Showing papers on "Lens (optics) published in 2021"

A soft and transparent contact lens for the wireless quantitative monitoring of intraocular pressure.

Abstract: Continuous detection of raised intraocular pressure (IOP) could benefit the monitoring of patients with glaucoma. Current contact lenses with embedded sensors for measuring IOP are rigid, bulky, partially block vision or are insufficiently sensitive. Here, we report the design and testing in volunteers of a soft and transparent contact lens for the quantitative monitoring of IOP in real time using a smartphone. The contact lens incorporates a strain sensor, a wireless antenna, capacitors, resistors, stretchable metal interconnects and an integrated circuit for wireless communication. In rabbits, the lens provided measurements that match those of a commercial tonometer. In ten human participants, the lens proved to be safe, and reliably provided accurate quantitative measurements of IOP without inducing inflammation.

Electrohydrodynamic Printing of a Dielectric Elastomer Actuator and Its Application in Tunable Lenses

Abstract: Optical lenses driven by dielectric elastomer (DE) actuators with tunable focal lengths are presented here. They are inspired by the architecture of the crystalline lens and the ciliary muscle of the human eye and have prompted a growing interest. The most commonly used DEs in tunable lenses have often required highly transparent films and also the need to encapsulate clear liquid silicone to act as the lens. There is a restriction on the properties of the tunable lens imposed by materials limitations. Here, the fabrication of a fully 3D printed tunable lens with an inhomogeneous structure is described. It exhibited a 29% change in focal length from 33.6 mm to 26.1 mm under a dynamic driving voltage signal control. Furthermore, it displayed excellent stability when the focal length was tuned from far to near (30.1 mm to 25.3 mm) for 200 cycles. The tunable lens obtained mimics the working principle of the human eye in auto adjusting the focal length and has evident potential applications in imaging, information storage, beam steering and bifocal technology.

Integrated contact lens sensor system based on multifunctional ultrathin MoS2 transistors.

Abstract: Summary Smart contact lenses attract extensive interests due to their capability of directly monitoring physiological and ambient information. However, previous demonstrations usually lacked efficient sensor modalities, facile fabrication process, mechanical stability, or biocompatibility. Here, we demonstrate a flexible approach for fabrication of multifunctional smart contact lenses with an ultrathin MoS2 transistors-based serpentine mesh sensor system. The integrated sensor systems contain a photodetector for receiving optical information, a glucose sensor for monitoring glucose level directly from tear fluid, and a temperature sensor for diagnosing potential corneal disease. Unlike traditional sensors and circuit chips sandwiched in the lens substrate, this serpentine mesh sensor system can be directly mounted onto the lenses and maintain direct contact with tears, delivering high detection sensitivity, while being mechanically robust and not interfering with either blinking or vision. Furthermore, the in vitro cytotoxicity tests reveal good biocompatibility, thus holding promise as next-generation soft electronics for healthcare and medical applications.

Electrically Actuated Varifocal Lens Based on Liquid-Crystal-Embedded Dielectric Metasurfaces.

Abstract: Compact varifocal lenses are essential to various imaging and vision technologies. However, existing varifocal elements typically rely on mechanically actuated systems with limited tuning speeds and scalability. Here, an ultrathin electrically controlled varifocal lens based on a liquid crystal (LC) encapsulated dielectric metasurface is demonstrated. Enabled by the field-dependent LC anisotropy, applying a voltage bias across the LC cell modifies the local phase response of the silicon meta-atoms, in turn modifying the metalens focal length. In a numerical implementation, a voltage-actuated metalens with continuous zoom and up to 20% total focal shift is demonstrated. The LC-based metalens concept is experimentally verified through the design and fabrication of a bifocal metalens that facilitates high-contrast switching between two discrete focal lengths upon application of a 9.8 Vpp voltage bias. Owing to their ultrathin thickness and adaptable design, LC-driven dielectric metasurfaces open new opportunities for compact varifocal lensing in a diversity of modern imaging applications.

Myopia control effect of defocus incorporated multiple segments (DIMS) spectacle lens in Chinese children: results of a 3-year follow-up study

Abstract: Aims To determine myopia progression in children who continued to wear the defocus incorporated multiple segments (DIMS) lenses or switched from single vision (SV) to DIMS lenses for a 1-year period following a 2-year myopia control trial. Methods 128 children participated in this study. The children who had worn DIMS lenses continued to wear DIMS lenses (DIMS group), and children who had worn SV lenses switched to wear DIMS lenses (Control-to-DIMS group). Cycloplegic spherical equivalent refraction (SER) and axial length (AL) were measured at 6-month interval. Historical controls were age matched to the DIMS group at 24 months and used for comparing the third-year changes. Results Over 3 years, SER and AL changes in the DIMS group (n=65) were −0.52±0.69D and 0.31±0.26 mm; these changes were not statistically significant over time (repeated measures analysis of variance, p>0.05). SER (−0.04±0. 38D) and AL (0.08±0.12 mm) changes in the Control-to-DIMS group (n=55) in the third year were less compared with the first (mean difference=0.45 ± 0.30D, 0.21±0.11 mm, p Changes in SER and AL in both groups over that period were significantly less than in the historical control group (DIMS vs historical control: mean difference=−0.18±0.42D, p=0.012; 0.08±0.15 mm, p=0.001; Control-to-DIMS versus historical control: adjusted mean differences=−0.30±0.42D, p Conclusions Myopia control effect was sustained in the third year in children who had used the DIMS spectacles in the previous 2 years and was also shown in the children switching from SV to DIMS lenses.

A Compact Beamsteering Metasurface Lens Array Antenna With Low-Cost Phased Array

Abstract: A metasurface (MTS) lens array (MLA) fed by a phased array with less phase shifters (PSs) is proposed for compact low-cost beamsteering applications. By dividing a single-large-aperture lens into $N$ small-aperture lens elements with the focus-to-diameter ratio of a lens antenna unchanged, the overall thickness of the proposed antenna is reduced by $N$ times. The beamsteering is achieved in two steps. First, the main beam direction of MLA antenna is switched over a large angular step by shifting the feeding antennas beneath each lens element. Then, the switched beams are fine steered by a low-cost $N$ -element phased array. Theoretical analysis using array theory is performed to work out a general design method with discussion on the taper and spillover effect of feed-power pattern on the lens array. Based on the proposed method, a three-lens linear MLA fed by a phased array is designed to operate at 10 GHz. The proposed antenna achieves a 3 dB beamwidth coverage range of ±30° with a beam crossing level higher than −3 dB and a gain tolerance of 1.6 dB with a maximum gain of 19.1 dBi. The presented antenna can be used to achieve volumetric beamsteering performance directly. The proposed design features the merits of higher gain, lower cost, simpler feeding network, less PSs, and lower profile compared with conventional full phased arrays and single-aperture lens antennas.

Gold Nanocomposite Contact Lenses for Color Blindness Management.

Abstract: Color vision deficiency (CVD) is an ocular congenital disorder that affects 8% of males and 0.5% of females. The most prevalent form of color vision deficiency (color blindness) affects protans and deutans and is more commonly known as "red-green color blindness". Since there is no cure for this disorder, CVD patients opt for wearables that aid in enhancing their color perception. The most common wearable used by CVD patients is a form of tinted glass/lens. Those glasses filter out the problematic wavelengths (540-580 nm) for the red-green CVD patients using organic dyes. However, few studies have addressed the fabrication of contact lenses for color vision deficiency, and several problems related to their effectiveness and toxicity were reported. In this study, gold nanoparticles are integrated into contact lens material, thus forming nanocomposite contact lenses targeted for red-green CVD application. Three distinct sets of nanoparticles were characterized and incorporated with the hydrogel material of the lenses (pHEMA), and their resulting optical and material properties were assessed. The transmission spectra of the developed nanocomposite lenses were analogous to those of the commercial CVD wearables, and their water retention and wettability capabilities were superior to those in some of the commercially available contact lenses used for cosmetic/vision correction purposes. Hence, this work demonstrates the potential of gold nanocomposite lenses in CVD management and, more generally, color filtering applications.

A Varifocal Graphene Metalens for Broadband Zoom Imaging Covering the Entire Visible Region.

Abstract: The ever-increasing demand for miniaturized optical systems has placed stringent requirements on the core element: lenses. Developing ultrathin flat lenses with a varifocal capability and broadband spectral response is critical for diverse applications, but remains challenging and has been the focus of intensive research. The recent demonstration of tunable focal length for a single wavelength with metalenses marked an important milestone for transforming the complex and bulky tunable lens kit into a single flat lens. However, achieving color imaging with desired tunability over the entire visible spectrum essential for practical applications still remains elusive. Here we propose and demonstrate experimentally a broadband varifocal graphene metalens (250 nm in thickness) covering the entire visible spectrum. It is able to simultaneously tune the focal lengths for different wavelengths continuously. By laterally stretching the lens, an over 20% focal length tuning range can be achieved for red (650 nm), green (550 nm), and blue (450 nm) light as three example wavelengths. Zoom imaging of different objects located along the axial direction has been demonstrated at these wavelengths by simply controlling the stretch ratio of the graphene metalens. This broadband graphene zoom lens enables enormous applications in miniaturized imaging devices such as cell phones, wearable displays, and compact optical or communication systems with multi-color-channel functionalities.

Ultra-Wideband Flat Metamaterial GRIN Lenses Assisted With Additive Manufacturing Technique

Abstract: This article presents the designs of ultrawideband microwave flat gradient index (GRIN) lenses, which realizes over a 108% fractional bandwidth (12–40 GHz). The frequency-independent ray optics method is employed to determine the radially varying permittivity profile of the lenses. The challenge of realizing such a radially varying profile and the limitations in dielectric material choices are overcome by two additive-manufacturing-aided approaches: 1) partially infilled dielectrics with a varied periodicity, which ensures the lens performance at the higher end of the frequency range and 2) artificially engineered dielectrics (AED) with subwavelength-scale metallic inclusions, which enables-high permittivity dielectrics and leads to benefits of thickness and mass reduction for the GRIN lenses. Measured results demonstrate that the GRIN lenses improve the gain of open-ended waveguide sources by 8.7–15.6 dB over a wide frequency range from 12 to 40 GHz, with the realized gain of up to 23.6 dBi. Both the simulation and measurements of the presented design confirm the potential of implementing the proposed GRIN lens design in high directivity and beamforming antenna applications, across an ultrawideband frequency range.

End-to-end complex lens design with differentiate ray tracing

Abstract: Imaging systems have long been designed in separated steps: experience-driven optical design followed by sophisticated image processing. Although recent advances in computational imaging aim to bridge the gap in an end-to-end fashion, the image formation models used in these approaches have been quite simplistic, built either on simple wave optics models such as Fourier transform, or on similar paraxial models. Such models only support the optimization of a single lens surface, which limits the achievable image quality. To overcome these challenges, we propose a general end-to-end complex lens design framework enabled by a differentiable ray tracing image formation model. Specifically, our model relies on the differentiable ray tracing rendering engine to render optical images in the full field by taking into account all on/off-axis aberrations governed by the theory of geometric optics. Our design pipeline can jointly optimize the lens module and the image reconstruction network for a specific imaging task. We demonstrate the effectiveness of the proposed method on two typical applications, including large field-of-view imaging and extended depth-of-field imaging. Both simulation and experimental results show superior image quality compared with conventional lens designs. Our framework offers a competitive alternative for the design of modern imaging systems.

Experimental Validation of a Metasurface Luneburg Lens Antenna Implemented With Glide-Symmetric Substrate-Integrated Holes

Abstract: In this letter, we present the experimental validation of a $K_{a}$ -band Luneburg lens antenna based on a novel cost-effective metasurface. The metasurface is composed of a parallel plate waveguide (PPW) loaded with quasi-periodic inclusions in both conductors. The inclusions are square holes printed on a substrate, with vias placed around the holes. The vias connect the printed layer of the substrate to the ground. This configuration is named substrate-integrated hole (SIH). It is demonstrated that the SIH metasurface can obtain a higher effective refractive index, compared to the conventional holey metasurface. To further increase the effective refractive index, the SIHs in the two conductors of the PPW are glide-symmetrically arranged. The refractive index distribution of the Luneburg lens is realized by locally tuning the dimensions of the SIHs. The lens is fed with 11 waveguide feeds with an angular separation of 10 $^{\circ }$ . Thus, the antenna can steer its radiation in a 100° angular range. A flare is integrated with the PPW to match the antenna to the free-space impedance. Since the wave propagates mainly in the PPW air gap, the dielectric losses are low. The measured radiation efficiency of the antenna is roughly 80%.

Near-field Localization with a Reconfigurable Intelligent Surface Acting as Lens

Abstract: Exploiting wavefront curvature enables localization with limited infrastructure and hardware complexity. With the introduction of reconfigurable intelligent surfaces (RISs), new opportunities arise, in particular when the RIS is functioning as a lens receiver. We investigate the localization of a transmitter using a RIS-based lens in close proximity to a single receive antenna element attached to reception radio frequency chain. We perform a Fisher information analysis, evaluate the impact of different lens configurations, and propose a two-stage localization algorithm. Our results indicate that positional beamforming can lead to better performance when a priori location information is available, while random beamforming is preferred when a priori information is lacking. Our simulation results for a moderate size lens operating at 28 GHz showcased that decimeter-level accuracy can be attained within 3 meters to the lens.

Domain multiplexed computer-generated holography by embedded wavevector filtering algorithm

Abstract: Computer-generated holography can obtain the wavefront required for constructing arbitrary intensity distributions in space. Currently, speckle noises in holography remain an issue for most computational methods. In addition, there lacks a multiplexing technology by which images from a single hologram and light source can be switched by a lens. In this work, we first come up with a new algorithm to generate holograms to project smoother images by wavevector filtering. Thereupon, we propose a unique multiplexing scheme enabled by a Fourier lens, as the incident light can be decomposed either by a superposition of spherical waves or plane waves. Different images are obtained experimentally in the spatial and wavevector domains, switchable by a lens. The embedded wavevector filtering algorithm provides a new prospective for speckle suppression without the need for postprocessing. The multiplexing technology can double the capacity of current holographic systems and exhibits potential for various interesting display applications.

3D Printed Contact Lenses.

Abstract: Although the manufacturing processes of contact lenses are well established, the use of additive manufacturing for their fabrication opens many new possibilities to explore. The current study demonstrates the fabrication of personalized smart contract lenses utilizing additive manufacturing. The study includes 3-dimensional (3D) modeling of contact lenses with the assistance of a computer aided designing tool based on standard commercial contact lens dimension, followed by the selection of the suitable materials and 3D printing of contact lenses. The 3D printing parameters were optimized to achieve the desired lens geometries, and a post processing treatment was performed to achieve a smooth surface finish. The study also presents functionalized contact lenses with built-in sensing abilities by utilizing microchannels at the contact lens edges. Tinted contact lenses were printed and nanopatterns were textured onto the contact lens surfaces through holographic laser ablation. 3D printed contact lenses have advantages over conventional contact lenses, offering customized ophthalmic devices and the capability to integrate with optical sensors for diagnostics.

Two-Dimensional Glide-Symmetric Dielectric Structures for Planar Graded-Index Lens Antennas

Abstract: In this letter, we propose and study a 2-D glide-symmetric dielectric periodic structure. We demonstrate that glide symmetry broadens the bandwidth of operation and achieves lower effective refractive indices when compared to non-glide configurations. These two properties are beneficial for producing graded-index lens antennas. To demonstrate the potential of the proposed unit cell, we designed a Luneburg lens operating in the K- and K $_\text {a}\!$ -bands. The lens was manufactured with conventional additive manufacturing and it has a potential use for future wireless communications given its low-cost and low-profile.

Computational Thinking Through an Empirical Lens: A Systematic Review of Literature:

Abstract: This article provides an overview of the diverse ways in which computational thinking has been operationalised in the literature. Computational thinking has attracted much interest and debatably ra...

A Compact High-Gain Wideband Lens Vivaldi Antenna for Wireless Communications and Through-the-Wall Imaging

Abstract: Compact high-gain wideband antenna systems for through-the-wall imaging and wireless communications, featuring 160% fractional bandwidth, are presented. Each radiating system, consisting of two orthogonal Vivaldi antennas forming a cross-shaped configuration so as to excite linear (horizontal/vertical) and circular polarization (CP), is equipped with a top-mount spherical–axicon dielectric lens. The optimized shaping of the lens and of the outer edge Vivaldi arms allow achieving gain levels exceeding 15 dBi with good front-to-back-ratio. The proposed antenna features a broadside gain diagram with stable radiation pattern and wideband impedance matching in the frequency range between 650 MHz and 6 GHz. CST Microwave Studio, implementing a full-wave locally conformal finite integration technique (FIT), was employed to design and characterize the antenna and to guide its physical realization. Two-port equivalent circuits were developed to characterize parasitic coupling effects between the Vivaldi antennas ports, while a full-wave analysis allowed characterizing their frequency- and time-domain behaviors. The numerical results concerning the antennas parameters, illustrating the suitability of the proposed antennas to support narrow and ultra-wideband signal waveforms, are found to be in good agreement with the experimental measurements performed on an antenna prototype.

Aberration-free pupil steerable Maxwellian display for augmented reality with cholesteric liquid crystal holographic lenses

Abstract: Maxwellian displays offer unique features like always-in-focus quality, high efficiency, and large field-of-view, but its small eyebox remains a major challenge for augmented reality. To enlarge the eyebox, pupil steering is a promising approach. However, previous pupil steering methods generally rely on changing the incident light angle on the lens coupler, which results in serious aberrations. In this Letter, we demonstrate a pupil steerable see-through Maxwellian display incorporating novel cholesteric liquid crystal (CLC) holographic lenses. By actively modulating the polarization state of the incident light, we can schematically choose which holographic lens to function, which fundamentally eliminates the aberrations.

TDCOSMO V: strategies for precise and accurate measurements of the Hubble constant with strong lensing

Abstract: Strong lensing time delays can measure the Hubble constant H$_0$ independent of any other probe. Assuming commonly used forms for the radial mass density profile of the lenses, a 2\% precision has been achieved with 7 Time-Delay Cosmography (TDCOSMO) lenses, in tension with the H$_0$ from the cosmic microwave background. However, without assumptions on the radial mass density profile -- and relying exclusively on stellar kinematics to break the mass-sheet degeneracy -- the precision drops to 8\% with the current data of the 7 TDCOSMO lenses, insufficient to resolve the H$_0$ tension. With the addition of external information from 33 Sloan Lens ACS (SLACS) lenses, the precision improves to 5\%, {\it if} the deflectors of TDCOSMO and SLACS lenses are drawn from the same population. We investigate the prospects to improve the precision of time-delay cosmography without relying on mass profile assumptions to break the mass sheet degeneracy. Our forecasts are based on the hierarchical framework introduced by Birrer et al. (2020). With existing samples and technology, 3.3\% precision on H$_0$ can be reached by adding spatially resolved kinematics of the 7 TDCOSMO lenses. The precision improves to 2.5\% with the further addition of kinematics for 50 non-time-delay lenses from SLACS and the Strong Lensing Legacy Survey (SL2S). Expanding the samples to 40 time delay and 200 non-time delay lenses will improve the precision to 1.5\% and 1.2\%, respectively. Time-delay cosmography can reach sufficient precision to resolve the Hubble tension at 3-5$\sigma$, without assumptions on the radial mass profile of lens galaxies. By obtaining this precision with and without external datasets, we will test the consistency of the samples and enable further improvements based on even larger future samples of time delay and non-time-delay lenses (e.g. from the Rubin, Euclid, and Roman Observatories).

Wideband Multimode Leaky-Wave Feed for Scanning Lens-Phased Array at Submillimeter Wavelengths

Abstract: In this article, we propose a hybrid electromechanical scanning lens antenna array architecture suitable for the steering of highly directive beams at submillimeter wavelengths with field-of-views (FoV) of ±25°. The concept relies on combining electronic phase shifting of a sparse array with a mechanical translation of a lens array. The use of a sparse-phased array significantly simplifies the RF front-end (number of active components, routing, thermal problems), while the translation of a lens array steers the element patterns to angles off-broadside, reducing the impact of grating lobes over a wide FoV. The mechanical translation required for the lens array is also significantly reduced compared to a single large lens, leading to faster and low-power mechanical implementation. In order to achieve wide bandwidth and large steering angles, a novel leaky wave lens feed concept is also implemented. A 550-GHz prototype was fabricated and measured demonstrating the scanning capabilities of the embedded element pattern and the radiation performance of the leaky wave fed antenna.

A Wideband PCB-Stacked Air-Filled Luneburg Lens Antenna for 5G Millimeter-Wave Applications

Abstract: This letter presents a novel wideband printed circuit board (PCB)-stacked Luneburg lens antenna with a flared open edge for multibeam scanning application at 5G millimeter-wave band. The lens consists of two groups of parallel PCBs. Each group includes 12 layers of low-cost FR4 PCB, which are fixed by metal screws. Inside the lens there is no dielectric, resulting in an air-filled structure. With drilling holes of different radius in each PCB layer (except the top and bottom layers), the air spacing between the two groups of PCBs varies discretely which approximates the graded refractive index. Eleven antipodal linearly tapered antennas are placed on the focuses of the lens as feed elements, permitting the beam to cover a wide angular range. To enhance the gain of the lens, the radiation aperture is flared, like an H-plane horn. Measurements of the lens antenna with a diameter of 130 mm show good agreement with the theoretical predictions. The measured impedance bandwidth covers 26–37 GHz with isolations better than 18.8 dB. The measured peak gain is around 15.4 dBi at 29 GHz. By switching the 11 feed elements, the overall 2-D beam scanning coverage is up to ±72°. The results indicate that the proposed Luneburg lens antenna demonstrates a good application potential for 5G millimeter wave wireless communication.

Hydrogel‐Based Diffractive Optical Elements (hDOEs) Using Rapid Digital Photopatterning

Abstract: Hydrogels, due to their optical transparency and biocompatibility, have emerged as an excellent alternative to conventional optical materials for biomedical applications. Advances in microfabrication techniques have helped convert conventional hydrogels into optically functional materials such as hydrogel-based diffraction optical elements (hDOEs). However, key challenges related to device customization and ease/speed of fabrication need to be addressed to enable widespread utility and acceptance of hDOEs in the field. Here, we report rapid printing of customized hDOEs on polyethylene glycol diacrylate (PEGDA) hydrogel using digital photopatterning; a novel method that combines simulated computer-generated hologram (SCGH) and projection photolithography. To showcase the versatility of this approach, a range of hDOEs are demonstrated, including 1D/2D diffraction gratings, Dammann grating, Fresnel zone plate (FZP) lens, fork-shaped grating and computer-generated hologram (CGH) of arbitrary pattern. Results demonstrate that printed hDOEs exhibit optical performance that is comparable with devices made with conventional materials. This versatile strategy can be potentially implemented with other photosensitive hydrogels to achieve user-defined hDOEs in a time-efficient and cost-effective fashion.

Collective-Mode Enhanced Matter-Wave Optics

Abstract: In contrast to light, matter-wave optics of quantum gases deals with interactions even in free space and for ensembles comprising millions of atoms. We exploit these interactions in a quantum degenerate gas as an adjustable lens for coherent atom optics. By combining an interaction-driven quadrupole-mode excitation of a Bose-Einstein condensate (BEC) with a magnetic lens, we form a time-domain matter-wave lens system. The focus is tuned by the strength of the lensing potential and the oscillatory phase of the quadrupole mode. By placing the focus at infinity, we lower the total internal kinetic energy of a BEC comprising 101(37) thousand atoms in three dimensions to 3/2 kB⋅38+6−7 pK. Our method paves the way for free-fall experiments lasting ten or more seconds as envisioned for tests of fundamental physics and high-precision BEC interferometry, as well as opens up a new kinetic energy regime.

A Dielectric Dome Antenna With Reduced Profile and Wide Scanning Capability

Abstract: The design and experimental validation of a wide scanning dome antenna with reduced profile is presented The antenna is based on the combination of a planar phased array with limited scanning capabilities and a dielectric lens which allows to broaden the field of view The angular variation of the scan loss can be almost arbitrarily designed if no constraint is imposed on the size of the dielectric lens However, the focus of this article is on the size minimization of the dome as required for applications where the form factor is critical Therefore, a lower boundary of the height of the dome is derived and imposed as a design constraint The antenna is analyzed using in-house ray tracing and physical optics software tools It is shown that, when the array is combined with the dielectric dome, a significant directivity enhancement can be achieved for wide scanning A demonstrator of the lens is designed, manufactured and combined with an available phased array working in $Ku$ -band The experimental tests confirm the theoretical predictions, validating the analysis tools, and show a scanning range of 70° in all scanning planes over a 15% bandwidth The directivity is enhanced by approximately 2 dB at the limits of the scanning range compared to the standalone illuminating array The active element pattern is rotationally symmetric, thus, the radiation performance is almost independent on the scanning plane Moreover, the dielectric lens allows to preserve the cross-polarization performance of the illuminating array without adding a significant contribution

3-D Printed Terahertz Lens to Generate Higher Order Bessel Beams Carrying OAM

Abstract: Conventional vortex beams carrying orbital angular momentum (OAM) suffer from the limitation of beam divergence in wireless communications applications. This article proposes novel 3-dimensional (3-D) printed discrete dielectric lenses (DDLs) for generation of nondiffractive OAM beams operating at 300 GHz. By virtue of its arbitrary aperture phase control capability, a terahertz (THz) DDL combining the functionalities of three conventional bulky refractive hyperbolic, spiral phase plane, and aixcon lenses is proposed to generate nondiffractive Bessel vortex beam carrying OAM. An aperture field analysis method is also developed to evaluate the radiation performance of the DDL antennas. Furthermore, to cover the OAM signal in an intended longitudinal region, two DDL synthesis methods are explored to generate extended higher order Bessel beams carrying OAM. The first approach is based on geometric optics, while the second uses the alternating projection method (APM) to optimize the aperture phase distribution of the DDL. Two THz DDLs are conveniently fabricated by 3-D printing technology. Measured results demonstrate that THz nondiffractive OAM beams can be successfully generated by the designed DDLs. The generated THz OAM beam with attractive nondiffractive characteristic may open new opportunities for next-generation ultra-high-speed wireless communications.