OPTICAL BANDWIDTH AND FABRICATION TOLERANCES OF MULTIMODE INTERFERENCE COUPLERS

Analytical expressions are derived which relate the optical bandwidth and the fabrication tolerances of multimode interference (MMI) coupler s to their most important design parameters. These expressions compare adequately with mode analysis simulations. For strong guided structur es, the optical bandwidth is shown to be inversely proportional to the number of input and output ports N and to the length of the device. T he fabrication tolerances are independent of N and proportional to the output channel separation D. Measurements on MMI couplers in InP/InGa AsP corroborate the theoretical predictions.