Miniaturization Of Optical Systems Research Articles

Highly efficient multifunctional metasurface integrating lens, prism, and wave plate

The miniaturization of optical systems is crucial for various applications, including compact augmented reality/virtual reality devices, microelectromechanical system sensors, ranging technologies, and microfabricated atomic clocks. However, reliance on bulky discrete optical elements has been a significant obstacle to achieving this miniaturization. This work introduces a highly efficient multifunctional metasurface (MFMS) that seamlessly integrates a lens, prism, and quarter-wave plate (QWP). This innovation allows simultaneous collimation, beam deflection, and polarization conversion within a singular thin element. Specifically, for the prism-QWP bifunctional integration, we achieved a high diffraction efficiency of 72.8% and a degree of circular polarization of −0.955 under exposure to linearly polarized light at a wavelength of 795 nm, proving its potential for ultracompact atomic clock applications. Moreover, the lens-prism-QWP trifunctional integration successfully showed diffraction-limited focusing performance with a numerical aperture of 0.4, which was sufficient to collimate a beam with a divergence angle of 20∘, corresponding to the light emitted from a standard vertical-cavity surface-emitting laser.

Intelligent Phase Contrast Meta-Microscope System.

Phase contrast imaging techniques enable the visualization of disparities in the refractive index among various materials. However, these techniques usually come with a cost: the need for bulky, inflexible, and complicated configurations. Here, we propose and experimentally demonstrate an ultracompact meta-microscope, a novel imaging platform designed to accomplish both optical and digital phase contrast imaging. The optical phase contrast imaging system is composed of a pair of metalenses and an intermediate spiral phase metasurface located at the Fourier plane. The performance of the system in generating edge-enhanced images is validated by imaging a variety of human cells, including lung cell lines BEAS-2B, CLY1, and H1299 and other types. Additionally, we integrate the ResNet deep learning model into the meta-microscope to transform bright-field images into edge-enhanced images with high contrast accuracy. This technology promises to aid in the development of innovative miniature optical systems for biomedical and clinical applications.

Technologies for depth scanning in miniature optical imaging systems [Invited

Biomedical optical imaging has found numerous clinical and research applications. For achieving 3D imaging, depth scanning presents the most significant challenge, particularly in miniature imaging devices. This paper reviews the state-of-art technologies for depth scanning in miniature optical imaging systems, which include two general approaches: 1) physically shifting part of or the entire imaging device to allow imaging at different depths and 2) optically changing the focus of the imaging optics. We mainly focus on the second group of methods, introducing a wide variety of tunable microlenses, covering the underlying physics, actuation mechanisms, and imaging performance. Representative applications in clinical and neuroscience research are briefly presented. Major challenges and future perspectives of depth/focus scanning technologies for biomedical optical imaging are also discussed.

Multiwavelength Achromatic Metalens in Visible by Inverse Design

AbstractAchromatic metalenses are promising alternatives to traditional lenses, allowing the miniaturization of optical systems. However, the limitation due to the group delay range of the meta‐atoms that can be fabricated requires a trade‐off relationship between the working bandwidth, numerical aperture (NA), and aperture of the achromatic metalens operating in a continuous spectrum. Considering that light sources used in most optical systems to illuminate or display images in most optical systems generate multiwavelength light with a narrow bandwidth, an efficient end‐to‐end inverse design framework for multiwavelength achromatic metalenses is implemented. As a proof of concept, an achromatic metalens with an NA of 0.3 and a diameter of 115 µm at four visible wavelengths and arbitrary linear polarization is designed and experimentally demonstrated. The measured results show a maximum focal length shift of 5.2778%. The proposed strategy avoids complicated physical models, enabling the integration of complex functionalities into a single metasurface, thereby driving the design of efficient and emerging devices.

A review on innovative optical devices for the diagnosis of human soil-transmitted helminthiasis and schistosomiasis: from research and development to commercialization.

Diagnosis of soil-transmitted helminth (STH) and schistosome infections relies largely on conventional microscopy which has limited sensitivity, requires highly trained personnel and is error-prone. Rapid advances in miniaturization of optical systems, sensors and processors have enhanced research and development of digital and automated microscopes suitable for the detection of these diseases in resource-limited settings. While some studies have reported proof-of-principle results, others have evaluated the performance of working prototypes in field settings. The extensive commercialization of these innovative devices has, however, not yet been achieved. This review provides an overview of recent publications (2010–2022) on innovative field applicable optical devices which can be used for the diagnosis of STH and schistosome infections. Using an adapted technology readiness level (TRL) scale taking into account the WHO target product profile (TPP) for these diseases, the developmental stages of the devices were ranked to determine the readiness for practical applications in field settings. From the reviewed 18 articles, 19 innovative optical devices were identified and ranked. Almost all of the devices (85%) were ranked with a TRL score below 8 indicating that, most of the devices are not ready for commercialization and field use. The potential limitations of these innovative devices were discussed. We believe that the outcome of this review can guide the end-to-end development of automated digital microscopes aligned with the WHO TPP for the diagnosis of STH and schistosome infections in resource-limited settings.

Optics of the metalens

A metalens is an ultra-thin lens made of a metasurface, with focusing and imaging functions, and with promising applications in miniature optical systems, such as mobile devices. This paper gives an introduction to the optics of metalenses. First, we examine the focusing and imaging characteristics of metalenses. And then, as an essential step, we derive the refraction law of metasurfaces from the Huygens’s principle. It is then that some basic formulas of the metalens, for focusing and imaging, are derived at a level appropriate for undergraduate students. We begin with the derivation of the phase profile of a metalens. Then we derive the lens equation of the metalens, which relates the object and image distance in a metalens. The paper closes with a discussion of the relationship between the metalens and the classical refractive lens.

High-efficiency, polarization-insensitive 1400-lines/mm retroreflective metagrating with cascaded nano-optical modes

A retroreflective grating with a high line density is one of the most desirable optical elements, as it is capable of channeling the reflected light toward the source with high angular resolution. Metagratings can steer the incident light into the desired diffraction order with ultrahigh deflection angle and unitary efficiency. However, in practice, the diffraction efficiency of a metagrating with a small period is very sensitive to the unit cells, thus leading to significant challenges in the fabrication process. In this Letter, a kind of high-efficiency, polarization-insensitive retroreflective metagrating with cascaded nano-optical modes on high-reflection films is proposed. It is found that the conception may increase the fabrication tolerance by a factor of more than two. A 1400-lines/mm metagrating is experimentally realized for the first time, to the best of our knowledge, which shows an excellent broadband diffraction spectrum with 96% efficiency over 50 nm in TE and TM polarization. This proposed novel metagrating will benefit miniature optical systems.

Atomic layer deposition of conformal anti-reflective coatings on complex 3D printed micro-optical systems

3D printing of micro-optics has recently become a very powerful fabrication method for sub-millimeter sized optics. Miniature optical systems and entire optical instruments such as endoscopes have become possible with this technique. 3D printed complex micro-optical systems are printed in one single process, rather than being assembled. This precludes anti-reflection coating of the individual lenses before assembly by conventional coating methods such as sputtering or directed plasma etching, as voids between the individual lenses cannot be reached by a directed coating beam. We solve this issue by conformal low-temperature thermal atomic layer deposition (ALD) which is compatible with the low glass transition temperature of the utilized 3D printed polymer materials. Utilizing 4-layer designs, we decrease the broadband reflectivity of coated flat substrates in the visible to below 1%. We characterize and investigate the properties of the coatings based on transmission measurements through coated and uncoated 3D printed test samples as well as through a double-lens imaging system. We find that the reflectivity is significantly reduced and conversely the transmission is enhanced, which is of particular interest for low-light applications. Furthermore, the physical durability and resistance against humidity uptake should also be improved.

Single-pixel imaging using a recurrent neural network combined with convolutional layers.

Single-pixel imaging allows for high-speed imaging, miniaturization of optical systems, and imaging over a broad wavelength range, which is difficult by conventional imaging sensors, such as pixel arrays. However, a challenge in single-pixel imaging is low image quality in the presence of undersampling. Deep learning is an effective method for solving this challenge; however, a large amount of memory is required for the internal parameters. In this study, we propose single-pixel imaging based on a recurrent neural network. The proposed approach succeeds in reducing the internal parameters, reconstructing images with higher quality, and showing robustness to noise.

Nanoscale Noncoplanar Beam Splitters With Tunable Split Ratio

Beam splitters, especially those with tunable split ratios, play significant role in interferometers, spectrometers, and communication systems. To this end, we proposed a polarization-controllable beam splitter based on dielectric metasurface composed of an array of dielectric pillars. The dielectric metasurface presents phase gradients along two orthogonal directions, say, x- and y- axis, with each phase gradient applicable to one of two orthogonal linear polarizations. Due to the orthogonality of the dual phase gradients in both position and polarization, an elliptically polarized incident beam can be diffracted into two refracted beams, one lies within xoz plane and the other in yoz plane. More importantly, the split ratio of the two refracted beams is continuously tunable by changing the ellipticity of incident beam. Under extreme case, x- or y- polarized incident beam is refracted into one beam, but in different planes for different kind of linear polarization. Besides, the refracted angle of each refracted beam in respective refracted plane can be easily set by adjusting the phase difference of adjacent rows or columns of metasurface. With same method, a polarization-controllable dual-wavelength beam splitter is also achieved on the basis of phase-gradient metasurface. Such a noncoplanar beam splitter with tunable split ratios may play significant role in novel miniature optical devices and systems.

Hybrid refractive-diffractive microlenses in glass by focused Xe ion beam

The combination of refractive and diffractive components in a single optical element provides miniaturization of optical systems and enhancement of their performance. Thus, hybrid singlet lenses with diffractive structures added on top of the refractive curved surface were shown to have reduced chromatic and spherical aberration. Optical systems based on such hybrid lenses have reduced dimensions as they require fewer lenses for aberrations-correction. Diffractive elements provide additional possibilities of light manipulation and enable the realization of miniaturized multifocal systems, spectrometers, and other devices. Glass hybrid lenses are typically realized by diamond turning or glass moulding. These techniques, however, are not applicable for the fabrication of lenses in brittle materials or microlenses (hundreds of micrometers in diameter or less). On the other hand, direct writing techniques, such as focused ion beam (FIB) milling (typically Ga), offer a high resolution and flexibility of patterning on curved lens surfaces made of a great variety of materials. The disadvantages of FIB milling are its slow speed and Ga implantation that may alter or degrade the optical performance of fabricated components. FIB systems based on high brightness plasma ion sources provide more than an order of magnitude increase in milling rates with noble gas ions (e.g., Xe) compared with Ga FIBs. Here, the authors demonstrate the feasibility of rapid, direct milling of hybrid refractive-diffractive microlenses in glass using >60 nA of Xe ion current. Microlenses with up to 300-μm diameter were milled and diffraction gratings were realized on top of their curved surfaces. The performance of the lenses was characterized by mapping the transmitted intensity at different positions. Due to the introduction of diffraction gratings on the surface of the lenses, their optical performance is modified with the emergence of additional focal spots spatially separated by distances consistent with the theoretical and simulated values. The results indicate the applicability of the plasma focused ion beam systems for rapid fabrication of high-quality hybrid optical elements directly in hard substrates.

Lithium Niobate Metasurfaces

AbstractLithium niobate is a multi‐functional material, which has been regarded as one of the most promising platforms for the multipurpose optical components and photonic circuits. Targeting miniature optical components and systems, lithium niobate microstructures with feature sizes of several to hundreds of micrometers are demonstrated, such as waveguides, photonic crystals, micro cavities, and modulators, and so on. In order to demonstrate the possibilities toward further shrinking the footprint of the lithium niobate devices with new optical functionalities, here, subwavelength nanograting metasurfaces are fabricated based on a crystalline lithium niobate film. Due to the collective lattice interactions between isolated ridge resonances, distinct transmission spectral resonances are observed, which could be tunable by varying the structural parameters. Furthermore, the metasurfaces are capable of showing high‐efficiency transmission structural colors as a result of structural resonances and intrinsic high transparency of lithium niobate in visible spectral range. The results pave the way for new types of ultracompact photonic devices based on lithium niobate.

Rapid method for fabricating polymeric biconvex parabolic lenslets.

Microlenslets as well as microlens arrays have shown tremendous attractions and successes in miniature optical systems in recent decades. However, the fabrication methods for microlenslets and microlenslet arrays are limited. In this Letter, a rapid and low-cost method for fabricating polymeric biconvex lenslets is presented. This newly developed process is simply based on wetting behavior at interface and is able to produce high-quality biconvex lenslets with controllable size and shape. This technology will greatly simplify the production process and reduce the manufacturing costs for micro-optics.

Goos-Hänchen shift in the miniaturized total internal reflection lens

For certain applications, total internal reflection (TIR) lenses are potentially more effective compared with refractive lenses and reflection mirrors since they permit more light power to go through the optical system. The efficiency of such lenses becomes even more prominent for miniature systems application where light absorption has negligible effect compared with the reflection losses at the interfaces. However, at such scales, the effect of Goos-Hänchen shift that associates the TIR should be accounted for in order to design a proper surface profile of the TIR lenses. It has been shown that a useful design that determines the total internal reflective surface profile can be obtained by solving an ordinary differential equation; such results facilitate realizing effective macro- and micro-scale lenses that are highly useful in integrated optics circuits and miniature optical systems.

Optical Systems for Point-of-care Diagnostic Instrumentation: Analysis of Imaging Performance and Cost

One of the key elements in point-of-care (POC) diagnostic test instrumentation is the optical system required for signal detection and/or imaging. Many tests which use fluorescence, absorbance, or colorimetric optical signals are under development for management of infectious diseases in resource limited settings, where the overall size and cost of the device is of critical importance. At present, high-performance lenses are expensive to fabricate and difficult to obtain commercially, presenting barriers for developers of in vitro POC tests or microscopic image-based diagnostics. We recently described a compact "hybrid" objective lens incorporating both glass and plastic optical elements, with a numerical aperture of 1.0 and field-of-view of 250 μm. This design concept may potentially enable mass-production of high-performance, low-cost optical systems which can be easily incorporated in the readout path of existing and emerging POC diagnostic assays. In this paper, we evaluate the biological imaging performance of these lens systems in three broad POC diagnostic application areas; (1) bright field microscopy of histopathology slides, (2) cytologic examination of blood smears, and (3) immunofluorescence imaging. We also break down the fabrication costs and draw comparisons with other miniature optical systems. The hybrid lenses provided images with quality comparable to conventional microscopy, enabling examination of neoplastic pathology and infectious parasites including malaria and cryptosporidium. We describe how these components can be produced at below $10 per unit in full-scale production quantities, making these systems well suited for use within POC diagnostic instrumentation.

Improved micro-optoelectromechanical systems deformable mirror forin vivooptical microscopy

Micro-optoelectromechanical systems (MOEMS) deformable mirrors are being developed for focus control in miniature optical systems including endoscopic microscopes and small form-factor camera lenses. A new process is described to create membrane mirrors made from the photoset polymer SU-8. The SU-8 also serves as the adhesive layer for wafer bonding, resulting in a simple, low cost fabrication process. The process details and the optical properties of the resulting focus control mirrors, which have a diameter of 2 mm, a stroke in excess of 8 μm and very low residual aberration, are described. Multiple actuation electrodes allow active control of more than 1.4 μm peak-to-peak of wavefront spherical aberration. The MOEMS mirror is demonstrated in a confocal microscope in which it provides focus control during capture of in vivo images.

Radiation distribution of 34-µm immersion LEDs in the far field

This article describes how the far-field radiation distribution and power varies with the geometrical parameters of immersion lenses made from silicon (n¯=3.4) and chalcogenide glass (n¯=2.4) mated with LEDs (λ=3.4µm) based on indium antimonide (n¯=3.5) and estimates the efficiency of using such devices in miniature optical systems.

Non-display bio-optic applications of liquid crystals

Liquid crystal (LC) devices have been largely developed for LC displays and in the last decade for optical telecommunications; however, their application in the field of optical imaging is just starting to emerge. They can be miniaturised and thus have a great potential to be used with miniature optical imaging systems for biomedical applications. LC devices specifically designed for integration into biomedical optical imaging systems are reviewed. Using a combination of a few LC retarders, spectropolarimetric imaging of tissue can be obtained. LC tunable filters with high dynamic range and large throughput are designed for hyperspectral imaging and for spectral domain optical coherence tomography. The designs are based on several concepts, both using the classical stack of retarders and using more modern designs based on single layer in a Fabry–Perot cavity, in a resonant waveguide structure or in a photonic crystal.

Design strategies to simplify and miniaturize imaging systems

We present the range of optical architectures for imaging systems based on a single optical component, an aperture stop, and a detector. Thanks to the formalism of third-order Seidel aberrations, several strategies of simplification and miniaturization of optical systems are examined. Figures of merit are also introduced to assess the basic optical properties and performance capabilities of such systems; by this way, we show the necessary trade-off between simplicity, miniaturization, and optical performance.

Lens integrated with self-aligned variable aperture using pneumatic actuation method

A method based on the combination of elastomeric molding and optofluidic technologies is proposed to realize the integration of pneumatically actuated variable aperture into a lens component for miniature optical systems. The main feature of the assembly is the self-aligning property between lens and aperture. All the structures are fabricated onto a polydimethylsiloxane (PDMS) substrate and the prototype is experimentally demonstrated to possess the self-aligning characteristic without requiring any tuning mechanisms. At the same time, additional tunability of the lens focal length can also be easily obtained with this design concept.