Telecentric Optical System Research Articles

Broadband achromatic thermal metalens with a wide field of view based on wafer-level monolithic processes

We present a monolithic metalens free of chromatic aberration over the 8–12 μm wavelength range for thermal imaging. The metalens consists of nano-donut-pillars for dispersion engineering. The proposed metalens design is based on a telecentric optical system, which effectively eliminates off-focus distortion and aberration, enhancing overall imaging quality. Offering a 90° field of view, the metalens ensures uniform focal spot sizes within a 45° field angle across the working wavelength. This enables the capture of high-quality thermal images with sharp images and minimal distortion. With a diameter of 5.75 mm, the metalens is suitable for integration into commercial thermal imaging cameras. The nano-donut-pillar structure of the metalens allows for relatively straightforward mass production, involving i-line stepper lithography and silicon deep etching processes.

Evolved design for telecentric optical systems based on particle swarm optimization and semi-supervised learning

Finite-distance systems are used extensively in the field of machine vision, and engineers need to rely on experience and mathematical basis to design such systems. In this paper, an evolved design method for finite-distance optical systems (telecentric systems) based on particle swarm optimization and semi-supervised learning is proposed. The method establishes a function value based on the Seidel aberration equation and innovatively introduces the Head-To-Tail method to generate the high-quality initial dataset in bulk. The feasibility of the method is verified with an example, and the user only needs to determine the magnification, working distance and NA to obtain a telecentric optical system directly. In this way, the time cost of searching for the initial structure and continuous trying is greatly reduced, and the design threshold is lowered. Meanwhile, it has a positive effect on shortening the design cycle of the whole lens and leaving a surplus for processing.

Optical system design of double-sided telecentric microscope with high numerical aperture and long working distance.

The working distance of the high numerical aperture visible video microscope is extremely short, which greatly limits its application scenarios. To solve this problem, this paper proposes an unobstructed design method of double-sided telecentric microscope with high numerical aperture and long working distance. First, aiming at the obstruction problem of the image-side telecentric catadioptric microscope objective, the structure of the catadioptric optical system is improved. Then, the aspheric design method based on the best aberration compensation is analyzed theoretically to better correct the primary aberration of the high-numerical aperture microscope objective. Finally, a double-sided telecentric microscope optical system with a numerical aperture (NA) of 0.8 and a working distance of 10.0 mm was designed, which is composed of a spherical reflector, a beam splitter plate, a collimating lens group, and an image-side telecentric eyepiece optical system. The design results show that the imaging resolution of this high numerical aperture video microscope is as high as 0.42 µm, and the microscope has a magnification of about 220× for the image with 1080P (1920 × 1080 pixels) resolution. This double-sided telecentric microscope has the advantages of a large field of view, compact structure, good stray light suppression ability, and manufacturability, and has high practical value in the field of high-precision measurement and detection.

Gear Profile Measurement Based on Thin Line Structured Light

In order to achieve the high precision 3D measurement of gear tooth profile, a telecentric optical measurement system with large FOV (field of view), WD (working distance) and measuring range was proposed, the system was applied to the gear tooth profile measurement experiment and obtained a good effect. Firstly, the composition and the principle of the system were introduced. The lights of projection and imaging with an angle of 45° from the normal line of the measured surface can reduce the requirement of DOF (depth of field) of the imaging objective lens. Secondly, in combine with the application background of small modulus gear tooth profile measurement, the magnification, NA (numerical aperture) and other optical parameters were calculated, the optical system was constructed and the system performance parameters are listed. Then, the calibration model of the system was demonstrated and the calibrations of depth pixel resolution and horizontal pixel resolution were completed through experiments. Finally, an involute artifact with a modulus of 2.9992mm and a total tooth profile deviation of 1.1μm was measured. The results show that the deviation of the total tooth profile measured is about 2μm, which is consistent with the calibration curve of the involute artifact.

Double-sided telecentric zoom optical system using adaptive liquid lenses.

In this paper, the adaptive liquid (AL) lenses are introduced into the double-sided telecentric zoom system, which could greatly decrease the mechanical motion group compared with the traditional zoom system, and only one movable aperture stop (STO) is retained. Firstly, this paper derived the Gaussian brackets used in this system, and we found the appropriate screening method to get the suitable initial structure parameters from the solution space. Then we used the lens module design method to create the initial system. Finally, we used CODEV to further optimize the system, and we got an excellent design result, which controlled the telecentricity of both sides within 0.1°, the distortion was controlled within 0.5%, and the MTF of each zoom configuration above 0.3. This optical system has high application potential and value in the field of precision machine vision. The design method proposed in this article can effectively solve the problem that the zoom system using adaptive liquid lenses lacks the initial structure.

Method of initial design of a two-element double-sided telecentric optical system.

An algebraic method for finding fundamental parameters of a starting design of a two-element double-sided telecentric lens is introduced in this work. The telecentric lens is formed by two objectives composed of an afocal meniscus lens followed by a cemented doublet. It is used the third-order aberration theory to find the fundamental parameters of the starting configuration of a given optical system. The method gives results which make possible to obtain a good initial design of such a telecentric lens for further optimization using optical design software. The proposed method is presented on an example of finding initial design parameters of the double-sided telecentric lens.

Design of a Concentric Multi-Scale Zoom Optical System Based on Wide Object Distance and High-Precision Imaging.

To effectively balance the trade-off between a large field of view (FOV) and high resolution of an optical system, as well as to solve the problem of image stitching misalignment after focusing, firstly, this paper conducts a theoretical analysis of the design principle of the concentric multi-scale optical system and the causes of image stitching misalignment after focusing. Secondly, the design idea of using a combination structure of a two-layer front concentric imaging group and an image-space telecentric relay imaging array and then a joint full-motion zoom relay imaging system is proposed. Finally, an image-space telecentric two-step zoom concentric multi-scale optical system with a 7 × 7 relay imaging array is designed. The FOV of this optical system is 60° × 45°; the focal lengths are 50 mm and 100 mm for the center channel and 50 mm for the other channels. This concentric multi-scale zoom system has the advantages of both high-precision imaging stitching with a wide object distance and high-resolution imaging, which makes up for the defects of the conventional concentric multi-scale optical system, making it a promising application in the fields of aviation and security.

The NAROO digitization center

The New Astrometric Reduction of Old Observations (NAROO) center can be found at the Paris Observatory in Meudon, and it is dedicated to the measurement of astrophotographic plates and the analysis of old observations. The NAROO digitizer consists of a granite-based Newport-Microcontrol open-frame air-bearing XY positioning table, a scientific sCMOS camera, and a telecentric optical system. The plate holder assembly is suited for mounting glass plates up to 350 mm squared. The machine positioning stability is better than 15 nm, and its repeatability is better than 40 nm. With real photographic plate data, we were able to produce measurements with an accuracy better than 65 nm. The renewed interest about photographic plates concerns the expansion of the database of transient objects evolving in time, since digitization now makes it possible to measure images with a high level of accuracy and to identify all the available objects. The information extracted from such materials can be of an astrometric, photometric, and spectroscopic nature, when not purely imaging, with consequences in planetology, near-Earth asteroid risk assessment, astrophysical phenomena, and general relativity, to mention but a few. Through our scientific program in the Gaia era, we detail examples of current and upcoming uses for the community. We invite researchers to use our facilities and digitize their collection by answering our call for proposals.

A method of fine size measurement for telecentricity-based error compensation

Focusing on the stable magnification, near zero distortion, and wide field of depth (DoF), the telecentric optical system is well suited for size measurements with a large range of working distances. However, suffering from the telecentricity-based error (TBE), the size measurement is connected with the working distances and imaging position of the image sensor, even within the DoF. Therefore, a model of TBE compensation is established, inspired by the radial distortion model in the camera calibration. With the correction of radial distortion coefficients for different working distances, the TBE is evidently improved. The feasibility of the proposed method is verified both in the theory and experiment. Our results show that the uncertainty of size measurement at different working distances of the DoF is improved obviously after the TBE compensation, which is attractive for fine size measurements in industry.

Design of telecentric relay optical system with broadband and real entrance pupil

Design of telecentric relay optical system with broadband and real entrance pupil

POLARIMETRIC CALIBRATION OF THE SPACEBORNE DIRECTIONAL POLARIMETRIC CAMERA INSTALLED ON THE GF-5 SATELLITE

Abstract. The Spaceborne Directional Polarimetric Camera (SDPC) is dedicated to obtain an accurate information of clouds and microphysical properties of aerosol particles via multi-angle, multi-spectral and multi-polarization observations. It images the Earth with 110° field of view (FOV) in 3 polarimetric spectral bands and 5 non-polarimetric spectral bands from visible to near infrared. Due to its wide FOV telecentric optical system and multi-channels, polarization sensitivity of optical components (PSOC) and non-uniform response of pixels (NURP) are the main uncertainty factors of polarimetric calibration.In this paper, a polarimetric calibration model of SDPC has been constructed for increasing the measurement accuracy. Combined an integrating sphere with a polarization generator as source, PSOC can be measured in high accuracy by using the Fourier series analysis method which reduces the impact form the alignment error of the generator. The sectional viewing field measurement method is used to acquire NURP while the large aperture integrating sphere served as reference source. Subsequently, the data of NURP have been corrected by the relative transmittance of high frequency and low frequency respectively for polarized channels. The result of validation experiment shows that the polarization measurement errors in 0°, 15°, 30°, and 45° half field of view (HFOV) are all less than 0.5% when the degree of linear polarization of reference source is larger than 0.1.

空间红外大口径折射式低温镜头设计与验证

Telecentric and cryogenic optical system is a good solution to space-based IR sensor with wide field, sensitivity and determination of accurate orientation. A refractive telecentric optical system was designed with squared field of view in 8 degrees, entrance pupil of 265 millimeters and operating at 200 K. The aperture of the lens was 280 millimeters. By multilevel spring holders,the opto-mechanism got a available tradeoff between enough stiffness at room temperature and stress-free at 200 K, accordingly prevents thermal stress on lens and heat leakage from room temperature supports to cryogenic lens. After lenses alignment, vibration test and image test at operating temperature were performed. The ensquared energy reached 75% on axis and 72% off-axis respectively.

Is the sky the limit?

We discuss the use of measurements of the solar granulation contrast as a measure of optical quality. We demonstrate that for data recorded with a telescope that uses adaptive optics and/or post-processing to compensate for many low- and high-order aberrations, the RMS granulation contrast is directly proportional to the Strehl ratio calculated from the residual (small-scale) wavefront error (static and/or from seeing). We demonstrate that the wings of the high-order compensated point spread function for the Swedish 1-m Solar Telescope (SST) are likely to extend to a radius of not more than about 2″, which is consistent with earlier conclusions drawn from stray-light compensation of sunspot images. We report on simultaneous measurements of seeing and solar granulation contrast averaged over 2 s time intervals at several wavelengths from 525 nm to 853.6 nm on the red-beam (CRISP beam) and wavelengths from 395 nm to 484 nm on the blue-beam (CHROMIS beam). These data were recorded with the SST, which has been revamped with an 85-electrode adaptive mirror and a new tip-tilt mirror, both of which were polished to exceptionally high optical quality. Compared to similar data obtained with the previous 37-electrode adaptive mirror in 2009 and 2011, there is a significant improvement in image contrast. The highest 2 s average image contrasts measured in April 2015 through 0.3−0.9 nm interference filters at 525 nm, 557 nm, 630 nm, and 853.5 nm with compensation only for the diffraction limited point spread function of SST are 11.8%, 11.8%, 10.2%, and 7.2%, respectively. Similarly, the highest 2 s contrasts measured at 395 nm, 400 nm, and 484 nm in May 2016 through 0.37−1.3 nm filters are 16%, 16%, and 12.5%, respectively. The granulation contrast observed with SST compares favorably to measured values with SOT on Hinode and with Sunrise as well as major ground-based solar telescopes. Simultaneously with the above wideband red-beam data, we also recorded narrowband continuum images with the CRISP imaging spectropolarimeter. We find that contrasts measured with CRISP are entirely consistent with the corresponding wideband contrasts, demonstrating that any additional image degradation by the CRISP etalons and telecentric optical system is marginal or even insignificant. Finally, we discuss the origin of the 48 nm RMS wavefront error needed to bring consistency between the measured granulation contrast and that obtained from 3D simulations of convection.

Optimization design and realization of a keratometer

To realize a simplified keratometer, we proposed a design proposal based on corneal reflex imaging. Six pointolites which arranged in a regular hexagon were used to emit parallel light to the surface of a cornea and were reflected by the cornea. Then the image was captured by a telecentric optical system in the object space to a CMOS camera. In order to obtain the corneal curvature, the distance between two pointolites located on the regular hexagonal diagonal in the corneal reflection images were calculated by using the center of gravity algorithm. The imaging quality, measuring range and measuring precision of the system were theoretically analyzed, and the Ziess's model eye and human eyes were used to conduct experiments to verify the theoretical analysis results. The experiment results have shown that the precision of the measurement error is ±0.02 mm and the measurement range is from 5.5 mm to 11.6 mm (30 m-1 to 60 m-1 in diopter of cornea). The research will provide technical supports for the design and optimization of automatic keratometer.

Ultra-low-distortion optical system design based on tolerance sensitivity optimization

This study theoretically analyzed the relationship between the primary aberrations and tolerances to meet the distortion requirements of an ultra-low-distortion optical system. Theoretical analysis shows that the distortion sensitivities of the optical system are related to the primary aberrations of the optical surfaces. Consequently, a method of optimizing the primary aberrations on the surface of the optical system to reduce the distortion sensitivities of sensitive tolerances is proposed. A distortion sensitivity analysis of manufacturing and assembly tolerance was carried out for the designed ultra-low-distortion and telecentric optical system. The distortion sensitivities of the sensitive tolerances were reduced by optimizing the primary aberrations on the surface of the optical system. A Monte Carlo analysis of the optimized ultra-low-distortion optical system showed that the proposed method has a remarkable effect on the distortion sensitivity optimization of the tolerances.

Depth reconstruction with coaxial multi-wavelength aperture telecentric optical system.

An optical system to measure depth information is proposed here. The proposed optical system has double coaxial multi-wavelength apertures, which makes it possible to simultaneously take an orthogonal projection image and a perspective projection image with these two images separated by wavelengths. The three-dimensional physical position of an object can be derived with the ratio of the radial distances of these separated images with the centers located on the optical axis. Validation of the system by a ray-tracing simulation and an experiment shows that the proposed optical system can be used for depth reconstruction.

Miniaturized Fourier-plane fiber scanner for OCT endoscopy

A forward-looking endoscopic optical coherence tomography (OCT) probe featuring a Fourier-plane fiber scanner is designed, manufactured and characterized. In contrast to common image-plane fiber scanners, the Fourier-plane scanner is a telecentric arrangement that eliminates vignetting and spatial resolution variations across the image plane. To scan the OCT beam in a spiral pattern, a tubular piezoelectric actuator is used to resonate an optical fiber bearing a collimating GRIN lens at its tip. The free-end of the GRIN lens sits at the back focal plane of an objective lens, such that its rotation replicates the beam angles in the collimated region of a classical telecentric 4f optical system. Such an optical arrangement inherently has a low numerical aperture combined with a relatively large field-of-view, rendering it particularly useful for endoscopic OCT imaging. Furthermore, the optical train of the Fourier-plane scanner is shorter than that of a comparable image-plane scanner by one focal length of the objective lens, significantly shortening the final arrangement. As a result, enclosed within a 3D printed housing of 2.5 mm outer diameter and 15 mm total length, the developed probe is the most compact forward-looking endoscopic OCT imager to date. Due to its compact form factor and compatibility with real-time OCT imaging, the developed probe is also ideal for use in the working channel of flexible endoscopes as a potential optical biopsy tool.

Hyperspectral imaging acousto-optic system with spatial filtering for optical phase visualization.

We report a method for phase visualization in the images of transparent specimens using analog image processing in incoherent light. The experimental technique is based on adaptive bandpass spatial filtering with an amplitude mask matched with an acousto-optic tunable filter in a telecentric optical system. We demonstrate the processing of microscopic images of unstained and stained histological sections of human thyroid tumor with improved contrast.

Proposal of a new optical system for prism-based surface-plasmon-resonance imaging

We propose a new prism-based surface-plasmon-resonance microscope (PB-SPRM) with a diffraction grating. Unlike the conventional PB-SPRM, the proposed one is free from distortion and blur, which were introduced because of the inclination of an object plane against one normal to the optical axis. To solve this problem, we inserted a reflection-type diffraction grating into the conventional PB-SPRM between the sample and the objective lens. Also, we placed an aperture on the back focal plane of the objective lens so that an object-side telecentric (OST) optical system was formed. By this optical configuration, a wide field of view (FOV) and a high frame rate were also obtained. We describe the theoretical background for designing the new PB-SPRM. In order to evaluate the performance of the proposed system, we show some numerical simulation results in detail. Mixing water and an ethanol–water solution along a micro-flow channel at a rate of 30 frames/s is also shown.

Calculation of overlapping pixels in focal plane based on optical butting

In order to eliminate the imaging gap of focal plane based on optical butting, an error analysis-based algorithm of overlapping pixels was proposed. Firstly, an imaging model for focal plane based on optical butting is established according to the imaging principle of camera. Then, the reason causing imaging gaps is analyzed which combined with telecentric and non-telecentric optical system. Combined with the decrease of MTF in the vignetting distortion caused by the reflector, the formula for computing the numbers of overlapping pixels between adjacent CCDs is obtained. Finally, an example is given. Experimental results show that the proposed algorithm can eliminate the imaging gap.