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An electrically controllable fiber-optic filter for broad-band rejection has been demonstrated by periodically poling a liquid-crystalline core in a hollow-core fiber by means of an external long-period-combed electrode. The periodically poled liquid-crystalline core in a period of 483 μm couples the fundamental core mode to the leaky cladding modes. A maximum loss dip of approximately 15-nm bandwidth and 6 dB band rejection has been obtained for a nonpolarized light with a combed 250-V external voltage modulation. The experimental result matches well with a numerical expectation, which has been analyzed by the discretized coupled-mode theory for an anisotropic perturbation.