Temperature-Dependent Group Delay of Photonic-Bandgap Hollow-Core Fiber Tuned by Surface-Mode Coupling

TL;DR

This paper demonstrates how surface-mode coupling in photonic-bandgap hollow-core fibers can be used to significantly tune the temperature dependence of group delay, offering a new method for designing time-sensitive optical devices.

Contribution

It introduces a novel approach to control group delay in PBG-HCF by leveraging surface-mode coupling and avoided crossing effects, expanding the tuning range beyond previous methods.

Findings

Redshift of avoided crossing wavelength with temperature affects group delay.

Tuning of thermal coefficient of delay from -400 to 400 ps/km/K.

Surface-mode coupling offers broader and more efficient tuning than previous methods.

Abstract

Surface modes (SM) are highly spatially localized modes existing at the core-cladding interface of photonic-bandgap hollow-core fiber (PBG-HCF). When coupling with SM, the air modes (AM) in the core would suffer a higher loss despite being spectrally within the cladding photonic bandgap, and would be highly dispersive around the avoided crossing (anti-crossing) wavelength. In this paper, we numerically demonstrate that such avoided crossings can play an important role in the tuning of the temperature dependence of group delay of AM of PBG-HCF. At higher temperatures, both the thermal-optic effect and thermal expansion contribute to the redshift of avoided crossing wavelength, giving rise to a temperature dependence of the AM dispersion. Numerical simulations show that the redshift of avoided crossing can significantly tune the thermal coefficient of delay (TCD) of PBG-HCF from -400 ps/km/K to 400 ps/km/K, approximately -120 ppm/K to 120 ppm/K. In comparison with the known tuning mechanism by the thermal-induced redshift of photonic bandgap [Fokoua et al., Optica 4, 659, 2017], the tuning of TCD by SM coupling presents a much broader tuning range and higher efficiency. Our finding would provide a new route to design PBG-HCF for propagation time sensitive applications.