Optical communication device, optical communication system, and optical communication method

1. An optical communication device comprising:

a transmission medium of a multimode type that transmits a reception-side signal light incident through a free space;

a reception-side multimode demultiplexer that distributes the reception-side signal light into a plurality of distributed reception-side signal lights at a distribution ratio, the distribution ratio being ratio depending on an intensity distribution of a plurality of mutually different propagation modes included in the reception-side signal light which has passed through the transmission medium;

a transmission-side demultiplexer that distributes a transmission-side signal light to be transmitted into a plurality of distributed transmission-side signal lights;

a signal processing device that includes a detection function and a setting function, the detection function being a function that detects either or both of a light intensity and a phase in each distributed reception-side signal light, the setting function being a function that sets a control target value for either or both of a light intensity and a phase to be controlled in each distributed transmission-side signal light to a value depending on a detection result by the detection function;

a modulator that adjusts either or both of a light intensity and a phase to be controlled in the distributed transmission-side signal light to the control target value set by the signal processing device; and

a multimode multiplexer that multiplexes the plurality of distributed transmission-side signal lights obtained after being adjusted by the modulator.

2. The optical communication device according to claim 1 , wherein the signal processing device sets the control target value in such a way as to cause the distributed transmission-side signal light to be in a phase-conjugated state with the reception-side signal light.

3. The optical communication device according to claim 1 , wherein the signal processing device detects either or both of the light intensity and the phase to be controlled in the transmission-side signal light multiplexed by the multimode multiplexer and, considering also a detection result, sets the control target value.

4. The optical communication device according to claim 1 , further comprising an amplifier that amplifies the multiplexed transmission-side signal light after being multiplexed by the multimode multiplexer.

5. The optical communication device according to claim 1 further comprising an amplifier that amplifies the distributed transmission-side signal light after being distributed by the transmission-side demultiplexer.

6. The optical communication device according to claim 1 comprising a optical multiplexer/demultiplexer that includes a function of both the reception-side multimode demultiplexer and the multimode multiplexer.

7. An optical communication system comprising:

an optical communication device that is disposed on a ground side; and

an optical communication device on a communication partner side that is included in a flying object that flies in midair and communicates with the optical communication device by a signal light, wherein

the optical communication device includes:

a transmission medium of a multimode type that transmits a reception-side signal light incident through a free space;

a reception-side demultiplexer that distributes the reception-side signal light into a plurality of distributed reception-side signal lights at a distribution ratio, the distribution ratio being ratio depending on an intensity distribution of a plurality of mutually different propagation modes included in the reception-side signal light which has passed through the transmission medium;

a transmission-side multimode demultiplexer that distributes a transmission-side signal light to be transmitted into a plurality of distributed transmission-side signal lights;

a signal processing device that includes a detection function and a setting function, the detection function being a function that detects either or both of a light intensity and a phase in each distributed reception-side signal light, the setting function being a function that sets a control target value for either or both of a light intensity and a phase to be controlled in each distributed transmission-side signal light to a value depending on a detection result by the detection function;

a modulator that adjusts either or both of a light intensity and a phase to be controlled in the distributed transmission-side signal light to the control target value set by the signal processing device; and

a multimode multiplexer that multiplexes the plurality of distributed transmission-side signal lights obtained after being adjusted by the modulator.

8. An optical communication method comprising:

receiving a reception-side signal light incident through a free space by using a transmission medium of a multimode type;

multi-mode demultiplexing the reception-side signal light into a plurality of distributed reception-side signal lights at a distribution ratio, the distribution ratio being ratio depending on an intensity distribution of a plurality of mutually different propagation modes included in the reception-side signal light after passing through the transmission medium;

detecting either or both of a light intensity and a phase in each distributed reception-side signal light;

demultiplexing a transmission-side signal light to be transmitted to a plurality of distributed transmission-side signal lights;

setting a control target value for either or both of a light intensity and a phase to be controlled in each distributed transmission-side signal light to a value depending on a result of the detecting;

adjusting either or both of a light intensity and a phase to be controlled in the distributed transmission-side signal light to the control target value after setting; and

multi-mode multiplexing a plurality of distributed transmission-side signal lights obtained after being adjusted and emitting a multiplexed transmission-side signal light.