking sensor 1115-1 is output to acquisition and tracking controller 1116-1.

[0037] The acquisition and tracking controller 1116-1 controls the gimbal 1109-1 and the tip-tilt mirror 1107-1 based on the apparent angle predicted by the attitude and orbit control computer 12-1 and the angle of arrival of the received light detected by the acquisition and tracking sensor 1115-1. In other words, the acquisition and tracking controller 1116-1 controls the angle of the gimbal 1109-1 and the angle of the tip-tilt mirror 1107-1 to align the optical axis of the optical telescope 1108-1 with the optical axis of the optical telescope 1108-2 in the free-space optical communications transceiver 11-2 that communicates with the free-space optical communications transceiver 11-1.

[0038] The attitude orbit control computer 12-1 predicts the apparent angle and the distance between the communicating mobile bodies based on the attitude and position information of the mobile body on which the free-space optical communications device 1-1 is mounted and the position information of the mobile body on which the free-space optical communications device 1-2 is mounted. The apparent angle is the relative direction of the free-space optical communications transceiver 11-2 with respect to the free-space optical communications transceiver 11-1. The distance between the communicating mobile bodies is the distance between the free-space optical communications transceiver 11-1 and the free-space optical communications transceiver 11-2. Information indicating the apparent angle predicted by the attitude orbit control computer 12-1 is output to the acquisition and tracking controller 1116-1. Information indicating the distance between the communicating mobile bodies predicted by the attitude orbit control computer 12-1 is output to the drive controller 1113-1.

[0039] The free-space optical communications device 1-2 is mounted on a mobile body and communicates with its communication partner, the free-space optical communications device 1-1. The free-space optical communications device 1-2 according to the first embodiment has a function of maintaining the optical intensity of the transmitted light received by the communication partner, the free-space optical communications device 1-1, constant, even when the distance of the free-space transmission path fluctuates, thereby enabling the establishment of a stable free-space optical communications path. As shown in FIG. 1, this free-space optical communications device 1-2 includes a free-space optical communications transceiver 11-2 and an attitude orbit control computer 12-2.

[0040] As shown in FIG. 1, the spatial optical communication transceiver 11-2 includes a light source 1101-2, an optical modulator 1102-2, an OHPA 1103-2, an OHPA controller 1104-2, a collimator 1105-2, a dichroic mirror 1106-2, a tip-tilt mirror 1107-2, an optical telescope 1108-2, a gimbal 1109-2, a beam splitter 1110-2, an optical demodulator 1111-2, a drive mechanism 1112-2, a drive controller 1113-2, a memory device 1114-2, an acquisition and tracking sensor 1115-2, and an acquisition and tracking controller 1116-2.

[0041] The light source 1101-2 generates a laser beam that is a carrier wave to be propagated through space. The laser beam generated by the light source 1101-2 is output to the optical modulator 1102-2. The light source 1101-2 may be, for example, an LD.

[0042] The optical modulator 1102-2 superimposes transmission data 101-2 onto the laser light generated by the light source 1101-2. The transmission data 101-2 is a communication signal input from outside the spatial optical communications transceiver 11-2. The laser light after superposition by the optical modulator 1102-2 is output to the OHPA 1103-2. The optical modulation method by the optical modulator 1102-2 can be selected appropriately, for example, OOK using intensity modulation of light or PSK using phase modulation of light.

[0043] The OHPA 1103-2 is an optical amplifier that uses a fiber as an input and output. This OHPA 1103-2 amplifies the optical intensity of the laser light after superposition by the optical modulator 1102-1. The laser light after amplified by this OHPA 1103-2 is output to the collimator 1105-2. Examples of this OHPA 1103-2 include a fiber amplifier such as an erbium-doped fiber amplifier (EDFA) or a semiconductor optical amplifier (SOA). In a fiber amplifier, signal light is amplified by injecting pumping light into the fiber. In a semiconductor optical amplifier, signal light is amplified by injecting current.

[0044] The OHPA controller 1104-2 is an optical amplifier controller that controls the gain of the OHPA 1103-2. That is, if the OHPA 1103-2 is a fiber amplifier, the OHPA controller 1104-2 controls the gain of the fiber amplifier by controlling the pumping light of the fiber amplifier. Also, if the OHPA 1103-2 is a semiconductor optical amplifier, the OHPA controller 1104-2 controls the gain of the semiconductor optical amplifier by controlling the injection current of the semiconductor optical amplifier.

[0045] The collimator 1105-2 converts the laser light amplified by the OHPA 1103-2 into spatial light close to parallel light and emits the spatial light as transmission light. The transmission light emitted by the collimator 1105-2 is output to the optical telescope 1108-2 via a dichroic mirror 1106-2 and a tip-tilt mirror 1107-2. The collimator 1105-2 is typically composed of a fiber connector 11051-2 and a collimator lens 11052-2. The collimator 1105-2 sets the distance between the end of the fiber connector 11051-2 and the collimator lens 11052-2 to the focal length of the collimator lens 11052-2, so that the output light from the collimator lens 11052-2 becomes parallel light, i.e., collimated light.

[0046] Dichroic mirror 1106-2 separates the wavelengths of the transmitted light emitted by collimator 1105-2 and the received light reflected by tip-tilt mirror 1107-2. That is, dichroic mirror 1106-2 transmits the transmitted light emitted by collimator 1105-2 and reflects the received light reflected by tip-tilt mirror 1107-2. The transmitted light that passes through dichroic mirror 1106-2 is output to tip-tilt mirror 1107-2, and the received light reflected by dichroic mirror 1106-2 is output to beam splitter 1110-2.

[0047] Tip-tilt mirror 1107-2 is a mirror that can adjust the angles in two axial directions for the transmitted light and the received light. Tip-tilt mirror 1107-2 reflects the transmitted light that has passed through dichroic mirror 1106-2 and reflects the received light that has been received by optical telescope 1108-2. The transmitted light reflected by tip-tilt mirror 1107-2 is output to optical telescope 1108-2, and the received light reflected by optical telescope 1108-2 is output to dichroic mirror 1106-2.

[0048] The tip-tilt mirror 1107-2 controls the angles of both the transmitted light and the received light using the same mirror. On the other hand, if the distance between the spatial optical communications transceivers 11 is long, a separate tip-tilt mirror that independently controls the angle of only the transmitted light may be added in addition to the tip-tilt mirror 1107-2. If the distance of the spatial transmission path is long, the spatial optical communications device 1-1, which is the communication partner and is mounted on a mobile object, moves while the light propagates through the spatial transmission path. Therefore, if the pointing direction of the communication partner is identified based on the received light from the communication partner and the pointing control of the transmitted light is performed, a pointing error occurs due to the movement of the mobile object during the time the light travels back and forth through the spatial transmission path. This is called optical aberration. To correct this optical aberration, a tip-tilt mirror for correcting optical aberration may be added between the dichroic mirror 1106-2 and the collimator 1105-2.

[0049] The optical telescope 1108-2 expands the beam width of the transmission light reflected by the tip-tilt mirror 1107-2 and radiates it onto the spatial transmission path. The optical telescope 1108-2 also receives the transmission light radiated by the optical telescope 1108-1 in the opposing spatial optical communications transceiver 11-1 as received light.

[0050] The gimbal 1109-2 is a device that can adjust the direction of the optical axis of the optical telescope 1108-2.

[0051] Beam splitter 1110-2 splits the received light reflected by dichroic mirror 1106-2 into two beams. One of the beams obtained by beam splitter 1110-2 is output to optical demodulator 1111-2, and the other beam is output to acquisition and tracking sensor 1115-2.

[0052] The optical demodulator 1111-2 performs photoelectric conversion on one of the received lights obtained by the beam splitter 1110-2 to demodulate the communication signal, and the communication signal demodulated by the optical demodulator 1111-2 is output to the outside as received data 102-2.

[0053] The driving mechanism 1112-2 drives the collimator lens 11052-2 of the collimator 1105-2. By driving the collimator lens 11052-2, the driving mechanism 1112-2 adjusts the optical axis direction of the collimator lens 11052-2 and the focal length of the collimator lens 11052-2.

[0054] The drive controller 1113-2 controls the drive of the drive mechanism 1112-2 based on the distance between the moving bodies predicted by the attitude orbit control computer 12-2 and the information stored in the storage device 1114-2. At this time, the drive controller 1113-2 determines the drive amount of the drive mechanism 1112-2 based on the distance between the moving bodies predicted by the attitude orbit control computer 12-2 so that the product of the free space loss calculated from the distance and the transmission gain determined by the beam divergence angle of the transmitted light is constant.

[0055] The storage device 1114-2 is a setting table that stores information indicating the relationship between the lens driving amount of the driving mechanism 1112-2 and the beam divergence angle of the transmitted light radiated from the optical telescope 1108-2 to the spatial transmission path.

[0056] The storage device 1114-2 may be, for example, a non-volatile or volatile semiconductor memory such as a RAM, a ROM, a flash memory, an EPROM, or an EEPROM, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a DVD.

[0057] 1 shows a case where the storage device 1114-2 is provided inside the free-space optical communications transceiver 11-2, but is not limited to this, and the storage device 1114-2 may be provided outside the free-space optical communications transceiver 11-2.

[0058] Acquisition and tracking sensor 1115-2 detects the angle of arrival of the other received light based on the other received light obtained by beam splitter 1110-2. Information indicating the angle of arrival of the received light detected by acquisition and tracking sensor 1115-2 is output to acquisition and tracking controller 1116-2.

[0059] The acquisition and tracking controller 1116-2 controls the gimbal 1109-2 and the tip-tilt mirror 1107-2 based on the apparent angle predicted by the attitude and orbit control computer 12-2 and the angle of arrival of the received light detected by the acquisition and tracking sensor 1115-2. That is, the acquisition and tracking controller 1116-2 controls the angle of the gimbal 1109-2 and the angle of the tip-tilt mirror 1107-2 to align the optical axis of the optical telescope 1108-2 with the optical axis of the optical telescope 1108-1 in the free-space optical communications transceiver 11-1 that communicates with the free-space optical communications transceiver 11-2.

[0060] The attitude orbit control computer 12-2 predicts the apparent angle and the distance between the communicating mobile bodies based on the attitude and position information of the mobile body on which the free-space optical communications device 1-2 is mounted, and the position information of the mobile body on which the free-space optical communications device 1-1 is mounted. The apparent angle is the relative direction of the free-space optical communications transceiver 11-1 with respect to the free-space optical communications transceiver 11-2. The distance between the communicating mobile bodies is the distance between the free-space optical communications transceiver 11-1 and the free-space optical communications transceiver 11-2. Information indicating the apparent angle predicted by the attitude orbit control computer 12-2 is output to the acquisition and tracking controller 1116-2. Information indicating the distance between the communicating mobile bodies predicted by the attitude orbit control computer 12-2 is output to the drive controller 1113-2.

[0061] The spatial transmission path is a medium that fills the space between the spatial optical communication transceiver 11-1 and the spatial optical communication transceiver 11-2, and the medium can be any medium, such as the atmosphere in the case of terrestrial communication, seawater in the case of underwater communication, or vacuum in the case of inter-satellite communication. In Figure 1, reference numeral 103 indicates the distance between the mobile bodies that communicate, i.e., the distance of the spatial transmission path.

[0062] Next, an example of the operation of the free-space optical communication system according to the first embodiment shown in Fig. 1 will be described. In this free-space optical communication system, data is transmitted from the free-space optical communication device 1-1 to the free-space optical communication device 1-2, and data is transmitted from the free-space optical communication device 1-2 to the free-space optical communication device 1-1. Here, the wavelength of the light transmitted from the free-space optical communication device 1-1 to the free-space optical communication device 1-2 is set to λa, and the wavelength of the light transmitted from the free-space optical communication device 1-2 to the free-space optical communication device 1-1 is set to λb.

[0063] Furthermore, since the free-space optical communications device 1-1 and the free-space optical communications device 1-2 operate in the same manner, the following description will be given taking as an example a case where data is transmitted from the free-space optical communications device 1-1 to the free-space optical communications device 1-2.

[0064] First, the output light of the light source 1101-1 in the spatial optical communications transceiver 11-1 is input to the optical modulator 1102-1, and the optical modulator 1102-1 superimposes transmission data 101-1, which is a communication signal input from outside the spatial optical communications transceiver 11-1.

[0065] The output light of this optical modulator 1102-1 is input to an OHPA 1103-1, and the light intensity is amplified by the OHPA 1103-1. Note that an OHPA controller 1104-1 controls the gain of the OHPA 1103-1.

[0066] The output light of this OHPA 1103-1 is converted into spatial light by a collimator 1105-1 and emitted as transmission light.

[0067] The output light from this collimator 1105-1 passes through dichroic mirror 1106-1, is reflected by tip-tilt mirror 1107-1, and enters optical telescope 1108-1. Note that dichroic mirror 1106-1 separates the transmitted light from free-space optical communications transceiver 11-1 from the received light from free-space optical communications transceiver 11-2, i.e., it transmits the wavelength λa and reflects the wavelength λb. As a result, the transmitted light from free-space optical communications transceiver 11-2 is reflected by dichroic mirror 1106-1 and does not enter the collimator 1105-1 side.

[0068] The output light from this optical telescope 1108-1 propagates through a spatial transmission path and is received as received light by the optical telescope 1108-2 of the spatial optical communications transceiver 11-2. The received light received by the optical telescope 1108-2 is reflected by the tip-tilt mirror 1107-2, reflected by the dichroic mirror 1106-2, and then split into two by the beam splitter 1110-2, and input to the acquisition and tracking sensor 1115-2 and the optical demodulator 1111-2, respectively.

[0069] Thereafter, in the optical demodulator 1111-2, the received light is photoelectrically converted by an internal photoelectric converter to demodulate the communication signal, which is then output to the outside as received data 102-2.

[0070] Furthermore, to secure a communication path between the free-space optical communications transceiver 11-1 and the free-space optical communications transceiver 11-2, the acquisition and tracking sensor 1115-1 detects the direction of arrival of the received light, and the acquisition and tracking controller 1116-1 controls the tip-tilt mirror 1107-1 and the gimbal 1109-1 based on this information. At this time, the attitude and orbit control computer 12-1 predicts the apparent angle, which is the relative direction of the free-space optical communications transceiver 11-2 with respect to the free-space optical communications transceiver 11-1, based on the attitude and position of the mobile body on which the free-space optical communications transceiver 11-1 is mounted, and the position of the mobile body on which the free-space optical communications transceiver 11-2 is mounted. The acquisition and tracking controller 1116-1 then determines the directivity angle of the gimbal 1109-1 based on this information and the direction of arrival of the received light, and suppresses the angle error to a range that can be corrected by the tip-tilt mirror 1107-1.

[0071] The above describes an example of operation when transmitting data from the free-space optical communications device 1-1 to the free-space optical communications device 1-2. In contrast, the same operation as above is performed when transmitting data from the free-space optical communications device 1-2 to the free-space optical communications device 1-1. As a result, in the free-space optical communications system, the optical axes of the optical telescopes 1108-1 and 1108-2 are aligned directly opposite each other, and by continuing angle control by the acquisition and tracking controllers 1116-1 and 1116-2, mutual tracking of the moving objects is achieved and the optical path is maintained.

[0072] The basic operation of the free-space optical communication device 1-1 and the free-space optical communication device 1-2 has been described above. However, when considering maintaining a communication path when there is a wide range of distance fluctuations from short to long distances, there is a possibility that loss fluctuations will occur that exceed the dynamic range of the photoelectric converter in the optical demodulator 1111-1 or the photoreceiver such as the acquisition and tracking sensor 1115-1. Here, the dynamic range represents the ratio between the minimum received light intensity and the saturation intensity.

[0073] Generally, the free space loss of light, G ｆｓ is expressed by the following equation (1). In equation (1), λ is the wavelength of the propagating light, and L is the propagation distance. As shown in equation (1), the free space loss varies as the square of the propagation distance. Therefore, for example, if the distance of the spatial transmission path varies by 20 dB from 100 km to 10,000 km, a dynamic range of 40 dB or more is required.

[0074] Another possible method for dealing with variations in the distance of the spatial transmission path is to electrically control the gain of the OHPA 1103-1. That is, the drive current or injection current of the pump light of the OHPA 1103-1 can be changed by the OHPA controller 1104-1 to control the gain of the OHPA 1103-1. However, with the high-gain OHPA 1103-1, it is difficult to electrically control the gain near the gain threshold when the gain is reduced. Furthermore, gain control in the direction of high gain induces ASE, degrading the NF and causing fluctuations in the S / N ratio of the communication path.

[0075] Therefore, in the first embodiment, a free-space optical communications transceiver 11-1 is realized that can accommodate variations in the distance of the free-space transmission path, without being based on electrical gain variation of the OHPA 1103-1, such as changing the current value of the OHPA controller 1104-1.

[0076] That is, in the free-space optical communications transceiver 11-1 according to the first embodiment, the beam divergence angle of the transmitted light emitted from the optical telescope 1108-1 is controlled by controlling the beam divergence angle of the transmitted light emitted from the collimator 1105-1. In the collimator 1105-1, the distance between the end of the fiber connector 11051-1 and the collimator lens 11052-1 is generally fixed so that the emitted light is parallel, and the focal length of the collimator lens 11052-1 is fixed. In contrast, in the free-space optical communications transceiver 11-1 according to the first embodiment, the focal length of the collimator lens 11052-1 is varied by the drive mechanism 1112-1.

[0077] An overview of varying the beam divergence angle of transmitted light by adjusting the focal length of the collimator lens 11052-1 will be described with reference to Figure 2. The example of Figure 2 shows a case where the collimator 1105-1 is a refractive collimator having a collimator lens 11052-1, and the optical telescope 1108-1 is a refractive optical telescope having a collimator-side lens 11081-1 and a spatial transmission path-side lens 11082-1. Also, assume that the focal length of the collimator lens 11052-1 is f1-1, the focal length of the collimator-side lens 11081-1 is f2-1, and the focal length of the spatial transmission path-side lens 11082-1 ​​is f3-1.

[0078] 2A, when the collimator lens 11052-1 is not adjusted, the distance between the collimator lens 11052-1 and the end of the fiber connector 11051-1 is f1-1, and the light emitted from the collimator 1105-1 is parallel. This light is expanded by the optical telescope 1108-1, which is an afocal optical system, and emitted from the optical telescope 1108-1 as transmitted light. Therefore, the transmitted light is almost parallel, and depending on the beam width determined by the aperture diameter on the spatial transmission path side of the optical telescope 1108-1, the transmitted light will diffractively widen if propagated over a long distance.

[0079] In contrast, as shown in Figure 2B, when the collimator lens 11052-1 is brought closer to the end of the fiber connector 11051-1, the light emitted from the collimator 1105-1 becomes divergent rather than parallel. As a result, the afocal imaging system in the optical telescope 1108-1 collapses, and the transmitted light becomes a beam that is more divergent than in the case of Figure 2A. Figure 2B shows the case where the distance between the collimator lens 11052-1 and the end of the fiber connector 11051-1 is f1'-1.

[0080] In the above example, the collimator 1105-1 is a refractive collimator and the optical telescope 1108-1 is a refractive optical telescope, but the same optical effect can be obtained with a configuration using a reflecting mirror.

[0081] The focal length of the collimator 1105-1 can be adjusted, for example, by the following method.

[0082] First, for example, there is a method of moving the collimator lens 11052-1 as shown in Fig. 3. In this case, for example, the collimator lens 11052-1 is fixed to the collimator 1105-1, and a linear actuator 11053-1 that can move the collimator lens 11052-1 along the optical axis is provided. Then, the drive mechanism 1112-1 adjusts the focal length of the collimator 1105-1 by driving the linear actuator 11053-1 using a drive control signal.

[0083] Another example is a method of moving the end of the fiber connector 11051-1, as shown in FIG. 4. In this case, for example, the fiber connector 11051-1 is fixed to the collimator 1105-1, and a cylindrical piezoelectric element 11054-1 that can move the end of the fiber connector 11051-1 along the optical axis direction is provided. The driving mechanism 1112-1 drives the piezoelectric element 11054-1 using a driving control signal, and adjusts the focal length of the collimator 1105-1 by controlling the position of the fiber connector 11051-1 through the expansion and contraction of the piezoelectric element 11054-1. In this case, compared to the case of FIG. 3, the configuration of the collimator 1105-1 enables precise driving without using a mechanical driving part.

[0084] 5, for example, a method of using a lens whose focal length changes when a voltage is applied as the collimator lens 11052-1 can be used. In this case, for example, an electro-optic material is used for the collimator lens 11052-1. The driving mechanism 1112-1 then adjusts the focal length of the collimator 1105-1 by controlling the lens power due to the electro-optic effect of the collimator lens 11052-1 using a driving control signal. In this case, compared to the case of FIG. 3, the configuration of the collimator 1105-1 allows for precise driving without using mechanical driving parts.

[0085] Furthermore, the attitude orbit control computer 12-1 can predict the distance between the free-space optical communications transceiver 11-1 and the free-space optical communications transceiver 11-2, and as a result, the free-space optical communications device 1-1 can predict free-space loss. As a method for the attitude orbit control computer 12-1 to calculate the distance of the free-space transmission path from the positions of the mobile body on which the free-space optical communications device 1-1 is mounted and the mobile body on which the free-space optical communications device 1-2 is mounted, for example, if the mobile body is a satellite, a method can be considered in which TLE (Two-Line Elements) is obtained from a ground station by another communication means and an orbit is calculated based on that. Alternatively, a method can be adopted in which the distance of the free-space transmission path is calculated using laser ranging or direct ranging using microwaves.

[0086] Here, the beam divergence angle of the output light from the optical telescope 1108-1 is θ ｔ When ｔ is expressed by the following equation (2): Therefore, the transmission gain deteriorates in proportion to the square of the beam divergence angle.

[0087] Then, the drive controller 1113-1 selects the lens drive amount so that the condition of the following equation (3) is satisfied based on the distance between the communicating mobile bodies predicted by the attitude orbit control computer 12-1, i.e., the distance of the spatial transmission path, and the information stored in the memory device 1114-1, and sets it for the drive mechanism 1112-1.

[0088] The receiving gain is determined by the aperture diameter of the opposing optical telescope 1108-2. Therefore, by performing the above control, the sum of the transmission gain, free space loss, and receiving gain becomes constant. As a result, the received light intensity at the acquisition and tracking sensor 1115-2 and the optical demodulator 1111-2 in the free-space optical communication device 1-2 is kept constant.

[0089] In addition, in the conventional configuration, the OHPA controller had to control the gain of the OHPA in accordance with the fluctuations in the distance of the spatial transmission path. In contrast to this, in the free-space optical communications transceiver 11-1 according to the first embodiment, the OHPA controller 1104-1 does not have to control the gain of the OHPA 1103-1 in accordance with the fluctuations in the distance of the spatial transmission path, and by continuing to operate at the maximum output that does not saturate, stable operation can be expected in terms of both the signal amplification effect and the noise that is added.

[0090] In the above explanation, the control of the light transmitted from the free-space optical communications transceiver 11-1 to the free-space optical communications transceiver 11-2 has been explained. In contrast, the control of the light transmitted from the free-space optical communications transceiver 11-2 to the free-space optical communications transceiver 11-1 is also similar to the above.

[0091] As described above, according to this embodiment 1, the spatial optical communications transceiver 11 comprises a light source 1101 that generates laser light, an optical modulator 1102 that superimposes a communication signal on the laser light generated by the light source 1101, an OHPA 1103 that amplifies the laser light superimposed by the optical modulator 1102, a collimator 1105 that has a fiber connector 11051 and a collimator lens 11052 and converts the laser light amplified by the OHPA 1103 into spatial light and emits transmission light, which is the spatial light, an optical telescope 1108 that expands the beam width of the transmission light emitted by the collimator 1105 and emits it onto the spatial transmission path, a drive mechanism 1112 that can adjust the focal length of the collimator lens 11052, and a drive controller 1113 that determines the drive amount of the drive mechanism 1112 so that the product of the free space loss calculated from the distance between the transceiver itself and the spatial optical communications transceiver 11 that is the communication partner and the transmission gain determined by the beam divergence angle of the transmission light is constant. As a result, the free-space optical communications transceiver 11 according to the first embodiment can accommodate variations in the distance of the free-space transmission path without electrically varying the gain, and can maintain a constant light intensity received by the receiving side. As a result, the communication distance range can be expanded compared to conventional systems. Furthermore, the free-space optical communications transceiver 11 according to the first embodiment can reduce internal optical system losses on the receiving side compared to conventional systems, thereby improving the feasibility of long-distance communication. Furthermore, the free-space optical communications transceiver 11 according to the first embodiment can prevent fiber damage caused by high-intensity light being locally focused compared to conventional systems.

[0092] Embodiment 2. Figure 6 is a diagram showing an example of the configuration of a free-space optical communications system according to embodiment 2. In the free-space optical communications system according to embodiment 2 shown in Figure 6, a wavefront measuring device 1117-1 is added to free-space optical communications transceiver 11-1, the functions of dichroic mirror 1106-1, drive controller 1113-1, and memory device 1114-1 are changed, and a wavefront measuring device 1117-2 is added to free-space optical communications transceiver 11-2, and the functions of dichroic mirror 1106-2, drive controller 1113-2, and memory device 1114-2 are changed. The other example of the configuration of the free-space optical communications system according to embodiment 2 shown in Figure 6 is the same as the example of the configuration of the free-space optical communications system according to embodiment 1 shown in Figure 1, so the same reference numerals are used and their description will be omitted.

[0093] Dichroic mirror 1106-1 separates the wavelengths of the transmitted light emitted by collimator 1105-1 and the received light reflected by tip-tilt mirror 1107-1. Dichroic mirror 1106-1 also separates a portion of the transmitted light emitted by collimator 1105-1. That is, dichroic mirror 1106-1 Fresnel-reflects a portion of the transmitted light emitted by collimator 1105-1, transmits the remainder, and reflects the received light reflected by tip-tilt mirror 1107-1. The transmitted light Fresnel-reflected by dichroic mirror 1106-1 is output to wavefront measuring instrument 1117-1, the transmitted light transmitted through dichroic mirror 1106-1 is output to tip-tilt mirror 1107-1, and the received light reflected by dichroic mirror 1106-1 is output to beam splitter 1110-1.

[0094] The wavefront measuring instrument 1117-1 detects the beam divergence angle of the transmitted light Fresnel-reflected by the dichroic mirror 1106-1. Information indicating the beam divergence angle of the transmitted light measured by this wavefront measuring instrument 1117-1 is output to the drive controller 1113-1. An example of this wavefront measuring instrument 1117-1 is a Shack-Hartmann wavefront sensor. The Shack-Hartmann wavefront sensor divides the wavefront using a lens array, focuses the light on an imager, and measures the displacement of the spot to measure the wavefront gradient at each point. The entire wavefront can be reconstructed by combining these results. For example, the Shack-Hartmann wavefront sensor can estimate the beam divergence angle by decomposing the measured wavefront into aberration components using, for example, Zernike polynomials and analyzing the defocus component.

[0095] The drive controller 1113-1 controls the drive of the drive mechanism 1112-1 based on the distance between the moving bodies predicted by the attitude orbit control computer 12-1 and information stored in the storage device 1114-1. At this time, the drive controller 1113-1 determines the drive amount of the drive mechanism 1112-1 so that the product of the free space loss calculated from the distance between the moving bodies predicted by the attitude orbit control computer 12-1 and the transmission gain determined by the beam divergence angle of the transmitted light is constant based on the beam divergence angle of the transmitted light detected by the wavefront measuring instrument 1117-1. In addition, if there is an error in the beam divergence angle with respect to the target value, the drive controller 1113-1 corrects the drive amount so as to cancel out the error.

[0096] The memory device 1114-1 is a setting table that stores information indicating the relationship between the lens drive amount of the drive mechanism 1112-1 and the beam divergence angle of the transmitted light radiated from the optical telescope 1108-1 to the spatial transmission path and the beam divergence angle of the transmitted light radiated by the collimator 1105-1.

[0097] Dichroic mirror 1106-2 separates the wavelengths of the transmitted light emitted by collimator 1105-2 and the received light reflected by tip-tilt mirror 1107-2. Dichroic mirror 1106-2 also separates a portion of the transmitted light emitted by collimator 1105-2. That is, dichroic mirror 1106-2 Fresnel-reflects a portion of the transmitted light emitted by collimator 1105-2, transmits the remainder, and reflects the received light reflected by tip-tilt mirror 1107-2. The transmitted light Fresnel-reflected by dichroic mirror 1106-2 is output to wavefront measuring instrument 1117-2, the transmitted light transmitted through dichroic mirror 1106-2 is output to tip-tilt mirror 1107-2, and the received light reflected by dichroic mirror 1106-2 is output to beam splitter 1110-2.

[0098] The wavefront measuring instrument 1117-2 detects the beam divergence angle of the transmitted light Fresnel-reflected by the dichroic mirror 1106-2. Information indicating the beam divergence angle of the transmitted light measured by this wavefront measuring instrument 1117-2 is output to the drive controller 1113-2. An example of this wavefront measuring instrument 1117-2 is a Shack-Hartmann wavefront sensor. The Shack-Hartmann wavefront sensor divides the wavefront using a lens array, focuses the light on an imager, and measures the displacement of the spot to measure the wavefront gradient at each point. The entire wavefront can be reconstructed by combining these results. For example, the Shack-Hartmann wavefront sensor can estimate the beam divergence angle by decomposing the measured wavefront into aberration components using, for example, Zernike polynomials and analyzing the defocus component.

[0099] The drive controller 1113-2 controls the drive of the drive mechanism 1112-2 based on the distance between the moving bodies predicted by the attitude orbit control computer 12-2 and information stored in the storage device 1114-2. At this time, the drive controller 1113-2 determines the drive amount of the drive mechanism 1112-2 based on the distance between the moving bodies predicted by the attitude orbit control computer 12-2 so that the product of the free space loss calculated from the distance and the transmission gain determined by the beam divergence angle of the transmitted light is constant. Furthermore, based on the beam divergence angle of the transmitted light detected by the wavefront measuring instrument 1117-2, if there is an error in the beam divergence angle with respect to the target value, the drive controller 1113-2 corrects the drive amount to cancel out the error.

[0100] The memory device 1114-2 is a setting table that stores information indicating the relationship between the lens drive amount of the drive mechanism 1112-2 and the beam divergence angle of the transmitted light radiated from the optical telescope 1108-2 to the spatial transmission path and the beam divergence angle of the transmitted light radiated by the collimator 1105-2.

[0101] Here, when controlling the beam divergence angle of the transmitted light from the optical telescope 1108-1 by driving and controlling the collimator 1105-1, it is necessary to control the beam divergence angle of the transmitted light from the collimator 1105-1 more precisely. The optical telescope 1108-1 generally has a larger aperture to increase the transmission gain and reception gain for the spatial transmission path, and outputs a beam with a wider beam width to the spatial transmission path. Therefore, the optical telescope 1108-1 has an optical lateral magnification of 1 or more with respect to the spatial transmission path from the inside of the spatial optical communications transceiver 11-1. In other words, from the spatial transmission path, the optical telescope 1108-1 has an optical angular magnification of 1 or more with respect to the inside of the spatial optical communications transceiver 11-1. Therefore, the beam divergence angle of the transmitted light from the optical telescope 1108-1 to the spatial transmission path changes more sensitively in response to the driving of the drive mechanism 1112-1 than the beam divergence angle of the transmitted light from the collimator 1105-1.

[0102] Therefore, in the spatial optical communications transceiver 11-1 according to the second embodiment, the Fresnel reflected light from the dichroic mirror 1106-1 of the transmitted light from the collimator 1105-1 is made incident on the wavefront measuring instrument 1117-1, and the beam divergence angle of the transmitted light from the collimator is measured by the wavefront measuring instrument 1117-1.

[0103] In the free-space optical communications transceiver 11-1 according to the second embodiment, in order to precisely control the beam divergence angle of the transmitted light from the collimator 1105-1, information indicating the beam divergence angle of the transmitted light detected by the wavefront measuring instrument 1117-1 is input to the drive controller 1113-1. The drive controller 1113-1 then sets the lens drive amount based on equations (2) and (3) so that the beam divergence angle of the transmitted light corresponds to the distance of the free-space transmission path. Thereafter, based on the beam divergence angle of the transmitted light detected by the wavefront measuring instrument 1117-1, if there is a deviation between the target value and the actual measured value of the beam divergence angle of the transmitted light in the free-space transmission path, the drive controller 1113-1 corrects the lens drive amount so as to cancel out this deviation.

[0104] In the above explanation, the control of the light transmitted from the free-space optical communications transceiver 11-1 to the free-space optical communications transceiver 11-2 has been explained. In contrast, the control of the light transmitted from the free-space optical communications transceiver 11-2 to the free-space optical communications transceiver 11-1 is also similar to the above.

[0105] As described above, according to the second embodiment, the free-space optical communications transceiver 11 includes the wavefront measuring instrument 1117 that detects the beam divergence angle of the transmitted light radiated by the collimator 1105, and the drive controller 1113 corrects the drive amount of the drive mechanism 1112 so as to cancel out the error when the beam divergence angle of the transmitted light measured by the wavefront measuring instrument 1117 has an error with respect to a target value. As a result, the free-space optical communications transceiver 11 according to the second embodiment can more precisely control the beam divergence angle of the transmitted light in the free-space transmission path than the free-space optical communications transceiver 11 according to the first embodiment, and can more stabilize the received light intensity on the receiving side.

[0106] Embodiment 3. In free-space optical communication between mobile bodies, it is necessary to control the beam based on the position information of the communication partner so that light can be received from each other. This is called initial acquisition.

[0107] One initial capture method is a beacon method that uses beacon light with a beam divergence angle and output power greater than that of communication light. For example, Patent Document 4 discloses a method that makes capture by a receiver easier by changing the divergence angle of light according to distance. While this beacon method can complete initial capture in a short time, it is disadvantageous in terms of SWaP (Size, Weight, and Power) because it requires a light source separate from the light source used for communication and a separate optical antenna for outputting the beacon. JP 2023-143242 A

[0108] On the other hand, there is another method called the beaconless method, which does not use a wide beam of high-intensity beacon light as described above, but instead uses communication light directly for initial acquisition. Initial acquisition using this beaconless method requires that the communication light be thoroughly swept within the error range of the communication partner's location information. Even if the error in location information remains constant, as the relative distance between the communication partner and the communication partner decreases, the angular range over which beam scanning must be performed widens, and beam sweeping takes time.

[0109] Therefore, in the spatial optical communication system according to the third embodiment, in order to solve the above-mentioned problems in the initial acquisition between spatial optical communication devices, a configuration is described that can shorten the sweep time by controlling the beam divergence angle.

[0110] Fig. 7 is a diagram showing an example of the configuration of a free-space optical communications system according to embodiment 3. In the free-space optical communications system according to embodiment 3 shown in Fig. 7, compared to the free-space optical communications system according to embodiment 1 shown in Fig. 1, the drive controller 1113-1, the acquisition and tracking sensor 1115-1, and the acquisition and tracking controller 1116-1 in free-space optical communications transceiver 11-1 are changed to drive controller 1113b-1, acquisition and tracking sensor 1115b-1, and acquisition and tracking controller 1116b-1, respectively, and the drive controller 1113-2, the acquisition and tracking sensor 1115-2, and the acquisition and tracking controller 1116-2 in free-space optical communications transceiver 11-2 are changed to drive controller 1113b-2, acquisition and tracking sensor 1115b-2, and acquisition and tracking controller 1116b-2, respectively. Other configuration examples of the free-space optical communication system according to embodiment 3 shown in Figure 7 are the same as the configuration example of the free-space optical communication system according to embodiment 1 shown in Figure 1, and the same symbols are used and their descriptions are omitted.

[0111] When establishing a spatial transmission path with the spatial optical communication transceiver 11-2, which is the communication partner, that is, when performing initial acquisition, the drive controller 1113b-1 determines whether the beam divergence angle of the transmitted light is 1 / L or 1 / L, where L is the distance between the communicating mobile bodies, based on the distance between the mobile bodies predicted by the attitude orbit control computer 12-1 and the information stored in the storage device 1114-1. ２ The drive amount of the drive mechanism 1112-1 is determined so that the change in the drive amount varies as follows: The drive controller 1113b-1 has the same functions as the drive controller 1113-1 shown in the first embodiment except for the above functions.

[0112] As shown in FIG. 7, the acquisition and tracking sensor 1115b-1 includes a coarse acquisition and tracking sensor 11151b-1 and a fine acquisition and tracking sensor 11152b-1.

[0113] The coarse acquisition and tracking sensor 11151b-1 is an acquisition and tracking sensor with a wider field of view than the fine acquisition and tracking sensor 11152b-1. This coarse acquisition and tracking sensor 11151b-1 detects the angle of arrival of the other received light based on the other received light obtained by the beam splitter 1110-1.

[0114] The fine acquisition and tracking sensor 11152b-1 has the same function as the acquisition and tracking sensor 1115-1 described in embodiment 1. That is, the fine acquisition and tracking sensor 11152b-1 detects the angle of arrival of the other received light based on the other received light obtained by the beam splitter 1110-1.

[0115] The acquisition and tracking controller 1116b-1 has an initial acquisition controller 11161b-1 and a tracking controller 11162b-1, as shown in FIG.

[0116] The initial acquisition controller 11161b-1 operates during initial acquisition. This initial acquisition controller 11161b-1 controls the angle of the gimbal 1109-1 based on position information of the mobile body on which the spatial optical communications device 1-2 is mounted, thereby directing the gimbal 1109-1 toward the spatial optical communications transceiver 11-2, which is the communication partner. The initial acquisition controller 11161b-1 then controls the tip-tilt mirror 1107-1 to spirally scan the transmitted light from the optical telescope 1108-1. The initial acquisition controller 11161b-1 also corrects the angle of the gimbal 1109-1 based on the angle of arrival of the received light detected by the coarse acquisition and tracking sensor 11151b-1.

[0117] The tracking controller 11162b-1 operates after the initial acquisition is completed. That is, the tracking controller 11162b-1 operates after the fine acquisition and tracking sensor 11152b-1 becomes able to detect the angle of arrival of the received light. This tracking controller 11162b-1 has the same function as the acquisition and tracking controller 1116-1 described in the first embodiment. That is, the tracking controller 11162b-1 controls the gimbal 1109-1 and the tip-tilt mirror 1107-1 based on the apparent angle predicted by the attitude and orbit control computer 12-1 and the angle of arrival of the received light detected by the fine acquisition and tracking sensor 11152b-1. That is, the tracking controller 11162b-1 controls the angle of the gimbal 1109-1 and the angle of the tip-tilt mirror 1107-1 to align the optical axis of the optical telescope 1108-1 with the optical axis of the optical telescope 1108-2 in the spatial optical communications transceiver 11-2 that communicates with the spatial optical communications transceiver 11-1.

[0118] When establishing a spatial transmission path with the spatial optical communication transceiver 11-1, which is the communication partner, i.e., when performing initial acquisition, the drive controller 1113b-2 determines whether the beam divergence angle of the transmitted light is 1 / L or 1 / L, where L is the distance between the communicating mobile bodies, based on the distance between the mobile bodies predicted by the attitude orbit control computer 12-2 and the information stored in the storage device 1114-2. ２ The drive amount of the drive mechanism 1112-2 is determined so that the change in the distance L1 varies as follows: The drive controller 1113b-2 has the same functions as the drive controller 1113-2 shown in the first embodiment except for the above functions.

[0119] As shown in FIG. 7, the acquisition and tracking sensor 1115b-2 includes a coarse acquisition and tracking sensor 11151b-2 and a fine acquisition and tracking sensor 11152b-2.

[0120] The coarse acquisition and tracking sensor 11151b-2 is an acquisition and tracking sensor with a wider field of view than the fine acquisition and tracking sensor 11152b-2. This coarse acquisition and tracking sensor 11151b-2 detects the angle of arrival of the other received light based on the other received light obtained by the beam splitter 1110-2.

[0121] The fine acquisition and tracking sensor 11152b-2 has the same function as the acquisition and tracking sensor 1115-2 described in embodiment 1. That is, the fine acquisition and tracking sensor 11152b-2 detects the angle of arrival of the other received light based on the other received light obtained by the beam splitter 1110-2.

[0122] As shown in FIG. 7, the acquisition and tracking controller 1116b-2 has an initial acquisition controller 11161b-2 and a tracking controller 11162b-2.

[0123] The initial acquisition controller 11161b-2 operates during initial acquisition. This initial acquisition controller 11161b-2 controls the angle of the gimbal 1109-2 based on position information of the mobile body on which the free-space optical communications device 1-1 is mounted, thereby directing the gimbal 1109-2 toward the free-space optical communications transceiver 11-1, which is the communication partner. The initial acquisition controller 11161b-2 then controls the tip-tilt mirror 1107-2 to spirally scan the transmitted light from the optical telescope 1108-2. The initial acquisition controller 11161b-2 also corrects the angle of the gimbal 1109-2 based on the angle of arrival of the received light detected by the coarse acquisition and tracking sensor 11151b-2.

[0124] The tracking controller 11162b-2 operates after the initial acquisition is completed. That is, the tracking controller 11162b-2 operates after the fine acquisition and tracking sensor 11152b-2 becomes able to detect the angle of arrival of the received light. This tracking controller 11162b-2 has the same function as the acquisition and tracking controller 1116-2 described in the first embodiment. That is, the tracking controller 11162b-2 controls the gimbal 1109-2 and the tip-tilt mirror 1107-2 based on the apparent angle predicted by the attitude and orbit control computer 12-2 and the angle of arrival of the received light detected by the fine acquisition and tracking sensor 11152b-2. That is, the tracking controller 11162b-2 controls the angle of the gimbal 1109-2 and the angle of the tip-tilt mirror 1107-2 to align the optical axis of the optical telescope 1108-2 with the optical axis of the optical telescope 1108-1 in the spatial optical communications transceiver 11-1 that communicates with the spatial optical communications transceiver 11-2.

[0125] Here, in the initial acquisition for establishing a spatial transmission path between the spatial optical communication transceivers 11-1 and 11-2, the angular error range (θ ｍａｘ ) has a relationship with the relative distance (L) as shown in FIG. 8 and the following formula (4), assuming that the position estimation error of the partner free-space optical communications device 1 is constant. FIG. 8 shows a case where the position estimation error of the partner free-space optical communications device 1 is 10 km.

[0126] In addition, the beam divergence angle (θ ｔ When the beam is scanned with the constant θ ｍａｘ Since it is proportional to the square of , the relationship shown in the following formula (5) holds: That is, the shorter the relative distance, the longer the time required for beam scanning.

[0127] In addition, the beam sweep speed is kept constant, and the angular error range is set to θ ｍａｘ Then, the beam divergence angle (θ ｔ ), the time (τ) required for beam scanning has the relationship shown in FIG. 9 and the following equation (6).

[0128] Here, the beam divergence angle (θ ｔ ) is expanded based on the following equation (7) (first case).

[0129] In this case, if the beam sweep speed is constant, θ ｍａｘ The effect of the beam divergence angle (θ ｔ ) depending on the relative distance, the relationship shown in the following equation (8) is obtained. Originally, as shown in equation (5), the time (τ) required for beam scanning depending on the distance variation (L) is 1 / L ２ Since the time required for the measurement was increasing, it can be expected that the time required for the measurement will be reduced.

[0130] Next, the beam divergence angle (θ ｔ ) based on the following equation (9) (second case). In this case, the time (τ) required for beam scanning can be kept constant.

[0131] In Fig. 9, the mark indicated by the reference numeral 51 represents the transmitted light beam used for beam scanning. The reference numeral 52 represents the angular error range. Fig. 9A shows the case where the angular error range is 1 mrad, and Figs. 9B and 9C show the case where the angular error range is 1.5 mrad. As shown in Fig. 9B, when the angular error range is wider than that of Fig. 9A, scanning using a narrow transmitted light beam takes a long time for beam scanning. In contrast, as shown in Fig. 9C, the time required for beam scanning can be shortened by enlarging the transmitted light beam in accordance with the angular error range.

[0132] So far, we have explained the time (τ) required for beam scanning, but we will also explain the beam divergence angle (θ ｔ ) also affects the feasibility of the free-space optical communication system. Here, we consider the free-space propagation loss and the transmitting antenna gain, which vary depending on the distance, while assuming that the loss of the internal optical system of the free-space optical communication device 1 and the receiving antenna gain do not change.

[0133] The free space propagation loss (L ｐａｓｓ ) can be expressed by the following equation (10) using wavelength (λ) and relative distance (L).

[0134] In addition, the transmit antenna gain (G Ｔ ) and beam divergence angle (θ ｔ ) have the relationships shown in the following equations (11) and (12).

[0135] Therefore, the beam divergence angle (θ ｔ ) is constant, the free space propagation loss and the transmitting antenna gain are combined to form the following relationship (13):

[0136] Next, two cases (first and second cases) where the beam divergence angle is variable will be considered. In the first case, the beam divergence angle is changed according to the relationship of equation (7), and therefore equation (14) below is obtained from equations (7) and (13), and the received light intensity detected by the acquisition and tracking sensor 1115b can be kept constant.

[0137] In the second case, the beam divergence angle is changed according to the relationship of Equation (9), and therefore Equation (15) below is obtained from Equations (9) and (13), and the received light intensity decreases when the distance is short. Therefore, it is necessary to ensure that the received light intensity at acquisition and tracking sensor 1115b does not become saturated or insufficient within the range in which the line is desired to be established.

[0138] As described above, in both the first and second cases, the initial acquisition time can be reduced compared to when the beam divergence angle is not varied. In the first case, the time (τ) required for beam scanning varies at 1 / L, and the received light intensity detected by the acquisition and tracking sensor 1115b is constant. In the second case, the time (τ) required for beam scanning is constant, and the received light intensity detected by the acquisition and tracking sensor 1115b is constant. ２ It changes with.

[0139] The beam divergence angle is the pointing error loss (L ｐ ) also contributes to the pointing error loss. ｐ ), it can be expressed as the following equation (16). ｔ ) tends to reduce losses, so it does not affect the establishment of a line.

[0140] Next, an example of operation during initial acquisition by the free-space optical communications system according to embodiment 3 will be described with reference to Fig. 10 and Fig. 11. First, an example of operation during initial acquisition by the free-space optical communications transceiver 11-1 according to embodiment 3 will be described with reference to Fig. 10. Note that the free-space optical communications transceiver 11-1 starts control at the same time as the free-space optical communications transceiver 11-2.

[0141] In an example of the operation of the spatial optical communications transceiver 11-1 of this embodiment 3 during initial acquisition, as shown in FIG. 10, the acquisition and tracking controller 1116b-1 first operates the initial acquisition controller 11161b-1 (step ST101).

[0142] Next, the attitude orbit control computer 12-1 predicts the distance between the communicating mobile bodies based on the position information of the mobile body on which the spatial optical communication device 1-1 is mounted and the position information of the mobile body on which the spatial optical communication device 1-2 is mounted (step ST102).

[0143] Furthermore, the initial capture controller 11161b-1 controls the angle of the gimbal 1109-1 based on the position information of the mobile body on which the free-space optical communications device 1-2 is mounted, thereby directing the gimbal 1109-1 toward the free-space optical communications transceiver 11-2, the communication partner (step ST103). At this time, an angle error occurs based on a position estimation error of the free-space optical communications transceiver 11-2 of the other party. Therefore, in this state, a free-space transmission path cannot be established between the free-space optical communications transceivers 11-1 and 11-2. Therefore, initial capture is performed by performing beam scanning of the transmitted light.

[0144] Next, the drive controller 1113b-1 determines whether the beam divergence angle of the transmitted light is 1 / L or 1 / L, where L is the distance between the mobile objects communicating with each other, based on the distance between the mobile objects predicted by the attitude orbit control computer 12-1 and the information stored in the storage device 1114-1. ２ In other words, when performing beam scanning, the beam divergence angle of the light transmitted from the optical telescope 1108-1 is controlled so that the condition of the first case or the second case is satisfied.

[0145] Next, the initial acquisition controller 11161b-1 controls the tip-tilt mirror 1107-1 to spirally scan the transmitted light from the optical telescope 1108-1 (step ST105). The above scanning process is repeated, for example, four or five times. In other words, by repeating the above scanning process multiple times, the probability of receiving light at the coarse acquisition and tracking sensor 11151b-2 of the communication partner, the free-space optical communications device 1-2, is improved, thereby ensuring reliable light reception.

[0146] Next, while the transmitted light is being spirally scanned in the spatial optical communications device 1-2, which is the communication partner, the coarse acquisition and tracking sensor 11151b-1 detects the angle of arrival of the received light based on the other received light obtained by the beam splitter 1110-1 (step ST106). Note that it is desirable for the coarse acquisition and tracking sensor 11151b-1 to have a wide field of view so that it can receive the transmitted light from the spatial optical communications transceiver 11-2, which is the communication partner, even if there is a large angle error during initial acquisition. Therefore, the coarse acquisition and tracking sensor 11151b-1 is, for example, a sensor with a large number of elements, such as an image sensor, that can ensure a wide field of view.

[0147] Next, the initial acquisition controller 11161b-1 corrects the angle of the gimbal 1109-1 based on the angle of arrival of the received light detected by the coarse acquisition and tracking sensor 11151b-1 (step ST107), thereby reducing the pointing error of the optical telescope 1108-1 with respect to the free-space optical communications transceiver 11-2.

[0148] Next, the fine acquisition and tracking sensor 11152b-1 detects the angle of arrival of the other received light based on the other received light obtained by the beam splitter 1110-1 (step ST108). If the fine acquisition and tracking sensor 11152b-1 cannot detect the angle of arrival of the received light in step ST108, the sequence returns to step ST105.

[0149] On the other hand, if the fine acquisition and tracking sensor 11152b-1 is able to detect the angle of arrival of the received light in step ST108, the acquisition and tracking controller 1116b-1 operates the tracking controller 11162b-1 (step ST109). That is, if the fine acquisition and tracking sensor 11152b-1 is able to detect the angle of arrival of the received light, it is determined that initial acquisition has been completed, and a spatial transmission path is established. Then, the controller operated by the acquisition and tracking controller 1116b-1 is switched from the initial acquisition controller 11161b-1 to the tracking controller 11162b-1.

[0150] Next, the tracking controller 11162b-1 controls the gimbal 1109-1 and the tip-tilt mirror 1107-1 based on the expected angle predicted by the attitude orbit control computer 12-1 and the angle of arrival of the received light detected by the fine acquisition and tracking sensor 11152b-1 (step ST110). Thereafter, the free-space optical communications transceiver 11-1 continues to control the free-space optical communications transceiver 11-2 to track it. As a result, a free-space transmission path is continuously established.

[0151] Next, an example of the operation of the free-space optical communications transceiver 11-2 according to the third embodiment during initial acquisition will be described with reference to Fig. 11. The free-space optical communications transceiver 11-2 starts control at the same time as the free-space optical communications transceiver 11-1.

[0152] In an example of the operation of the spatial optical communications transceiver 11-2 of this embodiment 3 during initial acquisition, as shown in FIG. 11, the acquisition and tracking controller 1116b-2 first operates the initial acquisition controller 11161b-2 (step ST201).

[0153] Next, the attitude orbit control computer 12-2 predicts the distance between the communicating mobile bodies based on the position information of the mobile body on which the spatial optical communication device 1-1 is mounted and the position information of the mobile body on which the spatial optical communication device 1-2 is mounted (step ST202).

[0154] Furthermore, the initial capture controller 11161b-2 controls the angle of the gimbal 1109-2 based on the position information of the mobile body on which the free-space optical communications device 1-1 is mounted, thereby directing the gimbal 1109-2 toward the free-space optical communications transceiver 11-1, the communication partner (step ST203). At this time, an angle error occurs based on a position estimation error of the free-space optical communications transceiver 11-1 of the other party. Therefore, in this state, a free-space transmission path cannot be established between the free-space optical communications transceivers 11-1 and 11-2. Therefore, initial capture is performed by performing beam scanning of the transmitted light.

[0155] Next, the drive controller 1113b-2 determines whether the beam divergence angle of the transmitted light is 1 / L or 1 / L, where L is the distance between the mobile objects communicating with each other, based on the distance between the mobile objects predicted by the attitude orbit control computer 12-2 and the information stored in the storage device 1114-2. ２ In other words, when performing beam scanning, the beam divergence angle of the light transmitted from the optical telescope 1108-2 is controlled so that the condition of the first case or the second case is satisfied.

[0156] Next, while the transmitted light is being spirally scanned in the spatial optical communications device 1-1, which is the communication partner, the coarse acquisition and tracking sensor 11151b-2 detects the angle of arrival of the received light based on the other received light obtained by the beam splitter 1110-2 (step ST205). Note that it is desirable for the coarse acquisition and tracking sensor 11151b-2 to have a wide field of view so that it can receive the transmitted light from the spatial optical communications transceiver 11-1, which is the communication partner, even if there is a large angle error during initial acquisition. Therefore, the coarse acquisition and tracking sensor 11151b-2 is, for example, a sensor with a large number of elements, such as an image sensor, that can ensure a wide field of view.

[0157] Next, the initial acquisition controller 11161b-2 corrects the angle of the gimbal 1109-2 based on the angle of arrival of the received light detected by the coarse acquisition and tracking sensor 11151b-2 (step ST206), thereby reducing the pointing error of the optical telescope 1108-2 with respect to the free-space optical communications transceiver 11-1.

[0158] Next, the initial acquisition controller 11161b-2 controls the tip-tilt mirror 1107-2 to spirally scan the transmitted light from the optical telescope 1108-2 (step ST207). The above scanning process is repeated, for example, four or five times. In other words, by repeating the above scanning process multiple times, the probability of receiving light at the coarse acquisition and tracking sensor 11151b-1 of the communication partner, the free-space optical communications device 1-1, is improved, thereby ensuring reliable light reception.

[0159] In addition, since the free-space optical communications transceiver 11-1 performs beam scanning first in step ST105 shown in Fig. 10, the angle formed by the optical axis of the optical telescope 1108-1 and the optical axis of the optical telescope 1108-2 is small. Therefore, in general, the scan range in step ST207 shown in Fig. 11 can be made smaller than the scan range in step ST105 shown in Fig. 10.

[0160] Next, the fine acquisition and tracking sensor 11152b-2 detects the angle of arrival of the other received light based on the other received light obtained by the beam splitter 1110-2 (step ST208). If the fine acquisition and tracking sensor 11152b-2 cannot detect the angle of arrival of the received light in step ST208, the sequence returns to step ST205.

[0161] On the other hand, if the fine acquisition and tracking sensor 11152b-2 is able to detect the angle of arrival of the received light in step ST208, the acquisition and tracking controller 1116b-2 operates the tracking controller 11162b-2 (step ST209). That is, if the fine acquisition and tracking sensor 11152b-2 is able to detect the angle of arrival of the received light, it is determined that initial acquisition has been completed, and a spatial transmission path is established. Then, the controller operated by the acquisition and tracking controller 1116b-2 is switched from the initial acquisition controller 11161b-2 to the tracking controller 11162b-2.

[0162] Next, the tracking controller 11162b-2 controls the gimbal 1109-2 and the tip-tilt mirror 1107-2 based on the expected angle predicted by the attitude orbit control computer 12-2 and the angle of arrival of the received light detected by the fine acquisition and tracking sensor 11152b-2 (step ST210). Thereafter, the free-space optical communications transceiver 11-2 continues to control the free-space optical communications transceiver 11-1 to track it. As a result, a free-space transmission path is continuously established.

[0163] In the above description, the case where the free-space optical communications transceiver 11-1 performs beam scanning first has been shown, but the free-space optical communications transceiver 11-2 may perform beam scanning first.

[0164] In the above description, the drive controller 1113, the acquisition and tracking sensor 1115, and the acquisition and tracking controller 1116 in the free-space optical communication system according to the first embodiment shown in Fig. 1 are replaced with the drive controller 1113b, the acquisition and tracking sensor 1115b, and the acquisition and tracking controller 1116b, respectively. However, the present invention is not limited to this, and the drive controller 1113, the acquisition and tracking sensor 1115, and the acquisition and tracking controller 1116 in the free-space optical communication system according to the second embodiment shown in Fig. 6 may be replaced with the drive controller 1113b, the acquisition and tracking sensor 1115b, and the acquisition and tracking controller 1116b, respectively, with the same effects as those described above being obtained.

[0165] As described above, according to the third embodiment, when establishing a spatial transmission path with the free-space optical communications transceiver 11, the drive controller 1113b determines the drive amount of the drive mechanism 1112 so that the beam divergence angle of the transmitted light changes by 1 / L when the distance between the own device and the free-space optical communications transceiver 11, the communication partner, is L, and the acquisition and tracking controller 1116b performs spiral scanning of the transmitted light by controlling the tip-tilt mirror 1107 when establishing a spatial transmission path with the free-space optical communications transceiver 11, the communication partner. Also, according to the third embodiment, when establishing a spatial transmission path with the free-space optical communications transceiver 11, the drive controller 1113b determines the drive amount of the drive mechanism 1112 so that the beam divergence angle of the transmitted light changes by 1 / L when the distance between the own device and the free-space optical communications transceiver 11, the communication partner, is L. ２The acquisition and tracking controller 1116b determines the drive amount of the drive mechanism 1112 so that the beam divergence angle varies depending on the distance between the OHPA 1103 and the mobile station, and the acquisition and tracking controller 1116b controls the tip-tilt mirror 1107 to perform spiral scanning of the transmitted light when establishing a spatial transmission path with the mobile station. As a result, the mobile station 11 according to the third embodiment can shorten the initial acquisition time of the mobile station 1 by controlling the beam divergence angle, compared to the mobile stations 1 according to the first and second embodiments. That is, in the free-space optical communication system according to the third embodiment, the divergence angle of the output light of the collimator 1105 is adjusted by varying the distance between the collimator lens 11052 of the collimator 1105, which outputs the output light of the OHPA 1103 into space, and the fiber connector 11051. In the free-space optical communication system according to the third embodiment, the divergence angle is changed depending on the distance between the mobile stations, and the angle error range is thoroughly swept. As a result, in the free-space optical communication system according to the third embodiment, it is possible to reduce the sweep time during initial acquisition.

[0166] Finally, with reference to FIG. 12 , an example of the hardware configuration of the free-space optical communications transceiver 11 according to embodiments 1 to 3 will be described. Below, an example of the hardware configuration of the free-space optical communications transceiver 11 according to embodiment 1 will be described, but the same applies to the example of the hardware configuration of the free-space optical communications transceiver 11 according to embodiments 2 and 3. The functions of the OHPA controller 1104-1, drive controller 1113-1, and acquisition and tracking controller 1116-1 in the free-space optical communications transceiver 11 are realized by a processing circuit 51. The processing circuit 51 may be dedicated hardware as shown in FIG. 12A , or may be a CPU (also referred to as a central processing unit, processing device, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor)) 52 that executes a program stored in a memory 53 as shown in FIG. 12B .

[0167] When the processing circuitry 51 is dedicated hardware, the processing circuitry 51 may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. The functions of the OHPA controller 1104-1, the drive controller 1113-1, and the acquisition and tracking controller 1116-1 may be realized individually by the processing circuitry 51, or the functions of the respective units may be realized collectively by the processing circuitry 51.

[0168] When the processing circuit 51 is a CPU 52, the functions of the OHPA controller 1104-1, drive controller 1113-1, and acquisition and tracking controller 1116-1 are realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in memory 53. The processing circuit 51 realizes the functions of each unit by reading and executing the programs stored in memory 53. In other words, the free-space optical communications transceiver 11 includes memory 53 for storing programs that, when executed by the processing circuit 51, result in the processing of each component. These programs can also be said to cause a computer to execute the procedures and methods of the OHPA controller 1104-1, drive controller 1113-1, and acquisition and tracking controller 1116-1. Here, examples of the memory 53 include non-volatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, and EEPROM, as well as magnetic disks, flexible disks, optical disks, compact disks, minidisks, and DVDs.

[0169] It is also possible to realize some of the functions of the OHPA controller 1104-1, the drive controller 1113-1, and the acquisition and tracking controller 1116-1 with dedicated hardware and some with software or firmware. For example, the functions of the OHPA controller 1104-1 can be realized by the processing circuit 51 as dedicated hardware, and the functions of the drive controller 1113-1 and the acquisition and tracking controller 1116-1 can be realized by the processing circuit 51 reading and executing programs stored in the memory 53.

[0170] In this way, the processing circuitry 51 can realize each of the above-described functions by hardware, software, firmware, or a combination of these.

[0171] It should be noted that the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted.

[0172] The spatial optical communications transceiver according to the present disclosure can accommodate variations in the distance of the spatial transmission path without electrical gain variation, and is suitable for use as a spatial optical communications transceiver mounted on a mobile body for transmitting data.

[0173] 1-1, 1-2 spatial optical communication device, 11-1, 11-2 spatial optical communication transceiver, 12-1, 12-2 attitude orbit control computer, 51 processing circuit, 52 CPU, 53 memory, 1101-1, 1101-2 light source, 1102-1, 1102-2 optical modulator, 1103-1, 1103-2 OHPA, 1104-1, 1104-2 OHPA controller, 1105-1, 1105-2 collimator, 1106-1, 1106-2 dichroic mirror, 1107-1, 1107-2 tip-tilt mirror, 1108-1, 1108-2 optical telescope, 1109-1, 1109-2 gimbal, 1110-1, 1110-2 Beam splitter, 1111-1, 1111-2 Optical demodulator, 1112-1, 1112-2 Drive mechanism, 1113-1, 1113b-1, 1113-2, 1113b-2 Drive controller, 1114-1, 1114-2 Storage device, 1115-1, 1115b-1, 1115-2, 1115b-2 Acquisition and tracking sensor, 1116-1, 1116b-1, 1116-2, 1116b-2 Acquisition and tracking controller, 1117-1, 1117-2 Wavefront measuring device, 11051-1, 11051-2 Fiber connector, 11052-1, 11052-2 Collimator lens, 11053-1 Linear actuator, 11054-1 Piezo element, 11081-1 collimator side lens, 11082-1 ​​spatial transmission path side lens, 11151b-1, 11151b-2 coarse acquisition and tracking sensors, 11152b-1, 11152b-2 fine acquisition and tracking sensors, 11161b-1, 11161b-2 initial acquisition controllers, 11162b-1, 11162b-2 tracking controllers.

Claims

1. A spatial optical communications transceiver comprising: a light source which generates laser light; an optical modulator which superimposes a communication signal on the laser light generated by said light source; an optical amplifier which amplifies the laser light superimposed by said optical modulator; a collimator which has a fiber connector and a collimator lens, converts the laser light amplified by said optical amplifier into spatial light and radiates transmission light which is the spatial light; an optical telescope which expands the beam width of the transmission light radiated by said collimator and radiates it to a spatial transmission path; a drive mechanism which can adjust the focal length of said collimator lens; and a drive controller which determines the drive amount of said drive mechanism so that the product of a free space loss calculated from the distance between said transceiver and the spatial optical communications transceiver which is the communication partner, and a transmission gain determined by the beam divergence angle of the transmission light, is constant.

2. The free-space optical communications transceiver according to claim 1, characterized in that the end of the fiber connector is provided with a piezoelectric element that can move along the optical axis, and the driving mechanism adjusts the focal length of the collimator lens by driving the piezoelectric element.

3. The free-space optical communications transceiver according to claim 1, characterized in that the collimator lens is a lens whose focal length changes when a voltage is applied to it, and the driving mechanism adjusts the focal length of the collimator lens by applying a voltage to the collimator lens.

4. The free-space optical communications transceiver according to claim 1, further comprising a wavefront measuring device that detects the beam divergence angle of the transmitted light radiated by the collimator, and wherein, when the beam divergence angle of the transmitted light measured by the wavefront measuring device has an error with respect to a target value, the drive controller corrects the drive amount of the drive mechanism so as to cancel out the error.

5. A free-space optical communications transceiver as claimed in claim 1 or claim 4, characterized in that it comprises: a gimbal capable of adjusting the optical axis direction of the optical telescope; a tip-tilt mirror capable of adjusting the angle in two axial directions of the transmitted light emitted by the collimator; an optical demodulator that demodulates a communication signal from the received light received by the optical telescope; an acquisition and tracking sensor that detects the angle of arrival of the received light received by the optical telescope; and an acquisition and tracking controller that aligns the optical axis of the optical telescope with that of the free-space optical communications transceiver that is the communication partner by controlling the gimbal and the tip-tilt mirror based on the apparent angle, which is the relative direction of the free-space optical communications transceiver to the own device, and the angle of arrival detected by the acquisition and tracking sensor.

6. The spatial optical communications transceiver according to claim 5, characterized in that, when establishing a spatial transmission path with a spatial optical communications transceiver that is a communication partner, the drive controller determines the drive amount of the drive mechanism so that the beam divergence angle of the transmitted light changes by 1 / L when the distance between the transceiver itself and the spatial optical communications transceiver that is the communication partner is L, and, when establishing a spatial transmission path with the spatial optical communications transceiver that is the communication partner, the acquisition and tracking controller controls the tip-tilt mirror to perform spiral scanning of the transmitted light.

7. When the drive controller establishes a spatial transmission path with a spatial optical communication transceiver that is a communication partner, the beam divergence angle of the transmitted light is 1 / L, where L is the distance between the drive controller and the spatial optical communication transceiver that is the communication partner. ２ and the acquisition and tracking controller determines a drive amount of the drive mechanism so that the drive amount changes according to a distance between the optical fiber and the communication partner, and controls the tip-tilt mirror to perform spiral scanning of the transmitted light when establishing a spatial transmission path with the communication partner, the communication partner, of the optical fiber.

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