In modern communication and data networks, fiber optic cables have become the core carrier supporting high-speed interconnection. Their working principle is based on the total internal reflection of light and the waveguide transmission characteristics, enabling long-distance, high-capacity information transmission through the directional propagation of light, fundamentally breaking through the performance limitations of traditional metal cables.
The basic structure of an optical fiber consists of a core, cladding, and outer sheath. The core is made of high-refractive-index glass or plastic, typically with a diameter of a few micrometers to hundreds of micrometers; the cladding is a low-refractive-index material that tightly wraps around the core; the outer sheath provides mechanical and environmental protection. When light travels from an optically denser medium (core) to an optically less dense medium (cladding), if the angle of incidence is greater than the critical angle, total internal reflection occurs at the core-cladding interface, confining the light within the core and propagating axially forward. This is the physical basis of fiber optic transmission-the optical waveguide effect.
The information loading process relies on the modulation technology of the optical signal. The transmitting end converts electrical signals into optical signals using a laser or light-emitting diode. Information is encoded by using sequences of light pulses of different intensities, phases, or wavelengths to correspond to binary data (such as "1" and "0"). These light pulses are transmitted sequentially through total internal reflection within the fiber core. Because the fiber core material has extremely low absorption and scattering losses at specific wavelengths (such as 1310nm and 1550nm), the signal can be transmitted over long distances of tens or even hundreds of kilometers with controllable attenuation.
The receiving end performs the reverse conversion using a photodetector: the optical signal is coupled into the detector, where it is converted into a weak current through the photoelectric effect. This current is then amplified, shaped, and restored to the original electrical signal before being output to the terminal equipment.
It is worth emphasizing that the low-loss characteristic of optical fiber stems from the purity of the materials and the structural design-high-purity quartz glass can reduce the loss in the 1550nm band to below 0.2dB/km. Combined with dispersion compensation technology, this further suppresses signal distortion and ensures the stability of high-speed (such as 100Gbps and above) transmission.
In short, optical fiber cables use light as the information carrier, constrain the transmission path through total internal reflection, and combine efficient modulation and detection technologies to build an information channel with "low loss, high bandwidth, and anti-interference" characteristics, continuously driving the evolution of communication networks towards higher speeds and greater reliability.