A GENERAL PLANAR WAVE-GUIDE AUTOREGRESSIVE OPTICAL FILTER

A general architecture for an autoregressive (AR) planar waveguide opt ical filter is demonstrated for the first time, Its advantages are a f latter passband, sharper rolloff and better rejection in the stopband compared to finite impulse response (FIR) filters with the same number of stages. The architecture can be extended to an arbitrary number of stages. A modified Levinson algorithm is derived for filter synthesis and analysis which includes waveguide loss and phase errors between s tages, The filter analysis algorithm allows the filter's coupling rati os and phase errors for each stage to be determined from the filter's spectral response, When combined with a postfabrication tuning process , this analysis method provides feedback for optimizing the response. Autoregressive lattice filters mere designed and fabricated using Ge-d oped silica waveguides. Measurements are reported which demonstrate th e synthesis and analysis algorithms. The impact of fabrication toleran ces on filter synthesis and of measurement uncertainties on filter ana lysis are investigated.