Backscattering Interference Research Articles

Orthogonal waveform-based backscattering interference suppression technique for underwater optical wireless communication

The backscattering effects degrade the detection performance in a full-duplex underwater optical wireless communication (UOWC) system when the power of received backscattering interference is comparable to that of a target signal. In this paper, the orthogonal waveforms with the Hermite–Gaussian function and prolate spheroidal wave function are first introduced for a pulse position modulation based dynamic UOWC system to alleviate the backscattering effects. Then, a joint maximum likelihood detection scheme is proposed accordingly. Experimental results verify the superiority of the proposed method with orthogonal waveforms over the scheme without orthogonal pulse shaping in a dynamic underwater bubbly channel.

Experimental investigation on backscattering interference cancellation for full-duplex UOWC based on time-reversal preprocessing

A co-frequency and full-duplex (FD) underwater optical wireless communication (UOWC) system has the potential to significantly enhance spectral efficiency, reduce complexity, and further facilitate UOWC networking. However, the inevitable performance degradation due to self-interference introduced by backscattering presents a significant challenge. In this paper, we first experimentally explore the inherent characteristics of the underwater backscattering channel. Subsequently, we propose a digital-domain backscattering interference cancellation (BIC) algorithm for FD-UOWC systems, incorporating a time-reversal preprocessing. We then experimentally investigate the communication performance of an FD-UOWC system to verify the feasibility of the proposed BIC algorithm under different channel conditions. The experimental results validate the effectiveness of the proposed method, yielding substantial enhancements in bit error rate performance across diverse scenarios.

Separation of noisy multitone signals based on variational mode decomposition

We have observed that Variational Mode Decomposition (VMD) exhibits instability in the denoising and separation of noisy multitone signals. Specifically, minor changes in factors such as signal-to-noise ratio, frequency spacing, sampling rate, and probability distribution can significantly impact the decomposition results. To address this issue, we have developed the Dual-VMD-correlation algorithm. This algorithm effectively mitigates the impact of beat effects when harmonics of closely spaced frequencies are superimposed, enabling stable denoising of noisy multitone signals and the separation of each individual tone signal. The algorithm holds promise for applications in frequency-modulated continuous wave laser detection. It can address challenges related to denoising laser echo signals interfered with by aerosols and the difficulty in separating backscatter interference from the target reflected signal spectrum.

Синтез поляризационных светоделителей для дальнего инфракрасного диапазона спектра

The technique and results of the synthesis of polarization beam splitters for the long-wavelength infrared region of the spectrum of 8–14 microns are presented. In this range, bodies with temperatures around zero degrees Celsius begin to emit. In addition, this radiation has a low attenuation in a relatively humid or aerosol-saturated atmosphere. Therefore, it is widely used in night vision devices, rangefinders and thermal imaging cameras, including mobile systems with a variable angle of the optical axis relative to the angle of arrival of the incident electromagnetic wave. In systems with active illumination, polarized radiation and beam splitters are used to reduce the effect of backscattering interference. A review of patents and literature showed the absence of finished products for the considered wavelength range. In this paper, original designs of polarization beam splitters are proposed and their spectral optical characteristics are obtained.

Performance evaluation of underwater vision systems

The article describes a methodology for performance evaluation of vision systems for remotely operated underwater vehicles. The methodology is based on a system approach and uses mathematical models of the aqueous medium where an optical signal propagates, the underwater object image registration system, and the mathematical model of the human visual system. The detection and recognition probabilities of underwater object image at a given registration range are used as performance evaluation indicators of underwater vision systems. The mathematical model of the aqueous medium developed by the authors allows quantitative evaluation of the influence of backscattering interference arising during objects illumination on the underwater vision system performance. The results of numerical experiments presented in the paper illustrate the possibility of using the proposed technique to optimize the underwater object image registration system parameters in order to achieve the required values of detection or recognition probabilities at the given ranges.

Bathymetry of a macro-pulsed chaotic laser based on a 520 nm laser diode subject to free space optical feedback.

We generate a macro-pulsed chaotic laser based on pulse-modulated laser diode subject to free space optical feedback, and demonstrate the performance of suppressing backscattering interference and jamming in turbid water. The macro-pulsed chaotic laser with a wavelength of 520 nm as a transmitter is used with a correlation-based lidar receiver to perform an underwater ranging. At the same power consumption, macro-pulsed lasers have higher peak power than in the continuous-wave form, enabling the former to detect longer ranging. The experimental results show that a chaotic macro-pulsed laser has excellent performance of suppressing the backscattering of water column and anti-noise interference compared with traditional pulse laser, especially by multiple accumulations about 10∼30 times, and target position can still be determined when SNR is -20 dB.

High-angular-resolution interferometric backscatter meter.

Backscatter limits many interferometric measurements, including gravitational wave detectors, by creating spurious interference. We describe an experimental method to directly and quantitatively measure the backscatter interference. We derive and verify experimentally a relation between backscatter interference, beam radius, and the scattering sample bidirectional reflectance distribution function. We also demonstrate that our method is able to measure backscatter from high-quality optics for angles as low as 500μ r a d with an angular resolution of 160μ r a d.

Dual-Polarized WDM Access Network With Fiber to the Extension (FTTE) Connection

In this study, a symmetric polarization-division-multiplexing (PDM) wavelength-division-multiplexing passive optical network (WDM-PON) with fiber to the extension (FTTE) architecture is presented and investigated. The proposed PON can also avoid the Rayleigh backscattering (RB) interference noise. Here, each WDM wavelength can produce 25 Gbit/s on-off keying (OOK) and 10 Gbit/s OOK modulation channels simultaneously in x- and y-polarizations (Pol <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> and Pol <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> ) through PDM method for 25 and 105 km single-mode fiber (SMF) transmissions without dispersion compensation. The measured minimal power budget of 25 and 10 Gbit/s downstream and upstream signals are 29 and 35.1 dB and 29.8 and 31.5 dB, respectively, at the forward error correction (FEC) target. Therefore, the proposed PDM WDM-PON architecture can not only offer symmetric 35 Gbit/s downstream and upstream connections by the dual-polarized wavelength, but also can avoid the RB-induced interference noise. In addition, the presented dual-polarized downstream signal also can provide information security in physical layer, when the unauthorized user occupies unlawfully.

Quench dynamics of a weakly interacting disordered Bose gas in momentum space

We theoretically study the out-of-equilibrium dynamics in momentum space of a weakly interacting disordered Bose gas launched with a finite velocity. In the absence of interactions, coherent multiple scattering gives rise to a background of diffusive particles, on top of which a coherent backscattering interference emerges. We revisit this scenario in the presence of interactions, using a diagrammatic quantum transport theory. We find that the dynamics is governed by coupled kinetic equations describing the thermalization of the diffusive and coherent components of the gas. This phenomenon leads to a destruction of coherent backscattering, well described by an exponential relaxation whose rate is controlled by the particle collision time. These predictions are confirmed by numerical simulations.

Влияние помехи обратного рассеяния на эффективность инфотелекоммуникаций при проведении подводного поиска

В результате анализа результатов идентификации объектов при проведении подводного поиска в статье в интересах повышения эффективности телекоммуникаций предложены пути, направленные на улучшение качества видеоинформации от телевизионных систем подводного видения. Для этого исследованы причины, снижающие контраст изображения от телекамер, и выполнен расчёт яркости помехи обратного рассеяния как главного фактора поражения видеоинформации в зависимости от угла засветки подводных световых приборов. В качестве вывода предложены пути увеличения дальности подводного видения, одним из которых является применение в качестве источников освещения лазерных систем, что существенно уменьшит углы засветки. Научно обоснованные результаты в совокупности с другими техническими решениями, приведенными в статье, позволят увеличить дальность видимости телекамер, размещаемых на подводных аппаратах. Это обеспечит возможность проведения подводного поиска объектов на гораздо больших отстояниях от грунта, повысит их поисковую производительность и снизит риски навигационных аварий в режиме придонного плавания. As a result of the analysis of the results of object identification during underwater search, the article proposes ways to improve the quality of video information from underwater vision television systems in order to increase the efficiency of telecommunications. To do this, the reasons that reduce image contrast from the cameras were investigated and the brightness of backscattering interference was calculated as the main factor of video information damage, depending on the illumination angle of underwater light devices. As a conclusion, there are presented ways of increasing the range of underwater vision, one of which is the use of laser systems as illumination sources, which will significantly reduce the illumination angles. Scientifically based results together with other technical solutions given in the article will increase the range of visibility of television cameras placed on underwater vehicles. This will ensure the possibility of conducting an underwater search of objects at much greater distances from the ground, increase their search performance and reduce the risks of navigation accidents in the bottom sailing mode.

Co- and counter-propagating wave effects in an absorbing medium

In this semi-tutorial paper, we revisit the interference phenomena caused by pairs of co-propagating or counter-propagating transverse electromagnetic waves by letting the host medium be absorbing. We first consider plane waves in an unbounded medium, summarize the standing-wave solution of the Maxwell equations, and discuss specific effects caused by nonvanishing absorption. We then consider the superposition of plane and spherical waves in the context of far-field electromagnetic scattering by a particle. To this end we modify the classical Jones lemma by allowing nonzero absorption in the host medium and consider its most obvious consequences such as forward- and backscattering interference. The physical similarity of the two scenarios (superpositions of plane waves and superpositions of plane and spherical waves) is discussed.

Symmetric >67 Gbps OFDM-IMDD based WDM access network for mitigating Rayleigh backscattering interference noise

In this paper, we propose a symmetric >67 Gbps/λ wavelength-division-multiplexing (WDM) access network with mitigation of Rayleigh backscattering (RB) interference noise by using the orthogonal frequency division multiplexing (OFDM) modulation and intensity modulation and direct detection (IMDD) method. According to the optimal OFDM bit-loading algorithm design, the fiber chromatic dispersion and RF fading can be improved after a length fiber connection of 20 km long. Moreover, the obtained OFDM modulation rate also can meet the forward error correction (FEC) target.

Magnetic orbital motion and 0.5e2/h conductance of quantum-anomalous-Hall hybrid strips

The magnetic-induced orbital motion of quasiparticles affects the conductance properties of a hybrid strip of a quantum-anomalous-Hall topological material with induced superconductivity. We elucidate the scenario of topological normal-superconducting-normal ideal junctions in the presence of orbital magnetic motion, showing how it leads to a halved quantized conductance 0.5e2/h even in the absence of Majorana modes. For vanishing energy, the magnetic orbital effect favors Fermionic charged modes with finite wave numbers, in contrast to chiral Majorana modes that are chargeless modes with the vanishing wave number. The bias sensitivity of the 0.5 conductance plateau allows distinguishing the two cases. Conductance oscillations due to backscattering interference are absent in the charged Fermion case.

Use of Same WDM Channels in Fiber Network for Bidirectional Free Space Optical Communication With Rayleigh Backscattering Interference Alleviation

In the paper, we present and demonstrate experimentally a 10 Gbit/s on-off keying (OOK) bidirectional wavelength-division-multiplexing (WDM) free space optical (FSO) communication architecture integrated in fiber network together with 5 m free space transmission length and 25 km fiber link, respectively. To achieve bidirectional FSO link, the all WDM wavelengths can be used simultaneously to serve as the downstream and upstream traffics in the proposed FSO-WDM system. Here, four pairs of line terminations (LTs) and optical wireless units (OWUs) are integrated arbitrarily in fiber access network for confidential and bidirectional FSO connection based on the requirement of practical environment. In the measurement, the relationship of FSO signal performance and detected tolerance are also discussed and analyzed. Moreover, the WDM-FSO transmission can also avoid the Rayleigh backscattering (RB) beat noise in fiber connection.

Active pulse television measuring systems for ensuring navigation of transport means in heavy weather conditions

This paper presents research results of the Active Vision Area, formed by the Active Pulse Television Measuring System in conditions of decreased transparency of propagation medium.&#x0D; Aim: To increase backscatter interference suppression efficiency by the Active Pulse Television Measuring System for ensuring navigation of transport means in heavy weather conditions.&#x0D; Methods: Simulation of Active Vision Area considering light energy attenuation is proportionate to the square of distance and attenuation caused by propagation atmosphere. Performance of experimental researches with the Prototype of Active Pulse Television Measuring System using Big Aerosol Chamber, simulating dense fog and smoke conditions.&#x0D; Results: The designed model of Active Vision Area allowed estimating the changes of light energy distribution in the observed space layer depending on range of observation and transparency of radiation propagation medium. With equal duration values of the illumination and strobing pulses of the photodetector in conditions of dense fog, significantly big residual backscatter interference was revealed, maximum intensity area of the radiation reflected from objects was displaced from a distance of strobing delay. Illumination pulse duration reduction led to increase of backscatter interference suppression efficiency, improvement of image contrast and increase of accuracy of determination of distance to the observed objects.&#x0D; Conclusion: The increase of backscatter interference suppression efficiency by the Active Pulse Television Measuring System for ensuring navigation of transport means in heavy weather conditions is a relevant task

The characteristics simulation of FMCW laser backscattering signals

A Monte Carlo simulation model of FMCW laser transmission in a smoke interference environment was established in this paper. The aerosol extinction coefficient and scattering coefficient changed dynamically in the simulation according to the smoke concentration variation, aerosol particle distributions and photon spatial positions. The simulation results showed that the smoke backscattering interference produced a number of amplitude peaks in the beat signal spectrum; the SNR of target echo signal to smoke interference was related to the transmitted laser wavelength and the aerosol particle size distribution; a better SNR could be obtained when the laser wavelength was in the range of 560–1660 nm. The characteristics of FMCW laser backscattering signals generated by simulation are consistent with the theoretical analysis. Therefore, this study was greatly helpful for improving the ability of identifying target and anti-interference in the further research.

All-Optical Virtual Private Network in OFDM-PON Using Microwave Photonic Filter

We propose and demonstrate a novel all-optical virtual private network (VPN) using a microwave photonic filter, which enables inter-communications among optical network units in a passive optical network system. In our scheme, an optical coupler based recirculating delay line is used at optical line terminal as an optical subsystem to implement a microwave photonic-bandpass filter (MP-BPF). The periodic passbands of an MP-BPF are used to transmit VPN signal, whereas stopbands are used for conventional upstream transmission. The proposed system has two critical issues, optical phase-induced intensity noise in the MP-BPF and Rayleigh back-scattering interference by a single-fiber loop back link. To overcome the issues, an RF clipping tone based spectrum-broadening technique is applied to uplink transmitter. The proposed all-optical VPN system is tolerant to wavelength of VPN optical carrier, and enables multi-VPN data transmission using multi-passbands of MP-BPF.

Fog backscattering interference suppression algorithm for FMCW laser fuze based on normalized frequency spectrum threshold

Fog backscattering can cause false alarm for laser fuze. The characteristics of the target echo signal and the fog echo signal of FMCW laser fuze are comparatively analyzed. Based on the frequency domain feature of beat signal in these two cases, a fog backscattering suppression method based on the normalized frequency spectrum threshold of beat signal is proposed. Experimental results from simulated laboratory environment showed that the algorithm can identify the target and the fog interference with the correct rate of 91%. This algorithm provides a new method to suppress the fog backscattering for the frequency modulated continuous wave laser fuze.

Abstract A25: A novel spectroscopic technology to image the native chromatin nanostructure in live cells

Abstract Proper regulation of higher-order chromatin structure is essential for normal gene regulation and cellular function. We have previously found that the nanoscale chromatin structure is significantly altered in early and field carcinogenesis using novel spectroscopic methods in parallel with biological assays (Backman and Roy, J Cancer, 2013, 3:251-261; Subramanian et al, Cancer Res, 2009, 13:5357-63; Stypula-Cyrus et al, PLoS One, 2013, 5:e64600). This was done in fixed human and animal model samples, suggesting that genetic/epigenetic alterations can serve as the earliest marker for neoplastic transformation. While chromatin is well understood at the nucleosomal level (&amp;lt;20nm) and chromosomal level (&amp;gt;200nm), little is known about the higher-order chromatin structure between these length scales. Current techniques available to study cellular structures below the diffraction limit (&amp;lt;200nm) require labeling that may alter the native cell structure, can only visualize a few molecules concurrently, and have poor temporal resolution. Here we present a new technique, BAck-Scattering Interference Spectroscopic (BaSIS) microscopy, with sensitivity to structures between 20-200nm that can quantify the dynamics of the nano-molecular organization in live cells without using exogenous labels. The BaSIS instrument was built into a commercial inverted microscope (Leica DMIRB) equipped with a high NA oil immersion objective with broadband illumination provided by a Xenon lamp. Refractive index fluctuations are measured by sampling backscattered light at each wavelength 500-700nm using a combination of a liquid crystal tunable filter (LCTF) and a CMOS camera. HeLa and CHO cells were first imaged in petri dishes with coverslip bottoms, and then incubated with Hoechst 33342, a nuclear stain that binds to AT-rich regions of the genome and has been reported to cause double-stranded breaks (DSBs) in the DNA (Pfeiffer et al, Mutagenesis, 2000, 4: 289-302). Additionally, mock-staining experiments were performed to compare the changes in nuclear structure due to Hoechst 33342 excitation compared to UV light exposure alone. We utilized a γ-H2A.X-Alexa488 conjugated antibody after Hoechst- and mock-staining to compare observed changes in BaSIS signal with the formation of DSBs. Using BaSIS, we show for the first time that the excitation of Hoechst 33342 immediately alters the native nuclear nanostructure and induces formation of DSBs, confirmed by the rapid phosphorylation of H2A.X. In our mock-stained control, we observed an average increase of 0.006% and 0.001% signal after UV exposure (p-value &amp;gt; 0.5), whereas the stained cells display a 17.01% and 7.1% decrease in HeLa and CHO nuclei, respectively (p-value &amp;lt; 0.001). Significantly, these changes in Hoechst-stained cells are detectable by BaSIS within seconds. This suggests that the mechanism responsible for the nuclear alteration detected by BaSIS is localized and immediate. We hypothesized that the observed transformation was due to the homogenization of chromatin through fragmentation and the concurrent chromatin decompaction, detected by refractive index fluctuations. Indeed, following Hoechst staining, we observed an accumulation of the γ-H2A.X antibody, whereas we observed little or no localization in the mock Hoechst-stained nuclei. Furthermore, traditional phase contrast microscopy, which is used for label-free imaging of living samples, did not show any changes in the higher-order chromatin structure following DSB formation in these experiments. In conclusion, BaSIS is a powerful tool for studying the dynamics of chromatin nanostructure and can serve as a natural supplement to super-resolution fluorescence techniques, providing quantified information about native cellular organization. With this technique, we demonstrated that using the Hoechst DNA-binding dye causes irreversible alterations in chromatin structure at time-scales (seconds) not previously recognized. As a result, BASIS can be applied to a broad range of critical studies in chromatin research. Current and future research include: (i) mRNA transport and the accessibility of euchromatin and heterochromatin to transcription factors; (ii) why and how high-order chromatin structure changes in cancer progression; (iii) the role of nuclear architecture as an epigenetic regulator of gene expression; and (iv) the effect of metabolism on chromatin structure; (v) damage/repair mechanisms and potentially, chemotherapeutic efficacy. Citation Format: Yolanda Stypula, Scott Gladstein, Luay Almassalha, Greta Bauer, John Chandler, Lusik Cherkezyan, Di Zhang, Hariharan Subramanian, Igal Szleifer, Vadim Backman. A novel spectroscopic technology to image the native chromatin nanostructure in live cells. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Sep 24-27, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2016;76(2 Suppl):Abstract nr A25.

English

A novel integration scheme from time-division-multiplex passive optical network (TDMPON) to wavelength-division-multiplex PON (WDM-PON) using differential Quadreture phase-shift keying (DQPSK) for the downstream signal and wavelength-shifted amplitude-shift keying (WS-ASK) for the upstream signal is illustrated. The migration scheme does not change the existing fiber infrastructure. An optical filter is preinstalled at the optical networking unit (ONU) to select the desirable downstream wavelength for the WDM-PON and simultaneously demodulate the downstream DQPSK signal. Signal remodulation is used to generate the upstream signal by reusing the downstream wavelength. In the ONU, by wavelength shifting the upstream optical spectrum with respect to the downstream optical spectrum, the Rayleigh backscattering (RB) interference beat noise affecting the upstream signal can be significantly mitigated. The optimum bandwidth for the downstream DQPSK demodulation is analyzed.