Analytical Design of a High Bandwidth Optoelectronic Signal Link for Use in an EMP (Electromagnetic Pulse) Plus Radiation Environment.

摘要

Electronic systems which must operate in an electromagnetic pulse (EMP) environment are often enclosed in a conducting box, or Faraday enclosure. The conducting walls must have apertures to allow communications with systems outside the enclosure. EMP leakage is minimized when the aperture diameter is small and has finite thickness. In addition, the penetration of a Faraday enclosure by a conductor may result in a significant portion of EMP induced noise inside the enclosure. Optical signals, because of their short wavelength, can efficiently traverse apertures that are highly attenuating to EMP signals. A communication link consisting of a Gallium Aluminum Arsenide laser diode source, optical fiber, and a photodiode detector is well suited to this application. Optical transport efficiency between an optical-fiber-coupled 10-stripe laser diode array and a radiation tolerant Aluminum Gallium Arsenide photodiode is optimized with a graded refractive index (GRIN) rod lens. The lens is positioned in the conducting wall of a Faraday enclosure. The radiation tolerant photodiode is contained inside the enclosure to control EMP induced degradation of the signal-to-noise ratio of the link. The Aluminum Gallium Arsenide photodiode double heterostructure design controls the ionizing-radiation-induced degradation of the link. An optical design analysis is performed to satisfy two criteria. First we select acceptable lens length-to-radius ratios for an aperture filled by a dielectric medium (the glass GRIN-rod lens). This criteria determines the upper limit on potential EMP leakage through the lens and into the Faraday enclosure. Second, we utilize the lens image condition to achieve 98% optical transfer between a nanosecond response, optical-fiber-coupled laser diode and the radiation hardened photodiode. 15 refs., 6 figs. (ERA citation 13:037384)