Showing papers on "Phase conjugation published in 2018"

Optical time reversal from time-dependent Epsilon-Near-Zero media

Abstract: We provide an efficient surface time-reversal of the incident electric field in an ENZ material producing both phase-conjugated and negative refracted beams. The results obtained exploiting degenerate four-wave mixing show an efficiency conversion over 200%.

Self-calibration of lensless holographic endoscope using programmable guide stars.

Abstract: Coherent fiber bundle (CFB)–based endoscopes enable optical keyhole access in applications such as biophotonics. In conjunction with objective lenses, CFBs allow imaging of intensity patterns. In contrast, digital optical phase conjugation enables lensless holographic endoscopes for the generation of pixelation-free arbitrary light patterns. For real-world applications, however, this requires a non-invasive in situ calibration of the complex optical transfer function of the CFB with only single-sided access. We show that after an initial calibration in a forward direction, a differential phase measurement of the back-reflected light allows for tracking and compensating of bending-induced phase distortions. Furthermore, we present a novel in situ calibration procedure based on a programmable guide star, which requires access to only one side of the fiber.

All-Optical Arbitrary-Point Stable Quadruple Frequency Dissemination With Photonic Microwave Phase Conjugation

Abstract: We present an all-optical stable quadruple frequency dissemination for an arbitrary-access-point fiber-optic loop link using photonic microwave phase conjugation. A two-tone optical carrier is transferred as a round-trip probe signal to undergo the propagation delay of the entire fiber loop link. When the probe signal returns to the local site, a Mach–Zehnder modulator biased at the null point is used as a phase conjugator to reverse its phase, thus, implementing photonic microwave phase conjugation. At an arbitrary remote site, the phase-conjugated signal is photomixed with a tapped forward transferred signal to obtain a stable frequency-quadrupled radio frequency (RF) signal in which the fiber-induced phase drift is automatically eliminated. Owing to photonic microwave phase conjugation and photomixing, the local oscillator leakage and harmonics interference of electrical mixers employed in the previous compensation schemes can be avoided. We demonstrate the stable dissemination of a 20-GHz frequency-quadrupled RF signal to two arbitrary remote sites located at a 20-km fiber-optic loop link. The residual root-mean-square timing jitter in an hour is no more than 0.86 ps. The relative frequency stability of 10 −16 level at 1000 s averaging time can be realized at every remote site.

Reference-free polarization-sensitive quantitative phase imaging using single-point optical phase conjugation.

Abstract: We propose and experimentally demonstrate a method of polarization-sensitive quantitative phase imaging using two photodetectors and a digital micromirror device. Instead of recording wide-field interference patterns, finding the modulation patterns maximizing focused intensities in terms of the polarization states enables polarization-dependent quantitative phase imaging without the need for a reference beam and an image sensor. The feasibility of the present method is experimentally validated by reconstructing Jones matrices of several samples including a polystyrene microsphere, a maize starch granule, and a mouse retinal nerve fiber layer. Since the present method is simple and sufficiently general, we expect that it may offer solutions for quantitative phase imaging of birefringent materials.

Automatic phase aberration compensation for digital holographic microscopy based on phase variation minimization.

Abstract: We propose a numerical and totally automatic phase aberration compensation method in digital holographic microscopy. The phase aberrations are extracted in a nonlinear optimization procedure in which the phase variation of the reconstructed object wave is minimized. Not only phase curvature but also high-order aberrations could be corrected without extra devices. The correction is directly carried out with the wrapped phase map, which is not affected by phase unwrapping or fitting errors. Numerical simulation proves that the proposed method is more accurate than the conventional surface fitting method without selecting a cell-free background. Experimental results demonstrate the availability of the proposed method in real-time analysis of living cells.

Analysis of the nonlinear Kerr effects in optical transmission systems that deploy optical phase conjugation.

Abstract: In this work, we will derive, validate, and analyze the theoretical description of nonlinear Kerr effects resulting from various transmission systems that deploy single or multiple optical phase conjugators (OPCs). We will show that the nonlinear Kerr compensation can be achieved, with various efficiencies, in both lumped and distributed Raman transmission systems. The results show that first order distributed Raman systems are superior to the discretely amplified systems in terms of the nonlinear Kerr compensation efficiency that a mid-link OPC can achieve. Also, we will show that the multi-OPC approach will diminish the nonlinearity compensation efficiency in any system as it will act as periodic dispersion compensators.

Reference-Free Single-Point Holographic Imaging and Realization of an Optical Bidirectional Transducer

Abstract: One of the fundamental limitations in photonics is the lack of a transducer for interconverting optical and electronic information. The experiments in this study demonstrate just such a bidirectional transducer, for measuring and modulating optical fields. The authors go on to propose an approach for reference-free holographic imaging by showing the unique determination of the pattern that maximizes focused intensity at a point as an optical phase conjugation, using the time-reversal symmetry of light scattering. Furthermore, broadband applicability of this approach is demonstrated, at visible and infrared wavelengths.

Reconstruction of structured laser beams through a multimode fiber based on digital optical phase conjugation.

Abstract: The digital optical phase conjugation (DOPC) technique is being actively developed for optical focusing and imaging through or inside complex media. Due to its time-reversal nature, DOPC has been exploited to regenerate different intensity targets. However, whether the targets with three-dimensional information through complex media could be recovered has not been experimentally demonstrated, to the best of our knowledge. Here, we present a method to regenerate structured laser beams based on DOPC. Although only the phase of the original scattered wave is time reversed, the reconstruction of a quasi-Bessel beam and vortex beams through a multimode fiber (MMF) is demonstrated. The regenerated quasi-Bessel beam shows the features of sub-diffraction focusing and a longer depth of field with respect to a Gaussian beam. Moreover, the reconstruction of vortex beams shows the fidelity of DOPC both in amplitude and phase, which is demonstrated for the first time, to the best of our knowledge. We also prove that the reconstruction results of DOPC through the MMF are indeed phase conjugate to the original targets. We expect that these results could be useful in super-resolution imaging and optical micromanipulation through complex media, and further pave the way for achieving three-dimensional imaging based on DOPC.

Brillouin Dynamic Gratings-A Practical Form of Brillouin Enhanced Four Wave Mixing in Waveguides: The First Decade and Beyond.

Abstract: Brillouin-Enhanced Four-Wave-Mixing techniques, which couple four optical beams through Brillouin nonlinearity, have gained popularity in the 1980’s largely owing to their phase conjugation properties Experiments were mainly conducted in liquid cells The interest in Brillouin-Enhanced Four-Wave-Mixing has reawakened in the 2000’s, following the quest for dynamically reconfigurable gratings in optical fibers Termed Brillouin Dynamic Grating this time around, it is, in fact, an acoustic wave, optically generated by stimulated Brillouin scattering process between two pump waves The acoustic wave either carries the coherent information encoded by the pump beams, or in the case of sensing applications, its properties are determined by the environmental parameters This information, in turn, is imparted to the third phase-matched optical probe wave through the elasto-optic effect Over the last decade, this mechanism allowed for the realization of many all-optical signal processing functions and has proven instrumental in distributed sensing applications This paper describes the basics, as well as the state of the art, of BDG-based applications in optical fibers It also surveys the efforts being done to carry over these concepts to the photonic chip level

Kilohertz binary phase modulator for pulsed laser sources using a digital micromirror device

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.

Experimental demonstration of 72% reach enhancement of 3.6Tbps optical transmission system using mid-link optical phase conjugation

Abstract: We experimentally demonstrate nonlinear noise compensation in an optical phase conjugation assisted 1st order Raman amplified 30x30Gbaud DP-QPSK transmission system with a spectral efficiency of 3.6b/s/Hz. We show that by optimizing the link symmetry, even with only 1st order Raman amplification a single, mid-link, optical phase conjugation compensates for 90% of the signal-signal nonlinear interference resulting in a 2.3dB performance enhancement. We show that increasing the number of optical phase conjugations in the presence of 10% residual nonlinearity results in a reduction in the performance enhancement owing to an enhancement in the nonlinear noise generation efficiency of the system. We achieve a record 72% optical phase conjugation enabled reach enhancement of the 30x30Gbaud DP-QPSK signals.

Intensity-based adaptive optics with sequential optimization for laser communications

Abstract: Wavefront distortions of optical waves propagating through the turbulent atmosphere are responsible for phase and amplitude fluctuations, causing random fading in the signal coupled into single-mode optical fibers. Wavefront aberrations can be confronted, in principle, with adaptive optics technology that compensates the incoming optical signal by the phase conjugation principle and mitigates the likeliness of fading. However, real-time adaptive optics requires phase wavefront measurements, which are generally difficult under typical propagation conditions for communication scenarios. As an alternative to the conventional adaptive optics approach, here, we discuss a novel phase-retrieval technique that indirectly determines the unknown phase wavefront from focal-plane intensity measurements. The adaptation approach is based on sequential optimization of the speckle pattern in the focal plane and works by iteratively updating the phases of individual speckles to maximize the received power. We found in our analysis that this technique can compensate the distorted phasefront and increase the signal coupled with a significant reduction in the required number of iterations, resulting in a loop bandwidth utilization well within the capacity of commercially available deformable mirrors.

Polarization-insensitive phase conjugation using single pump Bragg-scattering four-wave mixing in semiconductor optical amplifiers.

Abstract: We explain the generation of four wave mixing (FWM) components at the front and back facets of semiconductor optical amplifiers (SOAs) based on the Bragg-scattering from the propagating gratings in the SOAs. We propose a counter-propagating cross-polarized degenerate pumping scheme for the polarization-insensitive conjugate generation, simultaneously in both input and output ports of the SOA for the first time. The corresponding Bragg scattering processes along with the phase matching conditions are described and the detuning performance of the generated conjugate in either port are experimentally validated. Polarization-insensitive phase conjugate generation at both input and output ports of the SOA through Bragg scattering FWM is further demonstrated.

Enhancement of phase conjugation degenerate four-wave mixing using a Bessel beam

Abstract: We report on the enhancement of phase conjugation degenerate four-wave mixing (DFWM) in hot atomic Rb vapor by using a Bessel beam as the probe beam. The Bessel beam was generated using cross-phase modulation based on the thermal nonlinear optical effect. Our results demonstrated that the DFWM signal generated by the Bessel beam is about twice as large as that generated by the Gaussian beam, which can be attributed to the extended depth and tight focusing features of the Bessel beam. We also found that a DFWM signal with reasonable intensity can be detected even when the Bessel beam encounters an obstruction on its way, thanks to the self-healing property of the Bessel beam. This work not only indicates that DFWM using a Bessel beam would be of great potential in the fields of high-fidelity communication, adaptive optics, and so on, but also suggests that a Bessel beam would be of significance to enhance the nonlinear process, especially in thick and scattering media.

High-speed alignment optimization of digital optical phase conjugation systems based on autocovariance analysis in conjunction with orthonormal rectangular polynomials

Abstract: Digital optical phase conjugation (DOPC) enables many optical applications by permitting focusing of light through scattering media. However, DOPC systems require precise alignment of all optical components, particularly of the spatial light modulator (SLM) and camera, in order to accurately record the wavefront and perform playback through the use of time-reversal symmetry. We present a digital compensation technique to optimize the alignment of the SLM in five degrees of freedom, permitting focusing through thick scattering media with a thickness of 5 mm and transport scattering coefficient of 2.5 mm − 1 while simultaneously improving focal quality, as quantified by the peak-to-background ratio, by several orders of magnitude over an unoptimized alignment.

Phase conjugate digital inline holography (PCDIH).

Abstract: Digital inline holography (DIH) provides instantaneous three-dimensional (3D) measurements of diffracting objects; however, phase disturbances in the beam path can distort the imaging In this Letter, a phase conjugate digital inline holography (PCDIH) configuration is proposed for removal of phase disturbances Brillouin-enhanced four-wave mixing produces a phase conjugate signal that back propagates along the DIH beam path The results demonstrate the removal of distortions caused by gas-phase shocks to recover 3D images of diffracting objects

96-Gbaud PDM-8QAM Single Channel Transmission over 9,600 km by Nonlinear Tolerance Enhancement using PPLN-based Optical Phase Conjugation

Abstract: 96-Gbaud PDM-8QAM single carrier long-haul transmission is demonstrated employing polarization-diverse PPLN-based optical phase conjugator which increased the optimal fiber input power by 4dB and extends the transmission distance from 7,040 km to 9,600km.

Bidirectional image transmission through physically thick scattering media using digital optical phase conjugation

Abstract: We demonstrate the feasibility of bidirectional image transmission through a physically thick scattering medium within its memory effect range by digital optical phase conjugation. We show the bidirectional transmission is not simply the consequence of optical reciprocity. We observe that when the spatial light modulator (the device performing the digital optical phase conjugation) is relayed to the middle plane of the medium, the memory effect will be fully exploited and thus the transmitted images will have maximum field of view (FOV). Furthermore, we show that the FOV can be expanded n times by performing n times wavefront measurements.

Nonlinear graphene metasurfaces with advanced electromagnetic functionalities

Abstract: The optical nonlinear effects can provide different advanced electromagnetic functionalities, such as wave mixing and phase conjugation, which can be applied in a variety of new applications. However, these effects usually suffer from extremely weak nature and require high input intensity values in order to be excited. Interestingly, the large third order nonlinearity of graphene, along with the strong field confinement stemming from its plasmonic behavior, can be utilized to enhance several relative weak nonlinear effects at infrared (IR) and terahertz (THz) frequencies. Towards this goal, various nonlinear graphene metasurfaces are presented in this work to effectively increase the efficiency of different optical nonlinear effects and, as a result, decrease the required input intensity needed to be excited. In particular, we will show that the efficiency of four-wave mixing (FWM) can be improved by several orders of magnitude by using a nonlinear metasurface composed of patterned graphene ribbons, a dielectric interlayer, and a metallic reflector acting as substrate. We also demonstrate that the self-phase modulation (SPM) nonlinear process can be enhanced by using an alternative graphene nonlinear metasurface, operating as coherent perfect absorber, leading to a pronounced shift in the resonant frequency of the coherent perfect absorption (CPA) effect of this structure as the input intensity of the impinging incident waves is increased. This property will provide a robust mechanism to dynamically tune and switch the CPA process. Furthermore, it will be presented that strong negative reflection and refraction can be achieved by a single graphene monolayer film due to the enhancement of another nonlinear process, known as phase conjugation. This nonlinear process is envisioned to be used in the construction of a perfect imaging device with subwavelength resolution.

Link-Placement Characterization of Optical Phase Conjugation for Nonlinearity Compensation

Abstract: The impact of the OPC offset on the nonlinearity compensation is experimentally investigated, achieving gains up to 0.6-dB SNR and 0.17-bit/symbol mutual information with optimal mid-link OPC for dispersion-compensated transmission up to 966 km.

Silicon Waveguide with Lateral p-i-n Diode for Nonlinearity Compensation by On-Chip Optical Phase Conjugation

Abstract: A 1-dB Q-factor improvement through optical phase conjugation in a silicon waveguide with a lateral p-i-n diode enables BER

Optical Phase Conjugation in Installed Optical Networks

Abstract: We demonstrate a record throughput of 5.7 Tbit/s employing an optical phase conjugator to jointly compensate chromatic dispersion and increase the nonlinear threshold in an installed optical network using commercially available lumped amplifiers.

PDL Impact on Linearly Coded Digital Phase Conjugation Techniques in CO-OFDM Systems

Abstract: We investigate the impact of polarization-dependent loss (PDL) on the linearly coded digital phase conjugation (DPC) techniques in coherent optical orthogonal frequency-division multiplexing superchannel systems. We consider two DPC approaches: one uses orthogonal polarizations to transmit the linearly coded signal and its phase conjugate, while the other uses two orthogonal time slots of the same polarization. We compare the performances of these DPC approaches by considering both aligned- and statistical-PDL models. The investigation with an aligned-PDL model indicates that the latter approach is more tolerant to PDL-induced distortions when compared with the former. Furthermore, the study using the statistical-PDL model shows that the outage probability of the latter approach tends to zero at a root mean square PDL value of 3.6 dB. On the other hand, the former shows an outage probability of 0.63 for the same PDL value.

Distributed Raman Amplification for Combating Optical Nonlinearities in Fibre Transmission

Abstract: The paper reviews distributed Raman amplification technologies which can provide near symmetric signal power profiles, in order to maximize the efficiency of optical nonlinearity compensation in long-haul optical transmission systems using mid-link optical phase conjugation.

Quadruplicated frequency signal optical fiber arbitrary point steady-phase distribution system based on phase conjugation

Abstract: The invention provides a quadruplicated frequency signal optical fiber arbitrary point steady-phase distribution system based on phase conjugation and belongs to the technical field of optical fiber steady-phase distribution; the system comprises an annular optical fiber link structure mainly composed of a local end, n far-end stations, n +1 sections of optical fiber links and n optical fiber couplers, wherein the local station comprises a microwave source, a dual-carrier wave optical signal generating module, a phase conjugated optical signal generating module, an optical fiber coupler, a first photoelectric detector and an optical fiber circulator; and each of the far-end stations respectively comprises an electro-optical frequency mixing module, an optical amplifier, a second photoelectric detector, an electric amplifier and an electric filter. The main device used by the system is a photonic device; due to the high-frequency broadband characteristic of the photonic device, the system can achieve optical fiber long-distance stable phase distribution of higher frequency signals; and the problem of deterioration of the phase stability precision caused by local oscillator leakage and harmonic interference introduced when an electric mixer is used is effectively avoided.

Experimental implementation of multiplexing/demultiplexing in digital images using virtual phase conjugation for holographic data storage

Abstract: We experimentally implemented and proved the concept of multiplexing and demultiplexing in digital images using virtual phase conjugation, which was proposed in our previous study. In the experiment, we concluded that two digital images multiplexed in a single signal beam are recorded in a holographic medium, and these images are independently and successfully reproduced. In this method, the digital images are multiplexed by superimposing them on a complex amplitude, and not using volume hologram’s multiplexing. Thus, the exposure amount in the holographic medium is constant regardless of the number of multiplexing of digital images, and the method has great potential for achieving high recording density.

Optical phase conjugation of diffused light with infinite gain by using gated two-color photorefractive crystal LiNbO3:Cu:Ce.

Abstract: Light focusing in multiple scattering circumstances is important in biomedical imaging, manipulation, and therapy. Until now, many traditional photorefractive crystals have been used to generate an optical phase conjugated wavefront in an analogue time-reversed optical focusing technology. However, owing to erasure of a volume hologram during a reading procedure, the optical energy gain can never reach unity, limiting its application in delivering more energy into a target area. In this work, we investigated a gated two-color photorefractive crystal LiNbO3:Cu:Ce to generate optical phase conjugation of diffused light with infinite gain.

Phase conjugation and mode conversion in stimulated parametric down-conversion with orbital angular momentum: a geometrical interpretation

Abstract: We report on an experiment that investigates the spatial mode conversion in the process of parametric down-conversion seeded by a light beam in a superposition of orbital angular momentum modes. This process is interpreted in terms of a geometric representation of first-order spatial modes in a Poincar\'e sphere, providing an intuitive image of the phase conjugation and the topological charge conservation. We also make a comparison with the analogous phenomenon for optical parametric oscillators.

Salient Features of Temporal and Spatio-Temporal Metamaterials

Abstract: In this communication we explore both analytically and numerically the exciting phenomena that can be obtained when the electromagnetic material parameters (permittivity and/or permeability) are rapidly changed in time. We will show how such a temporal change can be exploited to achieve phase conjugation of a monochromatic wave using a rapid periodic temporal variation of permittivity/permeability in a in a spatio-temporal slab/lens. Moreover, it will be also shown how a rapid variation of permittivity from a positive to a negative value in a physically (spatially) unbounded medium can lead to the enhancement of a stationary electromagnetic wave (i.e., a frozen field in the space without propagation).