Optical filter having multiple interferometric stages
AssigneeAT&T Bell Laboratories
InventorsLeonard G. Cohen, Charles H. Henry, Rudolf F. Kazarinov, Mark E. Kuznetsov
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Abstract
We describe an interferometric, channel-dropping, optical filter that includes a pair of planar waveguides. The two waveguides are spaced apart by a distance which is periodically varied along the longitudinal axis of the filter in order to effect a periodic optical coupling between them. There are at least three coupling locations, each associated with a coupling constant. The two waveguides have nominally equal effective refractive indices. In preferred embodiments of the invention, the coupling constants decrease symmetrically from the center of the filter toward the ends.
Claims10
A spectrally discriminating optical filter which comprises a substrate having a longitudinal axis and first and second optical waveguides formed on the substrate, said waveguides having respective first and second effective refractive indices, wherein:
- a) the filter is subdivided into N stages, N at least 2, and N+1 approximately equally spaced-apart coupling sections, such that each stage is situated between two coupling sections;
- b) the first waveguide is optically coupled to the second waveguide in each of the coupling sections;
- and
- c) the optical path length within each stage is greater in the first waveguide than in the second waveguide,
- CHARACTERIZED IN THAT
- d) the first and second effective refractive indices are nominally equal.
Dependencies are inferred from the claim text.