Wavelength-selective optical add/drop using tilting micro-mirrors

TLDR: An optical switch particularly usable as a wavelength-division add/drop multiplexer (WADM) in a multi-wavelength communication system is described in this article, where four multwavelength beams optically coupled to the input, output, add, and drop channels are arranged in parallel in a rectangular array and are incident upon a diffraction grating.

Abstract: An optical switch particularly usable as a wavelength-division add/drop multiplexer (WADM) in a multi-wavelength communication system. Four multi-wavelength beams optically coupled to the input, output, add, and drop channels are arranged in parallel in a rectangular array and are incident upon a diffraction grating. The grating operating in one direction disperses the beams into their wavelength components and operating in the other direction recombines the wavelength components into a multi-wavelength beam. A lens focuses the components of the beams having a particular wavelength upon one of an array of tiltable micro-mirrors integrated on a silicon substrate. In one position, the mirror for a particular wavelength reflects that wavelength component from the input beam back to the output beam. In a second position, that mirror reflects that wavelength component from the input beam back to the drop beam and reflects that same wavelength component from the add beam back to the output beam. The same optics can be used for a second set of beams which are switched in synchronism with the first set. The array of mirrors can be fabricated to be tiltable to more than two positions so that the input beam can be selectively coupled to either the output beam or one of at least two drop beams while the output beam is correspondingly selectively coupled to either the input beam or one of at least two add beams.