Conventional Lens System Research Articles

Meta-Lens Particle Image Velocimetry.

Fluid flow behavior is visualized through particle image velocimetry (PIV) for understanding and studying experimental fluid dynamics. However, traditional PIV methods require multiple cameras and conventional lens systems for image acquisition to resolve multi-dimensional velocity fields. In turn, it introduces complexity to the entire system. Meta-lenses are advanced flat optical devices composed of artificial nanoantenna arrays. It can manipulate the wavefront of light with the advantages of ultrathin, compact, and no spherical aberration. Meta-lenses offer novel functionalities and promise to replace traditional optical imaging systems. Here, a binocular meta-lens PIV technique is proposed, where a pair of GaN meta-lenses are fabricated on one substrate and integrated with a imagingsensor to form a compact binocular PIV system. The meta-lens weigh only 116mg, much lighter than commercial lenses. The3Dvelocity field can be obtained by the binocular disparity and particle image displacement information of fluid flow. The measurement error of vortex-ring diameter is ≈1.25% experimentally validates via a Reynolds-number (Re) 2000 vortex-ring. This work demonstrates a new development trend for the PIV technique for rejuvenating traditional flow diagnostic tools toward a more compact, easy-to-deploy technique. It enables further miniaturization and low-power systems for portable, field-use, and space-constrained PIV applications.

Injection Molding of Encapsulated Diffractive Optical Elements.

Microstructuring techniques, such as laser direct writing, enable the integration of microstructures into conventional polymer lens systems and may be used to generate advanced functionality. Hybrid polymer lenses combining multiple functions such as diffraction and refraction in a single component become possible. In this paper, a process chain to enable encapsulated and aligned optical systems with advanced functionality in a cost-efficient way is presented. Within a surface diameter of 30 mm, diffractive optical microstructures are integrated in an optical system based on two conventional polymer lenses. To ensure precise alignment between the lens surfaces and the microstructure, resist-coated ultra-precision-turned brass substrates are structured via laser direct writing, and the resulting master structures with a height of less than 0.002 mm are replicated into metallic nickel plates via electroforming. The functionality of the lens system is demonstrated through the production of a zero refractive element. This approach provides a cost-efficient and highly accurate method for producing complicated optical systems with integrated alignment and advanced functionality.

Improved neck posture and reduced neck muscle activity when using a novel camera based workstation for manual precision inspection tasks

PurposeThis study investigates the effects of the usage of a novel camera system compared to a conventional lens system for manual precision tasks. Utilizing the novel camera system aims to improve neck posture, reduce neck muscle tension and thereby minimize the risk of neck pain. MethodsCamera and lens systems were compared by assessing the craniovertebral angle (CVA), electromyographic activity of the M.trapezius and perceived exertion. 16 healthy participants (n = 8 female, 24 ± 2 years; n = 8 male, 30 ± 5 years) performed manual precision tasks in a cross-over design using both systems in sitting and standing positions. ResultsAnalyses showed that using the camera system improved the CVA in sitting [28.4° (22.8°–33.9°) to 42.5° (38.9°–46.1°); p < 0.01] and decreased the M.trapezius activity in standing [13.1% (7.7%–18.6%) to 8.65% (5.49%–11.81%)]. Additionally, overall and neck specific perceived exertion decreased when using the camera system in standing. ConclusionsThe camera system may prevent neck pain in workers performing manual precision tasks in sitting and standing postures.

Resilient Graphene Ultrathin Flat Lens in Aerospace, Chemical, and Biological Harsh Environments.

The development of ultrathin flat lenses has revolutionized the lens technologies and holds great promise for miniaturizing the conventional lens system in integrated photonic applications. In certain applications, the lenses are required to operate in harsh and/or extreme environments, for example aerospace, chemical, and biological environments. Under such circumstances, it is critical that the ultrathin flat lenses can be resilient and preserve their outstanding performance. However, the majority of the demonstrated ultrathin flat lenses are based on metal or semiconductor materials that have poor chemical, thermal, and UV stability, which limit their applications. Herein, we experimentally demonstrate a graphene ultrathin flat lens that can be applied in harsh environments for different applications, including a low Earth orbit space environment, strong corrosive chemical environments (pH = 0 and pH = 14), and biochemical environment. The graphene lenses have extraordinary environmental stability and can maintain a high level of structural integrity and outstanding focusing performance under different test conditions. Thus, it opens tremendous practical application opportunities for ultrathin flat lenses.

Design studies of varifocal rotation optics

We present the design of a varifocal freeform optics consisting of two lens bodies each with a helical-type surface structure of azimuthally varying curvatures. This arrangement allows for tuning the optical refraction power by means of a mutual rotation of the lens bodies around the optical axis. Thus, the refraction power can be tuned continuously in a defined range. The shape of the helical-type surfaces is formed by a change in curvature subject to the azimuthal angle α. At the transition of the azimuthal angle from α = 2π to α = 0, a surface discontinuity appears. Since this discontinuity will seriously affect the imaging quality, it has to be obscured. In the initial state, i.e., zero-degree rotation, the curvatures of the opposing surfaces result in a specific refraction power, which is constant over the entire circular aperture. Rotating one of the lens bodies by an angle φ around the optical axis will change the opposing curvatures and result in a change of refraction power. Two circular sectors with different tunable optical refraction powers are formed, thus resulting in a tunable bifocal optics. Obscuring the minor sector will result in a tunable monofocal rotation optics. In contrast to conventional tunable lens systems, where additional space for axial or lateral lens movement has to be allocated in design, rotation optics allowing for a more compact design. A performance analysis of the rotation optics based on simulations is presented in dependence on aperture size as well as approaches to compensate for spherical aberrations.

Tip Enhanced Laser Ablation Sample Transfer for Mass Spectrometry

ABSTRACTMass spectrometry is one of the primary analysis techniques for biological analysis but there are technological barriers in sampling scale that must be overcome for it to be used to its full potential on the size scale of single cells. Current mass spectrometry imaging methods are limited in spatial resolution when analyzing large biomolecules. The goal of this project is to use atomic force microscope (AFM) tip enhanced laser ablation to remove material from cells and tissue and capture it for subsequent mass spectrometry analysis. The laser ablation sample transfer system uses an AFM stage to hold the metal-coated tip at a distance of approximately 10 nm from a sample surface. The metal tip acts as an antenna for the electromagnetic radiation and enables the ablation of the sample with a spot size much smaller than a laser focused with a conventional lens system. A pulsed nanosecond UV or visible wavelength laser is focused onto the gold-coated silicon tip at an angle nearly parallel with the surface, which results in the removal of material from a spot between 500 nm and 1 µm in diameter and 200 and 500 nm deep. This corresponds to a few picograms of ablated material, which can be captured on a metal surface for MALDI analysis. We have used this approach to transfer small peptides and proteins from a thin film for analysis by mass spectrometry as a first step toward high spatial resolution imaging.

High-numerical-aperture microlensed tip on an air-clad optical fiber

We show that a hemispherically shaped tip on an air-clad optical fiber simultaneously works as a high-numerical-aperture lens and efficiently collects photons from an emitter placed near the beam waist into the fundamental guided mode. Numerical simulations show that the coupling efficiency reaches about 25%. We have constructed a confocal microscope with such a lensed fiber. The measurements are in good agreement with the numerical simulation. The monolithic structure with a high-photon-collection efficiency will provide a flexible substitute for a conventional lens system in various experiments such as single-atom trapping with a tightly focused optical trap.

TRUNCATED CONTACT LENSES FOR PERIPHERAL VITRECTOMY

In vitrectomy, excision of the peripheral vitreous is important to obtain better surgical outcomes as well as to prevent postoperative complications, such as retinal detachment and endophthalmitis.1–3 There are several methods to observe peripheral fundus during vitrectomy: the wide-angle viewing system, prismatic contact lenses, and scleral depression. Although the wide-angle viewing system allows for observation of wider area, image resolution and stereopsis are limited when compared with the contact lens system.4 The conventional prismatic lens system provides a clear view of the surgical field, but prismatic lenses with greater prism angle (30 or 45°) have significant amount of chromatic aberrations, resulting in blurring of the peripheral image.5 In addition, observation of the ora serrate is not possible with the prismatic lenses. Scleral depression method offers observation with good image resolution and stereopsis, but it can be painful for patients and technically challenging in sutureless microincision vitrectomy. We developed new truncated prismatic contact lenses for clear view of the peripheral fundus during vitrectomy. Because the lenses are very thin with smaller prism angles, they have less chromatic aberrations and distortion, allowing for clearer view of the peripheral fundus.

Hyperlenses and metalenses for far-field super-resolution imaging

The resolution of conventional optical lens systems is always hampered by the diffraction limit. Recent developments in artificial metamaterials provide new avenues to build hyperlenses and metalenses that are able to image beyond the diffraction limit. Hyperlenses project super-resolution information to the far field through a magnification mechanism, whereas metalenses not only super-resolve subwavelength details but also enable optical Fourier transforms. Recently, there have been numerous designs for hyperlenses and metalenses, bringing fresh theoretical and experimental advances, though future directions and challenges remain to be overcome.

새로운 겔형 생체모방 가변초점 렌즈 시스템

In this paper, we propose a new gel-type biomimetic variable-focus lens system. The miniaturization of conventional lens system is limited due to the use of a set of glass lenses for adjusting the focal length. Biologically inspired by the focus adjustment mechanism of the human eye, a gel-type single lens system with variable-focus is presented. The proposed system consists of a gel-type lens, mechanical parts such as body, rotation ring, and winding-type SMA actuator. In addition, the proposed system is designed to operate with a simple and miniaturized mechanical structure using a new attachment and driving mechanism. The focusing performance of the proposed system is verified through a series of experiments and measurements of the shape of the lens using tomography.

Angular domain fluorescence lifetime imaging: a tissue-like phantom study

We describe a fluorescence lifetime imaging technique employing the collimation detection capabilities of an angular filter array (AFA). The AFA accepts minimally scattered photons emitted from fluorophores up to 2 mm deep within turbid media. The technique, referred to as Angular Domain Fluorescence Lifetime Imaging (ADFLI), is described and its performance evaluated in comparison to a conventional (lens and pinhole) system. Results from a tissue-mimicking phantom demonstrated that ADFLI provides better spatial resolution and image contrast for fluorescent probes at greater depths compared to a lens and pinhole system.

Focal Shift of Paraxial Gaussian Beams in a Left-Handed Material Slab Lens

Focal shift is inevitable in conventional lens systems due to the Fresnel number and angular aperture. In this Letter, we demonstrate that there is no focal shift when a paraxial Gaussian beam passes through a left-handed material slab lens without absorption or gain. However, the effect is exhibited in the presence of absorption or gain, and becomes larger as the absorption or gain increases. When the absorption is equal to the gain, the phenomenon of the focal shift caused by the gain is more obvious. In addition, the field distribution is not affected by the absorption or gain and always remains Gaussian both in internal and external focus planes.

Angular domain fluorescence imaging for small animal research

We describe a novel macroscopic fluorescent imaging technique called angular domain fluorescence imaging (ADFI) applicable to the detection of fluorophores embedded in biological tissues. The method exploits the collimation detection capabilities of an angular filter array (AFA). The AFA uses the principle of acceptance angle filtration to extract minimally scattered photons emitted from fluorophores deep within tissue. Our goal was to develop an ADFI system for imaging near-infrared fluorescent markers for small animal imaging. According to the experimental results, the ADFI system offered higher resolution and contrast compared to a conventional lens and lens-pinhole fluorescent detection system. Furthermore, ADFI of a hairless mouse injected with a fluorescent bone marker revealed vertebral structural and morphometric data that correlated well with data derived from volumetric x-ray computed tomography images. The results suggested that ADFI is a useful technique for submillimeter mapping of the distribution of fluorescent biomarkers in small animals.

SH02 HAROLD H. HOPKINS – BROUGHT LIGHT TO DARKNESS

There is no doubt endoscopy and minimal invasive surgery has revolutionised the diagnostic and therapeutic approaches of a multitude of surgical disorders. Some of the most important milestones in the development of endoscopy and minimal invasive surgery have been attributed to the work of Harold H. Hopkins.Harold H. Hopkins, born on December 6, 1918, was a renowned physicist for his contribution in optical science. The first notable invention of Hopkins was the zoom lens. However, his first notable contribution to medicine started when he met Hugh Gainsborough, a gastroenterologist dissatisfied with the instruments for performing gastroscopy. The development of the ‘fiberscope’, consisting of a bundle of very fine glass fibres that eventuated as the flexible fiberoptic endoscopes in use today.In 1959, the invention of the “rod‐lens” system represented a significant development in endoscopy from the conventional lens system used at the time by using glass rods that occupy most of the telescope tube, hence reducing the glass/air interfaces. The result was brighter images and smaller diameter of the telescope. Nevertheless, it was not until 1965 when the idea was recognised by Professor George Berci, a young Australian surgeon at the time, who introduced the system to Karl Storz in Germany and manufactured the first prototype. The subsequent range of rigid endoscopes produced became worldwide standards for their excellent image quality.Hopkins died on October 22, 1994, but his legacy in development of optical systems revolutionised the development and application of endoscopy and minimal invasive surgery.

Negative refraction and slab imaging of photonic crystals

Imaging using lenses with curved surfaces is a common experience in our daily life, as for example when we use digital or cellular-phone cameras or overhead projectors. However, the imaging properties of such conventional lens systems are limited by aberration and diffraction. Careful optical design can significantly reduce the former, but not the latter, because it is due to the fundamental nature of light, which blurs the image of a geometrical point object into a finite-sized spot. In 2000, John Pendry1 performed insightful simulations showing that a perfect lens could be realized in the form of a thin planar slab with refractive index n = −1. When light is refracted in a direction opposite to that of conventional refraction, the process is termed negative refraction as illustrated in Figure 1. Materials that can display a negative index include metals, silicon carbide, some polymers and dyes, as well as more versatilely engineered metamaterials and photonic crystals (PhCs).2 PhCs are nanostructured materials in which a periodic variation of the dielectric constant results in a photonic band gap. Those made from dielectric materials are particularly well-suited for optical imaging since there is little or no material loss. However, the negative refraction and imaging mechanisms of PhCs differ from those of metals and metamaterials. Since PhCs are periodic structures, electromagnetic Bloch modes that consist of an infinite number of wavevectors can form in the photonic lattice. Therefore, the light-lattice interaction is governed by diffraction, scattering, reflection, and resonance effects, which makes analytical methods generally impractical to characterize their imaging properties. Bloch wave propagation studies have shown that the effective index of refraction, neff, can be extracted from band structures. It is negative at the second band because the group velocity (i.e. the speed at which a pulse propagates in a PhC and equal to the energy velocity in periodic media) moves towards the scattering center Γ . Figure 1. Positive refraction (left) and negative refraction (right).

Source of low-energy coherent electron beams

The coherence of the electron beam emitted at a low applied field from a single micrometer size mineral particle deposited on a carbon membrane is demonstrated by holography experiments. The experimental design combining this electron source with a conventional electrostatic lens system opens a way to holographic microscopy with low-energy electrons.

Information-based analysis of simple incoherent imaging systems

We present an information-based analysis of three candidate imagers: a conventional lens system, a cubic phase mask system, and a random phase mask system. For source volumes comprising relatively few equal-intensity point sources we compare both the axial and lateral information content of detector intensity measurements. We include the effect of additive white Gaussian noise. Single and distributed aperture imaging is studied. A single detector in each of two apertures using conventional lenses can yield 36% of the available scene information when the source volume contains only single point source. The addition of cubic phase masks yields nearly 74% of the scene information. An identical configuration using random phase masks offers the best performance with 89% scene information available in the detector intensity measurements.

Hough transform for feature detection in panoramic images

Omni-directional sensors are useful in obtaining a 360° field-of-view. With a radially symmetric mirror and conventional lens system this can be achieved with a single camera. There are several proposed profiles for the mirror, but most violate the single viewpoint (SVP) criteria necessary to allow functional equivalence to the standard perspective projection, posing challenges that have not yet been addressed in the literature. Such a imaging system with a non-SVP optical system do not benefit from the affine quality of straight line features being represented as collinear points in the image plane. To utilize these non-SVP mirrors, a new method to recognize such features is required. This work describes an approach to detecting features in panoramic non-SVP images using a modified Hough transform. A mathematical model for this feature extraction process is given. Experimental results are presented to validate this model and show robust performance in identifying line features with only estimated calibration.

Comparison of focusing properties of conventional and diffractive lenses

We compare focusing properties of conventional lenses and diffractive lenses (DLs). To that end, we use a converging electric-dipole wave as a model of an optimal converging wavefront that emerges from a conventional lens system. Our numerical results show that DLs have better focusing properties than conventional lenses for f-numbers less than 1. Although both types of lenses give nearly indistinguishable co-polarized intensity components in the focal region at low f-numbers, DLs provide much lower longitudinally polarized components. However, at sufficiently low Fresnel numbers and high f-numbers DLs fail to provide a well-focused energy distribution.

Design and tolerancing of achromatic and anastigmatic diffractive–refractive lens systems compared with equivalent conventional lens systems

Since focal diffractive optics have been introduced, designing them has flourished, particularly as the manufacturing technology has developed to meet the performance requirements. My purpose is to introduce to hybrid diffractive-refractive optical systems not only the design procedure but also the optical and the mechanical aspects of optical tolerancing. A comparison is made with equivalent conventional (purely refractive) systems in the visible wave band (rather than the infrared wave band where there are many published designs) to seek advantages and disadvantages that systems with diffractive optics bring. The results of tolerancing comparisons show that for small-field systems the introduction of diffractive components has a powerful desensitizing effect, whereas for a wide-field anastigmatic system that has been investigated the desensitization effect of the inclusion of diffractive surfaces is less marked. These results come mainly from the fact that an achromatizing diffractive surface has little focal power, whereas an achromatizing refractive component has to have a large focal power.