What is the transmission method of optical fiber communication?
Publish Time: 2024-12-03
Optical fiber communication is a communication method that uses light waves as information carriers and optical fibers as transmission media. In principle, the basic material elements that constitute optical fiber communication are optical fibers, light sources, and light detectors. In addition to being classified by manufacturing process, material composition, and optical properties, optical fibers are often classified by purpose in applications, and can be divided into optical fibers for communication and optical fibers for sensing. Transmission medium optical fibers are divided into general-purpose and special-purpose types, while functional device optical fibers refer to optical fibers used to complete functions such as amplification, shaping, frequency division, frequency doubling, modulation, and optical oscillation of light waves, and often appear in the form of some functional devices.Principle of optical fiber communication:At the transmitting end, the transmitted information (such as voice) must first be converted into an electrical signal, and then modulated onto the laser beam emitted by the laser, so that the intensity of the light changes with the amplitude (frequency) of the electrical signal, and is transmitted through the optical fiber through the principle of total reflection of light; at the receiving end, the detector receives the optical signal and converts it into an electrical signal, and restores the original information after demodulation.Optical communication uses the principle of total reflection. When the injection angle of light meets certain conditions, the light can be totally reflected in the optical fiber, thus achieving the purpose of long-distance transmission. The light-guiding characteristics of optical fiber are based on the total reflection of light rays at the interface between the core and the cladding, which limits the light to be transmitted in the core. There are two kinds of light in the optical fiber, namely, meridional light and oblique light. Meridian light is the light ray located on the meridian plane, while oblique light is the light ray that is not transmitted through the axis of the optical fiber.The following takes the transmission of light in step-index optical fiber as an example to explain the principle of optical communication.It is a step-index optical fiber, the refractive index of the core is n1, the refractive index of the cladding is n2, and n1>n2, and the refractive index of air is n0. The meridional light transmitted in the optical fiber, referred to as the inner light, can only ensure that the light will be reflected multiple times in the core when the incident angle of the interface between the core and the cladding is greater than θc, so that the light can be transmitted along the optical fiber. However, the incident angle of the internal light depends on the refraction angle θ2 generated when the light incident from the air enters the fiber core. Therefore, the incident angle θi of the incident light on the interface between the air and the fiber core determines whether the light can be transmitted in the fiber in the form of total reflection. Corresponding to the critical angle θc of the incident angle of the internal light, the incident angle θi of the incident light of the fiber has a maximum value θmax.When the light is incident on the core end face with θi>θmax, the internal light will be projected onto the interface between the core and the cladding at an incident angle less than θc. Such a light has a refraction angle of less than 90 degrees in the cladding, and the light will enter the cladding and soon expose the fiber.When the light is incident on the core end face with θi<θmax, the incident light will be projected onto the interface between the core and the cladding in the fiber at an incident angle greater than θc. Such a light has a refraction angle of greater than 90 degrees in the cladding, and the light will produce multiple reflections at the interface between the core and the cladding, causing the light to be transmitted along the fiber.
