Continuously tunable bandpass filter based on liquid-filled photonic crystal fibers

The implementation of a novel continuously tunable bandpass filter based on liquid-filled photonic crystal fibers is reported. The filter function is based on the tunable overlapping bandgaps of two photonic crystal fibers resulting from the thermo-optic effect of the filled liquid. The center wavelength and the width of the filter can be easily designed by selecting the refractive indexes of the filled liquid, and the width of the transmission bands can be continuously widened or narrowed by heating different liquid-filled parts.