Phase behaviors for silicon-wire multistage delayed interferometric WDM filters across a whole 300-mm silicon-on-insulator wafer

Abstract

We report phase behaviors in silicon-wire multistage delayed interferometric (MDI) wavelength-division multiplexing (WDM) optical filters on a 300-mm silicon-on-insulator (SOI) wafer. In order to achieve spectrally uniform filter response and make clear the main factor for influencing spectral shape and uniformity across the SOI wafer, we fabricated 1 × 4 channel MDI-type WDM filters as a device under test (DUT) by using a 193-nm ArF-immersion lithography process and formulated the analytic calculation model, which can be fully adaptable to the measured data. By analyzing the measured filter response through an iterative fitting process with our analytic calculation model, we verified that phase behaviors in the DUT were the main factor to determine filter spectral shape and crosstalk, while the wavelength-sensitive coupling ratio of directional couplers had less influence on the filter performance within a 40-nm-wide spectral range. Phase fluctuations at each delayed interferometer (DI) were calibrated to be random processes at inter-dies across the wafer. In order to sustain good spectral shape and uniformity, it is important to minimize excess phase errors at each DI. Reduction of interaction lengths and equivalent refractive index variation of the waveguides could be one of the prominent ways to further improve WDM filter performances.