Doublet Lens Research Articles

A novel design of the electrostatic storage ring using quadrupole deflector

A novel electrostatic storage ring (ESR) design was created using an electrostatic quadrupole deflector (EQD) and quadrupole doublet lens (QDL). EQD was used to turn the electron beam 90 degrees in order to create an innovative ESR design. The impact of EQD designs on ESR performance was investigated, and the results showed that the performance of ESR was directly affected by the EQD design. The calculations showed that increasing the EQD diameter by 20% led to an enhancement in the electron beam dimensions by 88% for ∆x and 44% for ∆y for the initial angle of the electron beam α = 0.2°. Also, the design achieved its goal of keeping kinetic energy constant, where for an initial kinetic energy of 1000 eV, the difference between the energy of the injected electron beam and the emerging electron beam from the ESR is approximately 1–5 eV, i.e., despite changing the diameter of the EQD, the dimensions of the electron beam improve and the kinetic energy remains constant.

Diffractive microoptics in porous silicon oxide by grayscale lithography

We demonstrate focusing as well as imaging using diffractive microoptics, manufactured by two-photon polymerization grayscale lithography (2GL), that have been 3D printed into porous silicon oxide. While typical doublet lens systems require support structures that hold the lenses in place, our optics are held by the porous media itself, decreasing both the fabrication time and design constraints while increasing the optically active area. Compared to the typical two-photon polymerization fabrication process, 2GL offers better shape accuracy while simultaneously increasing throughput. To showcase 2GL manufactured optics in porous media, we fabricate singlet diffractive lenses with a diameter of 500 µm and numerical apertures of up to 0.6. We measure the intensity distribution in the focal plane, and along the optical axis. Furthermore, we design and fabricate a doublet lens system for imaging purposes with a diameter of 600 µm and thinner than 60 µm. We examine the imaging performance with a USAF 1951 resolution test chart and determine the resolution to be 287 lp/mm. 3D printing in porous SiO2 thus holds great promise for future complex and unconventional microoptical solutions.

A Simple Doublet Lens Design for Mid-Infrared Imaging.

Wide-field mid-infrared (MIR) hyperspectral imaging offers a promising approach for studying heterogeneous chemical systems due to its ability to independently characterize the molecular properties of different regions of a sample. However, applications of wide-field MIR microscopy are limited to spatial resolutions no better than ∼1 μm. While methods exist to overcome the classical diffraction limit of ∼λ/2, chromatic aberration from transmissive imaging reduces the achievable resolution. Here we describe the design and implementation of a simple MIR achromatic lens combination that we believe will aid in the development of resolution-enhanced wide-field MIR hyperspectral optical and chemical absorption imaging. We also examine the use of this doublet lens to image through polystyrene microspheres, an emerging and simple means for enhancing spatial resolution.

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.

Bichromatic UV detection system for atomically-resolved imaging of ions.

We present a compact bichromatic imaging system, located outside of the vacuum chamber of a trapped ion apparatus that collects the fluorescence of 230.6 and 369.5nm photons simultaneously on a shared electron-multiplying charge-coupled device (EMCCD) camera. The system contains two lens doublets, consisting of a sphere and an asphere. They provide a numerical aperture of 0.45 and 0.40 at 230.6 and 369.5nm, respectively, and enable spatially resolved state detection with a large field of view of 300 μm for long 115In+/172Yb+ Coulomb crystals. Instead of diffraction-limited imaging for one wavelength, the focus in this system is on simultaneous single-ion resolved imaging of both species over a large field, with special attention to the deep UV wavelength (230.6nm) and the low scattering rate of In+ ions. The introduced concept is applicable to other dual-species applications.

Development of a Tomography Camera System with a Doublet Lens Unit for Supersonic Collisional Merging Formation of FRC

Development of a Tomography Camera System with a Doublet Lens Unit for Supersonic Collisional Merging Formation of FRC

Extreme Refractive-, Diffractive- and Hybrid-Hyperchromats: Minimizing the Equivalent Abbe Number of a Two-Lens System

This work provides a comprehensive analysis of the maximum chromatic axial split of two-element hyperchromats, with the distance between the two lenses being a key variable. Purely refractive and diffractive systems are considered, as well as hybrid layouts combining refractive and diffractive elements. In order to achieve extreme chromatic axial splitting and accordingly a minimum equivalent Abbe number for lens combinations, a three-step procedure was used. In the first paraxial step, purely optical quantities such as focal lengths of the lenses, inter-lens distances and dispersion properties of the lenses were investigated. In the second step, which also takes place in the paraxial domain, additional geometric boundary conditions such as the radii, diameters and thicknesses of the lenses are taken into account. The results of this step serve as an input for the final optimization using optical design software, which derives practical solutions for minimum equivalent Abbe numbers with diffraction-limited image quality. As a significant result, the comparison with directly cemented lens doublets shows that the introduction of a distance between the elements allows for a much stronger chromatic decomposition for refractive, diffractive and also hybrid combinations. Quantitatively, the minimum equivalent Abbe number for refractive systems is reduced from 2.5 (without spacing) to 1.79 (with spacing). For hybrid combinations, a corresponding reduction from 0.4 to 0.29 is achieved.

Large field-of-view short-wave infrared metalens for scanning fiber endoscopy.

The scanning fiber endoscope (SFE), an ultrasmall optical imaging device with a large field-of-view (FOV) for having a clear forward view into the interior of blood vessels, has great potential in the cardiovascular disease diagnosis and surgery assistance, which is one of the key applications for short-wave infrared biomedical imaging. The state-of-the-art SFE system uses a miniaturized refractive spherical lens doublet for beam projection. A metalens is a promising alternative that can be made much thinner and has fewer off-axis aberrations than its refractive counterpart. We demonstrate a transmissive metalens working at 1310nm for a forward viewing endoscope to achieve a shorter device length and better resolution at large field angles. We optimize the metalens of the SFE system using Zemax, fabricate it using e-beam lithography, characterize its optical performances, and compare them with the simulations. The SFE system has a resolution of at the center of field (imaging distance 15mm), an FOV of , and a depth-of-focus of , which are comparable with a state-of-the-art refractive lens SFE. The use of the metalens reduces the length of the optical track from 1.2 to 0.86mm. The resolution of our metalens-based SFE drops by less than a factor of 2 at the edge of the FOV, whereas the refractive lens counterpart has a times resolution degradation. These results show the promise of integrating a metalens into an endoscope for device minimization and optical performance improvement.

Study of irregular electron beam correcting permanent-magnet-quadrupole doublet lens for irradiation accelerator.

In this paper, a permanent-magnet-quadrupole doublet lens with strong-focusing is designed and manufactured. Such an instrument could solve the problem of irregular beam spots produced by the weak focusing of conventional solenoid-focusing systems in low-energy electron irradiation accelerators. It could provide a better and more appropriate initial beam spot before the beam enters the subsequent magnetic spreading system or magnetic scanning system, thus, improving the irradiation uniformity. The association of the parameters of the rectangular permanent magnet with the quadrupole magnetic field is investigated. Focusing results, obtained using irregular beam spots with different profiles and different energies, and magnetic field measurement results, both from the instrument, verify the engineering feasibility of this permanent-magnet-quadrupole doublet lens.

Complex aspherical singlet and doublet microoptics by grayscale 3D printing.

We demonstrate 3D printed aspherical singlet and doublet microoptical components by grayscale lithography and characterize and evaluate their excellent shape accuracy and optical performance. The typical two-photon polymerization (2PP) 3D printing process creates steps in the structure which is undesired for optical surfaces. We utilize two-photon grayscale lithography (2GL) to create step-free lenses. To showcase the 2GL process, the focusing ability of a spherical and aspherical singlet lens are compared. The surface deviations of the aspherical lens are minimized by an iterative design process and no distinct steps can be measured via confocal microscopy. We design, print, and optimize an air-spaced doublet lens with a diameter of 300 µm. After optimization, the residual shape deviation is less than 100 nm for the top lens and 20 nm for the bottom lens of the doublet. We examine the optical performance with an USAF 1951 resolution test chart to find a resolution of 645 lp/mm.

Analytical Formulas for Refractive Indices of a Telescopic GRIN Lens for Aperture Magnification

In this letter, we derive a new closed-form analytical formula for the refractive index of a telescopic lens based on inhomogeneous graded index (GRIN) material. The telescopic lens is composed of two cylindrical confocal GRIN lenses, one divergent and one convergent. The scope of the telescopic lens is to magnify the aperture of a flat antenna placed at the first interface of the divergent-convergent lens doublet. This telescopic GRIN lens is useful for reusing already available medium-gain arrays and bring them to a high-gain, occupying a reduced volume as compared to traditional lenses or multireflector systems. The formulation used here is based on the solution of a regularized ray-congruence integral equation recently introduced by the authors, and applied in a previous work to treat convergent cylindrical GRIN lenses. The formulation is extended here to the case of a telescopic lens leading to analytical formulas for the two inhomogenous refractive indexes that involve five independent parameters; these parameters are eventually optimized to get the maximum gain boost.

Split achromatic doublet problem and lens element centering in a drop-in barrel

A split doublet is more sensitive to aberration because the inner surfaces are typically strong in curvature and can independently misalign. To improve the centering of a lens element, we discuss using a strip of material inserted in the gap between the lens edge and the barrel. This technique has the benefit of relaxing the barrel inner diameter tolerance. Four examples are provided where lens centering was estimated to range between 0.025 and 0.050 mm.

Hyperchromatic lens doublets with an extremely small equivalent Abbe number employing diffractive elements and refractive materials with exceptional dispersion properties.

Hyperchromatic systems are characterized by strong longitudinal chromatic aberrations that are quantitatively described by very small equivalent Abbe numbers. In this contribution, doublet systems are systematically studied with the aim of obtaining extreme values for the equivalent Abbe numbers. Both purely refractive combinations and hybrid systems of diffractive and refractive components are considered. Chromatic axial splitting is determined as a function of the optical powers of the individual components as well as the dispersion properties of the materials involved. In order to determine actual implementable configurations for extremely small equivalent Abbe numbers, a systematic ray-trace analysis is performed in addition to paraxial studies, taking into account geometric constraints on lens curvatures and considering also complete, continuous dispersion curves. As extreme values for systems with appropriate imaging quality, an equivalent Abbe number of υ~=-2.5 is obtained for the purely refractive approach, and υ~=0.4 for the hybrid case, which is more than 8 times smaller than the absolute value of a single diffractive lens.

Coupling light emission of single-photon sources into single-mode fibers: mode matching, coupling efficiencies, and thermo-optical effects.

We discuss the coupling efficiency of single-photon sources into single-mode fibers using 3D printed micro-optical lens designs. Using the wave propagation method, we optimize lens systems for two different quantum light sources and assess the results in terms of maximum coupling efficiencies, misalignment effects, and thermo-optical influences. Thereby, we compare singlet lens designs with one lens printed onto the fiber with doublet lens designs with an additional lens printed onto the semiconductor substrate. The single-photon sources are quantum dots based on microlenses and circular Bragg grating cavities at 930 nm and 1550 nm, respectively.

Performance evaluation of free space optics communication system in the scenario of triple play service using probabilistic shaping scheme

An advanced triple-play-services (TPS) system based on probabilistic shaping (PS) scheme for free- space-optical (FSO) communication network is proposed and experimentally demonstrated for the first time. In this paper, the PS-32-quadrature amplitude modulation (QAM) 10 Gb/s data, PS-32-QAM 10 Gb/s voice and PS based 2.5 Gb/s HDTV signal are successfully transmitted over 600-m FSO link employing doublet lens scheme. The PS and polarization multiplexing technique both are helped to upgrade the spectral efficiency and improve the system performance. Normalized-generalized-mutual-information (NGMI) threshold is 0.92 at FEC code rate 9/10 for voice/data and 0.82 at FEC code rate 4/5 for video signal are selected to successfully execute the experiment. The spectral efficiency of our system is achieved by calculating the NGMI and shaping parameter (α), 13.6 bits/s/Hz (voice and data) and 10.41 bits/s/Hz (video) spectral efficiency are obtained at maximum α. Experimental results prove that PS based FSO communication system provides flexible data rate and greater spectrum efficiency and also be a powerful candidate to alleviate pressure on modern optical transport system.

Near-infrared doublet zoom lens based on Ge2Sb2Te5 metasurface

Although numerous studies showcase the capability of metalenses to serve as crucial elements of miniaturized optical systems, tunable focusing remains an ongoing challenge. Here, we propose a doublet zoom lens based on a Ge2Sb2Te5 (GST) metasurface at a wavelength of 1.55 μm. Multistep zooming is realized by the joint control of incident circular polarization inversion and GST phase transition. Three tight focal spots, 0.91 λ, 1.09 λ and 0.89 λ, are achieved from the composite lens. The devised highly-integrated doublet lens, with advantages such as as being multi-foci, easily operated and responding quickly, can find applications in fields that require ultracompact zoom imaging and beam focusing.

Enabling consumer-grade 3D-printed optical instruments – a case study on design and fabrication of a spectrometer system using low-cost 3D printing technologies

3D printing of optical components can broaden access to optical fabrication. However, consumer options for 3D printing have been limited due to the form and roughness requirements for optics. Previous efforts have established a protocol for the fabrication of singlet lenses using a stereolithographic printer and simple post-processing techniques. Here we further elevate this research by building a consumer-grade 3D printed spectrometer utilizing achromatic doublet printed lenses. These lenses are fabricated using stereolithographic printers with a filled cavity and reduce chromatic focal shift by a factor of 6 over singlet lenses. The proof-of-concept spectrometer system incorporates a pinhole, two doublet lenses, and a dispersing prism. Opto-mechanics for the system were fabricated using an FDM 3D printer. Results from the fabricated system closely matched results obtained with a commercially available spectrometer device.

MEMS-tunable dielectric metasurface lens using thin-film PZT for large displacements at low voltages.

Tunable focusing is a desired property in a wide range of optical imaging and sensing technologies but has tended to require bulky components that cannot be integrated on-chip and have slow actuation speeds. Recently, integration of metasurfaces into electrostatic micro-electromechanical system (MEMS) architectures has shown potential to overcome these challenges but has offered limited out-of-plane displacement range while requiring large voltages. We demonstrate for the first time, to the best of our knowledge, a movable metasurface lens actuated by integrated thin-film PZT MEMS, which has the advantage of offering large displacements at low voltages. An out-of-plane displacement of a metasurface in the range of 7.2 μm is demonstrated under a voltage application of 23 V. This is roughly twice the displacement at a quarter of the voltage of state of the art electrostatic out-of-plane actuation of metasurfaces. Using this tunability, we demonstrate a varifocal lens doublet with a focal shift of the order of 250 μm at the wavelength 1.55μm. The thin-film PZT MEMS-metasurface is a promising platform for miniaturized varifocal components.

Influence on wide-angle doublet metalenses due to different types of all-dielectric metasurfaces.

It has been shown in previous literature that nearly diffraction limited focusing is possible by a doublet metalens up to almost 30 deg. This result indicates that metalenses can work well, even at oblique incidence. Although various meta-atoms have been proposed, as far as we know, there is no report that compares what kind of meta-atom is robust against oblique incidence. Here, we first numerically calculated the incident angle dependence of the three types of meta-atoms. The results show that the waveguide-type structure is the most robust to oblique incidence. Next, we performed rigorous electromagnetic simulations for the cylindrical doublet metalenses to compare the micropost type and waveguide type. These results indicate that a waveguide-type metasurface further improves the off-axis performance of the doublet lens previously introduced.

Confocal fluorescence microscopy with high-NA diffractive lens arrays.

Traditionally, there is a trade-off between the numerical aperture and field of view for a microscope objective. Diffractive lens arrays (DLAs) with overlapping apertures are used to overcome such a problem. A spot array with an NA up to 0.83 and a pitch of 75 µm is produced by the proposed DLA at a wavelength of 488 nm. By measurement of the fluorescence beads, the DLA-based confocal setup shows the capability of high-resolution measurement over an area of 3mm×3mm with a 2.5×0.07NA objective. Further, the proposed fluorescence microscope is insensitive to optical aberrations, which has been demonstrated by imaging with a simple doublet lens.