Showing papers on "Photonic crystal published in 1985"

Bandgap resonant optical nonlinearities in InAs and their use in optical bistability

Abstract: A detailed study of bandgap resonant optical nonlinearities in n-type InAs and their use in an optical bistable device is presented. The results of measurements of both nonlinear absorption and nonlinear refraction taken with an HF laser show good agreement with a band-filling model in which the contribution from the light-hole band and the effects of large initial free carrier densities are included. Evidence of the saturation of the nonlinear refraction through the carrier-density-dependent recombination rate is presented, and it is shown that this effect together with diffraction effects accounts for the critical power for bistability observed in the reflected signal from an InAs etalon at 77 K.

A low-crosstalk liquid crystal optical switch

Abstract: The performance of a low-crosstalk polarization-insensitive liquid crystal optical switch is reported. Polarization rotation by a nematic twist cell and attenuation by a dynamic scattering cell are the switching mechanisms. The maximum crosstalk ratio for this 1 × 2 optical switch is -82 dB, which is suitable for switching analog as well as digital signals.

Commercial Development of a Fluorescence Polarization Instrument for Clinical Use

Abstract: James T. Holen possible that works by forming large molecules from small Paul R. Schrier fluorescent dye-tagged molecules, the degree of the reaction Abbott Laboratories could be measured sensing the polarization changes of the emitted light as the reaction proceeds. Based on the 1976 proposal, the Abbott scientists comINTRODUCTION bined fluorescence polarization with techniques from immunology to develop new assays. The immunology phase OVER the last five to ten years, there has been a rise in the involves the injection of laboratory animals with a special Omonitoring of serum levels of therapeutic drugs, which is preparation of the substance, or analyte, for which the assay particularly important for drugs that have a narrow therapeuis being developed. If all goes well, after several months the tic range. Each individual absorbs, metabolizes, and excretes animal will develop antibodies to this analyte. In the assay, if drugs at a different rate. Thus, in order to assure the most the analyte is present, the specific antibodies will combine effective treatment, the patient's serum drug level should be with the analyte, reducing the number of fluorescent analyte periodically measured, so that the dosage may be adjusted as analogs (tracers) that can bind to the antibody, which results needed. in a relatively low polarization. If no analyte is present, more As the use of drug monitoring became more accepted, a of the tracer can bind to the antibodies, resulting in a high number of companies entered the business with a variety of polarization. The exact amount of analyte can be determined techniques and products intended to facilitate the testing of using a standardized calibration curve. patient serum in clinical laboratories. This article traces the Although the project was proposed in 1976, it was not until development of Abbott Laboratories' TDx System [1, 2, 31 April of 1977 that funding was finally approved, and several from its conception in 1977, through market entry in 1981, scientists and engineers were hired or transferred to work on and widespread clinical use by 1984. Also included are the the project. It was the first time at Abbott that scientists and solution of two specific technical problems, and a discussion engineers were put on the same team. This integration of some key factors contributing to the success of this resulted in better coordination and communication between instrument. people from two quite different disciplines. Simplification of the optical apparatus represented a signifiHISTORY cant technical problem in the development of a fluorescence In August of 1976, at a planning session, several scientists polarization instrument. To take a measurement, the plane of at Abbott Laboratories proposed that the company fund a polarization of the excitation beam must be periodically project to explore the applications of fluorescence polarizarotated 90 degrees. Previous apparatus employed special tion technology for measuring T4, a thyroid hormone, and polarizer crystals in mechanical mounts that were rotated digoxin, a cardiac drug. either by hand or by motor. An instrument based on these Although fluorescence polarization instrumentation had mechanically moved crystals would occupy most of the been developed as early as 1926 [41, no clinical use had been originally proposed cabinet space (48 cm wide x 38 cm deep made of this simple, yet sensitive technique. Fluorescence x 28 cm high). The mechanical hardware was costly and polarization is based on the principle of Brownian motion that would present increased reliability concerns. In addition, the small molecules rotate faster than large molecules [51. When crystals themselves are expensive. The problem was solved illuminated by polarized light of the correct wavelength, by replacing the mechanically operated crystals with a liquid fluorescent molecules that are oriented parallel to the plane of crystal rotater. A cholesteric fluid was sealed between two polarization will absorb some of the incident photons. Nanoparallel conductive glass plates. The plane of optical polarizaseconds later, these same molecules will emit photons of tion rotates upon the application of an electrical potential light at a longer wavelength. However, this light will be applied across the fluid. Thus, all moving parts were elimidepolarized to the extent that the molecules have rotated nated from the optics module. The entire device was only 25 between the time of excitation and emission. If an assay were mm square and 3 mm thick. By late 1978, the project was in danger of being canceled because of the difficulty in making the initial assays work. In October 1978, the project was assigned to a new project leader, who believed that fluorescence polarization was ideal for monitoring therapeutic drugs. However, upper management was skeptical about the potential for this new market. The project leader and key scientists did an extensive literature search to gather data showing that the monitoring of certain drugs would result in fewer medical complications and more effective treatment. The worldwide market was estimated then to be about $50 million per year. Abbott agreed to provide more funds and to change the program in order to develop a fully automated therapeutic drug monitoring system. The team started work on various drug assays and the