Optical Focal Length Research Articles

Proficient Calibration Methodologies for Fixed Photogrammetric Monitoring Systems

This work focuses on investigating the accuracy of 3D reconstructions from fixed stereo-photogrammetric monitoring systems through different camera calibration procedures. New reliable and effective calibration methodologies that require minimal effort and resources are presented. A full-format camera equipped with fixed 50 and 85 mm focal length optics is considered, but the methodologies are general and can be applied to other systems. Four different calibration strategies are considered: (i) full-field calibration (FF); (ii) multi-image on-the-job calibration (MI); (iii) point cloud-based calibration (PC); and (iv) self (on-the-job) calibration (SC). To evaluate the calibration strategies and assess their actual performance and practicality, two test sites are used. The full-field calibration, while very reliable, demands significant effort if it needs to be repeated. The multi-image strategy emerges as a favourable compromise, offering good results with minimal effort for its realisation. The point cloud-based method stands out as the optimal choice, balancing ease of implementation with quality results; however, it requires a reference 3D point cloud model. On-the-job calibration with monitoring images is the simplest but least reliable option, prone to uncertainty and potential inaccuracies, and should hence be avoided. Ultimately, prioritising result reliability over absolute accuracy is paramount in continuous monitoring systems.

X-ray astronomy from the lunar surface.

Motivated by efforts to return humanity to the Moon, three cases are reviewed for X-ray astronomy from the lunar surface: (i) facilitation of ambitious engineering designs including high-throughput telescopes, long focal length optics and X-ray interferometery; (ii) occultation studies and the gain they enable in astrometric precision; and(iii) multi-messenger time-domain coordinated observations. The potential benefits of, and challenges presented by, operating from the Moon are discussed. Some of these cases have relatively low mass budgets and could be conducted as early pathfinders, while others are more ambitious and will likely need to await improvements in technology or well-developed lunar bases. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades (part 2)'.

Ultralow dispersion and broadband gradient refractive index microlens arrays imprinted in chalcohalide glass by microthermal poling

Ultralow dispersion gradient refractive index (GRIN) microlens arrays (MLAs) covering the visible to mid-infrared wavelength range are imprinted in GeS2-Ga2S3-CsI chalcohalide glass by an efficient and economical microthermal poling process. The effect of poling voltage on GRIN microstructure, structural rearrangement, optical properties of the poled glasses, and imaging of the imprinted MLAs have been investigated. Optical focal length of the GRIN MLAs decreases from 353 to 63 μm with increasing the poling voltage from 200 to 1000 V, which is in accordance with imprinting-induced phase difference increase from 0.57λ to 1.19λ. Optimal chromatic aberration (between 520 and 850 nm) as low as 5% is achieved in the GRIN MLAs. Formation mechanism of GRIN MLAs is mainly associated with an enhanced transverse migration of Cs+ ions within mesh square area, which is provided by an improved anode of microthermal poling setup. Thus, an efficient and inexpensive process developed can produce broadband and ultralow dispersion GRIN MLAs for imaging, display, and photovoltaic applications.

Optimizing the Effectiveness of Magnetic Lenses by utilizing the Electron Optical Design (EOD) Software

This paper introduces a computational analysis that discusses an approach for optimal synthesis in the design of magnetic lenses, specifically focusing on the analytical method. A widely employed approach for magnetic lens design involves utilizing an analysis optimization procedure, which makes use of the finite element method and is supported by Munro programs. In this study, this approach has been employed to explore magnetic lenses using the Electron Optical Design (EOD) software. The study offers insights into the role of the air gap in magnetic lens design, highlighting its importance in optimizing objective and projector properties. The analysis reveals that variations in the air gap (S) significantly influence the performance of magnetic lenses. Decreasing the air gap when it is set to (3) leads to substantial improvements in objective optical properties and focal length. Conversely, increasing the air gap when it is set to (12) enlarges the half-width of the axial magnetic field while reducing the maximum magnetic field value. These findings underscore the importance of carefully optimizing the air gap to achieve desired lens performance. The focal length is determined using this input data and coefficients of aberration (spherical and chromatic) of the objective. The study focuses on the influence of a crucial geometric parameter, specifically the air gap (S), on both objective and projector properties. Its importance stems from its capability to pinpoint the suitable geometry for magnetic lenses, thereby facilitating their efficient application.

Super-Resolution Imaging Enhancement through a 2D Scanning Galvanometer: Algorithm Formulation and Application in Aerial Optoelectronic Systems

As the fields of aviation and aerospace optics continue to evolve, there is an increasing demand for enhanced detection capabilities in equipment. Nonetheless, in applications where both optical and mechanical constraints are stringent, the continuous expansion of optical aperture and focal length is impractical. Given the existing technological landscape, employing super-resolution algorithms to enhance the imaging capability of optical systems is both practical and highly relevant. This study capitalizes on using a 2D scanning galvanometer in optical systems to acquire micro-displacement information. Initially, an imaging model for optical systems equipped with a 2D scanning galvanometer was established, and the displacement vectors for both forward and sweep image motions were defined. On this foundation, we incorporated micro-displacement information that can induce high-frequency aliasing. Subsequently, the motion paths of the galvanometer were planned and modeled. To align image sequences with micro-displacement correlations, the Lucas–Kanade (L-K) optical flow method was employed with multi-layer pyramid iteration. Then, super-resolution reconstruction was performed using kernel regression techniques. Ultimately, we tested the algorithm on an aeronautical optoelectronic pod to evaluate its impact on optical resolution and imaging quality. Compared with the original images, the 16-frame image demonstrated a 39% improvement in optical resolution under laboratory conditions. Moreover, the algorithm exhibited satisfactory performance under both nighttime and daytime conditions, as well as during aerial tests.

P‐171: Late‐News Poster: Ultra‐light Liquid Crystal Lenses for AR and VR

Head mounted display systems are widely available, yet there remain key technical challenges to increase their utility in the market. One such challenge is the conflict for human vision between accommodation and vergence when viewing virtual images. At worst this leads to an uncomfortable viewing experience and at best it limits the stereoscopic range. The transition from fixed focal length optics to systems that can be tuned to match the virtual content promises to change to this paradigm. In this paper we describe a tunable liquid crystal lens based on Fresnel optics that allows variable focus of the virtual image. Crucially this is the first time this type of lens has been made with ultra‐thin, light bioplastic films instead of glass, uniquely enabling attractive product form factors.

Design of a confocal dispersion objective lens based on the GRIN lens.

Spectral confocal technology utilizes the principle of dispersion to establish the precise coding relationship between spatial position and wavelength in the axial focal point. The axial dispersion produced by the dispersion lens will affect the measurement range and resolution of the system. Taking into account the above advantages of the GRIN lens, the dispersion objective lens of spectral confocal displacement sensor based on the radial GRIN lens in this paper is proposed. The imaging characteristics of the GRIN lens are analyzed. By deducing the refractive index distribution and optical properties of the radial GRIN lens, the optical focal length and axial dispersion models of the GRIN lens are established. Then, based on the optical focus and dispersion function of the GRIN lens, the calculation of refractive index distribution is completed by MATLAB. The simulation design of the GRIN dispersion objective lens is completed by ZEMAX. Finally, the optimization design of the GRIN dispersion objective lens is completed. The designed results indicate that the dispersion objective lens based on radial GRIN lens can achieve axial dispersion of 1215 µm in the wavelength range of 420 nm ∼ 620 nm as well as the linear correlation coefficient between wavelength and axial dispersion is 99.69%. The resolution of GRIN dispersion objective lens is about 6.075 nm. The focusing effect of the lens at each wavelength is good, and the measurement range and dispersion linearity of the lens are better than those of the same kind of traditional dispersion objective lens. Compared with the same kind of traditional dispersion objective lens, the dispersion objective lens based on GRIN lens has compact structure and small diameter. And the measurement range and resolution of the system are improved. So it is easier to realize precise measurement. The research results of this paper have certain guiding significance and reference value for the application of the GRIN lens in the spectral confocal system.

Multiplane holographic augmented reality head-up display with a real-virtual dual mode and large eyebox.

We propose a multiplane augmented reality (AR) head-up display (HUD) with a real-virtual dual mode based on holographic optical elements (HOEs). The picture generation unit (PGU) is only a single free-focus projector, and the optical combiner includes a HOE lens (HOEL) for long-distance virtual image display and a HOE diffuser (HOED) for in-plane real image display. A HOED with directional scattering characteristics in the real image mode can significantly increase the size of the eyebox (EB) without increasing the size of the HOE, and a HOEL with a flexible design for the optical focal length in the virtual image mode can be used to achieve a different depth of the AR display. The proposed AR HUD system, which has a compact structure and offers high light transmittance, high energy usage, a multiplane display, and a large EB, is expected to be widely used in the future.

P‐15.1: Large Area and Low Cost Fingerprint on Display Technology

We developed a large area and low cost optical fingerprint recognition product based on LTPS (low temperature poly silicon) process. A high efficient a‐Si pin sensor is introduced, the quantum efficiency under white light is 70% and the dark state current density is E‐10 A / mm2. The “one‐to‐one” and “one to multiple” structures of sensor and micro lens are compared, and the “one‐to‐one” optical path structure is systematically analyzed and evaluated. The optical path focal length is about 100 μm. The fingerprint recognition effect is significantly improved by adding a BM shading layer, and this scheme can effectively avoid the screen burning problem caused by the high luminous intensity of pixels in the fingerprint unlocking area.

Order-of-magnitude increase in laser-target coupling at near-relativistic intensities using compound parabolic concentrators

Achieving a high conversion efficiency into relativistic electrons is central to short-pulse laser application and fundamentally relies on creating interaction regions with intensities ≫10^{18}W/cm^{2}. Small focal length optics are typically employed to achieve this goal; however, this solution is impractical for large kJ-class systems that are constrained by facility geometry, debris concerns, and component costs. We fielded target-mounted compound parabolic concentrators to overcome these limitations and achieved nearly an order-of-magnitude increase to the conversion efficiency and more than tripled electron temperature compared to flat targets. Particle-in-cell simulations demonstrate that plasma confinement within the cone and formation of turbulent laser fields that develop from cone wall reflections are responsible for the improved laser-to-target coupling. These passive target components can be used to improve the coupling efficiency for all high-intensity short-pulse laser applications, particularly at large facilities with long focal length optics.

A Double Swath Configuration for Improving Throughput and Accuracy of Trait Estimate from UAV Images.

Multispectral observations from unmanned aerial vehicles (UAVs) are currently used for precision agriculture and crop phenotyping applications to monitor a series of traits allowing the characterization of the vegetation status. However, the limited autonomy of UAVs makes the completion of flights difficult when sampling large areas. Increasing the throughput of data acquisition while not degrading the ground sample distance (GSD) is, therefore, a critical issue to be solved. We propose here a new image acquisition configuration based on the combination of two focal length (f) optics: an optics with f = 4.2 mm is added to the standard f = 8 mm (SS: single swath) of the multispectral camera (DS: double swath, double of the standard one). Two flights were completed consecutively in 2018 over a maize field using the AIRPHEN multispectral camera at 52 m altitude. The DS flight plan was designed to get 80% overlap with the 4.2 mm optics, while the SS one was designed to get 80% overlap with the 8 mm optics. As a result, the time required to cover the same area is halved for the DS as compared to the SS. The georeferencing accuracy was improved for the DS configuration, particularly for the Z dimension due to the larger view angles available with the small focal length optics. Application to plant height estimates demonstrates that the DS configuration provides similar results as the SS one. However, for both the DS and SS configurations, degrading the quality level used to generate the 3D point cloud significantly decreases the plant height estimates.

Innovative techniques for the improvement of industrial noise sources identification by beamforming

Abstract An innovative technique based on beamforming is implemented, at the aim of detecting the distances from the observer and the relative positions among the noise sources themselves in multisource noise scenarios. By means of preliminary activities to assess the optical camera focal length and stereoscopic measurements followed by image processing, the geometric information in the source-microphone direction is retrieved, a parameter generally missed in classic beamforming applications. A corollary of the method consists of the possibility of obtaining also the distance among different noise sources which could be present in a multisource environment. A loss of precision is found when the effect of the high acoustic reflectivity ground interferes with the noise source.

Full-Range Line-Field Optical Coherence Tomography for High-Accuracy Measurements of Optical Lens

A full-range line-field Fourier-domain optical coherence tomography (LF-FDOCT) system with an accuracy at nanoscale was proposed for high-accuracy measurements of optical lens surface profile. The LF surface curve information of optical lens could be obtained in one measurement which does not need point-by-point scanning used in the traditional 1-D FDOCT system. The measurement accuracy of surface profile curve could be improved from micrometer scale to nanoscale by applying spectral center correction method (SCCM) to the complex spectral interferogram. The corrected five phase-shifting (CFPS) method was employed to eliminate the complex-conjugate artifacts and the polychromatic error. The numerical simulation and experiment results demonstrated that the CFPS method had a better complex-conjugate suppression performance than other phase-shifting methods. Optical lens (e.g., cylindrical lens and spherical lens) was measured by the homemade LF-FDOCT system. After the analysis of the surface profile, the radius and the optical focal length of the measured lens were precisely obtained in a noncontact and nondestructive way. Therefore, the developed LF-FDOCT system has provided a new tool for high-accuracy measurements of optical lens surface profile and its parameters.

Optical and Reflective Characteristics Measurement and Focal Length Calculation of a Hollow Tetrahedral Corner and a Solid Highly Retroreflective Cubes

Corner cubes are one of the most important optical tools used in new optical devices and optical LIDAR. This paper compares two different designs of the hollow and solid tetrahedral corner cubes and determines the relation between the Retroreflection index and the surface quality N and the surface flatness ∆N and its effect on the focal length of the hollow and solid corner cube.

Pancharatnam–Berry optical lenses

In this paper, we analyze a few aspects of Pancharatnam–Berry (PB) phase optical lenses. First, we provide theoretical formulas on how the optical efficiency, focal length, and point spread function depend on wavelength and validate them with numerical calculations based on Fresnel diffraction theory. Second, we perform numerical studies on how optical efficiency is affected by discretization of the PB phase. We find that phase discretization significantly lowers the optical efficiency for low f-number PB lenses.

Compact reflective imaging optics in hard X-ray region based on concave and convex mirrors.

We demonstrated that the combination of a hyperbolic convex and elliptical concave mirrors works as a compact reflective X-ray imaging system with a short optical focal length and large magnification factor. We performed an experiment to form a one-dimensional demagnified image with a demagnification factor of 321 within an approximately 2-m-long optical setup at an X-ray energy of 10 keV. The results showed that this imaging optics system is capable of providing a resolution of ~40 nm. From wavefront analysis, it was confirmed that the optics possessed a wide field-of-view with a significant reduction of comatic aberration.

The analysis of transparent dielectric elastomer actuators for lens

To substitute the carbon grease electrodes, stretchable and transparent electrodes are desirable for dielectric elastomer actuators (DEAs). Hydrogels containing electrolyte can work as ionic conductors to actuate DEAs. Compliant electrodes, as a promising supplement for DEAs, should conduct under high voltages without electrolysis. A fixed volume of fluid is constrained by a DE membrane, and adheres tightly to a DE membrane; They both could deform with external force. Applied voltage, pre-load, and moisture content of electrodes affect the actuation responds. We study the theoretically data based on transparent VHB material coupling hydrogel electrodes, and present the transparent DEA that drives focus lens system. Computational results show basic characteristics of the DEAs for lens. When a voltage is applied to the fabricated lens module, optical focal length changes with the voltage. The lens system could find application in portable devices, such as digital cameras and cell phones, etc.

Autofocusing optical-resolution photoacoustic endoscopy.

Photoacoustic (PA) endoscopy has the potential to diagnose early diseases in the gastrointestinal tract. For the first time, to our knowledge, we developed an autofocusing PA endoscope (AF-PAE) for the usually irregular gastrointestinal tract imaging to solve the deterioration of transverse resolution caused by the defocus scanning of the probe. The 9-mm-diameter AF-PAE probe integrated a 6-mm aspheric lens and 6-mm liquid lens to automatically adjust the optical focal length, and an unfocused ultrasonic transducer with a center frequency of 15MHz is coaxially set for detecting PA signals. With this probe, the AF-PAE achieved a focus-shifting range from approximately 2 to 10mm with high transverse resolution and image contrast in a 360° field of view. Phantom experiment and vasculature distribution of a resected rabbit rectum have been performed to demonstrate the imaging ability of the AF-PAE for potential clinical applications in colorectal vessel imaging and subsequent diagnosis.

Research on Optical System Focal Length Measurement Technology based on CCD Imaging Technology

Research on Optical System Focal Length Measurement Technology based on CCD Imaging Technology

Two-axis polydimethylsiloxane-based electromagnetic microelectromechanical system scanning mirror for optical coherence tomography.

Compact size and fast imaging abilities are key requirements for the clinical implementation of an optical coherence tomography (OCT) system. Among the various small-sized technology, a microelectromechanical system (MEMS) scanning mirror is widely used in a miniaturized OCT system. However, the complexities of conventional MEMS fabrication processes and relatively high costs have restricted fast clinical translation and commercialization of the OCT systems. To resolve these problems, we developed a two-axis polydimethylsiloxane (PDMS)-based MEMS (2A-PDMS-MEMS) scanning mirror through simple processes with low costs. It had a small size of 15×15×15??mm3, was fast, and had a wide scanning range at a low voltage. The AC/DC responses were measured to evaluate the performance of the 2A-PDMS-MEMS scanning mirror. The maximum scanning angles were measured as ±16.6??deg and ±11.6??deg along the X and Y axes, respectively, and the corresponding field of view was 29.8??mm×20.5??mm with an optical focal length of 50 mm. The resonance frequencies were 82 and 57 Hz along the X and Y axes, respectively. Finally, in vivo B-scan and volumetric OCT images of human fingertips and palms were successfully acquired using the developed SD-OCT system based on the 2A-PDMS-MEMS scanning mirror.