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11 November 2008Ultra narrow flat-top filter based on multiple equivalent phase shifts
Instead of real phase shifts, equivalent phase shifts (EPS) are adopted to construct ultra narrow phase-shifted band-pass
filer in sampled Bragg gratings (SBG). Two optimized distributions of multiple equivalent phase shifts, using 2 and 5
EPSs respectively, are given in this paper to realize flat-top and ripple-free transmission characteristics simultaneously.
Also two demonstrations with 5 EPSs both on hydrogen-loaded and photosensitive fibers are presented and their
spectrums are examined by an optical vector analyzer (OVA). Given only ordinary phase mask and sub-micrometer
precision control, ultra-narrowband flat-top filters with expected performance can be achieved flexibly and cost-effectively.