Fine Resolution Photonic Spectral Processor Using a Waveguide Grating Router with Permanent Phase Trimming

Spectrally dispersed light from a fine resolution waveguide grating router (WGR) of 25-GHz free spectral range that radiates to free space is spatially filtered at ∼1 GHz optical resolution and 50 MHz spectral addressability using a liquid crystal on Silicon (LCoS) spatial light modulator (SLM). Fabrication imperfections leading to phase errors on the 32 waveguide arms of the WGR are corrected using a UV pulsed laser to inscribe permanent optical path changes to the waveguides. WGR phase errors are permanently trimmed waveguide-by-waveguide with an excimer laser by inducing stress in the glass cladding above the waveguide for coarse setting and using the photosensitivity effect for fine setting. The WGR was then mated with an LCoS SLM located at the Fourier plane to form a photonic spectral processor, for arbitrary spectral amplitude and phase manipulations.