Patent ID: 6888856

Claim:
A tunable filter for use in optical communication apparatus, said tunable filter being tunable to each selected center wavelength of a number of channels, and each of the channels centered on a corresponding gridline of a selected wavelength grid; said tunable filter comprising: a grid generator having reflective surfaces, mounted for optical alignment in an optical path of a beam, and the grid generator of a first selected optical path length determinative of a first free spectral range having a first plurality of transmission peaks corresponding to gridlines of the selected wavelength grid; a channel selector having reflected surfaces, mounted for optical alignment in the optical path of the beam, and the channel selector with a tunable second optical path length determinative of a second free spectral range having a second plurality of transmission peaks within the selected wavelength grid, wherein the second free spectral range (FSR2) is related to the first free spectral range (FSR1) by the equation: FSR 2â‰ˆ( M/MÂ± 1)( FSR 1) wherein M is the total number of channels within the selected wavelength grid; means for maintaining the first optical path length of the grid generator; and means for varying the tunable second optical path length of the channel selector to tune the optical beam to a selected channel of the wavelength grid and substantially attenuate the other channels of the wavelength grid.