Simple method to adjust polarization dependence in polymeric arrayed waveguide gratings

Polarization-dependent wavelength shift of a birefringent-polymeric arrayed waveguide grating (AWG) is found to be adjusted simply by controlling the thickness of the first upper cladding layer while forming the upper cladding by several sublayers. Polarization-dependent wavelength shift is reduced to 0.08 from 4.24 nm in a birefringent-polymeric 16 /spl times/ 16 channel AWG on a silicon substrate by this method.

I. Introduction

Polymeric waveguide devices with economic merits based on the simple fabrication process have been studied in many research groups, and developed up to commercial products such as thermooptic (TO) switches and variable optical attenuators [1], [2]. Fig. 1. Cross-sectional view of a waveguide of the 16 × 16 AWG. Polymeric waveguide devices are, however, in trouble even with their economic merits in expanding their application area into an arrayed waveguide grating (AWG) which is used as a multiplexer or a demultiplexer in wavelength-devision-multiplexing (WDM) systems. One of the critical problems with a polymeric AWG is its polarization-dependent wavelength characteristics which is as high as several nanometers [3], [4], while the polarization dependence of a silica AWG on a silicon substrate is as low as about 0.35 nm [5]. Polarization dependence of 0.1 nm was realized in a silica AWG on a silicon substrate by various methods such as inserting a half-wave plate across the channel waveguide gratings [5], or by compensating thermal stress induced by the mismatch of the coefficient of thermal expansion (CTE) between the silicon substrate and the silica film [6].