Epoxy Lens Research Articles

Measurements of the geometrical characteristics and refractive index of specimens made with X-ray interferometers

The theoretical background to the formation of interference fringes in a triple Laue X-ray interferometer by a specimen having plano-concave form is presented. The interference fringes in the general case have an elliptical form. The relation between the radius of the specimen, the refractive index and the radii of the interference fringes is established. For two epoxy lenses having different radii, the interference fringes are registered. The refractive index and the radii are determined by measuring the radii of the obtained interference fringes.

Passive anti-leakage of blue light for phosphor-converted white LEDs with crystal nanocellulose materials

A phenomenon known as "blue-light leakage" caused by overheating pcW-LEDs has recently been identified, and it poses a risk to users. This study focuses on investigating and optimizing a solution to address this issue. To tackle the problem of overheating and blue light leakage, we explored the application of a specific thermochromic material called crystal nano cellulose (CNC). We introduced CNC inside the epoxy lens of white LEDs. Importantly, under standard conditions, CNC has a negligible impact on the optical properties of the output white light. However, when overheating conditions arise, leading to blue light leakage, the temperature increase triggers a darkening effect in CNC. This thermochromic behavior of CNC allows it to strongly absorb the blue light, resulting in a significant suppression of the output luminous flux. As a result, the lamp dims, which not only prevents the user's eyes from being exposed to harmful bluish light but also serves as an indicator of aging in the pcW-LED. By implementing CNC as a responsive material in the design of white LEDs, this study offers a practical and effective solution to mitigate the negative effects of blue-light leakage caused by overheating. This improvement enhances the safety and comfort of users while also providing an early warning system for the aging of pcW-LEDs.

Downward viewing common-path optical coherence tomography guided hydro-dissection needle for DALK.

Deep anterior lamellar keratoplasty (DALK) is a partial-thickness cornea transplant procedure in which only the recipient's stroma is replaced, leaving the host's Descemet's membrane (DM) and endothelium intact. This highly challenging "Big Bubble" procedure requires micron accuracy to insert a hydro-dissection needle as close as possible to the DM. Here, we report the design and evaluation of a downward viewing common-path optical coherence tomography (OCT) guided hydro-dissection needle for DALK. This design offers the flexibility of using different insertion angles and needle sizes. With the fiber situated outside the needle and eye, the needle can use its' full lumen for a smoother air/fluid injection and image quality is improved. The common-path OCT probe uses a bare optical fiber with its tip cleaved at the right angle for both reference and sample arm which is encapsulated in a 25-gauge stainless still tube. The fiber was set up vertically with a half-ball epoxy lens at the end to provide an A-scan with an 11-degree downward field of view. The hydro dissection needle was set up at 70 degrees from vertical and the relative position between the fiber end and the needle tip remained constant during the insertion. The fiber and needle were aligned by a customized needle driver to allow the needle tip and tissue underneath to both be imaged within the same A-scan. Fresh porcine eyes (N = 5) were used for the studies. The needle tip position, the stroma, and DM were successfully identified from the A-scan during the whole insertion process. The results showed the downward viewing OCT distal sensor can accurately guide the needle insertion for DALK and improved the average insertion depth compared to freehand insertion.

Light Extraction Analysis of AlGaInP Based Red and GaN Based Blue/Green Flip-Chip Micro-LEDs Using the Monte Carlo Ray Tracing Method.

Micro-scale light emitting diodes (micro-LEDs) commonly employ a thin-film flip-chip (TFFC) structure whose substrate is lifted off by an excimer laser. However, flip-chip (FC) micro-LEDs with a substrate can provide a sharp rise on sidewall emission by increasing the sidewall area. Here, we investigate the influence of substrate thickness, encapsulation, surface texture, microstructures between the substrate and epilayer, as well as the size, cutting shape, and angle of the chip on the light extraction efficiencies (LEEs) of FC micro-LEDs by using the Monte Carlo ray tracing method. We find that the LEE of the blue FC micro-LED chip increases by 46.5% over that of the blue TFFC micro-LED chip. After the encapsulation with the epoxy lens is applied, the LEEs of the blue TFFC micro-LED and blue FC micro-LED increase by 129% and 110.5%, respectively. The underlying mechanisms for the use of surface texture, patterned sapphire substrate, air-void array, and chip shaping technologies to improve the LEEs of FC micro-LEDs are also investigated in detail. We find that the LEEs AlGaInP based red FC micro-LED and GaN based blue/green FC micro-LEDs exhibit a sharp rise when the chip size drops from 30 to 10 µm. The inverted trapezoid FC micro-LED with patterned sapphire substrate (PSS) and encapsulation shows extraordinarily strong top emission and high collimation. We believe that our study offers a promising and practical route for obtaining high efficiency micro-LEDs.

Common-path all-fiber optical coherence tomography probe based on high-index elliptical epoxy-lensed fiber

We propose and demonstrate high-index elliptical epoxy-lensed fiber probes designed specifically for endoscopic common-path (CP) swept-source optical coherence tomography (OCT) imaging inside wet tissues. The high-index epoxy lens uses a beam expansion region of a few hundred microns, which is capped with a spherical surface mounted at the end of an optical fiber. The probe is designed to operate inside wet tissues and shows improved performance over a long imaging depth, compared to bare or simple half-ball-lensed fiber probes. It allows optimal CP-OCT imaging in wet tissues by providing a stable reference power level and optimal beam waist for a long imaging depth. We have fabricated an array of these probes and one with a beam expansion region length of 288 μm and with a lens surface radius of 61 μm exhibiting 25-dB signal-to-noise ratio improvement compared to a bare fiber probe at 1.5-mm distance in water. The proposed probe is tested using a phantom sample comprising several layers of tape in water. The OCT images show that the probe is capable of high-resolution imaging over a distance of 1.5 mm.

Design and evaluation of a compound acoustic lens for photoacoustic computed tomography.

In photoacoustic computed tomography, the limited directivity of the detectors may cause deformation of off-center targets and lead to an imbalanced resolution in the imaging area. To improve the directivity of the acoustic detectors, several negative acoustic lenses have been proposed. In this study, we develop a new compound acoustic lens fabricated by integrating a concave polydimethylsiloxane (PDMS) lens and a convex epoxy lens. Both theoretical simulations and experimental evaluations demonstrate that the compound lens provides a larger directivity compared to single lenses made of PDMS, epoxy, and liquid. The measured acceptance angles of a 6-mm piezoelectric acoustic transducer equipped with the compound, epoxy, liquid, and PDMS lenses are 55°, 36°, 25°, and 20°, respectively. No deformation is observed in the off-center targets by using compound lens. However, serious deformation appears in the cases using single lenses.

On the formation of X-ray microbeams utilizing a short-focus refractive lens and a laboratory radiation source

The possibility of focusing an X-ray beam from a laboratory radiation source using a short-focus refractive composite lens is shown. The lens consists of 161 spherical biconcave epoxy lenses, each with a curvature radius of 50 μm. A Metal Jet (ExcilliumTM) microfocus X-ray tube, with a focal-spot size of 20 μm and containing a liquid helium anode, is used as a radiation source. The size of the focal spot in the image plane is 2.4 μm, which corresponds to the theoretical estimate. The possibility of using the composite refractive lens to form a parallel polychromatic X-ray beam is demonstrated. The results obtained allow discussion of the possibility of applying short-focus refractive X-ray lenses for X-ray microanalysis using laboratory sources; such microanalysis is currently a prerogative of synchrotron radiation sources only.

Dual Orientation 16-MHz Single-Element Ultrasound Needle Transducers for Image-Guided Neurosurgical Intervention.

Image-guided surgery is today considered to be of significant importance in neurosurgical applications. However, one of its major shortcomings is its reliance on preoperative image data, which does not account for brain deformations and displacements that occur during surgery. In this work, we propose to tackle this issue through the incorporation of an ultrasound device within the type of biopsy needles commonly used as an interventional tool to provide immediate feedback to neurosurgeons during surgical procedures. To identify the most appropriate path to access a targeted tissue site, single-element transducers that look either forward or sideways have been designed and fabricated. Micromolded 1-3 piezocomposites were adopted as the active materials for feasibility tests and epoxy lenses have been applied to focus the ultrasound beam. Electrical impedance analysis, pulse-echo testing, and wire phantom scanning have been carried out, demonstrating the functionality of the needle transducers at [Formula: see text]. The capabilities of these transducers for intraoperative image guidance were demonstrated by imaging within soft-embalmed cadaveric human brain and fresh porcine brain.

Fabrication and evaluation of a single-element Bi0.5Na0.5TiO3-based ultrasonic transducer

This paper discusses the fabrication and characterization of a single-element ultrasonic transducer with a lead-free piezoelectric active element. A piezoelectric ceramic with composition of 0.88Bi(0.5)Na(0.5)TiO(3)-0.08Bi(0.5)K(0.5)TiO(3)- 0.04Bi(0.5)Li(0.5)TiO(3) was chosen as the active element of the transducer. This composition exhibited a thickness coupling coefficient (kt) of 0.45, a dielectric constant of 440 (at 1 kHz), and a longitudinal piezoelectric coefficient (d(33)) of 84 pC·N(-1). To make the transducer, the ceramic was sandwiched between an epoxy-tungsten backing layer and a silver epoxy matching layer. An epoxy lens was also incorporated into the transducer's design to focus the ultrasound beam. The focused transducer with a center frequency of about 23 MHz demonstrated a -6-dB bandwidth of 55% and an insertion loss of -32 dB; the -20-dB pulsed length was measured to be 150 ns. A phantom made of copper wires (30 μm in diameter) was utilized to investigate the imaging capability of the transducer. The results indicated that the fabricated transducer, with a lateral resolution of 260 μm and a relatively high depolarization temperature, could be considered as a candidate for replacement of lead-based ultrasonic transducers.

Degradation of light emitting diodes: a proposed methodology

Due to their long lifetime and high efficacy, light emitting diodes have the potential to revolutionize the illumination industry. However, self heat and high environmental temperature which will lead to increased junction temperature and degradation due to electrical overstress can shorten the life of the light emitting diode. In this research, a methodology to investigate the degradation of the LED emitter has been proposed. The epoxy lens of the emitter can be modelled using simplified Eyring methods whereas an equation has been proposed for describing the degradation of the LED emitters.

Light extraction analysis of GaN-based light-emitting diodes with surface texture and/or patterned substrate

Light extraction analysis of GaN-based light-emitting diodes (LEDs) with Monte Carlo ray tracing is presented. To obtain high light extraction efficiency, periodic structures introduced on the top surface and/or on the substrate of various types of LED are simulated, including wire bonding, flip chip and Thin GaN. Micro pyramid array with an apex angle from 20o to 70o is shown to effectively improve the light extraction efficiency. In addition, for an LED encapsulated within an epoxy lens, the patterned substrate with pyramid array is found to be a more effective way to increase light extraction efficiency than the surface texture.

Development of a 35-MHz piezo-composite ultrasound array for medical imaging

This paper discusses the development of a 64-element 35-MHz composite ultrasonic array. This array was designed primarily for ocular imaging applications, and features 2-2 composite elements mechanically diced out of a fine-grain high-density Navy Type VI ceramic. Array elements were spaced at a 50-micron pitch, interconnected via a custom flexible circuit and matched to the 50-ohm system electronics via a 75-ohm transmission line coaxial cable. Elevation focusing was achieved using a cylindrically shaped epoxy lens. One functional 64-element array was fabricated and tested. Bandwidths averaging 55%, 23-dB insertion loss, and crosstalk less than -24 dB were measured. An image of a tungsten wire target phantom was acquired using a synthetic aperture reconstruction algorithm. The results from this imaging test demonstrate resolution exceeding 50 microm axially and 100 microm laterally.

Acoustic microscopy system: design and preliminary results

An acoustic microscopy system was designed to perform 2D imaging in the C-plane with a single-element transducer. The ultrasound transducer was fabricated by polishing bulk lithium niobate (LiNbO 3) to the required thickness (approximately 60 or 45 μ) for the desired operating frequency (55 or 75 MHz). The polished LiNbO 3 was attached to acoustic backing and matching layers. Finally, an epoxy lens was applied and the transducer mounted in a housing. The transducer was mounted in a 3D motorized positioning stage and operated by a high-frequency pulser/receiver. Received echoes were sampled with a 2 GHz ADC card and displayed on a PC using software developed in the Matlab environment. Transducer frequency and bandwidth were measured off a steel plate positioned at the focal length. A penny was scanned initially to confirm expected performance before acquiring data from liver ( n=3) and spleen ( n=3) specimens. For the first probe, the peak frequency was 54.05 MHz with a −6 dB bandwidth of 6.76 MHz. The axial and lateral resolutions were estimated to be 114 and 188 μm, respectively. For the second probe, the peak frequency was measured to 82 MHz with a −6 dB bandwidth of approximately 23 MHz. The axial and lateral resolutions were estimated to be around 33 and 81 μm, respectively. C-scans of the penny clearly showed detailed structures on front and back, while the capsule and the trabecular structures of the splenic tissues could easily be separated in different layers. In conclusion, an acoustic microscopy system operating at 55–75 MHz has been constructed and the feasibility of obtaining high-resolution images of tissue specimens demonstrated.

Microfabrication of saw-tooth refractive x-ray lenses in low-Z materials

Saw-tooth x-ray refractive lenses have been fabricated in silicon, epoxy and diamond. Silicon lenses were made by anisotropic wet etching of single crystalline silicon. Epoxy lenses were moulded from silicon masters. Diamond lenses were replicated by chemical vapour deposition on silicon masters and subsequent sacrificial etching of silicon. Beryllium saw-tooth test structures were embossed using a diamond master. Silicon and epoxy lenses gave sub-micron focal lines and provided gains of up to 40 when tested in a synchrotron set-up. Focal lengths ranged from 0.33 to 0.61 m for x-ray energies between 14 and 30 keV.

Design and fabrication of a miniaturized, integrated, high-frequency acoustical lens–transducer system

High-frequency ultrasound transducers have been developed for high-resolution imaging applications, such as nondestructive testing and medical diagnostics. Several of these devices employ miniaturized acoustical lenses to enhance the resolution of the system; however, research has been limited due to lens fabrication restrictions at or below the millimeter scale, which also increases the difficulty in creating lenses of identical geometric shape. Alignment and assembly problems on the micrometer scale have also necessitated the requirement for developing an in situ integrated transducer–lens system. Thus, the purpose of this study was to employ a new state-of-the-art micromachining technique to fabricate a high-precision, integrated, microacoustical lens–transducer system of identical geometric shape. Concave lenses (d = 1 mm) were fabricated from either PMMA® or epoxy using an ultra-high-precision micromilling machine. The lenses were designed for three different focal lengths (3 mm, 4 mm or 5 mm) with a center thickness of (3/4)λ. After fabrication, each lens was evaluated for compliance with the design criteria using scanning electron microscopy and a roughness/step tester. A total of 28 lenses with identical geometry were successfully fabricated. The errors of the radii of curvatures for all PMMA® and epoxy lenses were within 7.5 ± 5.8% and 6.0 ± 6.1%, respectively, of the designed values.

Microcavity light emitting diodes as efficient planar light emitters for telecommunication applications

Light emitting diodes (LEDs) can be coupled to optical fibers and used in telecommunication applications. Compared to laser diodes, the coupling is usually small, due to the isotropic emission of the source, combined with the large refractive index difference between the semiconductor and the outside medium. However, it is possible to greatly enhance the optical extraction of a planar LED by placing the source inside a microcavity which optical thickness is close to the wavelength of the emitted light. Some elementary design rules of a microcavity light emitting diode (MCLED) are explained here, and are illustrated on a real GaAs/Al x Ga 1− x As device emitting at 880 nm. The surface external quantum efficiency of this MCLED reaches 14% into air and 20.6% with an encapsulation into an epoxy lens. These values are about 10 times larger than for a usual LED and are in good agreement with theoretical values, calculated with a plane waves model. To cite this article: D. Ochoa et al., C. R. Physique 3 (2002) 3–14

High-Efficiency Zn-Diffused GaAs Electroluminescent Diodes

Electroluminescent GaAs diodes have been fabricated in heavily doped (n > 1018 cm−3) GaAs using ZnAs2 or a Zn–Ga solution as a diffusion source. Using the Zn–Ga source, efficiencies of 1.3–1.4% for planar uncoated devices and 3.2–3.5% with an Epoxy lens are reproducibly obtained, and uncoated devices with efficiencies as high as 1.7% have been observed. A variety of GaAs crystals were evaluated in order to determine the type most suitable for the fabrication of diffused electroluminescent diodes. The optimum material was found to be Si-doped GaAs with n in the range (2–3) × 1018 cm−3. Both Czochralski and boat-grown GaAs were investigated. The device efficiency has been found to depend strongly on the etch-pit density of the crystal, with maximum efficiencies obtained for boat-grown GaAs with Δ < 103 cm−2. A series of zero dislocation crystals grown using the Czochralski technique was investigated and found to yield lower efficiency devices than boat-grown GaAs with an etch-pit density between 102 and 103 cm−2.