Axis temperature of polarization-maintaining fiber

The polarization-maintaining performance of a PM fiber decreases with increasing temperature due to a reduction in birefringence, while the beat length along the fiber increases.Temperature Dependence of PM Fiber AxesPolarization-maintaining fibers, such as PANDA or bow-tie fibers, preserve the polarization of light by introducing strong, well-defined birefringence along two orthogonal axes: the slow and fast axes . The birefringence arises from stress rods embedded in the cladding, which create tension in the fiber core. This stress-induced birefringence is temperature-dependent because the stress rods and cladding have different coefficients of thermal expansion. As temperature increases, the tension in the core decreases, reducing the refractive index difference between the axes and thus lowering polarization-maintaining performance .Beat Length and Phase DelayThe beat length Lb of a PM fiber, defined as the distance over which one polarization mode accumulates a phase difference of one wavelength relative to the orthogonal mode, is inversely proportional to birefringence. As temperature rises, the birefringence decreases, causing the beat length to increase . This change affects the relative delay between the slow and fast axes, which can alter the output polarization state if light is not aligned with a single axis. For light polarized along one axis, the polarization remains stable, but for mixed polarization components, temperature variations induce elliptical polarization changes .Practical ImplicationsAlignment: When splicing or connecting PM fibers, the slow and fast axes must be precisely aligned to maintain polarization, and temperature changes can slightly shift the effective axis orientation .Polarization Extinction Ratio (PER): The PER may degrade with increasing temperature due to reduced birefringence, affecting applications like fiber interferometers, gyroscopes, and fiber lasers .Monitoring: Measuring the temperature-dependent delay between polarization components can provide insight into the fiber's birefringence and its ability to preserve polarization .SummaryThe axis temperature of a PM fiber primarily affects the fiber's birefringence and beat length. Higher temperatures reduce birefringence, increase beat length, and can modify the output polarization state for light not aligned with a single axis. Proper design, alignment, and temperature control are essential for maintaining high polarization performance in sensitive optical systems .