Showing papers on "Phase conjugation published in 1995"
TL;DR: A theoretical model is presented that supports observations of optical phase-conjugate gain in sodium vapor by showing that coherent population trapping can write large-amplitude nonlinear-optical gratings at laser intensities well below those needed to saturate the optical transitions.
Abstract: We have observed optical phase-conjugate gain (>50) in sodium vapor, using low-intensity pump lasers (1 W/cm2), with a response time of the order of 1 μs. Coherent population trapping is experimentally identified as the phase-conjugate mechanism. A theoretical model is presented that supports these observations by showing that coherent population trapping can write large-amplitude nonlinear-optical gratings at laser intensities well below those needed to saturate the optical transitions.
296 citations
TL;DR: In this article, the efficiency of a time reversal acoustic mirror to focus on a reflective target through an inhomogeneous media has been demonstrated and the theory of how the iterative time reversal process is built is based on a matrix formalism and treats the array of L transducers in a given medium as a linear system of L inputs/L outputs.
Abstract: The efficiency of a time reversal acoustic mirror to focus on a reflective target through an inhomogeneous media has been demonstrated. In a multitarget media, the ability of such a mirror to work in an iterative mode in order to focus selectively on the strongest target was shown [C. Prada, F. Wu, and M. Fink, J. Acoust. Soc. Am. 90, 1119 (1991)]. The theory of how the iterative time reversal process is built is based on a matrix formalism and treats the array of L transducers in a given medium as a linear system of L inputs/L outputs. The system is characterized at each frequency by its transfer matrix K and the time reversal iterative process is then described by a time reversal operator K*K. Because of the reciprocity principle, this operator is Hermitian. The following result is shown: If the scattering medium is a set of well resolved targets of different reflectivities then each eigenvector of the operator K*K with nonzero eigenvalue corresponds to one of the targets in the set and provides the opt...
228 citations
208 citations
TL;DR: A novel configuration for four-wave mixing (FWM) is proposed that offers the remarkable feature of inherently separating the FWM wave from the input pump and signal waves and suppressing their background amplified stimulated emission without optical filtering.
Abstract: A novel configuration for four-wave mixing (FWM) is proposed that offers the remarkable feature of inherently separating the FWM wave from the input pump and signal waves and suppressing their background amplified stimulated emission without optical filtering. In the proposed configuration, an optical parametric loop mirror, two counterpropagating FWM waves generated in a Sagnac interferometer interfere with a relative phase difference that is introduced deliberately. FWM frequency-conversion experiments in a polarization-maintaining fiber achieved more than 35 dB of input-wave suppression against the FWM wave.
51 citations
TL;DR: In this paper, the authors describe a solid-state master oscillator-amplifier-laser (MOPA) with a minimum number of elements for the double-pass single-rod amplifier.
Abstract: We describe a solid-state master oscillator-amplifier-laser (MOPA) with a minimum number of elements for the double-pass single-rod amplifier. It produces 100-W average output power of pulsed light with an almost diffraction limited beam. The Q-switched system works with an average repetition rate of about 3 kHz and the pulse width was 70 ns. As active material we used Nd:YALO (Nd:YAP) which has negligible depolarization. The strong thermal lens of the material with focal lengths of less than 15 cm at pump powers of 8 kW was compensated by a phase conjugating mirror based on stimulated Brillouin scattering (SBS). Therefore, the output power could be varied from 2 W up to 100 W without changing the transversal beam profile. The total efficiency of the amplifier including the phase conjugator is 1.25%. >
45 citations
Book•
01 Feb 1995
TL;DR: In this paper, the Scalar Helmholtz Equation for Nonuniform Media (SHE) is used to measure the information capacity of Holographic Memory with 3D Holograms.
Abstract: Speckles in Holography. Introduction to the Problem: Interference and Spatial Structure of a Light Beam. Properties of Speckle Fields. Types of Holograms of Speckle Fields. Main Parameters of Holograms. Diffraction of Light by Sinusoidal Grating. Noise Characteristics of HologramS. The Problem of Information Capacity of Holographic Memory: Light Beam Degrees of Freedom. Capacity Limit for Two-Dimensional Recording of Information. Holographic Memory with Three-Dimensional Recording. Estimates for Limiting the Information Retrieval Rate. First Born Approximation Theory of Hologram Readout: Derivation of the Scalar Helmholtz Equation for Nonuniform Media. Amplitude of Reconstructed Object Waves. Strength of the Hologram. Amplitude of Conjugate Waves. The Condition of Volume Regime. Spectral-Angular Selectivity. Photoresponse Saturation and Grating Strength. Holograms of Speckle Waves: Diffraction Efficiency of Holograms of Speckle Waves. Diffraction Efficiency and Noise at Photoresponse Saturation for Thin-Layer and Thick-Layer Holograms. Selectivity of Holograms of Speckle Fields. Spectral-Angular Distortions. Holograms of Speckle Reference Waves. Readouts of Holograms at High Grating Strength: Thin- and Thick-Layer Holograms of Enhanced Efficiency. Specklon. Calculation of Extinction Coefficients for Specklon. Reconstruction of Speckle Fields by Volume Holograms and Effect of Selectivity Curve Shift. Intramodulation Noise of 3-D Holograms. Referenceless Holograms. Superimposing Exposures at Partial Correlation between Object Fields. Hymn of Praise for 3-D Holograms. Self-Action of Speckle Beams in Nonlinear Media: Brief Review of Nonlinearities for Dynamic Holography. Self Phase Modulation of Speckle Beam. Suppression of Self-Focusing by Speckles. Self-Binding of a Speckle Beam. Two Wave Mixing: Plane Wave Model of Two Wave Mixing. Self-Phase Conjugation Via Backscattering. Transient Energy Transfer of Speckle Beams in Accumulating Media. Stabilization of Dynamic Recordings of Volume Holograms. Checking (Verifying) the Specklon Theory in Two-Wave Mixing Experiment. Two-Wave Coupling Via Diffusion Nonlinearity. Speckle Effects in Multiwave Mixing: Instability of Phase Conjugated Speckle Waves in Kerr-Like Media. Double Phase Conjugation. Self-Biting Scheme of Phase Conjugation. Build-up of Self-Conjugating Oscillation in Nonlinear Cavities.
44 citations
TL;DR: In this article, a two-region model was developed to account for the buildup of screening charges near the electrodes, and a simple method was proposed for the determination of the effective electro-optic coefficients based on applying a sufficiently high-frequency square-wave voltage to prevent screening charge buildup.
Abstract: An experimental investigation of the electric field in the bulk of a Bi12SiO20 crystal is carried out, and a two-region model is developed that can account for the buildup of screening charges near the electrodes. In light of our results, a simple method is proposed for the determination of the effective electro-optic coefficients based on applying a sufficiently high-frequency square-wave voltage to prevent screening charge buildup. A demonstration of this method for Bi12SiO20 leads to a value of 4.4 pm/V for the stress-free (unclamped) coefficient, and a subsequent consideration of piezoelastic contributions allows the strain-free (clamped) coefficient to be estimated at 3.7 pm/V.
35 citations
TL;DR: In this paper, the authors reported the first demonstration of atmospheric compensation at extended ranges by stimulated Brillouin-scattering phase conjugation at a 2.5m height above ground.
Abstract: We report the first demonstration to our knowledge of atmospheric compensation at extended ranges by stimulated Brillouin-scattering phase conjugation. With a field-of-view aperture product of 175 mm mrad, we studied horizontal ranges up to 6 km at a 2.5-m height above ground, with the refractive-index structure parameter Cn2 as large as 10−13 m−2/3. Compensation was achieved at all ranges, consistent with the turbulence-resolution capability of the 10-cm system aperture. The system was driven by frequency-doubled Nd:YAG lasers operating with ~10-ns pulses that were Raman shifted in gaseous hydrogen to the 683-nm operating wavelength. Raman amplification overcame as much as 85 dB of range and internal losses.
30 citations
TL;DR: In this article, the authors observed stimulated extraordinary-ordinary wave scattering and cross-polarized self-starting optical phase conjugation effects in a nematic liquid-crystal film.
Abstract: We have observed stimulated extraordinary-ordinary wave scattering and cross-polarized self-starting optical phase conjugation effects in a nematic liquid-crystal film. The basic mechanism involved is the nonresonant laser-induced nematic crystal axis reorientation. These processes require low optical power and are characterized by millisecond response speed.
30 citations
TL;DR: In this article, the effect of optical phase conjugation on Gordon-Haus jitter in long-distance soliton communication systems is considered, and a post-transmission line compensation scheme based on optical phase convolutions and soliton-supported dispersion compensation is proposed.
Abstract: The effect of optical phase conjugation on Gordon-Haus jitter in long-distance soliton communication systems is considered. In-line optical phase conjugation at an optimal point two-thirds of the way down the system reduces the rms jitter by a factor of three. A post-transmission-line compensation scheme based on optical phase conjugation and soliton-supported dispersion compensation reduces the rms jitter by a factor of two. >
29 citations
TL;DR: In this article, a single SOA was used to conjugate four 2.5 Gbit/s WDM channels with 2 nm channel spacings, and it was shown that penalties due to crosstalk between channels during conjugation can be acceptably small.
Abstract: Multichannel optical phase conjugation in a semiconductor optical amplifier (SOA) is reported. A single SOA is used to conjugate four 2.5 Gbit/s WDM channels with 2 nm channel spacings. Our results show that penalties due to crosstalk between channels during conjugation can be acceptably small.
TL;DR: A new nondestructive method based on optimum end-fire coupling by self-pumped phase conjugation in a photorefractive BaTiO3 crystal is presented which is applied to measure the propagation loss coefficient of ion-implanted KNbO3 channel waveguides with an accuracy of better than 5%.
Abstract: We present a new nondestructive method for measuring the propagation loss coefficient in waveguides based on optimum end-fire coupling by self-pumped phase conjugation in a photorefractive BaTiO3 crystal. In a first pass through the waveguide, the laser beam is adapted to the waveguide mode profile, and hence the phase-conjugated beam is automatically coupled back into the guide with the optimum coupling efficiency. The propagation loss coefficient is determined by measurement of the transmittance of the phase-conjugated beam in the second pass through the wave-guide. We apply this method to measure the propagation loss coefficient of ion-implanted KNbO3 channel waveguides with an accuracy of better than 5%.
TL;DR: In this paper, the spatial and temporal effects arising in photorefractive crystals during the process of double phase conjugation are analyzed numerically with a beam-propagation method.
Abstract: Spatial and temporal effects arising in photorefractive crystals during the process of double phase conjugation are analyzed numerically with a novel beam-propagation method. Slowly varying envelope wave equations in the paraxial approximation are solved under the appropriate boundary conditions. Our analysis includes dynamical effects caused by the buildup of diffraction gratings in the crystal and the turn-on of phase-conjugate beams as well as spatial effects caused by the finite transverse spread of beams and by the propagation directions of the beams. Various phenomena are observed, such as self-bending of phase-conjugate beams, convective flow of energy out of the interaction region, mode oscillations, critical slowing down at the oscillation threshold, and irregular spatial pattern formation. For a real beam-coupling constant and constructive interaction of interference fringes in the crystal we find steady or periodic behavior. For a complex coupling constant and/or induced phase mismatch in the grating a transition to spatiotemporal chaos is observed. We believe that under stable operating conditions the transverse double phase-conjugate mirror in the paraxial approximation is a convective oscillator, rather than an amplifier. Improved agreement with experimental results is obtained.
TL;DR: The holographic time-of-flight technique is applied in a photorefractive polymer and the electric-field, temperature, and drift-length dependencies of the hole-drift mobility are shown to be consistent with previously published data.
Abstract: The holographic time-of-flight (HTOF) technique is applied in a photorefractive polymer. The electric-field, temperature, and drift-length dependencies of the hole-drift mobility are shown to be consistent with previously published data. It is suggested that the shape of the HTOF signal reflects the degree of charge-transport disorder in this class of amorphous materials.
TL;DR: In this article, the authors used degenerate four-wave mixing in a LiNbO 3 :Fe 0.04 wt.% crystal and observed substantial enhancement of light scattered by crystal surface irregularities.
TL;DR: In this article, a macroscopic selfconsistent model for external-reflection near-field microscopy together with a similar model for photon scanning tunneling microscopy is used to describe phase conjugation of light that is emitted by a fiber tip placed near a phase-conjugating mirror.
Abstract: A macroscopic self-consistent model for external-reflection near-field microscopy together with a similar model for photon scanning tunneling microscopy is used to describe phase conjugation of light that is emitted by a fiber tip placed near a phase-conjugating mirror. The appropriate relations are obtained for a two-dimensional configuration, and numerical results for various trapezium-shaped fiber tips are presented. This modeling accounts for the main features of recent experiments on phase conjugation of optical near fields and emphasizes the significance of taking into consideration field components that are evanescent in air but propagating in the phase-conjugating mirror. The influence of fiber tip parameters on the spatial confinement of phaseconjugated light is discussed.
TL;DR: In this article, an unexpected fast response (35 ms) of beam fanning was measured in a fiber-like photorefractive sample of Bi/sub 12/TiO/sub 20/ (BTO) crystal.
Abstract: Unexpectedly fast response (35 ms) of beam fanning has been measured in a fiber-like photorefractive sample of Bi/sub 12/TiO/sub 20/ (BTO) crystal. Nonlinear interaction between different directions of fanned beams is responsible for unusual angular distribution of the fanning emerged from the fiber that can be used for double phase-conjugate mirror (DPCM) recording with higher efficiency in a wider range of the pump's incidence than in a bulk sample. The DPCM with conversion efficiency up to 8% has been recorded in the BTO fiber at /spl lambda/=632.8 nm for a 2/spl times/3 mW input light power. Practically, it means that no adjustment is needed to achieve an effective interaction of mutually incoherent beams, except introducing the pump beam into the fiber. >
Proceedings Article•
21 May 1995TL;DR: Four-wave mixing by gain saturation in a laser-pumped Ti:sapphire (Ti(3+):Al(2)O(3)) amplif ier is demonstrated for the first time to the authors' knowledge.
Abstract: Four-wave mixing by gain saturation in a laser-pumped Ti:sapphire (Ti3+:Al2O3) amplifier is demonstrated for the first time to our knowledge. Small-signal gain in excess of 250 has been obtained by intense laser pumping at 532 nm, resulting in observed four-wave mixing energy reflectivity as high as 360% for nanosecond pulses at 780 nm.
TL;DR: In this article, a four-wave mixing by gain saturation in a laser-pumped Ti:sapphire (Ti3+:Al2O3) amplifier is demonstrated for the first time.
Abstract: Four-wave mixing by gain saturation in a laser-pumped Ti:sapphire (Ti3+:Al2O3) amplifier is demonstrated for the first time to our knowledge. Small-signal gain in excess of 250 has been obtained by intense laser pumping at 532 nm, resulting in observed four-wave mixing energy reflectivity as high as 360% for nanosecond pulses at 780 nm.
TL;DR: In this article, it was shown that cascaded χ(2) processes can make a substantial contribution to the phase-conjugate signal in a material without inversion symmetry.
Abstract: The process of degenerate four-wave mixing in a material with a nonzero second-order susceptibility is theoretically investigated. The contributions by cascaded second-order processes to the overall third-order response are calculated by solution of the coupled-wave equations, assuming plane input fields. The driven coupling fields at frequencies 2ω = ω + ω and 0 = ω − ω, created by the second-order polarization, are very far from phase matching and are therefore calculated with proper boundary conditions without the use of the slowly varying envelope approximation. As a consequence of the large phase mismatch of the generated second-harmonic wave, the dominant pathway for cascading in degenerate four-wave mixing is via the generated dc field. With LiNbO3, KNbO3, and KTP as explicit numerical examples it is shown that cascaded χ(2) processes can make a substantial contribution to the phase-conjugate signal in a material without inversion symmetry.
Patent•
10 Oct 1995TL;DR: In this article, the authors present a solid-state laser architecture with a zig-zag amplifier, an image relaying telescope and a phase conjugation cell to produce a beam of extremely high quality and brightness.
Abstract: A solid-state laser architecture producing a beam of extremely high quality and brightness, including a master oscillator operating in conjunction with a zig-zag amplifier, an image relaying telescope and a phase conjugation cell. One embodiment of the laser architecture compensates for birefringence that is thermally induced in the amplifier, but injects linearly polarized light into the phase conjugation cell. Another embodiment injects circularly polarized light into the phase conjugation cell and includes optical components that eliminate birefringence effects arising in a first pass through the amplifier. Optional features permit the use of a frequency doubler assembly to provide output at twice optical frequencies, and an electro-optical switch or Faraday rotator to effect polarization angle rotation if the amplifier material can only be operated at one polarization. The zig-zag amplifier is cooled by flow of cooling liquid, preferably using longitudinal flow to minimize temperature gradients in a vertical direction, and has cooling channel seals disposed in dead zones that receive no light, to minimize optical damage to the seals. Light is input to the amplifier at a near normal angle of incidence, to minimize polarization by reflection and to permit a polarizer to be used to extract an output beam from the amplifier. Antireflective coatings on edges and on sides of the amplifier eliminate parasitic oscillations, and wedge-shaped windows provide uniform pumping by eliminating gaps between diode arrays.
TL;DR: In this article, the authors proposed a scheme of phase conjugation wave generation with a semiconductor microcavity, where a single pump beam directed normally to the planar cavity produces counterpropagating pump fields in the QW region.
Abstract: We propose a scheme of efficient phase conjugation wave generation with a semiconductor microcavity. We show experimental results for a GaAs single quantum well (SQW) in a planar AlGaAs microcavity at 13 K. A single pump beam directed normally to the planar cavity produces counterpropagating pump fields in the QW region. Using the quantum confined Stark effect, we tune the exciton resonance energy around the fixed cavity resonance. Large enhancement of the signal occurs when the exciton resonance coincides with the cavity resonance.
TL;DR: In this paper, the self-pumped phase conjugation (SPPC) in two BaTiO3:Ce crystals with different doping concentrations have been experimentally studied, and the pump beam was from dye lasers, with an overall tunable wavelength region lying between 570 and 680 nm.
Abstract: Formation mechanisms of self-pumped phase conjugation (SPPC) in two BaTiO3:Ce crystals with different doping concentrations have been experimentally studied. The pump beam was from dye lasers, with an overall tunable wavelength region lying between 570 and 680 nm. Variations of the optical beam path patterns as well as reflectivity of the phase conjugators with respect to the incident angle, the incident position, and the wavelength of the pump were investigated in two configurations. One configuration corresponds to that in which the pump enters an a face of the crystal; the other to that in which the pump enters the +c face of the crystal. It was found that SPPC is sometimes established in a way similar to that of a cat phase conjugator, but usually without the formation of a clear beam path loop. Sometimes SPPC is established by a stimulated photorefractive backscattering and four-wave mixing mechanism. In these cases, however, the crystal corners as well as the scattering centers on the crystal faces usually play an important role by seeding the stimulated photorefractive backscattering processes. In other cases SPPC is established by both the cat and the stimulated photorefractive backscattering and four-wave mixing mechanisms.
TL;DR: Nondegenerate optical parametric amplifiers can be used to simultaneously phase conjugate and amplify a pulse in a nonlinear optical fiber and if the remaining third-order and nonlinear dispersions balance, solitonlike pulses are able to propagate with subpicosecond pulse widths.
Abstract: Nondegenerate optical parametric amplifiers can be used to simultaneously phase conjugate and amplify a pulse in a nonlinear optical fiber. The gain in the amplifiers compensates the linear loss in the fiber, while the phase conjugation effectively neutralizes second-order dispersion, self-phase modulation, the Raman self-frequency shift, and Gordon–Haus jitter. If the remaining third-order and nonlinear dispersions balance, solitonlike pulses are able to propagate with subpicosecond pulse widths.
TL;DR: In this paper, a parametric self-pumped phase conjugation of the space heterogeneous light beam in an inverted Nd:YAG-rod with non-reciprocal feedback is investigated.
TL;DR: In this paper, a reflective optical mixer based on four-photon mixing is used to generate a phase conjugate copy of an input optical signal of arbitrary polarization for lightwave systems.
Abstract: A reflective optical mixer based on four-photon mixing is used to generate a phase conjugate copy of an input optical signal of arbitrary polarization. For some polarization states of the pump and signal, the phase conjugate signal is polarization-scrambled. Measurements at 1.8 Gb/s confirm the potential use of the reflective optical mixer in lightwave systems. >
TL;DR: In this paper, the conditions of high energy efficiency saturable-gain degenerate four-wave mixing process with orthogonally-polarized pump beams in a Nd:YAG amplifier at 106 μm were analyzed.
TL;DR: A new scheme for mutually pumped phase conjugation with two incoherent beams, using a 0.93-mm-thick plate-formed BaTiO3:Ce crystal, is demonstrated experimentally, with high reflectivity and power-dependent response time.
Abstract: We have demonstrated experimentally a new scheme for mutually pumped phase conjugation with two incoherent beams, using a 0.93-mm-thick plate-formed BaTiO3:Ce crystal. The highest phase was reflectivities obtained in our experiments are 30.5% (in the case of equal incident powers) and 71.6% (in the case of unequal incident powers). The variations of the phase-conjugate reflectivity with incident angles and is intensity ratio have been determined, as has the power-dependent response time.
TL;DR: In this article, the authors studied the near field coupling of dipole radiation to a phase conjugate mirror and showed that the coupling leads to a significant narrowing of the dynamical response.
TL;DR: Low-power phase conjugation of azobenzene-compound-doped poly(methyl methacrylate) films was studied and it was shown that this kind of polymer has appreciable third-order optical nonlinearity.
Abstract: Push–pull azobenzene compounds were synthesized by the diazocoupling reaction, and low-power phase conjugation of azobenzene-compound-doped poly(methyl methacrylate) films was studied with a He–Ne laser at 632.8 nm. It is shown that this kind of polymer has appreciable third-order optical nonlinearity, with a χ(3) of approximately 10−4 esu in the tail of absorption.