How are polarization-maintaining fibers made
Conventional optical fibers are developed based on quartz glass materials. After decades of development, the process procedures are basically finalized and widely used. The manufacturing process of conventional optical fibers is called a two-step process, namely: preform preparation and optical fiber drawing. The process of polarization-maintaining fiber is more complicated, but it also needs to start with the preparation of preforms.
01 Chemical Vapor Deposition (CVD)
The chemical vapor deposition (Chemical Vapor Deposition) process uses a quartz glass tube as the base material (liner), and the selected chemical gas is carried by oxygen into the quartz glass liner, and the traveling oxyhydrogen flame is used to move the lining along the tube. The tube heats up, causing a chemical reaction and sintering the deposited material inside the tube (vapor deposition). The number of deposited layers increases, the wall thickness increases, and the inner diameter decreases; finally, the hollow part of the glass tube is "pulled out" (thermally shrunk) by adjusting the pressure to become a solid glass rod, and the preparation of the preform is completed.
02 Polarization maintaining fiber preform
If it is a conventional single-mode fiber, after the preform is fabricated by chemical vapor deposition, the sleeve and the fiber are drawn, but the polarization-maintaining fiber is not so simple.
Taking panda polarization-maintaining fiber as an example, in addition to the preparation of the preform, it is also necessary to prepare the core rod, doping the stress rod, and punch holes in the preform. The optical fiber will not be drawn until the sleeve assembly of all the preforms is completed.
03 Fiber drawing
After the preparation of the optical fiber preform is completed, it needs to be cleaned and inspected before being loaded into the drawing tower. The optical fiber drawing tower is designed in a clean environment, usually with a height of more than 10 m, and some communication optical fiber drawing towers can reach tens of meters high.
The drawing of polarization-maintaining fiber is somewhat different from that of ordinary single-mode fiber, and some sealed joint structures are added, and the rest of the fiber drawing process is almost the same. The preform is gradually fed into the high-temperature furnace, the glass preform softens, and the bottom end drops to form a cone. The glass at the bottom is quickly "reeled", and the optical fiber is formed after the outer diameter is stable.
