The transmission principle of optical fiber is mainly based on the total reflection of light. Optical fiber is a kind of slender fiber made of glass or plastic, and its structure is mainly composed of three parts: core, cladding and coating layer.
Fiber core: Located at the center of an optical fiber and made of a material with a high refractive index (such as high-purity silicon dioxide with a small amount of dopants), it is used to transmit optical signals.
Cladding: Surrounded by the fiber core, made of the material with a slightly lower refractive index than the fiber core (also high purity silica mixed with a small amount of dopants), to provide a reflective surface and optical isolation for the transmission of light, ensuring that the optical signal is fully reflected in the fiber core and propagates along the axis.
Coating Layer: Located outside the cladding, it is typically made of materials such as acrylate, silicone rubber, nylon, etc. Its main function is to protect the optical fiber, enhancing its mechanical strength and flexibility.
When light enters one end of the optical fiber, if the angle of incidence is greater than the critical angle, the light will be fully reflected at the interface between the core and the cladding, and will continue to propagate along the axial direction of the fiber. This total reflection phenomenon repeats continuously, allowing the optical signal to transmit to the other end of the optical fiber. Since the propagation of light in the optical fiber is based on total reflection, the optical signal is barely weakened due to the loss of light, maintaining a long distance transmission.
This transmission mode of the optical fiber has the advantages of high speed, low loss and anti-interference, so that optical fiber has a wide range of applications in communication, network, sensor and other fields.
Optical fiber Types
Optical fibers can be classified into many types according to different classification standards, The following are some common types of optical fibers:
According to the material used to manufacture fiber:
Quartz optical fiber: It is the type of optical fiber commonly used in communication at present, and has the characteristics of high purity and low loss.
Plastic optical fiber: made of highly transparent polystyrene or polymethyl methacrylate (plexiglass), low manufacturing cost, but large loss, small bandwidth, suitable for short-distance low-rate communication.
According to the transmission mode of light in the fiber:
Single-mode optical fiber: The central glass core is very thin (core diameter is generally 9 or 10μm) and can only transmit one mode of optical signal. It has a high transmission bandwidth and a long transmission distance, suitable for long-distance communication and high-speed data transmission.
Multi-mode optical fiber: The center glass core is thicker (50 or 62.5μm) and can transmit a variety of modes of optical signals, but the inter-mode dispersion is large. The transmission distance is short, suitable for short-distance communication and low-speed data transmission.
According to the refractive index distribution:
Step optical fiber: The core refractive index is higher than the cladding refractive index, so that the input light energy continuously generates total reflection at the core-cladding interface and advances. This optical fiber has many transmission modes, but the inter-mode dispersion is high, and the transmission rate cannot be too high, which is suitable for short-distance low-speed communication.
Graded optical fiber: The core refractive index gradually decreases along the length of the fiber, reducing the mode dispersion and improving the transmission performance of the fiber. The graded multimode fiber is suitable for medium distance communication and medium speed data transmission.
Special optical fiber:
In addition to the above common types of optical fiber, there are some special types of optical fiber, such as dispersion compensation optical fiber, polarization holding optical fiber, etc., which have specific functions and application areas.
In summary, there are various types of optical fibers, and each type has its own unique characteristics and application scenarios. In practical applications, it is necessary to select the appropriate type of optical fiber based on specific requirements.
Post time: Jul-18-2024