Switchable Optical Phased Prism Arrays For Beam Steering Jianru Shi, Philip J. Bos Liquid Crystallnstitute, Kent State University, Kent, OH 44242-0001 Bruce Winker RockwellScient/Ic Company; FOB 1085, Thousand Oaks, CA 91358 Paul F. McManamon Wright- Patterson Air Force Research Laboratory, Dayton, OH 45433-7304 The Wollaston prism with large deflection angle usually has small cross section size, which constrains its application in beam steering. This paper investigates the possibility of assembling the prisms together to increase the cross section size. Single-layer- and double-layer- assembled Wollaston prisms are investigated. The compression ratio and transmission ratio associated with the diffraction efficiency of assembled prisms are calculated and formulated. 1. INTRODUCTION Blazed grating has been discussed in a previous paper1 in terms of beam steering application. The light blockage, beam shrinkage and phase mismatch in the new propagation direction are discussed. Three parameters associated with these effects, transmission ratio, compression ratio and phase mismatch parameter, are defined. It's concluded that phase mismatch will prevent the beam from directing to the right angle, and therefore phase compensation is necessary. After phase compensation, the deflection efficiency is simply the product of the two ratios mentioned above. In beam steering application, the blazed grating is usually required to be birefringent, which is difficult to fabricate, however. This paper will analyze the prism array in analog to blazed grating. The concepts of two ratios and the phase mismatch parameter are generalized to prism array. The single-layer and double-layer Wollaston prism arrays are studied. 2. PRISM ARRAY Consider two isotropic prisms with refractive index n1 and n2. Put them together face to face to form a rectangular compound prism. Lining up the compound prisms in an array forms an isotropic prism array. In each compound prism segment, if the lower prism has higher index value, the compound prism is called upright prism array; if the top prism has higher index value, it's called upside down prism array. The transmission ratio and compression ratio of blazed grating can be generalized to prism array directly without any change as shown in figure 1. b C e=— 6=— (1) d d When the refractive index n1>n2, the prism array possesses the same ratios as that of an upright blazed grating, and when n1<n2, it 's analogical to an upside down grating. (a) (b) Fig. 1 (a) Upright prisms, n1 > n2 (b) upside down prisms, n1 < n2 (c) 2 << Sd << d , 2 << 8/i << h The phase behavior of assemble prisms is much different than that of a blazed grating. For grating, the phase difference between two adjacent segments can be calculated by d(sin a —sin a0); for prism array, however, it's difficult to constrain all the segment length d and thickness h to be identical from segment to segment within the accuracy of less than one wavelength. Rather, Sd and 8/i are much larger than one C C (c) Advanced Wavefront Control: Methods, Devices, and Applications II, edited by John D. Gonglewski, Mark T. Gruneisen, Michael K. Giles, Proceedings of SPIE Vol. 5553 (SPIE, Bellingham, WA, 2004) 0277-786X/04/$15 · doi: 10.1117/12.581195 102