Compact Lens Research Articles

Effects of dual plasticizers for improved PVC gel-based varifocal tiny lens

Abstract Electroactive polyvinyl chloride (PVC) gel-based varifocal lenses are attractive due to their excellent transparency, simple fabrication, compact structure, and good flexibility. In this work, dibutyl adipate (DBA) and propylene carbonate (PC) were utilized to plasticize PVC for fabricating transparent, soft, and flexible gels by solvent casting method. The PVC gels were characterized by various experimental techniques to investigate their optical, electrical, mechanical, and thermal properties. Further, the PVC gels were examined to construct a compact plano-convex tiny lens structure for varifocal lens application under electrical stimulation. The work revealed that the introduction of a co-plasticizer PC improves the overall dielectric property as well as transparency of the PVC gels. The observed enhancement in dielectric constant of the PC incorporated gels increased up to 6 times of the only DBA plasticized PVC gel (D9) while the transmittance value is ~5% higher than that of D9 gel. Moreover, the optimal ratio of DBA and PC in PVC gel was found to be 8.6: 0.4: 1 (wt %) and the optimized D8.6P0.4 gel induces better actuation properties resulting in improved focal length variation for the developed lens. The proposed adaptive tiny lens could change its focal length from 3 mm to 20.5 mm with increasing input voltage from 0 V to 1000 V. The developed tiny lens exhibited excellent optical characteristics including fast response speed and good stability. Moreover, this study broadens the scope for property tuning strategies for the EAP design and application.

Metamaterial-based Luneburg Lens for RF Applications Using Additive Manufacturing

This article takes a detailed look at modeling, simulating, calculating, and fabricating a Luneburg lens using a single material and advanced 3D printing technology. The Luneburg lens is a type of gradient index lens that is spherically symmetrical, which simplifyies its manufacturing process and enhances its structural stability. However, fabrication may be expensive due to the special materials required for manufacturing. Discovering simpler and cost-effective production methods would enable the wider use of Luneburg lenses across various fields. The objective of this study was to use the lens to increase the gain and directivity of antennas at 5.8 GHz while maintaining a compact lens size and using low-cost material, such as ABS-like filament. A single-cell cross-shaped structure was utilized to construct the lens using 3D printing technology.

Directivity Improved Antenna with a Planar Dielectric Lens for Reducing the Physical Size of the On-Vehicle Communication System.

As the physical size of a communication system for satellites or unmanned aerial vehicles demands to be reduced, a compact antenna with high directivity is proposed as a core element essential to the wireless device. Instead of using a horn or an array antenna, a unit planar antenna is combined with a surface-modulated lens to convert a low antenna gain to a high antenna gain. The lens is not a metal-patterned PCB but is dielectric, which is neither curved nor very wide. This palm-sized lens comprises pixels with different heights from the backside of PolyPhenylene Sulfide (PPS) as the dielectric base. The antenna gain from the unit antenna of 4.5 cm × 4.5 cm is enhanced by 10 dB with the help of a compact dielectric lens of 7.5 cm × 7.5 cm at 24.5 GHz as the frequency of interest. The antenna design is verified by far-field measurement as well as near-field observation, including sensing a metal object behind a blocking wall by using an RF test bench. Moreover, antenna performance is understood by making a comparison with conventional designs of antennas in terms of directivity and physical sizes.

Generating optical vortex needle beams with a flat diffractive lens

We present a novel method for generating optical vortex needle beams (focused optical vortices with extended depth-of-focus) using a compact flat multilevel diffractive lens (MDL). Our experiments demonstrate that the MDL can produce focused optical vortices (FOVs) with topological charges l=1−4 (extendable to other l values), maintaining focus over distances significantly longer than conventional optical vortices. Specifically, FOVs exhibit non-diffracting behavior with a depth-of-focus (DOF) extended beyond 5 cm, compared to conventional optical vortices, which show continuous size increase due to diffraction. When the MDL is illuminated by an optical vortex of 3 mm diameter, it achieves a transmission efficiency of approximately 90% and extends the DOF several times beyond that of traditional lenses. Increasing the size of the input optical vortex further extends the DOF but introduces additional rings, with their number increasing proportionally to the value of l. Our approach, validated by both experimental results and numerical simulations, proves effective for beams such as optical vortex and Hermite-Gaussian modes and holds potential applications in high-resolution imaging, material processing, optical coherence tomography, and three-dimensional optical tweezers, offering a simple and efficient solution for generating non-diffracting beams.

Design and characterization of a compact Einzel lens for portable quadrupole mass spectrometry (QMS)

Quadrupole mass spectrometry (QMS) offers better resolution, selectivity and sensitivity than the metal-oxide, field effect transistors and thermal-based gas sensors. However, existing QMS systems are unsuitable for field applications. The miniaturized QMS requires dimensionally scaled components with comparable performance to the conventional bulky systems. For a portable quadrupole mass spectrometry, a compact focusing ion system is required to transfer the maximum number of ions from the ion source to the filter. The present paper discusses the design of a miniature focusing Einzel lens and the effect of design parameters on its performance. The three-cylindrical axially symmetric compact Einzel lens assembly was designed using commercially available software. The relationship between the design parameters is explored for compact and low-powered ion optics. The beam focal length was tuned by varying the bias voltage. The dimensions, as well as voltages across the Einzel lens, were reduced significantly to open a new way for portable point-of-care applications. At an applied voltage of 70 V, the focal length of the ions is 11 mm without being scattered, which is favorable for a portable quadrupole mass filter. The designed Einzel lens was fabricated using micromachining techniques and characterized at a vacuum of 3.05 × 10−4 mbar. The developed lens system shows a current output of 0.114 µA at 72 V lens voltage. A current of 94.8 µA is observed with a background noise of 0.01 µA for the system with nitrogen (28 amu) as the sample.

Compact Chromatic Confocal Lens with Large Measurement Range.

Spectral confocal sensors are effective for measuring displacements. The core of the spectral confocal measurement system is a dispersive objective lens that uses optical dispersion to establish a one-to-one correspondence between the focusing position and wavelength, achieving high-resolution measurements in the longitudinal direction. Despite significant progress in dispersive objective lenses for spectral confocal sensor systems, challenges such as a limited dispersion range, high cost, and insufficient measurement accuracy persist. To expand the measurement range and improve the accuracy of the spectral confocal sensor, we designed a compact, long-axial dispersion objective lens. This lens has a simple structure that requires only six lens elements, two of which form cemented doublets. The system length is 58 mm, with a working distance of 46 ± 6 mm and a dispersion range of 12 mm within the wavelength range of 450-656 nm. The lens has an object-side numerical aperture (NA) of 0.22 and an image-side NA between 0.198 and 0.24, ensuring high light energy utilization. Finally, a spectral confocal measurement system was constructed based on the designed dispersive objective lens, and performance evaluation tests were conducted. The test results showed that the system achieved a resolution of 0.15 μm and a maximum linear error of ±0.7 μm, demonstrating high-precision measurement capabilities. The proposed lens design enables the development of more portable and cost-effective spectral confocal sensors.

A design of compact plasmonic lens consisting of high index dielectric gratings and metal nano-film

In this paper, a hybrid ultra-thin planar subwavelength focusing structure consisting of a high refractive index dielectric grating and a nano metal film was designed. The thickness of this structure is only 200 nm. Surface plasmon polaritons (SPPs) were excited from the nano metal film, propagated along the metal-air interface, and were then converted into a radiation field by the dielectric grating, forming a focused spot in free space. By adjusting the grating position and width parameters, the shape of the focused optical field could be controlled. The simulation results showed that, under 532 nm light irradiation, the lens could produce a 270 nm (full width at half-maximum, FWHM) spot size at a focal length of 2.46λ. Moreover, under the illumination of 633 nm and 780 nm light, the designed lenses were found to produce focal spot sizes of 304 nm (0.48λ) and 364 nm (0.47λ), respectively, which were smaller than the diffraction limit. The simplicity of this plasmonic lens design, coupled with its reduced thickness and minimal absorption loss, offered significant advantages in terms of cost-effectiveness and ease of fabrication.

Differentiable design of a double-freeform lens with multi-level radial basis functions for extended source irradiance tailoring

Freeform optics are key for generating prescribed illumination patterns from given sources, which are crucial for solid-state lighting and machine vision illumination. There is an increasing demand for compact freeform optics, which presents a substantial challenge for current design methods since the source dimensions must be considered. Most current extended-source design methods, although requiring profound knowledge of optics and mathematics, focus on the modest goal of obtaining uniform irradiance distributions. We address a more challenging design problem of generating an irradiance distribution of arbitrary shape through a double-freeform lens that can fully encompass the extended source. We propose a differentiable design method whose uniqueness lies in the representation of the double-freeform surfaces using multi-level spherical radial basis functions, which has a natural link to a multi-scale optimization technique. In addition, we employ a sequential unconstrained minimization technology complemented with Lagrange multipliers that add key feasibility constraints on lens shape and size. The proposed method is flexible, general, and efficient in designing highly compact freeform lenses for generating both simple and complex irradiance distributions, as demonstrated through the design examples. This could enable a universal solution to the extended-source design problem.

Disentangling the Black Hole Mass Spectrum with Photometric Microlensing Surveys

From the formation mechanisms of stars and compact objects to nuclear physics, modern astronomy frequently leverages surveys to understand populations of objects to answer fundamental questions. The population of dark and isolated compact objects in the Galaxy contains critical information related to many of these topics, but is only practically accessible via gravitational microlensing. However, photometric microlensing observables are degenerate for different types of lenses, and one can seldom classify an event as involving either a compact object or stellar lens on its own. To address this difficulty, we apply a Bayesian framework that treats lens type probabilistically and jointly with a lens population model. This method allows lens population characteristics to be inferred despite intrinsic uncertainty in the lens class of any single event. We investigate this method’s effectiveness on a simulated ground-based photometric survey in the context of characterizing a hypothetical population of primordial black holes (PBHs) with an average mass of 30M ⊙. On simulated data, our method outperforms current black hole (BH) lens identification pipelines and characterizes different subpopulations of lenses while jointly constraining the PBH contribution to dark matter to ≈25%. Key to robust inference, our method can marginalize over population model uncertainty. We find the lower mass cutoff for stellar origin BHs, a key observable in understanding the BH mass gap, particularly difficult to infer in our simulations. This work lays the foundation for cutting-edge PBH abundance constraints to be extracted from current photometric microlensing surveys.

A compact wide-angle DUV lens suitable for SO2 monitoring

We report the design and development of a compact wide-angle deep ultraviolet (DUV) lens suitable for sulfur dioxide (SO2) monitoring. The lens (focal length = 10 mm, F-number = 4, full field of view = 35°) is made of synthetic quartz (SiO2, SQ) glass, sapphire (Al2O3) crystal, and calcium fluoride (CaF2) crystal whose dimensions are optimized for 290–320 nm wavelengths. Compared to a conventional doublet lens with the same focal length, F-number, and full field of view, our design exhibits slight vignetting and peripheral astigmatism but with corrected chromatic aberrations, smaller focal shifts (127 µm), tighter spot sizes (19–24 µm), and better image resolution and contrast (modulation transfer function, MTF ≥ 0.4). The lens properties have also been confirmed experimentally with the fabrication and evaluation of an actual lens based on our design. The actual lens exhibits a barrel-type distortion of 3.3 %, relative illumination of 94–100 % at 0–5° field angles, and a tangential MTF performance curve similar to what are expected from the design. Our compact lens is shown to exhibit better properties than conventional lenses and promises better performance in wide-angle DUV imaging applications, especially for SO2 detection.

Unveiling the properties of liquids via photothermal-induced diffraction patterns

The interaction of a laser with a liquid can cause temperature changes in the liquid from which some properties of the latter can be indirectly obtained. However, from just temperature changes, a sample cannot be identified. Here, we report on the interaction of tightly focused femtosecond infrared light into secondary hydrogen-bonded liquids like water, organic compounds, and binary mixtures. Such interaction induces a local change in the sample’s index of refraction. The latter alters the wavefront of a white-light probe beam, giving rise to unique diffraction patterns that can be observed in the far field. The specific diffraction patterns may be considered as the optical signatures or fingerprints of the liquids studied. The technique proposed here is noninvasive and simple to implement with commercially available supercontinuum sources and digital cameras. Thus, it may be useful for the development of compact thermal lens spectroscopic instruments for a number of practical applications.

Higher order wavefront correction and axial scanning in a single fast and compact piezo-driven adaptive lens.

We present a compact adaptive glass membrane lens for higher order wavefront correction and axial scanning, driven by integrated segmented piezoelectric actuators. The membrane can be deformed in a combination of rotational symmetry providing focus control of up to ± 6 m-1 and spherical aberration correction of up to 5 wavelengths and different discrete symmetries to correct higher order aberrations such as astigmatism, coma and trefoil by up to 10 wavelengths. Our design provides a large clear aperture of 12 mm at an outer diameter of the actuator of 18 mm, a thickness of 2 mm and a response time of less than 2 ms.

A Wideband GRIN Dielectric Lens Antenna for 5G Applications.

This paper proposes a graded effective refractive indexes (GRIN) dielectric lens for 5G applications. The inhomogeneous holes in the dielectric plate are perforated to provide GRIN in the proposed lens. The constructed lens employs a collection of slabs that correspond to the specified graded effective refractive index. The thickness and the whole lens dimensions are optimized based on designing a compact lens with optimum lens antenna performance (impedance matching bandwidth, gain, 3 dB beamwidth, and sidelobe level). A wideband (WB) microstrip patch antenna is designed to be operated over the entire band of interest from 26 GHz to 30.5 GHz. For the 5G mm-wave band of operation, the behavior of the proposed lens along with a microstrip patch antenna is analyzed at 28 GHz for various performance parameters, including impedance matching bandwidth, 3 dB beamwidth, maximum gain, and sidelobe level. It has been observed that the antenna exhibits good performance over the entire band of interest in terms of gain, 3 dB beamwidth, and sidelobe level. The numerical simulation results are validated using two different simulation solvers. The proposed unique and innovative configuration is well-suited for 5G high gain antenna solutions with a low-cost and lightweight antenna structure.

Extreme amplification regimes of the Schwarzschild gravitational lens

We investigated a complete set of relativistic images of a small source located at an arbitrary distance from a Schwarzschild black hole gravitational lens. This paper offers a description of a simple and efficient fully relativistic method for calculating the bolometric intensity amplification. We focused our analysis primarily on sources located at small radii and close angular distance from the caustic line, both behind and in front of the compact lens. We term the corresponding large deflection regime ‘extreme lensing’. We approximated the regime of fully-relativistic, extreme amplification of point sources by simple analytical formulae valid over a wide range of source distances. Using such approximations, we also derived formulae for the maximum amplification of extended sources close to or intercepted by the caustic line. Simple analytical approximations of the time delay between the brightest consecutive images in extreme amplification regimes are also presented.

Tailoring freeform beam-shaping lenses for edge-emitting lasers

The edge-emitting laser diodes (EELs) are widely used in various applications, however, the strongly asymmetric beam profile along the fast and slow axes gives a big challenge to the beam shaping of EEL. Traditional optical devices mainly focus on adjusting the asymmetric divergence angle of the fast and slow axes of the EEL, and it is difficult to achieve flexible and precise control of the luminous distribution of the EEL due to the limited freedom of the conventional beam-shaping element. In this article, we employ freeform lenses to flexibly reshape EEL beams and develop an approach to tackle the obstacles caused by the strongly asymmetric beam profile by generalizing the Monge–Ampère method to tailor freeform beam-shaping lenses. Three typical but challenging beam-shaping tasks show that both the intensity and wavefront of an EEL beam can be reshaped in a desired manner by using a single compact freeform lens without any symmetric restrictions on the architecture of the beam-shaping system.

Compact and Lightweight Additive Manufactured Parallel-Plate Waveguide Half-Luneburg Geodesic Lens Multiple-Beam Antenna in the K$_{\mathrm{a}}$-Band

In this letter, a parallel-plate waveguide half-Luneburg geodesic lens multiple-beam antenna optimized for additive manufacturing is designed and validated experimentally in the K <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{\mathrm{a}}$</tex-math></inline-formula> -band. Two prototypes were manufactured in AlSi <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{10}$</tex-math></inline-formula> Mg through laser powder-bed fusion and measured in an anechoic chamber. The compact and lightweight prototype optimized for additive manufacturing demonstrates excellent RF performance while significantly reducing mass and mechanical complexity. Specifically, misalignment errors present in previous studies are solved, improving sidelobe level by up to 10 dB. A maximum realized gain of 22.1 dBi is measured at 28 GHz. This single-piece, compact, and lightweight design is particularly attractive for applications having mass restrictions and limited space like millimeter-wave systems on board small satellites.

A Novel Methodology for Lens Matching in Compact Lens Module Assembly

Lens matching is a trial assembly step in compact lens module manufacturing that can effectively improve the production yield and compensate for the manufacturing error to some degree. However, conventional lens matching (i.e., through trial and error (T&E)) is extremely time-consuming and has a low success rate. To address this issue, this paper proposes a novel Genetic Algorithm (GA) based solution to improve the assembly success rate and the efficiency of lens matching. The study first formalizes the lens matching problem into an optimization format. Then, a DNN based surrogate model is built to replace expensive optical simulators in the optimization iterations. The DNN is used because it demonstrates a great balance between prediction accuracy and computation efficiency compared to other alternatives, e.g., Linear Regression (LR), Kriging, and Polynomial Chaos Expansion (PCE). Next, a GA-based solver is developed to find optimal lens matching operations. The effectiveness of the proposed method and its superiority over conventional lens matching is validated in the real-world lens production line through collaboration with the industry. Compared with conventional lens matching, the proposed method can significantly improve the production yield and lens matching efficiency. Note to Practitioners—This paper is motivated by a practical need for lens matching in the manufacturing process of the image capturing compact lens modules. The conventional practice of lens matching is tedious, time-consuming, and easy to fail. To address this issue, we mathematically characterize the lens matching problem into an optimization format that can practically be solved by the Genetic Algorithm (GA) or other methods. We then demonstrate the workflow to search for optimal lens matching solutions based on a DNN surrogate model. Simulative studies and preliminary real-world experiments indicate the proposed method can effectively improve overall production yield and is much more efficient than conventional lens matching. The results in mass production further justified the superiority of the proposed method over conventional lens matching.

Compact Multifunctional Gain Enhancing GRIN Lens for Widely Separated Frequency Band Shared Aperture Antennas

AbstractGradient index (GRIN) lenses embody a powerful technology that enables control of electromagnetic wave propagation over wide frequency bands. However, GRIN lenses that achieve multifunctional (i.e., dual broadband) performance have not been realized mainly due to the limitations of conventional techniques such as Transformation Optics (TO). This paper proposes a multi‐objective inverse‐design approach for the optimization of multi‐band GRIN lenses with highly constrained aperture sizes. A candidate lens design is fabricated from a ceramic material using a new additive manufacturing approach allowing for spatially‐varying permittivities between 2–6.5 to be achieved at sub‐cm resolution. Measured results validate the candidate functionalized ceramic GRIN lens's simulated multi‐band performance and demonstrate the efficacy of the proposed inverse‐design procedure.

Compact Long-Axial Dispersive Chromatic Confocal Lens

Compact Long-Axial Dispersive Chromatic Confocal Lens

Design of compact telephoto mobile phone lens based on freeform surface (invited)

Design of compact telephoto mobile phone lens based on freeform surface (invited)