Highly Birefringent Terahertz PCF Using Epsilon-Near-Zero (ENZ) Material for Polarization Maintaining Applications

We propose an innovative triangular lattice photonic crystal fiber (PCF) in terahertz (THz) that incorporates gain doping and epsilon-near-zero (ENZ) material to attain elevated birefringence and linear polarization. The selective filling of four holes with ENZ material in cladding's first ring, while leaving the other two as air-filled, results in an asymmetrical material and structural configuration. The considerable loss of ENZ material establishes a notable disparity in loss between the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$X$</tex>-polarized, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Y$</tex>-polarized, and other higher-order modes. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$X$</tex>-polarized mode exhibits a marginally greater field distribution in the ENZ material, thereby permitting only the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Y$</tex>-polarized mode to realistically persist in PCF after a brief propagation distance. The incorporation of doped gain material in core slots effectively mitigates losses in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Y$</tex>-polarized mode due to ENZ while maintaining the existing loss differential. This proposed PCF demonstrates a significant value of 0.6201 in birefringence, prominent differential loss of ~ 11.4 dB/cm, and 0.2 THz of Linear-Polarization Single-Mode (LPSM) bandwidth between 1.3 and 1.5 THz. This PCF seems to be the most significant birefringent photonic crystal fiber showcasing an extensive LPSM bandwidth documented in the THz range. These attributes enable this PCF to be critical for their applications in polarization-sensitive THz filters, modulators, and sensors.