Uniformity of Concentration Factor and BFL in Microlens Array for Image Detectors Applications (original) (raw)
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Journal of Lightwave Technology, 2000
We discuss the benefits of using microoptics concentration arrays in connection with image (or pixellated) photodetectors, in terms of: 1) recovery of area fill-factor; 2) reduction of equivalent dark-current; 3) mitigate dead-time issues; and 4) improved dynamic range. As an example of application, we describe the fill-factor recovery in connection to an array of 32 32 6-m diameter, 50-m pitch, single photon avalanche detector (SPAD). We use a 32 32 array of microlenses, fabricated by polymer casting in a photoresist replica mold. We demonstrate, for the first time to the best of our knowledge, an increase by a factor 25 of the effective spectral sensitivity of the final device. The lens array itself allows a 35 recovery, and projected improvements in excess of 50 appear feasible.
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Applied Optics, 1991
The imaging and radiometric properties of erect lens arrays made up of small biconvex microlenses are derived from a ray analysis. The lens arrays provide erect, unit magnification images. The relationship between the radii of curvature, the lens thickness, and the one-to-one conjugate distance is derived for both the single-layer case and a double-layer structure, which contains field lenses. Radiometric properties of the microlens and the array are derived for both structures. The results are compared to experimentally measured values obtained from arrays fabricated by a photothermal process.
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A two step process has been developed for the fabrication of diffraction limited concave microlens arrays. The process is based on the photoresist filling of melted holes obtained by a preliminary photolithography step. The quality of these microlenses has been tested in a Mach-Zehnder interferometer. The method allows the fabrication of concave microlens arrays with diffraction limited optical performance. Concave microlenses with diameters ranging between 30 µm to 230 µm and numerical apertures up to 0.25 have been demonstrated. As an example, we present the realization of diffusers obtained with random sizes and locations of concave shapes.
Parametric Study of Spherical Micro-Lens Array
Materials Science Forum, 2006
This study presents a concept to fabricate micro-lens devices using high-aspect-ratio lithography, extra-hardness electroplating, and hot embossing processes. A bath of electroplating electrolyte will be formulated to fabricate micro-optics mold inserts with extra-hardness Ni-Co alloy. It is a novel method to increase the life of the mold insert during fabricating micro-lens devices. With this high hardness, the mold inserts can resist high abrasiveness and wearness so as to extend the mold cycle life and reduce the idle time of replacing mold plates during fabrications. Therefore, the process of fabrications of micro-lens can be more cost-effective. In this study, parametric effects of reflow time, and temperature on micro-lens profiles will be characterized and discussed. Finally, the optical properties such as focal length of developed micro-lens will be measured and tested.
Optics express, 2007
We propose an array of non-imaging micro-concentrators as a mean to recover the loss of sensitivity due to area fill-factor. This is particularly important for those image photo detectors in which complex circuit functions are required and a substantial fraction of the pixel area is consumed, like e.g., 3D camera, SPAD arrays, fluorescence analyzers, etc., but also in CMOS sensors. So far, the low fill-factor was an unacceptable loss of sensitivity precluding from the development of such devices, whereas by using a concentrator array a recovery is possible, up to the inverse square of numerical aperture of the objective lens. By ray tracing, we calculate the concentration factors of several geometries of non-imaging concentrator, i.e., truncated cone, parabolic and compound parabolic, both reflective and refractive. The feasibility of a sizeable recovery of fill-factor (up to 50) is demonstrated.
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This paper presents the study of a fabrication technique of lenses arrays based on the reflow of glass inside cylindrical silicon cavities. Lenses whose sizes are out of the microfabrication standards are considered. In particular, the case of high fill factor arrays is discussed in detail since the proximity between lenses generates undesired effects. These effects, not experienced when lenses are sufficiently separated so that they can be considered as single items, are corrected by properly designing the silicon cavities. Complete topographic as well as optical characterizations are reported. The compatibility of materials with Micro-Opto-Electromechanical Systems (MOEMS) integration processes makes this technology attractive for the miniaturization of inspection systems, especially those devoted to imaging.
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Applied Optics, 2018
Microlenses are an important functional element of a modern imaging device. Typically, they are fabricated from organic materials on top of individual pixels. Though they are widely used, they do exhibit a number of limitations. These are, but not limited to, thermal stability, radiation sensitivity, outgassing properties, additional topography, and difficulty in manufacturing asymmetrical, noncircular microlens designs using conventional manufacturing techniques. In this paper, we present a novel approach for the fabrication of microlenses. We report on the design, manufacturing, and characterization of microlenses fabricated from classical dielectric materials used in the manufacturing of CMOS semiconductor devices. These microlenses rely on a Fresnel optical design, provide functionality similar to the classical microlenses, and do not suffer from their limitations. We subjected these microlenses to several environmental reliability stress conditions, including pressure, temperature, humidity, and their variation. Moreover, we test their sensitivity to gamma rays and protons.