Waveguide narrowband rejection filter

Abstract

An optical fiber filter including a length of single mode fiber having an operating wavelength .lambda..sub.0. Fiber designs may include a depressed inner clad fiber, a photosensitive matched inner clad fiber or a photosensitive depressed inner clad fiber. The length of fiber includes a core, an inner cladding, an outer cladding and an azimuthally asymmetric grating. The core allows the existence of a LP.sub.01 core mode having an effective index of n.sub.eff,01 and the cladding allows the existence of a LP.sub.1m cladding mode, m.gtoreq.1. The core has an index of refraction n.sub.co and a radius A. The inner cladding has an index of refraction n.sub.ic, an inner radius A, an outer radius AB, a thickness W, where W=AB-A, and a refraction difference .DELTA.n-, where .DELTA.n- is the difference between n.sub.ic and n.sub.oc and n.sub.co >n.sub.oc >n.sub.ic. The inner cladding may be photosensitive to a radius R.sub.grat and have a fractional photosensitivity .gamma.. The outer cladding generally laterally surrounds the inner cladding and has an inner radius AB, an outer radius B, and an index of refraction n.sub.oc, where .DELTA.n.sub.+ is the difference between n.sub.co and n.sub.oc. The grating has an effective tilt angle .theta. and a period (.LAMBDA.), where .LAMBDA..ltoreq.(.lambda..sub.0 cos .theta.)/(2n.sub.eff,01), the maximum relative coupling coefficient for the cladding mode max(RCC.sub.1m) being greater or equal to 0.2 and the ratio of peak reflectivities for the cladding mode and the core mode RR being greater or equal to 1.

Dependencies are inferred from the claim text.