Commercially available ray tracing programs by themselves are not adequate for modelling optical systems with holographic gratings. In this paper, we describe a suite of tools that we have developed specifically for working with volume phase holograms. One tool measures the diffraction efficiency of a grating with respect to angle and position. Our automated measurement process is described. The measured diffraction data is analyzed to extract key grating parameters; such as, grating thickness and index modulation. The theoretical basis for this analysis is described. The extracted grating parameters can be used to ray trace expected performance for comparison with direct measurements. Such a methodology has allowed us to develop modelling capabilities that can be confidently used to compare design options and guide development activities. In our environment, data is collected and grating parameters are extracted using LabView; ray tracing is performed using Zemax. The concepts, however, are quite general. An example of measuring a grating recorded in a photopolymer and extracting its grating parameters is given. Results are compared to published datasheet specifications.
Displaying video on a head-up display from an Enhanced Vision System camera or Synthetic Vision System engine
presents some unique challenges not seen on conventional head-down flight deck displays. All information displayed on
the HUD has to be seen against a background that can vary from bright sunlight to a dark night sky. The video has to
include enough grayshade information to support visual identification of runway features and the image shown on the
HUD has to be visually aligned to the real world accurately enough to support low-visibility operations at airports. The
pilot needs to clearly see the image on the HUD but also needs to see the real world through the display when it can be
seen with the naked eye. In addition, the video display cannot interfere with the display of existing flight information
symbology.
The development of a liquid crystal on silicon (LCOS) projector based Head-Up Display (HUD) is nearing completion and the first products are being readied for Flight Test. Rockwell Collins Flight Dynamics (RCFD) has reported previously on the designs, performance requirements, and measured performance of two prototype versions, as well as the potential benefits of the technology and the technical challenges remaining. This paper reviews some of the key performance requirements, enabling technologies, and preliminary measured results from the first pre-production units. There is also a comparison of the LCOS projector based HUD to two evolving digital HUD technologies.
LCD projection-based cockpit displays are beginning to make entry into military and commercial aircraft. Customers for commercial Head-Up Displays (HUDs)(including airframe manufacturers) are now interested in the adaptation of the technology into existing and future HUD optical systems. LCD projection can improve mean-time-between-failure rates because the LCDs are very robust and the light sources can be replaced with scheduled maintenance by the customer without the need for re-calibration. LCD projectors promise to lower the cost of the HUD because the cost of these displays continues to drop while the cost of CRTs remain stable. LCD projectors provide the potential for multi-colors, higher brightness raster, and all-digital communication between the flight computer and display unit. Another potential benefit of LCD projection is the ability to increase field of view and viewing eyebox without exceeding existing power budgets or reducing display lifetime and reliability compared to the capabilities provided by CRTs today. This paper describes the performance requirements and improved performance of a third-generation LCD projection image source for use in a wide field of view head-up display (HUD) optical system. This paper will focus on new HUD requirements and the application of various technologies such as LCOS microdisplays, arc lamps, and rear-projection screens. Measured performance results are compared to the design requirements.
There are many technical approaches to replacement of the CRT image source for a Head-Up Display (HUD). LCD projectors promise to greatly lower the cost of the HUD because the cost of these displays continues to drop while the cost of CRTs remains stable. LCD projectors allow the realization of multi-colors in the HUD. Their high luminance provides bright raster images, where CRTs are limited by the constraints of the scanning electron beam. Finally, LCD projectors have a digital interface. There are none of the high voltage power supplies, A/D converters, and deflection amplifiers found in CRT drive systems, further improving cost and reliability. This paper describes the performance requirements and achieved performance of an LCD projection image source for use in a wide field of view head-up display (HUD) optical system.
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