Potentiality of photorefractive CdTe

Abstract

For optical telecommunication networks, optical switching is now being studied. Different solutions have been proposed (integrated optics, free space switching, etc.), and reconfigurable optical interconnects, based on phase conjugation, should be one interesting method. For example, some results have been obtained with a double-phase conjugated mirror configuration, allowing reconfigurable connection between single-mode optical fibres. These phase-conjugated optics use photorefractive crystals and the first demonstration has been given using Bi 12 TiO 20 photorefractive crystals. In a telecommunication network, semiconductive crystals with a good efficiency in the near-IR wavelength are needed. Our first experiments were carried out with InP:Fe crystals at 1.3 μm. However, it is well known, from published studies, that II–VI materials are, in principle, more interesting for the following reasons. The electro-optic coefficient is higher (and therefore the figure of merit is higher). The solubility of dopants is higher (and therefore the space charge electric field, which modulates the refractive index of the material, may be higher). Next we tested a CdTe:V crystal and, in a two-wave mixing experiment without an external electric field, an amplification gain was observed and a high photosensitivity demonstrated at 1.3 μm. In this paper, we shall describe the photorefractive effect and explain our choice of the CdTe:V crystal, taking into account the parameters of this photorefractive effect and some other parameters required by the applications in the optical beam steering field. Next the results will be given, and finally an optical configuration using phase conjugation will be presented as an example of application.