Optical wireless communication device

Abstract

In an optical wireless communication device capable of precisely and synchronously controlling the communication direction of transmitted and received signal light, we aim to realize an optical wireless communication device that can reduce energy loss of signal light. [Solution] The transmitting optical system and the receiving optical system of the optical wireless communication device (1) are independent of each other. The optical paths (20, 30) from the antenna (4) for both transmitting and receiving signal light are parallel to each other. An integrated fast steering mirror (FSM) (5) is positioned across both optical paths.

Description

Technical Field

[0001] The present invention relates to an optical wireless communication device.

Background Art

[0002] Light is an electromagnetic wave like the radio waves currently used in communication, but in wireless communication, it can be freely used without being restricted by the Radio Law. Also, since light has high rectilinearity, it does not propagate over a wide range, and in wireless communication, it is advantageous in terms of security compared to radio waves that propagate over a wide range. Optical wireless communication is considered suitable for communication between fixed bases, and is also considered advantageous as a technology to complement radio waves in communication between artificial satellites in outer space. Therefore, in recent years, research on optical wireless communication technology has been advanced, and precise optical technologies accompanying the high speed and long distance of optical wireless communication are expected.

[0003] Such an optical wireless communication device is known in which transmission and reception of signal light are performed with one antenna, the optical system for transmission and the optical system for reception share the same optical axis, and one steering mirror is shared. Among them, a device is known in which a part of the optical system for transmission and the optical system for reception is configured coaxially, a steering mirror is arranged in the coaxial part of the optical system to synchronously control the emission angles of both the transmission and reception signal lights, and a polarization beam splitter or a dichroic mirror for separating the signal light is arranged in the coaxial part of the optical system to separate the transmission signal light and the reception signal light from the signal light in that part (see, for example, Non-Patent Document 1).

[0004] Also, an optical wireless communication device composed of a pair of transmission and reception devices and a space optical transmission device in which one optical system for transmission or reception can be arranged to face the other optical system for reception or transmission is commercially available.

Prior Art Documents

Non-Patent Documents

[0005] [Non-Patent Document 1] Alberto Carrasco-Casado and 5 others “Miniaturized Multi-Platform Free-Space Laser-Communication Terminals for Beyond-5G Networks and Space Applications” DOI: 10.3390 / photonics11060545 [Non-Patent Document 2] Kosuke Kiyohara, et al., "Development Status of LCTs for Inter-satellite Communication," Japan Society for Aeronautical and Space Sciences, Proceedings of the 67th Japan Space Science and Technology Conference, October 2023. [Overview of the project] [Problems that the invention aims to solve]

[0006] In the optical wireless communication device described in Non-Patent Document 1, the transmitted signal light and the received signal light traveling along the same optical axis are controlled by a common steering mirror. Therefore, it is possible to precisely and synchronously control the communication direction of the transmitted signal light and the received signal light.

[0007] On the other hand, the optical wireless communication device described in Non-Patent Document 1 separates the signal light using a dichroic mirror placed on the optical axis. As a result, backlighting occurs at the mirror, which can cause communication errors. Furthermore, because the signal light is separated according to wavelength, the transmitted signal light and the received signal light must be of different wavelengths, and therefore, signal light of the same wavelength cannot be used.

[0008] Furthermore, in the optical wireless device described in Non-Patent Document 1, a dichroic mirror arranged on the axis is used to separate the desired signal light from the transmitting and receiving signal light based on the difference in wavelength. As a result, wavelength selectivity occurs in the transmitted and received light. In addition, when separating the signal light using a polarizing beam splitter (PBS), the separation of transmitted and received light is based on polarization, so signal light that does not match the polarization is discarded by the PBS, and this also hinders the speed increase achieved by polarization.

[0009] In contrast, as described in Non-Patent Document 2, a method of separating transmission and reception using pupil division has also been devised. While this is an excellent method that does not depend on wavelength or polarization, it has the drawback that loss occurs because the pupil division mirror blocks the received light.

[0010] On the other hand, commercially available spatial optical transmission devices have independent optical systems for transmission and reception, enabling bidirectional data transmission using light. However, their transmission distance is limited to a few hundred meters, making them unsuitable for long-distance communication. Furthermore, they lack the configuration necessary to precisely control the direction of the signal light.

[0011] Thus, while conventional optical wireless communication devices can precisely and synchronously control the communication direction of the transmitted and received signal light, they are configured in such a way that nearly half of the signal light's energy is lost. At least in this respect, there is room for improvement in conventional optical wireless communication devices.

[0012] One aspect of the present invention aims to realize an optical wireless communication device that can reduce energy loss of signal light, in which the communication direction of transmitted and received signal light can be precisely and synchronously controlled. [Means for solving the problem]

[0013] To solve the above problems, an optical wireless communication device according to one aspect of the present invention includes a first optical system for transmitting signal light from the light source to the first antenna, which includes a light source for signal light and a first antenna for transmitting signal light, and a second optical system for transmitting signal light from the second antenna to the receiving unit, wherein the first optical system and the second optical system include a portion in which the optical path of signal light from the first antenna in the first optical system and the optical path of signal light from the second antenna in the second optical system are parallel to each other, and a plurality of optical driving elements capable of deflecting the signal light for the purpose of removing disturbances from the incident signal light are shared on both optical paths in the parallel portion. [Effects of the Invention]

[0014] According to one aspect of the present invention, an optical wireless communication device can be realized that can reduce energy loss of signal light, in which the communication direction of transmitted and received signal light can be precisely and synchronously controlled. [Brief explanation of the drawing]

[0015] [Figure 1] This figure schematically shows the configuration of an optical wireless communication device according to Embodiment 1 of the present invention. [Figure 2] This figure schematically shows the configuration of the antenna in Embodiment 1 of the present invention. [Figure 3] This figure schematically shows the configuration of an optical wireless communication device according to Embodiment 2 of the present invention. [Figure 4] This figure illustrates features of another embodiment of the present invention. [Modes for carrying out the invention]

[0016] [Embodiment 1] Figure 1 schematically shows the configuration of an optical wireless communication device 1 according to Embodiment 1 of the present invention. The optical wireless communication device 1 is an optical wireless communication device for artificial satellites and is a device that performs laser communication between artificial satellites or with ground stations.

[0017] The optical wireless communication device 1 includes a first optical system 2 for transmission, a second optical system 3 for reception, an antenna 4 for transmission and reception, a fast steering mirror 5 for precisely tracking the communication partner, a modem 6, a high-power amplifier 7, and a low-noise amplifier 8.

[0018] A modem 6 is a device that enables computers and other equipment to send and receive data over a communication line. It is a modulator / demodulator that converts analog signals to digital signals and digital signals to analog signals.

[0019] The high-power amplifier (High power amp) 7 amplifies the low-power optical signal output from the modem 6 while keeping it as an optical signal without converting it into an electrical signal. In optical wireless communication, mainly high-power optical fiber amplifiers (EDFAs) are used.

[0020] The low-noise amplifier (Low Noise Amplifier) 8 is a device that amplifies a signal input from, for example, an antenna. The low-noise amplifier 8 is used to improve the noise characteristics in the receiving device.

[0021] [First Optical System] The first optical system 2 includes a cable connector 21 that outputs the signal light to be transmitted (hereinafter also referred to as "transmission signal light"), a collimating optical system 22, an optical aberration correction mirror 24, a beam splitter 32, a fast steering mirror 5, and an antenna 4.

[0022] Since the cable connector 21 outputs the transmission signal light transmitted through the optical fiber cable in the first optical system 2, it corresponds to the light source of the signal light.

[0023] The collimating optical system 22 is set to output the transmission signal light as collimated light.

[0024] The optical aberration correction mirror 24 is a reflecting mirror driven by an actuator (not shown). The optical aberration correction mirror 24 is driven, for example, along the direction of the arrow in FIG. 1 to cancel the relative movement with the communication partner. Thus, the first optical system 2 further has a driving mirror capable of changing the direction of the mirror surface on which the transmission signal light is incident between the cable connector 21 and the beam splitter 32 described later.

[0025] The beam splitter 32 is a half mirror for the transmission signal light, which branches a part of the transmission signal light at an angle of 90° and transmits the rest.

[0026] The transmission signal light that passes through the beam splitter 32 is reflected by the fast steering mirror 5 and transmitted to the antenna 4, from which it is output towards the satellite of the communication partner. The fast steering mirror 5 and antenna 4 will be described later.

[0027] Furthermore, the first optical system 2 includes a focusing lens 33 that focuses the transmission signal light branched from the beam splitter 32 toward the next stage, and a first four-segment photodetector 29 that detects the reception position of the transmission signal light focused by the focusing lens 33. The first four-segment photodetector 29 is a detector capable of converting the detected light signal into an electrical signal, such as a CCD sensor. Thus, the first optical system 2 further includes a position detection mechanism that detects the position of the transmission signal light in the cross-section of the optical path 20 of the transmission signal light.

[0028] In the first optical system 2, the optical path of the transmitting signal light is indicated by the arrow labeled 20. The optical path 20 of the transmitting signal light is indicated by the optical axis of the transmitting signal light in the first optical system 2 and is the position of the center of the beam of the transmitting signal light in the radial direction. For example, the optical path 20 from the cable connector 21 to the aberration correction mirror 24 is a straight line connecting the centers of these optical elements, and the optical path 20 from the beam splitter 32 to the first four-segment photodetector 29 is a straight line connecting the centers of the focusing lens 33 and the first four-segment photodetector 29. The optical path 20 from the aberration correction mirror 24 to the antenna 4 will be described later.

[0029] [Second optical system] The second optical system 3 includes an antenna 4, a fast steering mirror 5, a beam splitter 25, a folding mirror 31, a focusing lens 23, and a cable connector 34.

[0030] The beam splitter 25 acts as a half-mirror for the received signal light, allowing a portion of the received signal light to pass through and reflecting the rest at a 90° angle.

[0031] The focusing lens 23 concentrates the received signal light reflected by the folding mirror 31 toward the cable connector 34, and the cable connector 34 receives the concentrated received signal light. The cable connector 34 receives the signal light transmitted through the second optical system 3, and therefore corresponds to the signal light receiving section.

[0032] Furthermore, the second optical system 3 includes a focusing lens 28 and a second four-segment photodetector 36. The second four-segment photodetector 36 is a detector that detects the reception position of the received signal light branched from the beam splitter 25 and focused by the focusing lens 28, and is a detector capable of converting the detected light signal into an electrical signal, such as a CCD sensor. Thus, the second optical system 3 further includes a position detection mechanism that detects the position of the received signal light in the cross-section of the optical path of the received signal light.

[0033] In the second optical system 3, the optical path of the received signal light is indicated by the arrow labeled 30. The optical path 30 of the received signal light is indicated by the optical axis of the received signal light in the second optical system 3 and is the position of the center of the beam of the received signal light in the radial direction. For example, the optical path 30 from the beam splitter 25 to the second four-segment photodetector 36 is a straight line connecting the centers of the optical elements in between, and the optical path 30 from the beam splitter 25 to the cable connector 34 is a straight line connecting the centers of the optical elements in between. The optical path 30 from the antenna 4 to the beam splitter 25 will be described later.

[0034] [Common parts structure] The first optical system 2 and the second optical system 3 share a fast steering mirror 5 and an antenna 4. Both of these components are located on the optical paths of both the transmitted and received signal light.

[0035] The fast steering mirror 5 is supported so as to be drivable by two or more actuators, for example, driven by a voice coil motor, and is configured to allow the orientation of the mirror surface to be freely changed. Thus, the fast steering mirror 5 is a two-dimensional driven mirror that can change the orientation of the mirror surface into which the signal light is incident, and is configured to precisely and quickly control the emission angle of the incident signal light to a specific emission angle. The fast steering mirror 5 is sometimes also called a "Fine Pointing Mirror" in the communications field.

[0036] Antenna 4 is an off-axis twin-lens antenna as shown in Figure 2. Antenna 4 has a primary mirror 41 and a secondary mirror 42. The primary mirror 41 has a concave surface and a window portion 43 opening in the center, and the concave surface is positioned so as to be concave outward along the central axis OA2. The secondary mirror 42 has a convex surface and is positioned opposite the window portion 43 in the center of the primary mirror 41 (on the central axis OA2), with its convex surface facing the primary mirror 41.

[0037] The primary mirror 41 is designed to reflect collimated light received from a direction along the central axis OA2 toward the secondary mirror 42, and to reflect signal light received from the secondary mirror 42 as collimated light in a direction along the central axis OA2.

[0038] The transmission signal light, transmitted through the optical path 20 and the window portion 43, is reflected by one side of the secondary mirror 42 (for example, the lower side in Figure 2), widening the beam diameter as it reaches the part of the primary mirror 41 on one side of the window portion 43 (for example, the lower side in Figure 2), and is emitted to the outside as collimated signal light.

[0039] Collimated signal light that reaches the part of the primary mirror 41 on the other side of the window portion 43 (for example, the upper side in Figure 2) from the outside is reflected by the primary mirror 41 and focused on the other side of the secondary mirror 42 (for example, the upper side in Figure 2). The secondary mirror 42 reflects the signal light reflected from the other side of the primary mirror 41 as collimated light that propagates along the central axis OA2, with the optical path 30 as the center of the beam diameter.

[0040] Thus, the first optical system 2 and the second optical system 3 share an antenna 4 that can transmit and receive multiple signal lights as a single unit. The first optical system 2 and the second optical system 3 have optical paths 20 for transmitting signal light and optical paths 30 for receiving signal light that are in a parallel positional relationship between the antenna 4 and the fast steering mirror 5.

[0041] For example, the straight line connecting the center of the fast steering mirror 5 and the center of the window portion 44 of the antenna 4 is defined as the central axis OA2, and the straight line passing from the transmitting / receiving side through the center of the transmitting / receiving optical path and through the center of the fast steering mirror 5 is defined as the central axis OA1. The optical path 20 extends in the same direction as the central axes OA1 and OA2, respectively, and is separated by a specific distance, and the optical path 30 extends in the same direction as the central axes OA1 and OA2 and the optical path 20, respectively, and is separated by a specific distance from these optical axes and the optical path 20.

[0042] The distance between the central axes OA1 and OA2 and the optical path 20 is greater than the beam radius of the transmitted signal light, and the distance between the central axes OA1 and OA2 and the optical path 30 is greater than the beam radius of the received signal light. It is preferable that these distances be small from the viewpoint of improving the accuracy of the fast-steering mirror 5's precise tracking of the communication partner, and from the viewpoint of reducing the optical path difference between the transmitted signal light and the received signal light. Therefore, it can be said that the distance between the central axes OA1 and OA2 and the optical paths 20 and 30 is preferable as small as possible within the range where the beams of the transmitted signal light and the received signal light do not overlap.

[0043] Thus, both the first optical system 2 and the second optical system 3 include a portion where the optical path 20 of the signal light from the antenna 4 in the first optical system 2 and the optical path 30 of the signal light from the antenna 4 in the second optical system 3 are parallel to each other. Furthermore, the first optical system 2 and the second optical system 3 share a fast steering mirror 5 on both optical paths in this portion where the optical paths 20 and 30 are parallel to each other.

[0044] [Optical Wireless Communication] The signal light, sufficiently amplified by the high-power amplifier 7, is transmitted from the cable connector 21 to the antenna 4 via the first optical system 2, and output from the antenna 4 as augmented collimated light. The received signal light received by the antenna 4 is transmitted to the cable connector 34 via the second optical system 3, and transmitted to the low-noise amplifier 8 via the cable connector 34. The received signal light is sufficiently amplified by the low-noise amplifier 8, and the generation of noise is suppressed. In this embodiment, the band signal is converted into a digital signal all at once, and this digital signal is converted into an optical signal and transmitted. Therefore, transmission with a high dynamic range that does not depend on the nonlinearity of the optical elements is realized.

[0045] If the relative positional relationship with the communication partner changes during optical wireless communication, the first optical system 2 drives the optical aberration correction mirror 24 according to the changed positional relationship to continue to track the communication partner during transmission. A portion of the transmission signal light is branched by the beam splitter 32 and focused by the focusing lens 33 to reach the first four-segment photodetector 29. When the optical aberration correction mirror 24 is driven, the detection position of the transmission signal light in the first four-segment photodetector 29 changes according to the drive of the optical aberration correction mirror 24. The drive of the optical aberration correction mirror 24 is controlled by feedback control according to the detection position information in the first four-segment photodetector 29, and the signal light continues to be transmitted to the communication partner.

[0046] On the other hand, during signal light reception, a portion of the received signal light is received by the second four-segment photodetector 36, and changes in the position of the received signal light are detected. This allows for the detection of changes in the relative position of the optical wireless communication device 1 and its communication partner, as well as changes in the position of the received signal light (such as fluctuations) due to external disturbances such as weather disturbances or cosmic propagation disturbances. The position information of the received signal light from the second four-segment photodetector 36 is used for feedback control to drive the optical aberration correction mirror 24 for optical aberration correction, or to drive the fast steering mirror 5 for correction against external disturbances. In addition, the acquisition of the relative positional relationship with the communication partner is also performed by controlling the attitude of the satellite on which the optical wireless communication device 1 is mounted.

[0047] As described above, the fast steering mirror 5 is configured to precisely and quickly control the emission angle of the incident signal light to a specific emission angle. In this embodiment, since the fast steering mirror 5 is shared by both the first optical system 2 and the second optical system 3, the effects of external disturbances (e.g., vibrations) on both the transmitted signal light and the received signal light can be simultaneously canceled out. Thus, in this embodiment, vibration isolation of the transmitted signal light and the received signal light, which are not coaxial with each other, is achieved by a single fast steering mirror 5.

[0048] [Main effects and benefits] While radio wave communication technologies such as 5G have achieved dramatic speed increases, their communication speeds have theoretically reached their upper limit, and various difficulties are expected in achieving further speed increases. From this perspective, optical wireless communication technology is attracting attention.

[0049] Optical wireless communication technology is in its infancy, and coaxial optical systems are generally used for long-distance communication. This is because the effects of disturbances during transmission and reception need to be eliminated by a single fast-steering mirror. As a result, conventional optical wireless communication devices suffer from problems such as an increase in the number of components and greater losses in the internal optical system, limitations on the wavelengths or communication methods that can be used, and the loss of approximately half the energy of the signal light due to the separation of transmitted and received light by polarization. These problems can be a factor that hinders the speed of communication in optical wireless communication technology.

[0050] Furthermore, conventional optical wireless communication devices suffer from light loss due to the separation of transmission and reception signals. Specifically, in conventional optical wireless communication devices, the optical systems for transmitting signal light and receiving signal light are arranged coaxially, and a fast steering mirror is placed on the same axis to correct vibrations. However, in this case, a polarizing beam splitter (PBS) must be used to separate the optical paths of the transmitting signal light and the receiving signal light, resulting in a halving of the signal light intensity and thus energy loss. In addition, there is also a pupil-splitting method in the conventional technology, but this conventional technology also has the same problems as the conventional technology that uses a polarizing beam splitter.

[0051] Furthermore, conventional technologies separate transmission and reception by wavelength or polarization, which hinders the high-speed communication expected in next-generation communications using wavelength division multiplexing or polarization. In addition, there is the problem of communication errors caused by reflected light from surface reflection during signal light separation, and this problem also hinders the increase in communication speed.

[0052] In the optical wireless communication device 1, the first optical system 2 for transmission and the second optical system 3 for reception include a portion in which the optical path 20 of the signal light from the antenna 4 in the first optical system 2 and the optical path 30 of the signal light from the antenna 4 in the second optical system 3 are parallel to each other, and both optical paths 20 and 30 in the parallel portion share a fast steering mirror 5 capable of deflecting the incident signal light. Thus, in this embodiment, the optical axes for transmission and reception are independent, the fast steering mirror 5 is shared, and the structure eliminates disturbances to the signal light by deflecting it. Therefore, separation after transmission and reception based on the wavelength or polarization of the signal light is not required. Therefore, it is possible to support high-speed operation by wavelength division multiplexing or polarization, which is expected to be implemented in the future. Furthermore, since this embodiment enables the transmission and reception of signal light without being affected by the wavelength of the signal light, it is also possible to support signal light of wavelengths usable in conventional optical wireless communication.

[0053] As described above, this embodiment employs a structure that separates the optical axes for transmission and reception and uses a common fast-steering mirror, thereby achieving separation of transmission and reception regardless of wavelength or polarization. This ensures that future methods of increasing communication speed using wavelength division multiplexing or polarization will not be hindered. Furthermore, because it is possible to receive light without being affected by the wavelengths used by existing optical wireless communication devices, it is also possible to receive data from other companies' optical wireless communication devices. As a result, the internal optical system can be simplified, and light loss can be reduced.

[0054] The optical system on the antenna side of the fast steering mirror 5 constitutes the antenna optical system. The antenna optical system corresponds to the optical system from the fast steering mirror 5 to the antenna 4, which is part of the common section between the first optical system 2 and the second optical system 3 described above. Sharing the antenna optical system between the optical system for transmitting signal light and the optical system for receiving signal light is preferable from the viewpoint of simplifying the construction of the optical system of the optical wireless communication device. The antenna optical system may be an off-axis type in which the primary mirror and secondary mirror are positioned such that the optical axis of the signal light inside the optical wireless communication device in the secondary mirror is offset from the optical axis of the signal light outside the optical wireless communication device in the primary mirror, or it may be a transmission type constructed with a lens that changes the beam diameter (increases it during transmission). In this embodiment, the antenna optical system functions as a type of beam expander.

[0055] The optical system from the cable connector 21 to the fast steering mirror 5 constitutes a transmitting optical system that collimates laser light from an optical fiber cable such as a single-mode fiber and transmits it to the antenna optical system. The transmitting optical system corresponds to the optical system on the signal light source side of the first optical system 2 described above, rather than the fast steering mirror 5. By configuring the transmitted signal light from the transmitting optical system to the antenna optical system as collimated light, it is possible to define the collimation diameter of the transmitted signal light. Therefore, this is advantageous from the standpoint of designing the size of the fast steering mirror 5, and also advantageous from the standpoint of arranging the aberration correction mirror 24 (transmitting tracking mirror (PAM)) or the first four-segment photodetector 29 (position sensor), etc.

[0056] The transmitting optical system may be an off-axis system that uses mirrors to change the direction of the optical axis, or a transmission system that uses lenses to change the beam diameter.

[0057] The optical system from the cable connector 34 to the fast steering mirror 5 constitutes a receiving optical system that reduces and focuses the collimated light of the received signal light from the other optical wireless communication device to an optical fiber cable such as a single-mode fiber. The receiving optical system corresponds to the optical system on the signal light detection side of the second optical system 3 described above, rather than the fast steering mirror 5. The fact that the received signal light of the receiving optical system is composed of collimated light is advantageous from the standpoint of designing the size of the fast steering mirror 5, similar to the transmitting optical system described above, because it is possible to define the collimated diameter of the received signal light, and is also advantageous from the standpoint of arranging the second four-segment photodetector 36 (position sensor), etc. The receiving optical system may be an off-axis type using a mirror, or a transmission type using a lens.

[0058] Furthermore, in this embodiment, by not arranging the optical paths of the transmitting signal light and the receiving signal light coaxially but maintaining a certain distance between them, the configuration of splitting the signal light with a polarizing beam splitter is eliminated, making it possible to construct a system that minimizes the reduction in power of both the transmitting and receiving signal light. In conventional coaxial systems, the optical axis of the signal light is usually located at the center of the fast steering mirror, but in this embodiment, since it is not a coaxial system, the optical axes of the transmitting and receiving signal light are located at the outer periphery (e.g., the edge) of the fast steering mirror, rather than at the center where the coaxial signal light reaches in the conventional system. As a result, it is possible to simultaneously correct vibrations of both the transmitting and receiving signal light with a single fast steering mirror, just as in the conventional coaxial system.

[0059] Furthermore, in the optical wireless communication device 1, since the optical paths of the transmitted and received signal light are independent of each other, it is not necessary to distinguish between the transmitted signal light and the received signal light as described above. Therefore, it is possible for both the transmitted and received signal light to be of the same wavelength. Also, it is not necessary to separate one of the transmitted signal light and the received signal light from the other. Therefore, there is no energy loss of the signal light due to the separation of the signal light, and no backlight, which can become noise in optical wireless communication, is generated during the separation of the signal light. Moreover, since no optical elements for separating the signal light are required, the optical system configuration in the optical wireless communication device 1 is simpler than that of conventional optical wireless communication devices that require the separation of signal light, and signal light loss can be further reduced.

[0060] Furthermore, even if signal light is collimated from a geometrical optical perspective, its beam angle changes from a wave optical perspective depending on the diameter of the emitted beam. If the diameter of the emitted beam of the signal light is large, the collimation is high and the emitted signal light ray is closer to parallel light. Conversely, as the diameter of the emitted beam of the signal light decreases, the collimation of the signal light decreases, and the beam angle of the signal light ray becomes larger (it moves towards a divergent state).

[0061] When optical wireless communication device 1 is applied to optical wireless communication in outer space, the distance between communicating optical wireless communication devices can be very far, for example, from 1000 km to 4000 km. Therefore, as the beam angle of the signal light increases, the beam diameter of the signal light reaching the other optical wireless communication device increases. The energy of the received signal light is determined by the beam diameter of the received signal light and the aperture of the receiving optical system. Therefore, in an optical wireless communication device, it is preferable for both the beam diameter of the transmitting signal light and the beam diameter of the received signal light to be larger in order to improve the efficiency of optical wireless communication. However, in reality, optical wireless communication devices have size constraints, so the size of the signal light beam diameter is also limited.

[0062] In conventional optical wireless communication devices, the optical paths for the transmitting signal light and the receiving signal light are coaxial, resulting in operation with the same aperture (same beam diameter). In contrast, in this embodiment, the optical paths for the transmitting signal light and the receiving signal light are not coaxial but separate. Therefore, since there is no energy loss of signal light due to the polarization beam splitter in conventional technology, it is possible to reduce the aperture of the optical system for the transmitting signal light compared to that of conventional technology. By independently reducing the beam diameter of the transmitting signal light, it is possible to increase the amount of energy of the signal light when it reaches the other optical wireless communication device compared to the amount of energy of the received signal light, taking into account the energy loss due to the polarization beam splitter in conventional technology. This allows for higher efficiency and miniaturization compared to conventional optical wireless communication devices.

[0063] Furthermore, the optical wireless communication device 1 has a fast-steering mirror 5, which is a two-dimensional driven mirror that can change the orientation of the mirror surface into which the signal light of each optical system is incident. Therefore, it is advantageous in terms of canceling out the influence of external disturbances on the communication light more quickly and precisely.

[0064] Furthermore, the optical wireless communication device 1 shares an integrated antenna 4 that can transmit and receive signal light as both a transmitting and receiving antenna. Therefore, it is advantageous from the standpoint of simplifying the antenna configuration of the optical wireless communication device 1.

[0065] In conventional optical wireless communication devices, the antenna optical system is almost always of the Cassegrain type. In the Cassegrain type, both the optical system for transmitting signal light and the optical system for receiving signal light can share the same antenna optical system. On the other hand, in the Cassegrain type, because the primary mirror and secondary mirror are directly facing each other, the aperture of the primary mirror becomes larger in proportion to the secondary mirror. Therefore, greater loss of signal light intensity is more likely to occur.

[0066] In this embodiment, an off-axis twin-lens antenna 4 is employed in the integrated antenna. Therefore, when the primary mirror 41 of the antenna 4 is divided into two parts, one part can be used for transmission and the other for reception. Thus, it is advantageous in terms of minimizing signal light loss during transmission and reception at the antenna.

[0067] Furthermore, in this invention, not only two lenses for transmitting and receiving light as in this embodiment, but also two or more lenses may be used. In that case, an optical path for transmitting signal light may be added, or an optical path for receiving signal light may be added, and the number of optical paths for signal light may be any number as long as the dimensions allow.

[0068] In this embodiment, since the optical paths of the transmitting signal light and the receiving signal light are not set on the same axis, there is no need to drill a hole in the center of the optical path (on the optical axis) as in the Cassegrain type. Therefore, it is preferable from the viewpoint of constructing an optical wireless communication device in which the loss of signal light intensity during transmission and reception at the antenna is reduced.

[0069] Furthermore, making the collimation diameter of the signal light the same in both the optical system for transmitting signal light and the optical system for receiving signal light makes it possible to make the collimation diameter of the transmitting and receiving signal light the same in the antenna optical system. Therefore, it becomes possible to make the transmitting aperture and receiving aperture of the antenna's primary mirror substantially the same. Consequently, the ratio of the internal energy of the transmitting signal light and the receiving signal light can be made equal, which is preferable from the viewpoint of high efficiency.

[0070] Furthermore, if there are size constraints on the optical wireless communication device, or if it is possible to sufficiently increase the energy of the transmitted signal light, the main body of the optical wireless communication device can be miniaturized by appropriately setting the beam diameter in the transmitting optical system and the beam diameter in the receiving optical system. In this embodiment, adopting a multi-lens system is also preferable from the viewpoint of achieving the above-mentioned miniaturization.

[0071] Furthermore, the optical wireless communication device 1 has a configuration in the first optical system 2 for detecting the position of the signal light in the cross-section of the optical path of the transmitted signal light (particularly a beam splitter 25 and a first four-segment photodetector 29), and a second position detection mechanism in the second optical system 3 for detecting the position of the signal light in the cross-section of the optical path of the received signal light (particularly a beam splitter 32 and a second four-segment photodetector 36). Therefore, it is advantageous in terms of capturing the communication partner in accordance with the detection of the position of the signal light and suppressing the effects of disturbances.

[0072] By arranging the position detection sensor within the optical path of the transmitting optical system and configuring it to provide feedback to the optical aberration correction mirror 24, the receiving optical wireless communication device can emit signal light with high accuracy. This improves the efficiency of communication. While such an optical system configuration includes a beam splitter, in this embodiment, the transmitting power itself can be made quite large, ranging from 1 to 10 watts. In this case, to avoid detection problems due to excessive light intensity, it is necessary to significantly reduce the energy reaching the position detection sensor. Therefore, the ratio of the transmitting signal light to the transmitting side (to the fast steering mirror 5) in the beam splitter of the transmitting optical system inevitably becomes large, making it possible to sufficiently reduce the energy loss for position detection in the transmitted signal light.

[0073] Furthermore, by placing a position detection sensor within the optical path of the receiving optical system as described above, and configuring it so that the detection results can be fed back to the fast steering mirror 5, minute vibrations that cannot be controlled by the gimbal (such as attitude control by the gyro sensor of the base body on which the optical wireless communication device 1 is mounted) can be corrected by the fast steering mirror 5, allowing the transmitting signal light from the other optical wireless communication device to be incident with greater precision, and further improving the reception efficiency. Generally, since the receiving optical system uses transmitted light from a long distance as the received signal light, the energy of the received signal light is significantly less than the energy of the transmitted signal light. However, by employing a highly sensitive position detection sensor, it is possible to sufficiently sense the received signal light with the position detection sensor.

[0074] Furthermore, the optical wireless communication device 1 has an optical aberration correction mirror 24 between the cable connector 21 and the beam splitter 32 in the first optical system 2. Therefore, it is advantageous in that it substantially cancels out the effects of communication caused by the relative movement of the communication partner.

[0075] [Embodiment 2] Figure 3 schematically shows the configuration of the optical wireless communication device according to this embodiment. The optical wireless communication device 10 has substantially the same configuration as the optical wireless communication device 1 of Embodiment 1 described above, except that it has two pairs of four wedge prism optical driving elements 52 instead of fast steering mirrors 5. Reference numeral 51 denotes a mirror.

[0076] The optical driving element 52 includes, for example, a first wedge prism pair consisting of a first wedge prism and a second wedge prism, a first voice coil motor for rotating the first wedge prism and the second wedge prism respectively, a second wedge prism pair consisting of a third wedge prism and a fourth wedge prism, and a second voice coil motor for rotating the third wedge prism and the fourth wedge prism respectively.

[0077] Each wedge prism is positioned in a movable frame, which is rotatably supported on a fixed frame. The fixed frame is an annular member when viewed from above and has a circular window in the center. Multiple coils are arranged on the surface of the fixed frame in a circular direction around the frame, and each coil is connected in series to a power supply. Hall elements are also positioned between the coils in the circumferential direction of the fixed frame. The movable frame is an annular member when viewed from above and has a circular window in the center into which the wedge prism is fitted. Magnets are positioned on the surface of the movable frame at positions corresponding to the coils of the fixed frame and at positions corresponding to the Hall elements.

[0078] Each wedge prism in the first pair of wedge prisms rotates in opposite directions to deflect the signal light in a specific direction (e.g., the pitch direction (vertical direction)), and each wedge prism in the second pair of wedge prisms rotates in opposite directions to deflect the signal light in a specific other direction (e.g., the yaw direction (horizontal direction)). In this way, the optical driving element 52 is configured to quickly and precisely deflect the transmitted signal light and the received signal light to any position on a plane perpendicular to the central axis OA2 of the wedge prisms.

[0079] The optical wireless communication device 10 also provides the same effects as the optical wireless communication device 1 of the embodiment described above.

[0080] [Other Embodiments] In embodiments of the present invention, two or more optical systems may be included. For example, the optical wireless communication device in an embodiment of the present invention may further include a third optical system and a fourth optical system in addition to the optical wireless communication devices 1 and 10 described above. For example, if four optical systems up to the fourth optical system are included, the mirror surface of the fast steering mirror 5 is divided into a number corresponding to each optical element, as shown in Figure 4. In Figure 4, the mirror surface of the fast steering mirror 5 is set to have four symmetrical regions corresponding to each of the four optical systems from the first to the fourth. According to such an embodiment, for example, the two upper regions in Figure 4 may be the regions for the transmitted signal light and the received signal light of wavelength A, and the two lower regions may be the regions for the transmitted signal light and the received signal light of wavelength B, making it possible to configure an optical wireless communication device that can handle two or more different wavelength bands (e.g., L band and C band) with a single optical wireless communication device. In this embodiment, it is preferable that the antenna also corresponds to the optical system, and it is preferable to employ a quad-lens antenna.

[0081] Here, "multi-lens" means that there are multiple positions for the optical axis of the signal light in the antenna. Therefore, in the present invention, the multi-lens configuration may consist of the same number of primary and secondary mirrors as the number of optical axes of the antenna, or each of the primary and secondary mirrors may have a region that receives each of the multiple signal lights corresponding to the respective signal light. The latter can be called "multi-axis".

[0082] Furthermore, the light source for the signal light in the first optical system may be a laser, and the light receiving unit of the second optical system may be a light-receiving element. Thus, the optical wireless communication device according to the embodiment of the present invention may be configured such that the signal light is directly output or detected.

[0083] Furthermore, antenna 4 may consist of two antennas: a first antenna for transmitting transmission signal light and a second antenna for receiving reception signal light. Also, the antenna may be a type other than the off-axis twin-lens antenna, as long as it can independently transmit transmission signal light and independently receive reception signal light. For example, the antenna may be a Cassegrain antenna. A Cassegrain antenna is also advantageous in simplifying the configuration of the optical wireless communication device compared to using two separate antennas, one for transmitting and one for receiving, because it can independently perform both transmission and reception as a single unit.

[0084] Furthermore, in embodiments of the present invention, it is also possible to communicate using signal light of a specific wavelength, for example, by using a bandpass filter.

[0085] 〔summary〕 A first aspect of the present invention is an optical wireless communication device (1) comprising: a first optical system (2) for transmitting signal light from the light source to the first antenna, which includes a light source (cable connector 21) for signal light and a first antenna (antenna 4) for transmitting signal light; and a second optical system (3) for transmitting signal light from the second antenna to the receiving unit, which includes a receiving unit for signal light and a second antenna (antenna 4) for receiving signal light, wherein the first and second optical systems include portions in which the optical path (20) of signal light from the first antenna in the first optical system and the optical path (30) of signal light from the second antenna in the second optical system are parallel to each other, and both optical paths in the parallel portions share an optical driving element (fast steering mirror 5) capable of deflecting the signal light to remove disturbances from multiple incident signal light. According to the first aspect, an optical wireless communication device can be realized that can reduce energy loss of signal light in an optical wireless communication device that can precisely and synchronously control the communication direction of the transmitted and received signal light.

[0086] A second aspect of the present invention is that, in the first aspect, the optical driving element is a two-dimensional driven mirror capable of changing the orientation of the mirror surface into which the signal light of each optical system is incident. The second aspect is even more effective in terms of canceling the influence of external disturbances on communication light more quickly and precisely.

[0087] A third aspect of the present invention is that, in the first or second aspect, the first optical system and the second optical system share an antenna, which is a first antenna and a second antenna, that is capable of transmitting and receiving signal light as a single unit. The third aspect is even more effective in terms of simplifying the antenna configuration.

[0088] A fourth aspect of the present invention is that, in the third aspect, the antenna is an off-axis twin-lens antenna. The fourth aspect is even more effective in reducing the loss of signal light due to transmission and reception at the antenna.

[0089] A fifth aspect of the present invention is that, in any of the first to fourth aspects, the first optical system further comprises a first position detection mechanism for detecting the position of the signal light in a cross-section of the optical path of the signal light to be transmitted, and the second optical system further comprises a second position detection mechanism for detecting the position of the signal light in a cross-section of the optical path of the received signal light. The fifth aspect is even more effective in terms of capturing the communication partner in accordance with the detection of the position of the signal light, and in terms of suppressing the effects of disturbances.

[0090] A sixth aspect of the present invention is that, in the fifth aspect, the first optical system further includes a drive mirror (optical aberration correction mirror 24) between the light source and the first position detection mechanism, which can change the orientation of the mirror surface into which the signal light from the light source is incident. The sixth aspect is even more effective in terms of canceling out the effects of communication due to the relative movement of the communication partner.

[0091] According to the embodiments described above, the present invention reduces the energy loss of signal light in optical wireless communication and increases the degree of freedom of the signal light by eliminating the need for a relationship (such as separability) between the transmitted signal light and the received signal light. The present invention, which achieves such effects, is expected to bring about groundbreaking progress and development in optical wireless communication technology and will contribute, for example, to achieving Sustainable Development Goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation," advocated by the United Nations.

[0092] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0093] 1.10 Optical wireless communication device 2 First optical system 3 Second optical system 4 Antennas 5. Fast steering mirror (optical drive element) 6 Modems 7. High-power amplifier 8. Low-noise amplifier 20, 30 light path 21, 34 Cable connectors 22 Collimated Optics 23. Focusing lens 24 Aberration Correction Mirror 25, 32 Beam splitter (for four-segment photodetector) 28, 33 Focusing lenses (for four-segment photodetectors) 29 First 4-segment photodetector 31 Folding Mirror 36 Second four-segment photodetector 41 Primary mirror 42 Secondary mirror 43 Window section 51 Mirror 52 Optical drive element OA1: Central axis of the antenna optical system (transmitter / receiving side) OA2 Antenna side central axis

Claims

1. A first optical system for transmitting signal light from the light source to the first antenna includes a light source for signal light and a first antenna for transmitting signal light, It includes a signal light receiving unit and a second antenna for receiving signal light, and a second optical system for transmitting signal light from the second antenna to the receiving unit, The first optical system and the second optical system are, The optical path of the signal light from the first antenna in the first optical system and the optical path of the signal light from the second antenna in the second optical system include a portion that is parallel to each other, and Multiple optical drive elements capable of deflecting the signal light to remove disturbances from the incoming signal light are shared on both optical paths of the parallel portion. Optical wireless communication device.

2. The optical wireless communication device according to claim 1, wherein the optical driving element is a two-dimensional driving mirror capable of changing the orientation of the mirror surface into which the signal light of each optical system is incident.

3. The optical wireless communication device according to claim 1, wherein the first optical system and the second optical system share an antenna that is integrated and capable of transmitting and receiving signal light, which serves as the first antenna and the second antenna.

4. The optical wireless communication device according to claim 3, wherein the antenna is an off-axis multi-lens antenna.

5. The first optical system includes a beam splitter positioned on the optical path of the signal light to be transmitted, and further includes a first position detection mechanism for detecting the position of the signal light. The optical wireless communication device according to claim 1, wherein the second optical system includes a beam splitter positioned on the optical path of the received signal light, and further comprises a second position detection mechanism for detecting the position of the signal light.

6. The optical wireless communication device according to claim 5, wherein the first optical system further includes a drive mirror between the light source and the first position detection mechanism, the drive mirror capable of changing the orientation of the mirror surface into which the signal light from the light source is incident.

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