Optical Processing Research Articles

Nonlinear optical cyanurate crystals

The exploration of ultraviolet (UV) nonlinear optical (NLO) crystals is of great significance in various fields, such as optical communication, medical diagnosis, deep space exploration and optical digital signal processing. Accordingly, cyanurates attracted widespread attention due to their strong second-harmonic-generation (SHG) effects, large birefringence for phase-matching, short UV cutoffs, high solar blind transmittances and easy crystal preparations. This article reviews the optical properties of so far reported cyanurate NLO crystals, describes the preparation approaches of cyanurates, compares their structures to further analyze the source of their large SHG effect, and provides some insights for designing and synthesizing new UV cyanurates in the future.

Stabilizing and Guiding Rogue Waves in a Cold Atomic Gas

AbstractRogue waves (RWs) are mysterious nonlinear waves and have attracted much attention in recent years. However, they are usually unstable during propagation. Here, a scheme for stabilizing and guiding optical RWs in a cold atomic gas working under the condition of electromagnetically induced transparency is presented. It is shown that an external potential for probe laser field can be created by using an assisting laser field. If the assisting laser field has the form of Gaussian beam, the instability of the RWs can be largely suppressed. It is also shown that the RWs can be stabilized and guided to propagate along curved trajectories if the assisting laser field has the form of Airy beam. The results reported here contribute to the effort for stabilizing and manipulating RWs, which may have potential applications in optical transmission and information processing.

Optical Image Processing using Eulerian Amplification

Recent advancements in digital photography, particularly through mobile phone cameras, microscopes, and satellite imaging, have made high-resolution image capture increasingly accessible. However, these captured images often contain subtle changes in color resolution and density that are challenging to observe with the naked eye. This study explores the application of Eulerian amplification as a method to detect and enhance such small-amplitude variations, making them visible for improved analysis. Unlike traditional approaches, Eulerian methods are particularly effective for processing smooth structures and high-quality printed materials where minor amplifications in color can reveal significant grading details. Using a pixel-by-pixel Eulerian path analysis, this method allows for a detailed comparison of color intensity values on a fine 8-bit scale, which ranges from 0 to 255. Through this analysis, color distribution patterns are visualized across the spatial structure of the image, which is particularly beneficial for identifying specific variations in quality in printed materials, such as highly graded cards. To manage large image structures, spatial decomposition using a multi-level Gaussian pyramid technique is employed. By applying temporal filtering within select frequency bands (0.4–4 Hz) at a coarse pyramid level, the algorithm effectively pools spatial data, enabling the detection of color density shifts that may indicate image defects. The amplified image data is further processed using a classifier neural network, which provides high sensitivity and specificity in detecting edge defects, image centering issues, scuffs, and breakages. The system demonstrates promising results in identifying true positives while maintaining low false-negative rates, thus confirming the reliability of deep machine learning algorithms in high-sensitivity defect detection. This paper presents the significance of Eulerian amplification in optical image processing, offering a robust tool for precise, automated defect detection across a variety of high-resolution image types.

Continuously-tunable, compact, freespace notch-filter design using an all-dielectric metagrating capped with a low-loss phase change material

Abstract Active metasurfaces utilizing phase change materials (PCMs) are currently under investigation for applications in free-space optical communication, optical signal processing, neuromorphic photonics, quantum photonics, and compact LiDAR. Attention has now turned towards novel PCM like Sb2S3 which exhibit lower optical absorption and reasonable values of refractive-index contrast in comparison to traditional data-storage PCM. We propose and numerically study the class of all-dielectric metagratings capped with low-loss PCM and predict the possibility of continuously tunable resonances whose quality factors degrade gracefully during the amorphous-to-crystalline phase transition of the PCM. Specifically, we consider the CMOS-compatible silicon-nitride on silica substrate material platform for simple and asymmetric metagratings (in particular, the symmetric-broken dimerization) and Sb2S3 capping. Our numerical study predicts that notch-filters operating around the 1550 nm NIR wavelength window can be achieved with tuning range of over 76 nm with Q-factors ranging from 784 (amorphous-phase) to 510 (crystalline-phase) (a degradation in Q of about 35%) and insertion loss of about 0.9 dB. These performance figures are a significant improvement over previously published designs utilizing data-storage PCMs and other traditional notch-filter mechanisms. We examine the influence of grating dimerization and geometrical parameters on performance metrics of the notch-filter and predicts the possibility to trade-off rejection-band and in-band spectral transmission properties. Lastly, we perform a study of all-optical phase change mechanism. Our study is promising for the miniaturization of tunable notch-filter based optical systems.

Retraction Note: Application of sensor-based image optical processing in the vision system of tea ware glaze design

Retraction Note: Application of sensor-based image optical processing in the vision system of tea ware glaze design

Tunable Fano-type resonance with quadrature squeezing in a double-cavity-waveguide structure of photonic crystals

We propose an optical approach to realizing Fano-type spectra of quadrature squeezing in a double-cavity-waveguide structure based on photonic crystals (PhCs). In this scheme, a partially transmitting element (PTE) in the waveguide creates the transmission and reflection light, which interferes with the outflow from the intracavity field and subsequently gives rise to Fano-type interference. Meanwhile, a degenerate parametric amplifier (DPA) embedded into the cavity is expected to yield quantum squeezed states in the interference process. After verifying the existence of the Fano resonance, we report that increasing the nonlinear gain of the DPA not only amplifies the transmitted intensity of the output field, but also improves its quadrature squeezing degree. More importantly, we illustrate that, when maintaining the high performance of quadrature squeezing, the linewidths and frequencies of the asymmetrical spectra can be modulated by adjusting the double-cavity coupling strength. This combination of Fano-type spectra and quadrature squeezing is beneficial for optimizing optical communications and signal processing with a low noise level.

High-temperature resistant boron nitride-based coatings for specialty silica optical fibers

h-BN is well known for its thermal stability. h-BN coated silica optical fibers were manufactured. The coating solution is compatible with optical fiber drawing process, which allows the preparation of tens of meter of h-BN coated fibers. In addition, it is possible to use this coating material for the preparation of short length fiber samples in a post-production approach. Bentonite acts as a binder and allows the adhesion of h-BN to the silica optical fiber. The thermal stability of this protected optical fiber has been demonstrated over a short period of time (several hours) up to 900 °C and over a long period of time (1500 h) up to 800 °C in air. Moreover, the coated optical fiber can resist up to 1000 °C in neutral atmosphere (tested over 6 h).

7219 Ocular Findings in Jansen Metaphyseal Chondrodysplasia

Abstract Disclosure: F. Obiezu: None. K. Pan: None. A. Ninan: None. K.L. Roszko: None. L.S. Weinstein: None. C.R. Ferreira: None. R.I. Gafni: None. T. Magone De Quadros Costa: None. M.T. Collins: None. S. Jha: None. Jansen Metaphyseal Chondrodysplasia (JMC) is an ultra-rare disorder, with only 30 patients estimated to have the disease globally. It is caused by heterozygous pathogenic variants in PTHR1 that result in constitutive activation of parathyroid hormone type 1 receptor (PTHR1) signaling. A detailed description of craniofacial manifestations of the disease is lacking. Here we characterize the ophthalmological manifestations in patients with JMC. Six patients (4 males, 67%) with genetically confirmed JMC underwent a detailed ophthalmological evaluation, spectral-domain optical coherence tomography (OCT), craniofacial CT and 18F-NaF PET/CT scans. Median age at the time of the visit was 27.5 [IQR: 29] years. On physical examination, all patients were noted to have widely spaced eyes; 5 of the 6 had down slanted palpebral fissures, proptosis, or ptosis. Two patients had incomplete or defective closure of the eyelids (lagophthalmos), of which one had a history of progressive right facial nerve palsy with profuse epiphora. The second patient had central visual field defects, bilateral moderate optic disc pallor and bilateral retinal nerve fiber layer (RNFL) atrophy on OCT exam with bilateral optic canal narrowing on CT. Notably, comparison of these findings with a prior scan performed 5 years earlier showed progressive decrease in RNFL bilaterally. This patient had a history of prolonged intravenous bisphosphonate therapy, initiated in infancy for hypercalcemia and continued for over a decade. A third patient had normal vision, subtle temporal pallor of the optic nerve heads on dilated fundus exam, normal average RNFL, but decreased retinal ganglion cell layer analysis (GCA) on OCT. GCA was decreased in 4 of the 6 patients compared to age-matched reference range indicating a chronic optic nerve atrophic process. These data represent the first comprehensive report of the ophthalmologic findings in a cohort of patients with JMC. They demonstrate that patients with JMC have significant eye findings that appear to be more prevalent and pronounced with age. This suggests age-related, progressive optic neuropathy, which can be assessed by demonstrating OCT retinal GCA and RNFL loss and, may be a feature of JMC. The benefit and effect of long-term bisphosphonate therapy in patients with JMC remains unclear. Patients with JMC should undergo regular ophthalmologic examination including optic nerve OCT, visual field testing, and craniofacial imaging. Presentation: 6/1/2024

Fourier Ptychographic Coherent Anti-Stokes Raman Scattering Microscopy with Point-Scanning for Super-Resolution Imaging.

Fourier ptychography (FP) is a high resolution wide-field imaging method based on the extended aperture in the Fourier space, which is synthesized from raw images with varying illumination angles. If FP is extended to coherent nonlinear optical imaging, the resolution could be further improved due to the increase of the cutoff frequency of the synthesized coherent optical transfer function (C-OTF) with respect to the order of nonlinear optical processes. However, there is a fundamental conflict between wide-field FP and nonlinear optical imaging, whereby the nonlinear optical imaging typically requires a focused excitation laser beam with high power density. To tackle the problem, in this work, a unique point-scanning FP (PS-FP) method is presented for super-resolution nonlinear optical imaging, in which the nonlinear optical signal is obtained by using focused laser beam, while the conventional FP algorithm can still be used to retrieve the super-resolution image. PS-FP coherent anti-Stokes Raman scattering (PS-FP-CARS) imaging on a variety of samples, where a 1.8-fold expansion of the OTF is achieved experimentally for enhancing vibrational imaging. Further theoretical calculation shows that the C-OTF of PS-FP higher-order CARS (PS-FP-HO-CARS) can be expanded up to ≈4.9-fold, thereby improving the spatial resolution by ≈3-fold in comparison with conventional point-scanning CARS with under tightly focused beams. The generality of PS-FP method developed in this work can be adapted to other coherent nonlinear optical imaging modalities for super-resolution imaging in tissue and cells.

Generation of sub-100 fs vortices from a Kerr-lens mode-locked Hermite-Gaussian Yb:CALGO oscillator.

Mode-locked oscillators with high-order transverse modes are excellent platforms for generating femtosecond optical vortices with high average power and good propagation stability. These have important applications in diverse fields such as optical communication, strong-field physics, and laser processing. So far, generating vortex pulses with ultrashort pulse duration remains a challenge. In this Letter, we report a Kerr-lens mode-locked Yb:CALGO laser oscillator delivering Hermite-Gaussian (HG) pulses with a pulse duration of 86 fs using a non-collinear pumping technique. 91 fs optical vortex pulses were generated by using a cylindrical-lens mode converter. To the best of our knowledge, this is the shortest pulse duration ever obtained from a diode pumped solid-state mode-locked oscillator with a pure high-order Hermite-Gaussian mode. The phase structures of the generated femtosecond vortices are characterized.

MicroLEDs for optical neuromorphic computing—application potential and present challenges

Abstract The slow non-radiative surface recombination velocity of gallium nitride (GaN) in combination with its highly efficient radiative recombination makes this material ideally suited for microLEDs with dimensions as small as 1 µm and even below, serving as the fundamental building block of micro-displays. However, due to their superior miniaturization potential and energy efficiency, GaN-based microLEDs have applications that extend well beyond display technology. Their capability to produce optical patterns with high resolution, which can be modulated at extremely high frequencies, makes them suitable for numerous other applications. We suggest exploiting these exciting properties for a new and potentially equally significant application: utilizing microLEDs in optical processing units for artificial intelligence workloads. In neuromorphic computing, relevant aspects of biological neural networks are emulated directly with either electronic circuits or photonic devices, avoiding the shortcomings of conventional digital computer technology for AI workloads, which generally require massively parallel information processing. GaN microLEDs are discussed here as a promising enabling technology for optical neuromorphic processing units. We see great potential to substantially decrease power consumption through massively parallel in-memory processing combined with efficient photon production and detection. A theoretical analysis of scalability and energy efficiency is provided. A macroscopic bench-top optical microLED demonstrator is presented, which experimentally proves the feasibility of our approach. Future potential and challenges associated with miniaturizing and scaling microLED-based optical processing units are discussed. Finally, we summarize the open research questions that require attention before fully functional and miniaturized optical neuromorphic processing units based on GaN microLEDs can be realized.

All-optical combinational logical units featuring fifth-order cascade

Modern computational technologies are increasingly encountering significant limitations, driving a shift towards alternative paradigms such as optical computing. In this study, we introduce novel all-optical combinational logic units based on diffractive neural networks (D2NNs), designed to perform high-order logical operations both efficiently and swiftly using only two modulation layers. This innovative design offers increased processing speed, improved energy efficiency, robust environmental stability, and high error tolerance, making it exceptionally well-suited for a broad spectrum of applications in optical computing and communications. By leveraging transfer learning, we successfully developed a fifth-order cascaded combinational logic circuit for practical information transmission system. Furthermore, we reveal a pioneering application of our device in Optical Time Division Multiplexing (OTDM), demonstrating its capability to manage high-speed data transfer seamlessly without the need for electronic conversion. Extensive simulations and experimental validations highlight the potential of our model as a foundational technology for future optical computing architectures, paving the way toward more sustainable and efficient optical data processing platforms.

Broadband and widely tunable second harmonic generation in suspended thin-film LiNbO3 rib waveguides

Our study demonstrates second harmonic generation (SHG) in a high confinement LiNbO3 rib waveguide through type-I birefringence phase matching of fundamental modes. The combination of micro-waveguide dispersion and material birefringence reveals unique SHG characteristics that complement the performance of standard LiNbO3 on insulator (LNOI) components. Dual-pump wavelength phase matching in the near-infrared and mid-infrared regions is shown in a given waveguide. These two wavelengths can be positioned in the 1.1–3.5 μm range or converge near 1.5 μm by adjusting the core waveguide size or through temperature tuning. A 25 °C temperature change enables a broad pump tunability band of 300 nm, ranging from 1350 to 1650 nm, with a conversion efficiency exceeding 40 %/W/cm2 within a single waveguide. A temperature tuning range of up to 900 nm is foreseen by tailoring the waveguide core size. In addition, a broadband response of 150 nm within the telecom window is demonstrated experimentally. The nonlinear waveguide, etched in a thin film membrane, is combined with titanium-indiffused waveguides to form a monolithic LiNbO3 component. This configuration provides low coupling losses of 0.8 dB and single-mode operation. It paves the way for a new generation of versatile and cost-effective frequency conversion components with wide-band spectral responses suitable for optical communications, environmental sensing, and quantum information processing.

A conical spiral methanol steam reforming reactor for spectral splitting-based concentrating photovoltaic-thermochemical hybrid production

The spectral beam splitting (SBS) photovoltaic-thermochemical hybrid system improves the solar thermal energy grade through photon energy cascade distribution and methanol steam reforming (MSR) reaction. Given the deficiency of MSR reactor development for dish-concentrating SBS systems, the conical spiral structure is introduced to the receiver/reactor in this work, thus facilitating efficient absorption of circular beams and ameliorating the adaptability of the production. Based on specially designed spectral beam splitter, the Monte Carlo ray tracing (MCRT) method is employed to simulate the non-imaging optical process and optimized reflective cone structure. Thermodynamics and kinetic models of the reactor are established and experimentally validated. The analysis results show that the reflective cone advances the optical efficiency of the reactor to 76.95%, and the conical spiral structure helps to enhance heat and mass transfer for utilization of the catalytic space. The mid/low-temperature reaction prefers a solution flow rate of less than 1.53 mL·s-1 and a water-methanol ratio of 1.4-1.9, with the maximum solar thermochemical conversion rate of 54.5%. Moreover, the upgrading in photothermal and photovoltaic heat exceeds respectively 0.62 and 8.97 at less than 600 W·m-2 of irradiation, demonstrating the adaptive potential of the reactor. In summary, the research results contribute to broadening the operating conditions of the hybrid production and the full-spectrum penetration of solar energy in distributed scenarios.

Characteristics study of a dual-wavelength polarization filter based on gold-filled square lattice photonic crystal fiber

This study proposes a polarization filter based on gold-filled photonic crystal fiber (PCF) with a square lattice structure. Utilizing the finite element method (FEM), the filtering characteristics of the model were numerically simulated. The dispersion relation and loss characteristics of this structure were analyzed, and the optimal structural parameters were obtained through structural adjustments. Furthermore, the performance of the filter was evaluated under a 2% variation in manufacturing tolerances for gold film thickness (), air hole spacing (), and air hole diameters () and (). Results indicated that at the 1310 nm and 1550 nm communication windows, the confinement losses of the filter were 1354.6 dB/cm and 869.04 dB/cm, respectively, while the losses for the -polarization were merely 16.97 dB/cm and 0.98 dB/cm. When the filter length was set to 0.5 mm, the maximum extinction ratios (ERs) for the two windows reached 588.2 dB and 370.6 dB, and the filter bandwidth extended to 640 nm. Moreover, the characteristics of the filter under manufacturing tolerances were computed, revealing that the filter’s performance remained stable and feasible despite manufacturing errors. The proposed rectangular gold-coated PCF is anticipated to have broad applications in optical fiber communication and optical information processing.

Dissimilar soliton molecule formed by dissipative pulses in a single-mode mode-locked fiber laser

Soliton molecules, or also known as optical bound states, are the most representative example of solitons’ particle nature and have given birth to diverse light-matter analogies. Despite detailed research on regular bound states, the soliton molecule synthesis of dissimilar pulses has rarely been reported. Here, soliton molecules formed by dissimilar dissipative solitons are demonstrated in a single-mode mode-locked fiber laser, with an in-depth analysis of their evolution dynamics. This novel bound state features pulse trapping between two ultrafast vector pulses with distinct pulse properties including energy, duration, and chirp, leading to unique temporal and spectral profiles. This laser provides an optimal platform for studying complex interactions between different types of dissipative solitons. The findings here can provide new degrees of freedom for the generation of optical soliton molecules and can fuel applications in optical information processing, metrology, and spectroscopy.

Retraction Note: Application of computer simulation based on optical image processing in monitoring metabolic regulation data during exercise training

Retraction Note: Application of computer simulation based on optical image processing in monitoring metabolic regulation data during exercise training

Physical prior-guided deep learning for SIM reconstruction: modeling object-to-image degradation

Structured illumination microscopy (SIM) provides an enhanced spatial resolution of up to twice the conventional capacity. Recently, many approaches have attempted to combine deep learning frameworks with SIM reconstruction for better capability. Nonetheless, the inadequacy of training samples highlights the challenge of limited credibility and low generalization ability of deep learning, thus significantly constraining the application in biology. To tackle this issue, we propose an object-to-image plane degradation network (OIDN) guided by the physical process of optical imaging. Specifically, the proposed OIDN embeds the object-to-image plane degradation process into the reconstruction network to provide explicit guidance. With a set of learnable point spread function (PSF) parameters constrained by physical prior, OIDN successfully converts the conventional image-to-image data pattern mapping into the object-to-image plane degradation mapping that highly aligns with the optical processes of SIM imaging. Comprehensive experiments demonstrate that the proposed method reliably yields high-quality images across signal-to-noise ratio conditions, exhibiting superior generalization ability across diverse datasets and sample types.

Optical properties of transition metals complex films derived from hydrazone oxime for optoelectronic devices

Hydrazone incorporating oxime nucleus and its Ni2+, Mn2+, Zn2+ and UO22+ metallic chelates have been prepared and completely characterized by different spectral, theoretical, and analytical techniques including NMR, FT-IR, mass, and EAS spectroscopy. The finding denoted that the Hydrazone ligand bonded as a dibasic tridentate chelator via deprotonated oximato nitrogen, enol carbonyl oxygen and hydrazono azomethine nitrogen atoms resultant in octahedral geometry for Ni2+, Mn2+, Zn2+ and UO22+. Theoretical studies by DFT/B3LYP/LANLDZ together with dipole moment, geometrical optimization, energetic parameters, and energy gap (HOMO–LUMO) were employed to support the geometrical structure of the synthetics. Additionally, these complexes were prepared in the form of thin film onto cleaned glass substrate by spin-coating technique. The values of the optical band gap (Eg) and film index of refraction (n) have been determined by many different methods. It was found that the hydrazone-oxime (OBBH2) film has the highest value of Eg (eV) where the UOBB complex film has the smallest value of Eg (2.56 eV). The latter is very close to the Eg value of ZnSe (2.58 eV). The refractive index changes with wavelengths show normal dispersion which is well discussed in terms of Sellmeier's dispersion model. Also, the nonlinear optical parameters viz. the first (χ(1)) and third (χ(3)) orders of nonlinear optical susceptibilities and the non-linear index of refraction (n2) have been studied. The complex dielectric constant (ε⌣=εr+iεi)), conductivity (σ⌣=σr+iσi), sheet resistance (Rs), and thermal have been investigated over the whole spectral range. According to the results of χ(1), χ(3) and n2 the complex films under study are candidates to be used in optical switching gadgets, optical modulators, and optical signal processing.

Cerebral Microcirculation: Progress and Outlook of Laser Doppler Flowmetry in Neurosurgery and Neurointensive Care.

Laser Doppler flowmetry (LDF) is a well-established technique for the investigation of tissue microcirculation. Compared to skin, the use in the human brain is sparse. The measurement of cerebral microcirculation in neurointensive care and during neurosurgery is challenging and requires adaptation to the respective clinical setting. The aim of the review is to present state of the art and progress in neurosurgery and neurointensive care where LDF has proven useful and can find clinical importance in the investigation of cerebral microcirculation. The literature in the field is summarized and recent technical improvements regarding LDF systems and fiber optical probe designs for neurosurgical and neurocritical care described. By combining two signals from the LDF unit, the measurement of the microcirculation (Perfusion) and gray whiteness (TLI) of the brain tissue, the full potential of the device is achieved. For example, a forward-looking LDF-probe detects high-risk hemorrhage areas and gray-white matter boundaries along intraoperative trajectories during stereotactic neurosurgery. Proof of principles are given for LDF as a guidance tool in deep brain stimulation implantation, brain tumor needle biopsies, and as long-term monitoring device in neurocritical care. With well-designed fiber optical probes, surgical fixation, and signal processing for movement reduction, LDF monitoring of the cerebral microcirculation is successful up to 10 days. The use of LDF can be combined with other physiological measurement techniques, for example, fluorescence spectroscopy for identification of glioblastoma during tumor surgery. Fiber optics can also be used during magnetic resonance imaging (MRI). Despite the many advantages, fiber optical LDF has not yet reached its full potential in clinical neuro-applications. Multicenter studies are required to further evaluate LDF in neurosurgery and neurointensive care. In conclusion, the present status of LDF in neurosurgery and neurointensive care has been reviewed. By combining Perfusion and TLI with tailored probe designs the full potential of LDF can be achived in measuring cerebral microcirculation. This includes guidance during DBS implantation and needle biopsies, and long-term monitoring in neurocritical care.