A 1 × 5 optical switch with a switching speed of microseconds is demonstrated. Switching between different channels in a planar lightwave circuit waveguide array was controlled using an electro-optic beam deflector. A single crystal of potassium tantalate niobate (KTa 1−x Nb x O 3 , KTN) was used as a deflector to realise this operation. A switching speed of 8.1 μs was demonstrated for the switching of two adjacent channels.Introduction: Optical switching using electro-optic (EO) deflectors has received a lot of attention because of their fast switching speed. An EO deflector deflects a launched optical beam to switch between spatially arranged output channels using an applied voltage. (Pb, La)(Zr, Ti)O 3 (PLZT), LiNbO 3 (LN) and LiTaO 3 (LT) with prism structures are commonly used to realise multi-channel and high-speed EO switches [1-3]. A potassium tantalate niobate (KTa 1-x Nb x O 3 , KTN) single crystal is also a promising material for an EO deflector because of its huge second-order EO (Kerr) effect. In addition to a KTN single crystal having superior material properties, a novel deflection technique has been proposed [4] based on the refractive index distribution inside the KTN crystal. With an EO crystal, the gradient of the refractive index cumulatively adds a phase delay as the optical beam propagates through it. Thus, it is possible to obtain a deflection angle of more than several degrees, which is much larger than those of the conventional prism-shaped EO deflectors. Therefore, we can expect a large number of switching channels when KTN is used as an EO switch. In this Letter, we describe a 1 × 5 optical switch with a switching speed of microseconds consisting of a KTN deflector and a planar lightwave circuit (PLC) waveguide array. The highest switching speed when switching two adjacent channels was 8.1 μs.