The paper describes a new three-dimensional (3D) MEMS optical switch. The switch consists of a collimator array for generating optical beams, and a MEMS mirror array for changing the directions of the beams. Each of the 18 optical ports can be either an input or an output, giving the switch a flexible configuration of 8/spl times/8, 2/spl times/16, and so on. The mirrors and the collimators are assembled passively in a compact package measuring 80/spl times/30/spl times/12 mm/sup 3/. The mean of measured insertion losses of all 64 paths in an 8/spl times/8 switch configuration was 1.1 dB; this confirms the low insertion loss of the developed switch.