Focal-plane processing algorithm and architecture for laser speckle interferometry

A focal-plane processing array for laser speckle interferometry is described. The imager consists of a 32 X 32 array of analog processing elements which determine the average phase shift of a holographic fringe pattern. The phase computation algorithm requires only the addition, subtraction and rectification (absolute value) of signals from adjacent pixels in the imager. Charge-coupled device structures are used to implement these operations in parallel and eliminate the need to read the pixel data off the array. This allows imager frame rates in excess of 104 frames/sec to be achieved. The imager sensitivity is currently limited by a 20% fill factor and non ideal performance of the rectifier. A higher resolution array is currently being designed which utilizes amorphous silicon photodiodes to improve the fill factor. This design also includes an integrated amplifier at each pixel to obtain photon shot noise limited sensitivity.