An optical switch on a planar optical circuit substrate includes a cantilevered arm having a control element selectively movable in a direction into the plane of the substrate into a waveguide slot of the substrate for switching optical signals carried by the waveguide. The arm can be actuated by thermal or piezoelectric actuators to deflect between a rest position allowing signal information from a waveguide to continue along the waveguide and a second position with the control element of the cantilevered arm extending into the slot for selectively blocking or changing the direction of the incoming signal. In an alternative embodiment of the invention, a second arm is provided which moves laterally and can be selectively actuated in sequence with the first cantilevered arm for overlying and latching the switching arm in the second or light controlling position, such that the MEMS switch can remain in an active state without further application of a control signal thereto. Arrays of MEMS switches are formed on a single wafer by selective etching and are bonded to arrays of optical waveguides to provide multiple switch modules.