Passive Phase Conjugation Research Articles

Transient effects in four-wave mixing in photorefractive Passive Phase Conjugate Mirrors

Partial differential equations are set up and solved partly analytically, partly numerically for the spatial and temporal variation of the amplitudes and phases of the four beams participating in four-wave mixing in a linear Passive Phase Conjugate Mirror. The instantaneous frequency of the resonating beam is also determined. It is shown that the duration and main features of the transient regime are determined not only by the properties of the photorefractive crystal but also by the external optical circuit, in particular by the quality factor and detuning of the resonator.

Numerical solution of four-wave mixing in passive phase conjugate mirrors

An iterative method is used to find the solution for all the field amplitudes and for the detuning of oscillations arising in a linear passive phase conjugate mirror (PPCM). The effect of crystal absorption is included and both transmission and reflection gratings are investigated. In particular, it is shown that a PPCM can be realized with the aid of a BSO crystal in the presence of an applied electric field. >

Optical phase conjugation in nonresonant and saturable absorptive/resonant systems

Recent results obtained at Alabama A&M University on optical phase conjugation in electrically unpoled BaTiO3, BANANA and SBN crystals are presented. The decay curves of the transient gratings and phase conjugation in these crystals indicate the involvement of more than one exponential process, possible reasons for which are indicated. Self induced gratings have been studied in electrically unpoled SBN crystal using a He−Ne Laser. The oscillations in a ring passive phase conjugator (RPPC) and in a unidirectional ring resonator using an electrically poled BaTiO3 crystal have, been found to be bistable. It is also found that bistable oscillations are possible in a geometry in which the crystal is used simultaneously in a RPPC and as a linear passive phase conjugate (LPCC) mirror. The auxiliary oscillations pumped by the RPPC are bistable with the oscillations in LPCC. A brief review of the recent literature on phase conjugation in saturable absorptive/resonant systems along with the experiments planned to be undertaken by the authors on such systems are presented.

Optical bistability in self-pumped phase-conjugate ring resonators

Bistable oscillations have been observed in BaTiO(3) pumped by a single-mode 30-mW (488-nm) argon-ion laser, which is used simultaneously as a ring passive phase conjugator (RPPC) and as a unidirectional ring resonator (UDRR). Strong oscillations in the UDRR increase the threshold coupling strength required for oscillation in the RPPC. The oscillations in the RPPC reduce the fanning in the crystal necessary for the startup of oscillation in the UDRR. Auxiliary resonators pumped by the RPPC are also bistable with the UDRR. Similar bistable oscillations have been observed when the crystal is used simultaneously as a RPPC and as a linear passive phase conjugator.

Coupling of diode laser arrays with photorefractive passive phase conjugate mirrors

An experimental study of the coupling of diode laser arrays to various photorefractive phase conjugate mirrors is presented. We demonstrate frequency locking of arrays as well as the control of their emitted light patterns.

Phase conjugation of mode scrambled optical beams: Application to spatial recovery and interbeam temporal information exchange

Coupling of temporal information between two beams is demonstrated using a combination of a multimode fiber and a photorefractive passive phase conjugation mirror. It is shown that the polarization and spatial properties are fully recovered but temporal information is exchanged. The theoretical explanation for these phenomena and possible applications are discussed.

Self-starting passive phase conjugate mirror with Ce-doped strontium barium niobate

We report the use of Ce-doped SrxBa1−xNb2O6, x=0.60 and 0.75, as the holographic four-wave mixing medium in the construction of a self-starting passive phase conjugate mirror using internal reflection. Without correcting for Fresnel reflections, a steady-state phase conjugate reflectivity of 25% was measured with Sr0.75Ba0.25Nb2O6:Ce. The distortion correcting property of such a mirror was demonstrated using an imaging experiment.

A novel technique for laser diode to single mode fiber coupling

Abstract An optical fiber coupler based on the semi-linear passive phase conjugate mirror is analyzed. The threshold coupling strength is determined from theoretical considerations. An estimate of 50% for the overall coupling efficiency is made, assuming there is good mode matching between the light incident on the fiber and the propagating mode. The coupler exhibits a high degree of alignment insensitivity allowing for simple manufacture.

Polarization recovery in phase conjugation by modal dispersal

We demonstrate scalar phase conjugation, i.e., one in which both transverse components of the incident beam are phase conjugated, which is achieved by tandem combination of a mode scrambling fiber and a photorefractive passive phase conjugate mirror.

Oscillation with photorefractive gain

We review theories and experimental demonstrations of oscillation with photorefractive gain. The unidirectional ring resonator; the linear passive phase conjugate mirror, a phase conjugate resonator (the semilinear passive phase conjugate mirror), and the double phase conjugate resonator are treated, the applications in path-length-to-frequency converting interferometers and one-way wavefront converters are described.

Self-induced frequency scanning and distributed Bragg reflection in semiconductor lasers with phase-conjugate feedback

A GaAlAs semiconductor laser with feedback from a barium titanate photorefractive ring passive phase-conjugate mirror can be made to perform repeating or nonrepeating frequency scans over a 10-nm range toward either the blue or the red. The direction of scanning and whether the scans repeat may be controlled by adjusting the overlap of the interaction beams in the crystal. This overlap region may be adjusted so that the diode frequency spectrum, originally occupying about 10 longitudinal modes, scans and narrows as the conjugate signal builds up, coming to rest often in one, but sometimes two or three, longitudinal modes as a result of self-generated distributed-feedback effects. We also report similar effects caused by feedback from the total-internal-reflection passive phase conjugate mirror. The alignment-control mechanism of the ring mirror is, however, not available in this case.

Photorefractive oscillation with intracavity image and multimode fiber

A photorefractive oscillation between two cascaded passive phase conjugate mirrors (2C-PPCM) with intracavity phase and amplitude modulation and multimode fibers is described. The two semilinear PPCM’s operate via four wave mixing in BaTiO3 crystals. A single beam pumps only one PPCM and generates all other self-starting beams of the two PPCM’s

Coherent coupling of diode lasers by phase conjugation

We report experimental demonstrations of the use of a photorefractive barium titanate ring passive phase conjugate mirror in the coherent coupling of two GaAlAs diode lasers. By cooling the crystal towards its tetragonal to orthorhombic phase transition, we were also able to achieve infrared photorefractive phase conjugation with gain.

Vibration resistance, short coherence length operation, and mode-locked pumping in passive phase conjugate mirrors

Because the ring and semilinear passive phase conjugate mirrors use dynamic transmission holograms, they are insensitive to vibration and may be pumped with light of short coherence length or with picosecond mode-locked laser light. Experimental demonstrations of these modes of operation are described.

Infrared photorefractive passive phase conjugation with BaTiO3: Demonstrations with GaAlAs and 1.09-μm Ar+ lasers

We report photorefractive passive phase conjugation of GaAlAs laser radiation at 815–865 nm and Ar+ laser radiation at 1090 nm. A ring passive phase conjugate mirror was used with BaTiO3 as the real-time holographic gain medium. With GaAlAs lasers phase conjugate reflectivities of up to 16% uncorrected for Fresnel losses were recorded. Effects of the strong associated feedback to the laser and attempts at mode locking are described. At 1090 nm the reflectivity remains approximately the same, but with a significantly longer time constant.

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.

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.

Optical bistability and hysteresis with a photorefractive self-pumped phase conjugate mirror

Bistability and hysteresis have been observed in a photorefractive passive phase conjugate mirror. A threshold basis for the effect is presented and the results of an experimental demonstration of the device are given.

Multicolor passive (self-pumped) phase conjugation

Passive phase conjugation of up to six lines (457, 476, 488, 496, 501, and 514 nm) of the all lines output of an argon ion laser is reported. Imaging characteristics and reflectivity measurements are given. In general, multiline operation results in some loss in both reflectivity and image resolution. This work opens the possibility for passive phase conjugation of full color images.

Theory and applications of four-wave mixing in photorefractive media

The development of a theory of four-wave mixing in photo-refractive crystals is described. This theory is solved in the undepleted pumps approximation with linear absorption and without using the undepleted pumps approximation for negligible absorption. Both the transmission and reflection gratings are treated individually. The results are used to analyze several photorefractive phase conjugate mirrors, yielding reflectivities and thresholds. The use of photorefractive crystals as optical distortion correction elements and experimental demonstrations of several of the passive phase conjugate mirrors are described.