All fiber dwdm multiplexer and demultiplexer

Abstract

A dense wavelength division multiplexing (DWDM) filter includes an optical fiber coupling device, having at least one multiple core optical fiber fusion coupled to a second optical fiber, and a dual core fiber grating. According to an especially preferred embodiment of the invention, two multiple core fibers are used with each multiple core fiber having a first core with a first effective index of refraction and a first propagation constant and a second core with a second effective index of refraction and a second propagation constant. Such an arrangement ensures a close match in effective index and propagation constant between the respective second cores. The first and second multiple core fibers are aligned and fused together such that the second core of the first multiple core fiber is in sufficient proximity to the second core of the second multiple core fiber as to obtain overlapping mode fields and efficient coupling of propagating optical signals therebetween, while the first core of the first multiple core fiber is sufficiently separated from the first core of the second multiple core fiber as to obtain weak or substantially no coupling of propagating optical signals therebetween. Accordingly, any signals propagating along the first core of the first fiber experience only very low loss, on the order of 0.2 dB. The dual core fiber grating provides wavelength selectivity to accommodate either wavelength addition or wavelength subtraction, depending upon whether a multiplexing or demultiplexing functionality is desired.