Paul H. Beckwith

Nondegenerate two-wave mixing in ruby.

We demonstrate energy exchange by nondegenerate two-wave mixing in ruby. Our results are in agreement with the theory of nondegenerate two-wave mixing when the theory is generalized to take into account a complex nonlinear index. Two-wave mixing gain exceeding the absorption and reflection losses is demonstrated, and we show that these experiments provide a simple and accurate method for determining the complex nonlinear index, response time, and saturation intensity of the medium.

Photorefractive Nonlinear Optics And Optical Computing

This paper describes various nonlinear optical phenomena in photorefractive media and selected applications in optical computing. These phenomena include optical phase conjugation, two- and four-wave mixing, and real-time holography. The applications include image amplification and subtraction, logic and matrix operations, and optical interconnection.

Correction of polarization and modal scrambling in multimode fibers by phase conjugation

When polarized light is incident upon a long multimode fiber, the emerging light is randomly distributed among the spatial and polarization modes. We present experimental and theoretical results demonstrating that recovery of the spatial and polarization modes of the incident light takes place only when a phase conjugator at the fiber output preserves polarization on reflection.

Image distortion in multimode fibers and restoration by polarization-preserving phase conjugation

Image restoration after a double pass through a multimode fiber using a polarization-preserving phase conjugator is demonstrated. Results indicate that the resolution of the restored image is limited by the number of guided modes and that the contrast is restored only when the phase conjugator preserves polarization on reflection.

Two-wave mixing and phase conjugation at 830 nm in BaTiO 3

We report two-wave mixing and self-pumped phase-conjugation measurements for GaAlAs laser-diode radiation at 830 nm in BaTiO(3). At 11 degrees C, two-wave mixing gain coefficients as large as 18 cm(-1) and response times of the order of 1 min have been observed by using an optimized mixing geometry. Phase-conjugate reflectivities as large as 56% with 10-sec response times have also been measured using BaTiO(3) in a passive ring conjugator when the source laser is optically isolated from the conjugator. These results represent significant improvements over corresponding values previously reported.

Energy transfer between injection-locked single-mode diode lasers by two-beam coupling in BaTiO(3).

Two-beam coupling in photorefractive BaTiO(3) is used to combine beams coherently from two injection-locked single-mode diode lasers operating at 830 nm. We are able to transfer more than 70% of the power in one beam to the other beam with this method.

Phase-conjugate multimode fiber gyro.

Phase conjugation is used to correct the detrimental effects of modal scrambling in a passive optical gyro that uses multimode fiber. A proof-of-principle demonstration of rotation sensing is presented.

Nonlinear optical techniques for obtaining high brightness from diode lasers

How nonlinear optics can be used to obtain high brightness from diode lasers is described. The use of two-wave mixing to combined and clean up the output of any frequency-locked high-power device is addressed. The application of phase conjugation for coupling to lock lasers is considered.

Photorefractive Optics At Near-Infrared Wavelengths

Measurements of two-wave mixing gain and phase-conjugate response in barium titanate using GaAlAs diode laser sources emitting at 830 nm are discussed. Gain coefficients as large as 18 cm-1 have been obtained with optimized mixing geometries. With an optically isolated barium titanate ring passive phase-conjugate mirror we have obtained phase-conjugate reflectivities as large as 56% (uncorrected for Fresnel reflection losses) and response times on the order of tens of seconds. These results represent significant improvements over corresponding values previously reported in the literature.