Study of vectorial properties of optical-fiber modes using a fiber resonator

Each eigenmode in optical fibers is experimentally analyzed individually by changing the resonance condition of the eigenmode in optical-fiber resonators. When a stress is applied to fibers, it is found that eigenmodes in a single-mode fiber and a two-mode fiber are LP modes, and eigenmodes in a fiber Faraday rotator are elliptically polarized modes. A significant result for the two-mode fiber is that the directions of polarization and orientation of the LP11modes are those of a transverse pressure and principal axes of the elliptical core, respectively. A coupled-mode theory is also presented to explain these experimental results.