Patent ID: 6967345

Claim:
A quantum well infrared photodetector (QWIP) comprising: a substrate formed of a semiconductor material; a plurality of photodetectors disposed relative to one another to form an array on said substrate, each photodetector having first and second quantum well structures, one stacked over the other and each comprising a plurality of alternating barrier layers and well layers, each well layer of each quantum well structure coupled between two barrier layers to support an intersubband transition between a bound ground energy state and an excited energy state within a common energy band where said excited energy state is substantially resonant with an energy of the well top, wherein materials, thicknesses and dimensions of said well layers and barrier layers are selected such that said first and said second quantum well structures effect intersubband transitions at first and second wavelengths, respectively, wherein none of said two quantum well structures is short circuited, and wherein said barrier layers are sufficiently thick to substantially eliminate carrier tunneling; a first set of optical cross gratings coupled to even rows of said detectors and optimized to diffract radiation at said first wavelength to be absorbed by said first quantum well structure; and a second set of optical cross gratings coupled to odd rows of said detectors and optimized to diffract radiation at said second wavelength to be absorbed by said second quantum well structure.