A method for amplitude response estimation in quadratic channels

Like other coherent optical storage channels, a volume holographic storage channel (VHSC) is a quadratic channel since its output is a function of the magnitude-square of the light incident on the photo-detector array. Because of such intensity detectione, the sign/phase information at the output is destroyed which makes the estimation of the amplitude response diffucult. In this paper, we present a new method called modified least mean squares (MLMS) method to estimate the amplitude channel response of a Volume Holographic Storage Channel in the presence of quadratic non-linearity. Numerical simulations show that MLMS is very effective in estimating the amplitude response of such channels under even severe loss of sign information.