Tunable spectral slicing filter utilizing sparse grating in Ti:LiNbO3
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A new type of tunable guided-wave spectral slicing filter at the 1530nm wavelength regime is reported. The design allows the selection of equally spaced frequency channels and simultaneously produces nulls that are equally spaced between the selected channels. This makes it attractive for minimizing crosstalk in dense wavelength division multiplexing (DWDM) applications. The spectral selection of the filter is based on co-directional polarization coupling between transverse electric (TE) and transverse magnetic (TM) orthogonal modes in a waveguide by means of a static strain induced index grating. An etalon-like response results from the sparse arrangement of the grating sections as N individual coupling regions in tandem with equal spacing between their centers, yielding N-1 equally spaced nulls between adjacent selected frequencies. Adjustments of the resulting filtering function may be obtained by proper choice of coupling regions' lengths and spacing. Devices were fabricated using single mode channel waveguides formed by Ti diffusion on x-cut y-propagating LiNbO 3 substrates. Static strain from a periodically delineated surface film was used for making N = 6 polarization coupling regions. Electrode patterns centered about the optical waveguide and defined by liftoff were used to tune the filter electrooptically. Experimental results are in good agreement with design theory. 2009 SPIE.
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Integrated Optics: Devices, Materials, and Technologies XIII