Electrooptical modulation characteristics of charge-addressed ferroelectric crystal spatial light modulators

Abstract

A charge sensitivity modulation transfer fimction (MTF) of charge-addressed ferroelectric crystal spatial light modulator, which consists of obliquecut crystal plate and two isotropically dielectric layers, is derived as a function of the geometrical parameters, dielectric and electro-optic coefficients. The electrooptical modulation characteristics such as sensitivity, resolution and longitudinal-to transversetransfer ratio are extracted from this function. The orientation dependence of these characteristics for (ZYw)B-cut LiNbO3 are presented with regard to the MSLM configuration. The results indicate some improvement aspects for device design.The transformation from the charge image to the readout light amplitude modulation is a fundamental process in several electrooptical spatial light modulators(SLM's) such as MSLM[ 11,, TITUS[3] and CTPSLM 's[4]. This process, in general, is performed by a charge-addressed modulation element in the device configuration, based on both the dielectric and electrooptic effects. So the performance of the SLMs is greatly determined by operation of these effects in the elements. The solutions for the electrostatic fields have been reported [5][6][7][8]. The linear longitudinal electrooptic effects in the ferroelectric crystals were studied [9][10][11]. The halfvoltage V , was generally used as a figure of merit, which is strongly dependent on the light and field direction in the crystals. So previous MSLMs took the (ZYw)SS0 cut L a o 3 in modulation element [l2]. However, in this case the dielectric coefficients are also anisotropical, a more complete treatment is necessary.In this paper we derive a charge sensitivity modulation transfer function of the element w t h regard to MSLM configuration, which represents the dependence of chargeaddressed electrooptical modulation transformation on orientation of the crystals. The characteristics such as charge sensitivity, resolution, longitudinal-to transverse-transfer ratio, and natural birefringence are treated Description of Theoretical DevelopmentA schematic diagram of the electrooptical modulation element is shown in Fig.1. In the operation mode of MSLM, as an example, a charge density distribution o(x,y) (=ab+a~cos;?~tf.r) induced by input image is deposited at z=O interface between vacuum gap 1, and blocking layer Id. The readout light is in the direction of OZ and reflected at the interface between ld and crystal plate 1, . The crystal is usually oblique-cut and anisotropic for dielectric and electrooptic effects. Here the transformation from charge distribution to output light -B c e, , 1 , v-z t 'x Fig.1. Schematic dielectric structure of charge-addressed modulation element. Orientation of coordinate system OXYZ related to Oabc is presented. is modeled as a space-invariant linear system with a charge sensitivity modulation transfer function (MTF), which can be divided into charge-voltage MTF and voltage-light amplitude transfer coefficients. The derived resultant charge sensitivity MTF can be written as: g;sinh[w(Z,, -/,)I W E...