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What is a SPUN FIBER?
A spun fiber (or spun polarization-maintaining fiber) is an advanced category of specialty optical fiber manufactured by rapidly rotating the glass preform while the fiber is being drawn. This structural twisting blends the fast and slow optical axes into a tight, helical pattern, which effectively averages out the fiber's linear birefringence.
The primary purpose of a spun fiber is to preserve circular polarization states and isolate the propagating light from external environmental perturbations, such as thermal fluctuations, mechanical vibrations, or physical bending.
HOW a SPUN FIBER Works
The mechanics of a spun fiber revolve around geometrical twisting to defeat unwanted phase shifts, functioning in three steps:
Preform Spinning
During the high-temperature drawing process, the raw glass preform—which possesses an asymmetric structural design like a "Tiger" or elliptical core—is rotated at a precisely controlled spin rate. This freezes a permanent, microscopic helical pitch directly into the core and cladding.
Birefringence Averaging
In a static fiber, structural asymmetry causes light to travel at different speeds along different axes (linear birefringence). By twisting these axes into a tight spiral shorter than the operational wavelength, the linear birefringence is averaged out to near-zero over the length of the fiber.
Circular Polarization Preservation
Because the linear phase errors are nullified, the fiber becomes highly receptive to holding and guiding circularly polarized light. When an optical signal is injected, it travels down the helical matrix securely, minimizing sensitivity to local thermal or vibrational variations that would otherwise deform the polarization state.
