Abstract

Numerous optical filter concepts have been proposed for dense wavelength division multiplexing (WDM) applications.^(1-7) For the lowest insertion loss and most reliably packaged device, an all-fiber solution is preferred. The present filter is based on grating assisted mode conversion and backwards coupling in the merged region of two dissimilar waveguides formed by adiabatically tapering and strongly fusing two single-mode optical fibers. From the theory of adiabatic following,⁽⁸⁾ the modes of the input fibers will evolve on a one-to-one basis into the first two eigenmodes of the merged region. These eigenmodes will propagate through the waist independently of one another, transform back into their original modes, and exit the device through their respective output fibers. This adiabatic mode evolution is lossless and free of optical crosstalk.

© 1997 Optical Society of America