Ray data files are a common way to model light sources, such as light emitting diodes (LEDs), in optical design software. Often, when an LED shall be placed at the focal point of a collimating lens, it is desirable to know the coordinates of just a single point, which is representative of the light source location, similar to the center of mass for a distribution of matter. In some communities, this point is known as the “virtual focus,” and some LED vendors publish the virtual focus coordinates with their ray data sources. However, it is hard to find a clear and precise definition of the virtual focus, and it is not clear how it can be computed in an efficient way. We explain our definition and provide an efficient algorithm and its MATLAB^® implementation.

To realize automatic zooming of presbyopia glasses, we proposed a gaze distance detection method based on binocular tracking. A theoretical model was built to calculate gaze distance based on the gaze directions of two eyeballs. The gaze direction of each eyeball was obtained by the pupil center corneal reflection method. Three light-emitting diodes (LEDs) and two miniature cameras were placed on the glasses frame around the eyeball. Then, gaze direction was derived by calculating the distances between the pupil center and the positions of three LED reflection images by the corneal from the images captured by cameras. The experiment setup was built to test the gaze direction and gaze distance. The experimental result demonstrates that it is an effective way to obtain the user’s gaze distance for automatically adjusting the focal length of the zoom glasses.

Sheared-beam imaging (SBI) is an effective way of imaging through turbulent medium, such as atmosphere or scattering liquid. Traditionally, the imaging is based on the laser transmitter array consisting of three beams or five beams for coherent illumination to the remote object. Compared with the existing SBI methods, the four-beam sparse sampling imaging method has been proposed, which may have more advantages; it not only sparses the detector elements but also reduces the number of emitted beams. However, the traditional phase retrieval algorithms are not suitable for the four-beam sparse sampling imaging. We propose a four-beam sparse phase retrieval (F-BSPR) algorithm, which uses the phase differences from both horizontal and vertical components and the phase differences from other components when the phase is retrieving. The proposed phase retrieval algorithm can better connect the phase difference and improve the accuracy of the phase retrieval. Furthermore, the imaging quality is improved. Simulation and experimental results show that the proposed algorithm is effective and feasible when the number of detector elements is sparse by 50%. Compared to the traditional four-beam phase retrieval method, the proposed F-BSPR method has better imaging quality and robustness.

Digital holography enables 3D imagery after processing frequency-diverse stacks of 2D coherent images obtained from a chirped-frequency illuminator. To compensate for object motion or vibration, which is a common occurrence for long-range imaging, a constant temporal frequency or “pilot-tone” illuminator can act as a reference for each chirped frequency. We examine speckle decorrelation between the chirped and pilot-tone illuminators and its effect on the resultant range images. We show that speckle decorrelation between the two illuminators is more severe for facets of the object’s surface that are more highly sloped, relative to the optical axis, and that this decorrelation results in noise in the range images in the areas of the object that are highly sloped. We develop a theoretical framework along with wave-optics simulations for 3D imaging with a pilot tone, and we examine the severity of this noise as a function of several imaging parameters, including the illumination bandwidth, pulse frequency spacing, and atmospheric turbulence strength; we show that 3D sharpness metric maximization can mitigate some of the noise induced by turbulence, all in a simulated framework.

The operation of a Geiger-mode avalanche photo diode (GM-APD) LIDAR is severely disturbed by background noise, which makes it challenging to rapidly and accurately estimate the target depth. Therefore, we propose an adaptive fading Kalman depth estimation technique based on chi-square hypothesis testing for GM-APD LIDARs. First, by analyzing the consistency of the echo photon distribution between adjacent pixels of the GM-APD, the pixels are fused to rapidly obtain the echo data of the target surface, thereby accelerating the depth estimation process. Second, we design a chi-square hypothesis test condition based on the statistical characteristics of the innovation vector, which can help evaluate whether the fading factor is introduced at the current moment, promote the convergence of the algorithm, and reduce the depth estimation time. Third, we propose a fading memory index weighted method to adaptively adjust the weight of the observed values to accurately estimate the innovation matrix covariance and determine the optimal fading factor. We demonstrate the effectiveness of the proposed algorithm through simulations and experiments. The results show that the proposed algorithm can rapidly and accurately estimate the target depth in the presence of strong background noise.

A high-precision extrinsic calibration is the underlying premise of the accurate perception of light detection and ranging (LiDAR) and camera systems commonly used in the autonomous driving industry. We propose a coarse-to-fine strategy to get rigid-body transformation between solid-state LiDAR with non-repetitive scanning and a RGB camera system using a chessboard as the calibration target. This method exploits the reflectance intensity characteristics of the LiDAR point cloud, which exhibit the distinct distribution in white and black blocks of chessboard. In the coarse calibration step, a reflectance intensity Gaussian mixture model was used to extract the unicolor block point cloud from the chessboard point cloud. Therefore, the initial estimate of the extrinsic parameter was obtained by aligning the corners in the point cloud and calculating the centroid of the unicolor block point cloud and corners in the image. In the refinement step, we extracted points on the border of each block as LiDAR features and designed an iterative optimization algorithm to align the intensity of LiDAR features with grayscale features in the image. This method utilizes the intensity information and compensates for corner errors in the point cloud due to reflectance intensity binarization. The results of the comparative experiment revealed that the proposed method outperformed existing methods in terms of accuracy. Experiments based on simulations and real-world conditions revealed that the proposed algorithm demonstrated a high accuracy, robustness, and consistency.

Most artisans visually characterize Chiapas amber, mainly in appreciating the blue-green color emitted by fluorescence when incident ultraviolet light illuminates it. However, false amber pieces generate this coloration, misleading local and international buyers. Thus, we propose an optomechatronic device (OD) to determine whether amber from Chiapas is authentic. This device measures the fluorescence intensity and, through a database, determines whether amber is authentic. The infrared and ultraviolet spectroscopy techniques validated the results obtained with the OD.

Recently, a single-shot N-step phase measuring profilometry was proposed by our research group. It not only maintains the single-shot real-time measuring characteristics but also makes its measuring accuracy selectable as appropriate N. But when the spectral aliasing in the captured deformed pattern is severe, the alternative current (AC) component may be extracted imprecisely or even failed. So, a double-shot N-step phase measuring profilometry (double-shot N-PMP) is proposed. While two complementary sinusoidal gratings are projected onto the measured object, the AC component of the captured deformed patterns can be extracted precisely even if spectrum aliasing is very serious. If the AC component multiplies with N frames of the AC components of the N-step phase-shifting fringe patterns captured from the reference plane in advance, a new N-step phase-shifting algorithm for the phase difference between the measured object and the reference plane is accomplished to reconstruct the measured object. The experimental results show the possibility and effectiveness of the proposed method. It can either improve the measuring accuracy or expand application scope. Though the double-frame gratings are needed, the real-time measuring characteristics can still maintain with the time-division multiplexing method.

Obtaining the wrapped phase is a crucial step in fringe projection profilometry. However, reliably and efficiently extracting the wrapped phase from fringe patterns under non-ideal conditions remains a challenging problem. Neural networks have demonstrated higher robustness under non-ideal conditions; however, they struggle to handle abrupt data at the edge of the phase cycle when directly predicting the wrapped phase. To address this issue, we propose “trigonometric phase net (TPNet),” an approach that leverages the distribution characteristics of wrapped phase data. TPNet uses a neural network to predict the wrapped phase in the form of sine and cosine values; the wrapped phase is then calculated using the a tan function. This approach not only avoids the direct processing of abrupt data by the neural network but also facilitates network convergence due to its similar distribution law as fringe patterns. We also introduce a new loss function, Loss_sincos, which is designed to align with the sine and cosine function distribution of the network’s output. This loss function improves the accuracy of the neural network in indirectly predicting the wrapped phase. Our experiments demonstrate that TPNet can accurately extract the wrapped phase from single frame fringe patterns under non-ideal conditions.

We propose an approach to reconstruct spectrum using artificial neural networks (ANNs) instead of directly solving a matrix equation using calibration coefficients. ANNs are particularly effective in reconstructing spectra in noise environment by learning the relationship between inputs and outputs with large amount of data training. There are several different training methods for ANNs. Compared with scaled conjugate gradient algorithm and Levenberg–Marquardt algorithm, Bayesian regularization (BR) algorithm is demonstrated to be a better training algorithm for spectral reconstruction. We also compare the spectral reconstruction of BR algorithm and that of the traditional algorithms. Experimental results indicate that the spectral reconstruction of BR algorithm is nearly in line with that measured by a commercial spectrometer. Obvious deviations are occurred in the spectral reconstruction of the traditional algorithms due to inevitable background noise, rounding errors, and temperature variations. Therefore, spectral reconstruction using ANNs with a train method of BR algorithm is a more suitable choice for the disorder dispersion spectrometer.

Nonlinear photonic crystals can be employed to generate holographic images in nonlinear optical processes. However, due to the limit of binary structure, the process of holographic imaging will lose part of the amplitude information and cause image hollowing, thus the imaging quality is reduced. Generative adversarial network, a deep learning network based on game theory, is used to restore images. The results of restoration show high similarity to the original images, effectively weakening the effect of image hollowing, suppressing the diffraction effect, and restoring grayscale values. This image post-processing approach completes the field of application of nonlinear holographic imaging, which is useful for non-visible source imaging, crosstalk avoidance, optical encryption, and so on.

I present the results of an optical design study into the performance benefits of non-rotationally symmetric “freeform” gradient-index (GRIN) media on a pupil-relay head-mounted display. A range of design variants are presented based on freeform-GRIN lenses consisting of ternary base-material combinations that are enabled by recent developments in additive manufacture. The optical performance of these designs is compared to homogeneous solutions comprising combinations of spherical, aspheric, toric, and freeform surfaces. I show that freeform-GRIN media represent powerful degrees of freedom for aberration correction in tilted and off-axis optical systems, performing comparably to homogeneous freeform optics while illustrating significant potential reductions in lens count and mass.

An optical imaging system’s image quality can deteriorate due to uncorrected astigmatism and defocus. An approach to correct these issues is proposed, which involves a non-mechanical, electronically adjustable system. This system consists of three liquid crystal-based cylindrical lenses, which adjust optical power depending on applied voltage values. The advantages of this system include a simple and low-cost structure, large aperture size, low-voltage drive, and compact design. This non-mechanical solution has great potential for various applications, such as wavefront correction for large telescopes, microscopy, augmented reality/virtual reality, and prescription eyeglasses. Design, fabrication, and optical characterization of the proposed device are discussed.

A hollow anti-resonant fiber with nested and double cladding structure is proposed. By optimizing the structural parameters, the confinement loss reaches 4 × 10 ^{− 4} dB / km at 1.55 μm, and the ratio of high-order mode loss to fundamental mode loss also reaches 20,000. In the O + E + S + C + L + U band, the loss is <0.01 dB / km and the ratio of high-order mode loss to fundamental mode loss is >10³, indicating that the designed fiber has excellent single-mode characteristics and wide bandwidth. In addition, the manufacturing tolerance of the fiber is also discussed. It is found that the loss can still be maintained below 0.01 dB / km within the tolerance range of 8%. Therefore, we believe that the fiber has potential applications in near-infrared communication and data transmission.

We investigate the digital glass forming process for depositing commercial SMF-28 single-mode optical fiber for photonic purposes. The process utilizes a CO₂ laser to locally heat the feedstock to fuse it onto a fused quartz substrate. We focus on how altering the deposition parameters, including the laser power, feed rate, and path plan, affects the deposited fiber morphology and how this affects the optical transmission. At high powers, the fiber bonds strongly to the substrate, resulting in significant changes in fiber morphology and core shape. With a gradient transition between the feedstock geometry and the deposition geometry, high optical transmission for straight line depositions can be achieved. Additional work was performed examining the optical losses when the fiber is deposited around a constant radius curve for different fiber morphologies, with higher losses recorded for higher power samples. Comparing the doping profile of these samples indicates that the gradient of Ge decreases at higher laser power, suggesting the losses are caused by diffusion of the fiber core. This work shows that for high input powers, the optical losses around curves are increased, leading to a tradeoff between the bonding strength and optical transmission for these geometries.

Laser-induced damage threshold (LIDT) is investigated at several wavelengths in the high-purity silica optical fiber. The finite element method (FEM) is used to study transmission mode, LIDT, temperature distribution, and thermal stress distribution of the fiber. Our results show that the center of the front surface is subjected to severe thermal effects under laser irradiation and consequently, and it is susceptible damage. The variations in temperature and thermal stress are identified as increasing with laser fluences, which show a similar tendency. When laser fluences surpass the LIDT, such as 35 GW / cm², the temperature at the front surface center shows a sudden growth and the melting damage appears, and no stress damage occurs at this time. Notably, the melting effect of high purity fused silica optical fiber is simulated by numerical calculation based on ray optics for the first time. Our research can provide systematic FEM simulations for the LIDT of silica optical fibers.

The infrared anti-reflection film is prepared by ion beam assisted thermal evaporation deposition technology. The film has good firmness and can meet the needs of wet transfer. By adjusting the number of layers of the graphene mesh, the electromagnetic shielding and optical transparency properties are simultaneously improved. The infrared anti-reflection film and graphene mesh are combined to design and prepare a compatible electromagnetic shielding infrared anti-reflection film device with sandwich structure. The test results of the device show that the peak transmittance of the graphene mesh/infrared film/substrate/infrared film combination structure in the 3 to 5 μm band is 95.06%, and the average transmittance is 93.40%. The peak shielding effectiveness (SE) in the 12 to 18 GHz frequency band is 14.50 dB, and the average SE is 12.98 dB. It shows that the film device of this structure maintains the high transmittance of the infrared anti-reflection film and has good electromagnetic shielding effectiveness.

Structural design of optical components launched into space requires fracture mechanics properties. To perform component design of a calcium fluoride (CaF₂) prism, the fracture toughness and slow crack growth (SCG) parameters were measured on the {100}, {110}, and {111} low index planes. The fracture toughness is lowest on the {111} plane at 0.35 ± 0.01 MPa√m with a very flat cleavage surface exhibited during both fracture toughness and strength testing. SCG was significant on the {111} plane with a power law exponent of n = 30 ± 8. For engineering purposes, SCG was insignificant on the {100} and {110} planes with n > 75. The facture surfaces have distinct patterns that are indicative of the cleavage plane. Biaxial testing with disks implies that design for general multiaxial states should be based on {111} strength and crack growth properties.

A highly sensitive one-dimensional photonic crystal magnetic and thermal sensor with lithium niobite (LiNbO₃) used as the defect layer is proposed. The rigorous coupled wave analysis theory and the wavelength interrogation method were performed to further investigate the effects of different defect layers and magnetic fluid film structure parameters on the sensitivity and figure of merit (FOM). The results show that the introduction of LiNbO₃ can significantly improve the sensing performance. When LiNbO₃ was introduced as the defect layer, the magnetic field detection sensitivity increased from 0.817 to 1.9133 nm / Oe, whereas the temperature detection sensitivity increased from −0.0724 to 0.304 nm / ° C. Meanwhile, it provides a high FOM value of 8.7099 Oe ^{− 1}. Our work provides a guideline for the future application of LiNbO₃ materials in magnetic and thermal sensors.

A high dopant concentration significantly reduces the peak current of the internal quantum efficiency (IQE) of the light-emitting diode (LED). The effect of the dopant concentration on the epitaxial layer toward the IQE, current density, and IQE droop of gallium nitride (GaN)-based LED chip is analyzed with the doping variation from 1 × 10¹⁵ cm ^{− 3} to 1 × 10²¹ cm ^{− 3}. The required current density for the dopant concentrations of 1 × 10¹⁵ cm ^{− 3} is 122.42 A / cm ^{− 2} with the IQE droop of 10%. Meanwhile, for the dopant concentrations of 1 × 10²¹ cm ^{− 3}, the required current density for achieving peak IQE is 0.67 A / cm ^{− 2} with an IQE droop of 51%. The increase in dopant concentrations reduces the current density necessary for achieving peak IQE while increasing IQE droop. The optimization is performed for the device performances based on the peak current and IQE droop. The optimal dopant concentration for this GaN-based LED lies between 1 × 10¹⁷ cm ^{− 3} and 1 × 10¹⁸ cm ^{− 3}, which is 4.47 × 10¹⁷ cm ^{− 3}, with a peak IQE of 69.1%. The proposed epitaxy structure provides the optimal doping concentration for the homojunction LED chip with a compatible activation current. The results achieved in this work may benefit the entire optoelectronics field.

Dual-detector and single-detector strategies are the main tracking methods used in pointing, acquiring, and tracking (PAT) system. The coarse pointing subsystem (CPS) and the fine pointing subsystem (FPS) have different detectors in dual-detector tracking method (DTM). In contrast, they use one common detector in single-detector tracking method (STM). These two methods have their own advantages and defects in terms of cost, volume, weight, and performance. Based on the analysis of these two methods, two modified STMs (MSTMs) are proposed to promote the tracking performance for the PAT system. In the first MSTM, the information of the tracking error of the FPS is introduced to construct a virtual detector for the CPS. This makes the proposed method have a tracking performance close to that of the DTM. Furthermore, the second MSTM is presented to balance the bandwidth difference between the CPS and the FPS. Compared with the first MSTM, the second one includes the first one as a special case and it provides more design degree of freedom for the PAT system. Experimental results have shown the effectiveness of the presented methods.

The existing multi-directional light-emitting diode (MD-LED) aided visible light positioning (VLP) scheme is difficult to physically implement. An improved MD-LED based VLP scheme is proposed, in which we devise an integrated single lamp that consists of a regular pyramid metal block and multiple standard Lambert radiation light-emitting diode chips, which are mounted on different planes of the metal block. In addition, a localization algorithm exploiting received signal strength ratio based on linear least squares is provided. Simulation and experiment results show that this scheme can achieve an average localization accuracy of 5 and 11 cm, respectively, at a known height in the realistic mobile user scenario with a tilting receiver. Compared with the existing MD-LED aided VLP scheme, this scheme implements the first ever prototype MD-LED lamp and has a low implementation cost.

For the simulation of anisoplanatic optical turbulence, split-step propagation is the gold standard. Within the context of the degradations being limited to phase distortions, one instead may focus on generating the phase realizations directly, a method that has been utilized in previous so-called multi-aperture simulations. Presently, this modality assumes a constant Cn2 profile. This work presents an alternative derivation for Zernike correlations under anisoplanatic conditions. Multi-aperture simulation easily incorporates these correlations into its framework and achieve a significantly higher degree of accuracy with a minimal increase in time. We additionally use our developed methodology to explain previously reported discrepancies in an empirical implementation of split-step with the analytic tilt correlation. Finally, we outline a major limitation for Zernike-based simulation that still remains.