Multiple wavelength band optical switching unit

A multiple wavelength band optical switch configured to receive an input optical signal and output an output optical signal, the input optical signal comprising light in a first wavelength band and light in a second wavelength band, the optical switch comprising

• a liquid crystal on silicon spatial light modulator controllable to direct or attenuate light in the first and second wavelength bands;
• an input device comprising:
• an optical demultiplexer configured to receive light and disperse the received light along a dispersion axis;
• and
• a light director configured to direct the light in the first wavelength band to the optical demultiplexer at a first angle of incidence and to direct the light in the second wavelength band to the optical demultiplexer at a second angle of incidence, the second angle of incidence being different from the first angle of incidence, the light director comprising:
• an array of input optical waveguides configured to receive the input optical signal and direct the input optical signal towards the optical demultiplexer, the array of input optical waveguides comprising:
• a first input optical waveguide configured to direct light in the first wavelength band to the optical demultiplexer;
• and a second input optical waveguide configured to direct light in the second wavelength band to the optical demultiplexer;
• and
• an input lens situated between the array of input optical waveguides and the optical demultiplexer, the input lens configured to receive light of the input optical signal from the array of input optical waveguides and steer the received light towards the optical demultiplexer;
• an array of output optical waveguides configured to output the output optical signal;
• and
• multiple output lenses situated between the array of output optical waveguides and the optical demultiplexer, the multiple output lenses configured to receive light from the optical demultiplexer and steer the received light towards the array of output optical waveguides,
• wherein the difference between the first and second angles of incidence causes the optical demultiplexer to output dispersed spectra of light corresponding to the first and second wavelength bands such that the dispersed spectrum of light corresponding to the first wavelength band is overlapped along the dispersion axis and separated along a switch axis relative to the dispersed spectrum of light corresponding to the second wavelength band at an incident surface of the liquid crystal on silicon spatial light modulator, the switch axis being perpendicular to the dispersion axis;
• and
• wherein the optical switch is configured such that light passes through the input lens only once between being received as the input optical signal at one of the input waveguides of the array of input optical waveguides and being output as the output optical signal at an output waveguide of the output optical waveguides.