an optical switch for an optical network , which can switch a light beam from and input fiber to an output fiber quickly and without expensive intermediate conversions to electrical form . the optical switch changes the relative phase of the individual portions of a cross section of a wave front of a beam using wave front interference and can be used in packet switching with switching speeds of about 10 nanoseconds . these optical switches use a phase spatial light modulators that include an array of phase shifting elements preferably of gires - tournois interferometers . each of the phase shifting elements has either a stationary reflective surface with a movable reflective surface or an electro - refractive medium sandwiched between two stationary surfaces . in the first embodiment , the stationary reflective surface with a movable reflective surface is kept a known distance apart by applied potential . in the second embodiment , an applied potential across the electro - refractive medium changes the optical wave path length of the phase shifting element . in a third embodiment , a prism or other spectral dispersing element is used to spectrally separate different wavelengths of a beam carrying a wavelength division multiplexed signal in a litrow configuration . a spatial light modular is then used to controllably steer the separated wavelengths to a desired directions .