A high-strength, low-linear expansion coefficient tight-jacketed optical fiber is proposed using thermotropic liquid crystal polymer (LCP). The 0.9-mm-diameter LCP-jacketed optical fiber with breaking strength of 51 kg at strain of 3.4% at 25 can be used over the wide 60 to 200 temperature range.

Primary silicone-rubber/secondary liquid-crystal-polyester (LCP)-coated optical fibers have loss increases as low as 18 dB/km even at liquid uitrogen temperatures. This result can be explained by both low contraction and the buffer effect against heat shock of the secondary LCP layer which results in less fiber bending.

The loss change for liquid-crystal-polymer(LCP)-jacketed optical fibers has been investigated under lateral load. A 0.7 mm LCP-jacketed optical fiber has the same lateral-load resistance as that of a conventional 0.9 mm nylon-jacketed fiber to continuing constant lateral load.

The influence of impurities in performs and of the drawing condition on the hydrogen-induced loss increase in the OH absorption band and the radiation-induced loss increase is investigated. The loss increase is much larger in fibers contaminated by sodium. Moreover, the loss increase in fibers with natural SiO2 clad, which is contaminated by alkali ions, increases with increasing maximum temperature in the drawing furnace and with decreasing drawing speed. By thermodynamically analyzing these results, the origin of the loss increase is identified as follows:(1) The OH loss increase and the radiation-induced loss increase are ascribed to the same origin.(2) The structural reorientation from GeO4 tetrahedrons to GeO6 groups thermally occurs in the drawing process, when the perform is contaminated by alkali ions.(3) The loss increase is induced through the reaction of H2 and radiation with GeO6 groups.