Narrowband electrooptic tunable notch filter.
We describe the theory of a narrowband electrooptic tunable filter based on a Fabry-Perot etalon with distributed Bragg reflectors. The filter can be in either bulk or waveguide form. The input to the filter must be prefiltered to the stop-band of the Bragg mirrors. Once this is accomplished, the etalon possesses a very narrow notch in the Bragg filter stop-band. The notch width is extremely narrow when the Bragg reflectance is high. The location of the notch in the Bragg stop-band is determined by the etalon cavity length and can be tuned by application of an electric field to the electrooptic material comprising the etalon cavity. Absorption in the cavity and Bragg reflectors is included in the theoretical model of the filter. The filter can be constructed from any one of several existing electrooptic organic polymer crystals, if the gratings are made either by partial polymerization of the monomer in crossed-UV beams or by corrugating the surface of the polymer. We show a theoretical example of a notch filter operating at a center wavelength of 1 microm that is 62.75 microm thick, with a notch width of under 1 A and a transmission of 35%. This type of filter should have applications in high-speed optical modulation and Q-switches for lasers.
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Lockheed Palo Alto Research Laboratory, 3251 Hanover Street, Palo Alto, California 94304, USA.
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