Phase conjugation

About: Phase conjugation is a research topic. Over the lifetime, 3694 publications have been published within this topic receiving 49099 citations.

Hybrid phase conjugator/modulators using self‐pumped 0°‐cut and 45°‐cut BaTiO3 crystals

Abstract: We report on the demonstration of a simple, passive, alignment‐free retromodulator/conjugator. By applying a time‐varying electric field across a self‐pumped phase conjugate mirror, simultaneous wave front reversal and temporal modulation encoding occur within the same volume. With modest signal fields (∼400 V/cm), we observe >90% depth‐of‐phase modulation, with a measured bandwidth in excess of 1 MHz (scalable to >10 GHz), and with excellent conjugation fidelity. We also demonstrate, for the first time, self‐pumped conjugation using a 45°‐cut crystal of BaTiO3 with improved performance: 62% conjugate reflectivity, 100% depth‐of‐phase modulation at ∼120 V/cm, and faster conjugate‐wave build‐up time (by a factor of ∼3). Applications of these devices to high modulation‐index and high optical‐power‐handling modulators, remote fiber sensors, and mode‐locked phase conjugate resonators are discussed.

Calibration of digital optical phase conjugation setups based on orthonormal rectangular polynomials

Abstract: Digital optical phase conjugation (DOPC) has proven to be a promising technique in deep tissue fluorescence imaging. Nonetheless, DOPC optical setups require precise alignment of all optical components to accurately read the wavefront of scattered light in a turbid medium and playback the conjugated beam toward the sample. Minor misalignments and possible imperfections in the arrangement or the structure of the optical components significantly reduce the performance of the method. In this paper, a calibration procedure based on orthogonal rectangular polynomials is introduced to compensate major imperfections including the optical aberration in the wavefront of the reference beam and the substrate curvature of the spatial light modulator without adding extra optical components to the original setup. The proposed algorithm also provides a systematic calibration procedure for mechanical fine tuning of DOPC systems. It is shown experimentally that the proposed calibration process improves the peak-to-background ratio when focusing light after passing through a highly scattering medium.

Generation of spatial subharmonic gratings in the absence of photorefractive beam coupling.

Abstract: Using a new experimental geometry, we have proved for the first time that the generation of spatial subharmonic gratings in photorefractive crystals is not dependent on optical nonlinearity. We present results which confirm that the subharmonic gratings result from a parametric excitation of ultra low-frequency eigenmodes of a crystal by a time modulated fundamental grating.

Generation of phase-conjugated vector wave fronts in atomic vapors.

Abstract: Using counterrotating circularly polarized waves as the pumping sources, we have demonstrated the generation of phase-conjugated vector wave fronts in the D(2) resonance line of sodium. Experimental results that are consistent with the calculation of the third-order nonlinear susceptibility in atomic lines have been obtained.

Polarization properties of phase conjugation by degenerate four-wave mixing in a medium of rigidly held dye molecules

Abstract: The saturation properties of dye molecules that are rigidly held in a solid host are qualitatively different from those of molecules that are free to rotate. We have found that these unique saturation characteristics can be exploited to achieve nearly perfect vector phase conjugation for field strengths near the saturation intensity. We have studied these properties experimentally by using fluorescein-doped boric acid glass as the nonlinear-optical material.