Optical communication equipment

Abstract

In optical communication equipment that uses an optical circulator to separate transmitted and received light, the influence of transmitted light received by the optical receiver is suppressed. [Solution] The optical communication device comprises an optical transmitter that outputs transmitted light and outputs a first transmitted complex value corresponding to the amplitude and phase of the first polarization component of the transmitted light to a demodulation means, the transmitted light being input to a first port of an optical circulator and output from a second port; and an optical receiver that receives output light output from a third port of an optical circulator and outputs a first received complex value corresponding to the amplitude and phase of the first polarization component of the output light and a second received complex value corresponding to the amplitude and phase of the second polarization component of the output light to a demodulation means, the output light including received light from another optical communication device input to a second port of an optical circulator, the demodulation means outputting a demodulated result of the received light based on the first transmitted complex value and the first and second received complex values.

Description

[Technical Field]

[0001] This disclosure relates to an optical communication device that separates transmitted signal light and received signal light using an optical circulator. [Background technology]

[0002] In free-space optical (FSO) communication systems, which transmit and receive optical signals via free space rather than using fixed media such as optical fibers, optical communication devices use optical antennas. The optical antenna transmits an optical beam based on the transmitted light, which is the signal light input from the transmitter. The optical antenna also receives an optical beam transmitted by another optical communication device, which is the communication partner, and outputs received light, which is the signal light. If separate optical antennas are provided for transmitting and receiving optical beams, the size of the optical communication device will increase. Therefore, a configuration in which the same optical antenna transmits and receives optical beams is advantageous in terms of size.

[0003] When transmitting and receiving optical beams using the same optical antenna, an optical circulator, such as the one disclosed in Non-Patent Document 1, is used to separate the transmitted light input to the optical antenna from the received light output by the optical antenna. For example, suppose the optical circulator is configured such that light input to the first port is output from the second port, light input to the second port is output from the third port, and light input to the third port is output from the first port. In this case, by connecting an optical transmitter to the first port, an optical antenna to the second port, and an optical receiver to the third port, the transmitted light from the optical transmitter is input to the optical antenna, and the received light from the optical antenna is input to the optical receiver. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Thorlabs Inc., Single-mode optical circulator, [online], [searched November 21, 2024], Internet,<URL:https: / / www.thorlabs.co.jp / newgrouppage9.cfm?objectgroup_id=373> [Overview of the project] [Problems that the invention aims to solve]

[0005] In the example above, ideally, the light input to the first port should be output only from the second port and not from the third port. However, in reality, some of the light input to the first port is also output from the third port. According to Non-Patent Literature 1, when light of first power is input to the first port, light with a power approximately 50 dB lower than the first power is output from the third port. Therefore, the optical receiver connected to the third port receives both the received and transmitted light. However, this is not a problem if the power of the transmitted light input to the optical receiver is sufficiently lower than the power of the received light.

[0006] However, if the power of the transmitted light input to the optical receiver becomes significantly larger than the power of the received light, it will affect the demodulation of the received light in the optical receiver. For example, when applying FSO communication to long-distance space optical communication, the power of the received light must be very small, while the power of the transmitted light must be very strong. As an example, if the power of the received light is around -50 dBm and the power of the transmitted light is +30 dBm, the optical receiver will receive transmitted light at -20 dBm, making it difficult to demodulate the received light properly.

[0007] This disclosure provides a technology for suppressing the influence of transmitted light received by an optical receiver in an optical communication device that uses an optical circulator to separate transmitted light and received light. [Means for solving the problem]

[0008] According to one aspect of the present disclosure, the optical communication device comprises: a demodulation means; an optical transmitter that outputs transmitted light modulated based on transmitted data and outputs to the demodulation means a first transmitted complex value corresponding to the amplitude and phase of a first polarization component of the transmitted light, wherein the transmitted light is input to a first port of an optical circulator and output from a second port of the optical circulator; and an optical receiver that receives output light output from a third port of the optical circulator and outputs to the demodulation means a first received complex value corresponding to the amplitude and phase of a first polarization component of the output light and a second received complex value corresponding to the amplitude and phase of a second polarization component orthogonal to the first polarization of the output light, wherein the output light includes received light from another optical communication device input to the second port of the optical circulator, wherein the demodulation means outputs a demodulation result of the received light based on the first transmitted complex value, the first received complex value and the second received complex value. [Effects of the Invention]

[0009] According to this disclosure, in an optical communication device that uses an optical circulator to separate transmitted light and received light, the influence of transmitted light received by the optical receiver can be suppressed. [Brief explanation of the drawing]

[0010] [Figure 1] A diagram showing an example configuration of an optical communication device. [Figure 2] A diagram illustrating the configuration of the processing unit. [Modes for carrying out the invention]

[0011] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be combined arbitrarily. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted.

[0012] <First Embodiment> Figure 1 is a diagram of the configuration of an optical communication device according to this embodiment. The optical communication device comprises an optical antenna 1, an optical transmitter 2, an optical receiver 3, an optical circulator 4, and a demodulation unit 7. The demodulation unit 7 includes a processing unit 5 and a determination unit 6. Note that the optical communication device may not include the optical antenna 1, but rather have an external optical antenna 1 connected to it. Alternatively, the optical communication device may not include the optical antenna 1 and the optical circulator 4, but may be connected to the optical antenna 1 via an external optical circulator 4.

[0013] The optical circulator 4 has three ports #1, #2, and #3. The optical circulator 4 is configured such that most of the light input to port #1 is output from port #2, most of the light input to port #2 is output from port #3, and most of the light input to port #3 is output from port #1. Port #2 of the optical circulator 4 is connected to the optical antenna 1.

[0014] Port #1 of the optical circulator 4 is connected to the optical transmitter 2. The optical transmitter 2 outputs a transmitted light to port #1 of the optical circulator 4, which is obtained by polarization multiplexing X-polarized modulated light (modulated from X-polarized continuous light) and Y-polarized modulated light (modulated from Y-polarized continuous light orthogonal to the X-polarization). This transmitted light is input to the optical antenna 1 via the optical circulator 4. The optical transmitter 2 outputs a complex value T that represents the amplitude and phase of each symbol of the X-polarized modulated light. x And the complex value T, which represents the amplitude and phase of each symbol of the Y-polarized modulated light. y The following is output to the processing unit 5. A single complex value T x This corresponds to the data value transmitted with one symbol of X polarization, and one complex value T y This corresponds to the data value transmitted with one symbol in Y polarization.

[0015] The optical antenna 1 transmits an optical beam based on the transmitted light toward another optical communication device that is the communication partner (hereinafter simply referred to as another optical communication device). Further, the optical antenna 1 receives the optical beam transmitted by another optical communication device and outputs received light. The received light is, like the transmitted light, obtained by polarization multiplexing the modulated lights of two mutually orthogonal polarizations respectively.

[0016] Port #3 of the optical circulator 4 is connected to the optical receiver 3. Therefore, the received light output by the optical antenna 1 is input to the optical receiver 3 via the optical circulator 4. As described above, a part of the transmitted light output by the optical transmitter 2 is also output from port #3 of the optical circulator 4. Therefore, the optical receiver 3 receives not only the received light but also the transmitted light. In the following description, the light including the transmitted light and the received light output from port #3 of the optical circulator 4 is referred to as "output light". The optical receiver 3 coherently receives the output light, and the complex value D x indicating the amplitude and phase of each symbol of the modulated light of the X polarization included in the output light, and the complex value D y indicating the amplitude and phase of each symbol of the modulated light of the Y polarization are output to the processing unit 5.

[0017] Here, the complex value D x and the complex value D y are obtained by coherently receiving the output light including the transmitted light and the received light. Therefore, the amplitude and phase of each symbol of the modulated light of the X polarization included in the transmitted light (the received light in the optical communication device in FIG. 1) transmitted by another optical communication device are represented by the complex value R x and the amplitude and phase of each symbol of the modulated light of the Y polarization are represented by the complex value R y Then, the complex value D x and the complex value D y are represented by the following equations.

[0018]

Equation

[0019]

number

[0020] By rearranging equation (1), the complex value R x and the complex value R y This can be calculated using the following formula.

[0021]

number

[0022] Note that in equation (2) as well, the multiplier that is applied to all elements in common has been omitted. Processing unit 5 calculates the complex value R according to equation (2). x and the complex value R y Determine the following: A single complex value R x This represents the amplitude and phase of one symbol of the X-polarized modulated light contained in the received light, and one complex value R. y This indicates the amplitude and phase of one symbol of the Y-polarized modulated light contained in the received light. Processing unit 5 calculates the complex value R x and the complex value R y The result is output to the determination unit 6.

[0023] The determination unit 6 determines the complex value R x Based on this, the system determines the data value transmitted by another optical communication device using X-polarized modulated light and outputs it as the first demodulation result. The determination unit 6 also determines the complex value R yBased on this, the system determines the data value transmitted by another optical communication device using Y-polarized modulated light and outputs it as the second demodulation result. For example, the determination unit 6 determines the complex value R from among a plurality of reference complex values ​​mapped to the data value in the modulation scheme used with X polarization. x The closest reference complex value is determined, and the data value mapped to that reference complex value is determined to be the data value transmitted by another optical communication device using X-polarized modulated light. The same applies to Y polarization.

[0024] The processing unit 5 and the determination unit 6 can be realized by having a digital signal processor (DSP) execute an appropriate program.

[0025] Figure 2 shows the functional blocks of the processing unit 5. The processing unit 5 comprises an adder 51, an adder 52, a multiplier 53 having four multipliers, a multiplier 54 having four multipliers, and a setting unit 55. The four multipliers of the multiplier 53 and the four multipliers of the multiplier 54 each use complex values ​​D x , D y , T x and T y It corresponds one-to-one with the complex value D. x , D y , T x and T y Each is input to the corresponding multiplier of the multiplication unit 53 and multiplication unit 54. A coefficient is set for each multiplier by the setting unit 55. Figure 2 h 11 ~h 14 and h 21 ~h 24 The 'x' represents the coefficient.

[0026] Each multiplier outputs the product of the input complex value and the set coefficient. Note that the eight coefficients in Figure 2 correspond to one element of the 2x4 matrix in equation (2). Specifically, the coefficient h nm (where n is an integer from 1 to 2, and m is an integer from 1 to 4) corresponds to the element in the nth row and mth column of the 2nd row and 4th column in equation (2). For example, the coefficient h 23 This corresponds to the element (ad-bc) in the second row and third column of the 2x4 matrix in equation (2).

[0027] The adder 51 adds the values ​​output by the four multipliers of the multiplier 53 and outputs the result. As is clear from equation (2), the values ​​output by the four multipliers of the multiplier 53 are complex values ​​R x Similarly, the adder 52 adds the values ​​output by the four multipliers of the multiplier 54 to obtain the complex value R. y Outputs.

[0028] Next, we will explain how to determine the eight coefficients to be set in the eight multipliers of the multiplication units 53 and 54. As an example, if both the optical communication device and another optical communication device are permanently installed, and the matrices U1 and U2 can be considered constant, the eight coefficients can be determined by measurements taken when the devices are installed and permanently set in the setting unit 55.

[0029] On the other hand, when at least one of the optical communication device and another optical communication device is installed on a moving object such as an artificial satellite, at least the matrix U1 described above changes over time. For this reason, the optical communication device and the other optical communication device may be configured to transmit a training signal known to the optical communication device and the other optical communication device at a predetermined timing. The predetermined timing may be, for example, a periodic timing. The setting unit 55 of the optical communication device sets a complex value T at the predetermined timing. x and complex value T y And the complex value D x and complex value D y And the complex value R corresponding to the training signal x and the complex value R y Based on this, eight coefficients can be determined and set. The complex value R corresponding to the training signal. x and the complex value R y Each of these values ​​is predetermined. Furthermore, during periods when no training signal is transmitted, the setting unit 55 can update the eight coefficients using, for example, a least squares error (LMS) algorithm. In other words, the setting unit 55 updates the complex value R x and the complex value R y Based on the error between the first demodulation result and the second demodulation result determined by the determination unit 6 and the corresponding reference complex value, the eight coefficients can be updated.

[0030] As shown in Figure 1, the complex value T output by the optical transmitter 2 to the processing unit 5 x and complex value T y The symbol of the transmitted light corresponding to this is input from the optical transmitter 2 to the optical receiver 3 via the optical circulator 4. Therefore, if the propagation delay of the transmitted light from the optical transmitter 2 to the optical receiver 3 is not negligible, the complex value T x and complex value T y The timing at which the complex value T is input to the multiplier of processing unit 5 needs to be adjusted according to the propagation delay. x and complex value T y The complex value D is generated when the optical receiver 3 receives the output light containing the symbol of the transmitted light corresponding to the output light. x and complex value D y The complex value T is input to the multiplier at the same time as the input to the multiplier. x and complex value T y The multiplier needs to be input to this value.

[0031] Here, since the propagation delay of the transmitted light from the optical transmitter 2 to the optical receiver 3 is unlikely to change due to environmental changes or timing, the propagation delay of the transmitted light from the optical transmitter 2 to the optical receiver 3 can be measured before the optical communication device is installed and set in the processing unit 5. In this case, the processing unit 5 calculates a complex value T for the time corresponding to the set propagation delay. x and complex value T y The signal is buffered and input to the multiplier. Alternatively, the propagation delay of the transmitted light from the optical transmitter 2 to the optical receiver 3 can be set in the optical transmitter 2. In this case, the optical transmitter 2 uses a complex value T. x and complex value T y The timing for outputting to the processing unit 5 is the complex value T x and complex value T y The timing at which the symbol of the transmitted light corresponding to that is output is delayed by a time corresponding to the propagation delay.

[0032] With this configuration, the processing unit 5 calculates a complex value T based on the transmitted light output by the optical transmitter 2 at the first timing. x and complex value T yand the complex value D based on the output light received by the optical receiver 3 at the second timing x and the complex value D y are input to each multiplier at the same timing. Here, the difference between the first timing and the second timing corresponds to the propagation delay of the transmitted light in the path from the optical transmitter 2 to the optical receiver 3 via the optical circulator 4.

[0033] Alternatively, instead of the configuration in which the processing unit 5 is delayed by a time corresponding to the propagation delay, based on a predetermined number of complex values that are temporally continuous, the complex value R x of one symbol and the complex value R y can be obtained by configuring the processing unit 5. For example, the complex value output by the optical receiver 3 at a certain time t is the complex value D x (t) and the complex value D y (t), and the complex value output by the optical transmitter 2 at the time t is the complex value T x (t) and the complex value T y (t). Then, for example, when using complex values over three times, the processing unit 5 uses the complex value D x (t) and the complex value D y (t), the complex value D x (t - 1) and the complex value D y (t - 1), the complex value D x (t - 2) and the complex value D y (t - 2), the complex value T x (t) and the complex value T y (t), the complex value T x (t - 1) and the complex value T y (t - 1), the complex value T x (t - 2) and the complex value T y (t - 2), and based on these, obtains the complex value R x (t) and the complex value R y (t).

[0034] In other words, the four multipliers in the multiplier unit 53 and the four multipliers in the multiplier unit 54 in FIG. 2 process complex values at the current time t. However, four multipliers that process complex values at time t-1 and four multipliers that process complex values at time t-2 can be added to the multiplier unit 53 and the multiplier unit 54, and the outputs of the total 12 multipliers can be added in the adder units 51 and 52. Note that the difference between time t-1 and time t corresponds to the symbol period, and the difference between time t-2 and time t-1 corresponds to the symbol period.

[0035] Even in a form that uses complex values at a plurality of consecutive times, when the matrices U1 and U2 can be regarded as constant, the coefficients set for each multiplier in the multiplier unit 53 and the multiplier unit 54 can be fixed values determined in advance. Also, even in a form that uses complex values at a plurality of consecutive times, a configuration can be adopted in which the coefficients set for each multiplier in the multiplier unit 53 and the multiplier unit 54 are dynamically updated based on a training signal.

[0036] For example, in the case of using three consecutive times, when the propagation delay of the transmitted light from the optical transmitter 2 to the optical receiver 3 corresponds to two symbol periods, the complex value D x (t-1) and the complex value D y (t-1), and the complex value D x (t-2) and the complex value D y (t-2), and the complex value T x (t) and the complex value T y (t), and the complex value T x (t-1) and the complex value T y (t-1) are input to the multiplier, and the coefficients of the multiplier converge to approximately 0 by the training signal, and the complex value T x (t-2) and the complex value T y (t-2), and the complex value D x (t) and the complex value D y (t), and based on these, the complex value R x (t) and the complex value R y (t) are output. That is, the propagation delay of the transmitted light in the path from the optical transmitter 2 to the optical receiver 3 is compensated by the coefficients of the multiplier.

[0037] The number of consecutive time periods processed in the processing unit 5 can be any value of 2 or more, determined based on the design value of the propagation delay of the transmitted light in the path from the optical transmitter 2 through the optical circulator 4 to the optical receiver 3.

[0038] Furthermore, although the optical communication device and another optical communication device performed polarization multiplexing communication using two orthogonal polarizations in the above explanation, it is also possible to configure the device to communicate using single-polarized light without polarization multiplexing. For example, when using X polarization, the optical transmitter 2 uses a complex value T x Only the complex value T is output to the processing unit 5. y The output is not sent to the processing unit 5. Alternatively, the optical transmitter 2 outputs the complex value T x And the complex value T has a value of 0. y The output is sent to the processing unit 5. Even if another optical communication device and optical transmitter 2 transmit only X-polarized modulated light, the optical receiver 3 receives output light containing both X-polarized and Y-polarized components due to polarization rotation. Therefore, in this case as well, the optical receiver 3 receives the complex value D x and complex value D y Output to processing unit 5.

[0039] When using only X polarization, the processing unit 5 needs to determine the complex value R. x Only the first demodulation result is determined by the determination unit 6. Therefore, the addition unit 52 and multiplication unit 54 in Figure 2 can be omitted. Also, the complex value T y Since is always 0, the coefficient in Figure 2 is h 14 The multiplier, which is also a multiplier, can be omitted. In other words, the processing unit 5 is a complex value D x and coefficient h 11 The product of and the complex value D y and coefficient h 12 The product of and the complex value T x and coefficient h 13 By multiplying and adding, we obtain the complex value R x The following is calculated. Note that, as with the use of X-polarization and Y-polarization, the processing unit 5 calculates the complex value T based on the transmitted light output by the optical transmitter 2 at the first timing. x And, at the second timing, the complex value D based on the output light received by the optical receiver 3. x and complex value Dy And are input to each multiplier at the same time. Here, the difference between the first timing and the second timing corresponds to the propagation delay of the transmitted light in the path from the optical transmitter 2 to the optical receiver 3 via the optical circulator 4.

[0040] The method for setting the three coefficients is the same as in the case of polarization multiplexing. For example, the three coefficients can be determined by measurements performed when the device is installed and fixedly set in the setting unit 55. Furthermore, the three coefficients can be updated by repeatedly sending and receiving training signals known to the optical communication device and another optical communication device. In this case, the setting unit 55 sets a complex value D based on the output light input to the optical receiver 3 at the timing of receiving the training signal. x and complex value D y And, based on the transmitted light output by the optical transmitter 2 at a timing predetermined period prior to that timing, T is a complex value. x And a predetermined complex value R corresponding to the training signal. x Based on this, three coefficients are set. The predetermined period corresponds to the propagation delay of the transmitted light in the path from the optical transmitter 2 to the optical receiver 3 via the optical circulator 4. Furthermore, at a timing different from the timing of receiving the training signal, the setting unit 55 may update the three coefficients by, for example, the LMS algorithm. In other words, the setting unit 55 sets the complex value R x Based on the error between the first demodulation result determined by the determination unit 6 and the reference complex value, the three coefficients can be updated. Also, similar to the case of polarization multiplexing, multiple complex values ​​T at multiple consecutive timings x and multiple complex values ​​D x and multiple complex values ​​D y Based on this, one complex value R x It is also possible to configure it to achieve the desired result.

[0041] Although the embodiment was described using FSO communication as an example, the above embodiment can be applied to any optical communication system that uses an optical circulator to separate transmitted and received light. For example, an optical circulator can be used to separate transmitted and received light even when transmitting and receiving light are carried by a single core of an optical fiber. In this case, instead of the optical antenna 1 in Figure 1, a single core of an optical fiber is connected to port #2 of the optical circulator 4. In other words, the above embodiment can be applied to an optical communication system in which an optical element for propagating light is connected to port #2 of the optical circulator 4 in Figure 1. The optical element for propagating light is, for example, the optical antenna 1 or an optical fiber.

[0042] In Figure 1, the optical transmitter 1 and the optical circulator 4 are directly connected, but they may also be connected via an optical amplifier or optical filter. The same applies to the connections between the optical receiver 2 and the optical circulator 4, and between the optical antenna 1 and the optical circulator 4. Furthermore, the X-polarization and Y-polarization may be linear or circular polarization. In addition, an optical component that converts transmitted light between linear and circular polarization may be provided in the path from the optical transmitter 2 to the optical antenna 1, and an optical component that converts received light between linear and circular polarization may be provided in the path from the optical antenna 1 to the optical receiver 3. The optical component that converts light between linear and circular polarization may be, for example, a quarter-wave plate.

[0043] With the above configuration, it is possible to suppress the influence of transmitted light received by the optical receiver in optical communication equipment that uses an optical circulator to separate transmitted and received light. Therefore, it becomes possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0044] The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention. [Explanation of symbols]

[0045] 1: Optical antenna, 2: Optical transmitter, 3: Optical receiver, 4: Optical circulator, 5: Processing unit, 6: Judgment unit, 7: Demodulation unit

Claims

1. Optical communication device, Recovery methods, An optical transmitter that outputs modulated transmitted light based on transmitted data, and outputs a first transmitted complex value corresponding to the amplitude and phase of the first polarization component of the transmitted light to the demodulation means, wherein the transmitted light is input to a first port of an optical circulator and output from a second port of the optical circulator, An optical receiver that receives output light output from the third port of the optical circulator and outputs to the demodulation means a first received complex value corresponding to the amplitude and phase of the first polarization component of the output light, and a second received complex value corresponding to the amplitude and phase of the second polarization component orthogonal to the first polarization of the output light, wherein the output light includes received light from another optical communication device input to the second port of the optical circulator, Equipped with, The demodulation means is an optical communication device that outputs the demodulation result of the received light based on the first transmitted complex value, the first received complex value, and the second received complex value.

2. The demodulation means outputs the demodulation result of the received light based on the first transmitted complex value based on the transmitted light output by the optical transmitter at the first timing, and the first received complex value and the second received complex value based on the output light received by the optical receiver at the second timing. The optical communication device according to claim 1, wherein the difference between the first timing and the second timing corresponds to the propagation delay of the transmitted light in the path from the optical transmitter to the optical receiver via the optical circulator.

3. The optical communication device according to claim 1, wherein the demodulation means outputs the demodulation result based on a value obtained by adding the value obtained by multiplying the first transmitted complex value by a first coefficient, the value obtained by multiplying the first received complex value by a second coefficient, and the value obtained by multiplying the second received complex value by a third coefficient.

4. The optical communication apparatus according to claim 3, wherein the first to third coefficients are pre-set in the demodulation means.

5. The demodulation result of the received light included in the output light input to the optical receiver at a predetermined timing is a predetermined complex value. The demodulation means sets the first to third coefficients based on the first and second received complex values ​​based on the output light input to the optical receiver at the predetermined timing, the first transmitted complex value based on the transmitted light output by the optical transmitter at a timing a predetermined period before the predetermined timing, and the predetermined complex value. The optical communication apparatus according to claim 3, wherein the predetermined period is a period corresponding to the propagation delay of the transmitted light in the path from the optical transmitter to the optical receiver via the optical circulator.

6. The optical communication apparatus according to claim 5, wherein the demodulation means updates the third coefficient from the first coefficient based on the demodulation result and the first transmitted complex value, the first received complex value, and the second received complex value used to obtain the demodulation result.

7. The optical transmitter further outputs a second transmission complex value corresponding to the amplitude and phase of the second polarization component of the transmitted light to the demodulation means. The optical communication device according to claim 1, wherein the demodulation means further uses the second transmitted complex value to output the demodulation result of the received light, and outputs another demodulation result of the received light based on the first transmitted complex value, the second transmitted complex value, the first received complex value, and the second received complex value.

8. The demodulation means outputs the demodulation result and the other demodulation result based on the first transmitted complex value and the second transmitted complex value based on the transmitted light output by the optical transmitter at the first timing, and the first received complex value and the second received complex value based on the output light received by the optical receiver at the second timing. The optical communication device according to claim 7, wherein the difference between the first timing and the second timing corresponds to the propagation delay of the transmitted light in the path from the optical transmitter to the optical receiver via the optical circulator.

9. The optical communication device according to claim 7, wherein the demodulation means outputs the demodulation result based on a value obtained by adding the value obtained by multiplying the first transmitted complex value by a first coefficient, the value obtained by multiplying the second transmitted complex value by a second coefficient, the value obtained by multiplying the first received complex value by a third coefficient, and the value obtained by multiplying the second received complex value by a fourth coefficient, and outputs the other demodulation result based on a value obtained by adding the value obtained by multiplying the first transmitted complex value by a fifth coefficient, the value obtained by multiplying the second transmitted complex value by a sixth coefficient, the value obtained by multiplying the first received complex value by a seventh coefficient, and the value obtained by multiplying the second received complex value by an eighth coefficient.

10. The optical communication apparatus according to claim 9, wherein the first to eighth coefficients are pre-set in the demodulation means.

11. The demodulation result and the other demodulation result of the received light included in the output light input to the optical receiver at a predetermined timing are a first predetermined complex value and a second predetermined complex value, The demodulation means sets the first to eighth coefficients based on the first and second received complex values ​​based on the output light input to the optical receiver at the predetermined timing, the first and second transmitted complex values ​​based on the transmitted light output by the optical transmitter at a timing a predetermined period before the predetermined timing, and the first predetermined complex value and the second predetermined complex value. The optical communication apparatus according to claim 9, wherein the predetermined period is a period corresponding to the propagation delay of the transmitted light in the path from the optical transmitter to the optical receiver via the optical circulator.

12. The optical communication device according to claim 11, wherein the demodulation means updates the first coefficient to the fourth coefficient based on the demodulation result and the first transmitted complex value, the second transmitted complex value, the first received complex value, and the second received complex value used to obtain the demodulation result, and updates the fifth coefficient to the eighth coefficient based on the other demodulation result and the first transmitted complex value, the second transmitted complex value, the first received complex value, and the second received complex value used to obtain the other demodulation result.

13. The optical communication apparatus according to claim 7, wherein the demodulation means outputs the demodulation result and the other demodulation result based on a plurality of first transmitted complex values ​​and a plurality of second transmitted complex values ​​input from the optical transmitter at a plurality of consecutive timings, and a plurality of first received complex values ​​and a plurality of second received complex values ​​input from the optical receiver at the plurality of timings.

14. The optical communication device according to any one of claims 1 to 13, further comprising the optical circulator.

15. The optical communication device according to any one of claims 1 to 13, wherein the received light input to the second port of the optical circulator is output by an optical antenna, and the transmitted light output from the second port of the optical circulator is input to the optical antenna.

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