Bidirectional-BPM analysis of a 90° integrated waveguide mirror in InGaAsP/InP

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Abstract
The size of waveguide bends is one of the crucial factors influencing the overall length of integrated optical components for fibre-optic communication systems. Recently, there has been a growing interest in large-angle abrupt bends, which are realised by etching a totally reflecting mirror through a 90° waveguide corner [3] [4] [5] (Fig.1.a). This technique is promising for the realisation of single bends or large lateral waveguide off-sets (Fig.1.b). So far, 90° waveguide mirrors were implemented both on GaAs/GaAIAs [3] [4] and InGaAsP/InP [5] and the measured insertion loss of the devices reported is of the order of a few dB. Various contributions to the mirror loss are simulated in this paper by the bidirectional BPM, which is a recently developed iterative extension of the one directional BPM taking into account discrete reflections [2]. In particular, the sensitivity to mirror displacement, waveguide width and vertical inclination of the mirror facet are investigated for both TM and TE polarisation. Analytical plane-wave solutions support the reliability of the results.