Self-trapping of two-dimensional optical beams and light-induced waveguiding in photorefractive InP at telecommunication wavelengths

Abstract

We demonstrated an experimental observation of self-trapping and self-deflection of a two-dimensional optical beam by the photorefractive effect at telecommunication wavelengths under an applied dc field. Self-trapping is effective for an intensity range related to the intensity-temperature resonance known for two-wave mixing in InP:Fe. The photorefractive index change giving rise to the trapping is measured at 10−4, while the photorefractive space-charge field is measured at about 50 kV/cm, ten times higher than the applied field. We show experimentally that this index change creates a waveguide that can be used to guide a second beam at 1.55 μm.

Experimental control of steady state photorefractive self-focusing in InP:Fe at infrared wavelengths

“…9 Note that crystals used in this paper originate from the same manufacturer, InPact society 10 As a side note, we would like to point out that the index contrast between the guide and the anti-guide is responsible for the higher than expected index variation previously measured [33].…”

“…For instance, in InP:Fe [31][32][33][34], or CdZnTe [35] the space charge field created by the PR effect can be several times higher than the external applied field. This 'amplification' of the electric field compensates for the lower electro-optic coefficient of the semiconductors, allowing the creation of an efficient waveguide [33].…”

“…For instance, in InP:Fe [31][32][33][34], or CdZnTe [35] the space charge field created by the PR effect can be several times higher than the external applied field. This 'amplification' of the electric field compensates for the lower electro-optic coefficient of the semiconductors, allowing the creation of an efficient waveguide [33]. Another particularity is that in semiconductors the focusing process switches from self defocusing to self focusing when the intensity of the beam increases, while in 'classical' materials the beam always focuses (or defocuses, depending on electric field direction), regardless of its intensity.…”

Assessment method for photo-induced waveguides

“…These waveguides can be formed in numerous medium such as polymers [1][2][3], liquid crystals [4], glass [1,5,6] or photorefractive crystals [7][8][9]. Realization of these structures would benefit from a technique allowing real time evaluation during the photo-induction process.…”

“…This would provide a tool to characterize the induction process and would ultimately give an accurate control of the characteristics of the fabricated waveguides. Different techniques such as refractive index mapping using interferometry [8] or higher order mode excitation [7] are already employed for this purpose but more versatile characterization tools that take advantage of the specificity of photoinduced waveguides would be helpful.…”