<title>Feedback correction of angular error in grating READOUT</title>

Abstract

Angular and wavelength READ beam errors in holographic interconnection systems are often a recurrent problem. Several strategies have been proposed to minimize or eliminate such READOUT misalignments. Some years ago, Chatterjee and co-workers proposed a method involving READ beam wavelength tuning to correct output angular errors. In this paper, we investigate the possibility of using an acousto-optic (A-O) Bragg cell with optoelectronic feedback to dynamically correct the scattered beam for deviations in the incidence direction of the READ beam of a hologram. The concept here is based on an acoustic frequency feedback strategy used recently by Balakshy and Kazaryan for laser beam directional stabilization. In the dynamic and adaptive method being proposed here, an acousto-optic Bragg cell is placed between the READ beam and the hologram. A photo-detector placed after the Bragg cell enables the estimation of scattered efficiency and hence (from the READ dephasing-based diffraction efficiency), the amount of the angular deviation. An algorithm for implementing the above scheme, to be used in a practical setup, is proposed and the results of numerical simulations are presented along with possible extensions to wavelength error correction and other applications.