Showing papers on "Phase conjugation published in 2012"
TL;DR: It is demonstrated for the first time to the authors' knowledge a digital phase conjugation technique for generating a sharp focus point at the end of a multimode optical fiber.
Abstract: We demonstrate for the first time to our knowledge a digital phase conjugation technique for generating a sharp focus point at the end of a multimode optical fiber. A sharp focus with a contrast of 1800 is experimentally obtained at the tip of a 105μm core multimode fiber. Scanning of the focal point is also demonstrated by digital means. Effects from illumination and fiber bending are addressed.
389 citations
TL;DR: This work presents fluorescence imaging beyond the ballistic regime by combining single cycle pulsed ultrasound modulation and digital optical phase conjugation, and demonstrates a near isotropic 3D localized sound-light interaction zone.
Abstract: Fluorescence imaging has revolutionized biomedical research over the past three decades. Its high molecular specificity and unrivaled single molecule level sensitivity have enabled breakthroughs in a variety of research fields. For in vivo applications, its major limitation is the superficial imaging depth as random scattering in biological tissues causes exponential attenuation of the ballistic component of a light wave. Here we present fluorescence imaging beyond the ballistic regime by combining single cycle pulsed ultrasound modulation and digital optical phase conjugation. We demonstrate a near isotropic 3D localized sound-light interaction zone. With the exceptionally high optical gain provided by the digital optical phase conjugation system, we can deliver sufficient optical power to a focus inside highly scattering media for not only fluorescence imaging but also a variety of linear and nonlinear spectroscopy measurements. This technology paves the way for many important applications in both fundamental biology research and clinical studies.
265 citations
TL;DR: The transfer of phase structure and of orbital angular momentum from near-infrared pump light to blue light generated in a four-wave-mixing process in 85Rb vapor demonstrates the parametric nature of the mode transfer.
Abstract: We report the transfer of phase structure and, in particular, of orbital angular momentum from near-infrared pump light to blue light generated in a four-wave-mixing process in 85Rb vapor. The intensity and phase profile of the two pump lasers at 780 and 776 nm, shaped by a spatial light modulator, influences the phase and intensity profile of light at 420 nm, which is generated in a subsequent coherent cascade. In particular, we observe that the phase profile associated with orbital angular momentum is transferred entirely from the pump light to the blue. Pumping with more complicated light profiles results in the excitation of spatial modes in the blue that depend strongly on phase matching, thus demonstrating the parametric nature of the mode transfer. These results have implications on the inscription and storage of phase information in atomic gases.
200 citations
TL;DR: This work demonstrates a method for phase conjugating fluorescence that can conjugate extremely weak, incoherent optical signals and potential applications are in imaging, optical trapping, and targeted photochemical activation inside turbid tissue.
Abstract: We demonstrate a method for phase conjugating fluorescence. Our method, called reference free digital optical phase conjugation, can conjugate extremely weak, incoherent optical signals. It was used to phase conjugate fluorescent light originating from a bead covered with 0.5 mm of light-scattering tissue. The phase conjugated beam refocuses onto the bead and causes a local increase of over two orders of magnitude in the light intensity. Potential applications are in imaging, optical trapping, and targeted photochemical activation inside turbid tissue.
146 citations
TL;DR: It is discussed how this mechanism provides a physical interpretation of soliton-induced Cherenkov radiation and associated spectral recoil in terms of phase-matched frequency mixing pumped by bichromatic pump pairs in the soliton spectrum.
Abstract: We report theoretical, numerical, and experimental studies of cascaded phase matching in fiber frequency combs and show how this mechanism is directly connected to the dynamics of supercontinuum generation. In particular, linking cascaded four-wave mixing with direct higher-order nonlinear processes allows us to derive a simple phase matching condition that governs nonlinear symmetry breaking in the presence of higher-order dispersion. We discuss how this mechanism provides a physical interpretation of soliton-induced Cherenkov radiation and associated spectral recoil in terms of phase-matched frequency mixing pumped by bichromatic pump pairs in the soliton spectrum. Theoretical and numerical predictions are confirmed via experiments using both quasicontinuous wave and picosecond pulse excitation.
124 citations
TL;DR: FWM theory shows that the 'noise' processes of OPC modules utilizing χ3 nonlinearities could be reduced by increasing the pump power, which will improve back-to-back performance with the OPC module.
Abstract: We experimentally demonstrate that mid-link optical phase conjugation (OPC) effectively compensates fiber nonlinearity in coherent optical OFDM super-channels. The OPC was produced by pump × subcarrier degenerate four-wave-mixing in a 1-km highly nonlinear fiber. The nonlinear threshold for the 10 × 80-km 604.7-Gb/s 16-QAM test system was increased by 4.8 dB. The performance at the optimum power was only improved by 0.2 dB because the OPC module produces a 1.6 dB penalty for the back-to-back system. FWM theory shows that the 'noise' processes of OPC modules utilizing χ3 nonlinearities could be reduced by increasing the pump power, which will improve back-to-back performance with the OPC module.
75 citations
TL;DR: Three-dimensional imaging through a thin turbid medium is demonstrated using digital phase conjugation of the second harmonic signal emitted from a beacon nanoparticle using a digitally phase-conjugated focus.
Abstract: We demonstrate three-dimensional imaging through a thin turbid medium using digital phase conjugation of the second harmonic signal emitted from a beacon nanoparticle. The digitally phase-conjugated focus scans the volume in the vicinity of its initial position through numerically manipulated phase patterns projected onto the spatial light modulator. Accurate three dimensional images of a fluorescent sample placed behind a turbid medium are obtained.
64 citations
TL;DR: In this paper, the authors theoretically study the stability conditions and excitation regimes of hyperparametric oscillation and Kerr frequency comb generation in continuously pumped nonlinear optical microresonators possessing an anomalous group velocity dispersion.
Abstract: We theoretically study the stability conditions and excitation regimes of hyperparametric oscillation and Kerr frequency comb generation in continuously pumped nonlinear optical microresonators possessing an anomalous group velocity dispersion. We show that both hard and soft excitation regimes are possible in the microresonators. Selection between the regimes is achieved via change in the parameters of the pumping light.
62 citations
04 Mar 2012
TL;DR: In this article, the authors demonstrate fiber nonlinearity mitigation using midlink digital phase conjugation in 40-Gb/s CO-OFDM-16QAM transmission over 100-km ultra-large-area-fiber spans, achieving a reach of 10,400 km, and reach and power-tolerance improvements of 53% and 4 dB, respectively.
Abstract: We demonstrate fiber nonlinearity mitigation using mid-link digital phase conjugation in 40-Gb/s CO-OFDM-16QAM transmission over 100-km ultra-large-area-fiber spans, achieving a reach of 10,400 km, and reach and power-tolerance improvements of 53% and 4 dB, respectively.
40 citations
TL;DR: An experimental investigation of time-reversed ultrasonically encoded optical focusing in biological tissue that can achieve a maximum penetration depth of 5 mm in a chicken breast sample and image optical contrasts within a tissue sample with a spatial resolution approximately equaling 1/√2 of the ultrasound focal diameter.
Abstract: We report an experimental investigation of time-reversed ultrasonically encoded optical focusing in biological tissue. This technology combines the concepts of optical phase conjugation and ultrasound modulation of diffused coherent light. The ultrasonically encoded (or tagged) diffused light from a tissue sample is collected in reflection mode and interferes with a reference light in a photorefractive crystal (used as a phase conjugation mirror) to form a hologram. Then a time-reversed copy of the tagged light is generated and traces back the original trajectories to the ultrasonic focus inside the tissue sample. With our current setup, we can achieve a maximum penetration depth of 5 mm in a chicken breast sample and image optical contrasts within a tissue sample with a spatial resolution approximately equaling 1/√2 of the ultrasound focal diameter.
37 citations
TL;DR: The current trends in stimulated Brillouin scattering and optical phase conjugation are overviewed in this paper, where the selected papers presented in the 2010 5th International Workshop on SBS and PHYP are summarized.
Abstract: The current trends in stimulated Brillouin scattering and optical phase conjugation are overviewed. This report is formed by the selected papers presented in the “Fifth International Workshop on stimulated Brillouin scattering and phase conjugation 2010” in Japan. The nonlinear properties of phase conjugation based on stimulated Brillouin scattering and photo-refraction can compensate phase distortions in the high power laser systems, and they will also open up potentially novel laser technologies, e.g., phase stabilization, beam combination, pulse compression, ultrafast pulse shaping, and arbitrary waveform generation.
TL;DR: A fiber-optic system design with optical backpropagation that uses an optical phase conjugator, high-dispersion fibers, and highly nonlinear fibers is investigated, and the proposed technique outperforms the midpoint opticalphase conjugation and digital back Propagation with the same step size.
Abstract: A fiber-optic system design with optical backpropagation that uses an optical phase conjugator, high-dispersion fibers, and highly nonlinear fibers is investigated. The proposed technique outperforms the midpoint optical phase conjugation and digital backpropagation with the same step size.
TL;DR: In this article, the nonlinear dynamics induced in suspended nanomembranes by their clampings were studied and the nonlocal character of nonlinearity was demonstrated via intermode couplings.
Abstract: We study the nonlinear dynamics induced in suspended nanomembranes by their clampings. The nonlocal character of the nonlinearity is demonstrated via intermode couplings. We also monitor the resonator phase-space trajectory and characterize its mechanical response in the presence of a strong pump excitation. We observe a shift in the oscillation frequency and phase conjugation of the mechanical mode. Such nonlinear effects are inherent to any submicron-scale mechanical resonator and are expected to play a role in their quantum dynamics as well.
TL;DR: In this paper, the optical field fluctuations produced by four-wave mixing processes in fibers are studied in detail, and formulas for the output quadrature means, variances, and correlations are derived for arbitrary pump-induced coupling and dispersion-and pump induced mismatch coefficients.
Abstract: In this tutorial, the optical field fluctuations produced by four-wave mixing processes in fibers are studied in detail. Modulation interaction and phase conjugation amplify input signals, whereas Bragg scattering frequency converts an input signal. If the input states are coherent, the quadrature fluctuations associated with the output states have Gaussian statistics. Formulas are derived for the output quadrature means, variances, and correlations, which are valid for arbitrary pump-induced coupling and dispersion- and pump-induced mismatch coefficients. These formulas allow one to determine the output Wigner distributions, which specify the output fields completely, and the effects of the aforementioned processes on the information carried by signals. The results of this paper are relevant to communication systems and quantum-information protocols based on continuous variables.
06 May 2012
TL;DR: In this paper, a decomposition of the time reversal operator allows selective and efficient focusing on individual scatterers, even through an aberrating layer, in a weakly scattering medium.
Abstract: We report on the optical measurement of the backscattering matrix in a weakly scattering medium. A decomposition of the time reversal operator allows selective and efficient focusing on individual scatterers, even through an aberrating layer.
TL;DR: In this paper, the authors show that the ideal phase-conjugating surface is, in principle, physically realizable and investigate the necessary properties of nonlinear and nonreciprocal particles which can be used to build a perfect lens system.
Abstract: It is theoretically known that a pair of phase-conjugating surfaces can function as a perfect lens, focusing propagating waves and enhancing evanescent waves. However, the known experimental approaches based on thin sheets of nonlinear materials cannot fully realize the required phase conjugation boundary condition. In this paper, we show that the ideal phase-conjugating surface is, in principle, physically realizable and investigate the necessary properties of nonlinear and nonreciprocal particles which can be used to build a perfect lens system. The physical principle of the lens operation is discussed in detail and directions of possible experimental realizations are outlined.
TL;DR: It is shown that backward difference-frequency generation can be exploited to achieve phase conjugation in a second-order nonlinear medium and the backward configuration can be utilized to achieve broadband quasi-phase-matching, compared with the forward counterpart.
Abstract: We show that backward difference-frequency generation can be exploited to achieve phase conjugation in a second-order nonlinear medium. The backward configuration can be utilized to achieve broadband quasi-phase-matching, compared with the forward counterpart. Our calculation shows that a nonlinear reflectivity of close to 100% is achievable from a laser emitting an output power of ~1 mW. Such an efficient phase conjugator is made feasible by placing the nonlinear medium inside a pump laser cavity. In addition, a Fabry-Perot resonator at the input frequency is used to significantly improve the nonlinear reflectivity.
TL;DR: A commercially available sound transducer is employed to generate two sound foci in parallel, doubled the wavefront measurement speed, and reduced the mechanical scanning steps of the sound Transducer to half.
Abstract: Ultrasound pulse guided digital phase conjugation has emerged to realize fluorescence imaging inside random scattering media. Its major limitation is the slow imaging speed, as a new wavefront needs to be measured for each voxel. Therefore 3D or even 2D imaging can be time consuming. For practical applications on biological systems, we need to accelerate the imaging process by orders of magnitude. Here we propose and experimentally demonstrate a parallel wavefront measurement scheme towards such a goal. Multiple focused ultrasound pulses of different carrier frequencies can be simultaneously launched inside a scattering medium. Heterodyne interferometry is used to measure all of the wavefronts originating from every sound focus in parallel. We use these wavefronts in sequence to rapidly excite fluorescence at all the voxels defined by the focused ultrasound pulses. In this report, we employed a commercially available sound transducer to generate two sound foci in parallel, doubled the wavefront measurement speed, and reduced the mechanical scanning steps of the sound transducer to half.
TL;DR: Temporal growth of an optical Kerr frequency comb generated in a nonlinear microresonator is studied experimentally in this article, where the authors show that the comb emerges on time scales significantly exceeding the ring-down time of the resonator modes and measure the time delay.
Abstract: Temporal growth of an optical Kerr frequency comb generated in a nonlinear microresonator is studied experimentally. We show that the comb emerges on time scales significantly exceeding the ring-down time of the resonator modes and measure the time delay. Experimental data are explained via numerical simulations.
TL;DR: In this paper, the phase control of the switch between bright and dark states in the transmitted probe, four-wave mixing (FWM) and fluorescence signals in a four-level ǫ85Rb atomic system was investigated.
Abstract: We first investigate the phase control of the switch between bright and dark states in the transmitted probe, four-wave mixing (FWM) and fluorescence signals in a four-level 85Rb atomic system. With the relative phase modulated from 0 to −π, pure dark state in the FWM and fluorescence channels can be switched to pure bright state, corresponding to the switch from electromagnetically induced transparency to electromagnetically induced absorption. Meanwhile, the results could be obtained in solid crystals. Such phase controlled switch could have potential applications in optical communication and quantum information processing.
TL;DR: This structure improves performance of the passive time reversal approach, even though the taps for combining span one symbol interval, and is demonstrated by a set of real data collected in a recent sea experiment.
TL;DR: In this article, phase conjugation metamaterials are used to produce time reversed signals with useful properties, such as negatively refracting imaging system, which can be improved upon to allow either completely wireless operation or more efficient phase-conv conjugate signal generation through the use of active loading elements.
Abstract: We present simulation and experimental results demonstrating the effectiveness of phase conjugation or, equivalently, time reversal metamaterials for imaging applications. Split-ring resonators are loaded with varactor diodes to enable straightforward, easy-to-fabricate phase conjugation metamaterial unit cells. These cells are improved upon to allow either completely wireless operation or more efficient phase conjugate signal generation through the use of active loading elements. The metamaterials are demonstrated experimentally to produce time reversed signals with useful properties. An array of metamaterial cells is then constructed and shown to act as a negatively refracting imaging system.
TL;DR: In this article, the optical phase conjugation signals were observed at low cw laser light intensities (<100 mW/cm2, λ λ = 532 nm, and the estimated value of third order optical susceptibility χ(3) ω= 2.8 ǫ× 10−17 m2/V2 is attributed to photoisomerization of azo-dye (disperse red 1) inducing molecular reorientation process of liquid crystal molecules.
Abstract: We report on optical phase conjugation phenomenon observed in chiral nematic liquid crystal showing band gap type Bragg reflection. The phase conjugate to the signal beam is observable only in the small temperature interval when the Bragg condition is fulfilled and only for circularly polarized light. The optical phase conjugation signals were observed at low cw laser light intensities (<100 mW/cm2, λ = 532 nm). Estimated value of third order optical susceptibility χ(3) = 2.8 × 10−17 m2/V2 is attributed to enhancement due to photoisomerisation of azo-dye (disperse red 1) inducing molecular reorientation process of liquid crystal molecules.
Book•
19 Nov 2012
TL;DR: In this paper, a beam combiner was developed to combine multiple-channel laser beams simultaneously with high input and output coupling efficiency, and beam cleaning and SBS piston error conjugation was used to phase two-pass amplifiers.
Abstract: : Brightness scaling lasers using stimulated Brillouin scattering (SBS) in optical fibers is explored. A multiple-channel amplifier approach is used to increase the total power of a laser system while avoiding a significant burden on a single channel. The work explores two approaches utilizing both SBS beam cleanup and SBS piston error conjugation. A unique beam combiner that takes advantage of the SBS beam cleanup properties of a long, gradient-index multimode fiber was designed and tested. The beam combiner was developed to combine multiple-channel laser beams simultaneously with high input and output coupling efficiency. The design for the SBS beam combiner is presented along with experimental demonstration of multiple-channel beam combining using the technique. Using SBS piston error conjugation to phase multiple-channel two-pass amplifiers is also explored. Various system configurations were investigated to demonstrate SBS beam phasing of both passive, unamplified channels and active channels containing fiber amplifiers. Beam phasing of the channels was successfully demonstrated with enough gain and power to merit consideration as a viable approach to multiple-channel laser power scaling. Methods for improving efficiency and scaling to include a greater number of channels were also tested.
TL;DR: In this article, the authors report on temporal oscillation in the first-order self-diffracted signal observed during the holographic grating recording in the azobenezne-functionalized polymer in the degenerate two-wave mixing experiment.
Abstract: The authors report on temporal oscillation in the first-order self-diffracted signal observed during the holographic grating recording in the azobenezne-functionalized polymer in the degenerate two-wave mixing experiment. Explanation of the oscillating character of the diffracted signal is given based on the assumption of appearance of symmetrical phase shift between the light intensity pattern and the diffraction grating. Simulations of the experimental results were performed based on simple theoretical considerations and they have shown a good agreement with the experimental data.
TL;DR: An intrinsic phase shift calibration of SHG holograms is developed, an algorithm that extracts the reference and object intensity directly from a set of phase-shifted holographic data, and a more robustphase-shifting holography reconstruction algorithm based on π-sh shifted hologram pairs that permits self-calibration of the phase shift and recovery of the complex field through a Hilbert transform.
Abstract: New techniques are presented that make phase-shifting holography viable for second-harmonic generation (SHG) holography with weak object fields. We developed an intrinsic phase shift calibration of SHG holograms, an algorithm that extracts the reference and object intensity directly from a set of phase-shifted holographic data, and a more robust phase-shifting holography reconstruction algorithm based on π-shifted hologram pairs that permits self-calibration of the phase shift and recovery of the complex field through a Hilbert transform.
TL;DR: The creation of the light-induced dynamical grating is described and the amplitude of the phase-conjugate wave is shown to follow the changes of the input signal, hence providing efficient distortion correction.
Abstract: Optical phase conjugation and slow light are obtained in dye-doped chiral nematics via degenerate four-wave mixing. The creation of the light-induced dynamical grating is described and the amplitude of the phase-conjugate wave is shown to follow the changes of the input signal, hence providing efficient distortion correction. Associated to these capabilities, slowing down of light pulses is obtained thanks to the dispersive properties of the wave mixing occurring in the cholesteric liquid crystals, opening the way to applications in interferometry and imaging through highly scattering media.
Patent•
26 Sep 2012
TL;DR: In this article, a system for improving the laser collimation precision by utilizing an optical phase conjugation principle, comprising a laser device, consisting of a polarizer, a beam expanding and collimation system, a first beam splitter, first polarization spectroscope and a reflector are sequentially arranged along an emitting light beam.
Abstract: The invention provides a system for improving the laser collimation precision by utilizing an optical phase conjugation principle, comprising a laser device, wherein a polarizer, a beam expanding and collimation system, a first beam splitter, a first polarization spectroscope and a reflector are sequentially arranged along an emitting light beam of the laser device; a position detector is arranged in a beam splitting direction of the first beam splitter; reflection light of the reflector is parallel to the emitting light beam of the laser device; a second polarization spectroscope, a Faraday rotator, a second beam splitter and a space optical phase modulating device are sequentially arranged on the reflection light of the reflector; a wave-front detector is arranged in the beam splitting direction of the second beam splitter; and the space optical phase modulating device and the wave-front detector are connected to a computer. The invention further provides a method for improving the laser collimation precision by utilizing the system; the system disclosed by the invention has a simple structure and influences of uneven atmosphere on the laser collimation can be effectively compensated; and the space optical phase modulating device is used as a phase conjugation mirror so that the system has the advantages of small size, easiness for controlling and the like.
01 Dec 2012
TL;DR: Optical phase conjugation through degenerate four-wave mixing is observed in 4-dimethylamino-styryl]-1-docosyl pyridinium bromide (DASPB) dye-doped in polymethyl methacrylate - metacrylic acid (PMMA-MA) polymer films under low power, continuous-wave laser irradiation as mentioned in this paper.
Abstract: Optical phase conjugation through degenerate four-wave mixing is observed in 4-[4-(Dimethylamino)styryl]-1-docosyl pyridinium bromide (DASPB) dye-doped in Polymethyl methacrylate - metacrylic acid (PMMA-MA) polymer films under low-power, continuous-wave laser irradiation. A maximum phase conjugate efficiency of 0.42% has been obtained for probe beam intensity at 2.5 W/cm2. Phase conjugation is observed for both parallel- and orthogonally-polarized probe and pump beams. The maximum PC reflectivity is achieved when the angle between probe beam and forward pump beam is 8 degrees. The effects of dye concentration, inter beam angle between probe and forward pump beam on phase conjugation reflectivity are also studied. PC signal strength first increases and then decreases with time. PC reflectivity is also increased by increasing the intensity of the backward and forward pump beam. The polarization and intensity profile are verified to be preserved in the conjugate signal. The predominant phase conjugation signal is attributed to the fact that saturable absorption and two photon induced florescence property of the dye molecules.
TL;DR: Analysis of the transmission and the reflection of light beams carrying orbital angular momentum through a dielectric multilayer structure containing phase-conjugating interfaces shows that the phase conjugation at the interfaces results in a characteristic angular and radial pattern of the reflected beam, a fact that can be exploited for the detection and the characterization of phase conjjugation in composite optical materials.
Abstract: We study the transmission and the reflection of light beams carrying orbital angular momentum through a dielectric multilayer structure containing phase-conjugating interfaces. We show analytically and demonstrate numerically that the phase conjugation at the interfaces results in a characteristic angular and radial pattern of the reflected beam, a fact that can be exploited for the detection and the characterization of phase conjugation in composite optical materials.