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Journal of Guangdong University of Technology

Testing Optical Path Difference of Two Beams along Opposite Directions in Photorefractive Crystal

Zheng Guang-zhao

Published Jan 1, 2003• 0 citations
OpenAlex

Abstract

It is reported to test the additional phase difference of two beams along two opposite directions in the photorefractive crystal using Sagnac interferometer. The additional phase difference is demonstrated by experiments when two beams of laser transit along two opposite directions in the photorefractive crystal. The experimental results show that the additional phase difference is dependent on the direction of optical axis of the photorefractive crystal. They mean the existence of the additional optical path difference when two beams of laser transit along two opposite directions in the photorefractive crystal. The effect may be named the effect of bilateral phase in the photorefractive crystal. Its cause may be the same as the fanning effect.

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We demonstrate for the first time, to our knowledge, second harmonic optical phase conjugation, using the second spatial harmonics of a nonsinusoidal grating formed in a photorefractive material. The possibility of harmonic phase conjugation has been considered previously for artificial Kerr media.1 We have applied the same idea to barium titanate, since the existence of the higher-order gratings in this material has been known to us for some time. In our experiment, two 1.06-µm cw Nd:YAG laser beams wrote a grating in a poled photorefractive barium titanate crystal. Then a second harmonic of the YAG at 0.532 µm read out the grating in a counterpropagating direction to one of the writing beams. In this geometry, the usual Bragg condition is not satisfied. The reflectivity of the 0.532-µm signal was rather weak, ~0.01%, with ~0.1-mW reading beam power. The buildup time was around 3 s, with loosely focused writing beams with 50-mW power in each beam. The same experiment with a SBN crystal showed no significant harmonic phase conjugation. Finally, we stress that this effect is different from the previously published result.2

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Optical bistability and switching are of great interest in the rapidly and developing field of photonics. Devices that display this behavior could potentially play a major role in the development of optical communication systems and computing. In this article we present experimental results concerning the optical bistability in ferroelectric of photorefractive BaTiO3 crystal. Two laser beams were used to interact with the photorefractive crystal which resulted in the bistability of the intensity of transmitted wave. This was achieved without the application of any optical resonator. High contrast optical bistability is found experimentally in the pump-ratio dependence of the output intensity.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Nov 29, 2007•0 citations
It is reported to test the additional phase difference of two beams along two opposite directions in the photorefractive crystal using Sagnac interferometer. The additional phase difference is demonstrated by experiments when two beams of laser transit along two opposite directions in the photorefractive crystal. The experimental results show that the additional phase difference is dependent on the direction of optical axis of the photorefractive crystal. They mean the existence of the additional optical path difference when two beams of laser transit along two opposite directions in the photorefractive crystal. The effect may be named the effect of bilateral phase in the photorefractive crystal. Its cause may be the same as the fanning effect.
Two-wave mixing allows one to change effectively Intensities, phases, space profiles, polarizations and time evolution of interacting beams [1,21. We will show, that two-wave mixing of partially coherent beams may be used to increase degree of coherence of these beams. The physics of the effect under discussion is as follows: two partially coherent beams write a refraction index grating in a nonlinear medium whose position and profile are practically stationary. Scattering of strong beam on this grating in the direction of the weak one means that this weak beam acquires an addition, that is coherent with the strong beam, thereby increasing degree of coherence of the beams. Similar effects were discussed in connection with scattering of different frequency components at the common running grating [3] and with Interaction of different polarization components [4,5].
The coherent interaction of Gaussian light beams polarised parallel to the [1 0] direction in a cubic optically active photorefractive crystal with the ( 0) cut is studied in an electric field applied to the crystal in the [00 ] direction. The effect of optical activity on the interaction of the light beams with the phase difference Δ =0, π/2, and π is theoretically studied. It is shown that, while a change in the intensity of a combined light beam at Δ =0 caused by the influence of optical activity in a 9-mm thick Bi 12 TiO 20 crystal is comparatively small (less than 8%), this change achieves 36% in the crystal of thickness 18 mm. The interaction of orthogonally polarised beams in this crystal is considered. It is found that, although the optical activity of the crystal results in the appearance of the 'breathing effect', a soliton-like nature of the combined beam is preserved. The results obtained can be used for the address positioning of soliton-like light beams.
We demonstrate for the first time, to our knowledge, second harmonic optical phase conjugation, using the second spatial harmonics of a nonsinusoidal grating formed in a photorefractive material. The possibility of harmonic phase conjugation has been considered previously for artificial Kerr media.1 We have applied the same idea to barium titanate, since the existence of the higher-order gratings in this material has been known to us for some time. In our experiment, two 1.06-µm cw Nd:YAG laser beams wrote a grating in a poled photorefractive barium titanate crystal. Then a second harmonic of the YAG at 0.532 µm read out the grating in a counterpropagating direction to one of the writing beams. In this geometry, the usual Bragg condition is not satisfied. The reflectivity of the 0.532-µm signal was rather weak, ~0.01%, with ~0.1-mW reading beam power. The buildup time was around 3 s, with loosely focused writing beams with 50-mW power in each beam. The same experiment with a SBN crystal showed no significant harmonic phase conjugation. Finally, we stress that this effect is different from the previously published result.2
Optical bistability and switching are of great interest in the rapidly and developing field of photonics. Devices that display this behavior could potentially play a major role in the development of optical communication systems and computing. In this article we present experimental results concerning the optical bistability in ferroelectric of photorefractive BaTiO3 crystal. Two laser beams were used to interact with the photorefractive crystal which resulted in the bistability of the intensity of transmitted wave. This was achieved without the application of any optical resonator. High contrast optical bistability is found experimentally in the pump-ratio dependence of the output intensity.