The application of a nematic liquid crystal infiltrated solid core photonic crystal fiber as a novel all-fiber in-line electronically controlled broadband fiber optic attenuator in the wavelength range from 1500 to 1600 nm is demonstrated.The device based on photonic bandgap transmission is electronically controlled and, due to its compact configuration, can be easily incorporated into an optical network. A low-insertion loss at zero attenuation state and a high-extinction ratio of ∼40 dB are obtained between the high and low transmission states of the attenuator. The device works on the application of a varying voltage applied perpendicular to the fiber axis. The attenuation varies linearly with an increase in voltage, with a ∼3.5 V increment required for 1 dB attenuation. The device is shown to have a flat spectral response for all attenuation states in the wavelength range. The device can be used as the core of a highly efficient in-line electronically controlled variable fiber optic attenuator. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:539–543, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25789