Photonic bandgap terahertz fibers based on honeycombed tubes

Terahertz fibers are highly applicable for short-haul stable terahertz transmissions, and thus have potential use in upgrading terahertz systems. In this paper, a photonic crystal structure consisting of honeycombed tubes is proposed. Numerical studies based on the plane wave expansion method demonstrate that, in comparison to the photonic crystal consisting of honeycombed airholes or triangulated tubes, the one proposed in this paper can deliver a broader and less dispersive bandgap, which has been further confirmed by another calculation based on the finite element method. Then a fiber structure is designed to perform the single mode guidance for a broad spectrum of terahertz waves. The second derivative of mode effective area is introduced to define the effective guiding spectrum for the bandgap terahertz fiber. Mode calculations are performed by use of the finite element method, in which the imaginary part of material refractive index is directly took into account. Obtained results show that the designed fiber suffers low transmission losses over a broad spectrum centered at 1 terahertz. Further, an optimized design is worked out to exhibit the lowest loss for the frequency of 1 terahertz, coming up to 0.3 dB/cm. Not only that, this design can also provide nearly zero flat dispersions with |β2| 1 ps2/cm over 0.81-1.12 terahertz, as well as negligible bending induced losses (< 10−11 dB/cm) for bending radii larger than 1 cm , indicative of a good transmission characteristic for terahertz pulses. Finally, we discuss possible fabrication methods on the proposed fiber.