Phoropters are the most common instrument used to detect refractive errors. During a refractive exam, lenses are flipped in front of the patient who looks at the eye chart and tries to read the symbols. The procedure is fully dependent on the cooperation of the patient to read the eye chart, provides only a subjective measurement of visual acuity, and can at best provide a rough estimate of the patient’s vision. Phoropters are difficult to use for mass screenings requiring a skilled examiner, and it is hard to screen young children and the elderly etc. We have developed a simplified, lightweight automatic phoropter that can measure the optical error of the eye objectively without requiring the patient’s input. The automatic holographic adaptive phoropter is based on a Shack-Hartmann wave front sensor and three computercontrolled fluidic lenses. The fluidic lens system is designed to be able to provide power and astigmatic corrections over a large range of corrections without the need for verbal feedback from the patient in less than 20 seconds.
The very first demonstration of our refreshable holographic display based on photorefractive polymer was published in
Nature early 2008<sup>1</sup>. Based on the unique properties of a new organic photorefractive material and the holographic
stereography technique, this display addressed a gap between large static holograms printed in permanent media
(photopolymers) and small real time holographic systems like the MIT holovideo. Applications range from medical
imaging to refreshable maps and advertisement. Here we are presenting several technical solutions for improving the
performance parameters of the initial display from an optical point of view. Full color holograms can be generated
thanks to angular multiplexing, the recording time can be reduced from minutes to seconds with a pulsed laser, and full
parallax hologram can be recorded in a reasonable time thanks to parallel writing. We also discuss the future of such a
display and the possibility of video rate.
A 40W one-cm laser diode array was coupled to a .22NA 200micron diameter optical fiber,
using a compact monolithic 3-D waveguide based device, with 50% coupling efficiency. No
auxiliary optical elements were used between the array and the coupler, or between the
coupler and the optical fiber.
The possibility of reducing information loss in holographic memory systems in which different wavelengths are used for data recording and reconstruction has been investigated. We suggest replacing a thick recording medium which provides selective reconstruction of the holographic data with a multilayer recording structure. It has been shown that such a structure has the selectivity which significantly exceeds the selectivity of a single layer. At the same time it permits compensation for the Bragg mismatch along the thickness of the recording medium when 2-wavelength reconstruction is implemented. We consider various methods for such compensation and the possibility of their realizations.
The application of volume M-type holograms for building multichannel geometries in pattern recognition system is considered. The results of theoretical and experimental investigations of the hologram's parameters as a function of their recording parameters and their use as filters in correlation setups are presented. Multichannel correlation schemes where the processed signals have either different or the same wavelength are proposed. We have shown that all the correlation schemes proposed allow one to increase data throughput several times over single- channel BR-based correlators.
The degree of protection for common types of security holograms is reviewed. The possibility of hologram recording directly from the holographic film being used for protection is demonstrated. We suggest the structure of security hologram allows one to prevent such unwanted copying. We also propose a detection system which provides for fast testing of a hologram's authenticity.