What are the characteristics of optical fiber?

Optical fiber is now one of the primary media for data transmission in our daily life and work, and it is indispensable to the development of the Internet. Next, let me walk you through the main characteristics and transmission principles of optical fiber.

Optical fiber transmission offers advantages such as low attenuation, wide frequency bandwidth, strong anti-interference capability, high security, small size, and light weight, giving it incomparable advantages in long-distance transmission and special environments. The transmission medium is a key factor determining transmission loss and the repeater spacing required for transmitted signals. As a transmission medium for optical signals, optical fiber features low loss. The frequency bandwidth of optical fiber can reach above 1.0 GHz, while the bandwidth of a typical image is only 8 MHz. One fiber core is more than sufficient to transmit one channel of video, and it is even more advantageous for transmitting voice, control signals, or contact signals. The carrier in optical fiber transmission is light waves, which are electromagnetic waves of extremely high frequency—far higher than the frequencies used in radio communications—and are therefore immune to interference. Moreover, optical fiber is made of glass material, which is non-conductive and does not generate sparks due to open circuits, lightning strikes, or other causes, making it highly safe and particularly suitable for flammable or explosive environments.

An optical fiber transmission system mainly consists of three parts: the light source (also known as the optical transmitter), the transmission medium, and the detector (also known as the optical receiver). In optical fiber transmission between computer networks, the functions of the light source and detector are generally implemented by media converters. Simply put, a media converter is a device that connects twisted pair cable to optical fiber. Its function is to convert signals transmitted over twisted pair cable into signals (optical signals) that can be transmitted through optical fiber. It is also bidirectional, capable of converting optical signals transmitted over fiber into signals that can be transmitted over twisted pair cable, enabling data transmission between networks. In ordinary video, audio, and data transmission processes, the functions of the light source and detector are generally implemented by optical terminals. An optical terminal is a device that converts multiple E1 signals into optical signals for transmission. E1 is a data transmission standard for trunk lines; the standard rate in China and Europe is 2.048 Mbps. The main function of an optical terminal is to achieve electrical-to-optical and optical-to-electrical conversion. Based on the conversion signal, optical terminals are classified into analog optical terminals and digital optical terminals. Therefore, optical fiber transmission systems can be classified into digital transmission systems and analog transmission systems based on the transmitted signal. An analog transmission system performs analog modulation of light intensity, converting the input signal into continuous variations in the amplitude (frequency or phase) of the transmitted signal. A digital transmission system converts the input signal into "1" and "0" pulse signals, which are used as the transmitted signal, and then restores the original signal at the receiving end. Of course, the equipment required varies depending on the type of signal transmitted over the optical fiber. As the transmission medium, optical fiber is a critical element of the optical fiber transmission system. It can be classified in different ways: By transmission mode: when light is transmitted only along the fiber core and only the fundamental mode is transmitted, it is called single-mode fiber (Single-Mode). When multiple modes are transmitted in the fiber, it is called multi-mode fiber (Multi-Mode).

By core diameter: graded-index multi-mode fiber, graded-enhanced multi-mode fiber, and graded-index single-mode fiber. By refractive index profile of the fiber core: step-index fiber (SIF), graded-index fiber (GIF), ring fiber, and W-type fiber.

Advantages of optical fiber transmission:

1. Wide frequency bandwidth: The width of the frequency band represents the transmission capacity. The higher the carrier frequency, the wider the frequency band that can be used to transmit signals.

2. Low loss: For light transmitted at 1.31 um, the loss per kilometer is below 0.35 dB. For light transmitted at 1.55 um, the loss per kilometer is even lower, reaching below 0.2 dB.

3. Light weight: Optical fiber is made of glass fiber with low specific gravity, giving it the characteristics of small diameter and light weight, making installation very convenient.

4. Strong anti-interference capability: Because the basic component of optical fiber is quartz, which only transmits light and does not conduct electricity, it is unaffected by electromagnetic fields. Optical signals transmitted within it are not affected by electromagnetic fields, so optical fiber transmission has strong resistance to electromagnetic interference and industrial interference.

5. High fidelity: Because optical fiber transmission generally does not require repeater amplification, no new nonlinear distortion is introduced by amplification. As long as the linearity of the laser is good, television signals can be transmitted with high fidelity.

6. Reliable performance: Optical fiber systems contain fewer devices (unlike cable systems that require dozens of amplifiers), so reliability is naturally higher. In addition, optical fiber equipment has a long service life, with a mean time between failures of 500,000 to 750,000 hours.

7. Continuously decreasing cost: Since the material used to make optical fiber (quartz) is abundantly available, costs will further decrease with technological advancement.

As a mainstream method of broadband access, optical fiber offers advantages such as large communication capacity, long repeater spacing, good confidentiality, strong adaptability, small size and light weight, and abundant raw materials with low prices. Therefore, optical fiber is becoming increasingly widely used in communication systems.