A research team from Shanghai Institute of Optics and Fine Mechanics (SIOM) of the Chinese Academy of Sciences (CAS) has proposed two types of Mobius fiber ring laser (MFRL), and investigated the polarization and longitudinal mode characteristics in detail. The related results were published in Optica on December 12, 2022.

Mobius structures have attracted great interest in optics for unique topological property. When Mobius structure is introduced in optical cavities, interesting phase and polarization properties of light have been observed. The property of Mobius optical cavity had been studied with microcavities, which requires high precision fabrication techniques. However, Mobius-like fiber ring cavity and even laser enjoy the advantage of easy-implementation.

In this study, the researchers have proposed fiber lasers with Mobius strip structure. A theoretical model is established with Jones matrix to solve the polarization eigenmodes and longitudinal modes of a twisted polarization-maintaining-fiber ring cavity.

It is found that the twisting of the fiber axis causes polarization hybridization and a geometry-dependent phase, which induces a frequency shift to the longitudinal modes. The Mobius cases (180° and 90° splicing) are analyzed in detail. The 90° case leads to peculiar polarization and longitudinal mode properties, which were verified experimentally by polarization and mode beating measurements of the laser output.

The results show that Mobius-like structure can be implemented easily with fiber optics. And geometric phase is introduced in fiber laser research for the first time. The researchers believe that the presented fiber ring laser provides a convenient platform to study lasers in a Mobius structure.

Fig. 1 (a) Schematic diagram of a twisted PM fiber ring cavity. (b) The experimental setup of MFRL. (Image by SIOM)

Fig. 2. The polarization properties of the MFRL. (a) DOP of light under different pump power. (b) Typical SOP of light in one eigenmode state presented on the Poincaré sphere. (Image by SIOM)

Article website:
https://doi.org/10.1364/OPTICA.474407

Contact:
WU Xiufeng
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: xfwu@siom.ac.cn
Web: http://english.siom.cas.cn/