To make compact delay lines it is essential to have low-loss single-mode straight guides, and compatible low-loss, small radius comers (or mirrors). Straight guide losses of a few tenths of a dB per centimetre have been achieved in III-V semiconductor waveguides, but these are not usually compatible with small radius comers [1,2]. Altematively, very low excess comer losses have been achieved with a bend radius as small as 30 µm using deep-etched guides, but the corresponding straight guide losses were very high [3]. In this paper we use deep-etched, vertical-walled GaAs/AlGaAs waveguides (λ= 1.064 µm). We compare sets of straight guides and corners for two wafer designs: (1) a smaller-guide wafer, with a 2.6 µm single-mode width; and (2) a larger-guide wafer, with a 4.2 µm single-mode width. We also compare measured losses of different waveguide comer designs, and demonstrate the advantages of using corners with an optimised near-hyperbolic shape, designed to minimise straight to curved guide mode mismatch. We show, for example, results for an optimised 90° comer, which has an excess loss of 0.5 dB for an equivalent radius of 100 µm.
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