Investigation of refractive index distribution in different photonic crystal fiber elements

摘要

The paper presents the last data regarding new elements based on photonic crystal fibers such as the low-loss patch cord with a single mode fiber, the fused coupler, the asymmetric coupler for an active fiber power pump. Their fundamental optical characteristics including wavelength depending loss as a coupling ratio are presented in this paper as well as their inner structure (cross section) obtained by SEM. However, the use of SEM for the investigation of the inner element structure is destructive, thus in the last part of the paper we present the tomographic in-line determination of geometry and refractive index distribution changes along the investigated photonic structure. The analysis of different approaches to the photonic crystal fiber data capture with a sufficient optical resolution is given. The data obtained from the Mach-Zehnder interferometer with different laser sources as well as from the in-line digital holographic setup are presented and compared. The further enhancement required for the digital in-line holography is discussed.