A wet etching method of removing silicon from a substrate includes depositing a layer comprising silicon in elemental form over a substrate. The optical switch switches a plurality of input signals to a plurality of output positions, in which a laminated structure that has a nonlinear optical layer and a buffer layer laminated in the same number as that of input parts intersects an optical path between the input parts and output parts. The stages are configured with cascode elements to obtain high impedances that enhance their signal gain and the common-mode feedback circuit is configured to controllably lower the output voltage of a current source that provides the tail current to thereby enhance the amplifier’s dynamic range. Sub-discussion topics may be defined for discussion topics. When the portable device is docked with the docking station, the magnetically permeable element in the portable device and the magnetically permeable element in the docking station are arranged to form a magnetic circuit, and the data transducer in the portable device and the data transducer in the docking station are arranged to exchange data.