In order to produce future generation micro-projection systems that can function independently or in conjunction with
small personal communication devices lasers are the preferred source of illumination over LEDs. Lasers are much
brighter and require less power than LEDs allowing for larger screen sizes and smaller battery requirements. In order to
illuminate the spatial light modulator used in the micro-projection system micro-optical elements are used within the
illumination path of a projector system to shape the RGB laser sources. Due to the diffractive nature of the optical
elements and the high coherence of the lasers a speckle pattern is produced in the final image reducing the overall image
quality. Diffractive diffusers are typically used in combination with micro-lens arrays in a time varying fashion in an
attempt to reduce the spatial coherence of the laser sources and hence reduce the speckle. Previous reduction techniques
have successfully used pseudo-random hadamard matrix diffusers to greatly minimize the contrast of the pattern. This
paper examines new reduction methods involving diffractive diffusing elements and presents measurements in the
reduction of speckle contrast for each technique.
Near field beam shaping optics, also called beam transformers, remap an input Gaussian profile to a top-hat profile.
The top-hat profile is created at some working distance away from the shaping element where a corrector element is
placed to "flatten" the phase of the top-hat profile to allow it to propagate some finite distance as a "collimated" beam.
Creating a top-hat profile requires the surface of the shaping element to be highly aberrated resulting in designs that are
typically either a diffractive surface or an aspheric surface each composed of many higher-order aspheric coefficients.
Diffractives and higher-order refractive designs offer several challenges and limitations in manufacturing. The design
space of using all spherical elements or even a combination of aspheric and spherical elements has not been completely
explored to see if there are any advantages of reducing the manufacturing tolerances or limitations for beam shaping
systems. This paper will explore the comparison of the number of elements required for diffractive, aspheric, and
spherical designs to meet the same beam shaping requirement and provide details related to the manufacturability of
each type of design.
Near-field beam shaping optics, also called beam transformers, re-map an input Gaussian profile to a top hat profile.
The top hat profile typically takes on a functional form such as a super Gaussian or a Fermi-Dirac function. The main
difference between a super Gaussian and a true top hat is the presence of rounded edges. The higher the order of the
super Gaussian, the sharper the profile. Sharper profiles tend to result in more diffraction effects while softer edges tend
to propagate further with a uniform distribution. A balance has to be determined that may depend heavily on the
application of the beam shaper with regards to performance parameters such as efficiency within the profile and the
uniformity of the flat top based on the edge shape of the functional form of the top hat profile. The paper will explore
different figures of merit for various functional forms that a Gaussian is typically re-mapped into and compared with
that of a perfect top hat with infinitely sharp shoulders.
Manufacturing processes have been developed to produce wafer scale optics in chalcogenide glass using semiconductor
fabrication. Chalcogenide materials are amorphous and covalently bonded solids containing one or more of elements in
Group VI in the periodic table, e.g. sulphur, selenium, or tellurium as a substantial constituent. For this paper, the
material selected for testing to determine the etching process was IG6 - As40Se60. Grayscale photolithography and
binary methods were used to pattern diffractive elements for use in infrared applications. Dual-band color correction,
incorporating diffractive optics, will be presented in the paper as an application of this development.
Standard UV materials, such as ArF-grade fused silica, have impurities that lead to low transmittance, high absorption,
and fluorescence when exposed to high irradiance. Calcium fluoride (CaF2), on the other hand, is a promising material
for use as an optical diffuser for applications at 157nm, 193nm, and 248nm due to its low defect density and high
transmission in the deep UV regime. In this paper, we discuss our method for fabricating Gaussian homogenizers in
calcium fluoride using a grayscale photolithography process. Refractive microlens array homogenizers and Gaussian
homogenizers have been fabricated in CaF2 and tested at 193nm for efficiency and uniformity. Using an excimer laser,
uniformity results were obtained for cylindrical lens arrays in tandem and crossed to observe the homogeneity in an
imaging configuration and for producing a square output. Efficiency, uniformity, and zero order measurements are
provided for the Gaussian homogenizers.
It is commonly known that a diffractive optic can be designed to split an incoming beam into many spots or orders to
produce various shapes and patterns. A desire to produce an equilateral triangle in the far-field for applications such as
ophthalmology surgery, topographical LIDAR mapping, and in material processing is an interesting case where there
are multiple design choices. In this paper, we will present grayscale and binary approaches of a corner cube array and
hexagonal phase plate that produce an equilateral triangle in the far-field with equal amount of energy in each of the
three spots. An efficiency analysis will be presented showing various results obtained using scalar wave theory versus
a rigorous coupled wave analysis.
Aligning of multiple micro-optical components is required for many systems composed of arrays of multiple lens elements, apertures, and filters. Methods of aligning two such wafers using mechanical features are discussed here. Alignment features include binary holes and posts, or grooves and ridges. With the circular holes or rectangular grooves etched into the two wafers, the mating pins or ridges are formed on both sides of a separate element to set both the lateral and vertical positioning. Grayscale technology allows for the printing of V-grooves and V-cones onto any substrate material over a wide range of aspect ratios. When integrated with cylindrical (fiber) or spherical (ball lens) mechanical features, this allows for accurate positioning. Some techniques allow for repositioning as well as disassembly and reassembly. The designs are kinematic or nearly kinematic. The paper discusses tolerances on mating components, and the associated precision of the overall alignment.
The central maximum of a Bessel beam offers a "non-diffracting" focal line of light that is useful in the fields of optical trapping and micromanipulation. This paper discusses the design and performance of diffractive optics for converting a Gaussian beam into a Bessel beam. The theoretical foundation of Bessel beams will be reviewed along with their optical properties. Bessel beams provide several unique characteristics such as a large depth of field and self-reconstruction. It is well known that the depth of field of a Bessel beam is larger than that of a Gaussian beam of equivalent size. However, this comes at the expense of very little power contained within the central maximum of the Bessel beam. Optical modeling and beam propagation methods are used to analyze what effect the number of rings has on the depth of field. This is an important consideration if Bessel beams are ever to be used in the fields of optical interconnects and imaging or in the area of laser processing. Where appropriate, comparisons are made between Bessel and Gaussian beams.
This paper presents the design, analysis, and testing of a diffractive optical element (DOE) to be part of the Lunar Orbiter Laser Altimeter (LOLA) instrument scheduled to launch in 2008. LOLA will be one of six instruments to orbit the Moon for a year or more as part of the Lunar Reconnaissance Orbiter (LRO). The various scientific instruments aboard the LRO will map the lunar environment in greater detail than ever before. LOLA will produce a topographic map of the Moon from a nominal 50km orbit during the one-year mission. LOLA works by bouncing laser pulses off the lunar surface as it orbits the Moon. By measuring the time it takes for light to travel to the surface and back, LOLA can calculate the roundtrip distance. Each pulse consists of five laser spots in a cross-like pattern spanning about 50 meters of the lunar surface. The spots are generated by a DOE from the single, collimated LOLA laser input beam. It is projected that LOLA will gather more than a billion measurements of the Moon's surface elevation creating a high resolution three-dimensional map of the surface.
This paper demonstrates a new tolerancing technique that allows the prediction of microlens optical performance based on metrology measurements taken during the fabrication process. A method for tolerancing microlenses to ensure operating performance using the optical design code ZEMAX(R) is presented. Parameters able to be measured by available metrology tools are assigned tolerances. The goal of the tolerance analysis is to assess the sensitivity of a microlens design to changes in the shape of the lens surface with regard to specific optical performance criteria related to the intended application. Two designs are presented with the tolerance analysis results. In the first design, the radius of curvature and conic constant are varied for an aspheric lens, and the change in the spot size is determined. For the second design, fiber-coupling efficiency is tabulated for a biconic lens. In each case, a metric can be produced showing the ability of the design to meet performance goals within the specified tolerances. A fabrication technician can then use this tolerancing metric with appropriate metrology data to determine if the device will yield acceptable performance. The metric can also determine if a design is overly sensitive to expected tolerances, thereby allowing the optical designer to evaluate the design from a manufacturing perspective.