Patent ID: 7177545

Claim:
An optical filter system which filters out at least a part of one of two spectral side-bands of a coded optical signal spectrum having a carrier wavelength, the system comprising: a first filter which transmits a first one of said side-bands which is a transmitted side-band; and a second filter which filters out a second one of said side-bands which is a vestigial side-band, wherein the first and second filters generate a transmission response in intensity having a maximum value at a central filter wavelength distinct from said carrier wavelength and located in said transmitted side-band, wherein the transmission response further comprises: a first filter part associated with a wavelength region including said carrier wavelength; and a second filter part associated with a wavelength region which does not include said carrier wavelength, wherein at a given value of transmission response distinct from said maximum value, said second filter part has a filter width smaller than the filter width of said first filter part.