Properties simulation of compact multimode interference 1×3 coupler in SOI

Abstract

Optical waveguide coupler is the basic component in integration optics. For reducing the scale of the 1×3 MMI coupler in SOI, several kinds novel structure couplers are analyzed. The structure factor changes are simulated by means of effective index method (EIM) and two dimensional beam propagation method (2D-BPM). In the simulation, the rib waveguide with large cross-section is used, and the width of MMI region is designed to be 100μm while the height and the etching depth is 10μm and 4μm, respectively. Symmetric interference structure is applied in the device. The width of MMI region is changed in horizontal direction from general straight shape to linear, exponential or parabolically taper shape, and the etching depth of MMI region is increased in perpendicular direction. The simulation results are as follows. The lengths of the device with the linear, exponential or parabolically taper structure are reduced between 30% to 50%, compared with that of conventional structure, but the device performance factors, including the excess loss and the uniformity, are both deteriorated. The excess loss and the length of deeply-etched MMI coupler are both better than conventional structure ones, and the uniformity is similar, but the length of the device is reduced only about 5% while the etching depth is increased 2μm. Moreover, the optimized methods of two different directions are combined in the simulation. Deeply-etched linear tapered MMI coupler shows that the length is reduced about 42%, the excess loss is increased 0.32dB, the uniformity is increased 0.1dB. Deeply-etched parabolically tapered MMI coupler shows that the length is reduced about 52%, the excess loss is increased 0.81dB, the uniformity is increased 0.01dB. Deeply-etched exponential tapered MMI coupler shows that the length is reduced about 46%, the excess loss is increased 0.47dB, the uniformity is increased 0.003dB. The effects of waveguide structure parameters and surroundings temperature on the excess loss of this coupler are analyzed.