Compensation Of Phase Distortions Research Articles

Spatial phase distortion compensation technology based on combinatorial optimization method in heterodyne detection

The spatial phase distortion caused by turbulent atmosphere, target speckle, or optical system aberration causes decoherence of heterodyne signals. The decoherence effect is the key problem that imposes restrictions on the application of laser heterodyne techniques. We propose an approach for spatial phase distortion correction based on a genetic algorithm by establishing a one-to-one correspondence between combination of spatial phase compensation amounts and heterodyne efficiency of the system. The spatial phase distortion compensation problem is converted into a combinatorial optimization problem. The experiment results show that the method achieves excellent compensation performance for the spatial phase distortion, significantly contributing to the applications of heterodyne techniques.

Compensation of Ionospheric Phase Distortion in HF Hybrid Sky-Surface Wave Radar Using Piecewise Polynomial Phase Modeling Method

Compensation of Ionospheric Phase Distortion in HF Hybrid Sky-Surface Wave Radar Using Piecewise Polynomial Phase Modeling Method

Scientific and Engineering Proposals for Improving the Noise Immunity of Receiving Multi-Position Signals in Channels with Variable Parameters

Introduction. An important task faced by the developers of modern telecommunication systems consists in increasing the noise immunity of signal reception in channels with variable parameters. Thus, the communication lines of DVB-T2, DVB-S, and DVB-S2/S2 standards widely apply signal structures (SS) of multi-position quadrature amplitude modulation (M-QAM). However, an analysis of scientific publications shows that the random nature of the phase change of the transformed signal constellation leads to a loss of noise immunity of the M-QAM signals. Engineering solutions for the effective reception of such signals are lacking. The proposed block diagram of a device for receiving quadrature amplitude signals and the developed operation algorithm for an amplitude-phase detector allow random phase changes to be considered and reduced.Aim. Development of scientific and engineering proposals to improve the efficiency of receiving M-QAM signals in radio channels with random phase changes.Materials and methods. The study was conducted using the methods of noise immunity research, as well as communication theory and signal theory.Results. A block diagram of a device for receiving quadrature amplitude signals and an operation algorithm for an amplitude-phase detector were proposed, which allow random phase changes to be considered and compensated for. Scientific and engineering proposals were formulated to improve the noise immunity of M-QAM reception in channels with variable parameters.Conclusion. The developed scientific and engineering proposals for increasing the noise immunity of multi-position quadrature signals in channels with variable parameters substantiate both the feasibility of using a transformed SS M-QAM with improved energy characteristics, as well as the application of the developed receiving device for processing quadrature amplitude signals and the operation algorithm of an amplitude-phase detector. The results obtained make it possible to perform demodulation with simultaneous compensation of phase distortions to increase the noise immunity of M-QAM signal reception.

Modeling of the Payload Signal Generator of the UAV Radio Transmitter based on the Phase Distortion Autocompensator

A block diagram of a payload signal generator of a UAV radio transmitter with an autocompensator for phase distortion of a digital computational synthesizer with improved spectral characteristics compared to known solutions is considered. Schematic diagrams and circuit design models of the main paths of the shaper in the Micro-Cap environment with the analysis of the characteristics of the necessary radio elements and microcircuits have been developed. The simulation of the device operation in the frequency domain is carried out. Based on the simulation results, the conditions for selecting the parameters of the shaper to achieve the greatest compensation of phase distortions are formulated.

High-quality 8-fold self-compression of ultrashort near-UV pulses in an Ar-filled ultrathin-walled photonic crystal fiber

We demonstrate generation of 7.6 fs near-UV pulses centered at 400 nm via 8-fold soliton-effect self-compression in an Ar-filled hollow-core kagomé-style photonic crystal fiber with ultrathin core walls. Analytical calculations of the effective compression length and soliton order permit adjustment of the experimental parameters, and numerical modeling of the nonlinear pulse dynamics in the fiber accurately predicts the spectrotemporal profiles of the self-compressed pulses. After compensation of phase distortion introduced by the optical elements along the beam path from the fiber to the diagnostics, 71% of the pulse energy was in the main temporal lobe, with peak powers in excess of 0.2 GW. The convenient setup opens up new opportunities for time-resolved studies in spectroscopy, chemistry, and materials science.

Application limitations of a laser guide star in adaptive optoelectronic systems caused by its jitter in the atmosphere

Application limitations caused by the jitter of a laser guide star used for the compensation of atmospheric phase distortions are considered for Earth-based adaptive optoelectronic systems for the observation of natural and artificial space objects. The spatial coherence radii (Fried parameter) for which a laser beam remains within the isoplanatic angle under the jitter effect during guide star formation are estimated using locally homogeneous and isotropic atmospheric turbulence models. Beam deflections in two mutually orthogonal directions are considered to be distributed normally, and the probability of the beam remaining within the isoplanatic angle is considered to be subject to the Rayleigh law. The angular divergence of the deflected beam is estimated for a short exposure with a duration less than the atmosphere freezing time for the far and near fields of the emitting laser aperture.

Glass tube cutting with aberration-corrected non-diffracting ultrashort laser pulses

The separation of complex inner and outer contours of glass articles with curved surfaces using ultrashort pulsed lasers is reported. Single-pass, full-thickness modifications along the entire substrate are achieved using a processing optics that allows for beam shaping of non-diffracting beams and, additionally, for aberration compensation of phase distortions occurring at the curved interface. The glass articles finally separated by thermal stress or via selective etching meet the demands of the medical industry in terms of micro-debris, surface quality and processing speed.

Compensation of SOA-induced nonlinear phase distortions by optical phase conjugation

To answer the question: "Is optical phase conjugation (OPC) capable of compensating nonlinear distortions caused by not only Kerr effect of optical fibre, but also the carrier dynamics of semiconductor optical amplifiers (SOAs)?", we investigate the effectiveness of OPC-based nonlinear compensation for SOAs amplifying a few-channel WDM signal modulated with m-QAM. We use a pair of SOAs with an OPC stage sandwiched between the two so that the combination works as a low-distortion amplifier. Symbol-period longer than the gain recovery time is chosen in our experiments to avoid bit-pattern effects introduced by the SOA. We amplify a 12Gbaud, 16QAM modulated three-channel WDM signal with this technique in the back-to-back configuration which remarkably outperforms a single SOA in the nonlinear regime of operation with an average Q2 improvement better than 4 dB for an output power of 4 dBm. We further demonstrate the practical advantage of the low distortion higher output power capability of the SOA shown in the back-to-back result by carrying out a transmission of the amplified signal through a 160-km fibre, where relatively high launch power is desirable. We also study the case of 64QAM signals and show that approximately a 3 dB Q2 factor improvement can be obtained over single SOA, while without nonlinear phase distortion compensation, the demodulation is nearly impracticable.

Adaptive system for wavefront correction of the PEARL laser facility

The results of the operation of a wavefront correction system based on a deformable bimorph mirror of the PEARL subpetawatt laser facility are presented. An improvement in the quality of focusing of laser radiation, which led to an increase in the Strehl ratio from 0.3 to 0.6, is demonstrated. The features of the compensation for phase distortions of the wavefront in the case of a low pulse repetition rate, as well as the correct allowance for the noise of the CCD camera when calculating the Strehl ratio are investigated.

Phasing of seven-channel fibre laser radiation with dynamic turbulent phase distortions using a stochastic parallel gradient algorithm at a bandwidth of 450 kHz

We have demonstrated an experimental setup for the coherent phasing of a seven-channel fibre laser system ( λ = 1064 nm) in a scheme comprising a master oscillator and a set of parallel amplifiers with lithium niobate-based fibre-optic phase modulators. Using a stochastic parallel gradient algorithm, an instrumental phase modulator control unit ensures a bandwidth of the system up to 450 kHz. The effectiveness of phasing of light transmitted through a turbulent medium with a characteristic time scale τturb has been studied experimentally as a function of phasing time τph. The results demonstrate that the average Strehl ratio begins to rise at τturb/τph ⩾ 2 and that the effectiveness of compensation for dynamic phase distortions in the beam propagation path rises sharply at τturb/τph ≈ 20. For τturb/τph ⩾ 30 – 40, the average Strehl ratio remains constant at the level reached.

Automatic Compensation of Digital Holographic Microscopic Phase Distortion Based on the Reference Objective

Automatic Compensation of Digital Holographic Microscopic Phase Distortion Based on the Reference Objective

Conjugate nonlinear-optical loop mirror (Conj-NOLM)-based phase-preserving multilevel amplitude regenerator

We propose a novel phase-preserving multilevel amplitude regenerator scheme by cascading two nonlinear-optical loop mirrors (NOLMs) with an intermediate optical phase conjugator (OPC) stage. Joint parameter optimization of the two NOLM units has been carried out to cancel the introduced phase distortion and enable a more power-efficient performance. Moreover, our scheme combines the operation of the NOLM and the OPC in a single subsystem, enabling the compensation of both amplitude and phase distortions when located symmetrically in a transmission link. To this end, extensive numerical simulations have been performed to evaluate the regeneration performance in a transmission link dominated by amplified spontaneous emission (ASE) noise and Kerr-induced nonlinear distortions (self-phase modulation-induced phase distortion), achieving over 100% reach extension compared to the cases of un-regenerative, or a mid-span OPC-based transmission links.

The method of forming probing signals of georadars on the basis of direct digital synthesizers for geodynamic monitoring

The features of the formation of probing signals based on direct digital synthesizers for geodynamic monitoring of medias using georadar probing are considered in the article. The basic requirements for the formers of probing signals and the shortcomings of known technical solutions are shown. To eliminate them, as a former of probing signals of georadars was suggested to use direct digital synthesizers with improved spectral characteristics, achieved by introducing circuit of an automatic compensation of phase distortion with a control device in the form of a phase-locked loop. With this construction, the device contains a combination of autocompensation and filter methods of improving the spectral characteristics of the output signal of the synthesizer. To analyze the effectiveness of the proposed solutions, were obtained the necessary mathematical relationships describing the functioning of the device under research and implemented its schematic simulation, which showed the possibility of improving the spectral characteristics of the proposed former of probing signals by 10-15 dB.

Analysis of Noise Characteristics of Multichannel Systems of the Formation of Signals of Georadars with Synthesized Aperture

The noise characteristics of multichannel systems of forming signals based on hybrid frequency synthesizers with automatic compensation of phase distortions of direct digital synthesizers, which are used in the composition of georadars with synthesized aperture, are investigated. It is established that the phase noise of the output signals of the formers at the 1 kHz detuning from the carrier oscillation at the output frequencies of the devices in the range from 500 to 3500 MHz is characterized by a level of minus 100 - minus 130 dB. In this case, the circuit of the signal former based on a hybrid frequency synthesizer with direct digital synthesizer as a reference oscillator of a phase locked loop is characterized by the worst noise characteristics but with the highest degree of autocompensation (about 13 dB). Conversely, the circuit of the signal former based on a hybrid frequency synthesizer with direct digital synthesizer as a support generator of the phase-locked loop has the best phase noises level from the considered variants of devices and least degree of autocompensation (about 6 dB).

Compensating Earth Ionosphere Phase Distortion in Spaceborne VHF Radar Sounders for Subsurface Investigations

Spaceborne low-frequency and wide bandwidth radar sounders are a promising technology to regularly investigate at global-scale Earth’s icy and arid regions. However, Earth ionosphere distorts the radar signal impacting performance parameters, such as subsurface resolution, of the radar system. One of the most relevant distortions that a sounder signal in the lower part of the very high-frequency (VHF) band (e.g., 40–50 MHz) encounters is the distortion of the phase component that could become mission critical if not properly compensated. Low-frequency and high fractional bandwidth radar systems are particularly affected by this issue. Previous works on radar sounder ionosphere phase distortion compensation addressed the Martian ionosphere and used techniques based on the Taylor series expansion. In this letter, we focus on the Earth ionosphere and we exploit a recently proposed ionosphere compensation technique based on the Legendre orthogonal polynomials expansion, which proved to be more accurate than the compensation based on Taylor expansion. Simulations show that the method allows a nominal compensation of the phase distortions under realistic ionosphere scenarios expected during the acquisitions. Furthermore, it proved to be accurate and robust for total electron content conditions expected during nighttime for all the geomagnetic latitudes. The results confirm that the method can accurately compensate the distorting effects on the phase component of a spaceborne VHF radar sounder.

Phase compensation in digital holographic microscopy using a quantitative evaluation metric

Abstract This study presents a simple metric to quantitatively evaluate the compensation of phase distortions in digital holographic microscopy. The metric calculates the difference between the minimum and maximum values in an unwrapped phase image. A phase compensation method based on the metric is proposed. Both the tilt and curvature distortions can be automatically compensated using this method, and specimen-free zones are unnecessary. It is also suitable for thick objects located in wide areas. The method using this evaluation metric has been tested and validated on several samples. With strong robustness and low computational complexity, this approach can result in accurate and effective quantitative phase imaging in holographic microscopy.

数字全息中的自动相位畸变补偿算法

数字全息中的自动相位畸变补偿算法

誘導ブリルアン散乱(SBS)位相共役鏡によるレーザー光の波面補償とその応用

誘導ブリルアン散乱(SBS)位相共役鏡によるレーザー光の波面補償とその応用

A High Efficiency and Low Distortion 6 W GaN MMIC Doherty Amplifier for 7 GHz Radio Links

This contribution presents a novel design methodology for Gallium Nitride (GaN) Monolithic Microwave Integrated Circuit (MMIC) Doherty Power Amplifiers (DPAs). The proposed solution allows to mitigate the relevant phase distortion (AM/PM) and gain penalty, typically registered in GaN DPAs, without worsening other key features such as back-off efficiency and amplitude distortion (AM/AM). To this purpose, a non-linear driver stage is introduced in both Carrier and Peaking branches, with the aim to provide a chip-level phase distortion compensation mechanism. The idea is to almost zeroing the overall phase distortion by achieving, in the driver stage, an opposite AM/PM behaviour with respect to the one of the final stage. The theoretical formulation is verified presenting the design and experimental characterization of a GaN MMIC DPA for 7 GHz radio links. The chip has been developed in a commercial $0.25\mu \text {m}$ GaN power process, resulting in a $3\times 3$ mm2 chip area. The realized DPA shows 38 dBm of saturated output power, 16 dB of gain, and less than 3° of phase distortion, with a power added efficiency higher than 41% in 6 dB of output power back off.

귀환 채널 추정 및 RFP 성능을 개선한 간섭 제거 기반의 동일 채널 중계기

#$%&'()*+,-./01102345, 678 9:1; >?@*0AB:CD>?EFG H(5*IDAB(Digital Audio Broadcasting)I :JHK, *:ATSC(Advanced Television Systems Committee)GLM&NIO. J (P=>>?/O>?QRST &'U*VW XCY, *&Z[ =\U, ]^_`EFG9Rabc?>?de*fbgGhi*jkHlV O.AbstractIn this paper, Method for the phase distortion compensation timing offset and DC eliminator for the pilot component estimation and removal, transmitted and received signal correlation in the delay scheme DAB interference cancellation based on the same channel for using for estimating the feedback signal based on a between for removal for the timing offset compensation It proposes a repeater. This was applied to the ATSC system. The on-channel repeater of the proposed interference cancellation based on the interference removing capability is improved in interference signal is 20dB greater than the primary transmission signal environment via the return channel estimation and improve performance RFP. Accordingly, it was confirmed by simulation that good signal is sent out with the improvement of the ability of the repeater.Keywords : ATSC system, on-channel repeater, interference cancellation