The iconic photos of NASA's first space missions and Moon landings from the 1960s onwards were captured with ZEISS camera lenses mounted on Hasselblad cameras. They adorned the covers of many newspapers and magazines and appeared in color for the first time ever, as special issues. Meanwhile, NASA's scientists were evaluating the scientific images: the photogrammetric images taken while in orbit were combined to form a detailed lunar map, the panorama pans on the lunar surface were turned into a topographic map of the landing area, and the pictures with broadband achromatized UV lenses gave insights into the overall soil conditions on the Moon and the Earth. The talk will provide an overview of all the camera lenses developed by ZEISS for NASA. It will look at their technical specifications, describe the development work done for these lenses, and delve into the history of the partnership between NASA, Hasselblad, and ZEISS. Just like space travel, the launch of mainframe computers at that time also spurred on optical design. Other ZEISS products for photography, cinematography, aerial photogrammetry, and optical lithography also benefited from these developments.

The higher flexibility of freeforms has opened the possibility to find better solutions than classical surfaces many optical problems, especially those whose specifications (either optical or geometrical) are far from rotational symmetry. For instance, short through distance multimedia projectors cannot be placed in front of the center of the projected image without blocking the spectators’ view, and this requires the projection to be done from one side. Offset rotational symmetric solutions are suboptimal, and a freeform projector can improve the image quality on the target area with the same number of surfaces or can match the quality with fewer optical surfaces 1. Similarly, many head-worn displays are located close to the eyes of the user to make the headset sleeker. In this case, some parts of the physical display are used at very high emitting angles and rotational symmetric cannot provide optimal solutions for this configuration. In nonimaging applications, low-beam headlamps of cars also need to produce an asymmetric pattern on the road to avoid blinding the incoming drivers. Freeforms permit to solve this design problem efficiently, and match aesthetic constraints. The continuous progress in the technology to produce and test freeforms, as occurred in the past with rotational aspherics, is pushing optical designers to consider more and more the use of freeforms in their designs. However, the also higher complexity of these surfaces introduces multiple challenges in their design since traditional design methods have been focused in rotational optics. These challenges go from finding the best mathematical description of the optical surfaces to the design algorithms themselves. We’ll review the main design techniques proposed to design freeforms and illustrating its use in specific examples for several applications.

This Plenary Presentation, “Lens design through the ages,” was recorded for the SPIE Optical Systems Design 2021 Digital Forum.

The Cubesat-compatible Morera optical instrument is a very compact, low F# LWIR camera designed to provide high resolution images at farm level to estimate evapotranspiration data and provide personalized irrigation recommendations directly to final users using a mobile device. A SW-defined system will use Big Data to combine all relevant information (AEMET, Copernicus, S-SEBI algorithms) to optimize water resources. Catadioptric systems are extensively used in very compact systems. However, the more compact the system the more difficult it is to implement baffles to shield any light not coming from the field of view. The search for a compact configuration that meets straylight performance is described in this paper. The selective spectral bandpass filter requires angles of incidence below 0.5°, adding telecentricity to the key requirements. Finally, photogrammetry imposes the need of low distortion, which can be controlled by freeforms while achieving the goal on angle of incidence.

A quasi-aplanatic two-lens design is proposed to correct astigmatism in Ritchey-Chr´etien (RC) telescopes at different spectral bands. This pair of lenses is designed analytically so that it can be used in existing RC telescopes without any modification of the mirror’s shapes while introducing only a small amount of coma. The field of view (FoV) is consequently increased due to the astigmatism being corrected by the two lenses and due to the final image being flattened. Astigmatism can be corrected individually for each spectral band by merely changing the distance between the two lenses.

LIDAX is developing the Laser Launch Telescope for the Gran Telescopio de Canarias (GTC) located at the Roque de los Muchachos Observatory on the island of La Palma, Canary Islands, Spain. This unique beam expander will be part of the GTC Adaptive Optics System (GTCAO) facility, managed by the IAC (Instituto de Astrofísica de Canarias), and will allow the creation of laser guide stars to feed the Adaptive Optics System of the GTC, removing the atmospheric turbulence to obtain high quality images of the stellar objects observed. This paper describes the opto-mechanical design and shows how the design- analysis process is performed to meet the performance requirements, explaining the STOP analysis carried out together with INTA-LINES. Such a process includes the initial mechanical design, the elaboration of both thermal and FEM models to analyze the behavior in terms of temperatures distribution, stiffness, and thermo-elastic effects, and of course the of lenses’ displacements and deformations under the different load cases and boundary conditions, which are transformed into Zernike Polynomials to evaluate the WFE of the Telescope, which allows to obtain, closing the loop, the best optical performance.

Freeform surface is one of the main advanced in lens design over the last two decades. These advances motivated by the new fabrication process and new equipment are now closed to maturity. Recently we start finding on the market more and more camera phone that claims to use freeform lenses. None of these suppliers explained how and why freeform lenses are required in details. In this presentation, we will dive into this to found answers. At the time of writing this abstract, we can identify three camera phones that use freeform lenses. The first one is the Huawei Mate 40 Pro+, which seems to be the first worldwide freeform lens used in a cell phone. Huawei uses the freeform to compensate distortion (they call it ‘anti-distortion’). The lens is an f/1.8 for a 20MP sensor. A second one is the OnePlus 9 Pro, which uses an f/2.2, 7 plastics for a 50MP as an ultra-wide camera. Finally, Oppo Find X3 Pro is also using freeform lens (f/2.2) on an IMX766 50MP (Sony sensor). From all the publicity from those camera-phones, we can found that the freeform used to compensate distortion in the corner of the image. Somehow, we can ask if it is a freeform lens or not, is it only marketing? We will add to this discussion some laboratory results from the Huawei freeform lens as well as image taking with the various cell phone.

Compared to the rotationally symmetric systems, the surface-decomposed aberrations of the symmetry-free system is harder for analysis, due to the invalidity of the conventional paraxial reference. To solve this problem, a novel higher-order aberration calculation method for symmetry-free systems is proposed based on the mixed ray-tracing method, which is proved as a good approximation of the full-order transverse aberration for generalized systems. Furthermore, the method is also applicable for intrinsic/induced aberration calculation, as well as the surface additive Zernike coefficient fitting. With various potential implementations, the method is considered a convenient and powerful tool for aberration analysis of off-axis systems.

Laser cutters are currently finding their way from industrial environments to home-use applications, driving the development towards low-cost and compact systems. We therefore target the design of a single beam-shaping lens for use in laser cutting applications, enabling the miniaturization of the laser scanning head while pursuing optimal cutting performance. Particularly, we target the design of a beam shaping lens for use with a high-power 450 nm laser diode (5.0 Watt, 14° x 46° beam divergence), enabling to transform the divergent elliptical laser diode beam into a circular focused spot, while maximizing the depth-of-focus. We cover the complete development chain, starting from the characterization and modelling of the laser diode, to the optical design, optimization and tolerancing of the focusing lens, and the manufacturing and demonstration of the laser cutting system. The optimized beam-shaping lens features a circular focused spot diameter <100 μm over a depth-of-focus of 4.8 mm. In contrast to the current laser diode circularization and focusing designs, comprising a combination of cylindrical and plano-convex lenses, we only use a single aspheric biconic lens, giving rise to a more compact design. A tolerance analysis was included on both the optical and mechanical parameters, enabling to evaluate the design for manufacturing. Following, the novel beam-shaping lens was manufactured using ultraprecision diamond turning, and afterwards characterized using a coordinate measurement machine. Finally, the performance is evaluated in a proof-of-concept demonstrator, validating the circular illumination beam and improved cutting performance. We successfully demonstrated the operation of our novel beam-shaping lens, featuring the beam circularization and focusing using a single lens, optimized for use in compact laser cutting devices. This novel lens design paves the way towards a further miniaturization of desktop laser cutters, while showing an excellent laser cutting performance, including an improved cutting resolution and depth-of-focus, enabling a wider range of materials and extended material thicknesses.

Many astronomical studies require obtaining detailed information about the spectrum of a celestial object, for which various types of spectrometers are effectively used. In the case of extended fields, it becomes necessary to optimally match the field image of an objective and the entrance slit of a spectrometer. For that, an optical scanning system is used. However, it becomes impossible to capture different events in real time this way. For the simultaneous capturing of a wide field, it is efficient to use an integral field unit (IFU). IFU is the optical system that allows slicing and transforming of a field into a set of long slits that are fed to a spectrometer. The design of the IFU optical system for the solar telescope-coronagraph (LST-3) is presented. LST-3 is the telescope with the main mirror of 3m, and it should operate in the wide spectral range, 0.4-1.6 μm. The telescope's objective field of rectangular shape, (1.1 x 2.2) mm, is transformed in two steps: slicing the image and reorganization of sub-images into a set of 8 long slits, (0.018 x 18.6) mm. The reorganization is performed using the system of two flat mirrors. The mirrors are rotated around two axes, which entails the accumulating error of a sub-image position in the image plane. For studying the offset error in an IFU, a simulation was performed. The expression of the error function makes it possible to consider it when using an IFU, while maintaining high spatial resolution and co-directionality of sub-image apertures in the slit plane. As a result of the work, it was confirmed that the use of two flat mirrors for geometric image transformation is possible when designing an IFU.

Lithium aluminoborate glass optically activated with the lanthanide ion dysprosium is investigated for its potential as luminescent light guide. For this, ray-tracing simulations are performed on the basis of transmission, photoluminescence, and quantum efficiency measurements. The luminous flux at the end of the light guide depends significantly on its length as well as on the roughness of the output face. The best results are obtained for a light guide length of approximately 70-80 mm with the side faces of the light guide coated with a 100 % reflecting mirror and a rough output face with Lambertian scattering characteristic. The input face is coated with a half-transmitting mirror which is transmissive for the excitation wavelength of 388 nm but reflective for the emission bands in the visible spectral range. For this light guide, a luminance of approximately 20 cd/mm2 is achieved for an excitation power density of 1W/mm². The geometry of the light guide (cuboid / cylinder) has only a slight effect on the maximum luminance value.

Infrared cameras could serve automotive applications by delivering breakthrough perception systems for both in-cabin passengers monitoring and car surrounding. However, low-cost and high-throughput manufacturing methods are essential to sustain the growth in thermal imaging markets for automotive applications, and for other close-to-consumer applications which have a fast growth potential. Fast low cost infrared lenses suitable for microbolometers are currently already sold by companies like Umicore, Lightpath, FLIR… They are either made of a single inverse meniscus Chalcogenide glass or of two Silicon optics. In this paper, we explore hybrid systems with a large field of view around 40° combining Chalcogenide and Silicon in order to take advantage of both materials. Both are compatible with wafer-level process. Silicon optics can be manufactured by photolithography process and are expected to be more cost-effective than Chalcogenide ones. However they are constrained in shape and sag height. On the other hand, Chalcogenide optics can be collectively molded and could have more free shapes. They are thus more suitable to reach high-demanding performance. So hybrid designs could be seen as a compromise between cost and performance. In this paper, we show that fast lenses with diameter constraints to few millimeters to make affordable wafer-level process lead to small size detectors. As a consequence, the pixel pitch reduction of microbolometers is a key point to maintain a good resolution. Finally, strategies to improve the production yield of hybrid lenses are explored.

Hybrid diffractive lenses are an enabling technology that allows the shaping and control of wavefronts by precisely controlled zone structures. In particular, they are extremely useful in the medium and long wave infrared spectral regions for performing colour correction, where the lens element count can be reduced (replacing two heavy and expensive infrared materials with a single element). Yet these surface structures are often modelled in a way that treats the surface purely as an attached phase function and not an actual physical structure. This makes some results dubious and provides a substantial difficulty in assessing and specifying tolerances. In the current presentation, we move to a more physical model based on the ideas of zone decomposition.

Controlling an accuracy of fabricating computer-generated holograms (CGH) is actual task. Such holograms are usually used for generating reference wavefront for interferometric testing of aspherical surfaces. The influence of external factors on the positioning systems of the writing system occurs during fabricating the holograms and leads to microstructure errors that affect the quality of the wavefront formed by such elements. Fabrication errors of CGH affect the accuracy and reliability of interferometric measurements. Controlling these errors allows determining the quality of the manufactured element and evaluating the accuracy of the wavefront which it forms. This paper presents the experimental results of using CGH error testing methods for laser writing systems that operate in a polar or cartesian coordinate system. These methods are based on writing of series of embedded small marks with gratings having 2-5 μm period and following measurement of light intensities in curtain diffraction orders. These marks consist of two parts, one of which is quickly formed before the fabrication of CGH and the second one during writing the pattern of the main CGH. The shift between the first and second segments of the mark makes it possible to determine the CGH writing errors caused by external influences on the positioning system for both circular and X-Y laser writing systems. To determine writing errors can be use simple optical diffractometer.

The Mid-infrared ELT Imager and Spectrograph (METIS) is one of the three first-generation instruments on the Extremely Large Telescope (ELT). It will provide 20 instrument configurations for direct and high-contrast imaging, medium and high resolution spectroscopy in the wavelength range of 3 − 13μ. The straylight will affect the image contrast and objects recognition thus influencing the final instrument performance. For this reason it should be taken into account and accurately modeled at the design stage. In the present study we consider straylight from the following sources: surface roughness and defects of the optical surfaces, multiple reflections and diffraction, which will all influence the instrument performance. We estimate their influence using a bottom-up modelling approach at the system level and derive the requirements for some critical parameters. Using empirical and analytical models and performing non-sequential raytracing we demonstrate that the target straylight level can be reached in the current design with reasonable specifications on the optical components.

A new process for prototype manufacturing of integrated optical components was investigated. Sodium ions near the surface of a glass wafer are exchanged with silver ions, which creates a layer of increased refractive index. Subsequently, parts of the glass surface are ablated using a femtosecond laser. The resulting ridges determine the final optical waveguide structure. However, manufacturing-related roughness leads to high optical losses. To reduce these losses and to optimize the index profile, a second ion exchange with sodium ions is performed. These ions are introduced into the glass from all three ridge surfaces, causing the silver ions to migrate towards the ridge center. This results in a gradient index waveguide. We created a numerical model, to simulate the ion exchanges. Experiments were conducted, to determine the parameters for the ion exchange and the laser ablation. Based on the results, a process window was defined for each step, thus enabling the manufacturing of integrated optical components.

Space-based telescopes are important tools in astronomy and Earth observations. They enable observation in spectral ranges outside of the atmospheric window, e.g. below 300 nm. One of the ways to decrease the mass of space telescopes is to use diffractive optical elements. They have unique capabilities when it comes to aberration corrections. By combining refractive and diffractive components it is possible to obtain a well-corrected system with fewer optical elements compared to purely refractive systems. In this paper we present an optical design of a hybrid refractive-diffractive telescope working in the 200 nm – 300 nm spectral range with improved performance and decreased mass compared to refractive system. The telescope has a large field of view 10°×10°, enabling observations of many objects simultaneously, focal length of 150 mm and f-number equal to F/1.67. We compare the performance of two systems optimized using different merit functions. In the first case the goal was to minimize spot size, in the other a widened point spread function was obtained in order to avoid undersampling. The results of tolerance analysis prove that the satisfactory imaging quality may be obtained with moderate tolerances. Moreover, the influence of the antireflective coating on the efficiency of the diffractive lens is discussed. Performed simulations show that the antireflective coating deposited on the diffractive structure gives an increase of the efficiency at the expected level.

The Thai National Telescope (TNT) is the largest telescope in Southeast Asia with a primary mirror of 2.3-meter diameter located at altitude 2457 meters, Chiang Mai, Thailand. This telescope is equipped with two photometric cameras and a medium resolution spectrometer. The maximum instantaneous field of view (FOV) is circular of diameter equal to 15 arcminutes, provided by the camera called the “TNT Focal Reducer”. In this paper, we present the design and performance estimation of a prime focus camera for the TNT with the objective to reach a FOV equal to 1 degree. The TNT prime focus camera is specified to operate over the spectral domain 0.400-0.850 μm for spectral bands g’, r’ and i’ of the Sloan Digital Sky Survey (SDSS) photometric system. This camera is designed to reach a resolution better than 2 arcseconds, slightly above the seeing limit in median atmospheric conditions. The prime focus camera is planned to be installed at the secondary mirror (M2) and mounted on a hexapod manufactured by Physik Instrumente (PI) company. This hexapod will provide a positioning accuracy of ±2.5 μm of 3-axis translation. The orientation will be adjusted with an accuracy equal to ±1.03 arcseconds of rotation. The prime focus camera comprises five lenses made of S-FPL53, N-BAK2, SF1, BAF50 and SK3. This camera includes one aspherical concave surface of conic constant equal to -0.076 and the other surfaces are spherical. We have dedicated tolerance analysis to calculate the effects of manufacturing errors, alignment errors and stability on the operational performance. The results show that the operational angular resolutions over the full field of view should be better than 1.61 arcseconds. The results of the stray light analysis show that the ghost irradiance should be five orders of magnitude smaller than the image irradiance, assuming that the second lens of the camera and the detector window have an Anti-Reflective coating of reflectivity lower than 1%.

Ariel is ESA M4 mission to survey exoplanet atmospheres through transit spectroscopy in the 0.5-7.8 μm waveband. Launch is scheduled for 2029. Ariel payload consists of a 1-m class, all-aluminum telescope operating below 50 K. Telescope mirrors will employ a protected silver coating to improve reflectivity and to prevent degradation. An initial estimation of the overall throughput achievable by the telescope for the entire scientific duration of the mission is presented here. The starting point is the reflectivity of the coated mirrors as measured on samples, and throughput losses caused by surface roughness, particulate and molecular contamination, and cosmetic defects.

As a large variety of intraocular lens (IOL) designs is commercially available in a growing market, selecting the best IOL for each patient has become a crucial task for a positive surgical outcome. Information about the measured or estimated performance of commercial lenses, as the through-focus modulation transfer function (TF-MTF) at a given frequency and pupil diameter, is routinely published. SimVis Gekko, a see-through simultaneous vision simulator based on temporal multiplexing, allows patients to experience the real world through different multifocal corrections prior to surgery. Implementing the maximum number of commercially available IOL designs into the portfolio of SimVis Gekko simulations is needed to provide a complete experience for the patients. We developed a new method to visually simulate IOL designs using temporal multiplexing, based only on publicly available information (mainly scientific literature or regulatory information), using the TF-MTF at 15cpd as input data to estimate the temporal coefficients that provide the best approximation to the real lens design. We validated the method with synthetic phase maps of equal area segmented bifocal and trifocal multifocal corrections for three pupil diameters of 3mm, 3.75mm and 4.5mm and applied it to three commercially available IOLs (trifocal or extended-depth-of-focus lenses). Through-focus visual acuity (TF-VA) curves were measured in seven patients using the SimVis simulations in the SimVis Gekko and matched, on average, the through-focus VA measurements in patients with implanted IOLs, reported in the scientific literature (on average logMAR RMS error=0.05, corresponding to less than 3 letters of visual acuity charts).

Today, almost all imaging systems include both an optical part and an image processing part in order to improve the final image quality. It therefore seems natural to optimize them simultaneously to obtain the best possible result. However, even if this “co-design” approach is more and more recognized at a conceptual level, it is still rarely used in practice for designing complex lenses with many ajustable parameters and constraints. This is due to the fact that the contribution of image processing is currently difficult to take into account in optical design software. Until now, the field of co-design has thus mainly focused on simpler imaging systems, consisting for example of single co-optimized optical elements such as phase masks. More recently, Robinson and Stork have been working on the possibility of integrating the image processing criterion known as mean square error (MSE) in the optical software Zemax OpticStudio. It is also possible to consider surrogate criteria instead of this MSE, built from more classical optical criteria (modulation transfer function, point spread function, etc.) [Burcklen et al. (2018)]. In this study, we investigate the possibility of implementing the MSE criterion in the CodeV optical design software in a way that is easily usable by an optical designer. We compare systems co-designed with this approach to systems jointly optimized with surrogate criteria or conventionally optimized. We focus on the performance differences between these different approaches and on the opportunities offered by CodeV for co-design.

SimVis Gekko is a novel see-through binocular visual simulator that is based on liquid-membrane tunable lenses (TLs) projected onto the pupil of the eye using a twisted miniaturized 4-f system. Following a temporal multiplexing approach that introduces periodic defocus variations in optical power at 50Hz, the TL generates multifocal images on the retina of the observer, that look static. In this study, the image quality of different tentative designs of SimVis Gekko was evaluated for different optical powers. The full optical system of SimVis Gekko was computer simulated to get the spot size, prismatic shift, angular magnification, and field curvature up to 20° of field of view. An image quality bench was developed to capture and process images through the SimVis Gekko simulator. The system comprises a grayscale camera and a 19- mm focal-length lens with an adjustable diaphragm. A high-resolution screen was placed at one meter with two different targets: (1) a checkerboard, imaged through a 1-mm diaphragm, to measure optical quality, prismatic shift, magnification, and optical distortion; (2) a binary noise, imaged through a 5-mm diaphragm, used to measure the local field curvature and image quality. Images were obtained from 1 to 3D of the TL and automatically analyzed. Theoretical simulations and experimental measurements showed good agreement. Magnification and curvature were the major differences across designs. The last version measured was free of optical distortions with a central curvature-free area with high optical quality. The developed system could guide the assembly and fine adjustment of active afocal optical systems.

A telescopic zoom system made of three spherical mirrors has been designed for the purpose of electron acceleration with lasers at LULI's Apollon facility. This system is based on a telescope with 3 or 4 mirrors, the distances of which can be varied continuously. We are constrained by laser damage considerations which prevents us from reducing the dimension of the incident laser beam and we will show that the 3-mirror solution can be made of a first convex mirror, a second concave mirror and a third convex mirror. It is possible to get a continuous range of focal lengths when translating the second mirror such that the final focal length will vary from 1 to 4 (zoom ratio 4x) and that the final focal spot will not move. When dealing with on-axis mirrors, we will get a central obscuration and the next step will be to go off-axis such that no obscuration will occult the beam propagation. Moreover our laser beams are fairly well collimated with a residual divergence much less than 100 μrad which means that we are not considering any field of view like it is for astronomical systems. The purpose of this paper is to describe the step-by-step method leading to the final compact zoom system that allows the focal length to be varied continuously. A mock-up of the system at a reduced scale is being built, first as a proofof-principle and second to work on the alignment of the 3-mirror zoom.

Gas sensing find tremendous applications in various fields like medicine, air quality, food processing or security and defence. The main challenge in industry is to create an integrated and compact sensor while maintaining its performance and power consumption. Photoacoustic spectroscopy (PAS) gains particular interest in this field due to its excellent selectivity while maintaining compactness. In tunable laser diode absorption spectroscopy (TDLS) the signal is proportional to optical path. Sensitivity in photoacoustic spectroscopy is proportional to the power of the laser, which allows to keep a good sensitivity even with small gas cells. The use of mechanical resonator with high quality factor allows improving the signal-to-noise ratio and avoid the use of an acoustic chamber. Micro-electro mechanical systems (MEMS) fabricated in silicon technology remain a reasonable choice to realize a compact and integrated sensor, including laser source and electronics. We propose a capacitive transduction method, which can be easily integrated, compact and highly sensitive. Due to the multi-physics problem, time and financial contains, a theoretical model seems to be a first step towards sensor performance improvement. We propose an analytical model for a new concept of photoacoustic gas sensing using capacitive transduction mechanism. The model was reinforced with computational methods implemented in Python programming environment. The study was carried out using silicon cantilever as a model, which brings an opportunity to obtain an analytical solution for all physical parameters. The goal of this research stands maximization of electrical signal output and signal-to-noise (SNR) ratio. Conducted study provides a solution to retrieve a cantilever dimensions and frequency for integrated compact gas sensor. Beyond optimization, the model provides a comprehensive tool to understand mechanisms of sensor working principles and therefore stands as a tool allowing a mechanical resonator to be developed with a more complex geometry and/or different transduction mechanism.

Integrating spheres are commonly used in aerospace and laboratory applications as stable reference calibration sources. Even with models containing simple geometries, tracing enough rays in order to achieve statistically converged output radiance distributions can be prohibitively time consuming unless the modeling is approached correctly. In this paper, we discuss the use of very high scatter level Monte Carlo raytracing to model the performance of an integrating sphere that includes the specular and scatter properties of the interior surface, distribution(s) of the light source(s) and the effects of misalignments. We also demonstrate the use of GPU ray tracing to dramatically shorten the analysis iteration cycle, leading to faster product development.

Due to their low-cost fabrication process and high efficiency, silicon-based Complementary Metal Oxide Semiconductor (CMOS) image sensors are the reference in term of detection in the visible range. However, their optical performances are toughly degraded in the Near Infrared (NIR). For such wavelengths, Silicon has a small absorption coefficient, leading to a very poor Quantum Efficiency (QE). A solution to improve it is to implement structures like pyramids that are etched in the Silicon layer. This will lead to diffraction inside the photodiode, enhancing the light path and therefore the absorption. Using Finite Difference Time Domain (FDTD) simulations, we demonstrated a huge QE enhancement at 940nm on real pixels, by implementing this kind of diffractive structures and we finally confirmed these results by characterizations. We obtained QE values up to 47% at 940nm for our 3.2μm pixel, corresponding to a gain of 2 comparing to a pixel without any diffractive structures. We also measured the Modulation Transfer Function (MTF), to evaluate how this figure of merit is impacted by the addition of these structures. As expected, the MTF was degraded when we added these diffractive patterns but were still high looking at the values. We indeed demonstrated MTF values going up to 0.55 at Nyquist/2 frequency and 0.35 at Nyquist frequency. Looking not only at QE values but also at MTF ones, these are very promising results that could be used in many different NIR applications like face recognition, Light Detection and Ranging (LIDAR) or AR/VR.

As an emerging nondestructive imaging technology, photoacoustic imaging (PAI), which is based on photoacoustic effect, combines the advantages of the high resolution and contrast of optical imaging and the high penetration depth of acoustic imaging. Thereinto, as a branch of photoacoustic imaging, photoacoustic microscopy inherited the advantages of photoacoustic imaging. The unique focusing mode of photoacoustic microscopy can meet the requirements of higher resolution in biological imaging and it has gained extensive applications in medical science field. In our previous work, in order to solve the shortcoming of traditional photoacoustic microscopy with a small depth of field, we have built a simulation platform for Airy-beam photoacoustic microscopy based on K-Wave MATLAB toolbox, which uses Airybeam to excite the initial photoacoustic signal. As non-diffraction beam, Airy-beam features the capacity of large depth of field. However, Airy-beam has sidelobe, which makes the edges of the image blurred. Convolution is a mathematical method of integrating transformations. The imaging result of optical system is the result of convolution of the sample and PSF of the system. PSF convolves with the sample, resulting in blurred image and reduced image resolution. The image can be restored by appropriate deconvolution techniques. In this paper, in order to weaken the influence of Airybeam’s sidelobe on the imaging results, Lucy-Richardson (LR) Algorithm is used to deconvolve the imaging results to obtain clearer restored images. LR Algorithm is a nonlinear iterative restoration algorithm based on Bayesian conditional probability model, and it is assumed that pixels in fuzzy images meet Possion distribution, and its optimal estimation criterion is maximum likelihood criterion. Using LR Algorithm for Airy-beam photoacoustic microscopy can greatly improve the system resolution and clearer imaging results can be obtained.

Photoacoustic imaging is a functional imaging method based on the photoacoustic effect, which combines the high contrast of optical imaging and the low dispersion characteristics of acoustic imaging. It has been developed rapidly in recent years. Photoacoustic microscopy, as an important branch, is widely used in biomedical imaging due to its high resolution, high contrast, and non-destructive characteristics. Compared with other medical imaging techniques, photoacoustic microscopy is simple, effective, low-cost, and does not generate ionizing radiation. But due to the need to focus the laser strongly, the depth of field is limited. Currently, most photoacoustic microscopy adopts an array scanning mechanism. Limited by the imaging depth of field and inherent scanning methods, photoacoustic microscopy cannot achieve large-volume, highresolution, and high-speed imaging at the same time. High-speed and large-scale tissue imaging is of great significance for the study of response mechanisms and the development of physiological and pathological processes. It is conducive to make accurate judgments for disease diagnosis. For the problems of photoacoustic microscopy, this paper proposes a highresolution three-dimensional information fusion technology suitable for photoacoustic microscopy, which provides richer structural and functional information for related physiological and pathological research. Combining the tomographic features of the data collected by the photoacoustic microscopy system with the traditional Laplacian pyramid transform, the depth of field of the photoacoustic microscopy is expanded. Two sets of single-focus image data sets of virtual photoacoustic microscopy platforms are collected and processed by three-dimensional high-resolution information fusion technology. The results demonstrates that a complete large-scale three-dimensional high-resolution structure has been successfully realized, and the reliability of the method is verified.

Design of an optical system implies definition of its' parameters including both continuous and discrete variables. The first group is corresponds to such parameters as radii of curvature and axial thicknesses, and the second one consists of the optical materials types. A number of algorithms to optimize both groups of variables simultaneously was developed and implemented in optical design software. However, as the working spectral range expands and requirements to the systems' aperture and performance increase, the efficiency of existing design tools for mixed-variables optimization may appear to be insufficient. On top of this, the standard optimization tools do not provide all the necessary control and customization options Therefore, we consider a custom optimization tool to perform a global search in mixed variables. It is based on the method of global optimization with selective averaging of variables. A positive selectivity coefficient is introduced into a positive decreasing functional kernel. With increase of the coefficient the averaging provides convergence of the target discrete variables to the optimal solution. We apply this principle to develop a custom optimization tool. It is used for optimization of an f/1.8 objective lens working in the NIR range of 0.9-1.8 microns with the field of view of 10 deg. We analyze the optimization process convergence in the continuous and discrete variables space and compare our results with the existing optimization tools.

Aberration-corrected holographic gratings are widely used in spectral instruments. They allow to achieve high resolution and uniformly distributed diffraction efficiency as well as to combine several functions in a single optical element. However, their performance is limited. In particular, when the optical system has a large aperture the hologram replay conditions vary significantly across its’ surface. Due to this variation the hologram aberration properties and its efficiency change locally thus leading to decrease of the resolution and efficiency of the entire system. In the present research we consider a composite volume phase holographic optical element used as a disperser in a spectrograph design. Such an optical element represent a hologram recorded by stitching of several elementary fields or zones. The refraction index modulation depth, the fringes tilt and the hologram spatial frequency may vary locally in each of the elementary fields to match the changing reconstruction conditions. This approach allows to implement a better aberrations correction and to maximize the overall diffraction efficiency. We demonstrate an exemplary spectrograph design with a composite hologram for the visible range of 400-800 nm. It is shown, that in the design as fast as f/2.1 the maximum aberrations can be decreased by factor of 1.19 and 2 in the X and Y directions, respectively, while the average diffraction efficiency increases by 15.6% at shorter wavelenghts. We continue the study by investigation of the composite hologram technological feasibility and demonstrate that it can be recorded with a standard precision of the moving sources positioning, achievable stroke of the auxiliary deformable mirror and reasonably high accuracy of the photosensitive layer’s parameters.

Digital twin of a test assembly setup was developed to simulate the different steps of the alignment sequence of a coupling system. Furthermore, a software framework was created that can control both the assembly setup and the simulation engine. According to the tests, the simulated results correlate well with the experimental data, even under different environmental conditions, such as the presence of background noise. This approach can enhance the development of assembly sequences for different kind of micro-optics modules

In recent years, with technological advances, head-mounted display systems (HMDs) for virtual reality (VR) and augmented reality (AR) have been adopted for their applications in the military, government, education, training, medical visualization, aerospace, entertainment industries, and tourism. For this reason, a compact and light HMD but without sacrificing their performance is necessary. In this paper, the optical design of a lightweight and compact head-mounted display (HMD) system is proposed. We use an off-axis three-mirror system (OTS) with freeform surfaces for the correction of the aberrations and obtain a wide field of view (FOV), a compact structure with an exit pupil size over 7 mm and eye relief of 25 mm.

Currently, in the field of optical design, there is great interest in assessing the complexity of an optical system prior to its actual design. In this paper, we propose a method that can estimate complexity by predicting the number of optical surfaces in a lens required to achieve diffraction-limited image quality. We show that it is sufficient to select the proper number of pupil points, field, and wavelength range to estimate aberration values at the design stage. Each control point corresponds to a ray passing through the optical system. The coordinates of the intersection of the input ray with the image plane are a function of the input ray and the parameters of the optical system. Thus, we can construct a system of equations from the functions of each control point. A solution exists when the number of variables (design parameters) is equal to the number of equations (control points). The basic idea is to determine the required number of control points of the field, pupil, and wavelength range, which gives us the number of design parameters. We have plotted empirical diagram for common combinations of focal length (F'), F-number (F#), field-of-view (FOV), and wavelength range. This information can be used to determine the desired number of control points and therefore to assess the complexity of the optical system being designed. Taking into account the geometric constraints and the variety of optical materials, the result of this method cannot be final, but it can be considered as a preliminary estimate of the complexity of the optical system.