A transistor may include: a gate insulting layer, a gate electrode formed on a bottom side of the gate insulating layer, a channel layer formed on a top side of the gate insulating layer, a source electrode that contacts a first portion of the channel layer, and a drain electrode that contacts a second portion of the channel layer. The switch uses a grating that separates multi-channel optical signals into a plurality of optical channels, and combines a plurality of optical channels into multi-channel optical signals. In some embodiments, each keyword maps to the same number of encrypted document identifiers. Communication links couple the output ports of the second stage multiplexers to the input ports of the first stage multiplexer.