Phase Conjugation Research Articles

A Wide-Angle and PON Fully Polarimetric Retrodirective Array at the X Band

A new type of fully polarimetric retrodirective array (RDA) using a PON-type structure is proposed in this paper. The fully polarimetric property is the result of the proposed phase conjugation circuits, which perform phase conjugation processing on the x, y, and z polarization electric field components of the incident wave when combined with a tri-polarized antenna array. It enables the retrodirective array to receive and retransmit an arbitrary polarized incident wave. The measured results of the monostatic radar cross-section (RCS) show that the −5 dB beam width of the array was greater than 95° at 9.6 GHz for different polarized incident waves. Furthermore, the proposed RDA has better retrodirectivity performance on arbitrary polarized incident waves when using a wide-beam antenna, and if we further incorporate modulation and demodulation into the circuits, it has the potential to be applied to the wireless communications field.

Optically enhanced pump-phase noise in mid-link optical parametric phase conjugation.

This paper discusses the impact of pump-phase noise in the χ(2)-based optical parametric amplification process on the phase-conjugated idler. We show that the dispersive fiber propagation of the phase-conjugated idler causes the optically enhanced pump-phase noise (OEPN) effect including a group-velocity jitter. The signal penalty caused by the OEPN in the mid-link optical phase conjugation systems was quantified analytically and proved by numerical simulations. We also experimentally evaluated the OEPN with an optical parametric phase conjugator using periodically poled LiNbO3 waveguides. With a 96-Gbaud probabilistically constellation-shaped 64QAM signal, the experimental results were in good agreement with the analytically derived penalty in a standard single-mode fiber link up to 800 km.

Vector modulation of fully-polarized phase conjugate light field through scattering media

Vector modulation of the light field through scattering media holds significant scientific and application value in areas such as optical imaging, optical communications, nonlinear optics, and biomedicine. Digital optical phase conjugation (DOPC), grounded in the time reversal principle, has been extensively investigated for wavefront shaping in scattering media. Nonetheless, reports on vector modulation of phase conjugate beams via DOPC remain scarce. In this study, we propose a vector DOPC to recover and modulate the polarization state of the phase conjugate beams based on vector decomposition and superimposition of light field. First, pre-set two orthogonal polarization basis probe beams to pass through a multimode fiber and use digital holography to record the phase distribution of their orthogonal polarization components in the speckle field. Then, perform polarization-preserving phase conjugation and vector superposition of both components simultaneously. By altering the phase difference and amplitude ratio between the two, vector modulation of the synthesized phase conjugate beam can be achieved. Theoretical analysis aligns well with experimental results, demonstrating a positive impact on understanding the physical properties of scattering media and expanding the applications of the DOPC technique.

Nonlinear dispersion of backward-wave four-wave mixing in a photorefractive semiconductor and its effect on group velocity

Photorefractive backward-wave four-wave mixing may be configured for the amplification of the phase conjugate output and the attenuation of the transmitted output. The nondegenerate-in-frequency interaction is studied in such a configuration, realized in a semiconductor CdTe crystal. The spectra measured at different outputs show the gain and attenuation resonances. The preliminary study of optical pulse propagation demonstrates that, due to different nonlinear dispersions at different outputs of the selected wave mixing configuration, a slowing down of light is observed at the phase conjugate output, while an acceleration of light is detected at the transmitted output for the same input pulse at the same interaction.

Study of a Crosstalk Suppression Scheme Based on Double-Stage Semiconductor Optical Amplifiers

An all-optical crosstalk suppression scheme is desirable for wavelength and space division multiplexing optical networks by improving the performance of the corresponding nodes. We put forward a scheme comprising double-stage semiconductor optical amplifiers (SOAs) for wavelength-preserving crosstalk suppression. The wavelength position of the degenerate pump in the optical phase conjugation (OPC) is optimized for signal-to-crosstalk ratio (SXR) improvement. The crosstalk suppression performance of the double-stage SOA scheme for 20 Gb/s quadrature phase shift keying (QPSK) signals is investigated by means of simulations, including the input SXR range and the crosstalk wavelength deviation. For the case with identical-frequency crosstalk, the double-stage SOA scheme can achieve equivalent SXR improvement of 1.5 dB for an input SXR of 10 dB. Thus, the double-stage SOA scheme proposed here is more suitable for few-mode fiber systems and networks.

Stability enhancement with nonlinear gain modulation in high-power SBS-PCM

Stimulated Brillouin scattering (SBS) is an effective method for compensating wavefront aberrations in high-energy lasers due to its phase conjugation property. However, SBS phase conjugate mirrors (SBS-PCMs) under high-power pumping often suffer from significant spatial aberrations and decreased energy reflectivity, indicating instability in the nonlinear gain. Here, a nonlinear gain modulation method is proposed to realize the stable output. Experiments show that the energy reflectivity of SBS decreased due to the thermal effect in high-repetition-rate pumped SBS-PCMs. The nonlinear gain modulation was accomplished with simultaneous adaptation of radial and axial focusing parameters resulting in a higher SBS gain under short-focus conditions. The feasibility of the method was experimentally confirmed by obtaining SBS energy reflectivity stabilized at 60%, while the root mean squares of steady-state Stokes energy and pulse time delay enhanced to 1.97% and 1.81%, respectively, in an HT-230 medium. This scheme ensures stable and efficient SBS output under high-power pumping, which is of great significance for expanding the application of SBS-PCMs in high-repetition-rate laser systems.

Atomic orbitals modulated dual functional bimetallic phosphides derived from MOF on MOF structure for boosting high efficient overall water splitting

The electronic modulation characteristics of efficient metal phosphide electrocatalysts can be utilized to tune the performance of oxygen evolution reaction (OER). However, improving the overall water splitting performance remains a challenging task. By building metal organic framework (MOF) on MOF heterostructures, an efficient strategy for controlling the electrical structure of MOFs was presented in this study. ZIF-67 was in-situ synthesized on MIL-88 (Fe) using a two-step self-assembly method, followed by low-temperature phosphorization to ultimately synthesize FeP-CoP3 bimetallic phosphides. By combining atomic orbital theory and theoretical calculations (density functional theory), the results reveal the successful modulation of electronic orbitals in FeP-CoP3 bimetallic phosphides, which are synthesized from MOF on MOF structure. The synergistic impact of the metal center Co species and the phase conjugation of both kinds of MOFs are responsible for this regulatory phenomenon. Therefore, the catalyst demonstrates excellent properties, demonstrating HER 81 mV (η10) in a 1.0 mol L−1 KOH solution and OER 239 mV (η50) low overpotentials. The FeP-CoP3 linked dual electrode alkaline batteries, which are bifunctional electrocatalysts, have a good electrocatalytic ability and may last for 50 h. They require just 1.49 V (η50) for total water breakdown. Through this technique, the electrical structure of electrocatalysts may be altered to increase catalytic activity.

Field trial of stable radio frequency transfer system in 200 km metropolitan optical fiber link.

In this paper, we demonstrate stable radio frequency (RF) transfer via metropolitan optical fiber link in the Beijing area. The phase variation of the RF signal is compensated by a phase conjugation method incorporating two high-performance phase-locked loops. The wavelength conversion module extends the transmission length to 200 km with only two parallel 50 km dark optical fibers available. We optimize the configuration of dispersion compensation and optical amplification due to the high loss (0.31 dB/km) of the optical fiber link. At the same time, comparative experiments verify the short-term instability limitation that arises from the group velocity dispersion of the optical fiber link. The measured standard Allan deviation of the 2.4GHz RF transmission system with dispersion compensation is 4.5 × 10-14/1 and 2.6 × 10-17/20 000s, which is superior to that of the reference rubidium clock. The short-term instability of the system is deteriorated to 2.5 × 10-13/1s without dispersion compensation.

High-precision alignment of optoelectronic devices for optical phase conjugation

Abstract Digital optical phase conjugation (DOPC) is considered as a promising solution to achieve optical focusing against scattering. The implementation of DOPC based on the digital micromirror device (DMD) has been proven to have great potential, supporting a large number of modulation modes and a high modulation rate. However, the accuracy of optical alignment seriously affects the focusing contrast, limiting the applications of DMD-based DOPC systems. Here we demonstrate a simple alignment protocol including a marker-assisted tuning and an embedded compensation. Our approach can realize an exact pixelwise optical conjugation between the DMD and detector, as well as a rapid compensation for aberrations and minor misalignment. Experimental results show that the proposed alignment protocol improves the focusing contrast to 66% of the highest value predicted in the theory.

Phase gradient metasurface for arbitrary three-dimensional shaped near-field

This paper proposes a methodology for generating arbitrary three-dimensional (3D) shaped near-field using phase gradient metasurface (PGMS) based on phase conjugation (PC) backtracking and shaped diffraction-free Bessel beam array techniques. The PGMS is designed by combining MATLAB and electromagnetic (EM) simulation software (CST). To the knowledge of the authors, for the first time, a 3D-shaped near-field is generated without increasing cost, structural and calculating complexity, and a methodology for generating arbitrarily shaped diffraction-free beam array is developed by MATLAB. To verify the technique, a planar PGMS is designed for dual x-polarized 3D-shaped near-fields: qq image “” in direction (θ1 = 5°, φ1 = 0°) and a flower image “” in direction (θ2 = 10°, φ2 = 180°). The advantages of the 3D-shaped near-fields are as follows: high conversion efficiency 30.5% (measured), wideband 60.5%, and low sidelobe -15 dB. The proposed technique is confirmed by the calculated, simulated, and measured results.

A Study of Degenerate Four‐Wave Mixing and Phase Conjugation in Metallic Nanohybrids

AbstractA theory of degenerate four‐wave mixing (DFWM) and phase conjugation is developed for metallic nanohybrids, which consist of an ensemble of interacting metallic nanoshells and noninteracting quantum dots (QDs). It is considered that three incident waves are applied to the metallic nanohybrid, and they produce a fourth output mixed wave. These waves induce dipoles in metallic nanoshells, generating surface plasmon polaritons, and interact with each other via the dipole–dipole interactions (DDI). In DFWM, the input and output waves travel in opposite directions, and this retroreflective nature is responsible for the phenomenon of phase conjugation. The analytical expressions for the input transmitted and output reflected wave intensities are calculated in the presence of the surface plasmon polaritons (SPPs) and the DDI polaritons. It is demonstrated that the phase conjugation, the phase coherent phenomena, and the intensities of both input transmitted and output reflected waves are enhanced due to SPPs and DDI polaritons. These findings indicate that the nanohybrid acts as a phase conjugate device and a phase coherent optical amplifier, which can be applied to fabricate optical nanoamplifiers, phase conjugate mirrors, and nanosensors by measuring the intensity of the output reflected wave.

STAR-FDTD: space-time modulated acousto-optic guidestar in disordered media

Abstract We developed a 2D Finite-difference time-domain (FDTD) method for modeling a space-time modulated guidestar targeting wavefront shaping applications in disordered media. Space-time modulation in general (a particular example being the acousto-optic effect) is used here as a guidestar for the transverse confinement of light around the tagged region surrounded by disorder. Together with the guidestar, the iterative optical phase conjugation (IOPC) method is used to overcome the diffusion of light due to multiple scattering. A phase sensitive lock-in detection technique is utilized to estimate the steady-state amplitude and phase of the modulated wavefronts emerging from the guidestar region continuously operating in the Raman-Nath regime. As the IOPC scheme naturally converges to the maximally transmitting eigenchannel profile, one could use the position of the guidestar within the disorder to channelize the maximal transmission through the tagged region. The associated code developed in MATLAB® is provided as an open source (The MIT License) package. The code package is referred by the acronym STAR-FDTD where STAR stands for Space-Time modulated Acousto-optic guidestaR.

Record bandwidth waveband-shift-free optical phase conjugation in nonlinear fiber optical loop mirror.

We present a novel configuration for broadband, wavelength-shift-free optical phase conjugation (OPC) utilizing four-wave mixing in a nonlinear fiber optical loop mirror (NOLM). In the proposed configuration, the input signals and the pump wave return to the input port of the NOLM whereas the phase-conjugated signals generated in the NOLM loop are transmitted through the output port. This allows the phase-conjugated copies to occupy the same wavelength band as the input signals, in line with the requirements for practical deployment of OPC in communication links. The demultiplexing of the phase conjugates from the input signals sharing the same band is achieved by imparting an asymmetric phase shift on the pump via a fiber Bragg grating. We experimentally demonstrate waveband-shift-free OPC with an extinction ratio between signals and conjugated copies at the NOLM output of 17 dB to 25 dB across a band of 35 nm. Whilst a 7-nm wide performance gap exists in the middle of the band, this is the record bandwidth for waveband-shift-free OPC in an all-fiber setup. We compare the experimental results with numerical simulations of the OPC-NOLM, identify the reason for the observed performance gap, and justify the route for further performance improvement.

Analysis of speckle-beacon size impact on wavefront sensing and closed-loop control in deep turbulence conditions

The impact of the laser beacon size on the performance of an ideal phase-conjugation-type adaptive optics (AO) system is analyzed using wave-optics-based numerical simulation. The analysis includes wavefront aberration sensing and closed-loop control for laser beam propagation both in vacuum and in distributed (volume) atmospheric turbulence with the beacon beam scattering off a flat extended target with Lambertian surface roughness. For mitigation of the impact of target-induced speckle effects on the performance of AO systems, speckle-average wavefront sensing and control approaches are introduced and analyzed. The results demonstrate that proposed speckle-average phase conjugation control algorithms enable partial mitigation of turbulence-induced aberrations in presence of strong speckle modulations.

Generating Arbitrary Shaped Near-Field With Arbitrary Polarization by Combining Tensor Holographic Impedance Metasurface and Phase Conjugation Techniques

Generating Arbitrary Shaped Near-Field With Arbitrary Polarization by Combining Tensor Holographic Impedance Metasurface and Phase Conjugation Techniques

3D fluorescence imaging through a scattering medium using the transport of intensity equation and Fresnel ping-pong algorithm.

A three-dimensional (3D) fluorescent imaging method through a scattering medium has been presented. The proposed method combines digital phase conjugate reconstruction of the scattered light wave by the transport of intensity equation-based 3D fluorescent imaging to the position of scattering medium and followed phase retrieval method by Fresnel ping-pong algorithm. The effectiveness of the proposed method is experimentally verified by measuring the 3D distribution of fluorescent beads and tobacco-cultured cells through a thin diffuser. Compared to other methods, the reconstructed images show enhancement of the detailed structure of the objects blurred by the diffuser in a wide area. In the simulation, the proposed method is capable of recovering images degraded by scattering in the phase modulation range from 0 to 2π. The capability to identify the depth position is also presented.

Hybrid optical-electronic compensation of fiber nonlinearity for long-haul coherent optical transmission

Abstract From the concepts of the dispersion-folded digital backward propagation (DBP) and optical phase conjugation (OPC), a hybrid optical-electronic nonlinearity-compensation scheme is proposed to enhance the system performance of the dispersion-managed transmission. The computational complexity of the proposed scheme, compared with that of the conventional DBP method, is reduced significantly while the performance penalty is negligible. The compensation efficiency of the proposed scheme has been validated in a 5 (and 9)-channel PM-16QAM system at 256 Gbit/s.

All-optical phase conjugation using diffractive wavefront processing

Optical phase conjugation (OPC) is a nonlinear technique used for counteracting wavefront distortions, with applications ranging from imaging to beam focusing. Here, we present a diffractive wavefront processor to approximate all-optical phase conjugation. Leveraging deep learning, a set of diffractive layers was optimized to all-optically process an arbitrary phase-aberrated input field, producing an output field with a phase distribution that is the conjugate of the input wave. We experimentally validated this wavefront processor by 3D-fabricating diffractive layers and performing OPC on phase distortions never seen during training. Employing terahertz radiation, our diffractive processor successfully performed OPC through a shallow volume that axially spans tens of wavelengths. We also created a diffractive phase-conjugate mirror by combining deep learning-optimized diffractive layers with a standard mirror. Given its compact, passive and multi-wavelength nature, this diffractive wavefront processor can be used for various applications, e.g., turbidity suppression and aberration correction across different spectral bands.

A Phase Conjugator Based on Fourth-Order Subharmonically Pumped Mixers

A Phase Conjugator Based on Fourth-Order Subharmonically Pumped Mixers

Low Concentration of Wenyang Tonglin Decoction Promotes Conjugation and Transfer of Drug-Resistant Plasmids among Heterologous Strains.

To investigate the effect of low concentration of Wenyang Tonglin Decoction (WTD) on the binding conditions of R45 plasmid conjugative transfer under liquid phase conjugation and its mechanism. Escherichia coli CP9 (R45) and Staphylococcus aureus RN450RF were cultured in medium containing WTD, and their minimum inhibitory concentration (MIC) values were obtained. Using promoter fusion technology, E. coli CP9 (R45) containing a promoter fusion was obtained. β-Galactosidase activity of TrfAp and TrbBp was tested, and the mRNA expression of regulatory factors (TrbA, KorA, and KorB) was detected by real-time fluorescent quantitative polymerase chain reaction. The MIC of E. coli CP9 (R45) was 400 g/L and that of S. aureus RN450RF was 200 g/L. When the drug concentration in the culture medium was 200 g/L, the highest number of conjugants was (3.47 ±0.20) × 107 CFU/mL At 90 h of conjugation, the maximum number of conjugants was (1.15 ±0.06) × 108 CFU/mL When the initial bacterial concentration was 108 CFU/mL, the maximum number of conjugants was (3.47 ± 0.20) × 107 CFU/mL. When the drug concentration was 200 g/L, the β-galactosidase activity of TrfAp and TrbBp significantly increased; the relative quantification of TrbA, KorA and KorB were significantly inhibited. Low concentration of WTD promoted the development of bacterial resistance by affecting promoters and inhibiting the expression of regulatory factors.