How does fiber optics work?

Optical fiber, short for optical fiber, is a fiber made of glass or plastic that acts as a light-transmitting tool. The transmission principle is "total reflection of light". Kao Kun, the former president of the Chinese University of Hong Kong, and George A. Hockham first proposed the idea that optical fibers can be used for communication transmission, for which Kao won the 2009 Nobel Prize in Physics.

Optical fiber is a slender and soft solid glass material, which consists of three parts: core, cladding and coating layer, and can be used as a light transmission tool.

Core: Located in the center of the optical fiber, the composition is high-purity silica, that is, glass.

Cladding: Located around the core, its composition is also high-purity silica. The cladding provides a reflective surface and optical isolation for the transmission of light, and plays a certain role in mechanical protection.

Coating: The outermost layer of an optical fiber, consisting of acrylic, silicone rubber, and nylon. The coating protects the fiber from water vapor and mechanical abrasion.

The realization of optical fiber communication is based on the principle of total reflection of light. When light enters the center of the fiber and propagates, the refractive index n1 of the fiber core is higher than that of the cladding n2, and the loss of the core is lower than that of the cladding, so the light will undergo total reflection, and its light energy is mainly transmitted in the core. Due to successive total reflections, light can be conducted from one end to the other.

The working principle of the optical fiber: at the transmitting end, the information to be transmitted (such as voice) is first converted into an electrical signal, and then transmitted to the laser beam through the laser. The intensity of the light changes with the frequency of the electrical signal, and is emitted through the optical fiber. At the receiving end, the detector receives the optical signal and converts it into an electrical signal, and restores the original information after processing.

The optical fiber made of glass fiber inside the optical fiber can transmit optical signals to thousands of kilometers away, and combine hundreds of thousands of optical fibers to make an optical cable like a cable, which not only improves the strength of the optical fiber , and greatly increased the communication capacity.

The propagation speed of light in different substances is different, so when shooting from one substance to another substance, refraction and reflection will occur at the junction of the two substances, and the angle of the refracted light will change with the angle of the incident light. However, when the angle of the incident light reaches or exceeds a certain angle, the refracted light will disappear, and all the incident light will be reflected back, which is the total reflection of light.

The optical signal is transmitted to the end point after repeated refraction in the fiber. The optical signal will be scattered or attenuated after repeated refraction, and the optical signal needs to be amplified every 50 kilometers.