Abstract

There are two major classes of nonlinear alloptical fiber switch, namely, (1) resonant devices which display characteristic sharp response, e.g., nonlinear couplers; (2) slow (sinusoidal) response devices such as nonlinear interferometers (Mach-Zehnders, loop mirrors). There is in fact a fairly straightforward connection between these types of device. All the devices operate in the weakly nonlinear regime where only the propagation constant is modified by the nonlinear change in index. Consider a single Mach-Zehnder (MZ) with four ports (two in, two out). This slow response device can only achieve complete switching from one port to the other if both couplers are balanced (50:50) and symmetry is broken by differences in the propagating arms. The assumption in this device is that nonlinear effects occur only in the arms not in the couplers themselves. If several MZs are joined together, complete switching can be obtained with identical arms but unbalanced couplers. It is shown that the requirements are that all the MZs should be similar and that linearly the light input in one port all couples out to one of the output ports. This concatenation is formally identical to a nonlinear coupler in the limit of a large number of MZs. It is shown from numerical simulations that all the features (critical power, etc.) of a nonlinear coupler can be obtained with a model with five MZs in one coupling length. General principles and new configurations are obtained from this new way of considering nonlinear couplers and similar resonant nonlinear devices.

© 1988 Optical Society of America