Abstract

Fiber optic switches that use liquid crystals to switch all the unpolarized light from multimode optical fibers have been known for some time. The operation of one type of switch uses the liquid crystal as a variable retarder that controls the polarization of light, which is separated into and recombined from orthogonal linear components by a polarizing beam splitter cube.¹ This combination of components results in a fully symmetric 2 × 2 switch, but its crosstalk is limited to worse than -20 dB, by even the best available dielectric polarizing beam splitter films. This short comingseverely limits the utility of such switches no matter what liquid crystal is used. We describe several switches that use these two components in new combinations to achieve crosstalk performance that can theoretically approach -40 dB. Our prototypes of the simpler switches exhibit crosstalk levels of -27 dB or better and insertion loss at about -3 dB. Since we used ferroelectric liquid crystals, they switch quickly between states with a rise time of 35 ps in response to 30 Vdc while requiring 1 nA of holding current. Our prototypes have operated at either 633 nm or 830 nm, but operation at other wavelengths should be possible.

© 1991 Optical Society of America