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.
