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 LiNbO3 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.
Bragg grating reflectors etched in amorphous silicon overlay films have been integrated with Ti:LiNbO3
optical waveguides. Narrow (0.05 nm) reflectance spectrum with > 20 dB dip in the transmittance
spectrum have been obtained at a wavelength of 1542.7 nm for TE polarization. The reflectance in the
channel waveguides depends strongly on the depth of the etched grating. The effect of the Bragg
waveguide loss factor on the transmittance and reflectance spectra is investigated using a model for
contradirectional coupling that includes an attenuation coefficient. Good agreement between model
predictions and experimental results is obtained. Applications of such integrated gratings in the fabrication
of distributed feedback type and Fabry-Perot type electrooptic intensity modulators, for low switching
voltage and high extinction needs, are demonstrated.
Tunable add-drop multiplexers are essential components for reconfigurable optical networks. Components that are based on electro-optic technology offer, in addition to add-drop capability, the desired features of rapid tuning and polarization-independent operation. A comparative overview of various technologies used in making such components, as well as the fabrication and results of a guided-wave electro-optic tunable add-drop multiplexer produced in LiNbO3 at the 1550 nm wavelength regime are presented.