Patent ID: 7196390

Claim:
A method for encoding information that is encoded in spatial variations of the intensity of light characterized by a first wavelength in light characterized by a second wavelength, the method comprising: transmitting the first wavelength light through a photo-conducting material in which electron-hole pairs are generated by absorbing photons from the first wavelength light to generate a first density distribution of electrons homologous with the spatial variations in intensity of the first wavelength light; passing electrons from the first density distribution through a structure comprising a plurality of graded-band-gap layers in which electrons are multiplied in an avalanche process to generate a second additional electron density homologous with the first electron density distribution; and trapping electrons from the first and second electron density distributions in a trapping region to generate an electric field homologous with the density distributions in a material that modulates a characteristic of light that passes therethrough responsive to an electric field therein; transmitting the second wavelength light through the modulating material and a reflector that reflects the first wavelength light through the photo-conducting material thereby modulating the second wavelength light in response to the electric field and encoding it with the information.