Far-field dot pattern generation is analyzed for a Gaussian beam source that illuminates a sinusoidal phase grating which is placed at a certain distance behind the beam waist. We obtain a bigger field of view with more numbers of points using a Gaussian beam in comparison to a plane wave illumination because of the initial curvature of the Gaussian beam. Light propagation modeling through the sinusoidal grating is carried out using different approximations for a thin and thick phase grating. Using thin element approximation (TEA), the complex field is carried out with low computational effort and accuracy. We compare TEA with more accurate methods, such as FFT-BPM and FDTD methods. For thin phase gratings, TEA can be used but for thick gratings, FDTD method is the only valid option. For thick phase gratings, the effect of reflection from phase grating on the field modulation increases and we use FDTD method to find the correct far field pattern distribution.
Using multiple optical channels increases the number of design possibilities for the objectives of mobile imaging devices. For easy wafer-level fabrication, we start from a single optical element—a monocentric plano-convex lens. The quality of the areal image is used to select the size of the field of each channel. Each channel optics is axially positioned to reduce the effect of the image field curvature. The resulting device has a small number of channels and it images a full field of view of ±40 deg with an f -number of 3. Details of the optical design, of the fabrication process, and of the device performance are reported.
In mobile imaging systems, the most difficult element to integrate is the objective lens. Here we present an intermediate approach between the costly traditional objectives and the low-resolution objectives inspired by the compound eyes of insects. Our multi-field approach uses a small number of optical channels each imaging a portion of the desired field of view. The full-field image is reconstructed digitally. The optics of each channel is kept simple for wafer-level fabrication and its size is sufficient to obtain a reasonable resolution. We present the design and fabrication of a prototype using 9 plano-convex lenses for 9 channels. Glass lenses glued on a wafer are used to image a full-field of ±40° with an f-number of 3. The images obtained shows field curvature correction. A simple image reconstruction scheme is presented. In conclusion, multi-field objectives fabricated with micro-optics technology are thin, simple to mount, robust, and easily replicated.
Advances in design, materials and production technology for micro-optical components have led to strong growth in their use in today's consumer products. In particular, micro-optical components produced by replication technologies such as UV embossing can now withstand the severe processing and environmental requirements of the consumer
electronics industry, including lead-free IR reflow and thermal shock. With their small size and low weight, as well as the possibility of optical function not achievable by conventional optics, micro-optical components and systems are finding applications in a wide variety of products. In the field of multimedia, novel designs and new production techniques are enabling applications in key areas such as illumination and display. The extreme compactness of micro-optical components, with typical thickness under 1 mm and footprints of only some millimeters square, makes them a natural candidate for consumer products such as mobile
phones, pocket projectors and displays. Advances in UV embossing technology, enabling micro-optics to be mounted over various light sources in a variety of different ways, also allow extremely compact opto-electronic modules to be realized at highly competitive prices. In this paper we summarize recent technology developments and describe a number of multimedia applications utilizing state-of-the-art micro-optics.
UV-NanoImprint Lithography (NIL) is a fast and low cost method, which becomes an increasingly important instrument for fabrication of μ-TAS and telecommunication devices. The key elements of UV-NIL are transparent molds and low viscosity resists. Two different transparent mold materials, allowing UV curing through the stamp, were developed: rigid quartz or flexible PDMS. Typical resist viscosities are in a range of <100mPas, ensuring fast and successful filling of the stamp cavities. UV-curing is carried out at a wavelength of 350-450 nm.
Replicated micro-optics is playing an increasingly important role in illumination and sensing systems in automobiles. The introduction of new design methods and improvements in materials and production technology has led to components which can offer superior performance, size and weight compared with classical optical elements. Diffractive Optical Elements (DOEs) for applications such as beam shaping can achieve optical performance which is not possible
with conventional optics. Beam forming elements for use with red and white LEDs play a major role in automotive optics. Customised DOEs can offer significantly more design flexibility and functionality over Fresnel lenses for the complex optical system based on a single or multiple LED source with reflector and wavelength converting resin. Thinner modules and improved efficiency are achieved. With CMOS imager sensors, micro-optical lenslet arrays can improve the effective sensitivity by many factors. UV-embossing and injection moulding are used to produce components in high volumes at low production costs. Replicated mounting and alignment features reduce assembly costs. New materials and processes have been developed to enable wafer-scale production by UV-embossing, producing glass-like components with excellent humidity and elevated temperature stability as well as IR-reflow process compatibility.
A wafer scale UV replication process is described that is suitable for mass production of micro-optical components. The fabrication process is divided into two phases. In phase 1, the design and mastering is done and a wafer-sized embossing tool is fabricated. In phase 2 of the process chain, the batch fabrication process is performed. From a single embossing tool, several identical wafer-sized replicas are fabricated that are then diced into the final components. Single-sided as well as double-sided replicas can be made. The economical flexibility of the UV replication chain is demonstrated through two application examples: High-quality components that pass strict environmental tests, which compete with etched silica structures, and low-cost micro-optical components, which compete with microinjection molded parts. All UV-replicated components have in common that they exhibit excellent optical quality and pass an IR reflow process.
For many high-volume applications of micro-optical elements and systems the most cost-effective fabrication technology is replication in polymer materials with techniques such as UV embossing, hot embossing, and injection molding. Replication significantly reduces the cost in volume production in comparison to silicon-based etched components. However, the temperature and humidity stability of most commercial polymers is not suitable for the application of replicated
elements in areas such as telecom or datacom. A process based on UV-replication in chemically durable polymers has been developed. Technologies for all fabrication steps from mastering over tooling to replication on wafer-scale, post-processing and characterization are described. We present results of various projects with double-sided micro-optics for telecom/datacom and various sensor applications.
We designed, fabricated and characterized a micro-optical beamshaping device, intended to optimize the coupling of an incoherent, linearly extended high-power diode-laser into a multimode fiber. The device uses two aligned micro-optical elements (DOEs) in combination with conventional optics. With a first prototype we achieved an overall efficiency of 28 %. Straightforward improvements, like antireflective coatings and the use of graytone elements, should lead to an efficiency of about 50 %. The device is compact and the fabrication is suited for mass production at low cost. We applied three different technologies for the fabrication of the micro-optical elements and compared the performance. The technologies were: direct laser writing, multiple projection photolithography in combination with reactive ion etching (RIE) in fused silica, and high-energy-beam-sensitive (HEBS) glass graytone lithography in photoresist. We found that the refractive type elements (graytone) yield better efficiency for large deflection angles, while diffractive elements give intrinsically accurate deflection angles.
We present an approach towards design and fabrication of optical microsystems based on UV-replication techniques using Ormocer materials. An integration of the structures on chip level is demonstrated for Vertical Surface Emitting Lasers (VCSEL). VCSEL's are of increasing interest for various fields such as telecommunications, optical sensing and optical interconnects. In terms of optical system integration, high technological requirements are imposed. UV-replication techniques using Ormocer materials offer a cost-effective way of integrating micro-optical elements directly on the chip with reduced assembly effort. Structures up to several hundred microns thickness and alignment tolerances in the order of few microns can be produced. The method is suitable for the fabrication of single elements, arrays and is extendable to wafer-scale processing. Here, we give an example for the coupling of VCSEL arrays into multimode optical fibers using two different approaches: Focusing of the VCSEL output into the fiber using replicated microlenses and fiber butt-coupling of the VCSEL lasers with help of replicated fiber alignment/guiding structures. Origination of the structure elements is accomplished by direct laser writing into photoresist and resist reflow techniques, respectively. Specific limitations of the corresponding fabrication method are already taken into account during element design and modeling. Results for the replicated lenses show a total fiber launch efficiency better than 70% over the laser operational range with alignment tolerances of approximately +/- 10 micrometers , which can be met by passive fiber alignment. In case of the replicated fiber alignment/guiding structures, fiber launch efficiencies better than 50% over the operation range and peak values better than 80% are reported.
We present a comparison of three different technologies for the fabrication of micro-optical elements with arbitrary surfaces. We used direct laser writing in photoresist, binary mask lithography in combination with reactive ion etching in fused silica, and High-Energy- Beam-Sensitive (HEBS) glass graytone lithography in photoresist. We analyzed the efficiencies and the deflection angles of different elements in order to quantify the performance of the different technologies. We found that higher effencies can be achieved with refractive type elements, while precise deflection angles can be obtained more easily with diffractive elements.
We report on recent progress in the fabrication of fused silica micro-optical elements, such as blazed gratings, refractive microlenses and microprisms. The elements are first made in photoresist and then they are transferred into fused silica by reactive ion etching. High selectivity etching is needed to realize structures with a high aspect ratio. Results are shown using various metallic etch masks. The shaping of optimized profiles is also presented to generate microlenses which are aspheric, or which have a low numerical aperture.
Fan—out phase gratings are micro—optical elements vhicli split an incoming beani into au arra of light beanis with equal power. whereas the diffracted beams are focused by a Fourie-transforin lens. These elements are used. for example. iii optical iiitercoiuiects. in multidetector systems. and in parallel optical processing [ I I. We present different concepts for the fabrication of lwbrid elements which combine the faii-out and focusing function. The combination of the refractive and diffractive function results in a monolithic element with miniaturized dimensions and has therefore a high potential for applications in optical microsystems. To achieve this functionality. we used two different designs and different fabrication technologies. The hybrid elements were fabricated by injection moulding. double-sided photolithographv. and direct laser writing. Single elements as well as large arrays of elements have been fabricated.
Diffractive optics represents a new and fundamental optical manufacturing technology that has tremendous potential in both the government and commercial sectors. Diffractive optics technology provides system designers with new and exciting degrees of freedom for the design and optimization of precision optical systems. Using diffractive optics one can: provide color correction for projection systems using a single, economical refractive material; create aspheric wavefronts without using aspheric surfaces; eliminate the need for exotic (and expensive) flint-type materials; produce high-performance, high-numerical-aperture, lightweight optical elements; produce high performance microlens arrays; construct custom diffusers for beam homogenization and beam shaping; convert Gaussian beams to a square- aperture, flat-top beam profile, create novel polarization components and narrowband filters; athermalize optical systems; and reduce the weight, complexity and cost of optical systems--all of which are important for projection display systems. In this paper, we describe several features of diffractive optical elements that are useful for projection display applications.
The design of kinoform fan-out elements with high efficiency and reduced sensitivity to vertical profile scaling errors is presented. We start from a high-efficiency continuous-phase fan-out solution and optimize the position of the 0-2π transitions in the phase function, in order to achieve a high fabrication-error tolerance. The sensitivity of Fourier-transform and focusing fan-out elements to vertical etch-depth errors is analyzed. The limitations for the fabrication of such structures by laserbeam writing are discussed. In particular, the influence of the finite writing-spot diameter on the fan-out performance is investigated. Design rules for fan-out elements, which consider fabrication constraints, are derived. Experimental results are presented for cylindrical focusing fanout elements with small uniformity error (2%) and weak profile scaling dependence.
A laser writing system for the fabrication of continuous-relief micro-optical elements in photoresist is described. The technology enables a wide range of planar micro-optical elements to be fabricated and replicated into polymer film using Ni shims electroformed from the photo-resist originals. The advantages and limitations of laser writing technology for micro-optics fabrication are discussed. Examples of fabricated micro-optical elements include Fresnel microlenses and microlens arrays, kinoforms, and other continuous-relief phase elements.
Progress in the fabrication of continuous-relief micro-optical elements by direct laser writing in photoresist followed by replication into epoxy or polymer materials is described. The technology enables a wide range of micro-optical elements to be fabricated and replicated using Ni shims electroformed from the photoresist originals. Examples of fabricated micro- optical elements are described, including microlens arrays, Fresnel microlenses, kinoforms, and other continuous microrelief phase elements.
Progress in the fabrication of diffractive optical elements (DOEs) as 2-dimensional continuous-relief microstructures is described. The elements are fabricated by laser-beam writing in photoresist and have typical microreliefs up to 5 micrometers and periods down to 10 micrometers . Examples include fan-out elements and Fresnel microlens arrays. The design and fabrication of a 9 X 9 fan-out DOE with a diffraction efficiency of 94% and an overall uniformity of +/- 8% is described. High quality replicas are produced by low-cost embossing and casting techniques.
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