Optical Signal Processing Research Articles

Calibrating laser Doppler anemometers utilizing an optical chopper

Abstract Laser doppler anemometers (LDAs) use scattered light to determine velocity components of a flowing fluid. The operating principal of LDAs is simple conceptually; however, it is impractical to trace the LDA-determined velocities to the SI by characterizing the LDA’s subsystems that generate, detect, and process optical signals because these subsystems are complex and include proprietary features. To circumvent this, we calibrated the complete LDA systems utilizing an optical chopper blade as an accurate, SI-traceable velocity standard. The calibrations achieved the expanded velocity uncertainty 0.094 % at a 95 % confidence level. We calibrated two LDAs that differed in manufacturer, focal length (in the ratio 3.3:1), sensing volume (in the ratio 100:1), and orientation (vertical and horizontal bisectors of the LDA's crossing beams). To compare the calibrations, we measured airspeeds in NIST's wind tunnel using both LDAs. The results differed from each other by, at most, 0.2 % throughout the airspeed range 0.5 m/s to 30 m/s.

Determination of Stable Proton Configurations by Black-Box Optimization Using an Ising Machine

Determination of Stable Proton Configurations by Black-Box Optimization Using an Ising Machine

Nonlinear Nitrogen‐Doped Carbon‐Based All‐Optical Switch and Wavelength Converter in Mid‐Infrared Region

AbstractExploring all‐optical devices built upon new nanomaterials and moving toward all optical signal processing has been attracted ever‐growing interest. Nitrogen‐doped carbon shows tremendous application potential in nonlinear optics due to its excellent and stable optoelectronic characteristics. Due to the reduction in scattering intensity as increasing optical wavelength, the midinfrared 2 µm band is less affected by atmospheric scattering. This study presents an experimental demonstration of a 2 µm optical Kerr switch on a microfiber, designed using nonlinear nitrogen‐doped carbon nanospheres (NCN), and combined with a highly nonlinear fiber (HNLF) to achieve cascaded four‐wave mixing (FWM) phenomena. Experimental results show that the Kerr switch exhibits an extinction ratio of approximately 12.5 dB under appropriate pump light application, indicating effective signal light control. Moreover, the maximum conversion efficiency of the first‐order cascaded FWM reaches −20.08 dB, and the second‐order efficiency reaches −39.3 dB, with a maximum wavelength spacing of 18 nm. This represents the first investigation of optical Kerr switching and cascaded FWM in the 2 µm wavelength range. This study provides new insights and approaches for developing optical signal processing technology and lays the foundation for future high‐performance photonic devices in this wavelength range.

Noise-augmented chaotic Ising machines for combinatorial optimization and sampling

Ising machines are hardware accelerators for combinatorial optimization and probabilistic sampling, using stochasticity to explore spin configurations and avoid local minima. We refine the previously proposed coupled chaotic bits (c-bits), which operate deterministically, by introducing noise. This improves performance in combinatorial optimization, achieving algorithmic scaling comparable to probabilistic bits (p-bits). We show that c-bits follow the quantum Boltzmann law in a 1D transverse field Ising model. Furthermore, c-bits exhibit critical dynamics similar to p-bits in 2D Ising and 3D spin glass models. Finally, we propose a noise-augmented c-bit approach via the adaptive parallel tempering algorithm (APT), which outperforms fully deterministic c-bits running simulated annealing. Analog Ising machines with coupled oscillators could draw inspiration from our approach, as running replicas at constant temperature eliminates the need for global modulation of coupling strengths. Ultimately, mixing stochasticity with deterministic c-bits yields a powerful hybrid computing scheme that can offer benefits in asynchronous, massively parallel hardware implementations.

Spontaneous symmetry breaking of an optical polarization state in a polarization-selective nonlinear resonator.

We exploit polarization self-rotation (PSR) in atomic rubidium vapor to observe spontaneous symmetry breaking and bistability of polarization patterns. We pump the vapor cell with horizontally polarized light while the vertical polarization, which is initially in the vacuum state, is resonated in a ring cavity. Microscopic field fluctuations in this mode experience cumulative gain due to the compound action of amplification due to the self-rotation and feedback through the resonator, eventually acquiring a macroscopic magnitude akin to an optical parametric oscillator. The randomness of these fluctuations results in a bistable, random macroscopic polarization pattern at the output. We propose utilizing this mechanism to simulate an Ising-like interaction between multiple spatial modes and as a basis for a fully optical coherent Ising machine (CIM).

Stochastic logic in biased coupled photonic probabilistic bits

Optical computing often employs tailor-made hardware to implement specific algorithms, trading generality for improved performance in key aspects like speed and power efficiency. An important computing approach that is still missing its corresponding optical hardware is probabilistic computing, used e.g. for solving difficult combinatorial optimization problems. In this study, we propose an experimentally viable photonic approach to solve arbitrary probabilistic computing problems. Our method relies on the insight that coherent Ising machines composed of coupled and biased optical parametric oscillators can emulate stochastic logic. We demonstrate the feasibility of our approach by using numerical simulations equivalent to the full density matrix formulation of coupled optical parametric oscillators.

Transfer of optical orbital angular momentum under nonreciprocity-reciprocity amplification conversion

Magnet-free optical nonreciprocity has significant applications in quantum communication, quantum networks, and optical information processing. In this research, considering a degenerate two-level thermal atomic system with the Doppler effect of thermal atoms, the nonreciprocal amplification (NRA) of dual-path degenerate four-wave mixing (FWM) signals is achieved under the action of a co-propagating pumping field. On this basis, spatially multiplexed multiple FWM processes are formed by introducing another counter-propagating pumping field, thereby the reciprocal amplification (RA) of the dual-channel FWM signals is realized. Furthermore, by using multiple sets of spiral phase plates to load spiral phases on the signal light and the pumping light respectively, higher-order Laguerre-Gaussian vortex beams carrying different optical orbital angular momentum (OAM) are generated and participated in the FWM process, which achieve the transfer of the OAM of the pumping light to the amplified FWM fields. Simultaneously, using the Mach-Zehnder interferometer, the conservation characteristics of the OAM of each FWM signal in the NRA-RA conversion are further analyzed. Furthermore, experimental results have demonstrated that in the multiple FWM process induced by a pair of counter-propagating pump fields, the OAM of the amplified FWM signal in each channel varies with the change of that of the pump field. However, the overall process maintains the OAM conservation. The study provides a feasible solution for expanding channel capacity using OAM based on NRA-RA system, and has potential application prospects in achieving high-capacity optical communication and multi-channel signal processing.

On-chip power efficient MHz to GHz tunable Brillouin microwave photonic filters

Stimulated Brillouin scattering (SBS) offers optically tunable, narrowband gain and loss resonances, which makes it ideal for optical filtering and signal processing applications. However, broadband filters utilizing Brillouin scattering typically necessitate multiple pump sources or linear frequency modulated waveforms, which necessitate the use of overall high pump powers to achieve broadband and multi-band filter configurations. To overcome the trade-off between bandwidth and power consumption, we introduce an on-chip broadband bandpass filter scheme leveraging the SBS response and the concept of radio frequency interference. We present the MHz to GHz reconfigurable microwave photonic filters on a chip. The bandwidth is tunable from 30 MHz to 1.2 GHz at a total pump power of only 15 dBm, corresponding to a figure of merit (maximum bandwidth/pump power) improvement of a factor of 25 compared to previously reported work. Furthermore, the filter exhibits frequency tuning capabilities ranging from 10 to 40 GHz (X to Ka-band) and can be configured from single- to multi-bandpass filter responses and switched from bandpass to bandstop.

Compact photonic device based on chalcogenide glass loaded lithium niobate on insulator

We propose a hybrid photonic platform based on chalcogenide glass (GeSbSe) integrated with lithium niobate on insulator (LNOI), providing enhanced performance and compactness for integrated photonics. Key photonic components, including grating couplers (GCs), micro-ring resonators, multimode interference (MMI), and the Mach–Zehnder interferometer (MZI), are designed and fabricated on this platform. The micro-ring resonator achieves an intrinsic quality factor of 72,000 and a propagation loss of ∼3 dB/cm. The multimode interference couplers demonstrate minimal excess loss, while the MZI exhibits an extinction ratio exceeding 30 dB over a bandwidth of 50 nm. This hybrid platform, leveraging the unique optical properties of GeSbSe and LNOI, offers scalability and low-loss photonic integrated circuits, with promising applications in high-speed optical communications and signal processing.

Dual-Band High-Throughput and High-Contrast All-Optical Topology Logic Gates.

Optical computing offers advantages such as high bandwidth and low loss, playing a crucial role in signal processing, communication, and sensing applications. Traditional optical logic gates, based on nonlinear fibers and optical amplifiers, suffer from poor robustness and large footprints, hindering their on-chip integration. All-optical logic gates based on topological photonic crystals have emerged as a promising approach for developing robust and monolithic optical computing systems. Expanding topological photonic crystal logic gates from a single operating band to dual bands can achieve high throughput, significantly enhancing parallel computing capabilities. This study integrates the topological protection offered by valley photonic crystals with linear interference effects to design and implement seven optical computing logic gates on a silicon substrate. These gates, based on dual-band valley photonic crystal topological protection, include OR, XOR, NOT, NAND, NOR, and AND. The robustness of the implemented OR logic gates was verified in the presence of boundary defects. The results demonstrate that multi-band parallel computing all-optical logic gates can be achieved using topological photonic crystals, and these gates exhibit high robustness. The all-optical logic gates designed in this study hold significant potential for future applications in optical signal processing, optical communication, optical sensing, and other related areas.

Tunable Optical Filter Based on Thin Film Lithium Niobate Photonic Crystals

In this paper, we propose a tunable optical filter with a high Q factor based on photonic crystal technology, achieving a Q factor of 442.85 using thin film lithium niobate technology. By proportionally adjusting the dimensions of the unit structure, this filter enables coarse tuning across the 1520–1570 nm range (C band). Furthermore, by utilizing the thermo-optic effect of lithium niobate, we can achieve fine-tuning of the optical filter within a temperature range of 300 K to 600 K, allowing for a center wavelength tuning capability of up to 3.7 nm. This design not only enhances the filter’s performance but also broadens its potential applications in optical communication and optical signal processing.

Advancing the problem-solving capabilities of Ising machines based on spin Hall nano-oscillators

Advancing the problem-solving capabilities of Ising machines based on spin Hall nano-oscillators

A 1024-Spin Scalable Ising Machine With Capacitive Coupling and Progressive Annealing Method for Combination Optimization Problems

A 1024-Spin Scalable Ising Machine With Capacitive Coupling and Progressive Annealing Method for Combination Optimization Problems

Quantum Computing in Community Detection for Anti-Fraud Applications

Fraud detection within transaction data is crucial for maintaining financial security, especially in the era of big data. This paper introduces a novel fraud detection method that utilizes quantum computing to implement community detection in transaction networks. We model transaction data as an undirected graph, where nodes represent accounts and edges indicate transactions between them. A modularity function is defined to measure the community structure of the graph. By optimizing this function through the Quadratic Unconstrained Binary Optimization (QUBO) model, we identify the optimal community structure, which is then used to assess the fraud risk within each community. Using a Coherent Ising Machine (CIM) to solve the QUBO model, we successfully divide 308 nodes into four communities. We find that the CIM computes faster than the classical Louvain and simulated annealing (SA) algorithms. Moreover, the CIM achieves better community structure than Louvain and SA as quantified by the modularity function. The structure also unambiguously identifies a high-risk community, which contains almost 70% of all the fraudulent accounts, demonstrating the practical utility of the method for banks’ anti-fraud business.

Tailoring Optical Performance of Polyvinyl Alcohol/Crystal Violet Band-Pass Filters via Solvent Features.

Optical filters are essential components for a variety of applicative fields, such as communications, chemical analysis and optical signal processing. This article describes the preparation and characterization of a new optical filter made of polyvinyl alcohol and incremental amounts of crystal violet. By using distinct solvents (H2O, dimethyl sulfoxide (DMSO) and H2O2) to obtain the dyed polymer films, new insights were gained into the pathway that underlies the possibility of tailoring the material's optical performance. The effect of the dye content on the sample's main properties was inspected via UV-VIS spectroscopy analysis combined with colorimetry, refractometry and atomic force microscopy experiments. The results revealed that the colorimetric parameters are affected by the dye amount and are dramatically changed when the solvent used for film preparation is different. The rise in the refractive index upon polymer dyeing was due to the synergistic effect of the larger polarizability of the dye and the occurrence of hydrogen bonds among the system components. Spectral data evidenced that samples prepared in H2O and DMSO preserve the absorption characteristics of the added dye, whereas H2O2 acts as an oxidizing agent and enhances transparency. Also, for the first two solvents, multiple absorption edges were noted as a result of dye incorporation, which was responsible for the occurrence of new exciton-like states, hence the band gap reduction. The films processed in H2O were able to block radiations in the 506-633 nm range while allowing other wavelengths to pass with a transmittance above 90%. The samples attained in DMSO presented similar properties, with the difference that the domain of light attenuation was shifted towards higher wavelengths. Atomic force microscopy showed the dye's effect on the level of surface roughness uniformity and morphology isotropy. The dyed polymer foils in non-oxidizing agents have suitable features for use as band-pass filters.

Fabrication of PbS QD-Mediated Organic-Inorganic Hybrid Swir Opds Using Azide Functional Ligand (FPA-S) and Study of Polymer Morphology Control

The efficiency of exciton dissociation and electron mobility in organic photodetectors (OPDs) is critically dependent on the microscale morphology of the interpenetrating network structures between electron donor and acceptor materials. Therefore, understanding the impact of phase separation within the active layer and the interactions between components is crucial for OPD performance.In this study, we propose a hybrid Short Wavelength Infrared (SWIR) photodiode that utilizes PbS quantum dots (QDs) minimally, leveraging their exceptional SWIR absorption properties, alongside an organic semiconductor matrix to counterbalance their poor charge transport characteristics. While similar concepts of organic-inorganic hybrid photodiodes have been suggested previously, the straightforward blending of organic semiconductors and QDs has been constrained by poor miscibility due to differences in surface energy between organic and inorganic phases. This results in reduced phase stability post-film fabrication and significant phase separation. Therefore, we introduce an azide-functional ligand (FPA-S) capable of coordinating with QDs and bonding with polymers via azide groups, to induce photo-crosslinking and suppress phase separation between polymers and QDs.Effectively separating excitons while minimizing the amount of PbS QDs, which are toxic and exhibit low charge mobility, necessitates controlling the morphology of the active layer. We optimized conditions such as solvent type, evaporation rate, volume ratio, and external humidity based on a quaternary phase diagram derived from Flory-Huggins interaction parameters. Additionally, we sought to identify the optimal condition by calculating the equilibrium state of the phase-separated structure of polymers using a phase-field model with the Ising machine.

Using continuation methods to analyse the difficulty of problems solved by Ising machines

Ising machines are dedicated hardware solvers of NP-hard optimization problems. However, they do not always find the most optimal solution. The probability of finding this optimal solution depends on the problem at hand. Using continuation methods, we show that this is closely linked to how the ground state emerges from other states when a system parameter is changed, i.e. its bifurcation sequence. From this analysis, we can determine the effectiveness of solution schemes. Moreover, we find that the proper choice of implementation of the Ising machine can drastically change this bifurcation sequence and therefore vastly increase the probability of finding the optimal solution. Lastly, we also show that continuation methods themselves can be used directly to solve optimization problems.

Enhanced Coplanarity and Giant Birefringence in Hydroxypyridinium Nitrate via Hydrogen Bonding between Planar Donors and Planar Acceptors

AbstractBirefringent crystals, which possess optical anisotropy, are important optical components. However, designing and synthesizing birefringent crystals faces the challenge of achieving anisotropic structures, especially coplanar geometries. Herein, we achieve a significant birefringence in an ionic compound (C5H6ON)+(NO3)−, (4‐hydroxypyridinium nitrate, 4HPN) by hydrogen bonding between planar donors and planar acceptors. We demonstrate that the interactions between the planar hydrogen bond donor ((C5H6ON)+) and planar hydrogen bond acceptor ((NO3)−) ensure the coplanarity during the crystal packing, generating the desired giant optical anisotropy. On two manually cut crystal chips, we observe a =0.494 ( =0.593), which is the largest among nitrates, or hydroxypyridinium derivatives. This value already surpasses those of the benchmark crystals, e.g., YVO4 and CaCO3, commonly used in the UV to visible and near IR spectral range. 4HPN also exhibits a strong second harmonic generation response (9.55×KDP). This strategy offers a promising avenue for the design and development of birefringent crystals with potential applications in optical communication, sensing and signal processing devices.

Enhanced Coplanarity and Giant Birefringence in Hydroxypyridinium Nitrate via Hydrogen Bonding between Planar Donors and Planar Acceptors.

Birefringent crystals, which possess optical anisotropy, are important optical components. However, designing and synthesizing birefringent crystals faces the challenge of achieving anisotropic structures, especially coplanar geometries. Herein, we achieve a significant birefringence in an ionic compound (C5H6ON)+(NO3)-, (4-hydroxypyridinium nitrate, 4HPN) by hydrogen bonding between planar donors and planar acceptors. We demonstrate that the interactions between the planar hydrogen bond donor ((C5H6ON)+) and planar hydrogen bond acceptor ((NO3)-) ensure the coplanarity during the crystal packing, generating the desired giant optical anisotropy. On two manually cut crystal chips, we observe a =0.494 ( =0.593), which is the largest among nitrates, or hydroxypyridinium derivatives. This value already surpasses those of the benchmark crystals, e.g., YVO4 and CaCO3, commonly used in the UV to visible and near IR spectral range. 4HPN also exhibits a strong second harmonic generation response (9.55×KDP). This strategy offers a promising avenue for the design and development of birefringent crystals with potential applications in optical communication, sensing and signal processing devices.

On-chip deep subwavelength optomagnetic bistable memory based on inverse Faraday effect related nonlinearity in graphene waveguide ring resonators

Integrated optical devices that possess bistable characteristics are key elements for optical digital signal processing and all-optical computing. In this paper we report on an optomagnetic bistable memory based on the inverse Faraday effect related nonlinearity in graphene waveguide ring resonators. The effective magnetic field via the plasmon-induced inverse Faraday effect in the graphene resonator has two discrete stable states that represent logic one and logic zero and magnetic switching for memory operation can be achieved by injecting an optical pulse and momentarily blocking the bias input light. Our proposed optomagnetic bistable device based on a graphene magnetoplasmonic configuration has great potential for the development of next generation magnetic memory. It has benefits of ultrafast magnetization switching, simplicity of the considered structure, on-chip compatibility, and a deep subwavelength platform. It also enhances the nonlinear interaction due to strong confinement of the graphene plasmon modes and high-quality factor of traveling modes in the graphene ring resonator, and tunability and robustness by adjusting the gate voltages of the graphene sheets. These advantages will satisfy the demand for fast magnetization switching, low-energy consumption, and high-density recording required in future magnetic memories. Published by the American Physical Society 2024