Diffractive Color Separating Filter Array
An array of dispersive diffractive micro lenses are formed in an array, such that they split the incoming white light into it’s blue, green and red components via the use of a diffraction grating (as shown in Fig. 1), which includes a focusing / concentrating feature to increase the fill factor of the image sensor array. The diffractive lens array is offset from the sensor array and is formed on the inside surface of the sensor package cover window. The sensor with the diffractive array digitizes the color image formed by the camera objective lens. The Diffractive Color Separating Filter array allows for the color digitization at the full sensor resolution rather than sacrificing the individual color resolution as with a Bayer pattern sensor. It also allows for the elimination of the RGB color absorption filters and the associated energy loss (67% more light transmitted). This approach allows the sensor to have 3X the light sensitivity of an absorptive color filter.
The diffractive micro lens array is formed with grayscale photolithography and RIE etching, or via replication of the master tooling formed formed using grayscale lithography. The photo on the upper right is a AFM of the diffractive optic etched into fused silica.