A system for manipulating optical signals in an optical switch utilizes a light-absorbing region. The region efficiently converts light to thermal energy and is in thermal communication with an index-matching fluid disposed within an intersecting gap between a first input optical waveguide and a first output optical waveguide. In one embodiment, exposing the region to optical radiation elevates the temperature of the fluid within the gap, resulting in vaporization of the fluid into gas. Filling the gap with gas creates a refractive index mismatch that causes light from the first input waveguide to be diverted to a second output waveguide. In another embodiment, the manipulation of optical signals is achieved by exposing a light-absorbing fluid to the source radiation.