Circular hole ENZ photonic crystal fibers exhibit high birefringence

Abstract

Abstract-A novel photonic crystal fiber (PCF) design that yields very high birefringence is proposed and analyzed. Its significantly enhanced birefringence is achieved by filling selected air holes in the cladding with an epsilon-near-zero (ENZ) material. Extensive simulation results of this asymmetric material distribution in the lower THz range demonstrate that the reported PCF has a birefringence above 0.1 and a loss below 0.01 cm -1 over a wide band of frequencies. Moreover, it exhibits near zero dispersion at 0.75 THz for both the X-and Y-polarization modes and a birefringence equal to 0.28. This THz PCF is then scaled successfully to optical frequencies. While the high birefringence is maintained, this optical PCF has a very high loss in its Y-polarization mode and, consequently, yields single-polarization single-mode (SPSM) propagation, exhibiting near zero dispersion at the optical telecom wavelength of 1.55 μm. The ideal ENZ materials used for these conceptual models are replaced with realistic ones for both the THz and optical PCF designs. With the currently available ENZ materials, the realistic PCFs still have a high birefringence, but with higher losses compared to the idealized results. Future developments of ENZ materials that achieve lower loss properties will mitigate this issue in any frequency band of high interest.

Highly Birefringent, Low-Loss, and Near-Zero Flat Dispersion ENZ Based THz Photonic Crystal Fibers

“…Considering the behavior of the PCF by varying different structural parameters i.e., d 1 , η, and , the PCF properties are discussed. Our PCF structure relies on circular air-holes of same diameter and has only one elliptical air-hole at the centre, whereas in [4] two dissimilar diameter of air-holes were used, making the structure extremely challenging to fabricate with the most common fiber drawing technique. Since elliptical air-hole has been possible to fabricate in the laboratory, our proposed PCF having only one elliptical air-hole seems experimentally feasible and realistic [13], [14].…”

“…Since our proposed Type-II PCF structure contains selectively filled air-holes with naturally occurring ENZ material, the implantation of ENZ material into the fiber air-holes is possible using the well-established fabrication techniques, e.g., direct thermal drawing [15], pressure-assisted melt filling technique [17], or chemical deposition technique [18]. We believe that our PCF structure can be practically implemented using the pressure-assisted melt filling technique to implant the bulk form of KCl into appropriate air-holes without any major complications [4].…”

“…Contrary to conventional fibers, PCFs offer unique guiding properties, such as, endlessly single mode propagation, tailorable dispersion, high birefringence and good confinement ability [3]. Among various guiding properties, birefringence is one of the key factors in THz PCFs, and is highly desirable in many applications, e.g., in sensing, filtering, splitting, and polarization-based THz wave guiding [4]. Another important application of THz PCFs is in the data transmission purpose, where zero-flat dispersion is the primary requirements.…”

“…Later, Habib et al designed and numerically investigated a PCF having decagonal arrangement of circular air-holes at the cladding region and eight elliptical air-holes oriented at core region with reported birefringence of 0.0299 and negative-flat dispersion of −558.96 ps/nm/km [7]. Recently, a simple hexagonal PCF is numerically investigated in both THz and telecom band with reported birefringence of 0.105 and 0.07, respectively [4]. The PCF is filled with the ENZ material (KCL in THz band and AZO in telecom band) to achieve this result.…”

“…The relation between the axes can be expressed as b = η × a, where η represents the ellipticity. In our study, we use TOPAS as the main fiber material which has a fixed refractive index of 1.53 near 6.3 THz [4]. The optimized parameter configuration of the PCF to achieve near zero-flat dispersion, high birefringence and low loss has = 25 μm, d/ = 0.95, a = 0.2 , η = 0.4.…”