Collaborative research between Foster-Miller and Brown University, under subcontract to Raytheon, resulted in successful development and demonstration of both large angle beam steering and beam blocking devices based on an electronically switchable Bragg grating (ESBG).  This approach uses a holographic polymer dispersed liquid crystal (H-PDLC) made into a layered optical grating that controls transmission or reflection of light with efficiency over 96 percent.  Brown University developed improved H-PDLC materials and we applied these materials to ESBG devices. Foster-Miller and Brown concentrated on identifying materials and processes that produce high efficiency ESBGs at the 1.55 (m wavelength.  ESBGs were produced for both 45 and 20-degree beam steering using slanted Bragg gratings designed to work with an orthogonal input beam.

After the beam steering development was successfully completed, new efforts concentrated on developing a H-PDLC beam-blocking device based on total internal reflection (TIR).  In the electric field-off state, the holographic planes are slanted such that the angle of the diffraction beam is greater than the TIR angle of the glass substrate. The beam is "trapped" in the substrate and propagates to the edge.  In the electric field-on state, the holographic grating is "erased" and the incident beam propagates directly through the sample. Contrast ratios of 10 dB and sub-millisecond response times have been demonstrated. 

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