Binary Phase Modulation Research Articles

Spectral compression by phase doubling in second harmonic generation

In second harmonic generation, the phase of the optical field is doubled, which has important implications. Here, the phase-doubling effect is utilized to solve a long-standing challenge in the power scaling of single-frequency laser. (-π/2, π/2) binary phase modulation is applied to a single-frequency seed laser to broaden the spectrum and suppress the stimulated Brillouin scattering in a high-power fiber amplifier. The second harmonic of the phase-modulated laser returns to single frequency because the (-π/2, π/2) modulation is doubled to (-π, π) for the second harmonic. A compression-to-single-frequency rate as high as 95% is demonstrated in experiments limited by the electronic bandwidth of the setup. Such phase manipulation in wave-mixing processes may open up a new field of development in nonlinear optics and laser technology.

Novel Multiplexing Scheme for Resolving the Velocity Ambiguity Problem in MIMO FMCW Radar Using MPSK Code

For the high-resolution DoA (Direction of Arrival) estimation, various multiplexing schemes are considered for the multi-input multi-output (MIMO) fast chirp frequency-modulated continuous-wave (FMCW) radar. However, current schemes such as time-division multiplexing (TDM) and binary-phase modulation (BPM) may reduce the maximum detectable velocity, which causes the velocity ambiguity problem. As an extension of the BPM scheme to mitigate this issue, we propose a novel multiplexing scheme using M phase-shift keying (MPSK) code which duplicates shifted target peaks at unequal intervals over the velocity domain. The proposed scheme finds the true peaks to resolve the velocity ambiguity problem by the inversion of the circulant matrix with low additional computation. In addition, the successful implementation of the proposed scheme is conducted with 4 by 8 MIMO uniform linear array (ULA) antennas through the state-of-the-art FMCW radar. Finally, the proposed scheme is compared to the conventional TDM based MIMO scheme regarding signal to noise ratio (SNR) and phase calibration issues for moving targets. The proposed scheme is to estimate the accurate 4D information of targets while resolving the velocity ambiguity problem in the MIMO FMCW radar systems.

Auto-focusing acoustic-vortex tweezers for obstacle-circumventing manipulation

Contactless manipulation of hard-to-reach objects, especially those behind obstacles, is highly demanded in many applications. In this work, auto-focusing acoustic-vortex (A-FAV) tweezers are developed based on-axis-symmetrically arranged and azimuthally phase-coded Half-Bessel (HB) beams, which can self-bend themselves along an arc-shaped trajectory and, hence, circumvent obstacles that are located on the beam path. To build such tweezers, active phase control and passive binary phase modulation for a simplified ring-array of sectorial planar transducers are integrated to build A-FAV beams of arbitrary order. Both theoretical and experimental results prove that the zero-force of A-FAV tweezers enables the stable object manipulation at the focus with improved axial and radial resolutions. Benefiting from the non-diffracting self-bending of HB beams, the enclosed bullet-shaped cavity whose inside pressure is close-to-zero can be created around the beam axis, defining the upper size limit of obstacles that can be bypassed. Moreover, A-FAV beams are capable of self-healing even parts of the mainlobes that are blocked. More importantly, the A-FAV tweezer with an obstacle-circumvention cavity is easily adjustable, exhibiting prosperous perspectives in obstacle-avoidant ultrasound imaging, ultrasound therapy, acoustic levitation, and object manipulation.

An IR-UWB IEEE 802.15.4z Compatible Coherent Asynchronous Polar Transmitter in 28-nm CMOS

A low-power IEEE 802.15.4z high-rate PHY (HRP) compatible coherent transmitter is described. The proposed transmitter uses a digital polar architecture with fixed amplitude steps in the power amplifier and asynchronous time-discrete pulse shaping. The pulse-shaping unit consists of a finite-impulse response (FIR) filter using current-starved inverter-based delay taps that can be calibrated on-chip. An injection-locked ring oscillator (ILRO)-based frequency synthesis enables wideband operation from 3- to 10-GHz frequency bands. The ILRO also allows for duty-cycled coherent mode operation with 2–4-ns phase locking time and binary phase modulation is applied directly on the oscillator. The on-chip digital front end enables duty cycling (DC) of analog front-end modules with a granularity of 2 ns. Implemented in 28-nm CMOS process, this chip is measured to consume 4.9-mW power in nominal mode with IEEE 802.15.4z high pulse repetition frequency (HPRF) compatible data rate of 6.81 Mb/s compliant with major spectrum mask regulations for channels 5 and 9. With DC of the oscillator enabled in the energy-efficient mode, a power consumption of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$430~\mu \text{W}$ </tex-math></inline-formula> is achieved for packets compatible with legacy pulse-position-modulated IEEE 802.15.4a standard with a data rate of 27.2 Mb/s.

Instantaneous response and suppression of SBS process in a short fiber system with binary sequence phase modulation.

We study the instantaneous response of stimulated Brillouin scattering (SBS) in a fiber system phase modulated by a binary sequence waveform. The buildup time constant of SBS kinetics is investigated analytically and experimentally. A series of binary sequences with adjustable dwell time and sequence period is constructed in order to examine both buildup and suppressing processes for SBS in 15 m short fiber. For a fiber system with SBS buildup time constant within several nanoseconds, the Stokes intensity can be effectively suppressed by implementing a binary sequence phase modulation with a dwell time close to or even less than the buildup time constant. Stokes intensity can be suppressed in several sequence periods, which exhibit a damped-oscillation-like trend.

High-performance railway perimeter security system based on the inline time-division multiplexing fiber Fabry-Perot interferometric sensor array

This paper proposes a high-performance railway perimeter security system based on the inline time-division multiplexing fiber Fabry-Perot interferometric (TDM-FFPI) sensor array. A rectangular-pulse binary phase modulation (RPBPM) method is used for phase demodulation and a field programmable gate array (FPGA)-based acquisition system is adopted for receiving and processing the signals with the advantages of low complexity and high real-time capability in this system. Besides, a three-polarizer polarization diversity receiver (tr-PDR) is used to overcome the polarization-induced fading elimination. For the demodulated phase signals, a real-time and accurate two-level pattern recognition method based on the support vector machines (SVM) is employed for the recognition of different events (non-intrusion events including environment, rain and wind, and four intrusion events including shaking, cutting, climbing and knocking). The feasibility of the present system is verified experimentally. The average recognition accuracy is up to about 94.5% with the integrating time less than 0.2 s, which satisfies the high accuracy and high real-time requirements.

Vibro-Thermal Wave Radar: Application of Barker Coded Amplitude Modulation for Enhanced Low-Power Vibrothermographic Inspection of Composites.

This paper proposes an efficient non-destructive testing technique for composite materials. The proposed vibro-thermal wave radar (VTWR) technique couples the thermal wave radar imaging approach to low-power vibrothermography. The VTWR is implemented by means of a binary phase modulation of the vibrational excitation, using a 5 bit Barker coded waveform, followed by matched filtering of the thermal response. A 1D analytical formulation framework demonstrates the high depth resolvability and increased sensitivity of the VTWR. The obtained results reveal that the proposed VTWR technique outperforms the widely used classical lock-in vibrothermography. Furthermore, the VTWR technique is experimentally demonstrated on a 5.5 mm thick carbon fiber reinforced polymer coupon with barely visible impact damage. A local defect resonance frequency of a backside delamination is selected as the vibrational carrier frequency. This allows for implementing VTWR in the low-power regime (input power < 1 W). It is experimentally shown that the Barker coded amplitude modulation and the resultant pulse compression efficiency lead to an increased probing depth, and can fully resolve the deep backside delamination.

Doppler disambiguation in MIMO FMCW radars with binary phase modulation

Multiple-input multiple-output arrays in frequency modulated continuous wave (FMCW) radars provide the angular resolution required to isolate objects in complex automotive scenes. However, the demodulation of individual antenna contributions increases the chirp repetition interval, which reduces the maximum unambiguously measurable velocity. Objects moving faster than this velocity are then incorrectly folded in the range-Doppler maps, leading to critical inaccuracies in the advanced driver assistance systems. Here, this problem is addressed from the binary phase modulation (BPM) perspective, which is a scheme particularly attractive due to its high signal-to-noise ratio, and whose intrinsic phase alterations prevent traditional disambiguation techniques from being reliable. The authors present a detailed analysis on the design, implementation, and validation of Doppler disambiguation techniques for BPM systems. The presented benchmark includes a variety of algorithms involving the Chinese remainder theorem, density-based spatial clustering of applications with noise (DBSCAN), hypothetical phase compensation, and an intuitive range-based approach. The techniques are extensively validated using synthetic data generated with MATLAB, and real data collected with a 77-GHz FMCW radar. The results show the best set of trade-offs for the enhanced DBSCAN (EDBSCAN) method in terms of robustness, computational overhead, velocity span, and disambiguation rate.

Broadband Efficient Dual‐Polarization Airy Beam Generation with Reflective Metasurface

This study demonstrates that continuous amplitude and binary phase modulation suitable for Airy beam encoding can be frequency‐independently obtained with not only cross‐polarized but also copolarized transmitted/reflected electromagnetic field components by rotation of unit cell with reflection symmetry. Maximum device efficiency can be achieved with relevant Airy beam generator, when the eigen polarization states of the unit cell are two orthogonal linear polarization states, and the copolarization reflections of them are out of phase and both have the amplitude of unity. As a proof of principle, broadband and high‐efficiency reflective Airy beam generators based on both copolarization and cross‐polarization modulation approaches are fabricated with cut‐wire structure as unit cell. The measured results show that the efficiency of the devices is approaching the theoretical limit in a wide frequency range.

Pipeline anti-vandalism monitoring system based on time division multiplexing interferometric fiber optic sensor array

A pipeline anti-vandalism monitoring system based on time division multiplexing (TDM) interferometric fiber optic sensor array is proposed and demonstrated in this paper to realize the anti-vandalism monitoring of buried pipelines. The sensor unit of the TDM quasi-distributed system can be responsible for a continuous monitoring area due to its high sensitivity through sensitization. Therefore, the TDM-supported quasi-distributed sensor technique only needs to dig at several sites to avoid digging deeply into ground along the pipeline. This can greatly reduce the system cost and accelerate the construction process. In addition, a phase detection method based on the rectangular pulse binary (RPB) phase modulation is used to realize the phase detection, and a field programmable gate array (FPGA)-based signal acquisition interrogation controller is adopted to realize the rapid and real-time acquisition of returned interference signals in the system. For the demodulated phase signals, by judging the three eigenvalues of level crossing time-domain statistics, peak-to-average ratio, and short-term energy, effective anti-vandalism alarm can be achieved. The system is tested and verified. The experiment results show that the system can achieve effective and real-time anti-vandalism alarm with accuracy rate over 90% within 1 ms.

Ultrashort pulse generation from binary temporal phase modulation

AbstractWe propose and numerically validate an all‐optical scheme to generate a train of optical pulses. Modulation of a continuous wave with a periodic binary temporal phase pattern followed by a spectral phase shaping enables us to obtain ultrashort pulse trains. An ideal step phase profile as well as a profile arisen from a bandwidth‐limited device is investigated. Analytical guidelines describing pulse train formation and their characteristics are provided. Pulses with a duration of a few picoseconds at a repetition rate of 10 GHz can be expected for realistic experimental conditions.

An Interferometric Optical Fiber Perimeter Security System Based on Multi-Domain Feature Fusion and SVM

In this paper, an interferometric optical fiber perimeter security system based on multi-domain feature fusion and support vector machine (SVM) is reported. To improve the intrusion event classification accuracy and reduce the overall cost, advanced optical fiber sensor technique and data analysis method are synthesized to build the system. For the optical component, the Michelson interferometer sensor structure and the rectangular-pulse binary phase modulation method are adopted to reduce the system complexity and cost. For the electronic data analysis component, mixed domains (including time, frequency and wavelet domains) features are selected and the SVM is adopted to classify the intrusion event type. Specifically, the zero-crossing rate (ZCR) is chosen as the feature element in the time domain, whose threshold is determined by analyzing the environmental noise. The variance of the power spectral density (PSD) of the phase signal in four frequency bands are selected as the feature element in the frequency domain. The energy of the phase signal by using the wavelet packet decomposition in four full frequency bands is chosen as the feature element in the wavelet domain. All the acquired features corresponding to various event conditions are combined into the feature vector data set, which are trained and predicted by the SVM. In the field experiment test, the proposed identification scheme was used to identify and classify five kinds of events, including non-intrusion, climbing, shaking, iron bar knocking and fiber cable shearing. The achieved average classification accuracy reached 94.4%.

A Reconfigurable Intelligent Surface at mmWave Based on a Binary Phase Tunable Metasurface

Originally introduced in the early 2010's, the idea of smart environments through reconfigurable intelligent surfaces (RIS) controlling the reflections of the electromagnetic waves has attracted much attention in recent years in preparation for the future 6G. Since reconfigurable intelligent surfaces are not based on increasing the number of sources, they could indeed pave the way to greener and potentially limitless wireless communications. In this paper, we design, model and demonstrate experimentally a millimeter wave reconfigurable intelligent surface based on an electronically tunable metasurface with binary phase modulation. We first study numerically the unit cell of the metasurface, based on a PIN diode, and obtain a good phase shift and return loss for both polarizations, over a wide frequency range around 28.5 GHz. We then fabricate and characterize the unit cell and verify its properties, before fabricating the whole 10 cm x10 cm reconfigurable intelligent surface. We propose an analytical description of the use that can be done of the binary phase RIS, both in the near field (reflectarray configuration) and in the far field (access point extender). We finally verify experimentally that the designed RIS works as expected, performing laboratory experiments of millimeter wave beamforming both in the near field and far field configuration. Our experimental results demonstrate the high efficiency of our binary phase RIS to control millimeter waves in any kind of scenario and this at the sole cost of the energy dissipated by the PIN diodes used in our design.

Low-coherence optical diffraction tomography using a ferroelectric liquid crystal spatial light modulator.

Optical diffraction tomography (ODT) is a three-dimensional (3D) label-free imaging technique. The 3D refractive index distribution of a sample can be reconstructed from multiple two-dimensional optical field images via ODT. Herein, we introduce a temporally low-coherence ODT technique using a ferroelectric liquid crystal spatial light modulator (FLC SLM). The fast binary-phase modulation provided by the FLC SLM ensures the high spatiotemporal resolution. To reduce coherent noise, a superluminescent light-emitting diode is used as an economic low-coherence light source. We demonstrate the performance of the proposed system using various samples, including colloidal microspheres and live epithelial cells.

Spectral Compression of Narrowband Single Photons with a Resonant Cavity.

We experimentally demonstrate a spectral compression scheme for heralded single photons with narrow spectral bandwidth around 795nm, generated through four-wave mixing in a cloud of cold ^{87}Rb atoms. The scheme is based on an asymmetric cavity as a dispersion medium and a simple binary phase modulator, and can be, in principle, without any optical losses. We observe a compression from 20.6MHz to less than 8MHz, almost matching the corresponding atomic transition.

Generation of subdiffraction longitudinal bifoci by shaping a radially polarized wave

Lenses with two or more foci along the longitudinal direction exhibit immense potential in several optical applications. In this study, we propose an approach for generating subdiffraction longitudinal bifoci by binary-phase bifocal super-oscillatory lenses (SOLs), which are realized by simple AND operation between two single-foci SOLs with different focal lengths. Three bifocal SOLs with radiusRlens=70λ are designed at an operating wavelength of λ=118.8µm. Simulation results demonstrate that the minimum full width at half maximum (FWHM) is 0.397λ, and the maximum FWHM is 0.449λ, which is still smaller than the Abbe diffraction limit of 0.510λ, while all the sidelobe ratios are small (<15.1%). By properly choosing the focal length of the single-foci SOLs in the design process, the distance between the two foci can be easily controlled. Significantly, the generated bifoci with relatively uniform intensity contain a strong longitudinal electric field, which indicates their excellent prospects in optical imaging, particle acceleration, and other optical applications. In addition, the proposed bifoci-SOLs are based on the binary phase modulation, which facilitates easy fabrication compared with other approaches. These outstanding properties indicate the wide application prospects of bifocal SOLs.

Nonlinear Beam Shaping with Binary Phase Modulation on Patterned WS2 Monolayer

The capability of controlling the phase of the nonlinear polarization of media is vital for nonlinear optical beam shaping. Achieving this control over nonlinear phase manipulation on the nanoscale...

Simple techniques to generate binary periodical polarization fields.

We report two new, to the best of our knowledge, methods to generate polarization gratings, whose basic cells are formed by sections that are orthogonally polarized. One of the methods employs a spatial filtering setup that modulates the diffraction orders in the Fourier domain of a Ronchi grating, with two orthogonal polarizations. In the second method, a binary phase modulation, generated by a liquid crystal device, is converted into orthogonal polarizations in different zones of an incident beam. The analysis of the generated polarization states is made at 1/4 of the Talbot distance of the generated gratings. The experimental results are in good agreement with the theoretical description.

Increasing the enhancement factor for DMD-based wavefront shaping.

Focusing through scattering media is a subject of great interest due to its direct impact in the field of biomedical optics. However, the greatest barrier currently limiting direct applications is the fact that most scattering media that we wish to deliver light through are dynamic. To focus or deliver light through dynamic scattering media, using a digital micromirror device (DMD) has been demonstrated to be a potential solution, as it enables fast modulation speeds. However, since a DMD is a binary amplitude modulator, the large number of controlled modes needed to acquire adequate focus enhancement has limited optimal usage. Here we demonstrate a novel (to the best of our knowledge) scheme to use the "thrown-away" components of light to effectively use a binary amplitude DMD as a binary phase modulator, thereby increasing the correction efficiency by a factor of two. Our concept can be applied to any iterative optimization algorithm and can speed up the iterative optimization process by increasing the enhancement factor, rather than the measurement or modulation speeds.

An Active Jamming Method Against ISAR Based on Periodic Binary Phase Modulation

Phase modulation technique is of great potential for generating jamming signal in electronic countermeasures. It is still a difficulty to devise a kind of jamming signal capable of generating both false targets deception jamming and barrage jamming. Attentions must be paid to phase modulation patterns and phase values. Inspired by scatter-wave jamming and phase modulation, an active jamming technique against inverse synthetic aperture radar (ISAR) is proposed based on periodic binary phase modulation in this paper. By imposing the periodic binary phase value (0 or π) onto the intercepted radar signal, the frequency properties of radar signal are changed, which result in the corresponding changes on the target echo. Accordingly, the imaging results are reformatted comparing with the target image. Radar pulses are sampled and phase-modulated in the fast time domain as well as the slow time domain, and then the jamming pulses are retransmitted to the target. After ISAR imaging, the false target images are induced. The principle and process of phase modulation are studied in detail. Then, the imaging model of jamming signal is established and the analysis of jamming effects are carried out. The simulation results with single scattering point and real data experiments with a ship show that both deception jamming and barrage jamming can be obtained. The theoretical analysis and simulation results prove the validity of the active jamming technique.