Abstract
The characteristics of GaAs directional couplers and electrooptic switches have been studied at 0.92 μm, 1.06 μm, and 1.15 μm. The devices were formed from pairs of closely spaced low-loss (α ~ 1 cm−1 at 1.06 μm) single-mode p+n−n+ channel-stop strip guides. It was found that the coupling length Lc varies faster than inversely with wavelength, especially near 0.92 μm, and that for each guide width and spacing, Lc increases as the guide thickness is increased. Modeling the couplers to first order as coupled slab waveguides, the wavelength-dependent results can be explained by a variation with wavelength of the effective guide index. This model also predicts a minimum in Lc as a function of the difference in effective index between the guides and their surrounding regions and is in agreement with the experimental increase of Lc with increasing guide thickness (i.e., decreasing confinement). Switching performance at each wavelength was evaluated using devices cleaved to their 1.06-μm coupling length. The zero-bias power isolation obtained at 1.06 μm was 17 dB. At optimum switching bias, i.e., power confined to the input guide, power isolation of 16 dB at 1.15 μm, 17 dB at 1.06 μm, and 18dB at 0.92 μm was obtained. Total power output is constant to ≤0.2 dB between zero bias and the switching bias at 1.06 μm and 1.15 μm. At 0.92 μm, a power decrease of 1.7 dB at the switching bias was observed. This effect could be attributable to electroabsorption effects.
© 1978 Optical Society of America
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