Survivability Of Army Fiber Optics Systems

Abstract T h:e Army is actively engaged in the development of fiber optics for tactical communica­ tions. Efforts have been underway in the development of fiber optic components that satis­ fy the unique requirements of the military environment. The major issues related to sur­ vival of fiber optics in the field are discussed. The militarized cable and connector, and underlying needs for high strength, fatigue resistant optical fibers able to survive the tactical nuclear environment are presented.IntroductionThe value of fiber optics to the Army.is as far reaching as the benefits offered to the other commerical enterprises - telephony, computer, and video systems. The successful field­ ing of fiber optic communication systems, however, presents a series of special survival considerations that will be highlighted in this paper. The fiber optic communication links under development are aimed primarily at the ground tactical communication trunking links which are responsible for internodal transfer of battlefield information. It is here where heavy and bulky trunk line metallic cable is currently used. This metallic cable is the "work-horse" of the present Army communications network. As such it is deployed and re­ trieved often through rough terrain and subject to the weather conditions of the battlefield. The fiber optic cable system designed to replace these links must be able to survive under these adverse conditions, be subject to rough handling and, in addition, hardened with­ stand the possibility of tactical nuclear deployment.It is the purpose of this paper to:(a) Define the fiber optic communication systemsthat address tactical applications;(b) Outline those aspects which separate the Army requirements from the commerical sys­ tems;(c) Present the most significant examples of developments necessary in the Army fiber optic programs;(d) Describe the critical needs in the area of high strength optical fibers and nuclear hardening. Although fiber strength is relevant to the ground communication system, the glass fiber strength requirement will be discussed as It related to a fiber guided missile.Fiber optics in the tactical environmentThe Army is pursuing the ground tactical application1 of fiber optic technology by addres­ sing replacement of two metallic transmission cables. The first, twin coaxial cable (CX- 11230) will be replacedby the Long Haul Fiber Optic Cable System. This system will interv face with external digital multiplexed traffic at rates from 72kb/s to l8.72Mb/s and trans­ mit at a fixed rate of 19.008Mb/s over optical cable path lengths from 1km to .8km repeater- less and up to 64km using seven repeaters. The second, 26 pair cable (CX-4566) will be re­ placed by the Local Distribution Fiber Optic Cable System. This system will interface with existing analog and digital terminal equipments, multiplexing up to 26 channels for transr- mission over optical cable up to 5km in length. The optical modem is being developed as an external applique unit to mount on standard signal entrance panels, allowing a dual fiber/ metallic capability. The Local Distribution System will use the same optical cable as is being developed for the Long Haul System. Plans are to further enhance the mobility of fi- ber optics in these systems through the development of an airr-layable fiber optic cable sys­ tem. A lightweight, expendable cable and dispensing package is under development that per­ mits high speed laying from a helicopter, ground vehicle, or back pack. This single fiber cable will be compatible with the above systems with the development of couplers by permit­ ting full duplex transmission.The feasibility of using fiber optics for telecommunications has been demonstrated by in­ dustry and the military. The survivability, however, in the tactical environment presents an added dimension to many of the fiber optic components. The significant differences be­ tween the operational tactical environment and strategic, fixed plant in commerical ap­ plications are reviewed in Table 1. These differences are the driving force behind military