Low Crosstalk Optical Add-Drop Multiplexer based on a Planar Silica-on-Silicon Mach-Zehnder Interferometer with UV-induced Bragg Gratings and UV-Trimming.

Optical Add-Drop Multiplexers (OADM) are key-components of multi-wavelength optical networks. Several techniques and designs may be used in order to achieve this function [1]. UV-induced Bragg gratings are of great interest since they enable construction of compact devices, and when written in the arms of a planar Mach-Zehnder interferometer they realise an OADM device with potentially low crosstalk. Moreover this device drops one channel without altering the other ones enabling cascading of several OADM's. Silica-on-Silicon planar OADM devices based on Mach-Zehnder interferometers have already been reported by other groups [2-5] but they were all limited by a low grating strength leading to a ratio between the -30 dB bandwidth in transmission and the -20 dB bandwidth in reflection, the so-called Bandwidth Utilisation parameter (BWU) [6], equal to zero and therefore a high intra-channel crosstalk. We present in this paper a planar OADM with a positive BWU obtained by writing strong gratings in waveguides [7].