Communication method, communication device, and communication system

Abstract

This communication method is executed by a communication device and includes: a step for detecting distortion of a wavefront of an arrived optical signal; a step for deriving each component from a high order component to a low order component in the distortion of the wavefront; a step for controlling, in accordance with the low order component, a tilt of a reflective surface of a first optical device that changes a propagation direction of the arrived optical signal; and a step for controlling, in accordance with the high order component, a phase modulation operation by a second optical device that modulates a phase of the wavefront of the optical signal for which the propagation direction was modified.

Description

[Technical Field]

[0001] The present invention relates to a communication method, a communication device, and a communication system. [Background technology]

[0002] Optical wireless communication between a transmitter and a receiver may be performed using an optical signal propagating through the atmosphere. In this case, the wavefront of the optical signal is distorted by the influence of the atmosphere. This causes spatial intensity variations (speckle) in the optical signal arriving at the receiver. This intensity pattern fluctuates over time depending on atmospheric turbulence. This intensity pattern is a major obstacle to realizing stable optical wireless communication.

[0003] Adaptive optics, which compensates for wavefront distortion of optical signals through closed-loop control in order to suppress the effects of atmospheric turbulence, has been studied (see Non-Patent Document 1). In this adaptive optics, a receiver observes the effects of atmospheric turbulence on an optical signal transmitted from a transmitter (opposing station). That is, the receiver observes the wavefront distortion (spatial phase distribution) of the arriving optical signal. Based on the observation results, the receiver derives a compensation pattern for the wavefront distortion. A wavefront control device provided in the receiver forms the compensation pattern for the wavefront distortion on the wavefront affected by the turbulence. This improves the quality of optical wireless communication. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Yongxiong Ren, Guodong Xie, Hao Huang, Nisar Ahmed, Yan Yan, Long Li, Changjing Bao, Martin PJ Lavery, Moshe Tur, Mark A. Neifeld, Robert W. Boyd, Jeffrey H. Shapiro, and Alan E. Willner, "Adaptive-optics-based simultaneous pre- and post-turbulence compensation of multiple orbital-angular-momentum beams in a bidirectional free-space optical link," Optica 1, 376-382 (2014) Summary of the Invention [Problem to be solved by the invention]

[0005] In general, low-order components of atmospheric turbulence (vertical or horizontal tilt components) are larger than high-order components of atmospheric turbulence. In the adaptive optics disclosed in Non-Patent Document 1, a deformable mirror forms a compensation pattern on a wavefront affected by turbulence. However, there is a problem in that the cost of the communication device (receiver) increases as the number of deformable mirror elements is increased in the communication device (receiver) in order to compensate for the high spatial frequency components contained in the distortion of the wavefront.

[0006] In addition, spatial light phase modulators (LCOS-SLM: Liquid Crystal on Silicon - Spatial Light Modulator) are inexpensive. Spatial light phase modulators are capable of compensation with high spatial resolution. However, when a spatial light phase modulator forms a compensation pattern for wavefront distortion in order to compensate for large low-order components, the effect of the compensation pattern changing stepwise cannot be ignored. This causes the beam of the optical signal with the compensated wavefront to become distorted, reducing the diffraction efficiency of the optical signal. As a result, there is a problem in that it is not possible to improve the accuracy of compensation for wavefront distortion of optical signals propagating through the atmosphere.

[0007] In view of the above circumstances, an object of the present invention is to provide a communication method, a communication device, and a communication system that can improve the accuracy of compensating for distortion of the wavefront of an optical signal propagated through the atmosphere. [Means for solving the problem]

[0008] One aspect of the present invention is a communication method executed by a communication device, the communication method including the steps of detecting distortion of a wavefront of an optical signal, deriving each component of the wavefront distortion from a high-order component to a low-order component, controlling the inclination of a reflecting surface of a first optical device that changes the propagation direction of the optical signal in accordance with the low-order components, and controlling the phase modulation operation by a second optical device that modulates the phase of the wavefront of the optical signal whose propagation direction has been changed in accordance with the high-order components.

[0009] One aspect of the present invention is a communication device comprising: a sensor that detects distortion of the wavefront of an optical signal; an analysis unit that derives each component of the wavefront distortion, from higher-order components to lower-order components; a first control unit that controls the inclination of the reflecting surface of a first optical device that changes the propagation direction of the optical signal in accordance with the lower-order components; and a second control unit that controls the phase modulation operation by a second optical device that modulates the phase of the wavefront of the optical signal whose propagation direction has been changed in accordance with the higher-order components.

[0010] One aspect of the present invention is a communication system comprising a first communication device and a second communication device, wherein the first communication device comprises a transmitting unit that transmits an optical signal, and the second communication device comprises a sensor that detects distortion of the wavefront of the optical signal arriving from the first communication device, an analysis unit that derives each component from high-order components to low-order components in the wavefront distortion, a first control unit that controls the inclination of the reflecting surface of a first optical device that changes the propagation direction of the arriving optical signal in accordance with the low-order components, and a second control unit that controls the phase modulation operation by a second optical device that modulates the phase of the wavefront of the optical signal whose propagation direction has been changed in accordance with the high-order components.

[0011] One aspect of the present invention is a communication system comprising a first communication device and a second communication device, wherein the first communication device comprises a transmitter that transmits an optical signal, a sensor that detects distortion of the wavefront of a reference optical signal transmitted from the second communication device, an analyzer that derives each component from high-order components to low-order components in the wavefront distortion, a first controller that controls the inclination of the reflecting surface of a first optical device that changes the propagation direction of the transmitted optical signal in accordance with the low-order components, and a second controller that controls the phase modulation operation by a second optical device that modulates the phase of the wavefront of the optical signal whose propagation direction has been changed in accordance with the high-order components, and the second communication device comprises a receiver that receives the phase-modulated optical signal. [Effects of the Invention]

[0012] According to the present invention, it is possible to improve the accuracy of compensating for distortion of the wavefront of an optical signal propagated through the atmosphere. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a communication system in a first embodiment. [Figure 2] FIG. 10 is a diagram showing an example of 12 Zernike modes in decreasing order of the Zernike polynomials in the first embodiment. [Figure 3] 5A to 5C are diagrams illustrating examples of components of wavefront distortion in the first embodiment. [Figure 4] FIG. 3 is a diagram showing an example of each component selected in a Zernike polynomial in the first embodiment. [Figure 5] 4 is a flowchart showing an example of the operation of the communication system in the first embodiment. [Figure 6] FIG. 10 is a diagram illustrating an example of the configuration of a communication system in a second embodiment. [Figure 7] 10 is a flowchart showing an example of the operation of a communication system in the second embodiment. [Figure 8] FIG. 2 is a diagram illustrating an example of a hardware configuration of a communication device in each embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. (First embodiment) 1 is a diagram showing an example of the configuration of a communication system 1a in the first embodiment. The communication system 1a is an optical communication system that performs wireless communication (optical wireless communication) using optical signals.

[0015] The communication system 1a includes one or more transmitters 2a (first communication devices) and one or more receivers 3a (second communication devices). In the communication system 1a, an optical signal propagates through the atmosphere between the transmitter 2a and the receiver 3a. In the first embodiment, the receiver 3a compensates for distortion (aberration) occurring in the wavefront of the optical signal propagated through the atmosphere using adaptive optics. In the communication system 1a, at least one of a tip-tilt mirror and a deformable mirror is used to compensate for low-order components (low-order modes) of the distortion occurring in the wavefront. A spatial optical phase modulator is used to compensate for high-order components (high-order modes) of the distortion occurring in the wavefront.

[0016] Next, the transmitting device 2a will be described. The transmission device 2a includes a generation unit 21 and a transmission unit 22. The generation unit 21 generates an electrical signal in accordance with data. The transmission unit 22 converts the electrical signal into an optical signal. The optical signal transmitted from the transmission unit 22 propagates through the atmosphere and arrives at (incident on) the first optical device 31.

[0017] Next, the receiving device 3a will be described. The receiving device 3a includes a first optical device 31, a second optical device 32, a splitter 33, a receiving unit , a sensor 35, an analyzing unit , a first control unit 37, and a second control unit .

[0018] The first optical device 31 and the second optical device 32 are configured in a multi-stage configuration. The first optical device 31 may be located in front of the second optical device 32 or in back of the second optical device 32. In the following description, the first optical device 31 is located in front of the second optical device 32, as an example.

[0019] The first optical device 31 is a mirror. This mirror is, for example, at least one of a tip-tilt mirror and a deformable mirror. The first optical device 31 changes the tilt of the reflecting surface of the first optical device 31 in accordance with the control of the first control unit 37. The first optical device 31 reflects the optical signal transmitted by the transmitter 22 in a direction according to the tilt of the first optical device 31. In this way, the first optical device 31 changes the propagation direction (deflection angle) of the optical signal arriving at the first optical device 31 in accordance with the control of the first control unit 37.

[0020] The optical signal whose propagation direction has been changed by the first optical device 31 arrives at the second optical device 32. The second optical device 32 is a spatial optical phase modulator. The second optical device 32 modulates the phase of the wavefront of the optical signal whose propagation direction has been changed. That is, the second optical device 32 modulates the phase of the wavefront of the optical signal reflected by the first optical device 31. The optical signal whose wavefront phase has been modulated arrives at the splitter 33.

[0021] The splitter 33 splits the optical signal, the wavefront of which has been phase-modulated by the second optical device 32, into a receiver 34 and a sensor 35. The receiver 34 converts the optical signal received from the splitter 33 into an electrical signal. The receiver 34 performs predetermined signal processing (e.g., demodulation processing) on ​​the converted electrical signal. The receiver 34 acquires data transmitted from the transmitter 2a using the optical signal from the electrical signal through the predetermined signal processing.

[0022] The sensor 35 is a wave-front sensor. The sensor 35 detects the distortion (aberration) of the wavefront of the optical signal split by the splitter 33 by observing the spatial phase distribution of the wavefront of the optical signal. In this way, the sensor 35 detects the distortion of the wavefront of the optical signal arriving at the splitter 33. The sensor 35 may also detect the distortion of the wavefront of the optical signal arriving at the first optical device 31 or the second optical device 32. The sensor 35 outputs a signal representing the distortion of the wavefront of the optical signal to the analysis unit 36.

[0023] The analysis unit 36 ​​acquires a signal representing the wavefront distortion of the optical signal from the sensor 35. The analysis unit 36 ​​derives each component, from higher-order components to lower-order components, of the detected wavefront distortion. For example, the analysis unit 36 ​​analyzes the breakdown of multiple components (modes) constituting the wavefront distortion by expanding the wavefront distortion into Zernike polynomials. The analysis unit 36 ​​outputs signals representing each component derived by the analysis to the first control unit 37 and the second control unit 38.

[0024] The first control unit 37 selects components having a predetermined first component amount or more from predetermined low-order components. That is, the first control unit 37 selects one or more principal components from the low-order components. The first control unit 37 derives a phase conjugate pattern of the selected component from the low-order components as a compensation pattern for the low-order components. The first control unit 37 controls the tilt of the reflecting surface of the first optical device 31 in accordance with the selected component. That is, the first control unit 37 controls the tilt of the reflecting surface of the first optical device 31 using the compensation pattern for the low-order component. In this way, the first control unit 37 controls the propagation direction of the optical signal received by the first optical device 31 in accordance with the selected component from the low-order components.

[0025] The second control unit 38 may select all of the high-order components of the Zernike polynomials, but selects components having a predetermined second component amount or more (high-order components having Zernike coefficients equal to or greater than a threshold) from among the predetermined high-order components. That is, the second control unit 38 selects a principal component from among the high-order components. The second control unit 38 derives a phase conjugate pattern of the selected component from among the high-order components as a compensation pattern for the high-order component. The second control unit 38 controls the operation of phase modulation by the second optical device 32 according to the compensation pattern. As a result, the second control unit 38 controls the phase of the wavefront of the optical signal arriving at the second optical device 32 according to the derived compensation pattern (phase conjugate pattern). Because the second control unit 38 selects components having a predetermined second component amount or more from among the predetermined high-order components, the amount of calculation required for compensation can be reduced compared to the amount of calculation required when all of the high-order components of the Zernike polynomials are selected. The amount of calculation required for compensation is, for example, the amount of calculation required for deriving the compensation pattern for the high-order component and reconstructing the wavefront. The second control unit 38 can reduce the amount of calculation required for compensation, thereby improving the speed of compensation processing for wavefront distortion. The second control unit 38 can improve the speed of compensation processing, thereby tracking time fluctuations in atmospheric turbulence and accurately compensating for wavefront distortion.

[0026] Next, the analysis of the wavefront distortion will be described. The analysis unit 36 ​​analyzes the breakdown of multiple components (modes) that make up the wavefront distortion by expanding the wavefront distortion into Zernike polynomials. That is, the analysis unit 36 ​​derives one or more Zernike modes (phase patterns) that make up the wavefront distortion (phase). The wavefront distortion "W(r, θ)" is expressed as in Equation (1).

[0027]

number

[0028] Here, "r" represents the distance from the origin in the polar coordinate system. "θ" represents the angle of deviation in the polar coordinate system. i " represents the Zernike coefficient. "i" represents the Zernike mode number. "Z i " represents a Zernike mode. Zernike mode "Z i " is expressed as equation (2).

[0029]

number

[0030] Here, "n" and "m" represent the order. The order "n" is a non-negative integer. The order "m" is an integer that satisfies "n≧|m|". "n" and "m" are determined according to the Zernike mode number "i". The column vector "W" of the wavefront phase "W(r,θ)" is expressed as in equation (3).

[0031]

number

[0032] Here, "Z" on the right side of equation (3) represents the Zernike mode "Z i " represents a column vector of Zernike modes "Z i The column vector of " is expressed as in equation (4).

[0033]

number

[0034] Moreover, the column vector "A" of the Zernike coefficients is expressed as in equation (5).

[0035]

number

[0036] 2 is a diagram showing an example of 12 Zernike modes in descending order of the Zernike polynomials in an embodiment. The Zernike modes (components) are orthogonal to each other.

[0037] In the following, the threshold for determining whether or not a component is a high-order component (whether or not it is not a low-order component) is, for example, "4." In the following, the predetermined first component amount is, for example, "3." In the following, the predetermined second component amount is, for example, "0.5."

[0038] FIG. 3 is a diagram showing an example of each component of wavefront distortion in an embodiment. Each component (each mode) from Zernike modes "Z1" to "Z3" is a low-order component (low-order mode) below the Zernike mode number threshold value "4." In FIG. 3, the component amount (Zernike coefficient "a1") of Zernike mode "Z1" is "0.001," which is less than the first component amount "3." The component amount (Zernike coefficient "a2") of Zernike mode "Z2" is "3," which is equal to or greater than the first component amount "3." The component amount (Zernike coefficient "a3") of Zernike mode "Z3" is "0.001," which is less than the first component amount "3."

[0039] Therefore, the first control unit 37 selects one or more Zernike modes that exhibit a first component amount of "3" or more. The first optical device 31 is used to compensate for the low-order components. The first control unit 37 uses the selected Zernike mode "Z2" to control the tilt of the first optical device 31 in order to compensate for the low-order components in the wavefront distortion.

[0040] Zernike mode "Z4" to "Z 12Each component (each mode) up to 1 is a high-order component (high-order mode) with a Zernike mode number threshold of 4 or more. In Figure 3, the component amount of Zernike mode "Z7" is 0.6, which is greater than the second component amount of 0.5.

[0041] Therefore, the second control unit 38 selects one or more Zernike modes that exhibit a second component amount of "0.5" or greater. The second optical device 32 is used to compensate for the higher-order components. The second control unit 38 uses the selected Zernike mode "Z7" to control the operation of the second optical device 32 (reconstructing the higher-order components in the wavefront distortion) for the purpose of compensating for the higher-order components. For example, the second control unit 38 uses the selected Zernike mode "Z7" to derive a phase pattern "(a7 × Z7) = (0.5 × Z7)" that constitutes the wavefront distortion. The second control unit 38 derives a phase conjugate pattern of the phase pattern, "-(0.5 × Z7)," as the compensation pattern. The second control unit 38 controls the operation of the second optical device 32 so that the second optical device 32 forms a compensation pattern for the wavefront distortion on the wavefront.

[0042] FIG. 4 is a diagram showing an example of each component selected in a Zernike polynomial in an embodiment. The column vector "W" of the wavefront phase "W(r, θ)" is expressed as the sum of the multiplication result of the Zernike coefficient "a2" and the Zernike mode "Z2" and the multiplication result of the Zernike coefficient "a7" and the Zernike mode "Z7." In other words, the phase pattern of the wavefront is expressed as "W = a2 × Z2 + a7 × Z7." Therefore, the compensation pattern (phase conjugate pattern) of the low-order component is expressed as "-a2 × Z2." Furthermore, the compensation pattern (phase conjugate pattern) of the high-order component is expressed as "-a7 × Z7."

[0043] The first control unit 37 derives the phase conjugate pattern "-a2×Z2" as a compensation pattern for the low-order components. The first control unit 37 uses "-a2×Z2" in the phase conjugate pattern to control the tilt of the first optical device 31 in order to compensate for the low-order components in the wavefront distortion.

[0044] The second control unit 38 derives the phase conjugate pattern "-a7×Z7" as the compensation pattern for the high-order component. The second control unit 38 controls the operation of the second optical device 32 so that the second optical device 32 forms the compensation pattern for the high-order component "-a7×Z7" on the wavefront.

[0045] Next, an example of the operation of the communication system 1a will be described. 5 is a flowchart showing an example of operation of the communication system 1a according to the embodiment. The sensor 35 detects the wavefront distortion (aberration) of the optical signal split by the splitter 33 (step S101). The analyzer 36 derives each component (each orthogonal mode) from the higher-order component to the lower-order component in the detected wavefront distortion. That is, the analyzer 36 expands the detection result of the wavefront distortion into Zernike polynomials (step S102).

[0046] The first control unit 37 selects a component having a first component amount or more from among predetermined low-order components. For example, the first control unit 37 selects the Zernike mode "Z2" having a first component amount of "3" or more from among the Zernike modes "Z1," "Z2," and "Z3" which are third-order or lower modes (step S103).

[0047] The first control unit 37 derives a phase conjugate pattern of the selected low-order component (step S104). The first control unit 37 controls the propagation direction of the optical signal reflected by the first optical device 31 by changing the tilt of the reflecting surface of the first optical device 31 according to the phase conjugate pattern of the low-order component (step S105).

[0048] The second control unit 38 selects components having a second component amount or more from among the predetermined high-order components (step S106). The second control unit 38 derives a phase conjugate pattern for the selected component from among the high-order components (step S107). The second control unit 38 controls the phase of the wavefront of the optical signal according to the derived phase conjugate pattern using the second optical device 32 (step S108). The second optical device 32 outputs the optical signal whose propagation direction and phase have been controlled to the splitter 33 (step S109).

[0049] As described above, the transmitter 22 of the transmitter 2a (first communication device) transmits an optical signal. The sensor 35 of the receiver 3a (second communication device) detects the wavefront distortion of the optical signal arriving from the splitter 33. That is, the sensor 35 detects the wavefront distortion of the optical signal arriving from the transmitter 2a. The analyzer 36 derives each component from higher-order components to lower-order components in the wavefront distortion. The first controller 37 controls the inclination of the reflecting surface of the first optical device 31, which changes the propagation direction of the arriving optical signal, in accordance with the lower-order components. The second controller 38 controls the phase modulation operation of the second optical device 32, which modulates the phase of the wavefront of the optical signal whose propagation direction has been changed, in accordance with the higher-order components.

[0050] This makes it possible to improve the accuracy of compensating for distortion of the wavefront of an optical signal propagated through the atmosphere. It is possible to accurately compensate for high spatial frequency components (higher-order mode components) and low spatial frequency components (lower-order mode components) in the distortion of the wavefront of an optical signal. Furthermore, the communication system 1a can perform stable optical wireless communication.

[0051] At least one of the analyzer 36, the first controller 37, and the second controller 38 may select a Zernike mode in which the amount of components (Zernike coefficients) in the Zernike polynomials is equal to or greater than a predetermined amount. The first controller 37 may control the tilt of the reflecting surface of the first optical device 31 in accordance with the Zernike mode selected for the low-order components. The second controller 38 may control the operation of phase modulation by the second optical device 32 in accordance with the Zernike mode selected for the high-order components.

[0052] (Second embodiment) The second embodiment differs from the first embodiment in that a transmitting device compensates for distortion occurring in the wavefront of a transmitted optical signal before the optical signal is transmitted. The second embodiment will be described focusing on the differences from the first embodiment.

[0053] FIG. 6 is a diagram illustrating an example of the configuration of a communication system 1b in the second embodiment. The communication system 1b includes one or more transmitting devices 2a (first communication devices) and one or more receiving devices 3b (second communication devices). In the communication system 1b, an optical signal transmitted from the transmitting device 2b toward the receiving device 3b propagates through the atmosphere between the transmitting device 2b and the receiving device 3b. In the communication system 1b, a reference optical signal transmitted from the receiving device 3b toward the transmitting device 2b propagates through the atmosphere between the transmitting device 2b and the receiving device 3b. In the second embodiment, the transmitting device 2b compensates for distortion (aberration) occurring in the wavefront of the optical signal propagating through the atmosphere by adaptive optics.

[0054] The transmitting device 2b includes a generating unit 21, a transmitting unit 22, a first optical device 31, a second optical device 32, a sensor 35, an analyzing unit 36, a first control unit 37, and a second control unit 38. The receiving device 3b includes a receiving unit 34 and a reference light transmitting unit 39.

[0055] The second optical device 32 modulates the phase of the wavefront of the optical signal reflected by the first optical device 31. The optical signal whose wavefront phase has been modulated arrives at the receiving unit .

[0056] The reference light transmitting unit 39 transmits a predetermined reference light signal to the sensor 35. The sensor 35 detects the distortion (aberration) of the wavefront of the reference light signal transmitted from the reference light transmitting unit 39 by observing the spatial phase distribution of the wavefront of the reference light signal. The distortion of the wavefront of the reference light signal propagated through the atmosphere is similar to the distortion of the wavefront of an optical signal propagated through the same atmosphere. The sensor 35 outputs a signal representing the distortion of the wavefront of the reference light signal to the analyzing unit 36.

[0057] The analysis unit 36 ​​acquires a signal representing the distortion of the wavefront of the reference light signal from the sensor 35. The analysis unit 36 ​​derives each component from the high-order component to the low-order component in the detected distortion of the wavefront.

[0058] Next, an example of the operation of the communication system 1b will be described. 7 is a flowchart showing an example of operation of the communication system 1b in the second embodiment. The sensor 35 detects the wavefront distortion (aberration) of the reference light signal transmitted from the reference light transmitter 39 (step S201). The analyzer 36 derives each component (each orthogonal mode) from the higher-order component to the lower-order component in the detected wavefront distortion. That is, the analyzer 36 expands the detection result of the wavefront distortion into Zernike polynomials (step S202).

[0059] The first control unit 37 selects a component having a first component amount or more from among predetermined low-order components. For example, the first control unit 37 selects the Zernike mode "Z2" having a first component amount of "3" or more from among the Zernike modes "Z1," "Z2," and "Z3" which are third-order or lower modes (step S203).

[0060] The first control unit 37 derives a phase conjugate pattern of the selected low-order component (step S204). The first control unit 37 controls the propagation direction of the optical signal reflected by the first optical device 31 by changing the inclination of the reflecting surface of the first optical device 31 according to the phase conjugate pattern of the low-order component (step S205).

[0061] The second control unit 38 selects a component having a second component amount or more from among predetermined high-order components (step S206). The second control unit 38 derives a phase conjugate pattern for the component selected from among the high-order components (step S207). The second control unit 38 controls the phase of the wavefront of the optical signal before transmission according to the derived phase conjugate pattern using the second optical device 32 (step S208). The second optical device 32 outputs the optical signal whose propagation direction and phase have been controlled to the splitter 33 (step S209).

[0062] As described above, the transmitting unit 22 of the transmitting device 2b (first communication device) transmits an optical signal to the first optical device 31. The sensor 35 detects the wavefront distortion of the reference optical signal transmitted from the receiving device 3b (second communication device). The analyzing unit 36 ​​derives each component of the wavefront distortion, from higher-order components to lower-order components. The first control unit 37 controls the inclination of the reflecting surface of the first optical device 31, which changes the propagation direction of the transmitted optical signal, in accordance with the lower-order components. The second control unit 38 controls the phase modulation operation of the second optical device 32, which modulates the phase of the wavefront of the optical signal whose propagation direction has been changed, in accordance with the higher-order components. The receiving unit 34 of the receiving device 3b receives the phase-modulated optical signal.

[0063] This makes it possible to improve the accuracy of compensating for distortion of the wavefront of an optical signal propagated through the atmosphere. It is possible to accurately compensate for high spatial frequency components (higher-order mode components) and low spatial frequency components (lower-order mode components) in the distortion of the wavefront of an optical signal. Furthermore, the communication system 1b can perform stable optical wireless communication.

[0064] (Example of hardware configuration) FIG. 8 is a diagram illustrating an example of the hardware configuration of the communication device 10 in each embodiment. The communication device 10 corresponds to at least one of a transmitting device (first communication device) and a receiving device (second communication device). Some or all of the functional units of the communication device 10 are realized as software by a processor 101, such as a CPU (Central Processing Unit), executing programs stored in a storage device 102 and a memory 103, which have non-volatile recording media (non-transitory recording media). The programs may be recorded on a computer-readable non-transitory recording medium. Examples of computer-readable non-transitory recording media include portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), and CD-ROMs (Compact Disc Read Only Memory), and storage devices such as hard disks built into a computer system. A communication unit 104 executes a predetermined communication process. The communication unit 104 may acquire data and programs.

[0065] Some or all of the functional units of the communication device 10 may be realized using hardware including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0066] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0067] The present invention is applicable to optical communication systems that perform wireless communication using optical signals. [Explanation of symbols]

[0068] DESCRIPTION OF SYMBOLS 1a, 1b...communication system, 2, 2a, 2b...transmitting device, 3, 3a, 3b...receiving device, 21...generation unit, 22...transmitting unit, 31...first optical device, 32...second optical device, 33...splitter, 34...receiving unit, 35...sensor, 36...analyzing unit, 37...first control unit, 38...second control unit, 39...reference light transmitting unit

Claims

1. A communication method performed by a communication device, comprising: detecting a distortion in a wavefront of an optical signal; deriving each component from a high-order component to a low-order component in the distortion of the wavefront; controlling the inclination of a reflecting surface of a first optical device that changes the propagation direction of the optical signal in accordance with a compensation pattern of the low-order component; controlling a phase modulation operation by a second optical device that modulates the phase of the wavefront of the optical signal whose propagation direction has been changed, in accordance with a compensation pattern of the high-order component; Including, the step of controlling in accordance with the compensation pattern of the low-order component includes deriving a phase conjugate pattern of a component selected from the low-order components as the compensation pattern of the low-order component, the step of controlling in accordance with the compensation pattern of the high-order component includes deriving a phase conjugate pattern of a component selected from the high-order components as the compensation pattern of the high-order component. Communication method.

2. the first optical device is at least one of a tip-tilt mirror and a deformable mirror; the second optical device is a spatial optical phase modulator; The communication method according to claim 1 .

3. the step of controlling in accordance with the low-order component includes selecting, for the low-order component, a Zernike mode whose component amount in a Zernike polynomial is equal to or greater than a first component amount, and controlling a tilt of the reflecting surface in accordance with the Zernike mode selected for the low-order component, the step of controlling in accordance with the higher-order component includes selecting, for the higher-order component, a Zernike mode whose component amount in the Zernike polynomial is equal to or greater than a second component amount, and controlling an operation of the phase modulation in accordance with the Zernike mode selected for the higher-order component. The communication method according to claim 1 or 2.

4. The optical signal is a signal arriving at the communication device or a signal being transmitted from the communication device. The communication method according to any one of claims 1 to 3.

5. a sensor for detecting distortion of a wavefront of an optical signal; an analysis unit that derives each component from a high-order component to a low-order component in the distortion of the wavefront; a first control unit that controls the inclination of a reflecting surface of a first optical device that changes the propagation direction of the optical signal in accordance with a compensation pattern of the low-order component; a second control unit that controls a phase modulation operation by a second optical device that modulates the phase of a wavefront of the optical signal whose propagation direction has been changed, in accordance with a compensation pattern of the high-order component; Equipped with the first control unit derives a phase conjugate pattern of a component selected from the low-order components as a compensation pattern for the low-order components; the second control unit derives a phase conjugate pattern of a component selected from the high-order components as a compensation pattern for the high-order component; Communication equipment.

6. A communication system comprising a first communication device and a second communication device, The first communication device a transmitter for transmitting an optical signal; the second communication device, a sensor for detecting distortion of a wavefront of an optical signal arriving from the first communication device; an analysis unit that derives each component from a high-order component to a low-order component in the distortion of the wavefront; a first control unit that controls a tilt of a reflecting surface of a first optical device that changes a propagation direction of the incoming optical signal in accordance with a compensation pattern of the low-order component; a second control unit that controls a phase modulation operation by a second optical device that modulates the phase of a wavefront of the optical signal whose propagation direction has been changed, in accordance with a compensation pattern of the high-order component; the first control unit derives a phase conjugate pattern of a component selected from the low-order components as a compensation pattern for the low-order components; the second control unit derives a phase conjugate pattern of a component selected from the high-order components as a compensation pattern for the high-order component; Communication system.

7. A communication system comprising a first communication device and a second communication device, The first communication device a transmitter that transmits an optical signal; a sensor for detecting distortion of a wavefront of a reference optical signal transmitted from the second communication device; an analysis unit that derives each component from a high-order component to a low-order component in the distortion of the wavefront; a first control unit that controls the inclination of a reflecting surface of a first optical device that changes the propagation direction of the transmitted optical signal in accordance with a compensation pattern of the low-order component; a second control unit that controls a phase modulation operation by a second optical device that modulates the phase of a wavefront of the optical signal whose propagation direction has been changed, in accordance with a compensation pattern of the high-order component; Equipped with the second communication device, a receiving unit that receives the phase-modulated optical signal, the first control unit derives a phase conjugate pattern of a component selected from the low-order components as a compensation pattern for the low-order components; the second control unit derives a phase conjugate pattern of a component selected from the high-order components as a compensation pattern for the high-order component; Communication system.

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