Polarization maintaining single-mode low-loss hollow-core fibres

Abstract

Hollow-core fibre (HCF) is a powerful technology platform offering breakthrough performance improvements in sensing, communications, higher-power pulse delivery and other applications. Free from the usual constraints on what materials can guide light, it promises qualitatively new and ideal operating regimes: precision signals transmitted free of nonlinearities, sensors that guide light directly in the samples they are meant to probe and so on. However, these fibres have not been widely adopted, largely because uncontrolled coupling between transverse and polarization modes overshadows their benefits. To deliver on their promises, HCFs must retain their unique properties while achieving the modal and polarization control that are essential for their most compelling applications. Here we present the first single-moded, polarization-maintaining HCF with large core size needed for loss scaling. Single modedness is achieved using a novel scheme for resonantly coupling out unwanted modes, whereas birefringence is engineered by fabricating an asymmetrical glass web surrounding the core.

Semi-analytical model for hollow-core anti-resonant fibers

“…In the same wavelength range, the sign of the birefringence keeps unchanged. The relatively lower birefringence comparing with a recently reported HC-PBGF ( n ∼ 2 × 10 −4 ) [11] should be attributed to the fact that the transmission bands of our ARF stay far away from any mode anti-crossing. Larger birefringence in ARF may be possible, if mode anti-crossing is carefully introduced.…”

“…transmission properties, e.g., attenuation and transmission bandwidth [11]. In ARF, the broadband transmission requirement restrains the utilization of the anti-crossing effect.…”

“…To our understanding, this unambiguous and quantitative interpretation on the guidance mechanism results in the fast development of HC-PBGF in the first decade of Twenty First century. The optical attenuation has reached a record of 1.2 dB/km [7]; entire fabrication procedure of a HC-PBGF can be completed within 1 day; the anti-crossing between the core mode and the surface mode has been clearly identified [8,9] and can be deliberately engineered for specific purposes, e.g., polarization maintaining in HC-PBGF [10,11]. However, the intrinsic ∼70 Thz transmission bandwidth originating from the PBG guidance mechanism and the low damage threshold caused by large spatial overlap of the core mode with the glass cladding [7,12] limit the lab-on-a-fiber applications in this kind of HCFs.…”

First design of high birefringence and polarising hollow core anti-resonant fibre

“…The rapid and significant change in effective index of an air-guided mode at the edges of the anti-resonant frequency window has been used in PBG fibres to introduce PB in previous works 3 . Here, we use a similar effect to introduce an effective index difference in the OPFM of a four-tube NANF.…”

“…However, high performance, low-loss HC with polarisation maintaining properties are not readily available. Some PM HC fibres based on photonic band gap (PBG) guidance have been presented recently 3 . Due to their different guiding mechanism, the PM property is typically achieved by exploiting the anti-crossing of coreclad modes instead of the conventional methods of solid core fibres.…”