High sensitivity long-period grating tunable filters in standard communication fibers and their PDL reduction

Abstract

In this paper we report the investigation results of tunable filters by using high-sensitivity cladding modes in standard communication fibers and their PDL reduction. By choosing temperature and strain sensitive cladding modes and through proper packaging to combine the strain effect into the temperature effect, enhanced temperature sensitivity has been achieved. A combined sensitivity of 250 pm/°C by temperature tuning has been demonstrated in standard fibers. We further found that the tunable filters using high sensitivity cladding modes show remarkably higher polarization dependent loss (PDL), compared to those using low sensitivity ones. We derived an expression to quantitatively link the filter PDL (through resonant wavelength separation) to the sensitivities of the cladding modes and other related birefringence sources, including the process (UV or CO2 laser) induced and the fiber intrinsic birefringence. We proposed PDL reduction methods and demonstrated that the PDL due to both the induced and the intrinsic sources can be removed.