The role of photomask resolution on the performance of arrayed-waveguide grating devices

The crosstalk performance of an arrayed-waveguide grating (AWG) multiplexer or demultiplexer is primarily caused by random optical phase errors introd uced in the arrayed waveguides. Because the layout of waveguides on a wafer is patterned via photomask through the photolithography process, the resol ution of a photomask has a direct influence on the phase errors of an AWG. This paper presents a theoretical analysis on the phase error caused by pho tomask resolution and other basic design parameters. Both calculation and m easurement results show that a high-resolution photomask (better than 25 nm ) is a critical requirement to produce low-crosstalk (less than -30 dB) AWG demultiplexers. We also investigate the effect of nonideal power distribut ion in the arrayed waveguides because it contributes considerable phase err ors when material impurity is not well controlled during wafer fabrication. Basic criteria of power profile truncation, number of grating waveguides, and material index variation are also summarized.