Analyses of optical rays in KTN optical beam deflectors for device design

The potassium tantalate niobate (KTN) optical beam deflector is an electro-optic deflector without any moving parts that works at frequencies higher than 200 kHz. In this paper, we discuss the performance parameters of this deflector. Optical beams are bent by the spatial distribution of the refractive index in the KTN crystal block used in this deflector. In addition to the deflection function, the index distribution operates as a cylindrical convex lens. Therefore, the deflector is often used with glass cylindrical lenses to cancel out the lens function. We analyzed optical rays curving in the block based on the graded index lens theory. We describe the way in which performance parameters, such as the deflection angle, change, depending on both the choice of the compensating lenses and the parameters of the KTN block, namely its size and charge density. We concentrate especially on methods designed to improve the resolvable spot number, which is the most important figure of merit for optical deflectors. One way to achieve improvement is to input a collimated beam or a slightly converging beam into the KTN block.