Shmuel Sternklar

Double phase-conjugate mirror: analysis, demonstration, and applications

We report on the operation of the double phase-conjugate mirror (DPCM). Two inputs to opposite sides of a photorefractive barium titanate crystal, which may carry different spatial images, are shown to pump the same four-wave mixing process mutually and are self-refracted without any external or internal crystal surface. This results in the phase-conjugate reproduction of the two images simultaneously. This device is analyzed theoretically, and applications in image processing, interferometry, and rotation sensing are discussed. We also demonstrate the operation of a ring laser, using the DPCM, as well as a photorefractive resonator with two facing DPCMs that can support spatial information in its oscillations.

Beam coupling and locking of lasers using photorefractive four-wave mixing

We discuss the use of photorefractive four-wave mixing for coupling and locking of lasers. A demonstration of the double phase-conjugate mirror and the semilinear passive phase-conjugate mirror, pumped simultaneously by different lasers, is described. Cleanup of a distorted laser beam using another local laser and configurations for the phase locking of lasers are discussed.

Image transmission and interferometry with multimode fibers using self‐pumped phase conjugation

A double‐pass image transmission through a single multimode fiber is demonstrated, using a passive phase conjugate mirror. An application to interferometry based on phase sensing is demonstrated, by implementing the multimode fiber and the passive phase conjugate mirror as one arm of a Michelson interferometer. Due to the unique properties of the self‐pumped conjugator, nonuniform distortions caused by modal dispersion in the fiber and other aberrations are cancelled out, while uniform phase changes are detected.

New optical gyroscope based on the ring passive phase conjugator

A new optical rotation sensor is described. It is a ring passive phase conjugator in which the ring may consist of a multimode fiber. A nonreciprocal phase shift in the ‘‘passive’’ like fiber ring activates a grating movement and subsequent frequency detuning of the beams in a photorefractive four‐wave mixer. This device has the advantages of natural reciprocal behavior of phase conjugate beams (essential for rotation sensing) and has several adjustable controlling parameters. It reveals a new class of interferometry in which changes in the ring’s optical phases, the beam’s intensities and losses, and the mixing crystal’s efficiency and electric field modulate a frequency detuning of the oscillating beams.

Self Bragg matched beam steering using the double color pumped photorefractive oscillator

A new method for steering light beams with automatic (self‐aligning) Bragg matching is presented. This device enables, in principle, a large beam deflection range which is not limited by the Bragg condition. It is based on a double color pumped photorefractive oscillator. Two input beams of different colors induce and pump a dynamic four‐wave mixing process in a photorefractive BaTiO3 crystal in which two other beams and a common grating are self‐generated. Steering is achieved by wavelength tuning of one of the pump beams. A deflection range of about 1.7°, with an efficiency ranging from 50 to 90%, is measured for a wavelength difference Δλ of ±30 nm for the two pumps (using argon ion laser lines). A deflection of 4.7° with an efficiency of 10% is seen for Δλ=144.8 nm (corresponding to pumps at 488 and 632.8 nm).

Photorefractive dynamic optical interconnects

We present and demonstrate a set of dynamic optical interconnects which are based on the double phase conjugate mirror with photorefractive wave mixing. These devices are bidirectional, self-adjusting, and controllable in real time. Uses in various interconnection modes are given.

Double-color-pumped photorefractive oscillator and image color conversion.

Can two laser beams of different colors interact with each other to initiate a photorefractive oscillation in a slowly responding (~1 sec) crystal? We report on the operation of this new nondegenerate four-wave mixing device, in which two other beams and the gratings are efficiently self-generated. An application for image color conversion is demonstrated. In an experiment, we used for the two pumps combinations of the lines of an argon-ion laser (514.5, 496.5, 488, 476.5, and 457.9 nm) and a He-Ne laser (632.8 nm). The mixing crystal was BaTiO(3) with a photorefractive time constant of the order of 1 sec.

Optical Information Processing With The Double Phase Conjugate Mirror

The operation of the double phase conjugate mirror (DPCM) is described. It can be regarded as a bidirectional spatial light modulator and controllable filter. Two independent image-bearing beams that may be derived from different lasers exchange their spatial information as they are coupled into each other in a photorefractive crystal. The,DPCM is also shown to be an optical thresholder and spatial filtering device, displaying edge enhancement. We propose the use of a resonator with two facing DPCMs to implement iterative image processing algorithms.

Spatial light modulation and filtering effects in photorefractive wave mixing

A study of photorefractive wave mixing with image bearing beams reveals unique capabilities in spatial modulation, filtering, and cleanup of amplitude and phase modulated beams. We study and explain the negligible image crosstalk in various photorefractive oscillators.

Tunable frequency shift of photorefractive oscillators

We report on an experimental study of the self-frequency detuning in wave mixing oscillators with the photorefractive barium titanate crystal. We show its dependence on a dc electric field on the crystal, optical phases in the oscillator cavity, and light intensity in the crystal. This resolves many aspects of previously observed and unexplained self-frequency detuning effects with similar oscillators and indicates the existence of an internal electric field in the mixing crystal.