Line chromatic confocal imaging (LCI) is an advanced system used for quick and accurate three-dimensional surface imaging without vertical mechanical scanning. It is extensively employed for fast industrial inspection. For high-speed and accurate measurement characteristics of the LCI technique, a rapid and accurate peak localization method is important. In this paper, we propose a gradient transform weight centroid method (GTWC) to improve the accuracy of peak positioning, without compromising high-speed characteristics. This method helps reconstruct the 3D profile at a higher axial resolution by reducing the full width at half maximum (FWHM) without altering the original structure of the LCI system. Both simulations and experiments show the feasibility and good performance of this method.

We present the target iterative assembly (TIA), an algorithm to generate freeform lenses for non-imaging systems from prescribed input rays and a distribution of targets, whose coordinates are functions of the positional and angular variables of the source distribution, granting the optical design unlimited customization and control over aberrations, whereas the angular iterative assembly (AIA) presented in a previous work was restricted to choosing output angles. The formalism employed seeks to generalize a class of existing point-by-point iterative construction methods. We also elaborate variations of the midpoint method, a predictor-corrector approach to enhance convergence of the solutions with fewer rays and analyze the sensibility of their error profiles to changes in the initial parameters. For N R rays, we obtained surface average errors and computing times proportional to (10 N R )−2 and 10−5 N R seconds, respectively, allowing for quick solutions within the precision limits of fabrication. We also discuss two algorithms for the generation of multiple successive surfaces, one which leads to apodization, and set the base for further developments, such as a 3D version to properly generate freeforms. The Python code with fully customizable system parameters is available.

How to find the specific measurement scheme to approach the quantum Cramér-Rao bound (QCRB) is an important issue in quantum metrology, especially for the continuous-variable optical interferometers input with non-classical states. In the ideal situation (i.e., without any photon loss), this can be usually achieved by using the parity measurement, which, however, does not work well when the photon loss occur. Alternatively, in this work we find that the coincidence measurements are more robust to the photon loss than the parity measurement. Importantly, in certain cases, the sensitivity with the coincidence measurement can even approach very closely to the QCRB despite of the photon loss. Though the results are obtained based on the analysis with the typical two-photon twin-Fock state, it might be also generalized for the other input ones. Thus, our work may provide an effective measurement scheme for beating the shot-noise limit in practical experiments.

A special cutoff filter is required at the Fourier plane of the imaging lens for the schlieren visualization technique. During short-pulse laser illumination, the energy density in the focal spot of the Fourier plane can surpass the damage threshold of commonly employed metals or metallic coatings used for filtering. While dielectric substrates have a much higher damage threshold, acquiring dielectric filters from commercial suppliers can be challenging. In this study, we present experimental and simulation results to demonstrate that commercially available, off-the-shelf, dielectric mirrors can serve as effective schlieren cutoff filters. These mirrors offer a much higher damage threshold, making them a viable alternative to traditional metal filters in high-energy laser applications.

The holographic Maxwellian display holds significant potential as a technique for augmented reality presentations due to its capability to address the vergence-accommodation conflict in see-through near-eye displays. However, conventional lensless holographic Maxwellian displays predominantly rely on amplitude-type holograms, facing challenges such as low diffraction efficiency and interference from conjugate images. To overcome these limitations, we propose a lensless phase-only holographic Maxwellian display tailored for optical see-through near-eye applications. In our approach, a complex amplitude distribution, calculated using the angular spectrum diffraction method, was encoded into a phase hologram via the double-phase decomposition algorithm. This phase hologram can effectively converge the virtual target image onto the viewer’s pupil by multiplying the phase hologram with a convergent spherical wave at the hologram plane, enabling viewers to consistently perceive all-in-focus images at the pupil location. Additionally, we introduced a digital grating to mitigate the interference caused by other-order diffraction images. Finally, experimental results demonstrated that our proposed near-eye display system can accurately generate see-through virtual images without the vergence-accommodation conflict issue by loading the designed phase hologram onto a phase-type spatial light modulator. Furthermore, the eye box expansion has been realized by multiplying the phase hologram with multiple convergent spherical waves.

Multimode fibres are now finding applications in the transport of complex modes and spatial information, such as images. Key to their use is recognising that fibres can be characterised in terms of a transmission matrix, relating any complex input field to the output field. Unfortunately, bending, stressing, or changing the temperature of the fibre changes this matrix, which traditionally then requires a time-consuming re-calibration. In this work, we characterize the stability of this transmission matrix by examining the changes in the transmitted speckle field as the fibre is substantially perturbed. We consider both step-index and graded-index fibres for three different types of fibre bend. Specifically, we examine both step- and graded-index fibres each supporting over one thousand transverse modes and show that, when averaged over the whole numerical aperture, the transmission matrix associated with the graded index fibres is significantly more stable than those for step index, for all types of fibre bend. Furthermore, the higher numerical aperture modes are always more stable than the low-numerical aperture ones. This work is important for selecting fibre type, bend constraints, and calibration bend positions for those using multimode fibres in data transmission or imaging applications.

All-optical logic gates (AO-LGs) are key elements that play a pivotal role in the development of future all-optical computing and all-optical computers. In this paper, benefiting from particle swarm optimization (PSO), an optimized metasurface unit cell in the far-infrared (FIR) frequency band is presented as the basis of four port controlling light with the light system. This system, known as coherent perfect absorption (CPA), could be applied as AO-LGs in certain conditions. NOT, AND, OR, NAND, NOR, XOR, and XNOR logic gates can be implemented with the proposed method. The remarkable innovation of this article is the use of a fuzzy inference system (FIS) instead of a crisp threshold. Different calculated parameters like extinction ratio (ER = 96.2 dB), contrast ratio (CR = 99.54 dB), amplitude modulation (AM = 0.7 dB), and eye-opening (EO = 99%), besides the possibility of utilizing the proposed system for various kind of CPA films, prove the impressive effects of FIS applying as a novelty in this work. Small dimensions and low power consumption are other characteristics of the proposed method that are obtained as a result of using optimized metasurface-based CPA.

We introduce a trident edge coupler design optimized for the simultaneous coupling of two widely separated wavelengths (2 µm and 1 µm) between a lensed fiber and a 600-nm-thick X-cut lithium-niobate-on-insulator (LNOI) waveguide. These wavelengths are commonly encountered in nonlinear wave mixing applications, representing either the fundamental and second harmonics in second harmonic generation (SHG) processes or the leading and trailing edges of an octave-spanning spectrum generated through broadband nonlinear processes such as frequency comb or supercontinuum generation. Achieving efficient coupling between fibers and strongly confined waveguides in integrated platforms, such as LNOI, can be challenging due to the significant difference in spot sizes between the two wavelengths. Our trident edge coupler offers coupling losses below 1.4 dB for the 2 µm and 1 µm spots simultaneously, showcasing an average transmission enhancement of around 10% compared to the baseline of a single linear taper. Furthermore, it enables a reduction of transmission at 1.5 µm, a typical pump wavelength, with an attenuation of transmission over 10 dB compared to those at the 2 µm and 1 µm wavelengths.

This work aims to define Sonine filters and introduce them for digital image processing. Their fundamental properties are described and an optimizing performance procedure is explained, exploiting the unique advantage that this kind of filters possess, which consists of having simple analytical finite Fourier transforms for circular, elliptical and rectangular domains. A comparison with various existing filters is also presented, like Gaussian, Hann, Hamming, Blackmann, etc. Some relations are provided to facilitate their applicability. Also, comprehensive optimized filter designs are provided. Finally, an experimental application for intensity normalization and noise reduction of fringe patterns is described, showing that this kind of filters could be helpful in digital image processing and particularly in the analysis of fringe patterns.

A numerical analysis of spatially chirped beams produced by single-pass grating pairs is presented. It is shown that focused pulse structures can deviate significantly relative to standard linear spatial chirp approximations depending upon the pulse bandwidth, the angle of incidence, and groove density of the gratings used.