Development of an Optical Feedback Based High Accuracy Beam Transmissometer

摘要

Work concentrated on the fabrication of the optical bridge components, specifically the implementation of the proposed light source and detector assembly. Significant progress has been made toward the development of a reliable package fabrication technique for the light source and detector assembly. The integrated light source assembly consisting of the header, Siemen's blue LED and reference detector has been tested to determine if sufficient power output is available to obtain a signal to noise ratio of 60 dB. The reference detector current was 0.1 microamps at an LED current of 100 milliamps. This detector current is adequate to obtain the required signal to noise ratio but the LED current is higher than anticipated. The Cree blue LED is expected to solve this problem since it should have higher power output then a thermistor will be added to the integrated light source package to monitor the reference detector temperature allowing one to compensate for temperature effects. Most of the effort during this period was expended in trying to package the LED and reference detector. The potting of the integrated device posed some difficult problems which are hopefully solved. As always air bubbles were removed in a vacuum and the impurities problem was solved by using a centrifuge. (JHD)