Optik 124 (2013) 229–233 Contents lists available at SciVerse ScienceDirect Optik jou rnal homepage: www.elsevier.de/ijleo Bright spatial solitons in biased centro-symmetric photorefractive medium under drift as well as diffusion effects S. Shwetanshumala a,∗,1 , Noushin Asif a , S. Konar a , Anjan Biswas b a Department of Applied Physics, Birla Institute of Technology, Mesra, Ranchi, Jharkhand, India b Department of Mathematical Sciences, Delaware State University, Dover, DE 19901-2277, USA a r t i c l e i n f o Article history: Received 28 June 2011 Accepted 17 November 2011 PACS: 42.65J 42.65S 42.65Tg 42.65Hw 42.70a 42.70 Keywords: Centro-symmetric photorefractive medium Spatial soliton Soliton trajectory a b s t r a c t This paper presents an investigation on the propagation characteristics of optical spatial solitons in a biased centro-symmetric photorefractive medium. Unlike earlier attempts on photorefractive solitons, in the present investigation, we have given equal significance to the effects of charge drift and their diffusion. We have obtained dynamical equations for solitons employing paraxial ray approximation and examined criteria for stationary propagation. Trajectories of stationary solitons have been examined. © 2011 Elsevier GmbH. All rights reserved. 1. Introduction Light–matter interaction results into a variety of interesting phenomena both from fundamental and technological view points. The manifestations of this interaction have opened a wide arena of theoretical as well as experimental field of investigations when the interaction is nonlinear. Formation of optical solitons being only one of those wide variety of phenomena. Optical spatial or temporal solitons [1–3] are localized concentration of electromag- netic field energy propagating through nonlinear media without any change in spatial or temporal profile. Self confinement of elec- tromagnetic energy is also possible simultaneously in spatial and temporal domain leading to spatiotemporal solitons [4,5]. Optical solitons have been observed in plasma, optical fiber, photorefrac- tive media etc. Photorefractive spatial solitons (PRSS) enjoy special status in the world of optical spatial solitons [6–16] because of var- ious reasons. The power requirement for photorefractive solitons is very small which is a few microwatt only. In addition, photorefrac- tive (PR) media possess saturating nonlinearity which prevents the ∗ Corresponding author. E-mail address: shwetanshumala@gmail.com (S. Shwetanshumala). 1 Permanent Address: Department of Physics, A.N. College, Patna, Bihar, India. collapse of higher dimensional optical solitons. Moreover, PRSS can be operated at telecommunication wavelength with fast response, response time being of the order of microsecond. The ease in pro- duction and the stability properties make PRSS potentially useful for various applications in optical switching, beam steering, optical interconnects, parallel computing, reconfigurable optical circuits etc. [17–19]. Segev et al. [6] were first to theoretically predict the possibility of photorefractive spatial solitons in the year 1992. Only a year later Duree et al. [7] were able to observe them experimentally. Till date, theoretical as well as experimental investigations have been made on different types of PR spatial solitons of which screening solitons (SS) [6,7,9,10,18], photovoltaic (PV) solitons [8,14] and screening photovoltaic (SP) solitons [11,13,15], being the most widely and thoroughly investigated categories. These solitons have been found to exist in bright, dark and grey, scalar as well as vector configura- tions. Most of the earlier experimental as well as theoretical work on photorefractive solitons employed non centro-symmetric pho- torefractive (NCSPR) materials. However, Segev et al. [19] predicted that centro-symmetric photorefractive (CSPR) materials may also support spatial solitons. Del Re et al. [20] confirmed the prediction by observing them in CSPR media. In the creation of space–charge field which leads to the refractive index change; charge drift and diffusion processes are 0030-4026/$ – see front matter © 2011 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijleo.2011.11.053