Accurate Control of Surface Modes in a Hollow-Core Photonic Bandgap Fiber

Abstract

The abrupt termination of periodic structures in hollow-core photonic bandgap fiber (HC-PBF) cladding introduces surface modes (SMs). This results in a high loss and small available bandwidth. This has become an important factor that restricts the development of HC-PBFs. For many years, there has been a lack of clear understanding of SMs. In this study, SMs were considered the main body of research. First, a pure HC-PBF platform was constructed to systematically observe the SMs inside the bandgap. The core wall was used as a control variable to achieve precise control of the SMs. The SMs are divided into two categories: fundamental and high-order SMs. We named the SMs and studied their characteristics, including the mode field shape, coupling bandwidth, and coupling speed. The coupling characteristics of SMs with different core diameters were compared and analyzed. Further, we compared the model with actual fiber to prove the practicality of the theoretical analysis. This study will deepen our understanding of HC-PBF and will have a positive impact on its development.