Analysis of generalized Mach-Zehnder interferometers forvariable-ratio power splitting and optimized switching

The nonideal integrated optical N×N generalized Mach-Zehnder interferometer (GMZI) employing multimode interference (MMI) couplers is analyzed using transfer matrix techniques. Deviations in the phase relations and the power splitting ratio of the MMI couplers are included in the theory, along with the effects of phase errors in the interferometer arms. The predictions of the theory are compared to the response of a 4×4 GMZI which has been fabricated. The device is operated as both a variable-ratio power splitter and a switch by compensating for the phase errors in the interferometer arms, but the performance is ultimately limited by the nonideal imaging in the MMI couplers. The practicality of these applications is investigated by performing a tolerance analysis for the operation of 1×N power splitters and switches for N up to 10     

Theory of variable-ratio power splitters using multimodeinterference couplers

In this letter, we analyze the integrated optical N×N generalized Mach-Zehnder interferometer (GMZI) employing multimode interference (MMI) couplers. A transfer matrix is used to derive analytic expressions for the intensity distribution at the output ports of the GMZI as a function of the phase shifts applied to the arms. These expressions form a system of nonlinear equations which are numerically solved for the phase shifts, enabling a new interpretation of the GMZI as a variable-ratio power splitter. The performance of the GMZI has been simulated, and it is found that the power splitting ratio is tolerant to both the accuracy of the applied phase shifts and to fluctuations in wavelength