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The fabrication and characterisation of extremely compact WDM zero-gap directional couplers with buried GaInAsP/InP waveguides is reported. A device with a centre length of 178 µm separated two channels at λ1 = 1.3 µm and λ2 = 1.52 µm with a crosstalk attenuation of 30 dB.
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Schienle et al. (1989) studied this question.
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