<title>A very unique pre-1970 fiber optic instrumentation system</title>

Abstract

Prior to 1970, when fiber optics was still in its infancy, an elaborate instrumentation system had already logged hundreds of hours of field operation using fiber optics for all command, control and data collection, as well as for some sensing. It seems highly improbable, when the best solid-state light sources of that period were not intended for communication purposes, fiber optic connectors were not commercially available, and the best fibers had losses measured in deciBels per meter (not kilometer).To totally eliminate all electrical wiring, the whole system was designed to run on nothing but compressed air, delivered by hoses composed only of dielectric material. This paper tells the unpublished story of some very early, very novel, fiber optic systems which were designed, built and operated by Boeing during the 1969 to 1974 time period to solve some extremely difficult instrumentation problems.A brief review of the early history of fiber optics is included to help the reader better understand the problems of those early days, as well as appreciate the vast improvements which have been made during the past 20 years. HISTORICAL PERSPECTIVESignaling with light, one way or another, is probably as old as the history of man. Ancient man is known to have used sunlight and primitive reflectors for visual communication over short distances. Shortly after inventing the telephone in 1874, Alexander Graham Bell (and others) became intrigued with the photoconductive properties of selenium and began experimenting with optical voice communication [1]. Using the sun as a light source, and a mechanical light-gate modulator for a transmitter, Bell successfully transmitted a voice message over a 213-meter path. In 1880, he was granted two U. S. patents, No. 235,199 and No. 235,496 [2,3] on his "photophone" [4]. For the next eighty years or so, many concepts were proposed for optical communications, but nearly all of them relied on atmospheric tranmission, and all of them suffered the same severe limitations because they were all vulnerable to mechanical vibration and a variety of thermal, atmospheric, and acoustic effects. Due to the invention of the laser and the desire to transmit light over more complicated paths and over longer distances, various ideas for an optical conduit emerged in the 1960s. Several of the concepts involved various systems of lenses [5] and prisms, and tubing with internally mirrored walls [6,7] . Considerable work was also done on a gas-filled conduit which was heated to produce an approximately parabolic refractive index profile [8,9] approximating that of a modern gradedindex fiber.