In the fourth quarter of FY 80, 8 km of ruggedized facsimile cable was wound, payed 

 out, and filmed with high-speed photography. The facsimile cables allowed us to check the 

 winding/fabrication technique of the spools and also the payout test procedures without 

 wasting expensive fiber-optic-cored cables. Payout tests of the facsimile cable proved that the 

 adhesive was of sufficient strength for packing the stiff cable and yet yielded only about 0.5 

 lb of tension at payout speeds of 10—65 knots. In parallel with the payout work, two 1-km 

 lengths of ITT fiber were ruggedized. Attenuation measurements before and after ruggedizing 

 indicated no measurable change in loss. Each 1-km length of ruggedized cable was then 

 precision-wound at the NOSC, San Diego, facility. One spool was taken to NOSC, Hawaii, 

 and pressure-tested to 7000 psi while the attenuation was monitored. The other spool was 

 taken to the Naval Underwater Systems Center, Newport, for payout tests where both 

 attenuation and tension could be monitored. At a 1000-psi pressure, excess attenuation of 

 0.1 and 0.6 dB/km at 0.83-Mm wavelength was detected on the different tests. The spool 

 remained structurally intact after being subjected to as much as 7000 psi. There was no 

 permanent damage to the optical fiber at 7000 psi since attenuation measurements conducted 

 many days after pressurization showed no significant change in the baseline loss characteristics. 

 The payout tests were done at speeds from 10—65 knots and no detectable increase in attenu- 

 ation resulted from payout stresses. Attenuation measurements on the cable before and after 

 ruggedizing and winding showed no adverse attenuation effects from either process. Tem- 

 perature cycling tests on the cable are planned for early FY 8 1 . 



3.1.5 FUTURE WORK 



Work to date has shown that an expendable fiber-optic cable of small size can be 

 deployed reliably at speeds from 10—65 knots. Lengths as great as 4 km have been ruggedized, 

 wound, and successfully payed out. In achieving this, it has been found that some ruggediza- 

 tion has been necessary to provide bending stiffness and added tensile strength to the bare 

 optical fiber. Excess attenuation attributable to pressure has been found to be small at 

 pressures up to 1000 psi, and to increase rapidly to unacceptable levels at pressures beyond 

 2000 psi. No excess attenuation was detected because of dynamic stresses on the cable during 

 payout. The ruggedization and precision winding of the optical fiber had no measurable effect. 



Future work will be directed at eliminating the pressure sensitivity of the cable as well 

 as any adverse temperature effects. An effort also will be made to reduce the size of the 

 ruggedized cable. This will result in a much better volumetric efficiency for the optical link. 

 The goal will be a 25-mil-OD cable. 



To reduce cable cost, an effort will be made to reduce the tensile strength of the 

 fiber to a level that can be compensated for by the ruggedizing layer. The goal will be to 

 achieve a 10— 20-pound tensile proof load on the composite cable. In a further effort to 

 reduce dramatically the mission cost of the cable, it is believed that the USGS program should 

 investigate the possibihty of reusing the cable for several missions. The major disadvantages 

 of this approach are the decreased reliabihty of the link with each use and the requirement to 

 reprepare the cable for winding. However, it should be noted that a USGS inspection mission 

 is not a weapon delivery situation, and that reuse of the cable can be facilitated by incorporat- 

 ing a thin, say 1 -mil-thick, layer of Hytrel around the ruggedizing material so that the spooling 

 provides a bond between the plastic layers rather than the ruggedizing material. During 

 deployment, the plastic sheath would become a tear-away layer, leaving the deployed cable 

 relatively clean and readily reusable. It is estimated that the cost of re-extruding the plastic 

 layer will be minimal. Future developments in sphcing the ruggedized cable also will tend to 

 make this multiple-use concept more attractive. 



26 



