Polarization-modulated communication systems.

A DP communication system comprising:

• a transmitter comprising:
• a laser configured to emit light,
• a splitter configured to split the light from the laser into a first input light and a second input light,
• a first modulator configured to modulate the first input light with a first data stream to yield a first modulated input light and a second modulator configured to modulate the second input light with a second data stream to yield a second modulated input light, the second data stream complementary to the first data stream, and
• an optical element comprising:
• a first input configured to receive the first modulated input light substantially unmixed with the second modulated input light, and
• a second input configured to receive the second modulated input light substantially unmixed with the first modulated input light, and
• wherein the optical element is configured to cause the first modulated input light and the second modulated input light to have orthogonal polarizations, combine the first modulated input light and the second modulated input light into transmit light, and provide the transmit light into a transmission link;
• and
• a receiver comprising:
• an input port configured to receive light from the transmission link,
• at least one second optical element configured to split the light from the transmission link into a first split light provided into a first optical transmission path and a second split light, with a different polarization in the transmission link, provided into a second optical transmission path, and
• a 2×2 multi-input-multi-output (MIMO) demultiplexer configured to receive light from the first optical transmission path and the second optical transmission path.

A method of performing DP transmission, the method comprising:

• generating light using a laser;
• splitting the light from the laser into a first input light and a second input light;
• modulating the first input light with a first data stream to yield a first modulated input light and modulating the second input light with a second data stream to yield a second modulated input light, the second data stream complementary to the first data stream;
• receiving the first modulated input light substantially unmixed with the second modulated input light and receiving the second modulated input light substantially unmixed with the first modulated input light;
• causing the first modulated input light substantially unmixed with the second modulated input light and the second modulated input light substantially unmixed with the first modulated input light to have orthogonal polarizations;
• combining the first modulated input light and the second modulated input light into transmit light;
• and
• providing the transmit light into a transmission link.