Context. The GRAVITY+ upgrade implies a complete renewal of its adaptive optics (AO) systems. Its complex design, featuring moving components between the deformable mirrors and the wavefront sensors, ...requires the monitoring and auto-calibrating of the lateral mis-registrations of the system while in operation. Aims. For preset and target acquisition, large lateral registration errors must be assessed in open loop to bring the system to a state where the AO loop closes. In closed loop, these errors must be monitored and corrected, without impacting the science. Methods. With respect to the first requirement, our method is perturbative, with two-dimensional modes intentionally applied to the system and correlated to a reference interaction matrix. For the second requirement, we applied a non-perturbative approach that searches for specific patterns in temporal correlations in the closed loop telemetry. This signal is produced by the noise propagation through the AO loop. Results. Our methods were validated through simulations and on the GRAVITY+ development bench. The first method robustly estimates the lateral mis-registrations, in a single fit and with a sub-subaperture resolution while in an open loop. The second method is not absolute, but it does successfully bring the system towards a negligible mis-registration error, with a limited turbulence bias. Both methods proved to robustly work on a system still under development and not fully characterised. Conclusions. Tested with Shack-Hartmann wavefront sensors, the proposed methods are versatile and easily adaptable to other AO instruments, such as the pyramid, which stands as a baseline for all future AO systems. The non-perturbative method, not relying on an interaction matrix model and being sparse in the Fourier domain, is particularly suitable to the next generation of AO systems for extremely large telescopes that will present an unprecedented level of complexity and numbers of actuators.
Abstract Conventional atmospheric retrieval codes are designed to extract information, such as chemical abundances, thermal structures, and cloud properties, from fully “reduced” spectra obtained ...during transit or eclipse. Reduced spectra, however, are assembled by fitting a series of simplified light curves to time-series observations, wavelength by wavelength. Thus, spectra are postprocessed summary statistics of the original data, which by definition do not encode all the available information (i.e., astrophysical signal, model covariance, and instrumental noise). Here, we explore an alternative inversion strategy where the atmospheric retrieval is performed on the light curve directly, i.e., closer to the data. This method is implemented in EXoplanet Panchromatic Light curve Observation and Retrieval (E x PLOR), a novel atmospheric retrieval code inheriting from the T au RE x project. By explicitly considering time in the model, E x PLOR naturally handles transits, eclipses, phase curves, and other complex geometries for transiting exoplanets. In this paper, we have validated this new technique by inverting simulated panchromatic light curves. The model was tested on realistic simulations of a WASP-43 b-like exoplanet as observed with the James Webb Space Telescope (JWST) and Ariel telescope. By comparing our panchromatic light-curve approach against conventional spectral retrievals on mock scenarios, we have identified key breaking points in information and noise propagation when employing past literature techniques. Throughout the paper, we discuss the importance of developing “closer-to-data” approaches such as the method presented in this work, and highlight the inevitable increase in model complexity and computing requirements associated with the recent JWST revolution.
Structured light carrying optical vortices have gained significant attention in information security as they offer high-dimensional orthogonal states for encoding. These states are usually associated ...with the orbital angular momentum of light. In this letter, we demonstrate a novel method for binary image encryption using structured phase encoding. The structured phase is obtained by multiple lattices of spatially distributed phase singularity points with varying azimuthal indices. It has been shown that data encoding using orthogonal sets of optical vortex modes enable noise-free decryption and provide robustness against atmospheric turbulence in short propagation distance.
Quantum Limits in Optical Communications Banaszek, Konrad; Kunz, Ludwig; Jachura, Michal ...
Journal of lightwave technology,
05/2020, Volume:
38, Issue:
10
Journal Article
Peer reviewed
Open access
This tutorial reviews the Holevo capacity limit as a universal tool to analyze the ultimate transmission rates in a variety of optical communication scenarios, ranging from conventional optically ...amplified fiber links to free-space communication with power-limited optical signals. The canonical additive white Gaussian noise model is used to describe the propagation of the optical signal. The Holevo limit exceeds substantially the standard Shannon limit when the power spectral density of noise acquired in the course of propagation is small compared to the energy of a single photon at the carrier frequency per unit time-bandwidth area. General results are illustrated with a discussion of efficient communication strategies in the photon-starved regime.
•The fluid-solid-acoustic coupling method is used to study the flow field of nozzle.•DPM-LES method can simulate nozzle flow process more accurately.•High-frequency vibration of SVC directly ...increases the dynamic pressure inside nozzle.•The increase of the orifice diameter and depth leads the SPL to first decrease and then increase.
Dust particle pollution endanger human health and cause safety hazards in industry. Twin-fluid atomization technology plays an important role in reducing the pollution of dust particles. In the current study, based on the Large Eddy Simulation (LES) model, the Discrete Phase Model (DPM) model and the Ffowcs Williams-Hawkings (FW-H) model, a fluid-solid-acoustic multi-physics coupling DPM-LES model is proposed, and the numerical simulation results under the multi-field coupling are compared and verified by experiments. Then, through the numerical simulation method, the flow field dynamic characteristics and acoustic characteristics inside and outside the gas-liquid twin-fluid nozzle (TFN) under different operating parameters and self-excited vibrating cavity (SVC) structure parameters are studied. Because the high-frequency vibration of the SVC caused by high gas flow leads to local severe turbulence and the rebound effect between the fluid and the SVC, the dynamic pressure value in most areas of the nozzle reached more than 7000 Pa. Due to the resistance of the air in the flow field and the friction and entrainment between the gas-liquid two phases during the movement, the axial distance in the atomizing flow field with a velocity exceeding 2 m/s can be as far as 2.13m when orifice depth L =1.0 mm. The SPL of the nozzle is gradually attenuated in the process of space propagation. The increased gas flow enhances turbulence, which intensifies nozzle noise. In this paper, the DPM-LES investigation on flow field dynamic and acoustic characteristics of a TFN by multi-field coupling method are studied, which can lay a theoretical foundation for the optimal design of TFN in engineering and provide a certain reference for the reduce of dust particle pollution.
Abstract Collective spin-wave excitations, magnons, are promising quasi-particles for next-generation spintronics devices, including platforms for information transfer. In a quantum Hall ...ferromagnets, detection of these charge-neutral excitations relies on the conversion of magnons into electrical signals in the form of excess electrons and holes, but if the excess electron and holes are equal, detecting an electrical signal is challenging. In this work, we overcome this shortcoming by measuring the electrical noise generated by magnons. We use the symmetry-broken quantum Hall ferromagnet of the zeroth Landau level in graphene to launch magnons. Absorption of these magnons creates excess noise above the Zeeman energy and remains finite even when the average electrical signal is zero. Moreover, we formulate a theoretical model in which the noise is produced by equilibration between edge channels and propagating magnons. Our model also allows us to pinpoint the regime of ballistic magnon transport in our device.
The feasibility of transmitting discrete-variable quantum key distribution channels with carrier-grade classical optical channels over multicore fibers is experimentally explored in terms of ...achievable quantum bit error rates, secret key rates as well as classical signal bit error rates. A coexistence transmission record of 11.2 Tb/s is achieved for the classical channels simultaneously with a DV-QKD channel over a 1 km-long 7-core multicore fiber. Coexistence over the same multicore fiber core is identified as a dominant factor for the performance of the quantum channel requiring optical bandpass filtering of 17 nm for the quantum channel to avoid the effect of Raman noise. Also, counter-propagation of classical channels and quantum channels probe more tolerance to noise proliferation than co-propagation. In addition, the performance of the quantum channel is maintained when more than three cores are used for the classical channels. Furthermore, by adding a second DV-QKD channel in the multicore fiber, the simultaneous transmission of classical channels as well as the generation of quantum-secured keys of two QKD channels is achieved with an operational range of 10 dB of launched power into the MCF.
The flexible joint robot (FJR) typically experiences parametric variations, nonlinearities, underactuation, noise propagation, and external disturbances which seriously degrade the FJR tracking. This ...article proposes an adaptive integral sliding mode controller (AISMC) based on a singular perturbation method and two state observers for the FJR to achieve high performance. First, the underactuated FJR is modeled into two simple second-order fast and slow subsystems by using Olfati transformation and singular perturbation method, which handles underactuation while reducing noise amplification. Then, the AISMC is proposed to effectively accomplish the desired tracking performance, in which the integral sliding surface is designed to reduce chattering based on two-state observers with no requirements of the velocity and acceleration measurements in the FJR system. Furthermore, an adaptive laws for switching gains are proposed for both slow and fast subsystems in the FJR to remove the requirements of knowing the up-bound of the disturbances and uncertainties. The closed loop stability of not only slow and fast subsystems but also the overall FJR is proved using the Lyapunov theorem. Finally, the simulation and experimental results demonstrate the superiority of proposed control in terms of less tracking error, significant noise suppression, and strong robustness in comparison with existing controllers.
Abstract
Aiming at the pain point that it is difficult to control the low-frequency noise of the substation equipment, a new noise reduction method is proposed. It can reduce the noise propagation of ...the equipment without changing the structure of the equipment. The discrete element model of particle dampers for substation equipment is established. The energy consumption value of the particle system is used as an evaluation index. It optimizes parameters such as filling rate and particle size and determines the parameters of the scheme with the best damping effect. Through the combination of simulation and test, the test prototype was built to verify the effect. The test data showed that the total noise extremes of the first and second-floor measurement points were reduced by 14.55 dB and 6.99 dB, respectively, after installing the particle damper. This solution adds a new means of low-frequency noise control for substation equipment.
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