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

Abstract

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.

400 Hz Volume Rate Swept-Source Optical Coherence Tomography at 1060 nm Using a KTN Deflector

“…The maximum deflection angle is given by the 200 V applied to the crystal. This is fundamentally limited by the thickness of the crystal block [10]. Due to the dependence of deflection angle on the polarization state, the KTN crystal is coupled to a suitably oriented PM fiber by the manufacturer.…”

Reduction of beam-divergence fluctuation for KTN optical beam deflector

“… Namely, the inverse of the focal length of a uniformly charge-distributed KTN crystal depends on ρ, and especially when L A 1,  is proportional to ρ 2 . Assuming that n 0 = 2.15, g = 0.11 m 4 C −2 , ρ = 75 C m −3 , and L = 4 mm, which are typical values for KTN, 15) we can estimate that L A is about 0.21 and the second equal sign in Eq. ( 1) holds within an error range of less than 1%.…”

“…where n 0 is the refractive index without an electric field, L is the interaction length between a propagating optical beam and an electric field in the crystal, and g is the second-order EO coefficient. 15,16) The second equal sign in Eq. (1) holds when L A 1.…”

Dynamic relaxation process of a 3D super crystal structure in a Cu:KTN crystal

“…In the past half century, potassium tantalate-niobate (KTN) crystals have attracted a lot of attention in the research and application field because of their exceptional electro-optic (EO) properties and wide transparent wavelength range [1][2][3][4][5][6][7][8] . Thus, they have been used in EO modulation [2,5] , beam deflection [6][7][8] , electric-controlled lenses [9] , and so on.…”

“…In the past half century, potassium tantalate-niobate (KTN) crystals have attracted a lot of attention in the research and application field because of their exceptional electro-optic (EO) properties and wide transparent wavelength range [1][2][3][4][5][6][7][8] . Thus, they have been used in EO modulation [2,5] , beam deflection [6][7][8] , electric-controlled lenses [9] , and so on. Recent research shows that in the proximity of the Curie temperature, a KTN crystal presents enhanced EO properties and a few kinds of fascinating critical phenomena, i.e., giant EO effects [7,10] , scale-free optics and anti-diffraction beam propagation [11,12] , solitons [13,14] , extreme nonlinearity [15] , and 3D super crystals [13,[16][17][18][19] .…”