Digital operation of an ytterbium-doped two-mode fiber interferometric optical intensity switch

Digital operation of an all-optical intensity switch is demonstrated in a two-mode interferometer constructed from ytterbium-doped fiber. We clamp the resonantly enhanced phase shift responsible for the switching by allowing the fiber to lase, resulting in a bistable, digital response. The degree of phase shift at the clamping point can be controlled by adjustment of the laser threshold, and for complete switching (phase shift of pi) the power length product PL(pi) was estimated to be 1.3 mW m . Isolation of 11 dB was observed, with switching speed limited by the relaxation time of ytterbium.