METHOD AND APPARATUS FOR AN OPTICAL FILTER

摘要

An optical device that can be used in a range of telecommunications applications including optical multiplexers/demultiplexers, optical routers and optical gain scalers. The optical device splits and combines optical signals of frequency division multiplexed optical communication channels which are evenly spaced apart in frequency from one another. In a embodiment of the invention the optical device includes a first and a second filter. The first filter splits and combines odd and even channels depending on the propagation direction of the optical signal. The first filter exhibits complementary phase retardations corresponding with odd integer multiples of half a wavelength for each center wavelength associated with a selected one of the odd and even set of channels and with integer multiples of a full wavelength for each center wavelength associated with a remaining one of the odd set and the even set. The second filter couples with the first filter to filter the odd and even sets of channels with phase retardations complementary to those experienced by the odd and even set of channels in the first filter. This complementary filtration has the effect of reducing dispersion in the device. In an alternate embodiment of the invention a modular optical filter is disclosed with two or more couplers with a pair of delay paths between each pair of couplers in a sequence to generate a range of optical filter functions. The desired filter profile/function is obtained by proper selection of the coupling ratio for each coupler and by the length of each pair of delay paths. The couplers may be implemented aspolarization or intensity beam splitters. In an embodiment of the invention the filter may be passively thermally stabilized.