Two-wave mixing with an applied field and a moving grating

Serguei I. Stepanov

Guoquan Zhang, Rong Dong, Jingjun Xu

We show theoretically that the group velocity of light pulses can be reduced significantly by use of the steep dispersion properties of the phase coupling effect in the photorefractive two-wave mixing process. The group velocity of light pulses of the order of 0.1 m/s can be achieved in typical photorefractive BSO crystals with an appropriate externally applied electric field and moving gratings of appropriate speeds. It is also shown that the slowly propagating light pulses can be set to be amplified after passing through the photorefractive material.

A. A. Sevenyuk, А. В. Сухов

Yiqi Zhang, Zhenkun Wu, Huaibin Zheng +4 more

For the first time, we investigate the nonreciprocal generation of six-wave mixing (SWM) in an inverted-Y type four-level system with spatially uniform distribution of atoms. The nonreciprocity results from a moving electromagnetically induced grating (EIG) which is formed by two coupling beams with different frequencies. We demonstrate that the nonreciprocity can be controlled by the frequencies of the coupling fields and the powers of the dressing beams. As the distribution of atoms is uniform, the atomic density cannot affect the nonreciprocity, but it will affect the formation of the photonic band gap structure of the moving EIG. This research can be used to make optical diodes or optical isolators, because the moving EIG, the speed of which is related to the frequency difference of the two coupling beams, can break time-reversal symmetry. We also demonstrate that the nonreciprocal SWM can form a nonreciprocal light droplet when it propagates in atomic vapors with third- and fifth-order nonlinear susceptibilities.

I. Lahiri, Robert M. Brubaker, David D. Nolte +1 more

Nonreciprocal energy transfer between two coherent laser beams during two-wave mixing requires a photorefractive phase shift between the interference pattern and the resulting space charge. The symmetry of the Stark geometry photorefractive quantum wells forbids a phase shift using either dc or ac fields. We present the first experimental demonstration of nonreciprocal energy transfer during two-wave mixing using moving gratings. Optical energy exchange is observed in photorefractive p-i-n quantum well diodes with photorefractive gains approaching 1000 cm−1 and exhibiting complex spatio-temporal dynamics.

Pochi Yeh