What is Polarization Maintaining(PM) fiber?
Theoretically, the fiber is a circular core which should not produce birefringence, and the polarization state in such a fiber will not change during transmission. In practice, there is always some external forces or other reasons which makes the fiber uneven or curved, and will cause a small amount of birefringence. When the fiber is subject to any external interference, such as wavelength, bending of the fiber, temperature and other factors, the polarization state of light will become chaotic when transmitted in polarization-maintaining fiber.
Fiber optic connectors are the most basic optical passive components for optical fiber communication systems. The basic specification requirements for them are low insertion loss (IL) and high return loss (RL), i.e. low back reflection (BR). However, as the most widely employed components, low cost and easy connection are equal important as the specifications.
Alignment of Optical Fibers
The core size of the single mode fiber (SMF) is about 8~10μm. The two connected fibers must be precisely aligned to ensure low loss. Fig.1 shows how much the lateral offset between two optical fibers influence the IL. The curve is exponential. A small lateral offset such as 2.4μm will introduce IL of 1dB. Thus the lateral offset between the two fibers must be kept <0.5μm for SMF fiber optic connectors.