A polarization-and wavelength-insensitive semiconductor guided-wave optical switch with a Yjunction is proposed. In this switch, an injected current at the p-n junction induces polarization-independent refractive index decrease through the plasma dispersion and bandfilling effects. The index change, in turn, introduces asymmetry to a symmetric Y junction waveguide, and a local mode of one of the branches becomes cut off, when the induced index change is sufficiently large to cancel out the built-in index difference of the waveguide. Therefore, this switch exhibits a so-called digital response with respect to current, and thus it can be used as a wavelength-insensitive 1 x 2 optical switch. The polarization-and wavelength-insensitive switching operation was confirmed with a fabricated GaAs/GaAIAs switch at wavelengths of 1.3 and 1.55 pm, and the O N~O F F ratio exceeded 20 dB at an injection current of 250 mA at these wavelengths.

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A new design in which a filter is embedded in a fiber fixed on a substrate is proposed, and it was successfully applied to fabrications of low loss fiber optic components for a single-mode fiber transmission system. These components are low in loss and wide in operational temperature range, and the design is easily adapted to a multifilter component or a multifiber component. Filter embedding was achieved in two ways. One is to insert a thin filter chip in a slit, which is machined into a fiber fixed on a substrate by a dicing saw ("filter inserted type"). The other is to evaporate a filter film directly on a fiber end face and butt this fiber to another fiber on a guide groove on a substrate (''filter evaporated type").