| 摘要 |
A broadband tunable in-fiber filter includes a grating with divergent ridges which can be translated transversely of a side-polished optical fiber to vary the periodicity at an exposed evanescent field. The divergence is gradual so that at any given transverse position of the grating, the ridge interacting with the evanescent field are effectively parallel. The divergence is great enough so that a tuning-to-reflected bandwidth ratio of about 33:1 is demonstrated. The grating is fabricated in an amorphous silicon film on a fused quartz substrate. The film is coated with photoresist which is exposed to a holographic interference front. The substrate is tilted with respect to an interference front created by two spherically diverging beams to achieve the desired divergence. Subsequent processing, including etching are standard.
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