We propose digital correction methods for recovering aberrated spectra in a portable low-cost miniaturized grating-based spectrometer, which is modelled in optical and numerical simulations. To realize the digital spectrum recovery, different Point Spread Function (PSF) modelling approaches for wavelength-dependent PSFs are proposed and implemented into four digital correction algorithms, namely inverse Fourier Transform (IFT) deconvolution, Wiener deconvolution, Lucy-Richardson (LR) and Landweber iterative algorithm. Results show that both LR and Landweber algorithms can improve the spectral resolution by about a factor of two. The enhanced spectral resolution is comparable to that of commercial table-top spectrometers, while our spectrometer has a much smaller packaging volume of about one cubic inch.
This study proposes a novel approach in response to the persistent challenge of achieving precise autofocus in Digital Lensless Holographic Microscopy (DLHM). It involves employing an enhanced Bluestein algorithm to simulate DLHM holograms under a variety of conditions, spanning amplitude-only, phase-only, and amplitude-phase objects. These simulated holograms are used to assess the performance of autofocus metrics, including the Dubois and Spectral Dubois metrics, gradient and variance-based approaches, and lastly a learning-based model. By considering the variety of sample types and geometrical configurations, this study delves into the robustness and limitations of these metrics across diverse scenarios. This research reveals different performances depending on sample characteristics, offering valuable insights into selecting the most suitable autofocus metric, which is a demanding step in practical DLHM applications.
This study proposes a novel approach in response to the persistent challenge of achieving precise autofocus in Digital Lensless Holographic Microscopy (DLHM). It involves employing an enhanced Bluestein algorithm to simulate DLHM holograms under a variety of conditions, spanning amplitude-only, phase-only, and amplitude-phase objects. These simulated holograms are used to assess the performance of autofocus metrics, including the Dubois and Spectral Dubois metrics, gradient and variance-based approaches, and lastly a learning-based model. By considering the variety of sample types and geometrical configurations, this study delves into the robustness and limitations of these metrics across diverse scenarios. This research reveals different performances depending on sample characteristics, offering valuable insights into selecting the most suitable autofocus metric, which is a demanding step in practical DLHM applications.
For many applications using Photomultiplier tubes (PMT) that require an efficient measurement of very weak light, it is a continuous challenge to collect as much light as possible. Regarding the improvement of the collection efficiency, there are some possible solutions, e.g., using a detector with a larger effective area or adding a large optical lens. However, there is also a demand to miniaturize detectors in certain application fields such as immunoassay analysis and underwater wireless optical communications. To overcome this challenge, we have developed a novel freeform condenser lens which shows a drastic size reduction and high light collection efficiency simultaneously. The lens has a very high collection efficiency to collect not only collimated light but also diffused light, which is usually difficult to collect for common detectors with a limited entrance aperture and acceptance angle. In this paper, we present the design and characteristics of this lens. We also present exemplary applications of the developed freeform condenser lens in an immunoassay analyzer and in underwater wireless optical communication by combining developed lens with a PMT.
Unsupervised deep learning has only been used in rotationally symmetric optical design. This work presents a differentiable three-dimensional ray tracing module and related loss functions, enabling unsupervised learning of non-rationally symmetric freeform optical systems.
Three-dimensional (3D) bioprinting approaches that enable large-scale constructs and high-resolution simultaneously are very attractive to tissue engineering applications and health industries. However, both characteristics hardly meet at reasonable printing times in current 3D bioprinting technologies, affecting the introduction of 3D scaffolds in medical applications. To overcome this limitation, we recently introduced a Vat Photopolymerization (VP)-based bioprinting method named Light Sheet Stereolithography (LS-SLA) and demonstrated the fabrication of centimeter-scale scaffolds with micrometer-scale features (⪆; 13 μm) by using off-the-shelf optical compounds. The high performance in LS-SLA results from using a rectangular uniform beam instead of a rotational symmetric laser beam, which generates light sheets with large length-to-width aspect ratios on the vat film. Beam shaping optics are components used to perform the beam transformation, and guarantee the accuracy, uniformity, and size of the 3D constructs. This work proposes freeform optics to perform the laser beam shaping in the LS-SLA device and describes the progress of our investigations from design to proof-of-concept-demonstrating. The results show that rectangular beams are readily produced by freeform optics resulting in compact and energy efficient systems, and that further considerations on the real laser output are necessary to deliver high beam uniformities. Tackling the design challenges of this work leads to energy efficient and high accuracy LS-SLA systems.
Recently, it becomes a tendency for cost-effective, portable spectrometers to have more applications from scientific research to daily life, e.g., in food safety and air pollution analysis. While most spectrometers utilize plane gratings, we demonstrate a more miniaturized, two-channel, broadband spectrometer based on variable-spacing concave gratings, combining the functionality of imaging optics and diffraction grating in one component. The added degree of design freedom in the micro-sized grating spacing further corrects most optical aberrations, thus the design achieves a tiny volume of <26 × 12 × 10 mm3 with a high spectral resolution. Simulation results show an optical resolution of <1.6 nm in the VIS-channel (400 to 790 nm) and <3.1 nm in the NIR-channel (760 to 1520 nm). The blazed structure of grating grooves provides a high overall diffraction efficiency in the whole spectral range, more than 50% on average. To further validate the feasibility for mass production, we successfully manufactured the variable-spacing concave gratings by using diamond tooling for fabricating the master mold and hot embossing for replication. Our fabricated variable-spacing grating replicas have a diffraction efficiency up to 70% in the VIS-channel and up to 60% in the NIR-channel. We built the prototype with fabricated concave gratings, and experimental results show a good match (error < 7 % ) in spectral resolution with the nominal design.
We present a generalized differentiable ray-tracing approach suitable for most optical surfaces, including freeform surfaces. The established freeform design method simultaneously calculates multi-surface coefficients with merely the system geometry known. In addition, we provide a ‘double-pass surface’ strategy with the desired overlap (not mutually centered) that enables a component reduction for very compact yet high-performing designs. Two different examples are used to demonstrate the effectiveness of the proposed method. This work provides a robust design scheme for reflective freeform imaging systems in general, and it unlocks a series of new ‘double-pass surface’ designs for very compact, high-performing freeform imaging systems.
The goal of the SensApp FET-Open project is to develop an innovative super-sensor that will be able to detect Alzheimer’s disease (AD) biomarkers (β-amyloid, Tau and pTAU) in peripheral blood. Considering that nowadays an accurate diagnosis of AD requires the highly invasive withdrawal and analysis of cerebrospinal fluid, SensApp will represent a breakthrough in the field of AD diagnosis thanks to the ability to detect the early stage of the disease by a simple blood collection. We call Droplet-Split-and-Stack (DSS) the new technology that will emerge from SensApp. The achievement of SensApp goal is enabled by the interdisciplinary cooperation between different research institutions and one company involved in the key fields of the project, Vrije Universiteit Brussels, VTT Technical Research Centre of Finland, University of Linz, Ginolis Ltd, IRCCS Centre “Bonino Pulejo”, under the coordination of CNR-Institute of Applied Sciences and Intelligent Systems. This communication will illustrate the progress of the activities.
The effective detection of very low abundant biomarkers can enable fast diagnosis of many severe and disabling diseases (e.g. Alzheimer’s Disease) at an early stage. To develop a cost-efficient, super-sensitive optical fluorescence detection microscope, we have proposed an optical modelling approach to predict the signal-noise-ratio that considers various noise sources introduced by the components of the detection system. After the optimal design is identified, a tolerance analysis regarding typical perturbations is performed for further mechanical design and assembly. Finally, experiments have demonstrated a limit of detection at a low abundant concentration reaching 0.05 pmol/ml.
Materials play a key role in tissue engineering for the construction of 3-dimensional scaffolds that support the formation of a new extracellular matrix. They should be biocompatible, and for the fabrication of functional scaffolds, they should be mechanically robust, provide high resolution and printability factors to use in one-photon polymerization microstereolithography (OPP μ-SLA) technologies. Furthermore, applications where those materials are used, such as tissue regeneration or tissue substitutes, require fabrication approaches that allow the scalability of 3D scaffold for their clinical use. Therefore, both materials and technology need to be optimized and improved. We tackle two research tracks, one to provide high resolution and biocompatible materials that can be used in OPP- μ-SLA, and a second one to obtain a new μ- SLA configuration that can boost large-size scaffold fabrication for tissue engineering applications. In this work, we report our progress towards the formulation of a hydrogel based on the prototype resin X HYDRORES INX X100 from XPECT INX and we describe the configuration based on the beam shaping of a laser source to print centimeter scale scaffolds while conserving micro-scale features. We printed scaffolds with a commercial ABS resin and the bio-inert hydrogel from XPECT INX that allow us to compare resolution, printability, and mechanical stability. Our results evidence structures with voxel widths up to 20 μm and lengths up to 23 mm by using uniform light sheets illumination patterns. This work set new alternatives for the material and the fabrication aspects of additive manufacturing for 3D biofabrication.
In general, optical designers employ combinations of multiple lenses with extraordinary dispersion materials to correct chromatic aberrations, which usually leads to considerable volume and weight. In this paper, a tailored design scheme that exploits state-of-the-art digital aberration correction algorithms in addition to traditional optics design is investigated. In particular, the proposed method is applied to the design of refractive telescopes by shifting the burden of correcting chromatic aberrations to software. By tailoring the point spread function in primary optical design for one specified wavelength and then enforcing multi-wavelength information transfer in a post-processing step, the uncorrected chromatic aberrations are well mitigated. Accordingly, a telescope of f-8, 1,400mm focal length, and 0.14° field of view is designed with only two lens elements. The image quality of the designed telescope is evaluated by comparing it to the equivalent designs with multiple lenses in a traditional optical design manner, which validates the effectiveness of our design scheme.
In this work, an optical design approach is presented to design an ultrashort throw distance projection system by combination of an off-the-shelf refractive lens and two off-axis freeform mirrors. These two freeform mirrors are used to greatly shorten the projection distance by more than three times compared to conventional (rotationally symmetric) systems, while still maintaining a good imaging quality. Firstly, a direct design method that enables the simultaneous calculation of two off-axis freeform-profile mirrors by partially coupling more than three fields is introduced. The specifications of the conventional refractive lens are taken into account during this procedure. The pupil matching principle is applied to ensure good performance between the two sub-systems. The calculated mirrors then serve as a good starting point for optimization using commercial optical design software. To step from freeform profiles to freeform surfaces, the calculated two profiles are fitted into odd polynomials to evaluate the image quality and then re-fitted into XY polynomials for further optimization. Finally, the polynomial coefficients of the two freeform mirrors are imported into the optical design program. The merit function is built from RMS spot radii over the full field, and additional constraints are made for correcting distortion. After optimization, the calculated initial design quickly converges to a well performing imaging system. As an example, an ultrashort throw distance projection lens with a large 80-inch diagonal image at 400mm throw distance is designed, analyzed and compared with literature data. The values of MTF are over 0.6 at 0.5 lp/mm and the distortion is less than 1.5%: showing a very good and well balanced imaging performance over the entire field of view.
In this paper, we propose a multi-fields direct design method aiming to calculate two freeform surfaces with an entrance pupil incorporated for wide field of view on-axis line imaging applications. Both infinite and finite conjugate objectives can be designed with this approach. Since a wide angle imaging system requires more than few discrete perfect imaging points, the multi-fields design approach is based on partial coupling of multiple fields, which guarantees a much more balanced imaging performance over the full field of view. The optical path lengths (OPLs) and image points of numerous off-axis fields are calculated during the procedure, thus very few initial parameters are needed. The procedure to calculate such a freeform lens is explained in detail. We have designed an exemplary monochromatic single lens to demonstrate the functionality of the design method. A rotationally symmetric counterpart following the same specifications is compared in terms of RMS spot radius to demonstrate the clear benefit that freeform lens brings to on-axis line imaging systems. In addition, a practical achromatic wide angle objective is designed by combining our multi-fields design method with classic optical design strategies, serving as a very good starting point for further optimization in a commercial optical design program. The results from the perspective of aberrations plots and MTF values show a very good and well balanced performance over the full field of view.
A multi-fields optical design method aiming to calculate two high-order aspheric lens profiles simultaneously with an embedded entrance pupil is proposed in this paper. The Simultaneous Multiple Surfaces design method in two dimensions (SMS2D) is used to provide a better understanding of how N surfaces allow perfect coupling of N ray-bundles. In contract to this perfect coupling, our multi-fields design approach is based on the partial coupling of multiple ray-bundles. This method allows calculating the Optical Path Lengths (OPL) during the process, directly building connections between different fields of view. Both infinite and finite conjugate objectives can be designed with this approach. Additional constraints like surface continuity and smoothness are taken into account to calculate two smooth and accurate surface contours. Sub-aperture sampling factor is introduced as a weighting function for different fields which allows for a very flexible performance control over a wide field of view. A RMS 2D spot size function is used to optimize the weighting factor to achieve a very well-balanced imaging performance. A wide-field objective and a moderate aperture lens are designed and analyzed to demonstrate the potential of this design method. The impact of different weighting functions for the sub-aperture sampling is evaluated accordingly. It’s shown that this design method provides an excellent starting point for further optimization of the surfaces coefficients and initial design parameters: resulting in a very good and well-balanced imaging performance over the entire field of view.
In this work, a multifields optical design method aiming to calculate two high-order aspheric lens profiles with an embedded entrance pupil is proposed. This direct design algorithm is capable of partially coupling more than three ray bundles that enter the same pupil with only two surfaces. Both infinite and finite conjugate objectives can be designed with this approach. Additional constraints such as surface continuity and smoothness are taken into account to calculate smooth and accurate surface contours described by point clouds. The calculated points are then fitted with rotationally symmetric functions commonly used in optical design tools. A presented subaperture sampling strategy that introduces a weighting function for different fields allows for a very well-balanced imaging performance over a wide field of view (FOV). As an example, a ±45 degf/7.5 wide-angle objective is designed and analyzed to demonstrate the potential of this design method. It provides an excellent starting point for further optimization of the surfaces’ coefficients and initial design parameters, resulting in a very good and well-balanced imaging performance over the entire FOV.
As a novel detection approach which simultaneously acquires two-dimensional visual picture and one-dimensional
spectral information, spectral imaging offers promising applications on biomedical imaging, conservation and
identification of artworks, surveillance of food safety, and so forth. A novel moderate-resolution spectral imaging system
consisting of merely two optical elements is illustrated in this paper. It can realize the function of a relay imaging system
as well as a 10nm spectral resolution spectroscopy. Compared to conventional prismatic imaging spectrometers, this
design is compact and concise with only two special curved prisms by utilizing two reflective surfaces. In contrast to
spectral imagers based on diffractive grating, the usage of compound-prism possesses characteristics of higher energy
utilization and wider free spectral range. The seidel aberration theory and dispersive principle of this special prism are
analyzed at first. According to the results, the optical system of this design is simulated, and the performance evaluation
including spot diagram, MTF and distortion, is presented. In the end, considering the difficulty and particularity of
manufacture and alignment, an available method for fabrication and measurement is proposed.
Fourier telescopy is an active unconventional imaging technique. Three or more beams from different spatially separated transmitters are pointed at a distant and faint object. The spatial Fourier spectrum of the object is carried on the reflected temporally modulated signals. The image of the target can be reconstructed from the back signals by demodulation and phase closure algorithm. The conventional demodulation processing is calculating spectrum directly by inverse Fourier transform of the signal. However spectrum estimated by inverse Fourier transform has non-negligible errors caused by frequency shift error of the Acoustic-optical modulator, the noise and the relative motion between beams and the target. An improved demodulation method based on spectrum correction of FT is proposed. The method corrects the amplitude and the phase on the demodulated frequency of the signal by which better reconstructed image can be obtained. In this paper, the effect of the frequency shift error in Fourier telescopy demodulation is investigated. The degradation of the reconstructed image is simulated. We summarize the new demodulation method based on spectrum correction and give the simulated comparison between the conventional demodulation and the developed method. The result confirms the effectiveness of the improved demodulation method.
In order to meet the needs of space borne and airborne hyperspectral imaging system for light weight, simplification and high spatial resolution, a novel design of Féry-prism hyperspectral imaging system based on Zemax multi-configuration method is presented. The novel structure is well arranged by analyzing optical monochromatic aberrations theoretically, and the optical structure of this design is concise. The fundamental of this design is Offner relay configuration, whereas the secondary mirror is replaced by Féry-prism with curved surfaces and a reflective front face. By reflection, the light beam passes through the Féry-prism twice, which promotes spectral resolution and enhances image quality at the same time. The result shows that the system can achieve light weight and simplification, compared to other hyperspectral imaging systems. Composed of merely two spherical mirrors and one achromatized Féry-prism to perform both dispersion and imaging functions, this structure is concise and compact. The average spectral resolution is 6.2nm; The MTFs for 0.45~1.00um spectral range are greater than 0.75, RMSs are less than 2.4um; The maximal smile is less than 10% pixel, while the keystones is less than 2.8% pixel; image quality approximates the diffraction limit. The design result shows that hyperspectral imaging system with one modified Féry-prism substituting the secondary mirror of Offner relay configuration is feasible from the perspective of both theory and practice, and possesses the merits of simple structure, convenient optical alignment, and good image quality, high resolution in space and spectra, adjustable dispersive nonlinearity. The system satisfies the requirements of airborne or space borne hyperspectral imaging system.
A novel moderate-resolution imaging spectrometer spreading from visible wavelength to near infrared wavelength range
with a spectral resolution of 10 nm, which combines curved prisms with the Offner configuration, is introduced.
Compared to conventional imaging spectrometers based on dispersive prism or diffractive grating, this design possesses
characteristics of small size, compact structure, low mass as well as little spectral line curve (smile) and spectral band
curve (keystone or frown). Besides, the usage of compound curved prisms with two or more different materials can
greatly reduce the nonlinearity inevitably brought by prismatic dispersion. The utilization ratio of light radiation is much
higher than imaging spectrometer of the same type based on combination of diffractive grating and concentric optics. In
this paper, the Seidel aberration theory of curved prism and the optical principles of Offner configuration are illuminated
firstly. Then the optical design layout of the spectrometer is presented, and the performance evaluation of this design,
including spot diagram and MTF, is analyzed. To step further, several types of telescope matching this system are
provided. This work provides an innovational perspective upon optical system design of airborne spectral imagers;
therefore, it can offer theoretic guide for imaging spectrometer of the same kind.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.