Shack-Hartmann sensors are widely used to measure wavefront aberrations. We present the fundamental and specific engineering steps in the design of Shack-Hartmann wavefront sensors. Typical performance requirements such as sensor dynamic range, sensitivity and accuracy are defined and discussed. We investigate the trade-offs between these performance metrics and the factors affecting the trade-offs. A first order approach for selecting the optimal parameters of the sensor central piece, the lenslet array, is presented. We also propose a quick tolerance analysis method that can predict the wavefront measurement error due to misalignments, using only the ray-tracing software.
The novel concept of the ET-HMPD, which consists of a Head-Mounted Projection Display (HMPD) with
an integrated Eye-Tracking (ET) capability, was recently presented as well as the design of some of its
components [Curatu, Hua and Rolland, Proceedings of the SPIE 5875, 2005]. In this paper, we present the
overall system design and performance, assuming an ideal cold cube and semi-transparent hot plate.
This paper presents the design, analysis, and fabrication of a telecentric f/1.3 thermal imaging lens. The 14.8 mm wideangle
lens provides a 62° diagonal field-of-view, and was designed to operate over the 8-14 μm infrared spectral band. Focus can be manually adjusted from 0.5 m to infinity, maintaining constant image quality over the entire range. A compact air-spaced doublet design limits the overall length to 34 mm and the maximum diameter to 28 mm. Lens materials were chosen to minimize chromatic aberrations, reduce cost, and fit within the molded chalcogenide glass
manufacturing capabilities. Combining a molded aspheric chalcogenide lens with a polished spherical Germanium lens eliminated the need for a diffractive surface to correct chromatic aberrations, and reduced the fabrication cost. Vignetting was purposely introduced at the extreme fields to compensate for the effects of aberrations on the relative illumination variation across the field-of-view. Athermalization of the lens was achieved mechanically over the entire operating temperature range (- 40 to + 80°C).
Numerous optical systems, such as telescopes, adaptive optics systems, and aberrometers, are equipped with wavefront sensors, which often use sampling devices measuring the slope of the wavefront at discrete points across the pupil (e.g. Shack-Hartmann sensors). The accuracy of the sampled output signal is always affected by the fabrication and alignment tolerances of the wavefront sensing optical system. Typically, it is a requirement to express the measurement error in terms of input wavefront, so the optical ray intercept error has to be converted into wavefront measurement error. This conversion cannot be obtained directly from a conventional tolerance analysis because of the wavefront breaking by the sampling device. The tolerancing method proposed in this paper solves the problem of converting conventional merit function degradation into input wavefront measurement error. The proposed method consists of two parts. First, a Monte Carlo tolerance analysis based on a specific merit function is performed, and a 90% border system is selected. Then, an optimization is applied to the 90% border system, by varying a "dummy" phase surface introduced at the entrance pupil of the system. A concrete example is presented.
We propose a novel conceptual design for a Head-Mounted Projection Display (HMPD) with Eye-Tracking (ET) capabilities. We present a fully integrated system that is robust, easy to calibrate, inexpensive, and lightweight. The HMD-ET integration is performed from a low-level optical configuration in order to achieve a compact, comfortable, easy-to-use system. The idea behind the full integration consists of sharing the optical path between the HMD and the Eye-Tracker. Along with lens design and optimization, system level issues such as eye illumination options, hardware alternatives are discussed.
MeteorWatch is a concept for the observation of small meteor events from a microsatellite in low earth orbit. To achieve high spatial resolution (about 1 km), fast update rate (up to 50 Hz), and large instantaneous coverage (107 km2), a distributed sensor is appropriate. The MeteorWatch sensor design has about 300 independent detection modules linked by a data bus to a central controller and image processor. Each detection module has a camera, digitizer, controller, image preprocessor, and bus interface. In operation, each detection module decides on the probability that a particular image has a meteor. Meteor event rates are expected to be low compared to the data rate, so that preprocessing at the detector modules reduces traffic on the data bus to the central controller. Image sequences with probable meteors are sent to the central controller for further processing and extraction of the meteor parameters. This paper gives an overview of MeteorWatch and describes the image processing approach, including partitioning of the tasks between the detection modules and the central image processor, the selection of clutter-rejection algorithms and the limits of detection for small meteors.