1. Optical fiber structure composition
Optical fiber can be divided into three layers: composed of core, cladding and coating. The core and cladding are generally composed of quartz (sio2), and the coating layer is composed of special plastic.
Core: The central part of an optical fiber, the refractive index is higher than that of the cladding, and light waves are mainly transmitted in the core.
Cladding: The area surrounding the core with a lower refractive index than the core to providing reflective surfaces or optical isolation.
Coating: ①protect the mechanical strength of the optical fiber; ②isolate the external stress that can cause slight loss.
Cladding diameter: 125±1μm
The outer diameter of natural fiber: 245±5μm
The outer diameter of colored fiber: 255±5μm
2. The difference between multi-mode and single-mode fiber
According to the different transmission modes, there are multi-mode fiber and single-mode fiber. Multi-mode fiber transmits multiple modes of optical signals at the same time. It is easy to interfere with each other, the loss is large, and the transmission distance is short. It is mostly used in indoor wiring and optical devices. : Such as light source, optical receiver, optical connector, etc.
Single-mode fiber allows only one mode of optical signal transmission at the same time and can be used for long-distance transmission with low loss. Currently, single-mode fiber is used in FFTX applications in access networks
It mainly distinguishes single-mode fiber and multi-mode fiber from six aspects: core diameter, light source, bandwidth, sheath color, modal dispersion, and price.
Single-mode fiber: Typical single-mode fiber has a core diameter of 8 and 10 µm, and a cladding diameter of 125 µm.
Multimode fiber: The usual multimode fiber has a core diameter of 50 and 62.5 µm, and a cladding diameter of 125 µm.
Single-mode fiber: using laser as light source, the price is more expensive than LED light source. The light generated by laser light source can be precisely controlled and has high power.
Multi-mode fiber: using LED as the light source, the light generated is more scattered
Single-mode fiber: It exhibits less modal dispersion than multi-mode fiber caused by multiple spatial modes, and has a higher bandwidth.
Multimode fiber: has a larger core size, supports multiple transmission modes, has a modal dispersion greater than that of a single-mode fiber, and a lower bandwidth than a single-mode fiber.
Single-mode fiber: Use yellow outer sheath.
Multimode fiber: use orange or water green outer sheath.
Single-mode fiber: The laser used to drive a single-mode fiber produces a single wavelength of light, so its modal dispersion is smaller than that of a multi-mode fiber.
Multimode fiber: Due to the use of LED light source, the dispersion of multimode fiber limits its effective transmission distance, and has a higher pulse expansion rate, which limits its information transmission capacity.
Single-mode fiber: The price is lower than that of dual-mode fiber, but the equipment of single-mode fiber is more expensive than that of multi-mode fiber, and the cost is higher than that of dual-mode fiber.
Multi-mode fiber: The price is higher than that of single-mode fiber. Multi-mode fiber equipment is cheaper than single-mode fiber equipment, so the cost of multi-mode fiber is much less than the cost of single-mode fiber.