Thermal stress analysis of side-hole optical fibers with elliptical core

Abstract

A thermal stress analysis of side-hole optical fiber with elliptical core has been presented in this work by using a finite element method. The birefringence because of the thermal stress, which is caused in the structure due to the different thermal expansion coefficients of core and cladding and also the geometrical birefringence are simultaneously considered here in this work. The analysis here is based on the plain strain approximation and potential energy principle in the finite element method, which in this case, results in a linear system of unknown displacements at the nodes. After checking the accuracy of finite-element calculations, thermal stress analysis of elliptical cored fibers and side hole fibers with elliptical core are performed. The influences of core ellipticity, air hole radius and position, as well as the thermal expansion coefficient of core and cladding materials on fiber birefringence are systematically assessed. Also, the work is further extended to calculate the changed refractive index in x and y polarized light due to photo-elastic effect. For a fiber with elliptical core, the birefringence increases with the core ellipticity as the stress in and around the core gets higher with the increase in the core ellipticity. Fiber birefringence increases with larger pitch length. Thus, fiber with higher core ellipticity and higher pitch length generates higher birefringence. On the other hand, the birefringence decreases with the increase in side-hole radius. Smaller side-holes can produce moderately higher birefringence if they are far from the core. Thus, the simulation results suggest that, elliptical core side-hole fiber can be treated as a good candidate for high birefringent polarization maintaining fiber (PMF), which finds increasing demands in coherent optical communication, optical fiber sensing devices and many other applications.