Compact Lens Research Articles

Compact diffractive optics for THz imaging

We present a compact diffractive silicon-based multilevel phase Fresnel lens (MPFL) with up to 50 mm in diameter and a numerical aperture up to 0.86 designed and fabricated for compact terahertz (THz) imaging systems. The laser direct writing technology based on a picosecond laser was used to fabricate diffractive optics on silicon with a different number of phase quantization levels P reaching an almost kinoform spherical surface needed for efficient THz beam focusing. Focusing performance was investigated by measuring Gaussian beam intensity distribution in the focal plane and along the optical axis of the lens. The beam waist and the focal depth for each MPFL were evaluated. The influence of the phase quantization number on the focused beam amplitude was estimated, and the power transmission efficiency reaching more than 90% was revealed. The THz imaging of less than 1 mm using a robust 50 mm diameter multilevel THz lens was achieved and demonstrated at 580 GHz frequency.

Multi-Aperture-Based Probabilistic Noise Reduction of Random Telegraph Signal Noise and Photon Shot Noise in Semi-Photon-Counting Complementary-Metal-Oxide-Semiconductor Image Sensor.

A probabilistic method to remove the random telegraph signal (RTS) noise and to increase the signal level is proposed, and was verified by simulation based on measured real sensor noise. Although semi-photon-counting-level (SPCL) ultra-low noise complementary-metal-oxide-semiconductor (CMOS) image sensors (CISs) with high conversion gain pixels have emerged, they still suffer from huge RTS noise, which is inherent to the CISs. The proposed method utilizes a multi-aperture (MA) camera that is composed of multiple sets of an SPCL CIS and a moderately fast and compact imaging lens to emulate a very fast single lens. Due to the redundancy of the MA camera, the RTS noise is removed by the maximum likelihood estimation where noise characteristics are modeled by the probability density distribution. In the proposed method, the photon shot noise is also relatively reduced because of the averaging effect, where the pixel values of all the multiple apertures are considered. An extremely low-light condition that the maximum number of electrons per aperture was the only 2 was simulated. PSNRs of a test image for simple averaging, selective averaging (our previous method), and the proposed method were 11.92 dB, 11.61 dB, and 13.14 dB, respectively. The selective averaging, which can remove RTS noise, was worse than the simple averaging because it ignores the pixels with RTS noise and photon shot noise was less improved. The simulation results showed that the proposed method provided the best noise reduction performance.

Compact Mikaelian Lens Synthesized by Metasurfaces

Synthesized using metasurfaces, we propose the implementation of the rectangular Mikaelian lens, one that is not only just flat but now also thin, thus enabling impingent wavefronts to converge at focal points over shorter distances, a feature that no other contemporary types of circularly shaped lenses are able to achieve. The subsequent savings of space and weight afforded by this unique property could be invaluable. By further postprocessing of the fields extracted from the simulations, the degree of focusing attained by the lens is also quantitatively characterized, thus offering insights beyond mere visual inspection of field patterns. The phenomenon of power concentration has been successfully demonstrated with simulations that are well corroborated by results of measurements carried out on a manufactured prototype.

Adjustable-focus ultracompact endoscopic lens design with ultrahigh optical performance.

An internally focusing design is developed for a compact endoscopic lens to have optical performance close to the diffraction limit. When changing the working distance from infinity to a predetermined short distance, the overall system length and the field of view remain constant. It is numerically demonstrated that the diffraction-limit-like performance is maintained over a wide range of working distances, showing a novel capability of adjustable focuses. The design concept is numerically proven to be feasible and can enable very high-resolution examination for doctors checking the positions of biological entities through the immediate capture of clear images at different working distances. The corresponding lens configuration, PNN, is shown to be useful in achieving the high-resolution performance once the number of lens elements is four, where P and N are used to denote positive and negative optical power, respectively, for the lens groups. A corresponding tolerance analysis is also presented.

Plasmonic Lens Based on Rectangular Holes

A compact plasmonic lens is proposed in this paper. This plasmonic lens consists of rectangular holes etched on the silver film and arranged on one straight line and possesses the characteristics of short focus length, ultrathin thickness, and strong focus ability. The theoretical design for the plasmonic lens abides by the constructive interference theorem, and the surface plasmon polaritons excited by the holes with linearly polarized light illumination focuses effectively. The plasmonic lenses with single and double focus spots are provided, and the simulation experiment gives the powerful verification. The distinct structure feature and the excellent focusing characteristic of this plasmonic lens are benefit for its applications in optical integration.

Design of compact micro-reduction lens based on thin lens aberrations

Design of compact micro-reduction lens based on thin lens aberrations

A hybrid defect detection method for compact camera lens

Production technology has increased rapidly with the development of industrial technology. Conventional human visual inspection is insufficient for conducting quality control under this increased capacity. Therefore, high-speed and high-accuracy automated optical inspection is becoming increasingly crucial. In this article, we propose an automated inspection method for a compact camera lens using a circle Hough transformation, weighted Sobel filter, and polar transformation. Our analysis of defects in the compact camera lens identified problems including of the circular texture and the non-fixed position of the inspection region. To overcome these problems, we design an inspection algorithm for locating and inspecting a circular region. A machine learning support vector machine method is then applied for obtaining a precise detection result. The experimental results show that the proposed inspection method is suitable for detecting defects in a complicated circular inspection region, and that the proposed system exhibited high performance.

Compact polarization-based dual-view panoramic lens.

Panoramic annular lens (PAL) is a type of special optical system that can transform the cylindrical side view onto a planar annular image. We propose a compact polarization-based dual-view panoramic lens to solve the two major limitations of the conventional PAL structure: large front annular lens and lack of forward view. Dual-view imaging capability, which is highly needed for some applications, is achieved by using a polarization technique. The diameter ratio of the proposed front PAL lens and the sensor is reduced to less than 1.5, while it is larger than 2.5 for traditional PAL systems, expanding its applications in space-confined environments.

Reconfigurable Antenna Systems for the Next Generation Devices Based on 4G/5G Standard

This article is devoted to showing the applications of innovative reconfigurable antenna systems suitable for the next generation 4G/5G devices. Microwave antenna technology can be very useful for next generation devices based on 4G/5G standards. Next generation tablets and smartphones based on 4G/5G standards will require high bandwidth and high velocity channels with respect to conventional devices. This work tries to present a complete overview of possible applications of advanced antenna technologies for 4G/5G devices and systems. Methodologies, such as phased and fully adaptive arrays, multiple-input and multiple-output (MIMO) antennas based on compact Rotman lenses or butler matrices, development of innovate reconfigurable antennas based on reconfigurable parasitic structures or new materials such as graphene, and unconventional modulation techniques have been investigated in this work. The work ends with some conclusions and considerations related to ideas for future works.

Designing an LED luminaire with balance between uniformity of luminance and illuminance for non-Lambertian road surfaces.

We present a method of designing a light-emitting diode (LED) luminaire for non-Lambertian road surfaces, in which we optimized the overlap between the lighting areas of a luminaire and its adjacent luminaires to attain balance between uniformity of luminance and illuminance. The goal of the balance is to approach highly uniform luminance and raise illuminance uniformity as high as possible. The optimal illuminance rendered by a single luminaire and the corresponding far-field intensity were derived from the optimal overlap condition, and, thus, the optical model was established. The performance of the model is as follows: overall uniformity of luminance (UO) is 0.91, longitudinal uniformity of Luminance (UL) is 0.92, threshold increment (TI) is 1.64%, uniformity of horizontal illuminance (UHE) is 0.66, and surround ratio (SR) is 0.52. Finally, a compact freeform lens capping an LED was constructed to realize the optical model. The performance of the luminaire designed with arrayed units of an LED capped by the freeform lens is as follows: UO is 0.80, UL is 0.85, TI is 3.57%, UHE is 0.56, and SR is 0.51. In addition, the luminaire provides 19,600 lumens of luminous flux, of which 68% and 54% are projected on the target area and roadway alone, respectively, while 27% is absorbed by the surrounding materials.

Achromatic super-oscillatory lenses with sub-wavelength focusing

Lenses are crucial to light-enabled technologies. Conventional lenses have been perfected to achieve near-diffraction-limited resolution and minimal chromatic aberrations. However, such lenses are bulky and cannot focus light into a hotspot smaller than a half-wavelength of light. Pupil filters, initially suggested by Toraldo di Francia, can overcome the resolution constraints of conventional lenses but are not intrinsically chromatically corrected. Here we report single-element planar lenses that not only deliver sub-wavelength focusing, thus beating the diffraction limit of conventional refractive lenses, but also focus light of different colors into the same hotspot. Using the principle of super-oscillations, we designed and fabricated a range of binary dielectric and metallic lenses for visible and infrared parts of the spectrum that are manufactured on silicon wafers, silica substrates and optical fiber tips. Such low-cost, compact lenses could be useful in mobile devices, data storage, surveillance, robotics, space applications, imaging, manufacturing with light and spatially resolved nonlinear microscopies.

Tunable-focus lens for adaptive eyeglasses

We demonstrate the implementation of a compact tunable-focus liquid lens suitable for adaptive eyeglass application. The lens has an aperture diameter of 32 mm, optical power range of 5.6 diopter, and electrical power consumption less than 20 mW. The lens inclusive of its piezoelectric actuation mechanism is 8.4 mm thick and weighs 14.4 gm. The measured lens RMS wavefront aberration error was between 0.73 µm and 0.956 µm.

Harmonic lens with an annular aperture

We have considered the design of a compact imaging lens based on a reflective circular harmonic lens. The performance of such a lens has been numerically simulated in the ZEMAX program. A point spread function has been calculated. A number of formulae describing the relationship between the key parameters of the lens have been obtained. We have shown that in this case it is possible to design a compact imaging lens whose length is by an order of magnitude smaller than its focal length.

High efficiency cross-polarized wave filter for non-vacuum transmission

Development of high-peak power laser system encounters difficulties in producing the pulses with high temporal contrast. To increase the pulse temporal contrast ratio, a nonlinear filter based on crossed-polarized wave (XPW) generation is proposed. The XPW generation relies on a third-order nonlinear process occurring in a nonlinear medium, such as barium fluorite (BaF2) crystal. The XPW process is quite straightforward:a linearly polarized laser pulse is focused on BaF2 crystal positioned between two orthogonally polarizers, high power main pulses due to nonlinear polarization rotation can pass through the second polarizer, while low power unconverted pre-and post-pulses are filtered by the second polarizer. With the XPW technique, pulse contrast can be enhanced by several orders of magnitude. Furthermore, XPW spectrum can be broaden by a factor with respect to the initial spectrum. This efficient pulse cleaner presents many advantages and has proved to be a simple and reliable pulse filter operating in a double chirped pulse amplification system. Most of previous XPW experiments utilize short focal systems or work off focus due to an intensity limit in the crystal (BaF2). These drawbacks result in a lower conversion efficiency (lower than 10%) when using a single crystal. Dual crystal setup is capable of achieving efficiency more than 20%, yet the configuration restricts the crystal separation to a millimeter level. The use of long focus lens in the XPW device is capable of reaching higher efficiency, with BaF2 crystal positioned in the focal plane. Hence for milljoule pulses, the setup distance increases to tens of meters, resulting in a complicated system and cumbersome configuration. Considering these limitations, a compact, highly efficient and stable XPW generation using dual-lens system suitable for non-vacuum transmission is presented. The measured nonlinear accumulated phase shows little deterioration of pulse quality. With a compact dual lens system, we realize an excellent XPW conversion of above 22% (internal efficiency of 30%) with using double BaF2 crystals, while a femtosecond laser pulse can experience a spectrum broadening up to a factor of 1.78. The dual-lens configuration overcomes the crystal separation limit, and conversion efficiency exceeds 20% for a crystal separation from 13 cm to 22 cm, which is conducible to flexibility and robustness. The stability for the setup to generate shorter pulses with very high contrast or compensate for spectral gain narrowing in the preamplifier is ensured due to the dual-lens focusing system.

Visualizing epithelial expression of EGFR in vivo with distal scanning side-viewing confocal endomicroscope.

Confocal endomicroscopy is an emerging imaging technology that has recently been introduced into the clinic to instantaneously collect “optical biopsies” in vivo with histology-like quality. Here, we demonstrate a fast scanner located in the distal end of a side-viewing instrument using a compact lens assembly with numerical aperture of 0.5 to achieve a working distance of 100 μm and field-of-view of 300 × 400 μm2. The microelectromechanical systems (MEMS) mirror was designed based on the principle of parametric resonance and images at 5 frames per second. The instrument has a 4.2 mm outer diameter and 3 cm rigid length, and can pass through the biopsy channel of a medical endoscope. We achieved real time optical sections of NIR fluorescence with 0.87 μm lateral resolution, and were able to visualize in vivo binding of a Cy5.5-labeled peptide specific for EGFR to the cell surface of pre-cancerous colonocytes within the epithelium of dysplastic crypts in mouse colon. By performing targeted imaging with endomicroscopy, we can visualize molecular expression patterns in vivo that provide a biological basis for disease detection.

Electrically tunable soft solid lens inspired by reptile and bird accommodation

Electrically tunable lenses are conceived as deformable adaptive optical components able to change focus without motor-controlled translations of stiff lenses. In order to achieve large tuning ranges, large deformations are needed. This requires new technologies for the actuation of highly stretchable lenses. This paper presents a configuration to obtain compact tunable lenses entirely made of soft solid matter (elastomers). This was achieved by combining the advantages of dielectric elastomer actuation (DEA) with a design inspired by the accommodation of reptiles and birds. An annular DEA was used to radially deform a central solid-body lens. Using an acrylic elastomer membrane, a silicone lens and a simple fabrication method, we assembled a tunable lens capable of focal length variations up to 55%, driven by an actuator four times larger than the lens. As compared to DEA-based liquid lenses, the novel architecture halves the required driving voltages, simplifies the fabrication process and allows for a higher versatility in design. These new lenses might find application in systems requiring large variations of focus with low power consumption, silent operation, low weight, shock tolerance, minimized axial encumbrance and minimized changes of performance against vibrations and variations in temperature.

Simple telecentric submillimeter lens with near-diffraction-limited performance across an 80 degree field of view.

A simple and compact telecentric lens based on two hemispheric optical elements arranged in a formation resembling an "hourglass" is proposed and evaluated. Our modeling and experimental results show the ability of this lens in achieving high resolution over a large field of view. A prototype with 500μm total thickness is built using silicon micromachining methods for a center wavelength of 1500nm. Experimental measurement shows near-diffraction-limited performance and good telecentricity over an 80° field of view at a numerical aperture of 0.2. All elements of the hourglass lens are in direct contact, and hence the alignment is extremely simple. We believe the proposed lens is a good candidate for compact and low-cost multi-aperture imagers.

Terahertz MMICs and Antenna-in-Package Technology at 300 GHz for KIOSK Download System

Toward the realization of ultra-fast wireless communications systems, the inherent broad bandwidth of the terahertz (THz) band is attracting attention, especially for short-range instant download applications. In this paper, we present our recent progress on InP-based THz MMICs and packaging techniques based on low-temperature co-fibered ceramic (LTCC) technology. The transmitter MMICs are based on 80-nm InP-based high electron mobility transistors (HEMTs). Using the transmitter packaged in an E-plane split-block waveguide and compact lens receiver packaged in LTCC multilayered substrates, we tested wireless data transmission up to 27 Gbps with the simple amplitude key shifting (ASK) modulation scheme. We also present several THz antenna-in-packaging solutions based on substrate integrated waveguide (SIW) technology. A vertical hollow (VH) SIW was applied to a compact medium-gain SIW antenna and low-loss interconnection integrated in LTCC multi-layer substrates. The size of the LTCC antennas with 15-dBi gain is less than 0.1 cm3. For feeding the antenna, we investigated an LTCC-integrated transition and polyimide transition to LTCC VH SIWs. These transitions exhibit around 1-dB estimated loss at 300 GHz and more than 35 GHz bandwidth with 10-dB return loss. The proposed package solutions make antennas and interconnections easy to integrate in a compact LTCC package with an MMIC chip for practical applications.

Direct three-dimensional design of compact and ultra-efficient freeform lenses for extended light sources

Achieving accurate control of the spatial energy distribution of extended sources is an ultimate goal of illumination design and has considerable significance in practical applications. To achieve this goal, we, for the first time, present a direct method to design compact and ultra-efficient freeform lenses for extended sources in three-dimensional geometries. Instead of using the traditional Monte Carlo ray-tracing and feedback methods to address the challenges caused by the extended sources, we develop a novel design method to numerically calculate both surfaces of the freeform lens directly. The proposed method is very efficient and robust in designing freeform lenses for Lambertian and non-Lambertian extended light sources. The final freeform lenses are very compact and highly efficient and can significantly reduce glare and light trespass.

Compact collimators designed with point approximation for light-emitting diodes

We present a novel freeform lens design method for application to light-emitting diode collimating illumination. The lens is designed with a point-source assumption to form compact collimators. The method is derived from a basic geometric-optics analysis and the associated construction approach. By using this method, a compact collimating lenses with an aspect ratio = 0.181 is developed. With optimization of initial parameters, a highly collimating lens for a Cree XP-E LED (chip size: 1.2 mm × 1.2 mm) with an optical efficiency of 88.5% under a beam angle of ± 1.9° is constructed by simulation. To verify the practical performance of the lens, a prototype of the collimator lens is also made. This has light distribution compatible with the simulation results.