Pseudo-random Phase Research Articles

Dual-Comb Spectroscopy With Enhanced Resolution by Pseudorandom Phase Modulation of Gain-Switched Optical Pulses

Dual-Comb Spectroscopy With Enhanced Resolution by Pseudorandom Phase Modulation of Gain-Switched Optical Pulses

Turbulence impacted wavefront corrections using beam modulation technique

New experimental technique have been proposed to discuss the turbulence impact reduction using beam shaping technique. In first phase of experiments, turbulence Impacted Vortex beam shaping technique has been introduced for a propagating beam which is effected by Kolmogorov type lab based turbulence simulator using Pseudo Random Phase Plate (PRPP). The new technique is executed with a spatially filtered collimated Gaussian beam that is propagated through computer controlled rotating PRPP to introduce the lab based turbulence on the beam profile. The turbulence impacted beam is then propagated through Vortex Phase Plate (VPP) to shape that beam into different topological charged Laguerre Gaussian modes and further collimated using two lens based configuration. We have measured the scintillation index of the spatial intensity profile collected from CCD. Comparative studies have been done by placing the image plane in five different positions on the propagation path of the beam so that we can detect Collimated, diverging and converging outputs. Four topological charges of LG beams and Gaussian beam have been used to envisage results.

Anisoplanatic effects on wave propagation through dynamic pseudo-random phase plate mimicking atmospheric turbulence

Atmospheric turbulence significantly impacts the performance of optical systems, causing wavefront distortions that degrade image quality and limit the capabilities of remote sensing, astronomical observations, and free-space communication. The phenomenon of angular anisoplanatism, where the angular extent of the isoplanatic patch becomes limited due to varying turbulence conditions across the field of view, poses a substantial challenge in achieving high-resolution imaging of extended objects through turbulent atmospheres. This paper presents a comprehensive investigation into angular anisoplanatism using a laboratory-based environment that employs a pseudo-random phase plate to generate Kolmogorov turbulence. Angular anisoplanatism has been studied by generating two beams using a robust cyclic interferometer type arrangement, such that one beam is considered as a reference and the other beam as a target. Here, we have investigated experimentally the correlation of Zernike coefficients, mean square error (MSE), and beam centroid displacement, as a function of the angular separation of two beams. Furthermore, we have also reported the correlation of Zernike coefficients of the Laguerre Gaussian beam with different charges and eventually compared its MSE with that of the Gaussian beam.

Robustness of partially coherent vortex beams to the impact of dynamic Kolmogorov kind of turbulence

The wave propagation characteristics of Gaussian-Schell model vortex beams passing through a dynamic Kolmogorov type of turbulence are analyzed at the laboratory level. The effect of a rotating pseudo-random phase plate, which simulates Kolmogorov-type atmospheric turbulence, on the Gaussian-Schell model beams carrying twist phase is characterized by calculating the scintillation index and intensity line profiles. Our analysis proves the resilience of Gaussian-Schell model vortex beams to the impact of dynamic turbulence. Simulation studies are further used to validate the experimental results. Because of the resemblance between our investigation conditions and real-world atmospheric turbulence, these findings have potential applications in free-space communication systems.

High-Spatial-Resolution Coherent Doppler Lidar With Pseudo-Random Phase-Shift Keying

A high-spatial-resolution coherent Doppler wind lidar (CDWL) incorporating pseudo-random phase-shift keying (PR-PSK) modulation is proposed and demonstrated. The pseudo-random phase coding technique can enhance the spatial resolution without broadening the backscattered spectrum but suffers from the non-instantaneous transition edges caused by the limited bandwidth. In this work, ideal binary PSK modulation is achieved by exploiting the zero crossing of the Mach-Zehnder modulator’s (MZM) transfer function, thus greatly reducing the bandwidth requirement. The amplitude shaping and phase modulation of the pulses are naturally aligned as they are realized together in one MZM. Meanwhile, a real-time bias monitoring scheme for the MZM is proposed to facilitate engineering applications. At laser peak power of 300 W, continuous radial wind profile measurement in 800 m is demonstrated, with spatial/temporal resolution of 3 m/0.5 s.

A 2 kW, 8 GHz-Linewidth Yb-Doped Polarization-Maintained Fiber Laser with Quasi-Flat-Top Pseudo Random Binary Sequence Phase Modulation for SBS Suppression.

We demonstrated a narrow-linewidth high-power Yb-doped polarization-maintaining (PM) fiber laser with near-diffraction-limited beam. The laser system consisted of a phase-modulated single-frequency seed source and four-stage amplifiers in the master oscillator power amplifier configuration. A quasi-flat-top pseudo random binary sequence (PRBS) phase-modulated single-frequency laser with a linewidth of 8 GHz was injected into the amplifiers for suppressing stimulated Brillouin scattering. The quasi-flat-top PRBS signal was readily generated from the conventional PRBS signal. The maximum output power was 2.01 kW with polarization extinction ratio (PER) of ~15 dB. The beam quality (M2) was less than 1.3 over the power scaling range.

High-density and broad band optical frequency combs generated by pseudo-random phase modulation of optically injected gain-switched semiconductor lasers

We have demonstrated optical frequency combs (OFCs) featuring low and continuously tunable line spacing in the kilohertz range. The OFCs are generated by pulsed gain-switching of optically injected commercial semiconductor lasers emitting at around 1.55 μm. After generation, the OFCs are efficiently densified by pseudo-random-binary-sequence phase modulation. The case of an OFC generated by gain-switching at a repetition rate of 1 GHz has been numerically and experimentally analyzed and the conditions for optimal densification have been found. In this case, the comb has been densified by a factor of 2047 and exhibits a 90 GHz flat and broad spectrum consisting of more than 184,000 spectral lines, separated 488 kHz. Although this densification factor is not the largest that can be achieved with the method, it is more than 100 times larger than previously reported factors for gain-switching OFCs. These results open prospects for the use of potentially integrable gain-switching OFCs in applications requiring sub-megahertz line spacing.

The resilience of zero order Bessel–Gaussian Beams to the impact of dynamic Kolmogorov type of turbulence

Propagation characteristics of Bessel–Gaussian beams and Gaussian beams passing through a dynamic Kolmogorov type of turbulence are analysed at the laboratory level using simulations and experiments. The impact of a rotating pseudo-random phase plate mimicking Kolmogorov type atmospheric turbulence on the Bessel–Gaussian and Gaussian beams is quantitatively characterized by calculating the scintillation index, beam wandering, and qualitatively analysed using intensity line profiles. The analysis is done in the Fresnel, Fourier, and Fraunhofer regions. This is the first time in the literature where the effect of a rotating dynamic turbulence on the Bessel–Gaussian beam is experimentally investigated. Our analysis clearly confirms the resilience of Bessel–Gaussian beams to the impact of dynamic turbulence in Fourier and Fraunhofer regions making them advantageous over conventional Gaussian beams when propagated through a dynamic Kolmogorov kind of turbulence. These results can be effectively applied in free-space optical communication systems.

1.8 m/0.5 s Resolution Coherent Doppler Wind Lidar Using Continuous Phase Modulation

A high-spatial-resolution coherent Doppler wind lidar (CDWL) with high modulation efficiency is reported. The pseudo-random phase coding (PRPC) links the spatial resolution to the modulation rate but suffers from the non-rectangular transition caused by the limited bandwidth. With the help of continuous phase modulation (CPM), the abrupt phase switching between successive bit intervals is avoided, thus significantly reducing the bandwidth requirement. By mapping the binary sequence into different transition states rather than phase levels, a 10-fold modulation efficiency improvement is realized. In experiments, the performance of the proposed lidar is compared with lidars in the PRPC method and conventional non-coding method. Continuous radial wind profile measurement of 800 m is demonstrated with spatial and temporal resolution of 1.8 m and 0.5 s, which is the highest spatial resolution realized by a pulsed CDWL to our best knowledge.

Spatial Resolution Enhancement of Coherent Doppler Lidar by Pseudo-Random Phase Coding

A high spatial resolution coherent Doppler wind lidar (CDWL) incorporating pseudo-random phase coding (PRPC) is proposed and demonstrated. Random phase coding of the transmitted lightwave spreads the atmospheric backscattered spectrum and the spatial resolution can be enhanced as only the signal with specific time delay could be despread during decoding. The narrow peak of the despread spectrum provides higher wind velocity retrieval accuracy compared with conventional pulsed CDWL with the same spatial resolution. Spectrum difference is applied to reduce the interference between the spread and despread spectra. The new method's performance is verified in a comparison experiment with a non-coding CDWL. Continuous radial wind profile measurement over 800 m is demonstrated with spatial/temporal resolution of 4.5 m/1 s, at laser peak power of 250 W.

Multiple E-Region Radar Propagation Modes Measured by the VHF SIMONe Norway System During Active Ionospheric Conditions

Multiple propagation modes between different bistatic radar links were measured during the operations of a very high frequency (VHF) 32.55 MHz radar system in northern Norway. The Spread Spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) Norway system detected meteor trails, direct transmitter to receiver signal propagation, over-the-horizon signal propagation from the SIMONe Germany system, ground and/or sea scatter, and ionospheric scatter on 27 August 2021 between 16:30–20:00 UT. These simultaneous detections were during an active ionospheric period with multiple occurrences of energetic charged particle precipitation. The SIMONe systems used continuous-wave (CW) pseudo-random phase modulated transmit signals and interferometry to make it possible to isolate each of these propagation modes and examine their characteristics. Different multistatic links at three receiver locations were analyzed, providing multistatic measurements of the regions with spatial and temporal resolutions on the order of 1.5 km and 2 s. The analysis techniques are described, with characteristics of the radar signal presented for each propagation mode and multistatic link. This study serves to highlight the capabilities of the SIMONe Norway system to research multiple aspects of ionospheric phenomena, specifically in the lower thermosphere-mesosphere boundary region.

Fried’s coherence length measurement of dynamic Kolmogorov type turbulence using the autocorrelation function

A new method to find the Fried’s coherence length of a dynamic Kolmogorov type turbulence in a laboratory environment is reported in this paper. This method utilises the autocorrelation function obtained from the quantitative characteristics of a rotating pseudo random phase plate in one of the arms of a Mach–Zehnder interferometer. Theoretical formalism and experimental verification are presented.

Effective Brillouin Gain Spectra Broadening for SBS Suppression Based on Pseudo Random Bit Sequence Phase Modulation in Fiber System

We describe stimulated Brillouin scattering process in a fiber system with light field phase modulated by lowpass filtered and amplified pseudo random bit sequence (PRBS) using localized nonfluctuating source model. The effective Brillouin gain spectra and the ratio of normalized Stimulated Brillouin Scattering (SBS) threshold to RMS optical linewidth is used to characterize the SBS suppression capability of the PRBS phase modulation. The normalized effective Brillouin gain spectra for different modulation parameters are calculated to exhibit the Brillouin gain broadening process. Based on the theoretical model, we find that the SBS threshold reaches a maximum for the ratio of cutoff frequency to clock rate <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r_c</i> = 0.53 and RMS modulation depth <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k_rms</i> = 0.55 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</i> for PRBS9. An effective Brillouin gain spectrum measurement setup is established, and the theoretical predictions are verified by the experiment.

Amplification of High Quality of Signal Strength Using Corner Reflector Antenna for Satellite Communications

The strengths of the corner reflector antenna (CRA) which spans space's dynamic pseudo-random phase wave-front, which can be used in frequency modulation of the echo, replacing doppler's typical style. Radiometric assumes that Imaging discoveries can change lives a kind of special geosynchronous in geostationary orbit for the extremely low SNR in this geometry, just have a very low signal to noise ratio (SNR) posit the use of such a matched filter to strengthen the SNR and enable the existence of good specificity. In this paper, the signal is amplified to send a high-quality signal to the transmitter for satellite communication using a corner reflector antenna. Apart from other antennas, the corner reflector antenna plays an important role in increasing the signal strength in satellite communication. Using this corner reflector antenna the system will be good and fast so that the transmitter or the receiver can transmit or receive the signal very fast. While transmitting the signal the noise or interference in the system can be eliminated for that reason the corner reflector antenna is used. The corner reflector antenna can reduce the system noise or interference so that the system will be in proper condition to transmit or receive the signal.

Insensitivity of higher order topologically charged Laguerre–Gaussian beams to dynamic turbulence impact

The propagation characteristics of topologically charged Laguerre–Gaussian​ beams through a dynamic (rotating) pseudo random phase plate mimicking atmospheric turbulence, like beam wandering, scintillation etc are measured in laboratory level. Our findings clearly show that the beam wandering and scintillation effects are higher for Laser Gaussian beams compared to topologically charged Laguerre–Gaussian beams. Also, the impact of turbulence reduces considerably when the topological charges of LG beams increase. This may help to use higher order topologically charged Laguerre–Gaussian beams for optical communications in free space.

PAPR assessment of OFDM and pseudo random phase sequences based PTS algorithm over diverse sub-carriers

Abstract Orthogonal frequency division multiplexing (OFDM) has been most important mainstream technology considered for high data transmission speed. But, high peak to average power ratio (PAPR) diminishes system performance. Consequently, in this research work, pseudo random phase sequences based partial transmit sequence algorithm (PRS-PTS-Algo) has been considered. In order to obtain information back at receiver only index value of column of the phase sequences can be utilized. In addition, 8-PSK (phase shift keying) and 16-PSK modulation methods and diverse sub-carriers are considered. Simulation results clearly show that PRS-PTS-Algo provides remarkable reduction in the PAPR issue as compared with conventional OFDM system (Conv-OFDM) along with very efficient generation of phase sequences.

Red blood cell classification in lensless single random phase encoding using convolutional neural networks.

Rapid cell identification is achieved in a compact and field-portable system employing single random phase encoding to record opto-biological signatures of living biological cells of interest. The lensless, 3D-printed system uses a diffuser to encode the complex amplitude of the sample, then the encoded signal is recorded by a CMOS image sensor for classification. Removal of lenses in this 3D sensing system removes restrictions on the field of view, numerical aperture, and depth of field normally imposed by objective lenses in comparable microscopy systems to enable robust 3D capture of biological volumes. Opto-biological signatures for two classes of animal red blood cells, situated in a microfluidic device, are captured then input into a convolutional neural network for classification, wherein the AlexNet architecture, pretrained on the ImageNet database is used as the deep learning model. Video data was recorded of the opto-biological signatures for multiple samples, then each frame was treated as an input image to the network. The pre-trained network was fine-tuned and evaluated using a dataset of over 36,000 images. The results show improved performance in comparison to a previously studied Random Forest classification model using extracted statistical features from the opto-biological signatures. The system is further compared to and outperforms a similar shearing-based 3D digital holographic microscopy system for cell classification. In addition to improvements in classification performance, the use of convolutional neural networks in this work is further demonstrated to provide improved performance in the presence of noise. Red blood cell identification as presented here, may serve as a key step toward lensless pseudorandom phase encoding applications in rapid disease screening. To the best of our knowledge this is the first report of lensless cell identification in single random phase encoding using convolutional neural networks.

Performance Investigations and PAPR Reduction Analysis Using Very Efficient and Optimized Amended SLM Algorithm for Wireless Communication OFDM System

The orthogonal frequency division multiplexing (OFDM) is the most encouraging multi-carrier modulation system chosen for the high data rates but the objective is to resolve intrinsic common issue of peak to average power ratio (PAPR). The projected algorithm is illustrated in this research study which is established upon selected mapping (SLM) with pseudo-random sequence under time domain μ law companding of signal. Besides the significant competitive characteristics of conventional SLM algorithm (ConvenSLM-Algo) (Mestdagh et al. in Electron Lett 32(22):2056–2057, 1996. https://doi.org/10.1049/el:19961384 ), it undergoes the tedious complexity in generation of phase sequence and for the recovery of sequence, side information is mandatory. The key concern, thus, to eliminate the tedious problem of designing of phase sequence along with the aim of reducing the fluctuation of signal with high PAPR. Henceforth, in the projected algorithm (Projected-Algo) a noteworthy strategy has been investigated and followed for the designing of phase sequence which is very easy and for the recovery of information at receiver, side information of index of column of phase sequences can be used because of straightforwardness in its establishment. Hence, we demonstrate the effective overall excellent performance of Projected-Algo along with analysis and also comparative study of Projected-Algo outperforms the conventional OFDM system (unchanged), ConvenSLM-Algo [16], SLM with new pseudo random phase sequences (ModSLM-Algo) given in literature (Ali et al. in Canadian conference on electrical and computer engineering, 2018. https://doi.org/10.1109/CCECE.2018.8447835 ).

Comparison of Stimuli for Nonlinear System Response Classification

As part of the development of an automated virtual design classification approach for nonlinear structural dynamics, alternative excitation functions are evaluated with respect to their overall performance and efficiency in feature-based response analysis. Robust design of nonlinear structures requires analysis of extensive parameter variations. Both the character of the stimulus and feature metrics used are central to the performance of a response classification approach. The main purpose of this study is to compare stimulus candidates with respect to their efficiency in response classification. A deterministic multilevel, multifrequency stepped-sine periodic test function is used as a baseline. Order-wise differences between generalized and linearized system frequency response functions are evaluated by a selected feature metric to allow categorization into primary, sub and super harmonic responses, as well as odd and even order response distortions. An alternative excitation function type is the pseudorandom phase multi-sine. Its robust variant estimates the best linear approximation of the generalized frequency response function and related nonlinear and noise variances, which can be used for response classification. The fast variant of this method further detects and classifies occurring even and odd order nonlinear responses using a hypothesis test. This article describes the application of these three methods to a virtually running two-piece rotor shaft model. Time response signals from simulated test parameter variations are used to calculate selected nonlinear feature metric values. The total simulation and measurement time, as well as the predictive performance in a few typical nonlinear response cases are evaluated.

Research on a Wind Lidar Without Blind Zone Based on the Technologies of Pseudo Random Code Phase Modulation and Heterodyne Detection

In this measurement method, a wind lidar system with no blind zone based on the technologies of heterodyne detection and pseudorandom code phase modulation is proposed. The simulation results show the feasibility of the method. 15m range resolution and 7.75cm/s line of sight (LOS) wind velocity resolution can be achieved from 0 m to 300m, when the laser transmitted power is 2mW, the transmitted pulse length is 100us, the receiving telescope aperture is 2cm, and an accumulation times of 10. The simulation results also show the positive effect of the transmitted pulse length.