[OPTICAL REVIEW Vol. 3, No. 2 (1996) 96-100]
Angular Multiplexing Gratings Characterization in Dichromated Gelatin and Thoughts on Diffractive Optical Memory
Slimane MECHAHOUGUI, Harry RAMENAH, Jacques HARTHONG and Patrick MEYRUEIS
Universite Louis Pasteur, Ecole Nationale Superieure de Physique, Laboratoire des Systemes Photoniques, Boulevard Sebastien Brant, F 67400, Ilkirch, France
(Received August 31, 1995; Accepted December 22, 1995)
We were mainly concerned here with multiple exposure gratings that allow interactions and coupling between gratings. We started the study of interactions and coupling with five gratings recorded in dichromated gelatin (DCG). Having determined experimentally the characteristic parameters of these five gratings, we used a method developed by Oxford University to synthesize the modulation profile. Entering these parameters of each grating into our computing programs (based on the alternative theory of diffraction in modulated media) and by varying the amplitude modulation, the latter was deduced by adjusting the numerical curve to the experimental one. We then extended the study to nine multiplexed gratings. This study allowed us to know the range of the amplitude modulation such that a certain number of angular multiplexing can be done in DCG. Several undesirable effects which we had experimentally observed appeared then during the reconstruction of any one of the multiplexed images, such as cross-talk effect. We noted the good concordance between experimental and theoretical results. We finally illustrated cross-talk effect in a diffractive memory where, if the amplitude modulation was first calculated, the number of multiplexing for an angular range could then be determined and the angular separation achieved to avoid cross-talk.
Key words : diffraction efficiency, modulation profile, optical memory