A 2×2 optical multi-input-multi-output (MIMO) demultiplexer is disclosed. A first optical phase shifter applies a first relative phase shift between a first pair of optical transmission paths that are received from MIMO inputs, and a first 2×2 optical coupler combines the first pair of optical transmission paths and outputs a second pair of optical transmission paths. A second optical phase shifter applies a second relative phase shift between the second pair of optical transmission paths, and a second 2×2 optical coupler combines the second pair of optical transmission paths and outputs a third pair of optical transmission paths. A third optical phase shifter applies a third relative phase shift between the third pair of optical transmission paths, and a third 2×2 optical coupler combines the third pair of optical transmission paths and outputs a fourth pair of optical transmission paths, which are output by a pair of MIMO outputs.

A 2×2 optical multi-input-multi-output (MIMO) demultiplexer is disclosed. A first optical phase shifter applies a first relative phase shift between a first pair of optical transmission paths that are received from MIMO inputs, and a first 2×2 optical coupler combines the first pair of optical transmission paths and outputs a second pair of optical transmission paths. A second optical phase shifter applies a second relative phase shift between the second pair of optical transmission paths, and a second 2×2 optical coupler combines the second pair of optical transmission paths and outputs a third pair of optical transmission paths. A third optical phase shifter applies a third relative phase shift between the third pair of optical transmission paths, and a third 2×2 optical coupler combines the third pair of optical transmission paths and outputs a fourth pair of optical transmission paths, which are output by a pair of MIMO outputs.

An optical IQ modulator includes Y branching elements each of which has one input and two outputs and which are cascade-connected, QQPSK modulators each of which performs QPSK modulation on a corresponding one of continuous beams of light branched by the Y branching elements so that four signal points are present in a first quadrant on an IQ plane, Y combining elements each of which has two inputs and one output and which are cascade-connected, a phase modulator that modulates output light of the Y combining element in accordance with a drive signal Z, and a phase modulator that modulates output light of the phase modulator in accordance with a drive signal W.

An optical IQ modulator includes Y branching elements each of which has one input and two outputs and which are cascade-connected, QQPSK modulators each of which performs QPSK modulation on a corresponding one of continuous beams of light branched by the Y branching elements so that four signal points are present in a first quadrant on an IQ plane, Y combining elements each of which has two inputs and one output and which are cascade-connected, a phase modulator that modulates output light of the Y combining element in accordance with a drive signal Z, and a phase modulator that modulates output light of the phase modulator in accordance with a drive signal W.

A coherent transmitter includes a first beam splitter that splits an input first optical signal to obtain a second optical signal and a third optical signal, a first modulator that modulates the second optical signal to obtain a first modulated signal, a phase shift adjustment unit that adjusts a phase of a first sub-signal in the first modulated signal and adjusts a phase of a fourth sub-signal in the phase-adjusted first sub-signal, a first beam combiner that combines a second sub-signal in the first modulated signal and the phase-adjusted fourth sub-signal to obtain a first combined signal, a first PD that performs optical-to-electrical conversion on the first combined signal to obtain a first electrical signal, and a controller that controls, based on the first electrical signal, a voltage applied to the phase shift adjustment unit.

A coherent transmitter includes a first beam splitter that splits an input first optical signal to obtain a second optical signal and a third optical signal, a first modulator that modulates the second optical signal to obtain a first modulated signal, a phase shift adjustment unit that adjusts a phase of a first sub-signal in the first modulated signal and adjusts a phase of a fourth sub-signal in the phase-adjusted first sub-signal, a first beam combiner that combines a second sub-signal in the first modulated signal and the phase-adjusted fourth sub-signal to obtain a first combined signal, a first PD that performs optical-to-electrical conversion on the first combined signal to obtain a first electrical signal, and a controller that controls, based on the first electrical signal, a voltage applied to the phase shift adjustment unit.

An optical signal processing method, a control unit, an optical transmission unit and a storage medium are disclosed. The optical signal processing method includes: acquiring an OSNR value from an optical receiving unit (S100); acquiring a spectrum shaping adjustment parameter according to the OSNR value (S200); and sending the spectrum shaping adjustment parameter to an optical transmission unit to adjust a filtering parameter of a shaping filter of the optical transmission unit, so that the optical transmission unit adjusts a spectrum waveform of an optical signal by utilizing the shaping filter after adjustment (S300).

An optical signal processing method, a control unit, an optical transmission unit and a storage medium are disclosed. The optical signal processing method includes: acquiring an OSNR value from an optical receiving unit (S100); acquiring a spectrum shaping adjustment parameter according to the OSNR value (S200); and sending the spectrum shaping adjustment parameter to an optical transmission unit to adjust a filtering parameter of a shaping filter of the optical transmission unit, so that the optical transmission unit adjusts a spectrum waveform of an optical signal by utilizing the shaping filter after adjustment (S300).

Arrangements for transmitting network credentials from a user device to a second device to enable the second device to connect to a network are disclosed. At the user device, a user inputs network credentials for the second device to enable the second device to connect to a network. The user device transmits modulated light to the second device. The light is modulated so that the transmitted light is encoded with the network credentials. The second device has a photo sensor for receiving the modulated light from the user device and a processor for processing the modulated light to obtain the network credentials from the received modulated light.

An optical transmitter transmits a data signal. The optical transmitter has an encoder configured to encode the data signal by selecting based on a bit sequence a first symbol and a second symbol from a set of four symbols for each one of at least two transmission time slots. The optical transmitter further has a modulator configured to use in each transmission time slot the first symbol to modulate a first carrier wave and the second symbol to modulate a second carrier wave, and to transmit the two carrier waves over orthogonal polarizations of an optical carrier. Symbols in consecutive transmission time slots have non-identical polarization states.