An extension of paraxial theory to systems with a single plane of symmetry is provided. This parabasal model is based on the evaluation of a differential region around the reference ray that is defined by the center of the object and the center of the stop. To include freeform surfaces in this model, the local curvatures at the intersection point of the reference ray and the surface are evaluated. As an application, a generalized Scheimpflug principle is presented. The validity of the derived formulas is tested for highly tilted surfaces and is in good agreement with the exact ray tracing results. The analytical expressions are used to provide a first-order layout design of a planar imaging system.
A contactless fingerprint sensor provides deformation-free, high-quality fingerprint images and offers users a cleaner and
more comfortable measurement environment. Here we propose and design an innovative prototype optical, contactless,
compact, fingerprint sensor that quickly produces high-quality, high-contrast interoperable fingerprint images. A proofof-
concept contactless, aliveness-testing (CAT) fingerprint sensor, which is connected to a PC via a firewire cable, was
constructed and is currently operating in our laboratory. The CAT sensor affords a more user-friendly interface
compared to existing contactless fingerprint sensors and also provides robust aliveness testing and spoof detection. In
this paper, we present the imaging system design concepts, finger aliveness detection techniques, and the user-friendly
interface approach. Various fingerprint matching results using the CAT sensor device are also presented and discussed.
When a fingerprint image is acquired via contactless means, the depth of field must be measured. Due to the natural
curvature of a finger, not all of the fingerprint will be in focus. Defocus introduced by such curvature may cause contrast
reduction, loss of certain spatial frequencies, blurriness, and contrast reduction and reversal. We need to ensure that the
imaging system has enough depth of field to compensate for the longitudinal displacement created by the finger
curvature. This paper presents theoretical and experimental techniques to simulate and measure the depth of field of an
imaging system. Experimentally, image contrast as a function of object position along the optical axis is measured for
several spatial frequencies of interest, and the defocused modulation transfer function (MTF) is determined. The
acceptable contrast range is defined by the system application and used to determine the corresponding depth of field. A
diffraction image irradiance theoretical model is developed, and the Zemax optical design program is used to simulate
depth of field. The experimental and simulated depth-of-field results are presented and applied to a contactless
Illumination is critical to achieve high-contrast, contactless fingerprint images. In this paper, we report results of
fingerprint imaging experiments performed under different illumination conditions. We studied how polarization states,
illumination wavelength, detection wavelength, and illumination direction influence the contrast of fingerprint images.
Our research findings provide a selection rule for optimum illumination and a basis for us to construct an illuminator that
generates uniform illumination and high-contrast contactless fingerprint images.
This paper develops a methodology to model ghost images that are formed by two reflections between the surfaces of a
multi-element lens system in the paraxial regime. An algorithm is presented to generate the ghost layouts from the
nominal layout. For each possible ghost layout, paraxial ray tracing is performed to determine the ghost Gaussian
cardinal points, the size of the ghost image at the nominal image plane, the location and diameter of the ghost entrance
and exit pupils, and the location and diameter for the ghost entrance and exit windows. The paraxial ghost irradiance
point spread function is obtained by adding up the irradiance contributions for all ghosts. Ghost simulation results for a
simple lens system are provided. This approach provides a quick way to analyze ghost images in the paraxial regime.
This past spring a new for-credit course on illumination engineering was offered at the College of Optical Sciences at
The University of Arizona. This course was project based such that the students could take a concept to conclusion. The
main goal of the course was to learn how to use optical design and analysis software while applying principles of optics
to the design of their optical systems. Projects included source modeling, displays, daylighting, light pollution, faceted
reflectors, and stray light analysis. In conjunction with the course was a weekly lecture that provided information about
various aspects of the field of illumination, including units, étendue, optimization, solid-state lighting, tolerancing, litappearance
modeling, and fabrication of optics. These lectures harped on the important points of conservation of
étendue, source modeling and tolerancing, and that no optic can be made perfectly. Based on student reviews, future
versions of this course will include more hands-on demos of illumination components and assignments.