In the early 1950s the researchers who produced the first clad glass optical

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问题 In the early 1950s the researchers who produced the first clad glass optical fibers were not thinking of using them for communications.【C1】H______, fiber optics was already a well-established commercial technology when the famous paper by Kao and Hockham,【C2】______ (claim)the use of low-loss optical fibers for communication, appeared in 1966. The first low-loss silica fiber was described in【C3】______which appeared in October of 1970. The date of this publication is sometimes【C4】______(cite)as the beginning of the era of fiber communication. Although this development did receive【C5】______(consider)attention in the research community at the time, it was far from inevitable that a major industry would evolve.
The technological barriers appeared formidable because there were serious doubts as to【C6】wh______these fiber components could ever be produced economically enough, but the market potential was very significant.【C7】______(consequence), research and development activity expanded rapidly, and a number of important issues were【C8】re______during the early 1970s. During the middle and late 1970s, the rate of progress towards marketable products accelerated as the emphasis【C9】______(shift)from research to engineering. Fibers with losses【C10】app______the Rayleigh limit of 2 dB/km at a wavelength of 0. 8 μm were produced.
By 1980 improvement in component performance, cost, and reliability led to major commitments on the part of telephone companies. [br] 【C9】

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答案 shifted

解析 shift指位置或方向的移动、改变；指由一种形式或用途改变为另一种形式或用途。

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