Broadband high birefringence and polarizing hollow core antiresonant fibers

Abstract

Abstract:We systematically study different approaches to introduce high birefringence and high polarization extinction ratio in hollow core antiresonant fibers. Having shown the ineffectiveness of elliptical cores to induce large birefringence in hollow core fibers, we focus on designing and optimizing polarization maintaining Hollow Core Nested Antiresonant Nodeless Fibers (HC-NANF). In a first approach, we create and exploit anti-crossings with glass modes at different wavelengths for the two polarizations. We show that suitable low loss high birefringence regions can be obtained by appropriately modifying the thickness of tubes along one direction while leaving the tubes in the orthogonal direction unchanged and in antiresonance. Using this concept, we propose a new birefringent NANF design providing low loss (~40dB/km) and high birefringence (>10 −4 ) over a record bandwidth of ~550nm, and discuss how bandwidth can be traded off to further reduce the loss to a few dB/km. Finally, we propose a polarization mode-stripping technique in the birefringent NANF. As a demonstration, we propose a polarizing birefringent NANF design that can achieve orthogonal polarization loss ratios as large as 30dB over the C-band while eliminating any undesirable polarization coupling effect thereby resulting in a single polarization output in a hollow core fiber regardless of the input polarization state.

Polarization-filtering and polarization-maintaining low-loss negative curvature fibers

“…Figure 1(a) shows a negative curvature fiber with two larger tubes in the y-direction, which are used to increase the birefringence and differential loss by coupling the fundamental core mode in one polarization to the tube mode, as indicated by the red-highlighted profile. Our simulation results show that the fundamental core modes in the x-and y-polarizations have similar effective indices even with an asymmetric core profile, which is consistent with other published results [27,29,30]. The tube modes in the x-and y-polarizations also have very similar effective indices.…”

“…The novelty in our design is the use of the coupling between the glass modes in the nested resonant tubes and the fundamental core mode to increase the birefringence and the differential loss between modes in two polarizations. The physics and mechanism for the proposed fiber design are different from those in previous works on polarization-maintaining negative curvature fibers [28,29]. As long as all the major tubes are antiresonant, the loss for the other polarization is still low and comparable to the loss of standard negative curvature fibers with one ring of antiresonant tubes.…”

“…Anisotropic, perfectly matched layers (PMLs) are positioned outside the cladding in order to reduce the size of the simulation window [37]. We simulate silica glass with a refractive index of 1.444 at a wavelength of 1550 nm for polarization-maintaining fibers [7,18,29]. The core diameter, D core , is 50 µm, which is around 30 times larger than the transmission wavelength [21,22,36].…”

“…Ding et al [28] showed that high birefringence can be achieved in negative curvature fibers by using tubes with slightly different thicknesses in two transverse orthogonal directions. Mousavi et al [29] proposed a structure that uses resonant and antiresonant tubes in two orthogonal directions to induce high birefringence. In this design, doubly-nested antiresonant tubes are required to confine the mode and achieve a low leakage loss.…”

A Dual Hollow Core Antiresonant Optical Fiber Coupler Based on a Highly Birefringent Structure-Numerical Design and Analysis

“…In this paper we present a concept of a DHC-ARF coupler suitable for the purpose of splitting orthogonal polarizations of the input signal. Using the nested capillary, high birefringence HC-ARF concept [44], we designed a DHC-ARF structure capable of efficient coupling of the x-polarized component of the input signal between the cores. This fiber's structure combines all the previously referenced knowledge on the topic of DHC-ARFs, so that low loss, high birefringence, and an optimal core proximity could be achieved within a single structure.…”