Random Polarization Research Articles

Polarization Diverse True Heterodyne Receiver Architecture for Continuous Variable Quantum Key Distribution

We present a polarization diverse receiver architecture for continuous variables quantum key distribution. Our receiver architecture forgoes the need for any polarization matching calibrations or feedback loops and is usable in any locally generated local oscillator key distribution system. We demonstrate experimentally that our system is capable of reliably achieving theoretical security against coherent attacks, even under very adverse random polarization drift scenarios, where the single polarization channels are unable to achieve security, and is capable of functioning for long periods of time.

Optical Field Recovery in Jones Space

Optical full-field recovery allows for fiber impairments compensation such as chromatic dispersion and polarization mode dispersion (PMD) in the digital signal processing. For cost-sensitive short-reach optical networks, some advanced single-polarization (SP) optical field recovery schemes are recently proposed to avoid chromatic dispersion-induced power fading effect and improve the spectral efficiency for larger potential capacity. Polarization division multiplexing (PDM) can further double both the spectral efficiency and the system capacity of these SP carrier-assisted direct detection (DD) schemes. However, the so-called polarization fading phenomenon induced by random polarization rotation is a fundamental obstacle that prevents SP carrier-assisted DD systems from polarization diversity. In this paper, we propose a receiver of Jones-space field recovery (JSFR) to realize polarization diversity with SP carrier-assisted DD schemes. Different receiver structures and simplified recovery procedures for JSFR are explored theoretically. The proposed JSFR pushes SP DD schemes towards PDM without an extra optical signal-to-noise ratio (OSNR) penalty. In addition, the JSFR shows good tolerance to PMD since the optical field recovery is conducted before polarization recovery. In the concept-of-proof experiment, we demonstrate 448-Gb/s reception over 80-km single-mode fiber using the proposed JSFR based on 2 × 2 couplers. Furthermore, we qualitatively compare the optical field recovery in Jones space and Stokes space in terms of the modulation dimension and hardware complexity.

Stable high-efficiency continuous-wave diamond Raman laser at 1178 nm

We demonstrate a high-efficiency continuous-wave (CW) diamond Raman laser operating at 1178 nm with enhanced stability by using a V-cavity design. A maximum Stokes power of 39 W with a conversion efficiency of 45% was achieved using a linearly-polarized 1018 nm Yb-doped fiber pump laser. The Stokes CW power stability showed superior stability over a linear cavity when characterized over periods up to 15 min. The Stokes output was found to switch between linear, elliptical, and random polarization with varying pump polarization. The results represent a major step towards stable, efficient and high-power CW lasers at 1178 nm and at wavelengths outside the main Yb, and Nd emission bands.

Full-aperture random polarization smoothing for a low-coherence laser facility.

Two new random polarization smoothing methods using full-aperture elements are proposed on low-coherence lasers, one using birefringent wedge and one using flat birefringent plate. By designing the crystal axis direction and wedge angle of the birefringent plates, the methods can selectively introduce time delay and spatial displacement, so as to obtain fast random evolution of transient polarization by utilizing low spatiotemporal coherence of the laser focal field. Both methods avoid the near field discontinuity and can be used under high fluence. The method using birefringent wedge can slightly improve focal spot uniformity, and the method using flat birefringent plate can obtain non-polarization with DOP lower than 2%. Theoretical studies show that the resulting focal polarization evolves rapidly on sub-picosecond timescales and rapidly covers the entire Poincaré sphere. The method using birefringent wedge is achieved in experiment. The results show that the degree of polarization of the focal spot is reduced from 1 to 0.27, which proves the effectiveness of the full-aperture random polarization smoothing. The full-aperture random polarization smoothing can generate a focal field very close to unpolarized thermal light, which is expected to suppress the laser plasmas instability.

Color code encryption based on exclusive-OR operation and double random polarization encryption

Color code encryption based on exclusive-OR operation and double random polarization encryption

Polarization-insensitive quantum key distribution using planar lightwave circuit chips

Self-stabilizing the quantum key distribution (QKD) system is essential to evaluate eavesdroppers’ information accurately. We develop and verify a polarization-insensitive time-bin decoder chip for QKD with the hybrid asymmetric Faraday-Michelson interferometer (AFMI) based on the planar lightwave circuit (PLC). Compared with existing chip-based QKD works, the scheme can intrinsically compensate for the polarization perturbation to quantum signals and thus work at arbitrary temperatures. We experimentally verify the chips in a time-bin QKD system at the clocking rate of 1.25 GHz and obtain an average secure key rate (SKR) of 1.34 Mbps over a 50 km fiber channel with an optimized analysis model. The steady variations of the quantum bit error and SKR with random polarization disturbance demonstrate that PLC-based AFMIs are available for developing self-stable QKD systems.

Microwave stray radiation losses in vacuum windows

Vacuum windows are required in magnetically confined fusion experiments to provide possibilities to observe the plasma in a wide range of electromagnetic wavelengths. The window disk consists of a dielectric, e.g. Fused Silica (SiO2), Sapphire or Chemically Vapourised Diamond (CVD). As electromagnetic waves pass through the disk, a fraction of the beam power is dissipated resulting in a temperature increase of the disk. In Electron Cyclotron Waves (ECW) heated plasmas the dissipation in the window disk can be very high. The computation of dielectric losses for a collimated beam with known incidence angle, polarisation and loss tangent (measure for the intrinsic dielectric loss) is well established. However, the dielectric losses in diagnostic windows mostly result from microwave stray radiation, which results from a modest, but inevitable, fraction of non-absorbed ECW. This fraction diffuses in the vessel by many reflections into rays with random k-vector and with random polarisation. In this work the thermal load on the window disk by microwave stray radiation is assessed. The load by a collimated beam is studied as a function of incidence angle and polarisation allowing to average over a distribution of incident rays. An experiment was commissioned measuring the loss tangent of a number of commercially available SiO2 disks at low power in an open resonator, and subsequently measuring the dielectric heating of these disks at high power stray radiation using the facility ’MISTRAL’ at Wendelstein-7X. The experimental results are compared to modelling and it is demonstrated that, in the parameter range considered, single-pass fractional absorption may be applied while taking a safety margin that arises from the minima and maxima due to multiple reflections.

Quantum Zeno and Anti-Zeno Probes of Noise Correlations in Photon Polarization.

We experimentally demonstrate, for the first time, noise diagnostics by repeated quantum measurements, establishing the ability of a single photon subjected to random polarization noise to diagnose non-Markovian temporal correlations of such a noise process. Both the noise spectrum and temporal correlations are diagnosed by probing the photon with frequent (partially) selective polarization measurements. We show that noise with positive temporal correlations corresponds to our single photon undergoing a dynamical regime enabled by the quantum Zeno effect (QZE), whereas noise characterized by negative (anti) correlations corresponds to regimes associated with the anti-Zeno effect (AZE). This is the first step toward a novel noise spectroscopy based on QZE and AZE in single-photon state probing able to extract information on the noise while protecting the probe state, a conceptual paradigm shift with respect to traditional interferometric measurements.

Generation of Decoy Signals Using Optical Amplifiers for a Plug-and-Play Quantum Key Distribution System

In most quantum key distribution (QKD) systems, a decoy-state protocol is implemented for preventing potential quantum attacks and higher mean photon rates. An optical intensity modulator attenuating the signal intensity is used to implement it in a QKD system adopting a one-way architecture. However, in the case of the plug-and-play (or two-way) architecture, there are technical issues, including random polarization of the input signal pulse and long-term stability. In this study, we propose a method for generating decoy pulses through amplification using an optical amplifier. The proposed scheme operates regardless of the input signal polarization. In addition, a circulator was added to adjust the signal intensity when the signal enters the input and exits the QKD transmitter by monitoring the intensity of the output signal pulse. It also helps to defend against Trojan horse attacks. A test setup for the proof-of-principle experiment was implemented and tested, and it was shown that the system operated stably with a quantum bit error rate (QBER) value of less than 5% over 26 h using a quantum channel (QC) of 25 km.

Cryptography Metasurface for One‐Time‐Pad Encryption and Massive Data Storage

AbstractCompared with traditional encryption methods, one‐time‐pad encryption shows theoretically unbreakable characteristics in cryptography owing to the randomness of the generated keys which are generally the same length as the target message. Here, a novel one‐time‐pad encryption strategy is proposed for combining one‐time‐pad keys storage and associated information authentication in metasurface platform. In the concept, visual secret sharing protocol is used to generated one‐time‐pad key by encoding each pixel of secret to two shared sub‐pixels, while each share reveals no information about original image. Then instead of overlaying the two shares to retrieve the secret, the two shares are further encoded to two random polarization key sequences of horizontal and vertical polarization states in an anisotropic metasurface for encryption. In decryption, a single anisotropic metasurface is adopted as the ciphertext to reconstruct target image combined with the doubly‐encrypted polarization keys. By replacing the conventional multichannel metasurface‐based encryption methods with the digital‐based one‐time‐pad encryption, this work enables the reusability of the metasurface and paves the way toward a new methodology for massive data storage.

Fast time-evolving random polarization beam smoothing for laser-driven inertial confinement fusion.

We propose a random polarization smoothing method for low-coherence laser to obtain focal spot with random polarization that evolves rapidly in sub-picosecond timescales. Random polarization smoothing is realized by a half-aperture wave plate with sufficient thickness. The degree of polarization and polarization evolution of the focal spot are studied theoretically. The calculation results show that random polarization smoothing can make the polarization of focal spot evolve rapidly and randomly in time and space. Experimentally, the polarization of the focal spot of low-coherence laser with random polarization smoothing is measured by a single-shot polarimeter. The measurement results show that the degree of polarization of the focal spot is reduced to 0.22 on average, which proves the effectiveness of random polarization smoothing. The random polarization smoothing technique on low-coherence laser is expected to reduce the laser plasmas instability through its multi-dimensional random evolution properties.

Development of polarization speckle with a finite number of K-distribution-amplitude steps

K− distribution plays a significant role in describing the statistics of the electromagnetic scattering with unique properties of random polarization characterized by the fluctuating Stokes parameters. Under the assumptions of K− distributed amplitudes for the contributing polarization phasors and a uniform distribution for the phase difference between two polarization components, we investigate the probability density functions of the Stokes parameters and study the development of polarization speckle when the number of steps in a random walk varies.

Multidimensional joint statistics of the Stokes parameters in a polarization speckle.

A model of multivariate Gaussian statistics has been applied to study the higher-order statistics of the polarization speckle at two spatial or temporal points. Based on the Gaussian assumption for the random electric field, the joint probability density functions of the Stokes parameters and the parameters characterizing the polarization ellipse for the produced random polarization fields at two points are obtained. Subsequently, the corresponding statistics of an isotropic polarization speckle at two points have been investigated to obtain the joint and conditional probability densities of these random variables.

Random polarization switching in gain-switched VCSELs for quantum random number generation.

In this paper, we report an experimental and theoretical study of the random excitation of the linearly polarized modes of a gain-switched VCSEL characterized by having polarization switching under continuous wave operation. We show that equal probability of excitation of both linearly polarized modes can be achieved by adjusting the modulation conditions and the sampling time. Our VCSEL is such that the bistable region associated to the polarization switching is very narrow, indicating that the random process of excitation of the polarizations works independently of the existence of those bistable regions. A characterization of the random polarization switching is performed by analyzing the dependence of the probability of excitation, autocorrelation, and histograms of both polarized signals on the modulation conditions and sampling times. We finally present preliminar results on random number generation using the analyzed system.

3D elastic multisource full waveform inversion on distributed GPU clusters

Full-waveform inversion (FWI) serves as a useful tool to quantitatively investigate the properties of the media. One of the greatest challenges is its enormous computational cost, especially for the three-dimensional (3D) case. The multisource encoding strategy is a crucial method to speed up FWI. However, current 3D elastic FWI algorithms with the simultaneous sources, such as random time series and random polarity methods, may be subjected to the crosstalk noise, which severely degrades inversion quality. We present a novel 3D elastic crosstalk-free multisource full-waveform inversion method (MFWI). The encoded sources with a series of single-frequency components are excited to perform the seismic wavefield simulation. Extracting the wavefield corresponding to each single-frequency harmonic source by phase-sensitive detection (PSD) algorithm, the multisource wavefield can be decomposed. Therefore, summing the gradients with respect to the model parameters of all decomposed single frequencies can effectively avoid the crosstalk in our MFWI algorithm. Furthermore, to increase the practicability and universality of the algorithm, we adopt the graphic processing unit (GPU) based on the domain decomposition to improve the MFWI algorithm. The multi-scale strategy with a flexible encoding number in each scale helps to enhance the robustness of our algorithm. The numerical examples demonstrate that our method can achieve domain decomposition simulation and obtain 3D crosstalk-free multisource elastic wave inversion results.

Polarisation signatures in radio for inclined cosmic-ray induced air-shower identification

Autonomous radio-detection, i.e., detection of air-showers with standalone radio arrays, is one of the major technical challenges to overcome for the next generation astroparticle detectors. In this context, we study polarisation signatures of simulated radio signals to perform an identification of the associated air-showers initiated by cosmic-rays and neutrinos. We compare the two sources of radio emission (the charge excess and geomagnetic) and show that the former is almost negligible for inclined (zenith angle >65°) cosmic-ray air-showers. This provides an efficient background rejection criterion at the DAQ level, based on the projection of the total electric field along the direction of the local magnetic field. This relevant quantity can be computed, — even in an online treatment — for antennas measuring three orthogonal polarisations. Independently of the experimental antenna layout, we estimate that assuming a random polarisation of noise events, a rejection from ≈72% (for a non favourable detector location) to ≈93% (for a favourable one) of the noise induced events and a trigger efficiency of 86% (93%) with a 3σ (5σ) trigger threshold level should be achievable. We also show that neutrino-induced showers present a charge excess to geomagnetic signal ratio up to ∼10 times higher than for cosmic ray showers. Although this characteristic makes the identification of neutrino-induced showers challenging via the method developed here, it provides an efficient criterion to perform an offline discrimination between cosmic-ray and neutrino primaries. The stronger charge excess emission will also help the reconstruction of air-shower parameters, such as the core position.

Active chemo-mechanical feedbacks dictate the collective migration of cells on patterned surfaces

Recent evidence has demonstrated that, when cultured on micro-patterned surfaces, living cells can move in a coordinated manner and form distinct migration patterns, including flowing chain, suspended propagating bridge, rotating vortex, etc. However, the fundamental question of exactly how and why cells migrate in these fashions remains elusive. Here, we present a theoretical investigation to show that the tight interplay between internal cellular activities, such as chemo-mechanical feedbacks and polarization, and external geometrical constraints are behind these intriguing experimental observations. In particular, on narrow strip patterns, strongly force-dependent cellular contractility and intercellular adhesion were found to be critical for reinforcing the leading edge of the migrating cell monolayer and eventually result in the formation of suspended cell bridges flying over nonadhesive regions. On the other hand, a weak force-contractility feedback led to the movement of cells like a flowing chain along the adhesive strip. Finally, we also showed that the random polarity forces generated in migrating cells are responsible for driving them into rotating vortices on strips with width above a threshold value (~10 times the size of the cell).

Thermal conduction mechanism of ferroelastic Zr‐Y‐Yb‐Ta‐Nb‐O high‐entropy oxides with glass‐like thermal conductivity

AbstractFerroelastic high‐entropy oxides (HEOs) with high fracture toughness and low thermal conductivity are promising topcoat materials for next‐generation thermal barrier coatings (TBCs). However, phonon transmission characteristics in the ferroelastic HEOs are less well understood due to their complicated and highly‐disordered structure. Here we prepared two types of ferroelastic Zr‐Y‐Yb‐Ta‐Nb‐O HEOs and investigated their thermal conduction behaviors at 100–900°C. Hybrid Monte Carlo and molecular dynamic simulations were employed to understand the thermal conduction mechanism in this high‐entropy system. Results show the HEOs present glass‐like, low thermal conductivity (< 1.30 W m–1 K–1 at 100°C), which is attributed to the diffused lattice vibration mode with random polarization distribution. Dominant delocalized phonon modes in the HEOs are beneficial to strengthening phonon scattering and consequently decrease the thermal conductivity significantly. Lower thermal conductivity can be achieved by tailoring the composition and crystal structure of the HEOs to increase the contribution from diffused lattice vibration and “diffusion”. This work provides a fundamental insight into the thermal conduction mechanisms of HEOs, which may facilitate materials design of low thermal conductivity materials for TBCs applications.

Weak Langmuir turbulence in disordered multimode optical fibers

We consider the propagation of temporally incoherent waves in multimode optical fibers (MMFs) in the framework of the multimode nonlinear Schr\"odinger (NLS) equation accounting for the impact of the natural structural disorder that affects light propagation in standard MMFs (random mode coupling and polarization fluctuations). By averaging the dynamics over the fast disordered fluctuations, we derive a Manakov equation from the multimode NLS equation, which reveals that the Raman effect introduces a previously unrecognized nonlinear coupling among the modes. Applying the wave turbulence theory on the Manakov equation, we derive a very simple scalar kinetic equation describing the evolution of the multimode incoherent waves. The structure of the kinetic equation is analogous to that developed in plasma physics to describe weak Langmuir turbulence. The extreme simplicity of the derived kinetic equation provides physical insight into the multimode incoherent wave dynamics. It reveals the existence of different collective behaviors where all modes self-consistently form a multimode spectral incoherent soliton state. Such an incoherent soliton can exhibit a discrete behavior characterized by collective synchronized spectral oscillations in frequency space. The theory is validated by accurate numerical simulations: The simulations of the generalized multimode NLS equation are found in quantitative agreement with those of the derived scalar kinetic equation without using adjustable parameters.

Thermal treatment effect on the random lasing polarization of polymer optical fiber

Influences of annealing process on silica optical fiber have been widely reported, while the thermal treatment effect on polymer optical fiber is still given less concern. In order to explore the application of polymer fiber random laser in magneto-optic effect, in this paper, polymer optical fibers doped with ferromagnetic nanoparticles and laser dye were fabricated. Polarization is a key parameter in magneto-optic effect, while the polarization degree of random laser may be affected or even degraded in thermal environment, so the effect of thermal treatment on polarization degree of random polymer optical fiber laser was verified. Anisotropic scattering leads to random lasing emission with high polarization degree. Experimental results show that the average polarization degree is up to 0.88 before the thermal treatment. The polarization degree remains high and increases to 0.99 after annealing, which indicates that random lasers with stable and high polarization degree have been realized.