We propose a method to reduce the speckle noise associated with phase, retrieved using off-axis digital holography with transport of intensity. Multiple decorrelated holograms are obtained by simultaneously varying the linear polarization state of the object and the reference beams, which are applied in the combined technique to retrieve the phase. Reduction in speckle noise is verified through statistical analysis of the intensity and phase contrasts.

To reconstruct dynamic scenes without motion blur and improve image quality of quantum image sensors, a motion deblurring method based on spatial correlation and frequency domain characteristics of images is proposed. First, the spatial correlation of images is utilized to effectively reduce image noise. Second, log-polar and phase correlation of the reflectance characteristic images are used to estimate motion. Finally, a clear image without motion blur is reconstructed by combining clear moving objects with background of images. The same test images are processed by the proposed method, I. Gyongy’s object tracking method, and K. Iwabuchi’s variance-based motion estimation method. The results demonstrate the proposed method can accurately estimate motion even in conditions of low light and fast motion. Compared with the other two methods, the proposed method can improve the peak signal-to-noise ratio of the reconstructed image by up to 3.62 dB for local motion scene and 18.92 dB for global motion scene. Moreover, it has shorter execution time while maintaining the quality of reconstructed images. Real-world testing further confirms the effectiveness of the proposed method.

Atmospheric light estimation is fundamental for image dehazing. Unlike previous research on the atmospheric light estimation, we reveal a vector orthogonality in the classical atmospheric color degradation model for the first time. It is demonstrated that atmospheric light vector is orthogonal to the normal vectors of color degradation plane. Furthermore, an estimation method for direction and magnitude of atmospheric light vector is proposed based on the vector orthogonality. The proposed method can accurately estimate the atmospheric light and improve the quality of image dehazing with a short constant processing time even if the image resolution is increasing. We provide an efficient approach for estimating atmospheric light for high-definition image dehazing applications, such as traffic surveillance, environmental monitoring, and aerial photography.

The temporally and spatially modulated Fourier transform imaging spectrometer (TSMFTIS) has the merits of high optical throughput, good mechanical stability, and simple interference configuration. However, the number and the density of pixels in the infrared (IR) focal plane array limit the spectral resolution of TSMFTIS. Thus, we proposed the interferometric supersampling levering multiple sub-pixel translations of the focal plane array detector to realize the supersampling of the interference fringes and improve the system’s spectral resolution. The experimental results show that 2.31 cm−1 spectral resolution is achieved by employing a 384×288 uncooled IR detector array.

Color accuracy is of immense importance in various fields, including biomedical applications, cosmetics, and multimedia. Achieving precise color measurements using diverse lighting sources is a persistent challenge. Recent advancements have resulted in the integration of LED-based digital light processing (DLP) technology into many scanning devices for three-dimensional (3D) imaging, often serving as the primary lighting source. However, such setups are susceptible to color-accuracy issues. Our study delves into DLP-based 3D imaging, specifically focusing on the use of hybrid lighting to enhance color accuracy. We presented an empirical dataset containing skin tone patches captured under various lighting conditions, including combinations and variations in indoor ambient light. A comprehensive qualitative and quantitative analysis of color differences (ΔE00) across the dataset was performed. Our results support the integration of DLP technology with supplementary light sources to achieve optimal color correction outcomes, particularly in skin tone reproduction, which has significant implications for biomedical image analysis and other color-critical applications.

A decoupling algorithm, based on mode signal, is proposed for the control of double deformable mirrors (DMs) in a woofer–tweeter adaptive optics system. The algorithm operates as follows: first, based on the orthogonality property of Zernike polynomials within the continuous region of the unit circle, we construct the signal vectors of the constrained modes of woofer and tweeter. Subsequently, control matrices for both the woofer and tweeter are generated by employing singular value decomposition and considering the response matrix of DM signal to slope. Finally, the aberration is determined using the measurement results from the Shack–Hartmann wavefront sensor, and the mode signal coefficient vectors of the two DMs are obtained through integration with the leaky integrator. These coefficient vectors are then multiplied by a transition matrix to derive mode signal control vectors for both the woofer and tweeter. Simulation results demonstrate that the proposed algorithm outperforms both the conventional Zernike mode decomposition control algorithm and the projection-based decoupling algorithm. The experiments demonstrate that the algorithm effectively utilizes the compensation capability of the woofer, enabling it to release tweeter stroke for compensating high-order aberrations and achieving superior correction outcomes.

A Bessel function method incorporating carrier modulation is introduced, which accurately determines the phase shift amplitude of vibration signals by analyzing the amplitude relationship between the carrier’s main frequency and its harmonics. Experiments with a programmable signal generator and interferometer probe confirmed its feasibility and superiority over traditional Bessel function methods in weak signal calculations. In the experiment, this method can precisely calculate phase shifts down to 3.9 mrad and achieve a minimum detectable phase shift of 22 μrad, making it suitable for signal calibration in weak signal scenarios and analysis of phase carrier modulation signals.

The wide application of grating in engineering puts forward higher requirements for fabrication efficiency and precision. Maskless lithography based on digital micromirror device (DMD) is considered to be a promising technology with the advantages of high efficiency, low cost, and good flexibility. However, DMD-based digital lithography has been implemented mostly for micron-scale fabrication, which restricts its application to microstructures with submicron feature sizes. In this study, to realize the rapid fabrication of the grating of variable submicron line width, we adopt two misaligned DMDs to collaboratively modulate the exposure dose. By flexibly adjusting the misalignment parameter and the feature size parameter of the original grating mask, the gratings of variable micrometer and submicron line width are fabricated. We also evaluate the fabrication results by the photomicrographs and the optical diffraction modulation effects of the gratings. DMDs collaborative modulation lithography may be a feasible solution for DMD-based digital lithography, which can balance the lithography resolution, the fabrication efficiency and the manufacturing cost.

Zero-mode waveguides (ZMWs) are nanostructures that drastically reduce the effective optical observation volume beyond the diffraction limit, thereby permitting the use of higher concentrations of fluorescently tagged molecules for single-molecule studies. This work presents the fabrication technology of quartz plasma etching to create tapered sidewalls for the application in ZMWs, utilizing an inductively coupled plasma (ICP) reactive ion etching tool. This method involves a meticulously designed two-step etching process to achieve quartz cavities with a minimum sidewall angle of approximately 60 deg. Initially, the process involves altering the photoresist pattern from a vertical to a tapered form, facilitated by the use of CF4/O2/Ar plasma at elevated radio frequency power settings. Subsequently, the quartz material is etched utilizing CF4 based plasma, with the tapered photoresist serving as a mask. This innovative approach allows for the successful transference of the tapered photoresist structure onto the quartz material, culminating in the formation of uniform and symmetrical tapered quartz cavities. Most importantly, the surface roughness (Rq) of the tapered quartz, measured to be around 3 nm, is extremely low and meets the stringent requirements for optical devices.

This work examines the possibility of real-time detecting of single nitro compounds microcrystals [cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN)] with sizes of ∼130 to 600 μm by the terahertz (THz) imaging. A THz video camera based on a microbolometer matrix was used to record images in transmission and reflection optical schemes. A photoconductive antenna was used as a THz source. It was experimentally demonstrated that the spectral selectivity of identifying of nitro compounds microcrystals in the THz range strongly depends on their size, and the results of mathematical modeling based on the Mie scattering theory showed that this effect is due to the complex dependence of the extinction cross section of the microcrystals on their size. The results of the work can be used in the development of real-time THz visualization systems.

Mode matching has proven effective in suppressing the mode hopping in external cavity diode lasers (ECDLs) without antireflection coating. However, prolonged operation of ECDLs is susceptible to mode hopping induced by fluctuations in the equivalent internal cavity length. In this study, we introduce a rapid mode hopping identification method by monitoring the first derivative of the frequency scanning interference signal. Subsequently, an adaptive mode hopping suppression method, based on the acquisition of a priori knowledge for the initial current traversal optimization range, is applied to ECDLs. The experimental results demonstrate a significant extension in the stable operation time of the ECDL by a factor of 17, surpassing 7 h using the proposed rapid adaptive mode hopping suppression method.

A key sensor in the automotive stride for autonomy as well as improvement in advanced driver assist is the depth sensor light detection and ranging (LiDAR). However, one issue with LiDARs in general is the lack of dynamic range. Objects with high reflectivity and near range produce very high signals and low reflectivity far away targets yield a very low signal return. While the target reflectivity is generally not within the LiDAR designer’s control, the signal return as a function of range is when utilizing a range-compensating lens (RCL). This unique receiving lens disrupts the one-over-range-squared attenuation and provides a more constant return over range as initially demonstrated by Mudge [Appl. Opt., 58, 7921-7928, (2019)] using a two-element RCL. In this work, we provide an RCL design for automotive autonomy and/or advanced driver assist using a three-element RCL for improved range compensation over a two-element design while balancing complexity with greater than three elements. Additionally, we employ a more easily manufacturable variant RCL type given the anticipated high manufacturing volume.

SPIE is working with SAE International to develop lidar measurement standards for active safety systems. This multi-year effort aims to develop standard tests to measure the performance of low-cost lidar sensors developed for autonomous vehicles or advanced driver assistance systems, commonly referred to as automotive lidars. SPIE is sponsoring three years of testing to support this goal. We discuss the second-year test results. In year two, we tested nine models of automotive grade lidars, using child-size targets at short ranges and larger targets at longer ranges. We also tested the effect of high reflectivity signs near the targets, laser safety, and atmospheric effects. We observed large point densities and noise dependencies for different types of automotive lidars based on their scanning patterns and fields of view. In addition to measuring point density at a given range, we have begun to evaluate the point density in the presence of measurement impediments, such as atmospheric absorption or scattering and highly reflective corner cubes. We saw dynamic range effects in which bright objects, such as road signs with corner cubes embedded in the paint, make it difficult to detect low-reflectivity targets that are close to the high-reflectivity target. Furthermore, preliminary testing showed that atmospheric extinction in a water-glycol fog chamber is comparable to natural fog conditions at ranges that are meaningful for automotive lidar, but additional characterization is required before determining general applicability. This testing also showed that laser propagation through water-glycol fog results in appreciable backscatter, which is often ignored in automotive lidar modeling. In year two, we have begun to measure the effect of impediments to measuring the 3D point cloud density; these measurements will be expanded in year three to include interference with other lidars.

Adaptive optics (AOs) ophthalmoscopy is a powerful technique for imaging retinas of living subjects at single-cell resolution. Traditional AO ophthalmoscopes use a fixed exit pupil diameter, which is matched to the ocular pupil of a subject. A more efficient ophthalmoscope would allow for a variable exit pupil size to match the variable ocular pupil size of a subject. One method to achieve this is an optical zoom system. To make a zoom system appropriate for use in adaptive optics ophthalmoscopy, it must be simultaneously well corrected for both the field conjugate and the pupil conjugate such that the aberration correction can be successfully applied. The system must also be made of reflective optics to minimize chromatic aberration and spurious back reflections propagating through the system. Both of these factors make for an zoom system that requires tools and methods to be developed to realize successful designs. We present here our work developing a first-order starting point generator, which creates valid first-order solutions that satisfy all the constraints of the system. We then show our techniques for modeling and optimizing the simultaneous conjugates of the system throughout the process of unobscuring the system. We find that to achieve the selected specifications that freeform optics must be used. These surfaces are critical for correcting the residual aberrations introduced in the unobscuring process.

Modern tasks of analyzing turbid media dictate the need to develop specialized tools necessary for the practical implementation of new theoretical approaches using commercially available equipment. This report presents a photometric module that makes it possible to implement in practice the theoretical concept of a composite film developed by the authors. Within this scenario, the absorption coefficient of the average element of the dispersed medium can be determined based on the dependence of light loss in heterogeneous films on their thickness. This was achieved through the design, fabrication, and testing of a photometric Ω-module for a fiber optic spectrometer. The Ω-module provides illumination of the sample within a fixed solid angle Ω0 and provides summation of the transmitted light at the inlet of the fiber optic spectrometer at the same solid angle. The effectiveness of the Ω-module is demonstrated by determining the absorption coefficient of a composite film material and the volumetric absorption coefficient of an average microparticle of yttrium aluminum garnet YAG:Ce3+ powder with an average size of 5.3 μm. The value of the absorption coefficient (774 cm−1) of YAG:Ce3+ crystalline inclusions embedded in supporting epoxy resin film was obtained for a wavelength of 456 nm using the composite films model based on the results of measuring the intensity of light passing through free-standing epoxy-phosphor films of various thicknesses (in the range of 100 to 500 μm) installed in the Ω-module.

Exact aplanatic solutions of telescopic catadioptric optical system and singlet lens are presented. Details of how solutions are derived are discussed. Numerical verification carried out through geometrical optics and ray tracing simulations on specific optics geometries confirms the validity of solutions.

Modern monocentric lenses are used in wide field-of-view and high-resolution optical devices. As many other refractive optical systems, monocentric lenses often require correction of chromatic aberration. Since monocentric lenses are essentially thick, methods of color correction for monocentric systems differ from those for thin lenses. Although this difference is taken into account in known chromatic aberration correction methods, which are specific for monocentric lenses, these methods are approximate and often result in significant errors in calculations. We present exact analytical paraxial theory of color correction for monocentric lens systems. The rigorous approach allows one to design achromatic and apochromatic monocentric lenses by algebraic calculations of modest complexity. The exact analytical calculations are especially useful for apochromatic lenses because the approximate methods lead to considerably inaccurate results. The outcome of computations according to the proposed theory is the set of design parameters of an optical system: radii of curvature of lenses, lens thicknesses, and air spaces.

We present an approach to achieving high-resolution spectrometry through the utilization of a double transmission grating, in which two planar transmission gratings are strategically placed at an angle. This arrangement enables the light to pass through the dispersive element twice, resulting in a double dispersion and significantly enhancing the spectrometer’s resolution. We rigorously derived theoretical formulas for dispersion and parameters of the double grating model. Simulation results indicate that employing two transmission gratings with a groove density of 900 l/mm, the transmission-double-grating spectrometer can effectively measure wavelengths from 825 to 900 nm, the simulated resolution results in for 0.11 to 0.12 nm and the experimentally tested full width half maximum is 0.12 nm. In addition, a prototype of the spectrometer has been built and tested, and the experimental results are in general agreement with the theoretical modeling and simulation.

Fibers with high birefringence and low loss offer notable benefits in the areas of sensing, communication, and polarization filtering. An asymmetry subwavelength suspended-core terahertz (THz) fiber composed of rectangular and arc-shaped dielectric layers is studied. Simulation results show that the fiber has both ultra-high birefringence and low loss characteristics. The birefringence value is higher than 0.038 from 0.8 to 1.0 THz, and the transmission losses of two polarization modes are lower than 0.5247 dB/cm when the thicknesses of all dielectric layers are the same. We note that the birefringence value can be further increased by adjusting the thickness of the rectangular dielectric layer. The birefringence value reaches the order of 10−1 in the frequency range of 0.82 to 1.98 THz. At 0.82 THz, the losses for x- and y-polarization modes are 0.3705 and 0.0754 dB/cm, respectively. Therefore, this type of fiber will be of great significance in eliminating the adverse influences of polarization effects in THz systems.

We report a fiber-optic sensor configuration with a cascaded fiber Bragg grating (FBG) and a silicon Fabry-Perot interferometer (FPI) for simultaneous measurement of temperature and strain. The sensor is composed of a 5 mm FBG on a single mode fiber and a 100 μm thick silicon FPI attached to the tip of the optical fiber. The FBG is surface mounted on the host structure, and the FPI tip is suspended. Due to the stress-free, cantilever configuration, the silicon FPI is insensitive to strain, but sensitive to temperature with a sensitivity much higher than the FBG due to the large thermo-optic coefficient of silicon. The sensor is tested from room temperature to 100°C with varying strain up to ∼150 με. The silicon FPI provides high temperature sensitivity of 89 pm/°C unaffected by strain. Since the FBG is attached to the host structure, it is affected by both thermal and mechanical strain; the sensitivity of these was experimentally obtained 32 pm/°C and 1.09 pm/με, respectively. Interrogated with a broadband light source and a high-speed spectrometer, the sensor shows temperature and strain resolutions of 1.9×10−3 °C and 0.042 με, respectively. Due to the small size, enhanced sensitivity, and high resolution, this cascaded FBG-FPI sensor can be used in applications where accurate measurement of temperature and strain is required.

An efficient, compact 970 nm laser diode end-pumped Er:YSGG laser operating in continuous and pulsed modes is reported. In the continuous-wave regime, an output power of ∼1.6 W mid-infrared laser with 2.79 μm wavelength is obtained, corresponding to an optical efficiency of 19.6% and slope efficiency of 25.3%. In the pulsed regime, an energy of 144 mJ and a slope efficiency of 43.5% are achieved with a 30 at. % Er:YSGG crystal in 3×3×5 mm3 dimensions. The high-pulse energy and the high efficiency indicate that Er:YSGG lasers can potentially be used for blood sampling.

Microfluidic devices have become increasingly popular in various fields, including biosensors and chemical analysis. Modification of the wetting properties of microchannels offers a wide range of possibilities, from separating aqueous and organic phases to increased mixing and analysis efficiency, and eliminating micropumps in microfluidic chips. In this study, we investigate changes in the wetting properties of microchannels fabricated on Poly methyl methacrylate following laser irradiation. It was found that after re-irradiation of microchannel surface at fluences below the ablation threshold, decreasing the laser fluence and increasing the number of pulses lead to increase the hydrophilicity of the super-hydrophobic microchannel surface formed by laser irradiation at a fluence above the ablation threshold. By altering the irradiation parameters, we fabricated super-hydrophobic and super-hydrophilic channels on the sample. The effective chemical and morphological changes were investigated.

We propose a split mirror ring terahertz metamaterial sensor with the material of gold and quartz, based on the bright-bright mode coupling of the plasma-induced transparency, that significantly improves the Q-factor of the two bright modes, and the Q-factor of the resulting transparent window is as high as 13.15. The generation principle of each resonance peak was analyzed through the electric-magnetic diagram. The theoretical refractive index sensitivities of the transparency and the two resonance valleys were obtained by simulation with 410, 490, and 480 GHz/RIU, respectively. Moreover, after normalization, we compared the theoretical refractive index sensitivities with similar sensors and found that the sensor we proposed performs better. Therefore, the excellent sensing performance makes the sensor promising for markerless and nondestructive testing.

Amid the rising demand for high-performance computing, photonic integrated circuits are increasingly overcoming the conventional two-dimensional barriers, transitioning toward more flexible multilayer structures. To fulfill this aim, we have engineered a wide-bandwidth, multilayer tunable power splitter that enables the transmission of information along the vertical direction while allowing for flexible allocation of optical power. The power splitter is constructed with an asymmetric coupler, complemented by a grating structure. The design of the coupler has been refined through optimization employing the particle swarm algorithm, while the grating structure has undergone optimization via the direct binary search algorithm. The simulation results indicate that the power divider can achieve proportional regulation from 0.285 to 3.5 across the 1400 to 1700 nm wavelength spectrum, with insertion losses (ILs) consistently below 0.34 dB. Significantly, the IL is <0.21 dB at a 1:1 power ratio. This compact, low-loss, high-bandwidth tunable power splitter was designed to offer a new idea for the multilayer integration of microchips.

This work deals with the effect of adaptive optics (AOs) configuration options, i.e., tip/tilt (N=3) and full AO (N=35) cases, on the intensity probability density functions (PDFs) associated with the turbulent channel. An ad hoc scintillation index model is proposed for the full AO options. This model is applicable for both power-in-the-bucket and power-in-the-fiber (PIF) signal receptions. The commonly used log-normal intensity PDF follows the no AO and tip/tilt experimental horizontal link data for two turbulence conditions but fails to accurately characterize the full AO option for those two cases, especially in depicting the perceived left skewness of the PDF in one case. The exponentiated Weibull distribution with the proposed full AO scintillation index model exhibits good agreement with the experimental data in the two cases and follows the strong left skewness in one case. These results also show that the median value for each PDF shifts to the right and the PDFs experience narrower shape changes, i.e., more received power, as AO Zernike modes are added. Finally, comparison of PIF PDF shifts with the estimated fiber coupling efficiencies is in reasonable agreement.

Multi-user, low-loss, and cost-efficient characteristics are highly desired for widely deployed passive optical networks (PON), which are constrained by the upstream power combining loss induced by optical splitters in optical distribution networks (ODNs). We propose a multi-user low-upstream-loss PON utilizing graded-index multi-mode fiber (GI-MMF) and a compact ODN constructed by a multi-mode transformer (MMT) for the first time. Enabled by the MMT, the ODN achieves multi-mode multiplexing for low-loss combining in upstream and power splitting in downstream, simultaneously. An implementation approach for MMT using a single MPLC is also proposed, and a 44-mode MPLC-based MMT is designed for verification. Simulation results show that the device achieves a combining loss of lower than 1.13 dB and a modal crosstalk of lower than −19.5 dB in upstream and an excess splitting loss of less than 1 dB in downstream for all modes. The bandwidth characteristics and tolerance are also investigated through simulation.

Although self-supervised depth estimation models based on transformers have achieved success, lightweight depth prediction networks exhibit a particularly pronounced issue with depth prediction blurriness at object boundaries compared to standard depth prediction networks. We found that this problem arises from the token dimension constraints, which limit the precise representation of semantic and spatial information. To address this challenge, we introduce a lightweight monocular self-supervised depth estimation network, RENA-Depth, which leverages convolutional neural network neighborhood attention-guided recursive Transformers to enhance depth estimation precision. Specifically, the design begins with the introduction of neighborhood adaptive attention (NA), which focuses on local and regional scales. This component adaptively mines latent semantic and spatial information from the neighborhoods of the input features of self-attention. Subsequently, a global feature recursive interaction module was developed to recursively refine the interaction between local and global information, enhancing the representation of semantic and spatial information without a significant increase in parameters. Finally, an attention equilibrium loss is proposed, which motivates richer semantic information representation and clarifies boundary depth by penalizing the orthogonality similarity of attention mechanisms. Extensive evaluations on the Karlsruhe Institute of Technology and Toyota Technological Institute and Make3D datasets have demonstrated that the proposed lightweight self-supervised depth estimation model, RENA-Depth, outperforms the most advanced lightweight depth detection algorithms, confirming its efficacy and innovation in improving depth prediction accuracy.

Unmanned aerial vehicle remote sensing image matching techniques are crucial for urban planning and environmental monitoring. However, existing feature matching methods have limitations due to the lack of effective extraction of key diverse features, which hinders the improvement of matching accuracy for diverse ground scenes. To address the above limitations, we propose a remote sensing image feature-matching method using optimally regularized nonlinear diffusion model. Specifically, we first use the accelerated-KAZE (AKAZE) algorithm framework to detect and characterize features within a nonlinear scale space. To improve the adaptation of diffusion to the local image structure, we propose the introduction of a novel Charbonnier regularized nonlinear diffusion model for constructing the diffusion coefficients. We then propose to combine Brute force with the K-nearest neighbor algorithm to eliminate invalid matches. Lastly, we modified the sampling approach of the random sample consensus (RANSAC) algorithm. Instead, we achieve iterative dataset purification using the progressive sample consensus algorithm, complemented by the implementation of a termination criterion for the sampling process. Experimental results show that our method achieves an average matching precision of 82.8%, 80.2%, 82.9%, and 91.2% when the test set undergoes scale, rotation angle, noise blurring, and luminance variations, respectively, outperforming the existing feature matching methods.