Multibeam coupling in photorefractive SBN:Ce

Abstract

Theoretical and experimental results are presented for simultaneous multibeam coupling in photorefractive SBN:Ce. Within a single crystal, multiple signals are amplified through a coupling process that employs a single pump. The coupling gain of each signal results from coupling both between the pump and the signal and between different signals. The amount of gain that each signal receives is dependent on the intensity of the incident signal; thus a competition for the gain exists among the various signals.The optical gain of two-beam mixing in a photorefractive material has been well established. 1 -3 This effect has a number of applications, including beam steering and optical switching, 4 ' 5 two-dimensional optical signal processing, 6 coherent image amplification, 7 and production of an optical oscillator. 8 However, certain optical information-processing procedures generally use a simultaneous multisignal process, e.g., optical associative holographic memory, 9 which is currently a topic of great interest. In this Letter we present a theoretical and an experimental study of multibeam coupling in photorefractive SBN:Ce crystals.In the situation illustrated in Fig. 1, the pump wave ER(r, t) and the signal waves E 8 j(r, t) are given by The total space-charge electric field E induced by the interference pattern is given by E = (kBTkg/q)/[l + (kg/ko) 2 ] (ej * eR),where kB is the Boltzmann constant, q is the charge of the mobile charge carriers, kg is the magnitude of the grating wave vector, and ko is a constant of the material that depends on the number density N of the avail- where nRj exp(ikRj) and nij exp(ioij) characterize the spatial holograms written by the spatial intensity interference of waves ER and Esj and waves Eji and ESj, respectively (which can be easily derived from Refs. 1 and 2), and 1 = IARI2 + lAjl2. In the absence of any applied or intrinsic electric field, the expressions for nRj and 0Rj are given by' 0 ' 1 '