Optical fibers are designed for many different application scenarios. To understand the different applications, it is important to understand the properties of different fiber types.

Two major types of optical fibers exist for communication system: multimode fiber and single mode fiber. The difference between them is that multimode fiber can carry many modes of light rays while single mode fiber can only carry one mode of light ray.

Single mode fiber does have some disadvantages though. The smaller fiber core diameter makes it much harder to couple light into the fiber. This increases the manufacturing cost of many single mode fiber optic components such as isolator, attenuator, etc. Mini Manual Variable Attenuator The tolerances for single mode connectors, mechanical splices are also much more demanding.

One important variety of single mode fiber is polarization maintaining fiber, or also called PM fiber. PM fiber carries only one polarization (the light's electronic field direction) of the light. PM fiber's major applications include coherent communication system and electro-optic modulators which serves as a light transmitter in high speed fiber optic system.

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