A tunable filter for polychromatic optical radiation comprising an electronically programmable spatial light modulator for displaying computer generated hologram patterns of data as a series combination of a first dynamically variable wavelength dispersive element, and a second static wavelength dispersive element. view more

A tunable filter according to claim 1, in which the first dynamically variable wavelength dispersive element (3) comprises an array of N sub-holograms (9).

A tunable filter according to claim 1, in which one or both of the first dynamically variable and second static wavelength dispersive elements (2,3) are reflective.

A tunable filter according to claim 1, further comprising a memory storing data for at least one computer generated hologram which when displayed in use, causes multiplexing of wavelengths in a predetermined manner.