Binary Phase Modulation Research Articles

RECEPTION ALGORITHM AS A WHOLE WITH ELEMENT-BY-ELEMENT DECISION MAKING USING THE PHASE MODULATION METHOD

The article is aimed to provide reception algorithm as a whole with element-by-element decision making. It belongs to the group of decision, making algorithms with feedback. It is used to demodulate discrete signals that have passed through a memory channel. The study presents an example of signal processing of a binary phase modulator. This example shows processing features that are not obvious for considering of the mathematical formula that describes demodulation algorithm. Another algorithm was developed for a quadrature phase modulator as well. The noise immunity for additive gaussian noise was estimated by the numerical simulations. The same researches was carried out using an equalizer filter that suppresses channel memory effect. Simulation results were used as the base for the graphs of the error probability versus signal-to-noise ratio.

Compact eternal diffractive neural network chip for extreme environments

Artificial intelligence applications in extreme environments place high demands on hardware robustness, power consumption, and speed. Recently, diffractive neural networks have demonstrated superb advantages in high-throughput light-speed reasoning. However, the robustness and lifetime of existing diffractive neural networks cannot be guaranteed, severely limiting their compactness and long-term inference accuracy. Here, we have developed a millimeter-scale and robust bilayer-integrated diffractive neural network chip with virtually unlimited lifetime for optical inference. The two diffractive layers with binary phase modulation were engraved on both sides of a quartz wafer. Optical inference of handwritten digital recognition was demonstrated. The results showed that the chip achieved 82% recognition accuracy for ten types of digits. Moreover, the chip demonstrated high-performance stability at high temperatures. The room-temperature lifetime was estimated to be 1.84×1023 trillion years. Our chip satisfies the requirements for diffractive neural network hardware with high robustness, making it suitable for use in extreme environments.

3.05 kW, 13.7 GHz linewidth fiber amplifier based on PRBS phase modulation for SBS suppression

In this paper, we establish a multi-stage fiber amplifier with pseudo-random binary sequence (PRBS) phase modulation. The stimulated Brillouin gain spectra of the main amplifier with both the unmodulated and pseudo-random binary sequence phase modulated configuration are measured (with corresponding output power), and the stimulated Brillouin scattering (SBS) threshold is investigated experimentally and theoretically. The pseudo-random binary sequence phase modulation parameters are optimized by theoretical simulation. With a two-stage preamplifier chain and a counter-pumping main amplifier stage, a maximum 3.05 kW output power with a slope efficiency of 85.9% is obtained experimentally. The central wavelength of the fiber amplifier is 1050 nm, associated with a full-width at half-maximum linewidth of 13.7 GHz. The stimulated Brillouin scattering reflectivity is below 0.01% at 3.05 kW at 13.7 GHz, which indicates that stimulated Brillouin scattering can be suppressed efficiently at this power and linewidth level.

Formation of multiple complex light structures simultaneously in 3D volume using a single binary phase mask

Complex structure formation inside or through turbid media is a challenging task due to refractive index inhomogeneity, random light scattering, and speckle noise formation. In this article, we have coupled the data regression model in the R-squared metric and used its advantages as a fitness function in the genetic algorithm to advance the resolution and structural uniformity. As a compatible system with the binary genetic algorithm, we have presented a cost-effective iterative wavefront shaping system-design with binary phase modulation using an affordable ferroelectric liquid crystal (FLC) based binary-phase spatial light modulator (SLM). R-squared metric in the genetic algorithm is analyzed to optimize the binary phase mask, and the prototype system based on iterative binary phase modulation has been validated with a 120-grit ground glass diffuser and fresh chicken tissues of thickness 307 {upmu }text {m} and 812 {upmu }text {m}. The detailed results show that the proposed cost-effective wavefront shaping system with data regression model assisted R-squared fitness function can construct high-resolution multiple complex hetero-structures simultaneously in 3D volume using an optimized single phase-mask.

Transceiver Designs Approaching the Entanglement-Assisted Communication Capacity

Preshared entanglement can significantly boost communication rates in the high thermal-noise and low-brightness transmitter regime. In this regime, for a lossy bosonic channel with additive thermal noise, the ratio between the entanglement-assisted capacity and the Holevo capacity---the maximum reliable communication rate permitted by quantum mechanics without any preshared entanglement---scales as $\mathrm{log}(1/{\overline{N}}_{S})$, where the mean transmitted photon number per mode, ${\overline{N}}_{S}\ensuremath{\ll}1$. Thus, preshared entanglement, e.g., distributed by the quantum internet or a satellite-assisted quantum link, promises to significantly improve low-power radio-frequency communications. In this paper, we propose a pair of structured quantum transceiver designs that leverage continuous-variable preshared entanglement (generated, e.g., from a down-conversion source), binary phase modulation, and non-Gaussian joint detection over a codeword block, to achieve this scaling law of capacity enhancement. Furthermore, we describe a modification to the aforesaid receiver using a frontend that uses sum-frequency generation sandwiched with dynamically programmable in-line two-mode squeezers, and a receiver backend that takes full advantage of the output of the receiver's frontend by employing a nondestructive multimode vacuum-or-not measurement to achieve the entanglement-assisted classical communication capacity.

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.

Modeling of a secondharmonic spectrum in passive phase demodulation.

Spectral compression by passive phase demodulation provides an effective way to obtain a high-power single-frequency second harmonic (SH) laser. In this method, a single-frequency laser is broadened by (0, π) binary phase modulation for stimulated Brillouin scattering suppression in a high-power fiber amplifier and compressed to single frequency after frequency doubling. The effectiveness of compressing is determined by the properties of the phase modulation system, including the modulation depth, frequency response of modulation system, and modulation signal noise. A numerical model is developed to simulate the influence of these factors on the SH spectrum. The simulation results reproduce the experimental observation well, including the reduction of the compression rate at higher-frequency phase modulation, emergence of spectral sidebands and pedestal.

Performance Analysis of Uncoordinated Interference Mitigation for Automotive Radar

As a key sensor for Advanced Driving Assistance System (ADAS), millimeter automotive radar has been a promising candidate for fulfilling tasks including adaptive cruise control and collision avoidance. However, the widely deployment of millimeter automotive radars may cause serious mutual interference among vehicles, thus degrading radar ranging performance severely. In this article, we analyze the mutual interference among multiple Frequency Modulated Continuous Wave (FMCW) radars. On one hand, we model the interference precisely by employing Matern Hard-Core Process (MHCP) model to characterize the distribution of vehicle nodes in practical bidirectional two-lane and multi-lane scenarios. Besides, the interference is analyzed in terms of the channel fading, the directional antenna pattern and the fluctuation of the target Radar Cross-Section (RCS) in two-lane and multi-lane scenarios. Besides, we analyze the reflected interference in detail. On the other hand, we evaluate the interference mitigation performance of the Random Frequency Division Multiplexing (RFDM) and Frequency Hopping (FH) approaches in terms of the probability of false detection and miss detection, effective detectable density and maximum number of interference-free radar. Finally, a novel AFH-PM mitigation approach is proposed to further improve the interference mitigation performance, which combines the adaptive FH technology with the binary phase modulation. Simulation results verify the proposed framework for interference analysis by employing Monte Carlo method, and the performance improvement of RFDM, FH and AFH-PM is 6.7 dB, 7.6 dB and 8.2 dB, respectively.

Optical asymmetric JTC cryptosystem based on binary phase modulation and image superposition-subtraction operation.

The joint transform correlator (JTC) cryptosystem is a simple and practical optical cryptosystem. But its identical key in both encryption and decryption brings security risks in the key distribution and management. To overcome these drawbacks, we first create a trapdoor one-way function based on image superposition and subtraction operation. Then combined with the one-way binary phase modulation, an optical asymmetric JTC cryptosystem is proposed in this paper. These two kinds of trapdoor one-way functions are not only effective and implementable, but also can greatly enhance the ability of our proposal to resist various attacks. In addition, we select the structured spiral phase mask (SSPM) controlled by its structural parameters as the key mask of the JTC cryptosystem to facilitate the key transmission. When the structural parameters of the SSPM are protected by the RSA algorithm during encryption and decryption, not only the security of the proposed cryptosystem can be enhanced, but also the key distribution and management will be improved. This also makes our proposal conform more closely to the basic agreement of the public key cryptosystem. Simulation analysis and initial experimental results verified the correctness and feasibility of our proposal.

High-dimensional orbital angular momentum comb

The article comments on a recently reported OAM comb. The proposed approach relies on a simple azimuthal binary phase modulation scheme to transform a Gaussian beam into a structured light beam containing multiple OAM components with equal spacing and uniform power. It provides a convenient way to simultaneously tailor multiple OAM channels, with the potential to impact many fields, including optical information technology.

Space-time analogy and its application to design schemes borrowed from Fourier optics for processing ultrafast optical signals

Square-wave pulse generation with a variable duty ratio can be realized with the help of the ideas of Talbot array illuminators formulated for binary phase gratings. A binary temporal phase modulation of continuous wave (CW) laser field propagating through a group-delay-dispersion circuit of the fractional Talbot length results in a well defined sequence of square-wave-form pulses. When P = 1 a duty ratio of the pulses D is for Q = 4 and for Q = 3 and 6. Maximum intensity of the pulses doubles and triples compared to the CW intensity for and , respectively. These pulses can be used for return-to-zero laser field modulation in optical fiber communication. For extra features between the pulses are found originating from a finite rise and drop time of phase in a binary phase modulation. A similar effect to the benefit of the time-space analogy is predicted for binary phase gratings and interpreted as gleams produced by imperfect edges of the components of the rectangular phase gratings.

Planar liquid crystal optics for simultaneously surface displaying and diffraction-limited focusing

Abstract Planar optical elements have attracted widespread attentions because of their precise light modulation. Liquid crystals (LCs) are well known for their applications in the current displaying field, and show great potential in planar optical elements with the development and innovation of LC micro-operation technology. However, previous researches on LC elements mainly involved only one type of optical manipulation, which inevitably limited the functional diversity. In this work, we propose a multifunctional LC element which integrates the surface display into a binary-phase focusing lens by controlling the complex amplitude of the incident light. The light modulation of the anisotropic LC molecule satisfies a sinusoidal variation, which can be regarded as the combination of a continuous amplitude modulation and a binary phase modulation. The element with millimeter size is then fabricated, and the experimental measurements agree well with our design with a high-definition surface pattern and high-quality optical focusing/imaging performance. Furthermore, as the complex amplitude modulation changes from sine to cosine function after rotating the sample by 45°, a bifocal lens with two different focal lengths is also demonstrated. We expect the proposed multifunctional LC elements can find applications in information multiplexing, image displaying, etc.

Shack–Hartmann Wavefront Sensing Based on Four-Quadrant Binary Phase Modulation

Aiming at the problem that it is difficult for the conventional Shack–Hartmann wavefront sensor to achieve high-precision wavefront reconstruction with low spatial sampling, a kind of Shack–Hartmann wavefront sensing technology based on four-quadrant binary phase modulation is proposed in this paper. By introducing four-quadrant binary phase modulation into each subaperture, the technology is able to use an optimization algorithm to reconstruct wavefronts with high precision. The feasibility and effectiveness of this method are verified at extreme low spatial frequency by a series of numerical simulations, which show that the proposed method can reliably reconstruct wavefronts with high accuracy with rather low spatial sampling. In addition, the experiment demonstrates that with a 2 × 2 microlens array, the four-quadrant binary phase-modulated Shack–Hartmann wavefront sensor is able to achieve approximately 54% reduction in wavefront reconstitution error over the conventional Shack–Hartmann wavefront sensor.

Ferroelectric liquid-crystal modulator with large switching rotation angle for polarization-independent binary phase modulation

In this work a ferroelectric liquid crystal (FLC) modulator with a non-standard large switching rotation angle, close to 90∘, is fabricated and characterized. The modulator acts as a switchable wave-plate with an in-plane rotation of the principal axis under the action of a bipolar voltage. In the ideal situation of half-wave retardance, the device is shown to behave as a binary π phase modulator independently of the input state of polarization. We provide physico-chemical properties of the liquid crystalline mixture used to fabricate the FLC modulator with such large switching angle. The characterization method of the device optical properties is presented, which allows the localization of the two LC stable states, the unambiguous determination of the rotation angle, and the evaluation of the spectral retardance function. We demonstrate the polarization-independent π phase shift using an adapted Young's type interferometer for real-time measurements, where we further analyze the operational frequency limits of the device. This FLC operational mode can be exploited to produce binary-phase polarization-independent diffractive optical elements.

Enhanced axial resolution of lattice light sheet microscopy by fluorescence differential detection.

Lattice light-sheet microscopy (LLSM) is promising in long-term biological volumetric imaging due to its high spatiotemporal resolution and low phototoxicity. However, three-dimensional (3D) isotropic spatial resolution remains an unmet goal in LLSM because of its poorer axial resolution. Combing LLSM with fluorescence differential detection, namely LLSDM, has been proposed to improve the axial resolution of LLSM in simulation. It demonstrates the possibility of further enhancing the axial resolution in 3D volumetric imaging with LLSM by specifically discarding the off-focus photons captured using a complementary optical lattice (OL) profile generated with additional 0-π phase modulation at the objective pupil plane. The direct generation of the complementary lattice profile using the binary phase modulator conjugated to the sample plane for amplitude modulation, as used in LLSM, is also permittable. Nevertheless, the previously proposed configuration fails to provide a symmetric complementary lattice pattern along the axial axis, thus leading to the imbalanced off-focus photon suppression in the reconstructed images after subtraction [Opt. Lett.45, 2854 (2020)10.1364/OL.393378]. Here, we modified the LLSDM theory which can produce an ideal complementary lattice pattern with central zero intensity and symmetrically distributed sidelobes. We also analyzed the impact of numerical aperture matching between the original and complementary lattice patterns and presented the consistency between the simulated and experimental results. As demonstrated by imaging the distribution of fluorescent beads and microtubules in fixed U2OS cells, as well as the dynamics of filopodia in live U2OS cells, LLSDM provides about 1.5 times improvement in axial resolution, and higher imaging contrast compared with traditional LLSM.

Evolutoin of algorithms for separation of optimal two mutually unorthogonal signals of binary phase modulation

A review of the results of the development of the methodology for the synthesis of the separation-demodulation algorithms of two mutually non-orthogonal binary phase modulation signals in the length of the information clock interval, synchronous and asynchronous according to the clock points, with continuous and intermittent radiation. The evolution of algorithms for optimal separation of two mutually non-orthogonal signals of binary phase modulation has the following sequence: signals are mutually synchronous by clock points (communication channel – with constant parameters, non-seeding oscillations are represented by functions integrated with the square; the signals are mutually synchronous in clock points, the second interfering signal is intermittent; signals are mutually asynchronous in clock points; the signals are mutually asynchronous in clock points, the second interfering signal is intermittent; signals are mutually synchronous in clock points, both signals are discontinuous. At the same time, the minimum probability of an error in the estimation of the discrete information parameter of the first (useful) signal was assumed as the optimality criterion. The results of a comparative review of algorithms for the separation of two mutually non-orthogonal binary FM signals demonstrate their evolutionary nature. The identified main regularities make it possible to obtain descriptions of signal separation procedures with mismatched clock frequencies without performing intermediate signal processing procedures. The gradual process of complicating synthesis tasks led to the discovery of gradual regularities in the structures of the separation-demodulation algorithms of two binary FM signals, which provides an opportunity to formulate directions for further research, which should be based on the provisions of the theory of multi-user detection. Namely, the revealed regularities are the basis for conducting further research in order to solve similar problems with the gradual further complication of the initial conditions. Priority consideration in the future will be given to tasks that have theoretical interest and practical value: when both signals are characterized by non-stationary intermittent emission modes and are asynchronous in clock points; when they are characterized by packet transmission mode; when band-efficient types of modulation are used (MSK, GMSK – first of all).

A High-Performance Multistep Phase-Shifting Interferometric Fiber Optic Sensing Method With Modulation Error Correction Capability

Modulation error is a main error source of phase-shifting technique in the field of interferometric fiber optic sensing. To solve this problem, a multistep phase-shifting method with modulation error correction capability using rectangular-pulse binary phase modulation is proposed in this paper. In this method, a pair of three-step interference signals are obtained with the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> /2 phase modulation to generate multistep phase-shifting interference signals. The cross-correlation operation of the two signals with the same phase shift is calculated. Then, precise control of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> /2 modulation can be realized using simulated annealing algorithm to correct the modulation error. In addition, compared with the three-step phase-shifting algorithm, the extracted five-step phase-shifting algorithm itself has a higher ability to suppress the modulation error. Simulation and experimental results demonstrate that this method can be used to demodulate the phase result with high effectiveness and stability, improve the time domain signal and reduce the total harmonic distortion (THD), which provides a novel perspective for high-performance fiber-optic sensing and phase-shifting technique. In the actual experiment, after the calibration of modulation error, THD is effectively reduced from 7.5% to 4.5%. In addition, the method is verified by the demodulation of 200 Hz and 1000 Hz signals. The method also shows excellent repeatability and linearity in demodulation of sensing signals.

Simultaneous Surface Display and Holography Enabled by Flat Liquid Crystal Elements

AbstractAs a fundamental material in the current mainstream display technology, liquid crystal (LC) exhibits excellent properties including controllable and reconfigurable LC orientation, high‐efficiency pure‐phase modulation, active tunability, etc., and becomes one of the most attractive candidates for the development of next‐generation flat optical devices. Current LC elements are suffering from the single functionality as only one type of the optical manipulation is involved. Integrating several functions together brings great flexibility and high integration but remains an urgent task. Here, flat LC elements are proposed to simultaneously accomplish near‐field display and far‐field holography. The anisotropic nature of the LC allows a complex amplitude modulation with a sinusoidal variation, promising a continuous amplitude change, and a binary phase modulation. Specifically, several two‐channel LC elements are experimentally demonstrated, which simultaneously generate a grayscale pattern at sample surface and project an independent holographic image in the far field. Furthermore, the position and spatial multiplexing methodologies are introduced to further improve the information capacity. The proposed LC elements with simple anisotropic structure and large fabrication size can empower the multifunctional design and have promising prospects in information multiplexing, image displaying, data storage, etc.

Terahertz Metagrating Emitters with Beam Steering and Full Linear Polarization Control.

We report the realization of broadband THz plasmonic metagrating emitters for simultaneous beam steering and all-optical linear polarization control. Two types of metagratings are designed and experimentally demonstrated. First, the plasmonic meta-atoms are arranged in a metagrating with a binary phase modulation which results in the nonlinear generation of THz waves to the ±1 diffraction orders, with complete suppression of the zeroth order. Complete tunability of the diffracted THz linear polarization direction is demonstrated through simple rotation of the pump polarization. Then, the concept of lateral phase shift is introduced into the design of the metagratings using interlaced phase gradients. By controlling the spatial shift of the submetagrating, we are able to continuously control the linear polarization states of the generated THz waves. This method results in a higher nonlinear diffraction efficiency relative to binary phase modulation. These functional THz metagratings show exciting promise to meet the challenges associated with the current diverse array of applications utilizing THz technology.

Robust single-frequency 589 nm fiber laser based on phase modulation and passive demodulation.

A robust 20-W continuous-wave single frequency 589 nm laser is developed to aim for sodium guide star in astronomy. The source is based on applying π-depth binary phase modulation to a single frequency seed laser along with 3 steps of strain in the gain fiber to suppress the stimulated Brillouin scattering in the high power 1178 nm amplifier and realizing the recovery of single frequency after frequency doubling in a periodically poled LiTaO3 crystal. The efficiency of frequency doubling reaches up to 41.6%. To the best of our knowledge, it is the highest power reported for continuous-wave 589 nm laser generation by single-pass frequency doubling. The approach significantly simplifies the sodium guide star laser design and improves robustness.