Showing papers on "Phase conjugation published in 1998"
TL;DR: In this paper, a phase conjugate array was implemented to spatially and temporally refocus an incident acoustic field back to its origin in the Mediterranean Sea by transmitting a 50-ms pulse from the SRT to the SRA, digitizing the received signal and retransmitting the time reversed signals from all the sources of the sRA.
Abstract: An experiment conducted in the Mediterranean Sea in April 1996 demonstrated that a time-reversal mirror (or phase conjugate array) can be implemented to spatially and temporally refocus an incident acoustic field back to its origin. The experiment utilized a vertical source–receiver array (SRA) spanning 77 m of a 125-m water column with 20 sources and receivers and a single source/receiver transponder (SRT) colocated in range with another vertical receive array (VRA) of 46 elements spanning 90 m of a 145-m water column located 6.3 km from the SRA. Phase conjugation was implemented by transmitting a 50-ms pulse from the SRT to the SRA, digitizing the received signal and retransmitting the time reversed signals from all the sources of the SRA. The retransmitted signal then was received at the VRA. An assortment of runs was made to examine the structure of the focal point region and the temporal stability of the process. The phase conjugation process was extremely robust and stable, and the experimental results were consistent with theory.
568 citations
TL;DR: In this work, an optical encryption system based on double-random phase encoding of the data at the input and the Fourier planes is implemented, and the key that is used during encryption can be used for decrypting the data, thereby alleviating the need for using a conjugate of the key.
Abstract: We implement an optical encryption system based on double-random
phase encoding of the data at the input and the Fourier planes. In
our method we decrypt the image by generating a conjugate of the
encrypted image through phase conjugation in a photorefractive
crystal. The use of phase conjugation results in
near-diffraction-limited imaging. Also, the key that is used during
encryption can also be used for decrypting the data, thereby
alleviating the need for using a conjugate of the key. The effect
of a finite space–bandwidth product of the random phase mask
on the encryption system’s performance is discussed. A theoretical
analysis is given of the sensitivity of the system to misalignment
errors of a Fourier plane random phase mask.
184 citations
TL;DR: In this article, the current state of the acoustic wave phase conjugation (PC) problem is reviewed with emphasis on the parametric method using electromagnetic pumping in solids, and the giant-amplification supercritical parametric PC mode is considered in detail.
Abstract: The current state of the acoustic wave phase conjugation (PC) problem is reviewed. The generation of phase conjugate ultrasonic waves is discussed with emphasis on the parametric method using electromagnetic pumping in solids. The giant-amplification supercritical parametric PC mode is considered in detail. Ultrasonic PC with a gain in excess of 80 dB is demonstrated for a soft magnetic ceramics-based amplifier. The high quality of supercritical parametric PC sound is confirmed by acoustic-optical visualization. Acoustic PC effects, such as anomalous sound reflection at the PC mirror and the autofocusing and self-targeting of phase conjugate sound beams incident on a scatterer in a liquid, are shown. Recent experimental results demonstrating the potential of PC for applications are presented.
85 citations
TL;DR: In this article, a two-dimensional free-space phase conjugation at 10.24 GHz was demonstrated using two types of interconnects, electrical and a more versatile optical technique.
Abstract: A technique has been developed and tested for achieving phase conjugation in the microwave and millimeter-wave regime. The effective nonlinearity required for this phase-conjugation process is provided by electronic mixing elements feeding an array of antennas. Using these balanced mixing circuits in conjunction with a one-dimensional array antenna, we have demonstrated two-dimensional free-space phase conjugation at 10.24 GHz. A critical factor of this technique is the delivery of a 2/spl omega/ pump signal to each array element with the same phase. Two types of interconnects, electrical and a more versatile optical technique, have been implemented to distribute the pump signal in our demonstrations. In both systems, two-dimensional free-space phase conjugation was observed and verified by directly measuring the electric-field amplitude and phase distribution under various conditions. The electric-field wave-fronts exhibited retro-directivity and the auto-correction characteristics of phase conjugation. Furthermore, these experiments have shown amplified conjugate-wave power up to ten times of that of the incoming wave. This amplifying ability demonstrates the potential of such arrays to be used in novel communications applications.
68 citations
TL;DR: In this paper, phase conjugation in dye-doped nematic liquid crystals has been obtained with 532 nm radiation from a cw doubled YAG laser of total power of 50 mW.
64 citations
44 citations
TL;DR: A novel low-power phase-conjugating mirror based on stimulated Brillouin scattering in a quartz fiber with an internal taper with reliable operation in both single- and multiple-longitudinal-mode operation was observed with conjugation fidelities larger than 95%.
Abstract: A novel low-power phase-conjugating mirror based on stimulated Brillouin scattering in a quartz fiber with an internal taper is reported. A peak-power threshold as low as 500??W and a maximum reflectivity of 92% were obtained with 30-ns pulses from a Q-switched Nd:YAG laser. The maximum peak powers of 130??kW demonstrated a dynamic range of 1:260. Reliable operation in both single- and multiple-longitudinal-mode operation was observed with conjugation fidelities larger than 95%.
36 citations
TL;DR: In this article, it is shown that it is possible to control with good accuracy the relative phase of several conjugate beams for a properly designed Brillouin-enhanced four-wave-mixing phase conjugation system.
Abstract: We show that it is possible to control with good accuracy the relative phase of several conjugate beams for a properly designed Brillouin-enhanced four-wave-mixing phase conjugation system. Three geometries, two that utilize two Brillouin cells and another that requires only one Brillouin cell, that achieve conjugate phase control are studied and many properties of each system are examined. We show that for our high-power laser application the one-cell geometry performs as well as or better than the other geometry. Phase control is shown to be useful for beam combination, vector phase conjugation, and optical path selection. A laser system that utilizes the one-cell geometry to enhance its performance is built and examined.
35 citations
TL;DR: In this article, the authors show that non-degenerate four-wave mixing in a Λ system yields strong suppression of quantum phase noise when the probe and conjugate beams are monitored via balanced homodyne detection.
28 citations
TL;DR: In this article, the origins of the diffraction gratings or holograms induced by a light intensity pattern in a dye-doped nematic liquid crystal sandwiched between two conducting glass plates are described.
Abstract: This paper describes low-molecular-mass liquid crystals doped with suitable dyes which can be used for real-time holographic purposes We describe the origins of the diffraction gratings or holograms induced by a light intensity pattern in a dye-doped nematic liquid crystal sandwiched between two conducting glass plates The mechanism is linked to electric-field-driven reorientation of the nematic director The modulation of the electric field is induced mainly by the bulk photoconductivity of the system Design and characterization (response time, diffraction efficiency) of the optically addressed spatial light modulator (OA-SLM) is presented Interesting applications of these materials enabling phase conjugation and optical correlation are discussed
28 citations
TL;DR: In this paper, a method of imaging by optical phase conjugation using a three-wave degenerate parametric interaction is presented, where the resolution in the phase conjogate image is about 90 μm and the image is amplified with a mean gain of 30 dB.
TL;DR: Restoration of an image through an aberrant plate has been achieved by use of optical phase conjugation in a type II parametric interaction in which the amplified signal and idler waves are reflected back through the aberrant medium.
Abstract: Restoration of an image through an aberrant plate has been achieved by use of optical phase conjugation in a type??II parametric interaction in which the amplified signal and idler waves are reflected back through the aberrant medium. The resolution of the restored phase-conjugate images is equal to 0.18??mm, and the amplification gain is ?4 dB.
TL;DR: Wave aberrations of refractive photoresist microlenses and siliconmicrolenses were measured with a lateral shearing interferometer and it is shown that the reproducibility can be kept below lambda/100 rms.
Abstract: Wave aberrations of refractive photoresist microlenses and silicon microlenses were measured with a lateral shearing interferometer. Because of the silicon elements, a near-infrared working wavelength (λ = 1.32 μm) was used. The wave front was evaluated by a phase step technique with four steps. Integration of the phase distributions was performed with a computationally efficient Fourier transformation algorithm. The influence of the detector vidicon nonlinearity on the measured wave front was calculated. The defocusing behavior of the interferometer was investigated by fitting the measured wave fronts with the help of Zernike circle polynomials. It is shown that the reproducibility can be kept below λ/100 rms. Examples for the measured wave fronts of plano–convex silicon microlenses are discussed in detail.
TL;DR: In this paper, a novel technique for optical wavelength conversion and phase conjugation by fiber four-wave mixing using inline fiber distributed-feedback lasers as orthogonally polarized pump sources was proposed.
Abstract: We propose and demonstrate a novel technique for optical wavelength conversion and phase conjugation by fiber four-wave mixing using inline fiber distributed-feedback lasers as orthogonally polarized pump sources. This technique features polarization independent operation and a simple all-fiber configuration without the need for externally injected pumps. Polarization dependency as low as 0.5 dB has been achieved using this technique.
TL;DR: Self-pumped phase conjugation in infrared-sensitive photorefractive rhodium-doped barium titanate (Rh:BaTiO(3) crystal) is investigated with a kilohertz-repetition-rate, diode-pumping Nd:YAG laser and the performances of the Rh:Ba TiO( 3) crystal are compared with those obtained with a conventional Brillouin mirror.
Abstract: Self-pumped phase conjugation in infrared-sensitive photorefractive
rhodium-doped barium titanate (Rh:BaTiO3) is
investigated with a kilohertz-repetition-rate, diode-pumped Nd:YAG
laser. We also demonstrate the operation of a diode-pumped Nd:YAG
master-oscillator power-amplifier system with such a compact and
solid-state phase-conjugate mirror for wave-front restoration. We
obtain near-diffraction-limited output pulses of 20-mJ energy at a
repetition rate of 200 Hz and a 1-min response time of the
phase-conjugate mirror. The performances of the
Rh:BaTiO3 crystal are compared with those obtained with a
conventional Brillouin mirror.
ETSI1
TL;DR: In this article, the optical phase conjugation (OPC) was used to compensate for composite second-order (CSO) distortion due to the interplay of fiber chromatic dispersion and self-phase modulation.
Abstract: Compensation for composite second-order (CSO) distortion due to the interplay of fiber chromatic dispersion and self-phase modulation in externally modulated amplitude modulated subcarrier multiplexing (AM-SCM) systems employing optical-phase conjugation (OPC) is investigated. The simulation results show that significant reductions (>20 dB) of fiber-induced CSO may be achieved using OPC, which results in an increase of the transmission distance in AM-SCM video distribution systems operating near 1550 nm. In addition, a comparison with another compensation technique, the phase modulation technique, is established, showing that OPC is much less sensitive to variations in the fiber length. However it is also calculated that for practical implementation of the OPC-based compensation technique, 25 to 30 dB reduction in the amplified spontaneous emission (ASE) associated with the OPC will be required.
TL;DR: In this article, the authors prove the coexistence of two-beam coupling and four-wave mixing experiments and demonstrate how to distinguish between them by two-and four-beam mixing experiments.
Abstract: Recently, amorphous organic photorefractive materials have generated great excitement because of their excellent performance, which permits applications in high-density holographic storage, real-time image processing, and phase conjugation. However, the heterostructure of the devices (consisting of glass cover slides, transparent electrodes, and the photorefractive material) and the tilted recording and readout geometry commonly used result in multiple reflected beams in addition to the normal object and reference beams. This result leads to several photorefractive gratings competing inside the photorefractive polymer device. We prove the coexistence of these gratings by two-beam coupling and four-wave mixing experiments and demonstrate how to distinguish between them.
TL;DR: In this paper, four-wave mixing experiments in a low-birefringence optical fiber reveal an unexpected sudden increase of the conversion efficiency as the signal power crosses a threshold value.
Abstract: Four-wave mixing experiments in a low-birefringence optical fiber reveal an unexpected sudden increase of the conversion efficiency as the signal power crosses a threshold value In this regime, peak frequency conversion is achieved outside the small-signal parametric gain spectrum A nonlinear model of wave mixing fits the measured data well
TL;DR: In this paper, the phase-conjugation properties of the backward-stimulated radiation from a two-photon-pumped frequency-upconversion lasing medium are studied.
Abstract: Optical phase-conjugation properties of the backward-stimulated radiation from a two-photon-pumped frequency-upconversion lasing medium are studied. The gain medium is a new dye solution pumped with ∼11-ns and ∼1064-nm laser pulses; a highly directional and phase-conjugate backward-stimulated emission at ∼616-nm wavelength could be obtained with a net conversion efficiency of ∼10%. The spectral, temporal, and output–input characteristics of this kind of stimulated emission are presented in detail. The phase-conjugation properties of the backward-stimulated emission have been demonstrated by both the far-field (beam-divergence) measurement and the near-field (image-reconstruction) measurement. The wave-front reconstruction behavior is not perfect, especially under a larger aberration influence.
TL;DR: In this article, the authors demonstrate that the additional acceleration of the positive feedback loop formation is required for successful generation of transient phase-conjugate wave fronts, provided by the high-intensity transient photorefractive surface wave that appears immediately after application of the external electric field.
Abstract: Mutually pumped phase conjugation with a recording time of few milliseconds is obtained in Bi12TiO20 crystals by use of transient photorefractive beam coupling under a dc external electric field. It is demonstrated that the additional acceleration of the positive-feedback-loop formation is required for successful generation of transient phase-conjugate wave fronts. This acceleration is provided by the high-intensity transient photorefractive surface wave that appears immediately after application of the external electric field as the result of coupling of the incident beam with the reflected fanning beams. To the authors’ knowledge, this is the first experimental observation of a transient photorefractive surface wave.
TL;DR: First report of highly efficient phase conjugation in a laser-pumped polymer-dye saturable amplifier with high reflectivity in the broad wavelength region from 556 to 567 nm is presented.
Abstract: We present the first report to the best of our knowledge of highly efficient phase conjugation in a laser-pumped polymer-dye saturable amplifier. Phase-conjugate reflectivity of as much as 210% at 560 nm has been obtained. Moreover, efficient reflectivity has been obtained in the broad wavelength region from 556 to 567 nm.
TL;DR: In this paper, the influence of the processing parameters to the optical density of the methylene blue and erythrosin gelatin films was analyzed in a degenerate four wave mixing experiment.
TL;DR: An experimental setup for measurement of optical absorption coefficients at 1.054 μm in high transparent liquids by means of the thermal lens effect was built, calibrated, and tested as discussed by the authors, where the critical energy for defocusing of laser beam Ecr≅3 J and the absorption coefficient α of order 10-6 cm-1 were precisely measured by this device in the fluorocarbon liquids FLUORINERT FC.
Abstract: An experimental setup for measurement of optical absorption coefficients at 1.054 μm in high transparent liquids by means of the thermal lens effect was built, calibrated, and tested. The critical energy for defocusing of laser beam Ecr≅3 J and the absorption coefficient α of order 10-6 cm-1 were precisely measured by this device in the fluorocarbon liquids FLUORINERT FC. Obtained data were used for an optimization of the high energy Stimulated Brillouin Scattering (SBS) phase conjugated mirror and SBS compressor based on FLUORINERT FC medium.
TL;DR: In this paper, a twyman-green interferometer with a phase conjugate mirror in one arm and a double mirror in another arm is described to measure divergence and to check the collimation of a laser beam.
Abstract: A Twyman-Green interferometer having a phase-conjugate mirror in one arm and double mirror in another arm is described to measure divergence and to check the collimation of a laser beam. It uses an internally self-pumped phase conjugation in BaTiO3 crystal as phase-conjugate mirror. The use of double mirror gives a dual interference field which results in improved sensitivity in collimation testing. The dual-field interferogram is also useful in easily distinguishing between the divergent and convergent nature of the test beam. Measurement results are presented.
TL;DR: In this paper, the phase-conjugation properties of the backward stimulated radiation from a one-photon pumped lasing medium have been studied, where the gain medium is a dye solution (pyrromethene 597 in ethanol) or the same dye doped poly(methyl methacrylate) (PMMA) rod pumped with 7ns and 532-nm laser pulses.
Abstract: Optical phase-conjugation properties of the backward stimulated radiation from a one-photon pumped lasing medium have been studied. The gain medium is a dye solution (pyrromethene 597 in ethanol) or the same dye doped poly(methyl methacrylate) (PMMA) rod pumped with /spl sim/7-ns and 532-nm laser pulses. A highly directional and phase-conjugate backward stimulated emission at /spl sim/573 nm wavelength could be obtained with a conversion efficiency of /spl sim/42% by using a 1-cm-long dye solution sample at the concentration level of d/sub 0/=0.000 15 mol/L. The spectral, temporal, output/input, and phase-conjugation properties of this backward stimulated emission are presented in detail. The induced aberration influence, which is much larger than the divergence angle of the input pump beam, can be basically removed by the backward stimulated emission; however, the fidelity of the near-field detail for the backward stimulated emission is relatively poor. A quasi-collinear holographic interaction model and a mathematical analysis are presented to explain the basic experimental results.
TL;DR: In this article, phase conjugation of magnetostatic waves by a local longitudinal pump in yttrium iron garnet films is observed experimentally, and theoretical expressions are obtained which describe the experimental curves well.
Abstract: Phase conjugation of magnetostatic waves by a local longitudinal pump in yttrium iron garnet films is observed experimentally. Theoretical expressions are obtained which describe the experimental curves well.
TL;DR: In this paper, a ring cavity laser is demonstrated using the gain mechanism of a four-wave mixing process, mediated by two-photon Zeeman coherence resulting from coherent population trapping in a rubidium vapor cell.
TL;DR: In this paper, phase locking and vector phase conjugation were used to reduce the depolarization losses of an oscillator-amplifier laser system, where the amplifiers were operated in a parallel arrangement.
Abstract: Phase- and polarization conjugation has been realized by phase locking and phase conjugating two linearly polarized components of a depolarized beam by means of stimulated Brillouin scattering in nitrogen at 75 bar. Hereby, depolarization losses of an oscillator-amplifier laser system have been reduced from 36% without polarization conjugation to 7.1% with vector phase conjugation. An application in a novel oscillator double- amplifier laser system is presented where the amplifiers are operated in a parallel arrangement. An average of 81 percent of the total optical energy generated in the system has been transferred into the output beam with a beam quality of M 2 < 1.1 and excellent pointing stability.
15 Jan 1998
TL;DR: Active Tracking System (ATS) as mentioned in this paper is a linear phase conjugation aberration compensation technique that uses a silicon spatial light modulator (SLM) as a dynamic wavefront reversing element, which continuously tracks the target and compensates for atmospheric and platform motion induced aberrations.
Abstract: Atmospheric induced aberrations can seriously degrade laser performance, greatly affecting the beam that finally reaches the target. Lasers propagated over any distance in the atmosphere suffer from a significant decrease in fluence at the target due to these aberrations. This is especially so for propagation over long distances. It is due primarily to fluctuations in the atmosphere over the propagation path, and from platform motion relative to the intended aimpoint. Also, delivery of high fluence to the target typically requires low beam divergence, thus, atmospheric turbulence, platform motion, or both results in a lack of fine aimpoint control to keep the beam directed at the target. To improve both the beam quality and amount of laser energy delivered to the target, Northrop Grumman has developed the Active Tracking System (ATS); a novel linear phase conjugation aberration compensation technique. Utilizing a silicon spatial light modulator (SLM) as a dynamic wavefront reversing element, ATS undoes aberrations induced by the atmosphere, platform motion or both. ATS continually tracks the target as well as compensates for atmospheric and platform motion induced aberrations. This results in a high fidelity, near-diffraction limited beam delivered to the target.