Austin V. Harton

Reliability Study of Holographic Optical Elements Made with DuPont Photopolymer.

We report reliability-test results of transmission-type holographic optical elements (HOEs) made with the DuPont photopolymer HRF-600. The reliability tests performed include 6000 cycles of liquid-to-liquid thermal-shock cycling (-55 degrees C-125 degrees C), 2200 cycles of air-to-air thermal cycling (-55 degrees C-125 degrees C), 1500 h of humidity testing (85 degrees C and a relative humidity of 85%), and 675 h of burn-in testing at 125 degrees C. A total of 210 holograms was tested, with 532 data points collected for diffraction-efficiency measurements. The results show that the average efficiency change after these tests is in the range of -4% to 0% and the standard deviation is only ~10%.

High dynamic range CMOS image sensor with pixel level ADC and in-situ image enhancement

We describe a CMOS image sensor with pixel level analog to digital conversion (ADC) having high dynamic range (>100db) and the capability of performing many image processing functions at the pixel level during image capture. The sensor has a 102x98 pixel array and is implemented in a 0.18um CMOS process technology. Each pixel is 15.5um x15.5um with 15% fill factor and is comprised of a comparator, two 10 bit memory registers and control logic. A digital to analog converter and system processor are located off-chip. The photodetector produces a photocurrent yielding a photo-voltage proportional to the impinging light intensity. Once the photo-voltage is less than a predetermined global reference voltage; a global code value is latched into the pixel data buffer. This process prevents voltage saturation resulting in high dynamic range imaging. Upon completion of image capture, a digital representation of the image exists at the pixel array, thereby, allowing image data to be accessed in a parallel fashion from the focal plane array. It is demonstrated that by appropriate variation of the global reference voltage with time, it is possible to perform, during image capture, thresholding and image enhancement operations, such as, contrast stretching in a parallel manner.

Enhanced reflective liquid crystal displays using DuPont holographic recording films

Holographic reflectors with high brightness and excellent environmental stability have been produced using DuPont holographic films. The center wavelength, color bandwidth and viewing cone are defined for the optimal viewing performance. Measurement methods used to quantify holographically enhanced reflective LCD performance are presented. The test results show that holographic reflectors based on the DuPont OmniDex film experienced less than 1 percent brightness degradation under 70 degrees and 95 percent relative humidity for 200 hours, with no measurable color shift. Two examples of how this technology can be extended to enhance color LCDs are also presented.

Holographic Reflectors for Enhanced Reflective LCDs

Monocolor and multicolor holographic reflectors have been designed and fabricated using DuPont holographic photopolymers. High brightness, saturated color and a choice of well-defined center wavelengths have been demonstrated. When affixed to the back of reflective LCDs, they provide enhanced contrast and brightness. The environmental stability and optical performance of DuPont films have demonstrated that they exceed the specifications of all Motorola portable products. Commercial products will be introduced in early 1998.

Experimental study on mechanical, thermomechanical, and optomechanical behaviors of holographic materials

This paper discusses material behaviors of holographic materials in terms of mechanical, thermomechanical properties and their effects on optical efficiency. Experiments were carried out to characterize coefficient of thermal expansion, stress strain curves, and dynamic mechanical behaviors of photopolymers. It has been found that in-plane deformation of photopolymer has a minimum effect on the diffraction efficiency while out-of-plane deformation can significantly contribute to the diffraction efficiency of holographic optical elements.

Reliability study of holographic optical elements made with DuPont photopolymer

In this paper, we report the reliability test results of transmission-type holographic optical elements made with DuPont photopolymer HRF-600. The reliability tests performed in this study include 6000 cycles of liquid-to-liquid thermal shock cycling, 2200 cycles of air-to-air thermal cycling, 1500 hours of humidity test, and 675 hours of burn- in test at 125 degrees C. A total of 210 holograms was tested, with 532 data points collected for efficiency measurements. The results show that the average efficiency change after these tests is negligible and that the standard deviation is only approximately 10 percent.

Circuit-level model of semiconductor photodetectors

In this paper, we present a circuit-level model of semiconductor photodetectors which accounts for photocurrent, dark current, junction capacitance, and other parasitic effects. We have implemented the model within a standard circuit-level simulation environment While parasitic elements will typically place the ultimate limit on high-speed device performance, in some cases the transit-time limited impulse response of the photocurrent can also be important. In order to properly account for this effect, prior circuit-level modeling efforts have been based on the modification of existing simulation code to account for the numerical convolution of an optical input signal with the impulse response. We, on the other hand, will demonstrate how existing linear component models can be used to describe the impulse response, thereby greatly simplifying the implementation of our model by circumventing the need to modify the simulator. Additional linear and nonlinear elements are added to account for dc and parasitic effects. These include the intrinsic current-voltage characteristics of the device, series resistance, and junction capacitance. After discussing the theory and implementation of our model, we demonstrate its ability to simulate device behavior during dc, small-signal, and transient operation.