A collimated globar source with a broadband output useful to a wavelength as long as 9 micrometers is shown and some characteristics of it are listed and illustrated. An infrared transmitting polymer Fresnel lens is used to focus this source to a small spot. A significant advantage of our polymer material’s virtually identical refractive index across both the visible and infrared regimes for our polymer material is confirmed by observing the stability of back focal length across different wavebands.
Maintaining the fidelity during mass production of nanostructures over large surface areas poses several challenges. Thin polymer optic components are susceptible to warping, birefringence, and errors in nanostructure form and periodicity. These issues can vary across the entirety of the surface, much more than in smaller injection molded parts. We discuss some of these challenges, their effects on the performance of the nanostructures, and some methods for mitigation.
Several types of polymer viewing screens for imaging thermal infrared scenes have been studied, both experimentally and theoretically. The best candidates will be used to evaluate the quality of polymer thermal imaging optics in a subsequent paper.
Transmissive optical components tend to be classified as either diffractive or refractive, based on which phenomenon more accurately describes the way they function. Although their optical functions are governed by distinct physical phenomena, Fresnel lenses are often confused or conflated with Diffractive Optical Elements (DOEs) like Fresnel zone plates and kinoforms; this is due to their similarities in shape, the method of defining their surfaces, and even the name. This research was conducted as an opportunity to describe the distinguishing characteristics of DOEs and Fresnel lenses, as well as the acceptable terminology to use with both classes of optics. First, background on diffraction and geometrical optics will be discussed, followed by methods used to design and fabricate both types of elements. Then, back focal distance metrology is performed to demonstrate the difference in function. The experiment performed supports the fact that DOEs and Fresnel lenses are not the same. This work is intended as a clarification of nomenclature and functionality, as well as an illumination of what makes DOEs and Fresnel lenses distinct.
Virtual reality and augmented reality devices require increasingly demanding optical components. Head mounted displays for VR systems often use molded Fresnel lenses, which can be affordably mass produced, maintain low weight, and still achieve high optical performance. Here, we describe an optical system designed for a wide field-of-view, consumer VR headset. Custom tooling was fabricated via diamond turning in order to injection mold the acrylic lenses. Each optical channel is composed of two lenses. The lenses have a spherical-convex surface and an aspheric-convex Fresnel on a spherical-concave surface; the radii of the spherical surfaces differ between the two lenses. Each lens pair relays the image from a compatible smartphone to the eye. To assess the quality of the lenses, the surface finish and surface profiles were measured using a white light interferometer and a contact profilometer, respectively. The lenses were assembled into a custom headset, and their performance was demonstrated via commercial VR software.
Electro-Chemical Polishing is routinely used in the anodizing industry to achieve specular surface finishes
of various metals products prior to anodizing. Electro-Chemical polishing functions by leveling the
microscopic peaks and valleys of the substrate, thereby increasing specularity and reducing light scattering.
The rate of attack is dependent of the physical characteristics (height, depth, and width) of the microscopic
structures that constitute the surface finish. To prepare the sample, mechanical polishing such as buffing or
grinding is typically required before etching. This type of mechanical polishing produces random
microscopic structures at varying depths and widths, thus the electropolishing parameters are determined in
an ad hoc basis. Alternatively, single point diamond turning offers excellent repeatability and highly
specific control of substrate polishing parameters. While polishing, the diamond tool leaves behind an
associated tool mark, which is related to the diamond tool geometry and machining parameters. Machine
parameters such as tool cutting depth, speed and step over can be changed in situ, thus providing control of
the spatial frequency of the microscopic structures characteristic of the surface topography of the substrate.
By combining single point diamond turning with subsequent electro-chemical etching, ultra smooth
polishing of both rotationally symmetric and free form mirrors and molds is possible. Additionally,
machining parameters can be set to optimize post polishing for increased surface quality and reduced
processing times. In this work, we present a study of substrate surface finish based on diamond turning tool
mark spatial frequency with subsequent electro-chemical polishing.
We have investigated the light collection and collimation properties of both Fresnel lenses and the nonimaging (TIR)
“cones” typically used with LEDs. We have measured the integrated light output and its spatial distribution, and we have
also measured the sensitivity of these two parameters to misalignment between the optic and the LED. We find that for a
given distance from the LED to the front of the optic, a Fresnel lens can produce a narrower (better collimated) beam
than can a nonimaging “cone.” Various design and manufacturability factors must be weighed when determining which
solution to choose for a given illumination problem, and some of these are discussed.
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