Showing papers on "Phase conjugation published in 2017"
20 Aug 2017
TL;DR: The optical memory effect is a well-known type of tilt/tilt wave correlation that is observed in coherent fields, allowing control over scattered light through thin and diffusive materials as mentioned in this paper.
Abstract: The optical memory effect is a well-known type of tilt/tilt wave correlation that is observed in coherent fields, allowing control over scattered light through thin and diffusive materials. Here we show that the optical memory effect is a special case of a more general class of combined shift/tilt correlations occurring in media of arbitrary geometry. We experimentally demonstrate the existence of these correlations, and provide an analytical framework that allows us to predict and understand this class of scattering correlations. This “generalized optical memory effect” can be utilized for maximizing the imaging field-of-view of deep tissue imaging techniques such as phase conjugation and adaptive optics.
169 citations
20 Feb 2017
TL;DR: This work develops a simpler but faster DOPC system that focuses light not only through, but also inside scattering media, and is an important step toward in vivo deep-tissue non-invasive optical imaging, manipulation, and therapy.
Abstract: Wavefront shaping based on digital optical phase conjugation (DOPC) focuses light through or inside scattering media, but the low speed of DOPC prevents it from being applied to thick, living biological tissue. Although a fast DOPC approach was recently developed, the reported single-shot wavefront measurement method does not work when the goal is to focus light inside, instead of through, highly scattering media. Here, using a ferroelectric liquid crystal based spatial light modulator, we develop a simpler but faster DOPC system that focuses light not only through, but also inside scattering media. By controlling 2.6×105 optical degrees of freedom, our system focused light through 3 mm thick moving chicken tissue, with a system latency of 3.0 ms. Using ultrasound-guided DOPC, along with a binary wavefront measurement method, our system focused light inside a scattering medium comprising moving tissue with a latency of 6.0 ms, which is one to two orders of magnitude shorter than those of previous digital wavefront shaping systems. Since the demonstrated speed approaches tissue decorrelation rates, this work is an important step toward in vivo deep-tissue non-invasive optical imaging, manipulation, and therapy.
128 citations
TL;DR: By using a transmission matrix inversion method to achieve focusing, within a limited field of view and under a low noise condition in transmission matrix measurements, the PBR of the focus can be higher than that achieved by conventional methods such as optical phase conjugation or feedback-based wavefront shaping.
Abstract: Focusing light through scattering media has broad applications in optical imaging, manipulation and therapy. The contrast of the focus can be quantified by peak-to-background intensity ratio (PBR). Here, we theoretically and numerically show that by using a transmission matrix inversion method to achieve focusing, within a limited field of view and under a low noise condition in transmission matrix measurements, the PBR of the focus can be higher than that achieved by conventional methods such as optical phase conjugation or feedback-based wavefront shaping. Experimentally, using a phase-modulation spatial light modulator, we increase the PBR by 66% over that achieved by conventional methods based on phase conjugation. In addition, we demonstrate that, within a limited field of view and under a low noise condition in transmission matrix measurements, our matrix inversion method enables light focusing to multiple foci with greater fidelity than those of conventional methods.
44 citations
TL;DR: It is demonstrated that ideal compensation of nonlinear noise could result in an increase in the signal-to-noise ratio of 50%, and that reaches may be more than doubled for higher order modulation formats.
Abstract: Compensation of the detrimental impacts of nonlinearity on long-haul wavelength division multiplexed system performance is discussed, and the difference between transmitter, receiver, and in-line compensation analyzed. We demonstrate that ideal compensation of nonlinear noise could result in an increase in the signal-to-noise ratio (measured in dB) of 50%, and that reaches may be more than doubled for higher order modulation formats. The influence of parametric noise amplification is discussed in detail, showing how increased numbers of optical phase conjugators may further increase the received signal-to-noise ratio. Finally, the impact of practical real world system imperfections, such as polarization mode dispersion, are outlined.
21 citations
TL;DR: A DMD-based optical design is introduced that overcomes limitations and achieves dispersion-free high-speed binary phase modulation and can be used to switch through binary phase patterns at the rate of 20 kHz in two-photon excitation fluorescence applications.
Abstract: The controlled modulation of an optical wavefront is required for aberration correction, digital phase conjugation or patterned photostimulation. For most of these applications it is desirable to control the wavefront modulation at the highest rates possible. The digital micromirror device (DMD) presents a cost-effective solution to achieve high-speed modulation and often exceeds the speed of the more conventional liquid crystal spatial light modulator, but is inherently an amplitude modulator. Furthermore, spatial dispersion caused by DMD diffraction complicates its use with pulsed laser sources, such as those used in nonlinear microscopy. Here we introduce a DMD-based optical design that overcomes these limitations and achieves dispersion-free high-speed binary phase modulation. We show that this phase modulation can be used to switch through binary phase patterns at the rate of 20 kHz in two-photon excitation fluorescence applications.
18 citations
TL;DR: In this article, the regeneration of a subwavelength optical focus by phase conjugation was demonstrated. But the regeneration was performed at the far-field region by coupling its wavefront into a single-mode optical reflector using a spatial light modulator.
Abstract: Due to its time-reversal nature, optical phase conjugation generates a monochromatic light wave which retraces its propagation paths. Here, we demonstrate the regeneration of a subwavelength optical focus by phase conjugation. Monochromatic light from a subwavelength source is scattered by random nanoparticles, and the scattered light is phase conjugated at the far-field region by coupling its wavefront into a single-mode optical reflector using a spatial light modulator. Then the conjugated beam retraces its propagation paths and forms a refocus on the source at the subwavelength scale. This is the first direct experimental realisation of subwavelength focusing beyond the diffraction limit with far-field time reversal in the optical domain.
15 citations
TL;DR: The results demonstrate that phase conjugation can be used even when the photon budget is extremely low, such as in high-speed focusing through dynamic media or imaging deep inside tissue.
Abstract: We demonstrate experimentally that optical phase conjugation can be used to focus light through strongly scattering media even when far less than a photon per optical degree of freedom is detected. We found that the best achievable intensity contrast is equal to the total number of detected photons, as long as the resolution of the system is high enough. Our results demonstrate that phase conjugation can be used even when the photon budget is extremely low, such as in high-speed focusing through dynamic media or imaging deep inside tissue.
15 citations
01 Jan 2017
TL;DR: In this paper, the phase conjugation (PC) in the SBS-mirror that consists of an angular selector of Stokes radia-tion, an ordered raster of small lenses, a main focusing lens, and an SBScell was determined.
Abstract: Using the most complete in literature physical model of the non-steady-state stimulated Brillouin scattering (SBS), the nu-merical study is carried out of phase conjugation (PC) in the SBS-mirror that consists of an angular selector of Stokes radia-tion, an ordered raster of small lenses, a main focusing lens, and an SBS-cell. The ordered raster with controlled varying ofits parameters allows to perform the effective angular filtering ofnon-conjugated Stokes component, to reduce the local lightloads, and to avoid the competitive nonlinear effects. An optimal configuration of such SBS-mirror has been determined. Ithas the unique properties as compared with the current SBS-mirrors. It fixedly yields the PC quality that is near to an ideal(the PC coefficient is about of or more than 95%) at the selector transmittance 50-70% and any level of SBS saturation, i.e.any reflection coefficient. In the SBS-mirrors of different types the high PC quality in the focused beams takes place at thehigh reflection coefficients only that is difficult to realize as a rule. The first experimental data obtained at a Nd laser facilityshow the validity of the simulation results. The developed conception of SBS-mirror with unique properties can be appliedfor the improvement of wide class of industrial lasers.Key words: phase conjugation, stimulated Brillouin scattering.
7 citations
TL;DR: In this paper, the inverse van Cittert-Zernike theorem holds for EM fields propagating in free space, which essentially implies that spatially incoherent partially polarized field distributions can be generated from spatially coherent partially polarized optical fields.
Abstract: By using the property of phase conjugation, we demonstrate that the inverse of van Cittert–Zernike theorem holds for electromagnetic (EM) fields propagating in free space. This essentially implies that spatially incoherent partially polarized field distributions can be generated from spatially coherent partially polarized optical fields. We further utilize phase conjugation with a polarization rotator to swap the spatial coherence properties of orthogonal polarization components of EM fields on propagation, at least in free space. This study suggests that the method of phase conjugation could be potentially useful in arbitrarily manipulating spatial coherence properties of vector optical fields in the field plane.
4 citations
TL;DR: In this paper, the authors demonstrate that the efficiency of four-wave mixing (FWM) can be enhanced by inserting monolayer graphene in a properly designed photonic crystal (PC).
Abstract: We demonstrate theoretically that the efficiency of four-wave mixing (FWM) can be enhanced by more than several orders in monolayer graphene by inserting it in a properly designed photonic crystal (PC). Two kinds of cases are considered. One is monolayer graphene embedded in defect PC, and the other is a stack of monolayer graphene in a dielectric multilayer structure. It is found that a larger enhancement of the efficiency in the FWM from the monolayer graphene can be obtained in two cases. Such an effective enhancement utilizes the improved field localization within the defect state or at the band-edge state. Due to the presence of a feedback mechanism at each interface of the multilayer, we demonstrate that the tunable phase conjugation by an external voltage can be effectively generated when only one pump wave is used.
3 citations
Patent•
26 Apr 2017
TL;DR: In this article, a high-precision distributed optical fiber frequency transfer method was proposed, where local transferred frequency signals are subjected to frequency halving and then serve as detection signals, the signals are transmitted back and forth between the local end and a remote end through bidirectional wavelength division multiplexing, and detection signals comprising optical fiber link phase noise are obtained at the local-end.
Abstract: The invention discloses a high-precision distributed optical fiber frequency transfer method. Local transferred frequency signals are subjected to frequency halving and then serve as detection signals, the signals are transmitted back and forth between the local end and a remote end through bidirectional wavelength division multiplexing, and detection signals comprising optical fiber link phase noise are obtained at the local end; the returned detection signals and the local transferred frequency signals are subjected to frequency mixing and filtering to obtain phase conjugation signals, and the phase conjugation signals are transmitted to the optical fiber link through another wavelength channel; all users detect forward conjugation signals and backward detection signals, and stable frequency signals are obtained through frequency mixing; and the remote end carries out frequency mixing on the received forward phase conjugation signals and the forward detection signals to obtain stable frequency signals. Influences on frequency transfer short-term stability by backscattering noise can be avoided; the users share the same wavelength, and the fiber frequency long-term stability influences and the cost due to increasing of users can be reduced; and by adopting passive compensation, the method has the advantages of relatively simple and unlimited dynamic range and quick compensation.
02 Jul 2017
TL;DR: It is analytically shown that PSA provides high gain for in-phase component and almost cancellation for quadrature- Phase conjugation component of signal relative to pump phase under low pump power approximation.
Abstract: We propose and numerically verify a scheme of phase-sensitive amplifier (PSA) using frequency-shift free optical phase conjugation. PSA is obtained by combining the conjugated wave with original signal. The frequency-shift free operation of phase conjugation helps in preserving the frequency of input signal during phase-sensitive amplification The expression for PSA signal output and PSA gain are derived and it is analytically shown that PSA provides high gain for in-phase component and almost cancellation for quadrature-phase component of signal relative to pump phase under low pump power approximation. We prove theoretically that the proposed PSA provides 0 dB noise-figure with high gain-extension ratio. We study the performance of PSA under the effects of pump-signal detuning, amplifier length, input signal phase and signal power. Simulation results shows that PSA output is forced to attain 0 or π phase regardless of large variation of phase in input signal. Nonlinear phase noise reduction of 40 Gbps DPSK signal transmitted over 1000 km standard single mode fiber confirms phase-regeneration by PSA.
TL;DR: A pulsed phase conjugator system that projects a laser beam possessing a scene-dependent energy distribution that could significantly enhance performance if incorporated into a foliage-penetrating lidar system.
Abstract: We describe a pulsed phase conjugator system that projects a laser beam possessing a scene-dependent energy distribution. We expand upon the inherent properties of optical phase conjugation (OPC) to include not only corrections for phase aberrations but to provide targeted laser beam illumination of partially obscured objects. For instance, if incorporated into a foliage-penetrating lidar system, OPC could significantly enhance performance. We demonstrate this OPC beam projection concept experimentally.
TL;DR: A two-stage simulation technique to simulate phase-conjugated light propagation through scattering medium with macroscopic dimensions is reported, suitable for finite-difference time-domain (FDTD) technique, pseudospectral time- domain (PSTD), and other simulation techniques based upon numerical solutions of Maxwell's equations.
26 Jun 2017
TL;DR: In this paper, a pulsed phase conjugator is used to project a laser beam possessing a scene-dependent intensity distribution, bypassing a partial obscuration, with potential for enhancing foliage-penetrating lidar applications.
Abstract: We describe a method to project a laser beam possessing a scene-dependent intensity distribution, using a pulsed phase conjugator. We demonstrate projection of light, bypassing a partial obscuration, with potential for enhancing foliage-penetrating lidar applications.
01 Jan 2017
TL;DR: In this paper, a set of algorithms for fast and accurate phase evaluation, by fringe pattern processing, were derived and verified by studies of the optical phase conjugation fidelity in photorefractive crystals.
Abstract: 900 Bucharest, RomaniaABSTRACTConjugated wavefront fidelity has been evaluated using an interferometer with a phase conjugate mirror andfringe pattern computer processing. The quantitative interpretation of the fringe patterns is performed using directspatial phase reconstruction methods (in the space and Fourier domains). A set of algorithms for fast and accuratephase evaluation, by fringe pattern processing, were derived. The result of optical interferograms evaluation appears interms of different phase representations. These methods have been verified by studies of the optical phase conjugationfidelity in photorefractive crystals.Keywords: optical phase conjugation fidelity, phase demodulation1. INTRODUCTIONThe phase conjugation is optically characterised by two parameters: the "reflectivity" of the phase conjugatemirror and the fidelity of the conjugated wavefront reconstruction. The fidelity is the key parameter in many importantapplications of the Optical Phase Conjugation (OPC): image projection by OPC, interferometer with OPC mirrors,adaptive optics, phase distortion compensation in waveguides and in stimulated scattering processes.The evaluation of the OPC fidelity was done by (i) methods based on measurements of the conjugate wave
TL;DR: In this article, a long-coherence-length laser and an optimized digital optical phase conjugation (OPC) system were used to focus 532 nm light through tissue-mimicking phantoms up to 9.6 cm and 2.5 cm, respectively.
Abstract: Optical phase conjugation (OPC) based wavefront shaping techniques focus light through or within scattering media, which is critically important for deep-tissue optical imaging, manipulation, and therapy. However, to date, the sample thicknesses used in wavefront shaping experiments have been limited to only a few millimeters or several transport mean free paths. Here, by using a long-coherence-length laser and an optimized digital OPC system that efficiently delivers light power, we focused 532 nm light through tissue-mimicking phantoms up to 9.6 cm thick, as well as through ex vivo chicken breast tissue up to 2.5 cm thick.
TL;DR: The method of adaptive optimization of the wavefront (AOWF) for auxiliary image formation is implemented, since the simplicity and universality of AOWF method, this approach is useful for the fast basic 3D holographic image formation.
Abstract: In this paper we propose an investigation of digital optical phase conjugation (DOPC) method applicability and efficiency for the problem of three-dimensional (3D) holographic imaging. We validate the basic properties of developed DOPC-based method for different cases of imaging objects, from simple two-dimensional (2D) case to 3D figure composed of 2D polygons. We implement the method of adaptive optimization of the wavefront (AOWF) for auxiliary image formation. Since the simplicity and universality of AOWF method, this approach is useful for the fast basic 3D holographic image formation.
01 Nov 2017
TL;DR: In this article, the authors proposed virtual phase conjugation based optical tomography (VPC-OT) incorporated with the compensation of the optical aberration for improving the imaging quality.
Abstract: We propose virtual-phase-conjugation based optical tomography (VPC-OT) incorporated with the compensation of the optical aberration for improving the imaging quality. The compensation scheme is implemented by optically measuring the transmission function of the beam propagation. Then, we confirmed that this scheme greatly improves the signal level of VPC-OT.
TL;DR: In this paper, a tilt-type micro mirror array (MMA) was proposed for high-speed phase manipulation at high-resolution optical systems with high frame rate capabilities, where the standard application is grayscale amplitude control.
Abstract: The full complex, spatial modulation of light at high frame rates is essential for a variety of applications. In particular, emerging techniques applied to scattering media, such as Digital Optical Phase Conjugation and Wavefront Shaping, request challenging performance parameters. They refer to imaging tasks inside biological media, whose characteristics concerning the transmission and reflection of scattered light may change over time within milliseconds. Thus, these methods call for frame rates in the kilohertz range. Existing solutions typically over frame rate capabilities below 100 Hz, since they rely on liquid crystal spatial light modulators (SLMs). We propose a diffractive MEMS optical system for this application range. It relies on an analog, tilt-type micro mirror array (MMA) based on an established SLM technology, where the standard application is grayscale amplitude control. The new MMA system design allows the phase manipulation at high-speed as well. The article studies properties of the appropriate optical setup by simulating the propagation of the light. Relevant test patterns and sensitivity parameters of the system will be analyzed. Our results illustrate the main opportunities of the concept with particular focus on the tilt mirror technology. They indicate a promising path to realize the complex light modulation at frame rates above 1 kHz and resolutions well beyond 10,000 complex pixels.
01 Jul 2017
TL;DR: In this article, the authors analyzed nonlinearity mitigation by mid-link spectral inversion (SI) in WDM systems and showed that better XPM mitigation is achieved when the SI is applied to each channel but channel wavelengths are not exchanged in a dispersion-managed system.
Abstract: Nonlinearity mitigation by mid-link spectral inversion (SI) in WDM systems is analyzed. It is shown that better cross-phase modulation (XPM) mitigation is achieved when the SI is applied to each channel but channel wavelengths are not exchanged in a dispersion-managed system. Such SI needs channel-by-channel SI that is suitably performed by electro-optic phase conjugators.
01 Jan 2017
TL;DR: In this paper, the phase conjugation in a nonlinear composite slab was studied when the counter propagating pump waves are completely absorbed by means of coherent perfect absorption, and under the undepleted pump approximation the coupling constant and the phase-conjugated reflectivity were shown to undergo a substantial increase and multivalued response.
Abstract: We study phase conjugation in a nonlinear composite slab when the counter propagating pump waves are completely absorbed by means of coherent perfect absorption. Under the undepleted pump approximation the coupling constant and the phase conjugated reflectivity are shown to undergo a substantial increase and multivalued response. The effect can be used for efficient switching of the phase conjugated reflectivity in photonic circuits.
Patent•
02 Mar 2017TL;DR: In this article, a quantum optical phenomenon based on ultrasound low light and nondegenerate phase conjugation was used to increase the signal-to-noise ratio of an ultrasound-modulated optical signal by overcoming the shallow depth problem of in vivo optical imaging in existing optical imaging.
Abstract: The present invention provides a method which can significantly increase the signal-to-noise ratio of an ultrasound-modulated optical signal by overcoming the shallow depth problem of in vivo optical imaging in existing optical imaging by use of a quantum optical phenomenon based on ultraslow light and nondegenerate phase conjugation and which can be applied directly not only to medical optical imaging, but also to medical photodynamic therapy, through slow light amplification of phase conjugate waves.
01 Jan 2017
TL;DR: In this article, the phase conjugator after the filter is used to reverse and amplify ultrasound-tagged photons and send them back to the area of interest. But, the phase-conjugation process in these media is performed in a special case of Praseodymium-ion-doped crystals.
Abstract: With the development of extremely precise spectral filters based on spectral hole burning and slow light effects, the idea of their implementation in an Ultrasound Optical Tomography (UOT) medical imaging technique arose. Simulations have shown that the resulting Contrast-to-Noise (CNR) ratio is fairly good at depths up to 5 cm but decreases dramatically when probing deeper in tissue. One of the possible enhancements of this technique is to include a phase conjugator after the filter to reverse and amplify ultrasound-tagged photons and send them back to the area of interest. This project tries to investigate the possibilities of using rare-earth-ion-doped crystals as potential phase-conjugating elements in the UOT and is specifically aimed at studying the properties of an optical phase conjugation process in these media. Experimental work was done on two crystals doped with Praseodymium and the phase-conjugated signal was studied as a function of different parameters with results discussed and presented in the respective section. In particular, efficient phase conjugation was observed in a 6-mm thick Pr:YSO crystal with reflectivity values reaching up to 124 \%. Further outlook and possible applications are given at the end of the thesis. (Less)
01 Jan 2017
TL;DR: In this paper, a self-pumped phase conjugate (SPPC) wave is formed based on backward photorefractive scattering, and it is shown that this wave has high reflectivities.
Abstract: We present a new photorefractive crystal (Ce:BaTiO3) with superior photorefractive properties. Theformation of a self-pumped phase conjugate (SPPC) wave is based on backward photorefractive scattering.For a 0°-cut and a 45°-cut Ce:BaTiO3 crystals the SPPC reflectivities of7O% and 83.5% were achieved atx = 5 1 5 nm respectively. It has been experimentally demonstrated that this crystal is probably the mostefficient self-pumped phase conjugator in the visible spectral regime so far. Keyword: Ce:BaTiOs crystals, self-pumped phase conjugation, two wave mixing. 1.INTRODUCTION Photorefractive materials offers great promise for applications in the area of optical informationprocessing and phase conjugation', BaTiO3 is a particularly promising material, because the very largeelectro-pptic coefficient2 r42=l 3 OOpmJv yields correspondingly large values of two beam coupling gain,and phase conjugate reflectivity. It is possible to realize a variety of applications, such as holographicmemories, optical interconnections, optical neural networks, and self-pumped phase conjugations3. The
01 Jan 2017
TL;DR: In this article, the temporal behavior of phase conjugation reflectivity at degenerate four-wave mixing (DFWM) in lnSb for a pulsed CO laser radiation is theoretically investigated.
Abstract: A temporal behaviour of a phase conjugation reflectivity R at degenerate four-wave mixing (DFWM) in lnSb for a pulsed CO laser radiation is theoretically investigated. It is shown, that R at a transient DFWM is determined by a response time of a nonlinear medium, which depends on intensity of a radiation, and can be some times higher then a reflectivity for non
05 Sep 2017
TL;DR: In this article, the authors systematically review the results on reconstructing image quality by second order nonlinear crystal composites and show that the broadband and polarization-insensitive optical phase conjugated beams are generated with pretty low power, and they are successfully utilized to remove distortion caused by dynamic atmospheric turbulence.
Abstract: We systematically review our recent research results on reconstructing image quality by second order nonlinear crystal composites. The broadband and polarization-insensitive optical phase conjugated beams are generated with pretty low power, and they are successfully utilized to real-time remove distortion caused by dynamic atmospheric turbulence. Compared with transmission configuration, reflection configuration can be more practically utilized in field deployment. With necessary modifications and miniaturization of setup, it can be potentially incorporated in satellite for space exploration.
TL;DR: In this article, a self-pumped phase conjugation technique which involves a BaTiO3 crystal was introduced to suppress scattering noise derived from the object arm, prior to recording stage.
Abstract: In digital holography, techniques of noise suppression from the perspective of reference arm have been maturely developed. The object counterpart, however, is still in its infancy. Self-pumped phase conjugation technique which involves a BaTiO3 crystal was introduced unto reflective-type digital holographic microscopy to suppress scattering noise derived from the object arm, prior to recording stage. A phase distorter was introduced as scattering source, and signal-to-noise ratio was calculated. Furthermore, induced method was proposed to speed up the response time.