Optimization of a tapered InP/InGaAsP spot-size transformer by simulation of wave propagation

Efficient power transfer between InP/InGaAsP-based optoelectronically integrated circuits (OEICs) and single-mode optical fibers can be realized by appropriate tapered waveguide- structures on the chip itself, so that the fiber can be directly butt-jointed to the chip. First, a simplified sample structure is considered for the purpose of testing a scalar and two different fully vectorial Finite Difference-Beam Propagation Methods (FD-BPM). The sample structure is excited with the eigenmode of the OEIC-chip waveguide and the optical waves propagating through the device are investigated by means of 3D BPM simulation. Starting from three already fabricated prototypes, scalar simulations with modified parameters of geometry are performed to predict performance of the devices in order to achieve an optimized design. Tapered structures with linearly and nonlinearly laterally tapered layers are investigated in order to minimize radiation loss by simultaneously maximizing coupling efficiency. Simulated data will be validated by measured results and numerically optimized structures will be presented.