A Phased, Optical, Coupler-Pair Switch

We analyze an optical switch consisting of two directional couplers with an intermediate phase-compensating network. The conditional requirements on coupler length, phase mismatch between guides in each coupler, and phase compensation between couplers are established such that two switching states exist. It is shown that, to switch between states, (i) The couplers must be 3 dB or stronger. (ii) Each coupler must be “adjusted” to become a hybrid by controlling the phase mismatch between guides. (iii) The differential phase φ must be initially set to turn on one state. (iv) An additional increment of π in the phase shift causes switching to the second state. It is estimated that the controlling voltage required to activate the bipolar switch is of the order of 1 to 2 V for a 3-µm guide with 3-mm-long electrodes in Ti-diffused LiNbO3. We are currently in the process of fabricating such devices.