Patent ID: 6067391
Filing Date: 2000-05-23
Classification: G02B

Abstract:
A filter structure comprising a wave guiding medium containing multiple periodic refractive index modulation patterns contained within or adjacent to a linear or planar optical waveguide, for producing one or more substantially equally spaced comb-like reflection peaks from an incident guided wave having a wavelength band width at least three times the spacing of adjacent said reflection peaks, wherein the peak half maximum widths are less than one half the peak spacing and each said pattern has an optical length d(v) equal to n(u,v)d(u,v), where n(u,v) is the local average real part of the optical refractive index of said medium and d(u,v) is a local periodic physical length, each of said patterns being a series of filter elements,f(1,1),f(1,2), . . . , f(1,2), . . . f(1,v),f(2,1),f(2,2), . . . f(2,v), . . . f(2,V), . . . f(u,1) . . . f(U-1,V)f(U,1) . . . f(U,V)with modulation amplitudes .DELTA.(u,v) wherein U and V are preselected integers not less than 2, and u=1 to U and v=1 to V in said series, the number of periodic physical lengths d(u,v) or optical lengths d(u,v) in a filter element f(u,v) is designated by M(u,v), and wherein the physical length of an element f(u,v) is designated as M(u,v)d(v)=s(u,v) and the optical length is n(u,v)s(u,v)=s (u,v), and wherein the physical length of adjacent elements having a common v designator is designated by L(u,v), and wherein the peak reflectance provided by any filter element f(u,v) of length s(u,v) is not greater than 70% and the length of filter elements, s(u,v) and the length L(u,v) are selected to provide a high degree of coherence for reflections at the entrance end of said filter structure from elements having equal v.