Fundamentals of Sagnac Phase Shift and Thermal Shupe Effect Cancellation
Quadrupolar winding cancels thermal Shupe non-reciprocity by spatially pairing symmetric fiber segments equidistant from the coil center.
Panda Fiber
Waveguide Structure
Polarization-maintaining optical waveguides preserve the polarization state of light by introducing a controlled asymmetric stress profile across the core. Using panda fiber achieves this with stress-applying parts on opposite sides of the core.
Birefringence Generation
Thermally induced stresses during drawing create a large difference in the refractive index along the orthogonal axes of the fiber core. This refractive index difference, or birefringence, ensures that the slow and fast axes have distinct propagation constants. When light is launched into panda fiber along one of these axes, it remains confined to that polarization state even when the fiber experiences external bending or twisting.
Polarization Stability
Sensor applications rely on this polarization stability to maintain high interference contrast in optical instruments. In fiber-optic gyroscopes and acoustic sensors, any rotation of the polarization state causes signal fading or measurement errors. By using panda fiber, designers prevent the polarization state from drifting due to temperature variations or mechanical vibrations, which stabilizes the output of the instrument.
Splicing Precision
Aligning these stress-applying parts during assembly requires specialized fusion splicing equipment equipped with profile alignment systems. Splicing tools analyze the end-face geometry to align the stress rods of both fibers before melting them together. An angular misalignment of even a few degrees can degrade the polarization crosstalk, making precise alignment critical during sensor assembly.