Spatial optical communication transceiver

Abstract

The present invention comprises: a light source (1101) that generates laser light; a light 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 light modulator (1102); a collimator (1105) that has a fiber connector (11051) and a collimator lens (11052), that converts the laser light amplified by the OHPA (1103) into spatial light, and that radiates transmitted light constituting the spatial light; an optical telescope (1108) that enlarges the beam width of the transmitted light radiated by the collimator (1105) and radiates the transmitted light along 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 the drive amount of the drive mechanism (1112) so as to render constant the product of free space loss, which is calculated from the distance between a host device and a spatial optical communication transceiver (11) serving as a communication partner, and transmission gain determined by a beam divergence angle of the transmitted light.

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] FIG. 2A is a diagram illustrating an example of the configuration of a free-space optical communication system according to a first embodiment. FIG. 2A and FIG. 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 according to the first embodiment, in which FIG. 2A is a diagram illustrating an example of a case where the position of the collimator lens is not adjusted, and FIG. 2B is a diagram illustrating an example of a case where the position of the collimator lens is adjusted. FIG. 2B is a diagram illustrating an example of a configuration of a collimator according to the first embodiment, in which the collimator lens is moved. FIG. 2C is a diagram illustrating an example of a configuration of a collimator according to the first embodiment, in which the end of a fiber connector is moved. FIG. 2D is a diagram illustrating an example of a configuration of a collimator according to the first embodiment, in which an electro-optic material is used in the collimator lens portion. FIG. 7A and FIG. 7B are diagrams illustrating an example of the hardware configuration of a free-space optical communication transceiver according to the first and second embodiments.

[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, the optical demodulator 1111-2 performs photoelectric conversion on the received light in an internal photoelectric converter, demodulating 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] Finally, with reference to FIG. 7 , an example of the hardware configuration of the free-space optical communications transceiver 11 according to the first and second embodiments will be described. Below, an example of the hardware configuration of the free-space optical communications transceiver 11 according to the first embodiment will be described, but the same applies to the example of the hardware configuration of the free-space optical communications transceiver 11 according to the second embodiment. 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. 7A , 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. 7B .

[0107] 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.

[0108] 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.

[0109] 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.

[0110] In this way, the processing circuitry 51 can realize each of the above-described functions by hardware, software, firmware, or a combination of these.

[0111] 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.

[0112] 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.

[0113] 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, 1113-2 drive controller, 1114-1, 1114-2 memory device, 1115-1, 1115-2 acquisition and tracking sensor, 1116-1, 1116-2 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 piezoelectric element, 11081-1 collimator side lens, 11082-1 ​​spatial transmission path side lens.

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.

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