The demand for disposable optics, especially in biomedical fields involving point of care testing systems has led to navigation for new low-cost and high quality optics fabrication processes. We demonstrate that 3D-printing of optics allows on-demand fabrication of polymer lenses at a low price, when no expensive initial tooling expenses are required. However, achieving high surface quality imaging optics has been challenging primarily when the lens diameter is greater than fivefold of a millimeter. In this work, we demonstrate an imaging quality 3D-printed polymer lens with high surface quality of RMS = 0.92 ± 0.33 nm (δ, N=25) and surface profile deviation of ± 500 nm within 0.5 inch aperture diameter. The 3D-printing method is based on Luxexcel’s Printoptical® Technology, using modified ink-jet printheads, by depositing micro-droplets of Opticlear, which is a UV-curable polymer with an inhomogeneity index of 1.1-1.3×10-5 for 0.5 mm plate. We demonstrate a spatial resolution limit below 5 μm using a USAF1951-1x imaging resolution target for the 3D-printed singlet lens that is comparable to an off-the shelf commercial LA1509 N-BK7 plano-convex lens with the same specification parameters. Another application area of the inch-scale printed lens is in low-cost DSLR cameras. Experimental photos taken with a 3D-printed singlet lens and a commercial glass lens are nearly identical. As a result, manufacturing of 3D-printed singlet lenses with repeatability of ±200 nm for small or medium volume production at once becomes feasible by placing the printheads in parallel. We expect further developments towards achromatic optics by development of new 3D-printable polymers.
A combination of light-emitting diodes (LEDs) with freeform optics has been recently investigated widely for energy efficient illumination due to its high optical performance and compact size. The freeform optics design methods are application specific. The transformation of the light source into the target irradiance distribution using freeform optics usually leads to solving an inverse problem, which can be formulated by using a point light source, geometrical optics, monotonic ray bending and lossless system. Here, a customized algorithm is proposed to design freeform lenses for both LED source based simple uniform rectangular illumination and collimated light source based complex image target irradiance distributions by numerically solving the elliptic Monge-Ampère equation. The optical performance of the lenses is examined theoretically by using commercial ray tracing software.
Additive manufacturing (also called as 3D printing), a layer-by-layer printing of patterned material, is considered as novel option for low-cost and rapid manufacturing of optics. Recently, 3D printed ISO-standard ophthalmic lenses have been produced using Printoptical® technology (US Patent No. 13/924,974): a modified ink-jet printing technology that deposits micro-droplets Opticlear, which is a PMMA-like UV-curable polymer. In our work, the Printoptical® technology is further extended to freeform lenses using Opticlear, which is a PMMA like UV-curable polymer. The metrology of the freeform lenses is studied using white-light interferometry and VR-3000 series 3D surface profile macroscope.
We propose and demonstrate a low cost, large area, and mass production compatible method to fabricate strip-loaded waveguide structures. The structure is fabricated by combination of Atomic Layer Deposition and replication technique without applying any etching process to form the strip. The waveguide was realized in ring resonator configuration which eases the characterization process. The guiding layer is a 200 nm-thick TiO2 layer integrated with polymer strips to load light in the high index thin film. Due to the characteristic of the applied fabrication technique, achieving a very low propagation losses is expected.
Scattering of light by random rough surface scan be numerically simulated by using an exact electromagnetic scattering theory. Unfortunately, the characterization of surfaces is almost impossible owing to the non-uniqueness of the inverse scattering problem and highly nonlinear relationship between the surface parameters and the scattering. Thus, existing practical methods for qualitative or quantitative characterization are almost entirely experimental. Here we apply neural networks for estimating statistically the surface parameters. Previously, we have successfully demonstrated that neural network as a statistical estimator for optical scatterometry is an efficient tool for characterizing periodic microstructures. We generate numerically random surfaces, which are characterized with the degree of roughness, i.e., rot-mean- square (rms) amplitude of the roughness and correlation length. Here we are mainly interest in the most demanding region of the rms amplitude in the so-called resonance domain, corresponding to height fluctuations and correlations up to 5 times the wavelength of light. The neural network model, which is her a self-organizing map, is first trained and calibrated with the known surface parameter and scattering data pairs. At characterization stage, using only measured intensity distributions, the neural network theory classifies surface parameters into discrete classes of the rms amplitude and the correlation length. For most cases the classification result deviates at most one class, corresponding to 0.5 wavelengths, from the correct values.
Characterization of the geometrical parameters of microstructures in electronics and photonics is an important problem from the point of view of fabrication methods. With UV and especially electron-beam lithography feature sizes of the order of hundreds of nanometers are attainable. However, there is a lack of methods for a fast, reliable, and quantitative inspection of these structures. Scanning electron microscopy and atomic force microscopy have a good resolution but they require expensive equipment and are not suitable as on-line methods. Optical scatterometry is a nondestructive technique which predicts the structure geometry from a scattered intensity distribution. We utilize optical scatterometry with a hierarchical system of neural networks for the characterization of diffractive gratings with submicrometer features. It is shown that five geometrical parameters may be predicted simultaneously from the grating with an accuracy of less than 5 nm for the depths of the grooves and the line widths. Furthermore, the hierarchical system reduces the requirements for a prior information of the grating structure.
We develop a novel and efficient method to simulate diffraction patterns in the far field and in the Fresnel region when the phase counters of a quantized diffractive optical element are approximated by arbitrary polygons. Approximation causes signal errors whose effects have not been extensively studied so far. We take the polygonal shapes into account without any further approximations in the simulation, in contrast to calculations based on direct application of the Fast Fourier Transform. The method is applied to diffractive Fresnel lenses, axicons and gratings with finite size.
Manufacture of continuous-phase diffractive free-space elements by thermal ion exchange in glass has been proposed and demonstrated. In contrast to aiming at binary phase modulation by trying to minimize the inevitable lateral diffusion, side diffusion to obtain a smoothly carrying continuous phase profile was deliberately employed. This can be done if the mask aperture configuration and ion exchange time are numerically optimized to result in the desired optical function.
The analysis and the design of diffractive optical elements beyond the paraxial domain that contain wavelength-scale features must be based on the rigorous electromagnetic theory, i.e. on the solution of Maxwell's equations without introducing deliberate approximations present in scalar theories. In this paper we given an overview of various rigorous diffraction analysis methods and describe in more detail a Fourier-expansion eigenmode method that we call the BKK method. We apply exact diffraction theory to the analysis and the design of conventional diffractive elements as well as to the synthesis of several novel types of components.
The operation of optical narrowband reflection filters based on resonance anomalies of waveguide gratings is well established for gratings of infinite extent. We investigate the properties of finite-aperture waveguide-grating resonance filters by means of rigorous electromagnetic theory and an approximate model. The rigorous approach illustrates the scattering of optical energy from the guided mode at and near the edges of the element, which leads to a reduced diffraction efficiency into the backward-diffracted zeroth order. The approximate approach provides an optical-engineering model for the estimation of the minimum grating size required to achieve a high resonance-wavelength reflectivity.
We demonstrate improvements to the double ion-exchange process proposed for the fabrication of synthetic diffractive optical elements in glass waveguides. In this process a potassium slab waveguide is first fabricated. Then the diffractive element is made with silver ion exchange. In the modified process a short silver ion exchange is used in the second process step and the double ion-exchanged waveguide remains single mode. The undesired undiffracted light can be nearly totally eliminated. The mode profile of the potassium and double ion-exchanged waveguides are very close to each other resulting in low coupling loss between these two waveguide regions.
We optimize experimentally the double ion-exchange process parameters to achieve a designed phase modulation for a wavefront passing through a computer-generated waveguide hologram. We also demonstrate a gradient-thickness waveguide hologram (kinoform) for 1/8 beam splitting.
We have designed a range of computer-generated guided-wave kinoform optical elements using the thin-grating decomposition method and nonlinear optimization. Kinoform (Fresnel) lenses with improved local and overall diffraction efficiency have been constructed. High- efficiency, low-noise guided-wave array generators with fan-out up to 16 have been optimized.
We propose the application of computer-generated Fourier domain holograms to wavefront synthesis and manipulation in integrated optics. In particular, we describe the use of such diffractive optical elements to split a guided plane wave into several equal-intensity output waves. Gratings with fan-out to 6, 7, and 8 are demonstrated with about +/- 25% (approximately +/- 1 dB) array uniformities.
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