The 50 most-cited articles in Applied Optics, 2024

Plasmonic logic gates are important components in integrated photonics. They are essential for high-speed Boolean computations and data transmission. For this purpose, an all-optical ultra-compact plasmonic logic gate is proposed in this paper. The design uses the metal–insulator–metal (MIM) configuration and the propagation of surface plasmon polaritons. The structure comprises three rectangular input slots coupled to the output slot through a rectangular resonator positioned on a gold (Au) surface with a footprint of 1000nm×800nm. The logic gate is numerically investigated using finite element method analysis. It has been demonstrated that the proposed design can operate as OR, XOR, NOT, and AND gates, and their transmission spectra for different input states are analyzed. This novel solution, to the best of our knowledge, excels in high contrast ratio values of 45.34 dB (OR), 18.29 dB (XOR), 18.29 dB (NOT), and 7.26 dB (AND). The resonant wavelengths of the logic gate are 821.21 nm (OR), 863.23 nm (XOR), 814.71 (NOT), and 787.69 nm (AND). The introduction of Au in this device…

A high-precision binocular camera calibration method is proposed to address the issues of poor calibration accuracy and large calibration errors in current practical applications. This method uses a triangular stereo sphere as the calibration object and employs steps, such as ellipse fitting, Cholesky decomposition, homography matrix solution, and nonlinear optimization, to compute the intrinsic and extrinsic parameters, distortion parameters, and relative pose of the binocular camera. Moreover, this method simplifies the correspondences between primitives, enabling simultaneous calibration of multiple viewpoint cameras. This method is also suitable for both binocular cameras consisting of two different structured monocular cameras and those composed of two image sensors within the same structure. Experimental results showed that this method outperforms traditional algorithms in terms of binocular camera calibration accuracy, calibration errors between left and right cameras, and robustness, resulting in a significant improvement in overall algorithm performance.

The Laser Megajoule (LMJ) is among the most energetic inertial confinement fusion laser facilities in the world, together with the National Ignition Facility (NIF) in the USA. The construction of the facility began back in 2003, and the first photons were emitted by the laser bundle #28 in 2014. Today, 11 laser bundles consisting of 88 large aperture 0.35×0.35m 2 laser beams are in operation, delivering daily up to 330 kJ of energy at the wavelength of 351 nm on a target placed in the center of a 10 m diameter vacuum chamber. In this paper, we describe the laser system and its operational performances. We also detail the first laser campaigns carried out to prepare an increase of energy and power on the target. These campaigns, along with the completion of additional bundles mounting, will bring LMJ performance to 1.3 MJ thanks to 22 bundles in operation.

We investigate the generation of an elliptical perfect optical vortex (EPOV) beam through the optical Fourier transformation of an elliptical Bessel-Gaussian beam and derive an analytical expression for its complex field amplitude. Our analysis includes the examination of the beam's propagation in free-space and the influence of topological charge on its transmission. The EPOV beam's propagation in free-space can be categorized into non-diffracting and diffracting stages. During the non-diffracting stage, the beam intensity and profile size are effectively preserved over a short transmission distance. Subsequently, in the diffracting stage, the beam profile initially contracts and then expands with a change in the beam intensity. Notably, the impact of topological charge on the beam intensity and profile size varies across different stages of propagation. We compare our results with those of the circular perfect optical vortex beam propagating in free-space, observing that the EPOV beam exhibits non-diffracting behavior for short propagation distances compared to its circular…

Security issues with optical access networks (OANs) are increasing as the number of users has dramatically grown. To address this problem, a full-system division multiplexing in both the time and wavelength domains has been utilized in a passive optical network second-generation (TWDM-NG-PON2) system. A secure approach to transfer data was presented by implementing the blowfish algorithm for image encryption and decryption in the OAN. Simulation results indicate effective realization of a bidirectional fiber link at 40 km with a splitting ratio of 1:256. The minimum accepted receiver sensitivity is −30.9dBm for uplink and −33.9dBm for downlink, and a symmetric high capacity of 160 Gbps rate has been obtained. The proposed algorithm in TWDM-PON offers high security with large bandwidth and an advanced long-haul network that provides effective resource usage and reinforced network authenticity.

Hybrid lenses are created by combining metasurface optics with refractive optics, where refractive elements contribute optical power, while metasurfaces correct optical aberrations. We present an algorithm for optimizing metasurface nanostructures within a hybrid lens, allowing flexible interleaving of metasurface and refractive optics in the optical train. To efficiently optimize metasurface nanostructures, we develop a scalar field, ray-wave hybrid propagation method. This method facilitates the propagation of incident and derived adjoint fields through optical elements, enabling effective metasurface optimization within the framework of adjoint gradient optimization. Numerical examples of various lens configurations are presented to illustrate the versatility of the algorithm and showcase the benefits offered by the proposed approach, allowing metasurfaces to be positioned beyond the image space of a lens. Taking a F/2, 40° field-of-view, midwave infrared lens as an example, the lens exhibits an average focusing efficiency of 38% before the integration of metasurfaces. Utilizing…

Frequency-modulated continuous-wave (FMCW) laser ranging technology is an important development direction of light detection and ranging (LiDAR) for the future. It has the advantages of high ranging accuracy, high resolution, wide range, and no ranging blind zone. A distributed feedback laser can be used as a high-quality light source in FMCW laser ranging systems because of its wide frequency modulation range, simple frequency modulation mode, and small package. Aiming at the nonlinear problem of the laser in the frequency modulation process, we present a novel, to our knowledge, predistortion algorithm based on interpolation linear fitting to enhance the linearity of the FMCW laser for LiDAR systems. The sweeping frequency curve of the laser is obtained using the Hilbert transform, and then the sweeping frequency curve is segmented and linearly fitted to calculate the interpolated driving current signals corresponding to linear frequency changes. Using this method, we achieved a nonlinearity error lower than 1e-7 for the swept-frequency signal and demonstrated that the ranging…

In this study, we employ a two-dimensional photonic crystal structure to design a NOR logic gate, utilizing dielectric rods in air. The compact size and simplicity of the design make this optical gate particularly suitable for integration into photonic integrated circuits. To optimize the optical NOR gate design and achieve superior results, we leverage machine learning techniques, specifically XGBoost and RandomForestRegressor. By fine-tuning the radii of defect rods within the photonic crystal lattice, we maximize output power and ensure optimal gate functionality across various input scenarios. Through extensive simulations and comparative analyses, we showcase the effectiveness of our approach in accurately predicting optimal rod radii and enhancing NOR gate performance. Notably, our design utilizes only two defect rods, highlighting the structure’s efficiency. Moreover, alongside the simplicity of our proposed design, it boasts high output power for logical 1 and low power for logical 0. This feature contributes to minimized errors in logical output detection, further…

Due to the fact that the existing generation of wireless communication cannot possibly keep up with the current traffic explosion and emerging applications, research and development on next-generation (i.e., sixth generation, 6G) wireless technologies is being carried out worldwide. In this regard, it is anticipated that the space-air-ground (SAG) network with free space optics (FSO) communication can provide the terabits per second throughput necessary to sustain various potential 6G applications. However, FSO communications are susceptible to atmospheric turbulence, pointing errors, and beam scintillation effects. To remedy the severe atmospheric effects, we propose a multiple high-altitude platform station (HAPS)-based SAG network with a HAPS selection scheme. For the proposed system, we have derived the closed-form expressions for outage probability, average symbol error rate (SER), ergodic capacity, and outage capacity over Málaga distribution with pointing errors. Further, the asymptotic expressions for outage probability, average SER, and outage capacity were derived to…

High angular resolution imaging is an increasingly important capability in contemporary astrophysics. Of particular relevance to emerging fields such as the characterization of exoplanetary systems, imaging at the required spatial scales and contrast levels results in forbidding challenges in the correction of atmospheric phase errors, which in turn drives demanding requirements for precise wavefront sensing. Asgard is the next-generation instrument suite at the European Southern Observatory's Very Large Telescope Interferometer (VLTI), targeting advances in sensitivity, spectral resolution, and nulling interferometry. In this paper, we describe the requirements and designs of three core modules: Heimdallr, a beam combiner for fringe tracking, low order wavefront correction, and visibility science; Baldr, a Zernike wavefront sensor to correct high order atmospheric aberrations; and Solarstein, an alignment and calibration unit. In addition, we draw generalizable insights for designing such system and discuss integration plans.

In underwater wireless optical communication (UWOC), vortex beams carrying orbital angular momentum (OAM) can improve channel capacity but are vulnerable to oceanic turbulence (OT), leading to recognition errors. To mitigate this issue, we propose what we believe to be a novel method that combines the Gerchberg–Saxton (GS) algorithm-based recovery with convolutional neural network (CNN)-based recognition (GS-CNN). Our experimental results demonstrate that superposed Laguerre–Gaussian (LG) beams with small topological charge are ideal information carriers, and the GS-CNN remains effective even when OT strength C n 2 is high up to 10 −11 K 2 m −2/3 . Furthermore, we use 16 kinds of LG beams to transmit a 256-grayscale digital image, giving rise to an increase in recognition accuracy from 0.75 to 0.93 and a decrease in bit error ratio from 3.98×10 −2 to 6.52×10 −3 compared to using the CNN alone.

This paper proposes a high-performance refractive index sensor based on an all-dielectric metasurface consisting of four silicon arcs arranged back-to-back on a silicon dioxide substrate. A sharp Fano resonance with a high quality factor (Q-factor) in the near-infrared (NIR) wavelength is innovatively excited by electric quadrupole (EQ) resonance by varying the size of the inner angle. And electromagnetic field distribution and mode assessment further demonstrate that the EQ resonance mode is governed by quasi-bound states in the continuum (Q-BICs). Additionally, the ability to precisely control Fano resonance peaks is demonstrated by tuning the geometrical parameters of the structure, which makes the designed metasurface a promising gas refractive index sensing candidate. The results show that the highest Q-factor, sensitivity (S), and figure of merit (FOM) are 23,236, 603 nm/RIU, and 9869RIU −1 , respectively. The proposed structure provides a good application prospect for nonlinear optical devices and air refractive index sensors.

In this paper, a graphene-vanadium dioxide-based reconfigurable metasurface unit structure is proposed. Using the change at a graphene Fermi energy level on the surface of the unit structure to satisfy the 2-bit coding condition, four reflection units with a phase difference of 90 ∘ can be discovered. The modulating impact of the multi-beam reflection wave with 1-bit coding is then confirmed. Then we study the control of a single-beam reflected wave by metasurfaces combined with a convolution theorem in a 2-bit coding mode. Finally, when vanadium dioxide is in an insulating condition, the structure can also be transformed into a terahertz absorber. It is possible to switch between a reflection beam controller and a terahertz multifrequency absorber simply by changing the temperature of the vanadium dioxide layer without retooling a new metasurface. Moreover, compared with the 1-bit coded metasurface, it increases the ability of single-beam regulation, which makes the device more powerful for beam regulation.

Using the self-developed fused indium wetting technology and planar waveguide, the uniform heat dissipation of the slab crystal and uniform pumping of the pump light were achieved, respectively. Based on the master oscillator power amplification (MOPA) scheme, the power was then amplified when the seed light source passed through the Nd:YAG slab crystal three times. Additionally, the image transfer system that we added to the amplified optical path achieved high beam quality. Finally, we obtained a rectangular pulsed laser with an output average power of 4461 W, a repetition frequency of 20 kHz, a pulse width of 62 ns, an optical-to-optical conversion efficiency of 26.8%, and a beam quality of β x =7.0 and β y =7.7.

Two-wavelength adaptive optics (AO), where sensing and correcting (from a beacon) is performed at one wavelength $\lambda_\text{B}$ and compensation and observation (after transmission through the atmosphere) is performed at another $\lambda_\text{T}$, has historically been analyzed and practiced assuming negligible irradiance fluctuations (i.e., weak scintillation). Under these conditions, the phase corrections measured at $\lambda_\text{B}$ are robust over a relatively large range of wavelengths, resulting in a negligible decrease in AO performance. In weak-to-moderate scintillation conditions, which result from distributed-volume atmospheric aberrations, the pupil-phase function becomes discontinuous, producing what Fried called the ``hidden phase'' because it is not sensed by traditional least-squares phase reconstructors or unwrappers. Neglecting the hidden phase has a significant negative impact on AO performance even with perfect least-squares phase compensation. To the authors' knowledge, the hidden phase has not been studied in the context of two-wavelength AO. In…

Future far-infrared astrophysics observatories will require focal plane arrays containing thousands of ultrasensitive, superconducting detectors, each of which require efficient optical coupling to the telescope fore-optics. At longer wavelengths, many approaches have been developed, including feedhorn arrays and macroscopic arrays of lenslets. However, with wavelengths as short as 25 µm, optical coupling in the far infrared remains challenging. In this paper, we present an approach to fabricate far-infrared monolithic silicon microlens arrays using grayscale lithography and deep reactive ion etching. The fabricated microlens arrays presented here are designed for two different wavebands: 25-40 µm and 135-240 µm. The microlens arrays have sags as deep as 150 µm, are hexagonally packed with a pixel pitch of 900 µm, and have an overall size as large as 80 by 15 mm. We compare an as-fabricated lens profile to the design profile and calculate that the fabricated lenses would achieve 84% encircled power for the designed detector, which is only 3% less than the designed performance. We…

Lateral resolving power is a key performance attribute of Fizeau interferometers, confocal microscopes, interference microscopes, and other instruments measuring surface form and texture. Within a well-defined scope of applicability, limited by surface slope, texture, and continuity, a linear response model provides a starting point for characterizing spatial resolution under ideal conditions. Presently, the instrument transfer function (ITF) is a standardized way to quantify linear response to surface height variations as a function of spatial frequency. In this paper, we build on the ITF idea and introduce terms, mathematical definitions, and appropriate physical units for applying a linear systems model to surface topography measurement. These new terms include topographical equivalents of the point-, line-, and edge-spread functions, as well as a complex-valued transfer function that extends the ITF concept to systems with spatial-frequency-dependent topography distortions. As an example, we consider the experimental determination of lateral resolving power of a coherence…

This paper presents experimental results for a free-space optical-fiber converged (FSO-FC) communication system under varying turbulence and foggy conditions. Based on the experimental measurements, we statistically characterize the FSO channel under different levels of turbulence and fog in terms of their respective probability density functions (PDFs). Our experimental PDFs fit well with the theoretical PDFs proposed in the literature. We experimentally evaluate the average bit error rate (ABER) of the considered FSO-FC communication system under different levels of turbulence and fog. Further, to compensate for the effects of turbulence and fog, we use multimode fiber as the receiver and compare the results with single-mode fiber as the receiver. Finally, we show the improvement in ABER under varying turbulence and fog by adding cyclic redundancy check bits to data bits.

We developed a method for optical adjustment using a deep learning model to quantitatively predict misalignment of optical components. The proposed model predicts the misalignment parameters using only through-focus images of a point source, while conventional methods require specialized measurements or extensive manual analysis. There is no need for special preparation for measurements, and quantitative prediction will reduce the cost of optical adjustment. A distinctive aspect of our method is that the training dataset is not obtained through measurements but generated using ray-tracing simulation, which produces through-focus images with various type of aberrations. By applying the method to a simple parabolic mirror and a reflecting telescope, we demonstrated its prediction accuracy. The through-focus images obtained from simulated optics, according to the predicted misalignment parameters, matched the measured images. We adjusted two optics and confirmed that the measured images after adjustment were in good agreement with the simulation images of the designed optics.

Because of the extremely high sampling rate of fiber optic distributed acoustic sensing (DAS) equipment, the amount of DAS seismic data collected is enormous, which poses great challenges to the transmission and storage of DAS seismic data. Therefore, it is essential to study the compression methods of DAS seismic data. Existing data compression methods such as wavelet transform, cosine transform, and convolutional autoencoder (CAE) still have room for improvement in the compression performance and compression ratio (CR). Thus, we have proposed what we believe to be is a novel deep learning model called the recurrent autoencoder (RAE) for high-performance compression of DAS seismic data. Under different CRs, we have designed performance evaluation experiments for RAE models based on different RNN modules with different loss functions. When the CR of the RAE model is 8, the signal-to-noise ratio (SNR) of the reconstructed DAS seismic data reaches 40.60 dB, which is better than that of the CAE’s 11.58 dB. The ultimate CR was increased to 512 without reducing the compression quality,…

Shack-Hartmann wavefront sensing is a technique for measuring wavefront aberrations, whose use in adaptive optics relies on fast position tracking of an array of spots. These sensors conventionally use frame-based cameras operating at a fixed sampling rate to report pixel intensities, even though only a fraction of the pixels have signal. Prior in-lab experiments have shown feasibility of event-based cameras for Shack-Hartmann wavefront sensing (SHWFS), asynchronously reporting the spot locations as log intensity changes at a microsecond time scale. In our work, we propose a convolutional neural network (CNN) called event-based wavefront network (EBWFNet) that achieves highly accurate estimation of the spot centroid position in real time. We developed a custom Shack-Hartmann wavefront sensing hardware with a common aperture for the synchronized frame- and event-based cameras so that spot centroid locations computed from the frame-based camera may be used to train/test the event-CNN-based centroid position estimation method in an unsupervised manner. Field testing with this hardware…

In this article, we describe the first demonstration of an optical fiber sensor based on two cascaded architectures of Mach-Zehnder interferometer (MZI) with up-down-tapered (UDT) hetero-core fiber structure for simultaneous pH measurement at two different spatial locations. The two fiber structures, namely structures I and II, were fabricated by sandwiching a 45 mm and 60 mm long piece of no-core fiber (NCF) between two single-mode fibers (SMF), respectively. By inserting a down taper between two adjacent up tapers in the NCF section using the over-fusion splicing technique, the UDT hetero-core fiber structure was achieved. The down taper works as an optical attenuator, while the two up tapers each function as a fiber splitter/combiner. By cascading the two sensor structures I and II, two distinct interference dips were obtained, resulting in dual sensing points (so-called: sensing points I and II). According to experimental results, it was shown that the proposed sensing points I and II are pH-sensitive, and exhibit sensitivities of 1.0428 nm/pH and -1.7857 nm/pH for simultaneous…

Chromatic dispersion (CD) is a major concern in high speed fiber optics communication systems. This work presents an efficient optical compensation technique with reduced complexity to mitigate CD effects in single mode fiber (SMF) at high data rates. The proposed method includes a post-dispersion mitigation system using a single linear chirped fiber Bragg grating (CFBG) with tanh apodization. Here, various parameters of CFBG, such as grating length, effective refractive index, and apodization function, are optimized to achieve effective CD compensation. Then, the system is extended to a 16-channel WDM link with each channel carrying data at 25 Gbps over 100 km. The simulation results show that the proposed model enhances the system performance while minimizing overall system complexity. The proposed system is also compatible with the prevailing fiber optics networks. The results are consistent with the findings published in recent studies.

In prior art, advances in adaptive optics scanning laser ophthalmoscope (AOSLO) technology have enabled cones in the human fovea to be resolved in healthy eyes with normal vision and low to moderate refractive errors, providing new insight into human foveal anatomy, visual perception, and retinal degenerative diseases. These high-resolution ophthalmoscopes require careful alignment of each optical subsystem to ensure diffraction-limited imaging performance, which is necessary for resolving the smallest foveal cones. This paper presents a systematic and rigorous methodology for building, aligning, calibrating, and testing an AOSLO designed for imaging the cone mosaic of the central fovea in humans with cellular resolution. This methodology uses a two-stage alignment procedure and thorough system testing to achieve diffraction-limited performance. Results from retinal imaging of healthy human subjects under 30 years of age with refractive errors of less than 3.5 diopters using either 680 nm or 840 nm light show that the system can resolve cones at the very center of the fovea, the…

A rapid and accurate photoalignment technique was proposed for the fabrication of liquid crystal Pancharatnam-Berry phase diffractive optical elements (LC PB-DOEs). The in-plane orientation of LCs was precisely manipulated through the polarized illumination of an optimized liquid crystal on silicon (LCOS) device. LCOS and thereafter spatial light modulator (SLM) can generate polarization patterns at pixel level at will. The quality of such alignment was improved significantly by minimizing the phase flicker of the phase-only LCOS SLM. This was confirmed by the increase of the measured quality of the holographic images reconstructed using our DOE in terms of structural similarity (SSIM) and peak signal-to-noise ratio (PSNR) at 30% and 5%, respectively. Furthermore, a bi-focal LC PB-lens was fabricated and used as a high quality Fourier lens in holographic display to validate the usefulness of such LC PB-DOEs. This work illustrated a ubiquitous approach of fabricating different types of lightweight and thin form factor DOEs of random phase patterns at pixel level with low cost and…

In digital holographic microscopy, the quantitative phase image suffers from phase aberrations and coherent noises. To solve these problems, two independent steps are applied sequentially in the reconstruction procedure to compensate for the phase aberrations and denoising. Here we demonstrate for the first time, to the best of our knowledge, that the reconstruction process can be simplified by replacing the two step methods with a deep learning-based algorithm. A convolutional neural network is trained simultaneously for phase aberration correction and denoising from an only wrapped phase map. In order to train the network, a database consists of massive wrapped phase maps as input, and noise-free sample phase maps as labels are constructed. The generated wrapped phase maps include a variety of phase aberrations and faithful coherent noises that are reconstructed from a practical apparatus. The trained network is applied to correct phase aberrations and denoise of both simulated and experimental data for the quantitative phase image. It exhibits excellent performance with output…

A Fresnel zone plate (EFZP) with an extended depth of focus can maintain focused monochromatic light at different distances compared to a general Fresnel zone plate (FZP). The focal distances are determined by dividing the zone plate into multiple areas based on the desired order. The EFZP has potential applications in various research fields such as microscopy, direct laser lithography, and optical coherence tomography. However, manufacturing an EFZP is challenging due to the high precision requirements and difficulties associated with the calculation and simulation processes. In this research, a complete process is presented to design, simulate, and fabricate an EFZP using a Fourier optics design, simulations, and a direct laser lithographic machine. The resulting EFZP has an increased depth of focus of about nine times compared to a general Fresnel zone plate with similar parameters, while maintaining the focal spot diameter. The performance of this EFZP is evaluated through optical verification and mathematical simulation methods.

Phase retrieval from a single-frame interferogram is a challenge in optical interferometry. This paper proposes an accurate physics-based deep learning method for one-shot phase retrieval. This approach involves both data-driven pre-training of a phase-shifting network and subsequent model-driven fine-tuning. The well-designed pre-training network is capable of simultaneously generating π /2, π , and 3 π /2 phase-shifted versions of the input interferogram to facilitate phase extraction. Moreover, integrating the interferometric model into the testing dataset enables self-supervised fine-tuning, optimizing the use of both data and physics-based priors. Simulations and experiments demonstrate the effectiveness of the proposed method in overcoming the common generalization limitation of data-driven models and achieving accurate phase retrieval. The proposed method not only enhances the accuracy of phase retrieval but also improves the generalization capability, making it robust under experimental conditions for interferometric applications.

In this paper, a new underwater optical wireless communication (UOWC) system is proposed. It integrates dual-polarization (DP) states with orbital angular momentum (OAM) beams. By leveraging the inherent orthogonality of different OAM modes, the system achieves enhanced signal quality and increased transmission capacity. Each polarization state carries data of four OAM beams, with each capable of carrying 10 Gbps of information. Additionally, a single laser diode (LD) source operating at 532 nm is employed. To evaluate the performance of the proposed system, the effects of attenuation across various water types are considered. Propagation range, bit error rate (BER), and eye diagrams are utilized as comprehensive performance metrics. The obtained results indicate that, below the error correction threshold (3.8×10 −3 ), our proposed UOWC system achieves impressive underwater transmission ranges. Specifically, we observe a longer range of 44 m for pure sea (PS) water that exhibits the lower attenuation, which is decreased to 26.5 m for clear ocean (CL) and 15.5 m for coastal ocean…

We investigate terahertz time-domain spectroscopy using a low-noise dual-frequency-comb laser based on a single spatially multiplexed laser cavity. The laser cavity includes a reflective biprism, which enables generation of a pair of modelocked output pulse trains with slightly different repetition rates and highly correlated noise characteristics. These two pulse trains are used to generate the THz waves and detect them by equivalent time sampling. The laser is based on Yb:CALGO, operates at a nominal repetition rate of 1.18 GHz, and produces 110 mW per comb with 77 fs pulses around 1057 nm. We perform THz measurements with Fe-doped photoconductive antennas, operating these devices with gigahertz 1 µm lasers for the first time, to our knowledge, and obtain THz signal currents approximately as strong as those from reference measurements at 1.55 µm and 80 MHz. We investigate the influence of the laser's timing noise properties on THz measurements, showing that the laser's timing jitter is quantitatively explained by power-dependent shifts in center wavelength. We demonstrate…

For free-space optical communication or ground-based optical astronomy, ample data of optical turbulence strength ( C n 2 ) are imperative but typically scarce. Turbulence conditions are strongly site dependent, so their accurate quantification requires in situ measurements or numerical weather simulations. If C n 2 is not measured directly (e.g., with a scintillometer), C n 2 parameterizations must be utilized to estimate it from meteorological observations or model output. Even though various parameterizations exist in the literature, their relative performance is unknown. We fill this knowledge gap by performing a systematic three-way comparison of a flux-, gradient-, and variance-based parameterization. Each parameterization is applied to both observed and simulated meteorological variables, and the resulting C n 2 estimates are compared against observed C n 2 from two scintillometers. The variance-based parameterization yields the overall best performance, and unlike other approaches, its application is not limited to the lowest part of the atmospheric boundary layer (i.e. the…

Wind speed and sonic temperature measured with ultrasonic anemometers are often utilized to estimate the refractive index structure parameter C n 2 , a vital parameter for optical propagation. In this work, we compare four methods to estimate C n 2 from C T 2 , using the same temporal sonic temperature data streams for two separated sonic anemometers on a homogenous path. Values of C n 2 obtained with these four methods using field trial data are compared to those from a commercial scintillometer and from the differential image motion method using a grid of light sources positioned at the end of a common path. In addition to the comparison between the methods, we also consider appropriate error bars for C n 2 based on sonic temperature considering only the errors from having a finite number of turbulent samples. The Bayesian and power spectral methods were found to give adequate estimates for strong turbulence levels but consistently overestimated the C n 2 for weak turbulence. The nearest neighbors and structure function methods performed well under all turbulence strengths tested.

We present an approach for the realization of controlled spiral-shaped mass transfer in azopolymer thin films and the fabrication of spiral microreliefs. For such laser processing, we propose to use light fields with structured polarization distributions generated by a transmissive spatial light modulator. The projection lithography approach is utilized, transferring the pattern directly to the surface of azopolymer thin films. The shaped polarization distributions with different dependencies of the polarization vector orientation on the azimuthal angle allow us to drive surface waves on the sample along a spiral trajectory. Additionally, the ability to control the concavity of the formed microreliefs is demonstrated. This approach can be effectively modified for the direct laser fabrication of more complex nano-/micro-elements as well as their arrays.

This paper presents a decagonal patch antenna loaded with graphene designed for terahertz (THz) frequency applications, with a specific emphasis on its potential for early breast cancer detection. The proposed antenna features a hybrid structure, integrating both copper and graphene materials. A decagonal graphene strip is intricately incorporated into the copper patch, yielding significant improvements in reflection coefficient, bandwidth, and gain. The antenna, with dimensions of 155µm×130µm×13µm, is designed on a polyimide substrate, characterized by a dielectric constant of 3.5 and a loss tangent of 0.0027. To ensure relevance in medical contexts, the design is optimized to operate within the frequency range of 2.1 to 5.7 THz, a critical spectrum for medical applications. Simulation results validate the effectiveness of the proposed antenna, demonstrating S 11 <−10dB within the frequency band of 2.1 to 5.7 THz (92.3% fractional bandwidth). The antenna exhibits an impressive bandwidth of 3.6 THz and a gain of 7.87 dBi at 4 THz. These findings establish the graphene-loaded…

The spatial photonic Ising machine has achieved remarkable advancements in solving combinatorial optimization problems. However, it still remains a huge challenge to flexibly map an arbitrary problem to the Ising model. In this paper, we propose a general spatial photonic Ising machine based on the interaction matrix eigendecomposition method. The arbitrary interaction matrix can be configured in the two-dimensional Fourier transformation based spatial photonic Ising model by using values generated by matrix eigendecomposition. The error in the structural representation of the Hamiltonian decreases substantially with the growing number of eigenvalues utilized to form the Ising machine. In combination with the optimization algorithm, as low as ∼65% of the eigenvalues are required by intensity modulation to guarantee the best probability of optimal solution for a 20-vertex graph Max-cut problem, and this percentage decreases to below ∼20% for near-zero probability. The 4-spin experiments and error analysis demonstrate the Hamiltonian linear mapping and ergodic optimization. Our work…

We first review transport of intensity and phase and show their use as a convenient tool to directly determine the unwrapped phase of an imaged object, either through conventional imaging or using digital holography. For both cases, either the traditional transport of intensity and phase, or with a modification, viz., electrically controllable transport of intensity and phase, can be used. The use of digital holography with transport of intensity for 3D topographic mapping of fingermarks coated with columnar thin films is shown as an illustrative application of this versatile technique.

Free space optical (FSO) communication systems experience turbulence-induced fading. As a possible solution, adaptive transmission, which adjusts transmitter parameters based on instantaneous channel state information (CSI), can be used. Most of the existing channel estimation methods ignore the impact of detection noise at the receiver, which will lead to additional estimation errors. In this paper, a joint estimation model based on convolutional neural networks (CNNs) is proposed to estimate detection noise and turbulence fading parameters. We obtained turbulence channel simulation data sets considering the background of detection noise based on the edge probability distribution function of the receive signal. The training of the CNN estimator is carried out through maximum pooling, adaptive learning rate, and regularization, ultimately accurately estimating channel characteristics based on the optimal output results of the network. The simulation results show that the proposed CNN joint estimator performs better in high-detection-noise environments compared with traditional…

Laser interference lithography is an effective approach for grating fabrication. As a key parameter of the grating profile, the duty cycle determines the diffraction characteristics and is associated with the irradiance of the exposure beam. In this study, we developed a fabrication technique amplitude-splitting flat-top beam interference lithography to improve duty cycle uniformity. The relationship between the duty cycle uniformity and irradiance of the exposure beam is analyzed, and the results indicate that when the beam irradiance nonuniformity is less than 20%, the grating duty cycle nonuniformity is maintained below ±2%. Moreover, an experimental amplitude-splitting flat-top beam interference lithography system is developed to realize an incident beam irradiance nonuniformity of 21%. The full-aperture duty cycle nonuniformity of the fabricated grating is less than ±3%. Amplitude-splitting flat-top beam interference lithography improves duty cycle uniformity, greatly reduces energy loss compared to conventional apodization, and is more suitable for manufacturing highly uniform…

In this study, an uncooled 2D nanohole array PtSi/p-Si Schottky mid-infrared (MIR) photodetector, which is essential for on-chip Si-based low-barrier MIR detectors, is presented. Room temperature operation introduces susceptibility to thermal noise and can impact stability. Through modulation frequency and reverse bias optimization, the stability improved by 7 times at 170 Hz and −3.5V, respectively. The effective light detection and stability were confirmed through ON/OFF response measurements over a longer time. The wavelength-dependent responsivity, measured with a tunable MIR laser, confirmed the responsiveness of the device in the MIR region of 2.5 µm to 4.0 µm, with a maximum specific detectivity (D*) of 2.0×103cmHz1/2W−1 at 3.0 µm; this result shows its potential applicability for noninvasive human lipid monitoring. Overall, this study focuses on the crucial role of signal analysis optimization in enhancing the performance of MIR photodetectors at room temperature.

Obtaining the complex refractive index vectors n ( ν ~) and k ( ν ~) allows calculation of the (infrared) reflectance spectrum that is obtained from a solid in any of its many morphological forms. We report an adaptation to the KBr pellet technique using two gravimetric dilutions to derive quantitative n ( ν ~)/ k ( ν ~) for dozens of powders with greater repeatability. The optical constants of bisphenol A and sucrose are compared to those derived by other methods, particularly for powdered materials. The variability of the k values for bisphenol A was examined by 10 individual measurements, showing an average coefficient of variation for k peak heights of 5.6%. Though no established standards exist, the pellet-derived k peak values of bisphenol A differ by 11% and 31% from their single-angle- and ellipsometry-derived values, respectively. These values provide an initial estimate of the precision and accuracy of complex refractive indices that can be derived using this method. Limitations and advantages of the method are discussed, the salient advantage being a more rapid method to…

This work presents the solutions to the alignment of two Gaussian beams representing two sides of the optical connection between a fiber and a photonic integrated circuit (PIC). The focus is to use these solutions to derive equations that allow for the straightforward calculation of alignment tolerances for displacement in all three directions, as well as two axes of rotations. These equations can be used to aid in the design of photonic packages by allowing the determination of precision necessary for fabrication of mechanical alignment features, in addition to packaging process development.

An optical sensor based on a defective photonic crystal is proposed to identify the Chikungunya virus in blood components, including plasma, platelets, red blood cells (RBCs), and uric acid. Under healthy conditions, each blood component has a unique refractive index; this value is altered if the person is infected with the Chikungunya virus. The infected blood sample results in a deviation in the refractive index of the sample as compared to a normal sample due to the presence of the infection in the human blood. With the help of our suggested structure, this alteration can be detected, and the normal cell can be distinguished from the infected one. To simulate the results, the transfer matrix method (TMM) is applied. The sensitivity of the suggested structures loaded separately with the sample containing plasma, platelets, red blood cells, and uric acid is found to be 1411, 1352, 1335, and 795 nm/RIU, respectively. These results are enough to support our claim that the present design can be used as an ultra-sensitive nanophotonic biosensor for the detection of the Chikungunya…

In fringe projection profilometry (FPP), end-to-end depth estimation from fringe patterns for FPP attracts more and more attention from fringe patterns. However, color images provide additional information from the RGB channel for FPP, which has been paid little attention in depth estimation. To this end, in this paper we present for the first time, to the best of our knowledge, an end-to-end network for depth estimation using color composite fringes with better performance. In order to take advantage of the color fringe pattern, a multi-branch structure is designed in this paper, which learns the multi-channel details of the object under test by using three encoders for each RGB channel and introduces an attention module to better capture the complex features and modalities information in the input data. Experiments from simulated and real datasets show that the proposed method with color fringe pattern is effective for depth estimation, and it outperforms other deep learning methods such as UNet, R2Unet, PCTNet, and DNCNN.

In this paper, a two-port graphene–silicon-based aerial is planned and inspected. Features that make the planned radiator unique include the following: (i) aperture expended to stimulate the dielectric makes CP waves from 2.4 to 2.56 THz; (ii) loading of partial reflecting surface over the dual-port radiator creates beam tilting by an amount of ±45 ∘ ; and (iii) mirror positioning of the feeding slot provides the polarization diversity and enhances the separation close to 25 dB. A layer of graphene above the silicon ceramic with varying chemical potential makes the radiator frequency reconfigurable. After comparing the optimized outcome obtained from HFSS with a CSTEM simulator, it is established that the planned radiator operates efficiently between 2.35 and 3.15 THz with a peak gain of 6.5 dBi. The addition of pattern diversity features improves the MIMO parameters of the proposed antenna and makes it appropriate for THz built cellular applications.

This paper presents a novel, to the best of our knowledge, high-speed transmission system that integrates a new structured light beam, specifically the perfect vortex Laguerre-Gaussian (PVLG) beam, with an optical code division multiple access (OCDMA) system utilizing a premutation vector (PV) code. The PVLG beams are distinguished by their unique shape, which remains nearly invariant during propagation regardless of the azimuthal order of the orbital angular momentum (OAM), facilitating the multiplexing of multiple OAM beams within the same spatial area. Additionally, the system employs hybrid multimode fiber (MMF) and free space optics (FSO) channels, with consideration of foggy weather conditions in the FSO channel. A comparative analysis between the performance of PVLG beams and standard LG beams is conducted. Performance evaluation metrics include the Q -factor, bit error rate (BER), and eye diagrams, providing comprehensive insights into received signal quality. The results demonstrate that the system utilizing PVLG beams outperforms the one using standard LG beams.…

Obtaining quantitative geometry of the anterior segment of the eye, generally from optical coherence tomography (OCT) images, is important to construct 3D computer eye models, used to understand the optical quality of the normal and pathological eye and to improve treatment (for example, selecting the intraocular lens to be implanted in cataract surgery or guiding refractive surgery). An important step to quantify OCT images is segmentation (i.e., finding and labeling the surfaces of interest in the images), which, for the purpose of feeding optical models, needs to be automatic, accurate, robust, and fast. In this work, we designed a segmentation algorithm based on deep learning, which we applied to OCT images from pre- and post-cataract surgery eyes obtained using anterior segment OCT commercial systems. We proposed a feature pyramid network architecture with a pre-trained encoder and trained, validated, and tested the algorithm using 1640 OCT images. We showed that the proposed method outperformed a classical image-processing-based approach in terms of accuracy (from 91.4% to…

We present an estimate of the Atacama Cosmology Telescope (ACT) detector polarization angle systematic uncertainty from optics perturbation analysis using polarization-sensitive ray tracing in CODE V optical design software. Uncertainties in polarization angle calibration in CMB measurements can limit constraints on cosmic birefringence and other cosmological parameters sensitive to polarization leakage. Our framework estimates the angle calibration systematic uncertainties from possible displacements in lens positions and orientations, and anti-reflection coating (ARC) thicknesses and refractive indices. With millimeter displacements in lens positions and percent-level perturbations in ARC thicknesses and indices from design, we find the total systematic uncertainty for three ACT detector arrays operating between 90 and 220 GHz to be at the 10th of degree scale. Reduced lens position and orientation uncertainties from physical measurements could lead to a reduction in the systematic uncertainty estimated with the framework presented here. This optical modeling may inform…

The resonant fiber optic gyroscope (RFOG) driven by a broadband light source has advantages over conventional RFOGs in terms of structure, solution, etc., and provides new ideas for the commercialization of RFOGs. In this paper, the basic working principle of RFOG driven by a broadband light source is introduced. The optimal modulation coefficients are provided for sinusoidal wave modulation. The influence of the length of the fiber-optic ring resonator (FRR) and the coupling coefficient of the fiber coupler on the sensitivity is analyzed. The FRR is constructed in the over-coupled state to improve the utilization of optical power, and thus significantly increase the system sensitivity. In experiments, an RFOG prototype with a diameter of 13 cm, a height of 7 cm, and a fiber ring length of 210 m is produced. A bias instability (BI) of 0.06°/h and an angular random walk (ARW) of 0.01 ∘ /h are obtained.

Distributed fiber-optic sensor utilizing optical interference signal detection of the Rayleigh backscattering (RBS) light along the fiber under test (FUT) has greatly progressed over the past 20 years. It can now realize real-time sound signal recovery along the FUT with a good fidelity and high sensitivity. However, the performance of the practical distributed fiber-optic sound sensor is still limited by the fading problem, as invalid spatial channels at unknown positions arise due to the low signal intensity at these positions and the resulting near-zero signal-to-noise ratio (SNR). In this paper, we propose a novel, to the best of our knowledge, fading-free fiber sensor structure by incorporating an acousto-optic frequency shift (AOFS) loop into the light source in a dual-pulse phase optical time domain reflectometry (Φ-OTDR). As a result of stable frequency shifting and feedback within the loop, the loop source can output a high-repetition-rate narrow pulse train consisting of multiple separated frequencies. This pulse train is further shaped into two pulse bursts by an…

The Gerchberg-Saxton (GS) algorithm has been extensively employed in computational holography and beam shaping with the advantages of quick iteration speed and high energy utilization. However, the GS algorithm is prone to trapping into local optima and not reaching ideal outcomes, leading to poor shaping quality. In this paper, a method of random disturbance superposition (RDS) was proposed to feedback GS amplitude, which could stably and universally achieve over 95% high uniformity shaping of multiple beams without other complex operations. In light of this, this paper also covered how this technique affected energy utilization. It has been discovered that the introduction of perturbation could decrease the energy utilization. By analyzing the mechanism, a phase value replacement (PVR) method was proposed, which could effectively improve energy utilization without reducing uniformity. Finally, the simulation results were experimentally validated and met expectations very well. This method helps to accurately control the energy distribution of multiple beams and has a driving…