Characterization and inhibition of photorefractive optical damage of swift heavy ion irradiation waveguides in LiNbO_3

Abstract

The photorefractive effect and the corresponding optical damage thresholds of novel LiNbO 3 waveguides fabricated by swift ion irradiation have been investigated. TE-and TM-mode operation have been characterized, and the influence of the beam propagation length analyzed. Optical damage levels similar to those of proton-exchanged waveguides have been found. In order to reduce optical damage, the influence of temperature has been investigated. An increase of more than a factor of 100 in the optical damage threshold has been obtained by moderate heating up to 90°C. The results are briefly discussed under the two-center model for the photorefractive effect in undoped LiNbO 3 , and compared with data from other types of LiNbO 3 waveguides.

Photovoltaic laser beam degradation in lithium niobate planar waveguides: two-center model approach

“…As the beam profile broadens with the propagation length, l, the Δn profile becomes smoother, giving rise to a flat output intensity profile rather than the initial Gaussian one. However, the simulations do not present any filamentation effect as was found in some reported experiments [9][10][11]. As we will see in the next section, to find filamentation effects in our simulations it is necessary to consider the linear propagation (in air) of the decoupled distorted beam before it reaches the detector.…”

“…To some extent, the results can be applied to other guide geometries and to bulk crystals. Nevertheless, when photovoltaic charge transport is in the waveguide plane, more complex phenomena than those described here may occur, such as catastrophic optical damage by noise amplification [4][5][6][7][8][9][10][11][12][13][14][15].…”

“…We have applied the algorithm to simulate beam propagation in planar waveguides because there are a variety of well-documented experimental results to compare with theory. Specifically, the numerical simulations will be compared with data on self-defocusing and beam filamentation that have been recently reported [8][9][10][11]. Finally, this method will provide a reliable way to predict the complex phenomena occurring at high light intensities in LiNbO 3 .…”

“…Although it is accepted that this distortion roughly consists in a self-defocusing effect [5][6][7], recent experiments revealed a rich variety of additional nonlinear effects, including filamentation and temporal instabilities [8][9][10][11], that becomes important when the light intensity increases. This range of light intensities should be reached when designing efficient nonlinear optical devices such as second harmonic generators in waveguide configuration [12].…”