Optical space communication device and optical space communication method

Abstract

To provide an optical space communication device capable of starting optical axis alignment without matching timing between optical space communication devices.SOLUTION: An optical space communication device includes transmission means for transmitting a first signal for optical axis alignment with another optical space communication device including a reflector, the first signal being modulated using a first spreading code, and reception means for detecting, from a received optical signal, a reflected signal of the first signal reflected by the reflector of the other optical space communication device using the first spreading code, and detecting, from the received optical signal, a second signal for optical space communication transmitted from the other optical space communication device using a second spreading code different from the first spreading code.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an optical space communication device and an optical space communication method. [Background technology]

[0002] Free-space optical communication (also called FSO (Free-Space Optics)) has been developed, which uses light propagating through free space to perform communication. In free-space optical communication, it is necessary to align the optical axes between communication devices. Techniques described in Patent Document 1 and Non-Patent Document 1 are known as methods for aligning the optical axes.

[0003] Patent document 1 describes a technique in which an optical signal is transmitted from one communication device to another communication device while changing the emission pattern, and the other communication device receives the optical signal and transmits a control signal generated based on the optical signal to the one communication device.

[0004] Non-Patent Document 1 describes that one communication device is designated as a master and the other as a slave, and the two devices alternately perform scanning. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-65492 [Non-patent literature]

[0006] [Non-Patent Document 1] Space Development Agency (SDA), Optical Communications Terminal (OCT) Standard Version 3.1.0, 2023 / 3 / 31 Summary of the Invention [Problem to be solved by the invention]

[0007] In the optical axis alignment described in Patent Document 1 and Non-Patent Document 1, it is necessary to start the optical axis alignment in a synchronized timing between the optical space communications devices.

[0008] The present disclosure has been made in consideration of the above-mentioned problems, and one exemplary purpose thereof is to provide a technology that enables optical axis alignment to be started without the need to synchronize timing between optical space communication devices. [Means for solving the problem]

[0009] An optical space communications device according to one exemplary aspect of the present disclosure comprises a transmitting means and a receiving means, wherein the transmitting means transmits a first signal modulated using a first spreading code for aligning an optical axis with another optical space communications device equipped with a reflector, and the receiving means detects, from the received optical signal, a reflected signal of the first signal reflected by a reflector of the other optical space communications device using the first spreading code, and detects, from the received optical signal, a second signal for optical space communications transmitted from the other optical space communications device using a second spreading code different from the first spreading code.

[0010] An optical space communication method according to one exemplary aspect of the present disclosure is an optical space communication method performed by an optical space communication device, and includes transmitting a first signal modulated using a first spreading code for aligning an optical axis with another optical space communication device equipped with a reflector, detecting a reflected signal of the first signal reflected by a reflector of the other optical space communication device from the received optical signal using the first spreading code, and detecting a second signal for optical space communication transmitted from the other optical space communication device from the received optical signal using a second spreading code different from the first spreading code. [Effects of the Invention]

[0011] According to one exemplary aspect of the present disclosure, it is possible to provide a technique that can start optical axis alignment without having to synchronize timing between optical space communication devices, which is an exemplary effect. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram illustrating a configuration of an optical space communications device according to the present disclosure. [Figure 2] 1 is a flow diagram showing the flow of an optical space communication method according to the present disclosure. [Figure 3] 1 is a block diagram illustrating a configuration of an optical space communications device according to the present disclosure. [Figure 4] 10A and 10B are diagrams illustrating an optical axis alignment operation of the optical space communications device according to the present disclosure. [Figure 5] 10A to 10C are diagrams illustrating an optical axis alignment operation and an optical space communication operation of the optical space communication device according to the present disclosure. [Figure 6] 10A and 10B are diagrams illustrating an example of the reception level of a received optical signal when the signal level of a direct wave is greater than that of a reflected wave in an optical space communications device according to the present disclosure. [Figure 7] 10A and 10B are diagrams illustrating an example of a reception level of an optical signal after clipping in an optical space communications device according to the present disclosure. [Figure 8] FIG. 1 is a block diagram illustrating a configuration of a computer that functions as an optical space communications device according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following are examples of embodiments of the present invention. However, the present invention is not limited to the exemplary embodiments shown below, and various modifications are possible within the scope of the claims. For example, embodiments obtained by appropriately combining the technologies (part or all of the products or methods) employed in the exemplary embodiments shown below may also be included in the scope of the present invention. Furthermore, embodiments obtained by appropriately omitting some of the technologies employed in the exemplary embodiments shown below may also be included in the scope of the present invention. Furthermore, the effects mentioned in the exemplary embodiments shown below are examples of effects expected in the exemplary embodiments, and do not define the scope of the present invention. In other words, embodiments that do not exhibit the effects mentioned in the exemplary embodiments shown below may also be included in the scope of the present invention.

[0014] First Exemplary Embodiment A first exemplary embodiment, which is an example of an embodiment of the present invention, will be described in detail with reference to the drawings. This exemplary embodiment is the basic form of each exemplary embodiment described later. The scope of application of each technology employed in this exemplary embodiment is not limited to this exemplary embodiment. That is, each technology employed in this exemplary embodiment can also be employed in other exemplary embodiments included in the present disclosure, to the extent that no particular technical obstacles arise. Furthermore, each technology shown in the drawings referenced to explain this exemplary embodiment can also be employed in other exemplary embodiments included in the present disclosure, to the extent that no particular technical obstacles arise.

[0015] (Configuration of optical space communications device) The configuration of the optical space communications device 1 will be described with reference to Fig. 1. Fig. 1 is a block diagram showing the configuration of the optical space communications device 1. For ease of explanation, Fig. 1 also shows not only the optical space communications device 1 but also an optical space communications device 2 (another optical space communications device) that is the communication partner of the optical space communications device 1.

[0016] As shown in Fig. 1, the optical free space communications device 1 includes a transmitter (transmitting means) 11 and a receiver (receiving means) 12. Also, as shown in Fig. 1, the optical free space communications device 2 includes a reflector 26. The reflector 26 is, for example, a passive reflector such as a corner cube reflector (CCR) or a retroreflector, and can be configured to reflect light in a direction toward its source.

[0017] The transmitter 11 has a function of transmitting an optical signal. In this exemplary embodiment, the transmitter 11 transmits a first signal for optical axis alignment with the optical space communications device 2, modulated using a spreading code (first spreading code) for optical axis alignment. The spreading code may be, for example, an optical orthogonal code (OOC) or a prime code used in optical CDMA technology.

[0018] The receiver 12 has a function of receiving an optical signal. In this exemplary embodiment, the receiver 12 detects, from the received optical signal, a reflected signal of the first signal reflected by the reflector 26 of the optical space communications device 2, using a spreading code (first spreading code) for optical axis alignment.

[0019] In addition, the receiving unit 12 detects the second signal for optical space communication transmitted from the optical space communication device 2 from the received optical signal using a spreading code (second spreading code) for reception by optical space communication that is different from the spreading code (first spreading code) for optical axis alignment.

[0020] (Effects of optical space communication device) As described above, the optical space communications device 1 employs a configuration in which the first signal for optical axis alignment with the optical space communications device 2 is reflected by the reflector 26 of the optical space communications device 2 and received by the receiving unit 12. Furthermore, the optical space communications device 1 employs a configuration in which the reflected signal of the first signal reflected by the reflector 26 of the optical space communications device 2 is detected using a spread code for optical axis alignment (first spread code), and the second signal for optical space communications transmitted from the optical space communications device 2 is detected using a spread code for reception by optical space communications (second spread code) that is different from the spread code for optical axis alignment (first spread code). Therefore, the optical space communications device 1 can transmit the first signal to start optical axis alignment even when optical axis alignment has not started in the optical space communications device 2 and the second signal for optical space communications is being transmitted from the optical space communications device 2. This provides the effect of allowing optical axis alignment to be started without synchronizing timing between the optical space communications devices.

[0021] (Flow of optical space communication method) The flow of the optical space communication method S1 will be described with reference to Fig. 2. Fig. 2 is a flow diagram showing the flow of the optical space communication method S1. The optical space communication method S1 is executed by the optical space communication device 1, and as shown in Fig. 2, includes a transmission process S11 and a reception process S12.

[0022] In the transmission process S11, the optical space communication device 1 transmits a first signal for optical axis alignment with the optical space communication device 2 (another optical space communication device) equipped with a reflector 26, modulated using a spreading code (first spreading code) for optical axis alignment.

[0023] In the receiving process S12, the optical space communications device 1 detects the reflected signal of the first signal reflected by the reflector 26 of the optical space communications device 2 from the received optical signal using a spreading code (first spreading code) for optical axis alignment.

[0024] In addition, in the receiving process S12, the optical space communications device 1 detects the second signal for optical space communications transmitted from the optical space communications device 2 from the received optical signal using a spreading code (second spreading code) for receiving by optical space communications that is different from the spreading code (first spreading code) for optical axis alignment.

[0025] (Effects of optical space communication methods) As described above, the optical space communication method S1 employs a configuration in which the first signal for optical axis alignment with the optical space communications device 2 is reflected by the reflector 26 of the optical space communications device 2 and received by the optical space communications device 1. Furthermore, the optical space communication method S1 employs a configuration in which the reflected signal of the first signal reflected by the reflector 26 of the optical space communications device 2 is detected using a spread code for optical axis alignment (first spread code), and the second signal for optical space communications transmitted from the optical space communications device 2 is detected using a spread code for reception by optical space communications (second spread code) that is different from the spread code for optical axis alignment (first spread code). Therefore, according to the optical space communications method S1, even when optical axis alignment has not started in the optical space communications device 2 and the second signal for optical space communications is being transmitted from the optical space communications device 2, the first signal can be transmitted to start optical axis alignment. This provides the effect of allowing optical axis alignment to be started without synchronizing the timing between the optical space communications devices.

[0026] Second Exemplary Embodiment A second exemplary embodiment, which is one example of an embodiment of the present invention, will be described in detail with reference to the drawings. Components having the same functions as those described in the above exemplary embodiment will be assigned the same reference numerals, and their description will be omitted as appropriate. The scope of application of each technology employed in this exemplary embodiment is not limited to this exemplary embodiment. That is, each technology employed in this exemplary embodiment can also be employed in other exemplary embodiments included in the present disclosure, to the extent that no particular technical hindrance occurs. Furthermore, each technology shown in each drawing referenced to explain this exemplary embodiment can also be employed in other exemplary embodiments included in the present disclosure, to the extent that no particular technical hindrance occurs.

[0027] (Configuration of optical space communications device) The configuration of the optical space communications device 1A will be described with reference to Fig. 3. Fig. 3 is a block diagram showing the configuration of the optical space communications device 1A. For ease of explanation, Fig. 3 also shows not only the optical space communications device 1A but also an optical space communications device 2A (another optical space communications device) with which the optical space communications device 1A communicates. However, the configuration of the optical space communications device 2A is shown in a simplified form.

[0028] In addition to the transmitting unit (transmitting means) 11 and receiving unit (receiving means) 12 that the optical space communications device 1 has, the optical space communications device 1A also has a phase transition determination unit (control unit) 14, a threshold setting unit (setting means) 15, and a reflector 16.

[0029] The transmitter 11 has a function of transmitting an optical signal. The transmitter 11 transmits a first signal for optical axis alignment with the optical space communications device 2, modulated using a spreading code (first spreading code) for optical axis alignment. The transmitter 11 also transmits a third signal for optical space communications, modulated using a spreading code (third spreading code) for transmission to the optical space communications device 2 by optical space communications.

[0030] Specifically, the transmitter 11 may include a code generator 111. The code generator 111 generates a spreading code based on the parameters. The spreading code may be, for example, an optical orthogonal code (OOC) or a prime code used in optical CDMA technology.

[0031] The parameters may be input in advance to the optical space communications device 1, or may be notified to the optical space communications device 1. The code generation unit 111 can generate different spread codes by using different parameters. For example, the code generation unit 111 may generate a spread code for optical axis alignment (first spread code), a spread code for reception by optical space communications (second spread code), and a spread code for transmission to the optical space communications device 2 by optical space communications (third spread code).

[0032] The transmitter 11 may also include a random signal generator 112. The random signal generator 112 generates a signal to be transmitted at random timing.

[0033] The transmitter 11 may also include a spreading processor 113. The spreading processor 113 modulates the signal to be transmitted using the spreading code generated by the code generator 111.

[0034] The transmitter 11 may also include a transmission processing unit 114. The transmission processing unit 114 transmits the signal modulated by the spreading processing unit 113 as an optical signal.

[0035] The receiving unit 12 has a function of receiving an optical signal. The receiving unit 12 detects, from the received optical signal, a reflected signal of the first signal reflected by the reflector 26 of the optical space communications device 2, using a spreading code (first spreading code) for optical axis alignment. The receiving unit 12 also detects, from the received optical signal, a second signal for optical space communications transmitted from the optical space communications device 2, using a spreading code (second spreading code) for reception by optical space communications that is different from the spreading code (first spreading code) for optical axis alignment.

[0036] In particular, the receiving unit 12 may include a receiving processing unit 121. The receiving processing unit 121 receives an optical signal and converts it into a received signal.

[0037] The receiver 12 may also include a limiter 122. The limiter 122 clips the received signal so that the signal level of the received signal is equal to or lower than a threshold value.

[0038] The receiver 12 may also include a despreading processor 123. The despreading processor 123 demodulates the received signal using a spreading code to detect the desired signal.

[0039] The phase transition determination unit 14 determines that the optical space communication device 1A will perform at least one of an optical axis alignment operation (reflected wave phase) for aligning the optical axis with the optical space communication device 2A, and an optical space communication operation (direct wave phase) for performing optical space communication with the optical space communication device 2A.

[0040] In one aspect, the phase transition determination unit 14 may determine to perform the optical space communication operation if the direction of the optical space communications device 2A can be determined in the optical axis alignment operation. Also, the phase transition determination unit 14 may determine to perform the optical axis alignment operation if communication with the optical space communications device 2A is interrupted in the optical space communications operation.

[0041] The threshold setting unit 15 sets the threshold used by the limiter unit 122 .

[0042] The reflector 16 may be a passive reflector such as a corner cube reflector (CCR) or a retroreflector, and may be configured to reflect light back towards its source.

[0043] The optical free-space communications device 2A has the same configuration as the optical free-space communications device 1A, and detailed description thereof will be omitted. To avoid complexity, Fig. 3 shows only the transmitter 21, receiver 22, and reflector 26 of the components of the optical free-space communications device 2A. The transmitter 21 has the same configuration as the transmitter 11, the receiver 22 has the same configuration as the receiver 12, and the reflector 26 has the same configuration as the reflector 16.

[0044] (Optical axis alignment operation) The optical axis alignment operation of the optical space communications device 1A will now be described. Fig. 4 is a diagram illustrating the optical axis alignment operation of the optical space communications device 1A. As shown in Fig. 4, in the optical axis alignment operation, the optical space communications device 1A searches for the direction of the optical space communications device 2A by changing the direction and transmitting a first signal.

[0045] In this exemplary embodiment, the optical space communications device 1A can start optical axis alignment at its own timing. Even if the optical space communications device 2A does not know that the optical space communications device 1A has started optical axis alignment, the optical space communications device 1A can search for the direction of the optical space communications device 2A without relying on the reception processing of the optical space communications device 2A by transmitting a first signal for optical axis alignment to the optical space communications device 2A and detecting a reflected signal of the first signal reflected by the reflector 26 of the optical space communications device 2A.

[0046] The first signal transmitted by the optical space communications device 1A has a certain degree of spread, so when it is irradiated onto the optical space communications device 2A, it is expected to be irradiated onto both the receiver 22 and the reflector 26 of the optical space communications device 2A.

[0047] In this exemplary embodiment, light is irradiated onto the reflector 26 at an angle (for example, in the range of approximately 20 degrees) that allows the reflector 26 to reflect the light in a direction toward its source. In one aspect, it is preferable to adjust the orientations of the optical space communications devices 1A and 2A according to their relative positions. The relative positions of the optical space communications devices 1A and 2A can be determined, for example, from GPS (not shown) provided in the optical space communications devices 1A and 2A or from location information of the optical space communications devices 1A and 2A.

[0048] In one embodiment, the receiving unit 12 can reliably receive the reflected signal of the first signal by having a light-receiving angle corresponding to the scanning angle of the transmitting unit 11. For this reason, the receiving unit 12 may include an optical system such as a lens for widening the light-receiving angle, a light-receiving element array, a mechanism for adjusting the orientation of the receiving unit 12 to follow the transmission direction of the transmitting unit 11, and the like.

[0049] (Transition between optical axis alignment and free space optical communication) Fig. 5 is a diagram illustrating the optical axis alignment operation (reflected wave phase) and the optical free space communication operation (direct wave phase). Note that Fig. 5 shows a scene in which the optical free space communications device 1A and the optical free space communications device 2A are in the same operation (phase), but the operations (phases) of the optical free space communications device 1A and the optical free space communications device 2A may be different.

[0050] As shown in the upper part of Fig. 5, in the optical axis alignment operation (reflected wave phase), the transmitter 11 of the optical space communications device 1A transmits a first signal for optical axis alignment, the transmitted first signal is reflected by the reflector 26 of the optical space communications device 2A, and the receiver 12 of the optical space communications device 1A detects the reflected signal of the first signal. Furthermore, the transmitter 21 of the optical space communications device 2A transmits a fourth signal for optical axis alignment, the transmitted fourth signal is reflected by the reflector 16 of the optical space communications device 1A, and the receiver 22 of the optical space communications device 2A detects the reflected signal of the fourth signal. In the optical axis alignment operation, the reflected signal (reflected wave) is received by each receiver, and therefore the phase in which the optical axis alignment operation is performed is also referred to as the reflected wave phase.

[0051] As shown in the lower part of Figure 5, in an optical space communication operation (direct wave phase), the transmitter 21 of the optical space communication device 2A transmits a second signal for optical space communication, and the receiver 12 of the optical space communication device 1A detects the second signal. Also, the transmitter 11 of the optical space communication device 1A transmits a third signal for optical space communication, and the receiver 22 of the optical space communication device 2A detects the third signal. In an optical space communication operation, an unreflected signal (direct wave) is received by each receiver, and therefore the phase in which the optical space communication operation is performed is also referred to as a direct wave phase.

[0052] After completing mutual azimuth search using reflected signals during the optical axis alignment operation (reflected wave phase), the phase transition determination unit 14 of the optical space communications device 1A executes an optical space communications operation (direct wave phase) for bidirectional transmission and reception, thereby establishing a direct wave communications system. Furthermore, after transitioning to the optical space communications operation, the optical axis alignment operation is executed again due to fluctuations in azimuth angle error caused by device shaking due to wind or vibration. The phase transition determination unit 14 of the optical space communications device 1A may cause the control means to execute at least a portion of the optical axis alignment operation and at least a portion of the optical space communications operation in an overlapping manner. The phase transition determination unit of the optical space communications device 2A may also operate in a similar manner.

[0053] The key here is whether or not a smooth transition can be made from the optical axis alignment operation to the optical free-space communication operation in order to ultimately achieve optical free-space communication using direct waves. Although the reflector and transmitter are located within the same device, they are different devices, and therefore the signal level entering the receiver may differ depending on the positional misalignment between the devices. However, switching the hardware from a configuration that receives reflected waves to a configuration that receives direct waves carries the risk of requiring readjustment.

[0054] In this exemplary embodiment, the optical space communications device 1A receives both the first signal reflected by the reflector 26 of the optical space communications device 2A in the optical axis alignment operation and the second signal transmitted from the transmitter 21 of the optical space communications device 2A in the optical space communications operation at the same receiver 12, and detects each of them using the spread code. Similarly, the optical space communications device 2A receives both the fourth signal reflected by the reflector 16 of the optical space communications device 1A in the optical axis alignment operation and the third signal transmitted from the transmitter 11 of the optical space communications device 1A in the optical space communications operation at the same receiver 12, and detects each of them using the spread code.

[0055] In this exemplary embodiment, the receiver can simultaneously distinguish between reflected waves and direct waves, thereby reducing the risk of readjustment. Furthermore, since the receiver continues to receive reflected waves even after final adjustment using direct waves has begun in free-space optical communication operations, it becomes easy to return to optical axis alignment operations.

[0056] (Signal detection using spreading codes) In this exemplary embodiment, a signal is detected using a spreading code, for example, as in an optical CDMA system. More specifically, intermittent transmission (pulse transmission) is performed using a pulse signal modulated using the spreading code.

[0057] Intermittent transmission (pulse transmission) allows for higher output power. In addition, integrating the pulse signal improves reception sensitivity, making it possible to scan long distances and wide areas.

[0058] Furthermore, by detecting signals using spreading codes in the time domain, new optical devices for different wavelengths or polarizations are not required, thereby reducing costs.

[0059] During the optical axis alignment operation (reflected wave phase), if the devices are facing each other directly, a phenomenon may occur in which the signal continues to be reflected between reflectors, but the impact is generally small because the received power decreases with each reflection. Even if an impact does occur, it can be dealt with by using rake reception, which is performed via wireless communication using spread codes.

[0060] Furthermore, for example, among the optical signals received by the receiving unit 12 of the optical space communication device 1A, the second signal (direct wave) may have a higher signal level than the reflected signal (reflected wave) of the first signal due to differences in propagation distance and reflection loss, and the reflected signal (reflected wave) of the first signal may be buried.

[0061] Fig. 6 is a diagram showing an example of the reception level of a received optical signal when the signal level of the direct wave is greater than that of the reflected wave. As shown in Fig. 6, when the signal level of the direct wave is several times greater than that of the reflected wave, if despreading processing is performed using a spreading code, the reflected wave may not be detected accurately due to the large noise in the direct wave.

[0062] To solve this problem, in one embodiment, the receiver 12 may clip the received optical signal so that the signal level is equal to or lower than a threshold level, detect a reflected signal of the first signal from the clipped optical signal in the optical axis alignment operation, and detect a second signal from the clipped optical signal in the optical space communication operation. Note that in one embodiment, the threshold level is set to be closer to the signal level of the reflected signal of the first signal than to the signal level of the second signal.

[0063] Fig. 7 shows an example of the reception level of an optical signal after clipping. As shown in Fig. 7, clipping brings the signal level of the direct wave closer to the signal level of the reflected wave, so that when despreading is performed using a spreading code, the reflected wave can be accurately detected.

[0064] In one embodiment, the threshold setting unit 15 may set the threshold level. The threshold level is preferably one that reduces the direct wave, which is an unwanted wave, to at least the signal level of the reflected wave, but this varies depending on the distance between the transmitter and receiver and the propagation conditions. In particular, the propagation conditions may change due to the influence of atmospheric fluctuations.

[0065] In this exemplary embodiment, the threshold setting unit 15 may set the threshold level by the following process: First, the transmitter 11 transmits the first signal multiple times at random timings. Then, the threshold setting unit 15 may set the threshold level based on the lowest level of the reception level of the reflected signal of the first signal transmitted multiple times.

[0066] That is, by repeatedly transmitting the first signal multiple times, it is possible to receive only the reflected signal of the first signal at a timing that does not overlap with the second signal at least once. In particular, by randomizing the timing of transmitting the first signal, it is possible to further prevent overlap with the second signal. Then, the lowest level among the reception levels of the reflected signal of the first signal transmitted multiple times can be considered to correspond to the reception level when only the reflected signal of the first signal is received, and the threshold level can be set based on that lowest level. For example, the threshold level may be set to that lowest level, or a value shifted by a certain amount from that lowest level may be used as the threshold level.

[0067] Furthermore, in order to reduce the influence of atmospheric fluctuations, the transmitter 11 may transmit the first signal multiple times in multiple sets, and the threshold setting unit 15 may tally up the lowest level of the reception level of the reflected signal of the first signal in each set and set the threshold level based on the average value.

[0068] (Effects of optical space communication device) The application of the optical free space communications device 1A is not particularly limited, but an example would be to configure a network that sequentially tracks the situation (progress of the work) at a construction site. Such a network is preferably temporary and reduces the workload and construction work, and an optical free space communications network (FSO link) using optical free space communications technology is suitable. Examples include a portable temporary network or mobile network using FSO, and a multi-hop wireless network using FSO.

[0069] However, FSO links are highly directional and are significantly affected by misalignment between transmitter and receiver due to wind and vibration, so it would be extremely useful to provide a mechanism that can tolerate this.

[0070] In the optical space communications device 1A, optical axis alignment can be started asynchronously without synchronizing the timing between the connected communications devices, and each communications device can be configured in a flat manner without the need for prior coordination such as a master-slave system. Furthermore, intermittent transmission (pulse transmission) also enables long-distance and wide-angle scanning. Furthermore, the use of a reflector minimizes the number of cost-influencing devices, such as laser diodes, from the perspective of cost reduction. Furthermore, smooth transitions can be made between the optical axis alignment operation (reflected wave phase) and the optical space communications operation (direct wave phase).

[0071] Specifically, the optical space communications device 1A employs a configuration in which the receiver 12 clips the received optical signal so that the signal level is equal to or lower than a threshold level, detects a reflected signal of the first signal from the clipped optical signal, and detects a second signal from the clipped optical signal, the threshold level being set to be closer to the signal level of the reflected signal of the first signal than to the signal level of the second signal. Therefore, the optical space communications device 1A has the effect of being able to accurately detect the reflected signal of the first signal in addition to the effect achieved by the optical space communications device 1.

[0072] The optical space communications device 1A further includes a threshold setting unit 15 that sets a threshold level, and employs a configuration in which the transmitter 11 transmits the first signal multiple times, and the threshold setting unit 15 sets the threshold level based on the lowest level of the reception levels of the reflected signals of the first signal transmitted multiple times. Therefore, the optical space communications device 1A further has the effect of being able to set an appropriate threshold level for clipping.

[0073] Furthermore, the optical space communications device 1A employs a configuration in which the transmitter 11 transmits the first signal multiple times at random timings, which further provides the effect of being able to set an appropriate threshold level for clipping.

[0074] Furthermore, in the optical space communications device 1A, the transmitter 11 transmits the first signal multiple times in multiple sets, and the threshold setting unit 15 sets the threshold level based on the average value of the lowest reception level of the first signal in each set. Therefore, the optical space communications device 1A has the further advantage of being able to set an appropriate threshold level for clipping.

[0075] The optical space communications device 1A further includes a phase transition determination unit 14 that causes the optical space communications device 1A to perform at least one of an optical axis alignment operation and an optical space communication operation, and the transmitter 11 transmits a first signal in the optical axis alignment operation and transmits a third signal for optical space communication in the optical space communication operation, and the receiver 12 detects a reflected signal of the first signal in the optical axis alignment operation and detects the second signal in the optical space communication operation. Therefore, the optical space communications device 1A has the effect of being able to smoothly transition between the optical axis alignment operation and the optical space communication operation in addition to the effects of the optical space communications device 1.

[0076] Furthermore, the optical space communications device 1A employs a configuration in which the phase transition determination unit 14 executes at least a part of the optical axis alignment operation and at least a part of the optical space communications operation in an overlapping manner, which further provides the effect of enabling a smooth transition between the optical axis alignment operation and the optical space communications operation.

[0077] The optical space communications device 1A also has a configuration in which it is further provided with a reflector 16. Therefore, in addition to the effects of the optical space communications device 1, the optical space communications device 1A has the effect of enabling the optical space communications device 2A to align its optical axis in the same way as the optical space communications device 1A.

[0078] Furthermore, the optical space communications device 1A employs a configuration in which the transmitter 11 changes the transmission direction of the first signal, which provides the effect of being able to suitably search for the direction of the optical space communications device 2A.

[0079] [Software implementation example] Some or all of the functions of the optical space communications devices 1, 1A (hereinafter also referred to as "each of the above devices") may be realized by hardware such as an integrated circuit (IC chip), or by software.

[0080] In the latter case, each of the above devices is realized by, for example, a computer that executes instructions of a program, which is software that realizes each function. An example of such a computer (hereinafter referred to as computer C) is shown in Figure 8. Figure 8 is a block diagram showing the hardware configuration of computer C that functions as each of the above devices.

[0081] The computer C includes at least one processor C1 and at least one memory C2. The memory C2 stores a program P for causing the computer C to operate as each of the above-mentioned devices. In the computer C, the processor C1 reads and executes the program P from the memory C2, thereby realizing the functions of each of the above-mentioned devices.

[0082] The processor C1 may be, for example, a central processing unit (CPU), a graphic processing unit (GPU), a digital signal processor (DSP), a micro processing unit (MPU), a floating point number processing unit (FPU), a physics processing unit (PPU), a tensor processing unit (TPU), a quantum processor, a microcontroller, or a combination thereof. The memory C2 may be, for example, a flash memory, a hard disk drive (HDD), a solid state drive (SSD), or a combination thereof.

[0083] The computer C may further include a RAM (Random Access Memory) for expanding the program P during execution and for temporarily storing various data. The computer C may also include a communication interface for transmitting and receiving data to and from other devices. The computer C may also include an input / output interface for connecting input / output devices such as a keyboard, mouse, display, and printer.

[0084] Furthermore, the program P can be recorded on a non-transitory tangible recording medium M that can be read by the computer C. Such a recording medium M can be, for example, a tape, a disk, a card, a semiconductor memory, or a programmable logic circuit. The computer C can acquire the program P via such a recording medium M. The program P can also be transmitted via a transmission medium. Such a transmission medium can be, for example, a communication network or broadcast waves. The computer C can also acquire the program P via such a transmission medium.

[0085] Furthermore, the functions of each of the devices may be realized by a single processor provided in a single computer, by multiple processors provided in a single computer working in cooperation, or by multiple processors provided in each of multiple computers working in cooperation. Furthermore, the programs for causing each of the devices to realize the functions may be stored in a single memory provided in a single computer, or may be distributed and stored in multiple memories provided in a single computer, or may be distributed and stored in multiple memories provided in each of multiple computers.

[0086] [Appendix 1] This disclosure includes the techniques described in the following appendices. However, the present invention is not limited to the techniques described in the following appendices, and various modifications are possible within the scope of the claims.

[0087] (Appendix 1) An optical space communications device, A transmitting means; receiving means, The transmitting means transmitting a first signal modulated using a first spread code for aligning an optical axis with another optical space communications device equipped with a reflector; The receiving means detecting, from the received optical signal, a reflected signal of the first signal reflected by a reflector of the other optical space communications device using the first spread code; an optical space communications device that detects, from a received optical signal, a second signal for optical space communications transmitted from the other optical space communications device using a second spreading code different from the first spreading code.

[0088] (Appendix 2) The receiving means Clipping the received optical signal so that the signal level is below a threshold level; detecting a reflected signal of the first signal from the clipped optical signal; detecting the second signal from the clipped optical signal; 2. The optical space communications device according to claim 1, wherein the threshold level is set to be closer to the signal level of the reflected signal of the first signal than to the signal level of the second signal.

[0089] (Appendix 3) further comprising a setting means for setting the threshold level; The transmitting means transmitting the first signal a plurality of times; The setting means 3. The optical space communications device according to claim 2, wherein the threshold level is set based on the lowest level among the reception levels of the reflected signals of the first signal transmitted multiple times.

[0090] (Appendix 4) The transmitting means 4. The optical space communications device according to claim 3, wherein the first signal is transmitted multiple times at random timings.

[0091] (Appendix 5) The transmitting means transmitting the first signal a plurality of times in a plurality of sets; The setting means 5. The optical space communications device according to claim 3, wherein the threshold level is set based on an average value of the lowest reception levels of the first signals in each set.

[0092] (Appendix 6) The optical space communications device further includes a control unit that causes the optical space communications device to perform at least one of an optical axis alignment operation and an optical space communications operation, The transmitting means In the optical axis alignment operation, the first signal is transmitted; In the optical space communication operation, a third signal for optical space communication is transmitted; The receiving means In the optical axis alignment operation, a reflected signal of the first signal is detected; 6. The optical space communications device according to any one of appendices 1 to 5, wherein the second signal is detected in the optical space communications operation.

[0093] (Appendix 7) The control means 7. The optical space communications device according to claim 6, wherein at least a portion of the optical axis alignment operation and at least a portion of the optical space communications operation are executed in an overlapping manner.

[0094] (Appendix 8) 8. The optical space communications device according to any one of claims 1 to 7, further comprising a reflector.

[0095] (Appendix 9) The transmitting means 9. The optical space communications device according to any one of appendices 1 to 8, wherein the transmission direction of the first signal is changed.

[0096] (Appendix 10) An optical space communication method executed by an optical space communication device, Transmitting a first signal modulated using a first spread code for optical axis alignment with another optical space communications device equipped with a reflector; Detecting, from the received optical signal, a reflected signal of the first signal reflected by a reflector of the other optical space communications device using the first spread code; and detecting, from the received optical signal, a second signal for optical space communication transmitted from the other optical space communication device using a second spreading code different from the first spreading code.

[0097] (Appendix 11) An optical space communications program for causing a computer to operate as the optical space communications device according to any one of appendices 1 to 11, the optical space communications program causing the computer to function as each of the means.

[0098] [Appendix 2] This disclosure includes the techniques described in the following appendices. However, the present invention is not limited to the techniques described in the following appendices, and various modifications are possible within the scope of the claims.

[0099] (Appendix 1) An optical space communications device, at least one processor, A transmission process; Execute the receiving process, In the transmission process, the at least one processor transmitting a first signal modulated using a first spread code for aligning an optical axis with another optical space communications device equipped with a reflector; In the receiving process, the at least one processor: detecting, from the received optical signal, a reflected signal of the first signal reflected by a reflector of the other optical space communications device using the first spread code; an optical space communications device that detects, from a received optical signal, a second signal for optical space communications transmitted from the other optical space communications device using a second spreading code different from the first spreading code.

[0100] The optical space communications device may further include a memory, and the memory may store a program for causing the at least one processor to execute each of the processes.

[0101] (Appendix 2) In the receiving process, the at least one processor: Clipping the received optical signal so that the signal level is below a threshold level; detecting a reflected signal of the first signal from the clipped optical signal; detecting the second signal from the clipped optical signal; 2. The optical space communications device according to claim 1, wherein the threshold level is set to be closer to the signal level of the reflected signal of the first signal than to the signal level of the second signal.

[0102] (Appendix 3) the at least one processor further performs a setting process to set the threshold level; In the transmission process, the at least one processor transmitting the first signal a plurality of times; In the setting process, the at least one processor 3. The optical space communications device according to claim 2, wherein the threshold level is set based on the lowest level among the reception levels of the reflected signals of the first signal transmitted multiple times.

[0103] (Appendix 4) In the transmission process, the at least one processor 4. The optical space communications device according to claim 3, wherein the first signal is transmitted multiple times at random timings.

[0104] (Appendix 5) In the transmission process, the at least one processor transmitting the first signal a plurality of times in a plurality of sets; In the setting process, the at least one processor 5. The optical space communications device according to claim 3, wherein the threshold level is set based on an average value of the lowest reception levels of the first signals in each set.

[0105] (Appendix 6) the at least one processor further executes a control process to cause the optical space communications device to perform at least one of an optical axis alignment operation and an optical space communications operation; In the transmission process, the at least one processor In the optical axis alignment operation, the first signal is transmitted; In the optical space communication operation, a third signal for optical space communication is transmitted; In the receiving process, the at least one processor: In the optical axis alignment operation, a reflected signal of the first signal is detected; 6. The optical space communications device according to any one of appendices 1 to 5, wherein the second signal is detected in the optical space communications operation.

[0106] (Appendix 7) In the control process, the at least one processor 7. The optical space communications device according to claim 6, wherein at least a portion of the optical axis alignment operation and at least a portion of the optical space communications operation are executed in an overlapping manner.

[0107] (Appendix 8) 8. The optical space communications device according to any one of claims 1 to 7, further comprising a reflector.

[0108] (Appendix 9) In the transmission process, the at least one processor 9. The optical space communications device according to any one of appendices 1 to 8, wherein the transmission direction of the first signal is changed. [Explanation of symbols]

[0109] 1,1A...Optical space communication equipment 11 Transmitter 111...Code generation section 112 Random signal generator 113 Diffusion processing unit 114 Transmission processing unit 12 Receiving unit 121 Limiter section 122 Despreading processing unit 123 Receiving processing unit 14 Phase transition determination unit 15 Threshold setting section 16...reflector 2,2A...Optical space communication equipment 21 Transmitter 22 Receiving unit 26...reflector

Claims

1. An optical space communications device, A transmitting means; receiving means, The transmitting means transmitting a first signal modulated using a first spread code for aligning an optical axis with another optical space communications device equipped with a reflector; The receiving means detecting, from the received optical signal, a reflected signal of the first signal reflected by a reflector of the other optical space communications device using the first spread code; An optical space communications device that detects, from a received optical signal, a second signal for optical space communications transmitted from the other optical space communications device using a second spreading code different from the first spreading code.

2. The receiving means Clipping the received optical signal so that the signal level is below a threshold level; detecting a reflected signal of the first signal from the clipped optical signal; detecting the second signal from the clipped optical signal; The optical space communications device according to claim 1 , wherein the threshold level is set to be closer to a signal level of a reflected signal of the first signal than to a signal level of the second signal.

3. further comprising a setting means for setting the threshold level; The transmitting means transmitting the first signal a plurality of times; The setting means The optical space communications device according to claim 2 , wherein the threshold level is set based on a minimum level among reception levels of the reflected signals of the first signal transmitted a plurality of times.

4. The transmitting means The optical space communications device according to claim 3 , wherein the first signal is transmitted multiple times at random timings.

5. The transmitting means transmitting the first signal a plurality of times in a plurality of sets; The setting means The optical space communications device according to claim 3 , wherein the threshold level is set based on an average value of the lowest reception levels of the first signals in each set.

6. The optical space communications device further includes a control unit that causes the optical space communications device to perform at least one of an optical axis alignment operation and an optical space communications operation, The transmitting means In the optical axis alignment operation, the first signal is transmitted; In the optical space communication operation, a third signal for optical space communication is transmitted; The receiving means In the optical axis alignment operation, a reflected signal of the first signal is detected; The optical space communications device according to claim 1, wherein the second signal is detected in the optical space communications operation.

7. The control means The optical free space communications device according to claim 6 , wherein at least a part of the optical axis alignment operation and at least a part of the optical free space communications operation are executed in an overlapping manner.

8. The optical free space communications device according to claim 1 , further comprising a reflector.

9. The transmitting means The optical space communications device according to claim 1 , wherein the transmission direction of the first signal is changed.

10. An optical space communication method executed by an optical space communication device, Transmitting a first signal modulated using a first spread code for optical axis alignment with another optical space communications device equipped with a reflector; Detecting a reflected signal of the first signal reflected by a reflector of the other optical space communications device from the received optical signal using the first spread code; and detecting, from the received optical signal, a second signal for optical space communication transmitted from the other optical space communication device using a second spreading code different from the first spreading code.

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