A 2 x 2 multimode interference coupler with exponentially tapered waveguide

An exponentially tapered structure is introduced into multimode interference ( MMI) devices. Compared with a parabolically tapered structure, which has been successfully used in MMI devices, this structure can further reduce the length of these devices. The performances of the 2 x 2 MMI coupler with exponentially tapered structure, such as the optical transmission, the splitting ratio, the wavelength response and the fabrication tolerance, are investigated by the 2D finite difference beam propagation method. Results show that the exponentially tapered MMI coupler exhibits a similar property to that with a parabolically tapered structure except for the splitting ratio. The exponentially tapered structure can offer a possible application in MMI couplers with a free choice of the splitting ratio.