Coupled Mach--Zehnder interferometer

InGaAsP photonic integrated circuit. The system acts as an optical flip-flop, with optical set and reset functions. A schematic diagram of the device is shown in Fig. 1. Each MZI in the device is constructed from the following components: a 72 / 28 splitting ratio multimode interference coupler 6 at the MZI input (left side of Fig. 1), a 1450 #m long electro-optic phase shifter (PS) in one MZI arm, 7 a 750 #m long SOA in the other MZI arm, and, following the SOA, another 72 / 28 multimode interference coupler. This coupler is employed to couple light out of the system, such that the system's state can be observed, and also to couple in light that is used to switch between states. The two MZIs share a common 50 / 50 multimode interference coupler. The couplers employ tapered access waveguides for accurate coupling ratios and low excess loss. 8 A theory on the way in which two coupled MZIs can interact to form a 1 bit memory is given in Ref. 5. Here, MZI 1 and MZI 2 share a co