Space 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

Technical Field

[0001] The present disclosure relates to a space optical communication transceiver mounted on a moving body for data transmission.

Background Art

[0002] Space optical communication has a very high carrier frequency of terahertz or higher and can secure a wide bandwidth. In addition, space optical communication has high directivity in space propagation. For these reasons, space optical communication is expected to be used for long-distance high-speed communication.

[0003] On the other hand, in a space optical communication transceiver mounted on a moving body, when considering maintaining a communication path in the case of a wide distance variation from a short distance to a long distance, there is a possibility that a loss variation exceeding the dynamic range of a light receiver such as a photoelectric converter or a capture and tracking sensor in an optical demodulator may occur. Here, the dynamic range represents the ratio of the minimum received light intensity to the saturation intensity.

[0004] The free space loss in the space transmission path of optical space communication varies with the square of the propagation distance. Therefore, for example, when the distance of the 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] On the other hand, in the device disclosed in Patent Document 1, for example, by adjusting the space optical attenuator on the receiving side, the incident light amount on the light receiving element is corrected, the light receiving sensitivity of the light receiving element is corrected, and the gain of the amplifier circuit after light reception is changed. Thereby, this device corrects the change in the incident light amount in a wide range.

[0006] However, in this device, the components on the receiver side increase and the configuration becomes complicated. In addition, in this device, the adjustment range of the light amount depends on the attenuation rate that can be realized by the variable attenuator. Therefore, in this device, in long-distance optical communication, the loss of the internal optical system on the receiver side increases, deteriorating the line establishment performance.

[0007] Also, as a method for coping with distance fluctuations in a spatial transmission path, a method of electrically controlling the gain of the OHPA (Optical High Power Amplifier) of a space optical communication transceiver is also conceivable. That is, the drive current or injection current of the pump light of the OHPA is changed by an OHPA controller to control the gain of the OHPA. However, in a high-gain OHPA, it is difficult to perform electrical control near the gain threshold. Also, when performing gain control in the high-gain direction, ASE (Amplified Spontaneous Emission) is induced and the NF (Noise Figure) deteriorates, causing fluctuations in the S / N of the communication path.

[0008] On the other hand, in the devices disclosed in Patent Document 2 or Patent Document 3, for example, by controlling the distance between the spatial optical systems or the position of the condenser lens in the optical axis direction, the coupling efficiency of the spatial light to the fiber is changed, and the intensity of the optical signal is increased or decreased. As a result, in this device, in the OHPA, particularly in the fiber amplifier, electrical control is not required and the output optical intensity of the OHPA can be adjusted.

[0009] However, in this device, it is configured to couple the spatial light to the fiber again. Therefore, in this device, surplus light when adjusting the output optical intensity is locally irradiated outside the fiber core, which may damage the fiber.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] As described above, when using a variable attenuator on the receiver side to expand the communication distance of a free-space optical communication device, the internal optical system loss increases and the line establishment performance deteriorates. Further, when electrically controlling the gain of the optical amplifier of the transmitter to expand the communication distance of the free-space optical communication device, it is difficult to perform electrical control near the gain threshold, and S / N fluctuations in the communication path occur due to changes in the noise characteristics when the gain is changed.

[0012] The present disclosure has been made to solve the above problems, and an object thereof is to provide a free-space optical communication transceiver that can cope with distance fluctuations in a free-space transmission path without performing electrical gain variation.

Means for Solving the Problems

[0013] The free-space optical communication transceiver according to the present disclosure includes 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 after superimposition by the optical modulator, a fiber connector and a collimator lens, a collimator that converts the laser light amplified by the optical amplifier into free-space light and emits the transmitted light that is the free-space light, a telescope that expands the beam width of the transmitted light emitted by the collimator and emits it to the free-space transmission path, a drive mechanism capable of adjusting 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 own device and the free-space optical communication transceiver that is the communication partner and the transmission gain determined by the beam divergence angle of the transmitted light is constant.

Effects of the Invention

[0014] According to the present disclosure, since it is configured as described above, it is possible to cope with distance fluctuations in a free-space transmission path without performing electrical gain variation.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments will be described in detail with reference to the drawings. Embodiment 1. FIG. 1 is a diagram showing a configuration example 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, two-way communication is performed between the free-space optical communication device 1-1 and the free-space optical communication device 1-2. Here, when it is necessary to distinguish between the free-space optical communication device 1 and the configurations of the free-space optical communication device 1, a suffix (-1, -2) is added to the reference numeral for indication.

[0017] The free-space optical communication device 1-1 is mounted on a moving body and communicates with a free-space optical communication device 1-2 that is a communication partner. Note that the free-space optical communication device 1-1 according to Embodiment 1 has a function of making the light intensity of the transmitted light received by the free-space optical communication device 1-2, which is a communication partner, constant even when there is a distance variation in the free-space transmission path, and establishing a stable free-space optical communication path. As shown in FIG. 1, this free-space optical communication device 1-1 includes a free-space optical communication transceiver 11-1 and an attitude and orbit control computer 12-1.

[0018] As shown in FIG. 1, the free-space 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 chip 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 storage device 1114-1, a capture and tracking sensor 1115-1, and a capture and tracking controller 1116-1.

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

[0020] The optical modulator 1102-1 superimposes the transmission data 101-1 on the laser light generated by the light source 1101-1. Note that the transmission data 101-1 is a communication signal input from outside the space optical communication transceiver 11-1. The laser light after being superimposed by this optical modulator 1102-1 is output to the OHPA 1103-1. Note that, as the method of optical modulation by the optical modulator 1102-1, for example, OOK (On-Off Keying) by intensity modulation of light, or PSK (Phase Shift Keying) by phase modulation of light, etc. can be mentioned, and it can be appropriately selected.

[0021] The OHPA 1103-1 is an optical amplifier with fibers for input and output. This OHPA 1103-1 amplifies the optical intensity of the laser light after being superimposed by the optical modulator 1102-1. The laser light after being amplified by this OHPA 1103-1 is output to the collimator 1105-1. As this OHPA 1103-1, for example, a fiber amplifier such as an erbium-doped fiber amplifier (EDFA: Erbium Doped Fiber Amplifier), or a semiconductor optical amplifier (SOA: Semiconductor Optical Amplifier) can be mentioned. In a fiber amplifier, signal light is amplified when pump light is injected into the fiber. Also, in a semiconductor optical amplifier, signal light is amplified by current injection.

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

[0023] The collimator 1105-1 converts the laser light after amplification by the OHPA 1103-1 into spatial light close to parallel light and emits the transmitted light, which is this spatial light. The transmitted light emitted by this collimator 1105-1 is output to the optical telescope 1108-1 via the dichroic mirror 1106-1 and the chip tilt mirror 1107-1. This collimator 1105-1 is usually composed of a fiber connector 11051-1 and a collimator lens 11052-1. And this collimator 1105-1 makes the output light from the collimator lens 11052-1 into parallel light, that is, collimated light, by setting the distance between the end of the fiber connector 11051-1 and the collimator lens 11052-1 to be the focal length of the collimator lens 11052-1.

[0024] The dichroic mirror 1106-1 separates the transmitted light emitted by the collimator 1105-1 and the received light reflected by the chip tilt mirror 1107-1 by wavelength. That is, the dichroic mirror 1106-1 transmits the transmitted light emitted by the collimator 1105-1 and reflects the received light reflected by the chip tilt mirror 1107-1. The transmitted light that has passed through this dichroic mirror 1106-1 is output to the chip tilt mirror 1107-1, and the received light reflected by the dichroic mirror 1106-1 is output to the beam splitter 1110-1.

[0025] The chip tilt mirror 1107-1 is a mirror capable of adjusting the angles in the biaxial directions in the transmitted light and the received light. And the chip tilt mirror 1107-1 reflects the transmitted light that has passed through the dichroic mirror 1106-1 and reflects the received light received by the optical telescope 1108-1. The transmitted light reflected by this chip tilt mirror 1107-1 is output to the optical telescope 1108-1, and the received light reflected by the optical telescope 1108-1 is output to the dichroic mirror 1106-1.

[0026] The chip tilt mirror 1107-1 controls the angles of both the transmitted light and the received light with the same mirror. On the other hand, when the distance between the space optical communication transceivers 11 is long, in addition to the chip tilt mirror 1107-1, a chip tilt mirror for independently controlling only the angle of the transmitted light may be added separately. When the distance of the space transmission path is long, while the light propagates through the space transmission path, the space optical communication device 1-2, which is the communication partner mounted on the moving body, moves. Therefore, based on the received light from the communication partner, when the pointing direction of the communication partner is specified and the pointing control of the transmitted light is performed, a pointing error corresponding to the movement of the moving body during the time when the light travels to and fro through the space transmission path occurs. This is called optical aberration. In order to correct this optical aberration, a chip tilt mirror for optical aberration correction 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 transmitted light reflected by the chip tilt mirror 1107-1 and radiates it into the space transmission path. Also, the optical telescope 1108-1 receives the transmitted light radiated by the optical telescope 1108-2 in the opposing space optical communication transceiver 11-2 as received light.

[0028] The gimbal 1109-1 is a device capable of adjusting the optical axis direction of the optical telescope 1108-1.

[0029] The beam splitter 1110-1 bifurcates the received light reflected by the dichroic mirror 1106-1. One of the received lights obtained by this beam splitter 1110-1 is output to the optical demodulator 1111-1, and the other received light is output to the 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 and demodulates the communication signal. The communication signal demodulated by this optical demodulator 1111-1 is output to the outside as received data 102-1.

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

[0032] The drive controller 1113-1 performs drive control of the drive mechanism 1112-1 based on the distance between the moving bodies predicted by the attitude trajectory computer 12-1 and the information stored in the storage device 1114-1. At this time, based on the distance between the moving bodies predicted by the attitude trajectory computer 12-1, the drive controller 1113-1 determines the drive amount of the drive mechanism 1112-1 such 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 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 space transmission path.

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

[0035] In addition, in FIG. 1, the case where the storage device 1114-1 is provided inside the space optical communication transceiver 11-1 is shown. However, it is not limited to this, and the storage device 1114-1 may be provided outside the space optical communication transceiver 11-1.

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

[0037] The acquisition and tracking controller 1116-1 controls the gimbal 1109-1 and the chip tilt mirror 1107-1 based on the expected angle predicted by the attitude and orbit control computer 12-1 and the arrival angle of the received light detected by the acquisition and tracking sensor 1115-1. That is, the acquisition and tracking controller 1116-1 controls the angle of the gimbal 1109-1 and the angle of the chip 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 space optical communication transceiver 11-2 that communicates with the space optical communication transceiver 11-1.

[0038] The attitude and orbit control computer 12-1 predicts the expected angle based on the attitude and position information of the moving body on which the space optical communication device 1-1 is mounted and the position information of the moving body on which the space optical communication device 1-2 is mounted, and predicts the distance between the moving bodies that communicate. The expected angle is the relative direction of the space optical communication transceiver 11-2 with respect to the space optical communication transceiver 11-1. Also, the distance between the moving bodies that communicate is the distance between the space optical communication transceiver 11-1 and the space optical communication transceiver 11-2. Information indicating the expected angle predicted by this attitude and orbit control computer 12-1 is output to the acquisition and tracking controller 1116-1. Also, information indicating the distance between the moving bodies that communicate predicted by the attitude and orbit control computer 12-1 is output to the drive controller 1113-1.

[0039] The space optical communication device 1-2 is mounted on a moving body and communicates with the space optical communication device 1-1 that is the communication partner. Note that the space optical communication device 1-2 according to Embodiment 1 has a function that enables a stable space optical communication path to be established by keeping the light intensity of the transmitted light received by the space optical communication device 1-1 that is the communication partner constant even when there is a distance variation in the space transmission path. As shown in Fig. 1, this free-space optical communication device 1-2 includes a free-space optical communication transceiver 11-2 and an attitude and orbit control computer 12-2.

[0040] As shown in Fig. 1, the free-space 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 chip 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 storage device 1114-2, a capture and tracking sensor 1115-2, and a capture and tracking controller 1116-2.

[0041] The light source 1101-2 generates laser light, which is a carrier wave for free-space propagation. The laser light generated by this light source 1101-2 is output to the optical modulator 1102-2. Note that, for example, an LD can be used as the light source 1101-2.

[0042] The optical modulator 1102-2 superimposes transmission data 101-2 on the laser light generated by the light source 1101-2. Note that the transmission data 101-2 is a communication signal input from outside the free-space optical communication transceiver 11-2. The laser light after being superimposed by this optical modulator 1102-2 is output to the OHPA 1103-2. Note that, as the method of optical modulation by the optical modulator 1102-2, for example, OOK by intensity modulation of light, or PSK by phase modulation of light, etc. can be mentioned, and it can be selected as appropriate.

[0043] The OHPA 1103-2 is an optical amplifier with fibers for input and output. This OHPA 1103-2 amplifies the optical intensity of the laser light after being superimposed by the optical modulator 1102-1. The laser light after being amplified by this OHPA 1103-2 is output to the collimator 1105-2. Examples of the OHPA1103-2 include fiber amplifiers such as erbium-doped fiber amplifiers (EDFAs) or semiconductor optical amplifiers (SOAs). In a fiber amplifier, signal light is amplified when pump light is injected into the fiber. In a semiconductor optical amplifier, signal light is amplified by current injection.

[0044] The OHPA controller 1104-2 is an optical amplifier controller that performs gain control of the OHPA1103-2. That is, when the OHPA1103-2 is a fiber amplifier, the OHPA controller 1104-2 controls the pump light of the fiber amplifier to perform gain control of the fiber amplifier. When the OHPA1103-2 is a semiconductor optical amplifier, the OHPA controller 1104-2 controls the injection current of the semiconductor optical amplifier to perform gain control of the semiconductor optical amplifier.

[0045] The collimator 1105-2 converts the laser light amplified by the OHPA1103-2 into spatial light close to parallel light and emits the transmitted light, which is the spatial light. The transmitted light emitted by the collimator 1105-2 is output to the optical telescope 1108-2 via the dichroic mirror 1106-2 and the chip tilt mirror 1107-2. The collimator 1105-2 is generally composed of a fiber connector 11051-2 and a collimator lens 11052-2. By setting 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, the output light from the collimator lens 11052-2 becomes parallel light, that is, collimated light.

[0046] The dichroic mirror 1106-2 separates the transmitted light emitted by the collimator 1105-2 and the received light reflected by the chip tilt mirror 1107-2 in terms of wavelength. That is, the dichroic mirror 1106-2 transmits the transmitted light emitted by the collimator 1105-2 and reflects the received light reflected by the chip tilt mirror 1107-2. The transmitted light that has passed through this dichroic mirror 1106-2 is output to the chip tilt mirror 1107-2, and the received light reflected by the dichroic mirror 1106-2 is output to the beam splitter 1110-2.

[0047] The chip tilt mirror 1107-2 is a mirror capable of adjusting the biaxial angles in the transmitted light and the received light. Then, the chip tilt mirror 1107-2 reflects the transmitted light that has passed through the dichroic mirror 1106-2 and reflects the received light received by the optical telescope 1108-2. The transmitted light reflected by this chip tilt mirror 1107-2 is output to the optical telescope 1108-2, and the received light reflected by the optical telescope 1108-2 is output to the dichroic mirror 1106-2.

[0048] The chip tilt mirror 1107-2 controls the angles of both the transmitted light and the received light with the same mirror. On the other hand, when the distance between the space optical communication transceivers 11 is long, in addition to the chip tilt mirror 1107-2, a chip tilt mirror for independently controlling the angle of only the transmitted light may be added separately. When the distance of the space transmission path is long, while the light propagates through the space transmission path, the space optical communication device 1-1, which is the communication partner mounted on the moving body, moves. Therefore, based on the received light from the communication partner, the pointing direction of the communication partner is specified and the pointing control of the transmitted light is performed, resulting in a pointing error corresponding to the movement of the moving body during the time when the light travels back and forth through the space transmission path. This is called optical aberration. To correct this optical aberration, a chip tilt mirror for optical aberration correction 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 transmitted light reflected by the chip tilt mirror 1107-2 and radiates it into the spatial transmission path. Also, the optical telescope 1108-2 receives the transmitted light radiated by the optical telescope 1108-1 in the opposing space optical communication transceiver 11-1 as received light.

[0050] The gimbal 1109-2 is a device capable of adjusting the optical axis direction of the optical telescope 1108-2.

[0051] The beam splitter 1110-2 bifurcates the received light reflected by the dichroic mirror 1106-2. One of the received lights obtained by this beam splitter 1110-2 is output to the optical demodulator 1111-2, and the other received light is output to the acquisition and tracking sensor 1115-2.

[0052] The optical demodulator 1111-2 photoelectrically converts one of the received lights obtained by the beam splitter 1110-2 and demodulates the communication signal. The communication signal demodulated by this optical demodulator 1111-2 is output to the outside as received data 102-2.

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

[0054] The drive controller 1113-2 performs drive control of the drive mechanism 1112-2 based on the distance between the moving bodies predicted by the attitude and 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 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, based on the distance between the moving bodies predicted by the attitude and orbit control computer 12-2.

[0055] The memory device 1114-2 is a setting table that stores information indicating the relationship between the lens driving 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 free space transmission path.

[0056] Examples of the memory device 1114-2 include non-volatile or volatile semiconductor memories such as RAM, ROM, flash memory, EPROM, and EEPROM, magnetic disks, flexible disks, optical disks, compact disks, mini disks, or DVDs.

[0057] In FIG. 1, the case where the memory device 1114-2 is provided inside the free space optical communication transceiver 11-2 is shown. However, the present invention is not limited to this, and the memory device 1114-2 may be provided outside the free space optical communication transceiver 11-2.

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

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

[0060] The attitude and orbit control computer 12-2 predicts the angle of arrival and the distance between the mobile bodies that communicate, based on the attitude and position information of the mobile body on which the space optical communication device 1-2 is mounted, and the position information of the mobile body on which the space optical communication device 1-1 is mounted. The angle of arrival is the relative direction of the space optical communication transceiver 11-1 of the space optical communication transceiver 11-2. Also, the distance between the mobile bodies that communicate is the distance between the space optical communication transceiver 11-1 and the space optical communication transceiver 11-2. The information indicating the angle of arrival predicted by this attitude and orbit control computer 12-2 is output to the acquisition and tracking controller 1116-2. Also, the information indicating the distance between the mobile bodies that communicate predicted by the attitude and orbit control computer 12-2 is output to the drive controller 1113-2.

[0061] Note that the space transmission path is a medium that fills the space between the space optical communication transceiver 11-1 and the space optical communication transceiver 11-2, and it does not matter whether the medium is the atmosphere for communication on the earth, seawater for underwater communication, or vacuum for inter-satellite communication. In FIG. 1, reference numeral 103 indicates the distance between the mobile bodies that communicate, that is, the distance of the space transmission path.

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

[0063] Also, since the space optical communication device 1-1 and the space optical communication device 1-2 perform the same operation, hereinafter, the case of transmitting data from the space optical communication device 1-1 to the space optical communication device 1-2 will be described as an example.

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

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

[0066] The output light of this OHPA 1103-1 is converted into space light by the collimator 1105-1 and radiated as transmission light.

[0067] The output light of this collimator 1105-1 passes through the dichroic mirror 1106-1, is reflected by the chip tilt mirror 1107-1, and is incident on the optical telescope 1108-1. Note that the dichroic mirror 1106-1 separates the transmission light of the space optical communication transceiver 11-1 and the received light from the space optical communication transceiver 11-2. That is, it transmits the wavelength of λa and reflects the wavelength of λb. As a result, the transmission light from the space optical communication transceiver 11-2 is reflected by the dichroic mirror 1106-1 and is not incident on the collimator 1105-1 side.

[0068] The output light of this optical telescope 1108-1 propagates through the space transmission path and is received as received light by the optical telescope 1108-2 of the space optical communication transceiver 11-2. The received light received by the optical telescope 1108-2 is reflected by the chip tilt mirror 1107-2, reflected by the dichroic mirror 1106-2, and then bifurcated 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, and the communication signal is demodulated. The communication signal demodulated by this optical demodulator 1111-2 is output to the outside as received data 102-2.

[0070] In addition, when securing a communication path between the space optical communication transceiver 11-1 and the space optical communication transceiver 11-2, the acquisition and tracking sensor 1115-1 detects the arrival direction of the received light, and based on this information, the acquisition and tracking controller 1116-1 controls the chip tilt mirror 1107-1 and the gimbal 1109-1 to achieve this. At this time, the attitude and orbit control computer 12-1 predicts the expected angle, which is the relative direction of the space optical communication transceiver 11-2 with respect to the space optical communication transceiver 11-1, based on the attitude and position of the moving body on which the space optical communication transceiver 11-1 is mounted and the position of the moving body on which the space optical communication transceiver 11-2 is mounted. Then, based on this information and the arrival direction of the received light, the acquisition and tracking controller 1116-1 determines the pointing angle of the gimbal 1109-1 and suppresses the angular error within the range that can be corrected by the chip tilt mirror 1107-1.

[0071] Note that in the above, an operation example in the case of data transmission from the space optical communication device 1-1 to the space optical communication device 1-2 has been shown. In contrast, the same operation as above is performed for the case of data transmission from the space optical communication device 1-2 to the space optical communication device 1-1. As a result, in the space optical communication system, the optical axes of the optical telescopes 1108-1 and 1108-2 are made to face each other, and by continuing the angle control by the acquisition and tracking controller 1116-1 and the angle control by the acquisition and tracking controller 1116-2, mutual tracking of the moving bodies is realized and the optical path is maintained.

[0072] In the above, the basic operations of the space optical communication device 1-1 and the space optical communication device 1-2 have been described. On one hand, when considering maintaining the communication path in the case of a wide distance variation from short distance to long distance, loss variations exceeding the dynamic range of a light receiver such as a photoelectric converter or a capture and tracking sensor 1115-1 in the photoreceiver 1111-1 may occur. Here, the dynamic range refers to the ratio of the minimum received light intensity to the saturation intensity.

[0073] Generally, the free space loss G of light fs is expressed by the following formula (1). In formula (1), λ is the wavelength of the propagating light, and L is the propagation distance. As shown in formula (1), the free space loss varies with the square of the propagation distance. Therefore, for example, when the distance of the space transmission path varies by 20 dB between 100 km and 10,000 km, a dynamic range of 40 dB or more is required. TIFF0007696516000001.tif15166

[0074] Also, as a method for coping with the distance variation of the space transmission path, it is conceivable to electrically control the gain of the OHPA1103-1. That is, the gain of the OHPA1103-1 can be controlled by changing the drive current or injection current of the excitation light of the OHPA1103-1 with the OHPA controller 1104-1. However, in the case of the high-gain OHPA1103-1, it is difficult to perform electrical control near the gain threshold when the gain is decreased. Also, when performing gain control in the high-gain direction, ASE is induced and the NF deteriorates, causing fluctuations in the S / N of the communication path.

[0075] Therefore, in Embodiment 1, a space optical communication transceiver 11-1 capable of coping with the distance variation of the space transmission path is realized without relying on the gain variability of the electrical OHPA1103-1, such as changing the current value of the OHPA controller 1104-1.

[0076] That is, in the space optical communication transceiver 11-1 according to Embodiment 1, the beam divergence angle of the transmitted light radiated from the optical telescope 1108-1 is controlled by controlling the beam divergence angle of the transmitted light radiated from the collimator 1105-1. In the collimator 1105-1, generally, the distance between the end of the fiber connector 11051-1 and the collimator lens 11052-1 is fixed so that the emitted light becomes parallel light, and the focal length of the collimator lens 11052-1 is fixed. On the other hand, in the space optical communication transceiver 11-1 according to the first embodiment, the driving mechanism 1112-1 varies the focal length of the collimator lens 11052-1.

[0077] The outline of the variable beam divergence angle of the transmitted light by adjusting the focal length of the collimator lens 11052-1 will be described with reference to FIG. 2. In the example of FIG. 2, the 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 free-space transmission path-side lens 11082-1 is shown. 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 free-space transmission path-side lens 11082-1 is f3-1.

[0078] When the adjustment of the collimator lens 11052-1 shown in FIG. 2A is not performed, the distance between the collimator lens 11052-1 and the end of the fiber connector 11051-1 is f1-1, and the emitted light of the collimator 1105-1 becomes parallel light. The light is enlarged by the optical telescope 1108-1, which is an afocal optical system, and is emitted from the optical telescope 1108-1 as transmitted light. Therefore, the transmitted light becomes almost parallel light, and when propagated over a long distance according to the beam width determined by the aperture on the free-space transmission path side of the optical telescope 1108-1, the transmitted light diffracts and spreads.

[0079] On the contrary, as shown in Fig. 2B, when the collimator lens 11052-1 is brought closer to the end of the fiber connector 11051-1, the emitted light of the collimator 1105-1 is not parallel light but has divergence. Therefore, in the optical telescope 1108-1, the afocal imaging system collapses, and the transmitted light becomes a more divergent beam compared to the case of Fig. 2A. Fig. 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, the case where the collimator 1105-1 is a refractive collimator and the optical telescope 1108-1 is a refractive optical telescope is taken as an example, but the same optical effect can be obtained for a configuration using a reflecting mirror.

[0081] Also, as a method for adjusting the focal length of the collimator 1105-1, for example, the following methods can be mentioned.

[0082] First, for example, as shown in Fig. 3, there is a method of moving the collimator lens 11052-1. In this case, for example, in the collimator 1105-1, the collimator lens 11052-1 is fixed, 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 drives the linear actuator 11053-1 by a drive control signal to adjust the focal length of the collimator 1105-1.

[0083] Also, for example, as shown in Fig. 4, there is a method of moving the end of the fiber connector 11051-1. In this case, for example, a fiber connector 11051-1 is fixed to the collimator 1105-1, and a cylindrical piezo element 11054-1 that can move along the optical axis direction at the end of the fiber connector 11051-1 is provided. Then, the drive mechanism 1112-1 drives the piezo element 11054-1 by a drive 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 piezo element 11054-1. In this case, compared with the case of FIG. 3, as the configuration of the collimator 1105-1, it is possible to perform precise driving without using a mechanical driving part.

[0084] Also, for example, as shown in FIG. 5, as a method for the collimator lens 11052-1, there is a method of using a lens whose focal length changes when a voltage is applied. In this case, for example, an electro-optic material is used for the collimator lens 11052-1. Then, the drive mechanism 1112-1 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 by a drive control signal. In this case, compared with the case of FIG. 3, as the configuration of the collimator 1105-1, it is possible to perform precise driving without using a mechanical driving part.

[0085] Also, the attitude orbit control computer 12-1 can predict the distance between the free space optical communication transceiver 11-1 and the free space optical communication transceiver 11-2. As a result, the free space optical communication device 1-1 can predict the free space loss. Incidentally, as a method for the attitude and orbit control computer 12-1 to calculate the distance of the space transmission path from the positions of the mobile body equipped with the space optical communication device 1-1 and the mobile body equipped with the space optical communication device 1-2, for example, if the mobile body is a satellite, a method of acquiring TLE (Two-Line Elements) from a ground station by another communication means and performing orbit calculation based on it can be considered. Alternatively, a method of calculating the distance of the space transmission path using direct distance measurement by laser ranging or microwave may be adopted.

[0086] Here, when the beam divergence angle of the output light of the optical telescope 1108-1 is θ t the transmission gain G t is expressed by the following formula (2). Therefore, the transmission gain deteriorates with the square of the beam divergence angle. TIFF0007696516000002.tif15166

[0087] Then, the drive controller 1113-1 selects the lens drive amount so that the condition of the following formula (3) is satisfied from the distance between the mobile bodies for communication predicted by the attitude and orbit control computer 12-1, that is, the distance of the space transmission path, and the information stored in the storage device 1114-1, and sets it for the drive mechanism 1112-1. TIFF0007696516000003.tif11166

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

[0089] In the conventional configuration, the OHPA controller had to perform gain control of the OHPA according to the distance variation of the spatial transmission path. On the other hand, in the space optical communication transceiver 11-1 according to Embodiment 1, the OHPA controller 1104-1 does not need to perform gain control of the OHPA 1103-1 according to the distance variation of the spatial transmission path, and by continuously operating at the maximum output that does not saturate, stable operation can be expected in terms of both the signal amplification effect and the applied noise.

[0090] In the above description, the control of the transmitted light from the space optical communication transceiver 11-1 to the space optical communication transceiver 11-2 has been described. On the other hand, the control of the transmitted light from the space optical communication transceiver 11-2 to the space optical communication transceiver 11-1 is the same as above.

[0091] As described above, according to this Embodiment 1, the space optical communication transceiver 11 includes a light source 1101 that generates a laser beam, an optical modulator 1102 that superimposes a communication signal on the laser beam generated by the light source 1101, an OHPA 1103 that amplifies the laser beam after the superimposition by the optical modulator 1102, a fiber connector 11051 and a collimator lens 11052, a collimator 1105 that converts the laser beam after amplification by the OHPA 1103 into spatial light and emits the transmitted light that is the spatial light, a telescope 1108 that expands the beam width of the transmitted light emitted by the collimator 1105 and emits it to the 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 that the product of the free space loss calculated from the distance between the own device and the space optical communication transceiver 11 that is the communication partner and the transmission gain determined by the beam divergence angle of the transmitted light is constant. Thereby, the space optical communication transceiver 11 according to Embodiment 1 can cope with the distance variation of the spatial transmission path without performing electrical gain variation, and can make the received light intensity received by the receiving side constant. As a result, the communication possible distance range can be expanded compared with the conventional case. In addition, the space optical communication transceiver 11 according to Embodiment 1 can suppress the internal optical system loss on the receiving side compared with the conventional case, and can improve the line establishment performance at long distances. In addition, the space optical communication transceiver 11 according to Embodiment 1 can prevent damage to the fiber caused by locally concentrating high-intensity light as compared with the prior art.

[0092] Embodiment 2. FIG. 6 is a diagram showing a configuration example of a space optical communication system according to Embodiment 2. In the space optical communication system according to Embodiment 2 shown in FIG. 6, a wavefront measuring device 1117-1 is added to the space optical communication transceiver 11-1, and the functions of the dichroic mirror 1106-1, the drive controller 1113-1, and the storage device 1114-1 are changed with respect to the space optical communication system according to Embodiment 1 shown in FIG. 1. A wavefront measuring device 1117-2 is added to the space optical communication transceiver 11-2, and the functions of the dichroic mirror 1106-2, the drive controller 1113-2, and the storage device 1114-2 are changed. Other configuration examples in the space optical communication system according to Embodiment 2 shown in FIG. 6 are the same as those in the configuration example in the space optical communication system according to Embodiment 1 shown in FIG. 1, and the same reference numerals are given and the description thereof is omitted.

[0093] The dichroic mirror 1106-1 wavelength-separates the transmitted light emitted by the collimator 1105-1 and the received light reflected by the chip tilt mirror 1107-1. In addition, the dichroic mirror 1106-1 separates a part of the transmitted light emitted by the collimator 1105-1. That is, the dichroic mirror 1106-1 Fresnel-reflects a part of the transmitted light emitted by the collimator 1105-1 and transmits the rest, and reflects the received light reflected by the chip tilt mirror 1107-1. The transmitted light Fresnel-reflected by this dichroic mirror 1106-1 is output to the wavefront measuring device 1117-1, the transmitted light that has passed through the dichroic mirror 1106-1 is output to the chip tilt mirror 1107-1, and the received light reflected by the dichroic mirror 1106-1 is output to the beam splitter 1110-1.

[0094] The wavefront measuring device 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 device 1117-1 is output to the drive controller 1113-1. Examples of such a wavefront measuring device 1117-1 include a Shack-Hartmann wavefront sensor. The Shack-Hartmann wavefront sensor divides the wavefront by a lens array, condenses it onto an imager, measures the displacement amount of the spots, measures the wavefront gradient at each point, and can restore the entire wavefront by combining the 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] Based on the distance between the moving bodies predicted by the attitude trajectory control computer 12-1 and the information stored in the storage device 1114-1, the drive controller 1113-1 performs drive control of the drive mechanism 1112-1. At this time, based on the distance between the moving bodies predicted by the attitude trajectory control computer 12-1, 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 and the transmission gain determined by the beam divergence angle of the transmitted light is constant. Further, when there is an error in the beam divergence angle with respect to the target value based on the beam divergence angle of the transmitted light detected by the wavefront measuring device 1117-1, the drive controller 1113-1 corrects the drive amount to cancel the error.

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

[0097] The dichroic mirror 1106-2 separates the transmitted light emitted by the collimator 1105-2 and the received light reflected by the chip tilt mirror 1107-2 by wavelength. Also, the dichroic mirror 1106-2 separates a part of the transmitted light emitted by the collimator 1105-2. That is, the dichroic mirror 1106-2 Fresnel-reflects a part of the transmitted light emitted by the collimator 1105-2 and transmits the rest, and reflects the received light reflected by the chip tilt mirror 1107-2. The transmitted light Fresnel-reflected by this dichroic mirror 1106-2 is output to the wavefront measuring device 1117-2, the transmitted light that has passed through the dichroic mirror 1106-2 is output to the chip tilt mirror 1107-2, and the received light reflected by the dichroic mirror 1106-2 is output to the beam splitter 1110-2.

[0098] The wavefront measuring device 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 device 1117-2 is output to the drive controller 1113-2. Examples of this wavefront measuring device 1117-2 include a Shack-Hartmann wavefront sensor. The Shack-Hartmann wavefront sensor divides the wavefront by a lens array and condenses it on an imager, measures the displacement amount of the spot, measures the wavefront gradient at each point, and can restore the entire wavefront by combining those results. For example, the Shack-Hartmann wavefront sensor can estimate the beam divergence angle by decomposing this measured wavefront into aberration components using, for example, Zernike polynomials and analyzing the defocus component.

[0099] The drive controller 1113-2 performs drive control of the drive mechanism 1112-2 based on the distance between moving bodies predicted by the attitude trajectory 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 such 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, based on the distance between moving bodies predicted by the attitude trajectory control computer 12-2. Further, when there is an error in the beam divergence angle with respect to the target value based on the beam divergence angle of the transmitted light detected by the wavefront measuring device 1117-2, the drive controller 1113-2 corrects the drive amount so as to cancel the error.

[0100] The storage device 1114-2 is a setting table that stores information indicating the relationship between the lens drive amount of the drive mechanism 1112-2, the beam divergence angle of the transmitted light radiated from the optical telescope 1108-2 to the space 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 the collimator 1105-1, it is necessary to more precisely control the beam divergence angle of the transmitted light from the collimator 1105-1. The optical telescope 1108-1 generally enlarges the aperture to increase the transmission gain and reception gain with respect to the space transmission path, widens the beam width, and outputs a beam to the space transmission path. Therefore, the optical telescope 1108-1 has an optical lateral magnification of 1 or more with respect to the space transmission path from the inside of the space optical communication transceiver 11-1. That is, from the space transmission path, the optical telescope 1108-1 has an optical angular magnification of 1 or more with respect to the inside of the space optical communication transceiver 11-1. Therefore, with respect to the drive of the drive mechanism 1112-1, the beam divergence angle of the transmitted light from the optical telescope 1108-1 to the space transmission path changes more sensitively than the beam divergence angle of the transmitted light from the collimator 1105-1.

[0102] Therefore, in the space optical communication transceiver 11-1 according to Embodiment 2, among the transmitted light from the collimator 1105-1, the Fresnel reflected light of the dichroic mirror 1106-1 is made incident on the wavefront measuring device 1117-1, and the wavefront measuring device 1117-1 measures the beam divergence angle of the transmitted light from the collimator.

[0103] Then, in the space optical communication transceiver 11-1 according to Embodiment 2, 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 device 1117-1 is input to the drive controller 1113-1. Then, based on Equation (2) and Equation (3), the drive controller 1113-1 sets the lens drive amount so that the beam divergence angle of the transmitted light corresponds to the distance of the space transmission path. After that, based on the beam divergence angle of the transmitted light detected by the wavefront measuring device 1117-1, if there is a deviation between the target value and the measured value of the beam divergence angle of the transmitted light in the space transmission path, the drive controller 1113-1 corrects the lens drive amount to cancel this deviation.

[0104] In the above description, the control of the transmitted light from the space optical communication transceiver 11-1 to the space optical communication transceiver 11-2 has been described. On the contrary, the control of the transmitted light from the space optical communication transceiver 11-2 to the space optical communication transceiver 11-1 is the same as the above.

[0105] As described above, according to this Embodiment 2, the space optical communication transceiver 11 includes a wavefront measuring device 1117 that detects the beam divergence angle of the transmitted light emitted by the collimator 1105. When there is an error in the beam divergence angle of the transmitted light measured by the wavefront measuring device 1117 with respect to the target value, the drive controller 1113 corrects the drive amount of the drive mechanism 1112 to cancel the error. Thereby, the space optical communication transceiver 11 according to Embodiment 2 can more precisely control the beam divergence angle of the transmitted light in the space transmission path compared to the space optical communication transceiver 11 according to Embodiment 1, and can more stabilize the received light intensity received on the receiving side.

[0106] Embodiment 3. In the free-space optical communication of a moving object, it is necessary to control the beam based on the position information of the communication partner so that light can be received mutually. This is called initial acquisition.

[0107] As a method of initial acquisition, there is a beacon method that uses beacon light whose beam divergence angle and output power are larger than those of the communication light. For example, Patent Document 4 discloses a method of facilitating acquisition at a receiver by changing the light divergence angle according to the distance. While this beacon method can complete the initial acquisition in a short time, it is disadvantageous in terms of SWaP (Size, Weight and Power) because it is necessary to prepare a light source different from the light source for communication and another optical antenna for outputting the beacon. [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2023-143242

[0108] On the other hand, as another method, there is a beamless method that directly uses the communication light for initial acquisition instead of spreading and irradiating the beacon light with high intensity as described above. In the initial acquisition by this beamless method, it is necessary to sweep the communication light without omission within the error range of the position information of the communication partner. Also, even if the error of the position information is constant, as the relative distance to the communication partner becomes shorter, the angular range in which beam scanning must be performed widens, and beam sweeping takes time.

[0109] Therefore, in the free-space optical communication system according to Embodiment 3, in order to solve the problems in the initial acquisition between the above-described free-space optical communication devices, a configuration capable of shortening the sweeping time by controlling the beam divergence angle will be described.

[0110] FIG. 7 is a diagram showing a configuration example of the free-space optical communication system according to Embodiment 3. In the space optical communication system according to Embodiment 3 shown in FIG. 7, for the space optical communication 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 the space optical communication transceiver 11-1 are respectively changed to the drive controller 1113b-1, the acquisition and tracking sensor 1115b-1, and the acquisition and tracking controller 1116b-1, and the drive controller 1113-2, the acquisition and tracking sensor 1115-2, and the acquisition and tracking controller 1116-2 in the space optical communication transceiver 11-2 are respectively changed to the drive controller 1113b-2, the acquisition and tracking sensor 1115b-2, and the acquisition and tracking controller 1116b-2. Regarding other configuration examples in the space optical communication system according to Embodiment 3 shown in FIG. 7, they are the same as the configuration examples in the space optical communication system according to Embodiment 1 shown in FIG. 1, and the same reference numerals are given and their descriptions are omitted.

[0111] When establishing a space transmission path with the space optical communication transceiver 11-2, which is the communication partner, that is, when performing initial acquisition, the drive controller 1113b-1 determines the drive amount of the drive mechanism 1112-1 based on the distance between the moving bodies predicted by the attitude and orbit control computer 12-1 and the information stored in the storage device 1114-1. When the distance between the moving bodies for communication is L, the beam divergence angle of the transmitted light is 1 / L or 1 / L 2 so as to change. The drive controller 1113b-1 has the same functions as the drive controller 1113-1 shown in Embodiment 1 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 arrival angle of the received light based on the other received light obtained by the beam splitter 1110-1.

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

[0115] As shown in FIG. 7, the capture and tracking controller 1116b-1 includes an initial capture controller 11161b-1 and a tracking controller 11162b-1.

[0116] The initial capture controller 11161b-1 operates during the initial capture. Based on the position information of the moving body on which the space optical communication device 1-2 is mounted, the initial capture controller 11161b-1 controls the angle of the gimbal 1109-1 to direct the gimbal 1109-1 toward the space optical communication transceiver 11-2, which is the communication partner. Then, the initial capture controller 11161b-1 controls the chip tilt mirror 1107-1 to scan the transmitted light from the optical telescope 1108-1 in a spiral shape. Also, the initial capture controller 11161b-1 corrects the angle of the gimbal 1109-1 based on the arrival angle of the received light detected by the coarse capture and tracking sensor 11151b-1.

[0117] The tracking controller 11162b-1 operates after the initial capture is completed. That is, the tracking controller 11162b-1 operates after the arrival angle of the received light can be detected by the fine capture and tracking sensor 11152b-1. This tracking controller 11162b-1 has the same functions as the capture and tracking controller 1116-1 shown in the first embodiment. That is, based on the predicted angle of view predicted by the attitude and orbit control computer 12-1 and the arrival angle of the received light detected by the fine capture and tracking sensor 11152b-1, the tracking controller 11162b-1 controls the gimbal 1109-1 and the chip tilt mirror 1107-1. That is, by controlling the angle of the gimbal 1109-1 and the angle of the chip tilt mirror 1107-1, the tracking controller 11162b-1 aligns the optical axis of the optical telescope 1108-1 with the optical axis of the optical telescope 1108-2 in the space optical communication transceiver 11-2 that communicates with the space optical communication transceiver 11-1.

[0118] When establishing a space transmission path with the space optical communication transceiver 11-1, which is the communication partner, that is, when performing initial capture, the drive controller 1113b-2 is based on the distance between the moving bodies predicted by the attitude and orbit control computer 12-2 and the information stored in the storage device 1114-2. When the distance between the moving bodies performing communication is L, the drive amount of the drive mechanism 1112-2 is determined so that the beam divergence angle of the transmitted light changes at 1 / L or 1 / L 2 thereby. Except for the above functions, the drive controller 1113b-2 has the same functions as the drive controller 1113-2 shown in the first embodiment.

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

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

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

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

[0123] The initial capture controller 11161b-2 operates during initial capture. Based on the position information of the moving body on which the space optical communication device 1-1 is mounted, this initial capture controller 11161b-2 controls the angle of the gimbal 1109-2 to direct the gimbal 1109-2 toward the space optical communication transceiver 11-1, which is the communication partner. Then, the initial capture controller 11161b-2 controls the chip tilt mirror 1107-2 to scan the transmitted light from the optical telescope 1108-2 in a spiral shape. Also, the initial capture controller 11161b-2 corrects the angle of the gimbal 1109-2 based on the arrival angle of the received light detected by the coarse capture and tracking sensor 11151b-2.

[0124] The tracking controller 11162b-2 operates after the initial capture is completed. That is, the tracking controller 11162b-2 operates after the arrival angle of the received light can be detected by the fine capture and tracking sensor 11152b-2. This tracking controller 11162b-2 has the same functions as the capture and tracking controller 1116-2 shown in the first embodiment. That is, the tracking controller 11162b-2 controls the gimbal 1109-2 and the chip tilt mirror 1107-2 based on the expected angle predicted by the attitude and orbit control computer 12-2 and the arrival angle of the received light detected by the fine capture 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 chip 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 space optical communication transceiver 11-1 that communicates with the space optical communication transceiver 11-2.

[0125] Here, in the initial capture for establishing the space transmission path between the space optical communication transceivers 11-1 and 11-2, the angular error range (θ max ) required for beam scanning has the following relationship with the relative distance (L) as shown in FIG. 8 and the following formula (4), assuming that the position estimation error of the other space optical communication device 1 is constant. FIG. 8 shows the case where the position estimation error of the other space optical communication device 1 is 10 km. TIFF0007696516000004.tif14166

[0126] Also, when beam scanning is performed with the beam divergence angle (θ t ) of the beam to be scanned kept constant, the time (τ) required for beam scanning is proportional to the square of θ max , resulting in the relationship shown in the following formula (5). That is, the shorter the relative distance, the longer the time required for beam scanning. TIFF0007696516000005.tif15166

[0127] Also, if the beam sweep speed is kept constant and the angular error range is θ max , the time (τ) required for beam scanning has the relationship shown in FIG. 9 and the following formula (6) with respect to the beam divergence angle (θ t ). TIFF0007696516000006.tif14166

[0128] Here, consider expanding the beam divergence angle (θ t ) based on the following equation (7) (first case). TIFF0007696516000007.tif14166

[0129] In this case, if the beam sweep speed is constant, the effect that θ max varies according to the relative distance and the effect that the beam divergence angle (θ t ) varies according to the relative distance result in a relationship as shown in the following equation (8). Originally, as shown in equation (5), the time (τ) required for beam scanning according to the distance variation (L) increased as 1 / L 2 , so it can be seen that a time shortening effect can be expected. TIFF0007696516000008.tif14166

[0130] Next, consider expanding 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 made constant. TIFF0007696516000009.tif14166

[0131] In FIG. 9, the mark indicated by reference numeral 51 indicates the transmitted light that performs beam scanning. Further, reference numeral 52 indicates 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 widened compared to the case of FIG. 9A and scanning is performed using a thin transmitted light, it takes time for beam scanning. On the other hand, as shown in FIG. 9C, when scanning is performed by expanding the transmitted light according to the angular error range, the time required for beam scanning can be shortened.

[0132] So far, the time (τ) related to beam scanning has been explained. However, making the beam divergence angle (θ t ) variable also affects the line establishment of the free space optical communication system. Here, it is assumed that there is no change in the loss of the internal optical system of the free space optical communication device 1 and the receiving antenna gain, and the free space propagation loss that varies according to the distance and the change in the transmitting antenna gain will be considered.

[0133] The free space propagation loss (L pass ) between the transmission and reception of the free space optical communication devices 1-1 and 1-2 can be expressed by the following formula (10) using the wavelength (λ) and the relative distance (L). TIFF0007696516000010.tif15166

[0134] Also, the transmitting antenna gain (G T ) and the beam divergence angle (θ t ) of the optical telescope 1108 have the following relationships as shown in the following formulas (11) and (12). TIFF0007696516000011.tif34166

[0135] Therefore, when the beam divergence angle (θ t ) is constant, when combining the free space propagation loss and the transmitting antenna gain, the following relationship as shown in the following formula (13) holds. TIFF0007696516000012.tif14166

[0136] Next, two cases (the first case and the second case) when the beam divergence angle is variable will be considered. In the case of the first case, since the beam divergence angle is changed according to the relationship of formula (7), formula (14) is obtained from formula (7) and formula (13), and the received light intensity detected by the acquisition tracking sensor 1115b can be made constant. TIFF0007696516000013.tif12166

[0137] Also, in the case of the second case, since the beam divergence angle is changed according to the relationship of Equation (9), Equation (15) is obtained from Equation (9) and Equation (13), and the received light intensity decreases when the distance is short. Therefore, it is necessary to prevent the received light intensity in the acquisition tracking sensor 1115b from saturating and being insufficient within the range where the line is to be established. TIFF0007696516000014.tif11166

[0138] From the above, in both the first case and the second case, the initial acquisition time can be reduced compared to the case where the beam divergence angle is not variable. In the case of the first case, the time (τ) required for beam scanning changes in accordance with 1 / L, and the received light intensity detected by the acquisition tracking sensor 1115b remains constant. Also, in the case of the second case, the time (τ) required for beam scanning remains constant, and the received light intensity detected by the acquisition tracking sensor 1115b changes in accordance with L 2 and varies.

[0139] Note that the beam divergence angle also contributes to the pointing error loss (L p ). The pointing error loss can be expressed as in the following Equation (16) with respect to the beam pointing error (θ p ). Since this shows a tendency for the loss to decrease as the beam divergence angle (θ t ) increases, it has no effect on line establishment. TIFF0007696516000015.tif15166

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

[0141] In the operation example at the time of initial capture by the space optical communication transceiver 11-1 according to the third embodiment, for example, as shown in FIG. 10, first, the acquisition tracking controller 1116b-1 operates the initial acquisition controller 11161b-1 (step ST101).

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

[0143] Also, based on the position information of the moving body on which the space optical communication device 1-2 is mounted, the initial acquisition controller 11161b-1 controls the angle of the gimbal 1109-1 to direct the gimbal 1109-1 toward the space optical communication transceiver 11-2 that is the communication partner (step ST103). At this time, an angular error based on the position estimation error of the space optical communication transceiver 11-2 on the other side occurs. Therefore, in this state, the space transmission path between the space optical communication transceivers 11-1 and 11-2 cannot be established. Therefore, initial acquisition is performed by performing beam scanning of the transmitted light.

[0144] Next, based on the distance between the moving bodies predicted by the attitude orbit control computer 12-1 and the information stored in the storage device 1114-1, when the distance between the moving bodies that perform communication is L, the drive controller 1113b-1 determines the drive amount of the drive mechanism 1112-1 so that the beam divergence angle of the transmitted light changes by 1 / L or 1 / L 2 (step ST104). That is, when performing beam scanning, the beam divergence angle of the transmitted light from the optical telescope 1108-1 is controlled so that the conditions of the first case or the second case are satisfied.

[0145] Next, the initial acquisition controller 11161b-1 controls the chip tilt mirror 1107-1 to scan the transmitted light from the optical telescope 1108-1 in a spiral shape (step ST105). The above scan process is repeated about 4 or 5 times, for example. That is, by repeating the above scan process a plurality of times, the light reception probability in the coarse acquisition and tracking sensor 11151b-2 of the free space optical communication device 1-2, which is the communication partner, is improved, and light reception can be surely performed.

[0146] Next, in a state where the transmitted light is scanned in a spiral shape in the free space optical communication device 1-2, which is the communication partner, the coarse acquisition and tracking sensor 11151b-1 detects the arrival angle 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 secure a wide field of view so that it can receive the transmitted light from the free space optical communication transceiver 11-2, which is the communication partner, even if the angle error is large in the initial acquisition. Therefore, as the coarse acquisition and tracking sensor 11151b-1, for example, an element such as an image sensor with a large number of elements and a wide field of view that can be secured is used.

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

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

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

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

[0151] Next, an operation example at the time of initial capture by the space optical communication transceiver 11-2 according to Embodiment 3 will be described with reference to FIG. 11. Note that the space optical communication transceiver 11-2 starts control at the same time as the space optical communication transceiver 11-1.

[0152] In the operation example at the time of initial capture by the space optical communication transceiver 11-2 according to this Embodiment 3, for example, as shown in FIG. 11, first, the capture and tracking controller 1116b-2 operates the initial capture controller 11161b-2 (step ST201).

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

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

[0155] Next, when the distance between the moving bodies for communication is set as L, the drive controller 1113b-2 determines the drive amount of the drive mechanism 1112-2 based on the distance between the moving bodies predicted by the attitude and orbit control computer 12-2 and the information stored in the storage device 1114-2, so that the beam divergence angle of the transmitted light changes at 1 / L or 1 / L 2 That is, when performing beam scanning, the beam divergence angle of the transmitted light from the optical telescope 1108-2 is controlled so that the conditions of the first case or the second case are satisfied.

[0156] Next, in a state where the transmitted light is scanned in a spiral shape in the space optical communication device 1-1 that is the communication partner, the coarse capture tracking sensor 11151b-2 detects the arrival angle 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 capture tracking sensor 11151b-2 to secure a wide field of view so that it can receive the transmitted light from the space optical communication transceiver 11-1 that is the communication partner even if the angular error is large in the initial capture. Therefore, as the coarse capture tracking sensor 11151b-2, for example, an element such as an image sensor with a large number of elements and a wide field of view that can be secured is used.

[0157] Next, the initial capture controller 11161b-2 corrects the angle of the gimbal 1109-2 based on the arrival angle of the received light detected by the coarse capture tracking sensor 11151b-2 (step ST206). As a result, the pointing error with respect to the space optical communication transceiver 11-1 of the optical telescope 1108-2 is reduced.

[0158] Next, the initial acquisition controller 11161b-2 controls the chip tilt mirror 1107-2 to scan the transmitted light from the optical telescope 1108-2 in a spiral shape (step ST207). The above scan process is repeated about 4 or 5 times, for example. That is, by repeating the above scan process a plurality of times, the light reception probability at the coarse acquisition tracking sensor 11151b-1 of the space optical communication device 1-1, which is the communication partner, is improved, and light reception can be surely performed.

[0159] Note that in step ST105 shown in FIG. 10, since the space optical communication transceiver 11-1 performs beam scanning first, 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, generally, 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 tracking sensor 11152b-2 detects the arrival angle of the received light based on the other received light obtained by the beam splitter 1110-2 (step ST208). In this step ST208, if the fine acquisition tracking sensor 11152b-2 cannot detect the arrival angle of the received light, the sequence returns to step ST205.

[0161] On the other hand, in step ST208, when the fine acquisition tracking sensor 11152b-2 can detect the arrival angle of the received light, the acquisition tracking controller 1116b-2 operates the tracking controller 11162b-2 (step ST209). That is, when the fine acquisition tracking sensor 11152b-2 can detect the arrival angle of the received light, it is determined that the initial acquisition is completed, and the space transmission path is established. Then, the controller operated by the acquisition 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 chip tilt mirror 1107-2 based on the predicted angle of view predicted by the attitude and orbit control computer 12-2 and the arrival angle of the received light detected by the fine capture tracking sensor 11152b-2 (step ST210). Thereafter, the space optical communication transceiver 11-2 continues to be controlled to track the space optical communication transceiver 11-1. As described above, the space transmission path is continuously established.

[0163] Note that in the above description, the case where the space optical communication transceiver 11-1 performs beam scanning first is shown, but the space optical communication transceiver 11-2 may perform beam scanning first.

[0164] Also, in the above description, the case where the drive controller 1113, the capture and tracking sensor 1115, and the capture and tracking controller 1116 are respectively changed to the drive controller 1113b, the capture and tracking sensor 1115b, and the capture and tracking controller 1116b with respect to the space optical communication system according to Embodiment 1 shown in FIG. 1 is shown. However, the present invention is not limited to this, and the drive controller 1113, the capture and tracking sensor 1115, and the capture and tracking controller 1116 may be respectively changed to the drive controller 1113b, the capture and tracking sensor 1115b, and the capture and tracking controller 1116b with respect to the space optical communication system according to Embodiment 2 shown in FIG. 6, and the same effects as described above can be obtained.

[0165] As described above, according to this Embodiment 3, when the drive controller 1113b establishes a space transmission path with the space optical communication transceiver 11 which is a communication partner, when the distance between the own device and the space optical communication transceiver 11 which is a communication partner is L, the drive amount of the drive mechanism 1112 is determined so that the beam divergence angle of the transmitted light changes at 1 / L, and the capture and tracking controller 1116b controls the chip tilt mirror 1107 when establishing a space transmission path with the space optical communication transceiver 11 which is a communication partner, thereby performing spiral scanning of the transmitted light. Further, according to the third embodiment, when establishing a free-space transmission path with the free-space optical communication transceiver 11 which is a communication partner, the drive controller 1113b sets the distance between its own device and the free-space optical communication transceiver 11 which is the communication partner as L, and the beam divergence angle of the transmitted light is 1 / L 2 so as to change, determines the driving amount of the drive mechanism 1112, and the acquisition and tracking controller 1116b controls the chip tilt mirror 1107 when establishing a free-space transmission path with the free-space optical communication transceiver 11 which is a communication partner, thereby performing spiral scanning of the transmitted light. Thereby, the free-space optical communication transceiver 11 according to the third embodiment can shorten the initial acquisition time of the free-space optical communication device 1 which is a communication partner by controlling the beam divergence angle compared with the free-space optical communication transceiver 11 according to the first and second embodiments. That is, in the free-space optical communication system according to the third embodiment, the distance between the collimator lens 11052 of the collimator 1105 that outputs the output light of the OHPA 1103 into space and the fiber connector 11051 is made variable during initial acquisition, thereby adjusting the divergence angle of the output light of the collimator 1105. Then, in the free-space optical communication system according to the third embodiment, this divergence angle is changed according to the distance between the moving bodies, and the inside of the angular error range is scanned without omission. Thereby, in the free-space optical communication system according to the third embodiment, it is possible to shorten the scanning time in initial acquisition.

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

[0167] When the processing circuit 51 is dedicated hardware, the processing circuit 51 corresponds to, 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 each part of the OHPA controller 1104-1, the drive controller 1113-1, and the acquisition and tracking controller 1116-1 may be realized by the processing circuit 51 respectively, or the functions of each part may be realized together by the processing circuit 51.

[0168] When the processing circuit 51 is a CPU 52, the functions of the OHPA controller 1104-1, the drive controller 1113-1, and the acquisition and tracking controller 1116-1 are realized by software, firmware, or a combination of software and firmware. The software and firmware are described as programs and stored in the memory 53. The processing circuit 51 realizes the functions of each part by reading and executing the programs stored in the memory 53. That is, the space optical communication transceiver 11 includes a memory 53 for storing a program that, when executed by the processing circuit 51, causes the processing of each configuration to be executed as a result. Also, these programs can be said to cause a computer to execute the procedures and methods of the OHPA controller 1104-1, the drive controller 1113-1, and the acquisition and tracking controller 1116-1. Here, examples of the memory 53 include non-volatile or volatile semiconductor memories such as RAM, ROM, flash memory, EPROM, and EEPROM, magnetic disks, flexible disks, optical disks, compact disks, mini-disks, or DVDs.

[0169] Regarding each function of the OHPA controller 1104-1, the drive controller 1113-1, and the acquisition and tracking controller 1116-1, part of them may be realized by dedicated hardware and part by software or firmware. For example, for the OHPA controller 1104-1, its function can be realized by the processing circuit 51 as dedicated hardware, and for the drive controller 1113-1 and the acquisition and tracking controller 1116-1, their functions can be realized by the processing circuit 51 reading and executing the programs stored in the memory 53.

[0170] In this way, the processing circuit 51 can realize the above-mentioned functions by hardware, software, firmware, or a combination thereof.

[0171] Note that free combinations of each embodiment, or modifications of any component of each embodiment, or omissions of any component in each embodiment are possible.

Industrial Applicability

[0172] The space optical communication transceiver according to the present disclosure can cope with distance variations in a space transmission path without performing electrical gain variation, and is suitable for use in a space optical communication transceiver mounted on a moving body for transmitting data and the like.

Explanation of Signs

[0173] 1-1, 1-2 Space optical communication device, 11-1, 11-2 Space optical communication transceiver, 12-1, 12-2 Attitude and 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 Chip 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 Piezoelectric element, 11081-1 Collimator side lens, 11082-1 Space transmission path side lens, 11151b-1, 11151b-2 Coarse acquisition and tracking sensor, 11152b-1, 11152b-2 Fine acquisition and tracking sensor, 11161b-1, 11161b-2 Initial acquisition controller, 11162b-1, 11162b-2 Tracking controller.

Claims

1. A light source for generating laser light; an optical modulator that superimposes a communication signal onto the laser light generated by the light source; an optical amplifier that amplifies the laser light after the superposition by the optical modulator; a collimator having a fiber connector and a collimator lens, converting the laser light amplified by the optical amplifier into spatial light and emitting a transmission light which is the spatial light; an optical telescope that expands the beam width of the transmission light radiated by the collimator and radiates the expanded beam into a spatial transmission path; a driving mechanism capable of adjusting the focal length of the collimator lens; a drive controller that determines the drive amount of the drive mechanism so that the product of a free space loss calculated from the distance between the device itself and a communication partner free space optical communication transceiver and a transmission gain determined by a beam divergence angle of a transmission light is constant; A free-space optical communications transceiver comprising:

2. a piezoelectric element capable of moving an end of the fiber connector along an optical axis; The driving mechanism adjusts the focal length of the collimator lens by driving the piezoelectric element.

2. The free-space optical communications transceiver according to claim 1.

3. The collimator lens is a lens whose focal length changes when a voltage is applied thereto, The driving mechanism adjusts a focal length of the collimator lens by applying a voltage to the collimator lens.

2. The free-space optical communications transceiver according to claim 1.

4. a wavefront measuring device for detecting a beam divergence angle of the transmitted light radiated by the collimator; The drive controller corrects the drive amount of the drive mechanism so as to cancel out the error when the beam divergence angle of the transmission light measured by the wavefront measuring device has an error with respect to a target value.

2. The free-space optical communications transceiver according to claim 1.

5. a gimbal capable of adjusting the optical axis direction of the optical telescope; a tip-tilt mirror capable of adjusting angles in two axial directions of the transmitted light radiated 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 for detecting an angle of arrival of light received by the optical telescope; and an acquisition and tracking controller that controls the gimbal and the tip-tilt mirror based on an angle of sight, which is a relative direction of the communication partner spatial optical communication transceiver to the communication partner, and an arrival angle detected by the acquisition and tracking sensor, thereby aligning the optical axis of the optical telescope with that of the communication partner spatial optical communication transceiver.

5. The free-space optical communications transceiver according to claim 1 or 4.

6. the drive controller determines a drive amount of the drive mechanism such that a beam divergence angle of a transmission light changes in proportion to 1 / L when a distance between the drive controller itself and the spatial optical communications transceiver that is the communication partner is set to L when a spatial transmission path is established between the drive controller itself and the spatial optical communications transceiver that is the communication partner; The acquisition and tracking controller performs spiral scanning of the transmitted light by controlling the tip-tilt mirror when establishing a spatial transmission path with a spatial optical communication transceiver that is a communication partner.

6. The free-space optical communications transceiver according to claim 5.

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 determining a drive amount of the drive mechanism so as to change in proportion to The acquisition and tracking controller performs spiral scanning of the transmitted light by controlling the tip-tilt mirror when establishing a spatial transmission path with a spatial optical communication transceiver that is a communication partner.

6. The free-space optical communications transceiver according to claim 5.

Images