Abstract

We have successfully demonstrated and characterized a novel 1x2 optical switch using a pair of identical binary phase gratings. A binary phase grating consisting of a series of parallel rectangular grooves (~0.7 μm wide and 1 μm deep, separated by 0.9 μm) was recently fabricated by etching on a thin (~1 mm) quartz plate. In general, such a grating diffracts an incident collimated beam into multiple beams (different diffraction order). In the appropriate conditions, depending on the grating spacing, wavelength, and the angle of incidence, almost all the input optical energy can be essentially confined to 0 and the -1 diffraction orders. When two such identical gratings are placed in parallel adjacent to each other, the overall diffraction efficiency depends on their relative position. In principle, when they are exactly 180° out of phase, the optical phase modulation introduced by the first element is exactly canceled out by the other leading to a zero diffraction efficiency with all the energy being directed to the 0-order output port. In other words, the incoming beam does not feel the presence of the grating-pair due to complete cancellation of the two and simply passes through with no energy diffracted into the -1 port. In practice, the cancellation may not be complete because of misalignment and/or non-uniformity. Strong diffraction occurs when the gratings are exactly in phase. By proper choice of the depth of the gratings, 100% diffraction efficiency can be achieved. The switching is accomplished by shifting one grating relative to the other by a distance of the order of half a grating period, which is typically a fraction of a micron.

© 1991 Optical Society of America