What Are Fiber-Optics?

Optical fiber is short for optical fiber. It is a fiber made of glass or plastic, which can be used as a light transmission tool.

Light and its characteristics:

Light is a

Until 1960, the American scientist Maiman invented the world's first laser, which provided a good light source for optical communications. For more than two decades, people

Optical fiber is composed of two layers of glass with different refractive indices. The inner layer is a light inner core with a diameter of several micrometers to several tens of micrometers, and the outer layer has a diameter of 0.1 to 0.2 mm. Generally, the refractive index of inner glass is 1% larger than that of outer glass. According to the principle of light refraction and total reflection, when the angle at which the light strikes the interface between the inner core and the outer layer is greater than the critical angle at which the total reflection occurs, the light cannot pass through the interface and be totally reflected.

The main factors causing fiber attenuation are:

The optical fiber currently used in communication is generally a quartz fiber. The chemical name of quartz is silicon dioxide (SiO2), which is the same as the main component of the sand we use every day to build a house. But ordinary quartz fiber cannot be used for communication. Communication fibers must be composed of extremely high purity materials; however, the inclusion of trace amounts of dopants in the host material can make the refractive indices of the core and cladding slightly different, which is beneficial to communication.

In practical applications, the optical fiber and the optical fiber are generally connected by two methods: thermal welding and cold welding.

According to the classification method of different fiber classification standards, the same fiber will have different names.

Classification by fiber material

According to the materials of optical fibers, the types of optical fibers can be divided into quartz optical fibers and all-plastic optical fibers.

Quartz fiber generally refers to an optical fiber composed of a doped quartz core and a doped quartz cladding. This fiber has very low loss and moderate dispersion. At present, most of the communication optical fibers are quartz optical fibers.

All-plastic optical fiber is a new type of communication optical fiber, which is still in the development and trial stage. All-plastic optical fiber has the characteristics of large loss, thick core (diameter 100 600m), large numerical aperture (NA) (usually 0.3 0.5, which can be coupled with a light source with a larger spot), and lower manufacturing cost. At present, all-plastic optical fiber is suitable for shorter length applications, such as indoor computer networking and communication within ships.

Classification by refractive index profile of fiber profile

According to the refractive index profile of the optical fiber, the types of optical fibers can be divided into step-type fibers and graded-type fibers.

Classification by transmission mode

According to the number of optical fiber transmission modes, the types of optical fibers can be divided into multimode optical fibers and single-mode optical fibers.

A single-mode fiber is a fiber that can transmit only one mode. Single-mode fiber can only transmit the fundamental mode (lowest order mode), there is no delay difference between modes, and it has a much larger bandwidth than multi-mode fiber, which is very important for high code rate transmission. The mode field diameter of a single-mode fiber is only a few microns (m), and its bandwidth is generally one or two orders of magnitude higher than the bandwidth of a graded multimode fiber. Therefore, it is suitable for large-capacity, long-distance communication.

Classification according to international standards (classification according to ITU-T recommendations)

In order to have a uniform international standard for optical fibers,

At the beginning of the development of polymer optical fiber, it was only used for the control and decoration of automotive lighting. Now it is mainly used in medicine, decoration, automobiles, ships, etc., mainly display elements. In terms of communication and image transmission, the application of polymer optical fiber is increasing, and it is used in industry for light guides, display panels, signs, switch-type lighting adjustments, and optical sensors.

Color discrimination

Yellow represents single mode

Orange stands for multimode

Identification of jacket logo

50/125, 62.5 / 125 are multimode and may be marked with mm

9/125 (g652) is single mode and may be marked with sm

Fiber Polished End

Distinguishable under a magnifying glass, multimodes are concentric circles

There is a black dot in the middle of the single mode

Distinguishable from the screen when the splicer is spliced

No white bar in the middle of the multi-mode fiber

There is a white bar in the middle of the single mode

At the same time, the fusion splicer does not calculate the fusion splicing loss for the multimode optical cable. Furthermore, single-mode and multi-mode fiber fusion splicers cannot be fusion spliced.

Single-mode transceivers can be used for multi-mode fiber optic cable links, but note that multi-mode jumpers are used.

According to the signal transmission mode in the optical fiber, there are two main categories: single-mode and multi-mode. The mode usually refers to the transmission path of the optical signal in the optical fiber, and the transmission path of the single mode is the central axis; the optical fiber is cut along the central axis to a plane, and the optical signal is transmitted on the plane using total reflection. An optical fiber can have an unlimited number of such planes, so there will be an unlimited number of optical signal transmission paths, that is, an unlimited number of modes. The optical fiber thus transmitted is called a multimode fiber.

The core size of single mode is generally 8 ~ 10um. In single mode, the signal propagates along a straight line, which is a mode. The multi-mode fiber core is relatively large, 50um or 62.5um, and can transmit multiple modes at the same time.

The single-mode transmission bandwidth is high and the transmission distance is long. It is mainly used for medium and long-distance signal transmission systems, such as fiber-to-the-home, subway, and road long-distance networks. However, because the single-mode fiber core is relatively small, it needs to be accurately docked when connected to the transmitter, so that it is coupled to a higher light source. This makes the price of other accessories of single-mode fiber network systems higher, and the price of single-mode optical transmitters is much more expensive than multi-mode ones. When using a single-mode connector for termination, pay attention to accurate butting, otherwise a higher value of insertion loss will occur, reducing the optical fiber transmission performance.

The multi-mode energy is mainly used to meet the transmission of short-distance networks. In fact, multimode fiber can support vertical subsystem wiring and short-distance building group subsystem wiring within 550 meters of 10 Gigabit Ethernet, and data center wiring within 150 meters of 40G / 100G networks. In addition, the multi-mode fiber optic system's photoelectric conversion elements are cheaper than single-mode, and field installation and termination are simpler.

As a mainstream method of broadband access, optical fiber has the advantages of large communication capacity, long relay distance, good security performance, strong adaptability, small size, light weight, and wide range of raw materials and low prices. In the future, broadband Internet access The application is expected to be very extensive.

According to market research and forecast company IDC, the number of China's optical fiber access users is expected to exceed 26.6 million in 2012, maintaining a compound annual growth rate of 56.4% over the next five years, and China has become one of the world's largest optical network equipment markets. By the end of 2011, the number of fiber optic access ports in China had exceeded 100 million, a year-on-year increase of more than 100%; the number of fiber-optic access users in China had reached 15.56 million, a year-on-year increase of more than 370%. Compared with China's 158 million broadband users, the number of fiber access users will have a very broad upside. According to China s fiber optic broadband development plan, by 2015 the nation s Internet export bandwidth will reach 5T, and the bandwidth capacity of urban households will basically reach more than 20M, and the bandwidth capacity of rural households will basically reach more than 4M; household fiber access will cover more than 5 million households; The scale of public operation hotspots will exceed 150,000; at that time, the city's non-profit institutions will reach 100% of the fiber optic arrival rate, and all science and technology parks, industrial parks, commercial buildings, hotels and other business-like business places will have fiber-to-the-floor buildings and offices.

All these data show that China's broadband market has huge potential, and it will certainly be one of the main battlefields for future broadband operators. The popularity of fiber optic broadband is also the general trend. So the battle of the future broadband market is largely a battle of fiber broadband.

Jin Dongbin, deputy chief engineer of China Telecom Group, said that the number of China Telecom's optical fiber broadband users will exceed 100 million in three years, reaching the world's leading level. China Unicom also specified 10 million new fiber-to-the-home households in 2012. China Mobile's bids for fiber optic cables in the three major operators reached 40% to 50% in 2010. It can be seen that major operators have paid great attention to the promising business of optical fiber broadband.

The father of optical fiber-Gao Yan

Gao Yan theoretically proved the possibility of using optical fiber as a transmission medium to realize optical communication, and predicted the possibility of manufacturing ultra-low-consumption optical fiber for communication. Known as the "father of fiber".