Optical communication is one of the earliest communication methods used by human beings. From beacon transmission signals, to signal lights, semaphores and other communication methods, it is the category of optical communication. However, due to limitations such as line-of-sight, atmospheric attenuation, and terrain blocking, the development of optical communication has been slow. One day in 1870, British physicist Tindal went to the lecture hall of the Royal Society to talk about the principle of total reflection of light. He made a simple experiment: drilling a hole in a wooden bucket filled with water, and then using a lamp to put it from the top of the bucket Water illuminates. The results surprised the audience. People saw that the water that was shining out came out of the small hole of the bucket. The water flow was curved, and the light was also curved. The light was actually captured by the curved water (Figure 4-11). It has been found that light energy travels along a stream of fine wine sprayed from wine barrels; it has also been found that light energy travels along curved glass rods. Why is this? Isn't the light going straight anymore? These phenomena have attracted the attention of Tyndall. After his research, he found that this is the effect of total reflection, that is, the light is emitted from the water to the air. When the incident angle is greater than a certain angle, the refracted light disappears and all the light is reflected back into the water. On the surface, light seems to bend forward in the current. In fact, in the curved water flow, the light still propagates in a straight line, but there are multiple total reflections on the inner surface, and the light propagates forward through multiple total reflections. What is fiber optic communication ? Optical fiber is short for optical fiber. Optical fiber communication is a communication method that uses light waves as an information carrier and optical fibers as a transmission medium. From a principle point of view, the basic material elements that constitute optical fiber communication are optical fiber, light source and photodetector. In addition to optical fiber classification according to manufacturing process, material composition and optical characteristics, in application, optical fiber is often classified according to use, which can be divided into optical fiber for communication and optical fiber for sensing. Transmission medium fiber is divided into two types: general purpose and special purpose, and functional device fiber refers to the fiber used to complete the functions of light wave amplification, shaping, frequency division, frequency doubling, modulation, and optical oscillation. The form appears. Principles of optical fiber communication The principle of optical fiber communication is: at the sending 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 light intensity changes with the amplitude (frequency) of the electrical signal And sent out through the optical fiber; at the receiving end, the detector converts it into an electrical signal after receiving the optical signal, and restores the original information after demodulation. Application field The application field of optical fiber communication is very extensive, mainly used for local telephone trunks. The advantages of optical fiber communication can be fully exerted here, and gradually replace the cable and be widely used. It is also used for long-distance trunk line communication, which used to rely on cable, microwave, and satellite communication. Now it is gradually using optical fiber communication and has formed a global dominant bit transmission method. Level trunks, provincial secondary trunks and sub-county branches); it is also used for high-quality color television transmission, industrial production site monitoring and dispatching, traffic monitoring and control command, urban cable television network, and common antenna (CATV) system. It is used in optical fiber local area network and others such as in aircraft, spaceship, ship, underground, power department, military and corrosive and radiation. The optical fiber transmission system is mainly composed of: optical transmitter, optical receiver, optical cable transmission line, optical repeater and various passive optical devices. To achieve communication, the baseband signal must also be processed by the electrical terminal and sent to the optical fiber transmission system to complete the communication process. It is suitable for optical fiber analog communication system, but also suitable for optical fiber digital communication system and data communication system. In the optical fiber analog communication system, electrical signal processing refers to processing such as amplification and pre-modulation of the baseband signal, and electrical signal inverse processing is the reverse process of originating processing, that is, demodulation, amplification and other processing. In the optical fiber digital communication system, electrical signal processing refers to amplifying, sampling, and quantizing the baseband signal, that is, pulse code modulation (PCM) and line code encoding processing, etc., and electrical signal inverse processing is also the reverse process of the origin. For data optical fiber communication, electrical signal processing mainly includes amplifying the signal. Unlike digital communication systems, it does not require code conversion. Optical Fiber Communication Characteristics The laser used for communication is generally propagated in a special pipe, optical fiber. At present, the main component of the optical fiber is silica. Optical fiber communication has many outstanding advantages: Frequency bandwidth The width of the frequency band represents the size of the transmission capacity. The higher the frequency of the carrier, the greater the bandwidth of the signal that can be transmitted. In the VHF band, the carrier frequency is 48.5MHz ~ 300Mhz. With a bandwidth of about 250MHz, it can only transmit 27 TV sets and dozens of FM broadcasts. The frequency of visible light reaches 100,000 GHz, which is more than one million times higher than the VHF band. Although the optical fiber has different losses to light of different frequencies, which affects the bandwidth, the bandwidth in the lowest loss area can also reach 30000 GHz. At present, the bandwidth of a single light source only accounts for a small part of it (the frequency band of multi-mode fiber is about several hundred megahertz, and a good single-mode fiber can reach more than 10GHz). With advanced coherent optical communication, 2000 light can be arranged in the range of 30000GHz Carrier wave, wavelength division multiplexing, can accommodate millions of channels. Low loss Firing of optical fiber In a system composed of coaxial cables, the best cable has a loss of more than 40dB per kilometer when transmitting 800MHz signals. In contrast, the loss of the optical fiber is much smaller. The transmission of 1.31um of light, the loss per kilometer is less than 0.35dB. If the transmission of 1.55um of light, the loss per kilometer is smaller, up to 0.2dB. This is 100 million times less than the power loss of the coaxial cable, which allows it to transmit much longer distances. In addition, there are two characteristics of optical fiber transmission loss. First, it has the same loss in all cable TV channels. It does not need to be equalized by an equalizer like cable trunks. Second, its loss hardly changes with temperature, so do n’t worry Mains level fluctuations due to changes in ambient temperature. Light weight Because the optical fiber is very thin, the diameter of the single-mode fiber core is generally 4um to 10um, and the outer diameter is only 125um. With the addition of a waterproof layer, ribs, and sheath, the diameter of the optical cable composed of 4 to 48 fibers is less than 13mm. It is much smaller than the standard coaxial cable with a diameter of 47mm. In addition, the optical fiber is glass fiber and the specific gravity is small, which makes it have the characteristics of small diameter and light weight, and it is very convenient to install. Strong anti-interference ability Because the basic component of optical fiber is quartz, it only transmits light, is not conductive, and is not affected by the electromagnetic field. The optical signal transmitted in it is not affected by the electromagnetic field. Therefore, optical fiber transmission has a strong resistance to electromagnetic interference and industrial interference. Because of this, the signal transmitted in the optical fiber is not easy to be eavesdropped, which is conducive to secrecy. High fidelity Because fiber transmission generally does not require relay amplification, it will not cause new nonlinear distortions due to amplification. As long as the linearity of the laser is good, the TV signal can be transmitted with high fidelity. Practical tests have shown that the carrier combination triple beat ratio C / CTB of a good AM fiber system is above 70dB, and the intermodulation index cM is also above 60dB, which is much higher than the non-linear distortion index of general cable trunk systems. Reliable working performance We know that the reliability of a system is related to the number of devices that make up the system. The more equipment, the greater the chance of failure. Because the number of equipment included in the optical fiber system is small (unlike the cable system, which requires dozens of amplifiers), the reliability is naturally high, and the life of the optical fiber equipment is very long, and the trouble-free working time reaches 500,000-750,000 hours. The shortest life is the laser in the optical transmitter, the minimum life is also more than 100,000 hours. Therefore, the working performance of a well-designed, properly installed and debugged optical fiber system is very reliable. Costs are falling At present, someone has proposed a new Moore's Law, also known as the Optic Law (OpTIcal Law). The law states that the bandwidth of optical fiber transmission information doubles every 6 months, while the price decreases by a factor of two. The development of optical communication technology has laid a very good foundation for the development of Internet broadband technology. This clears the last obstacle for the large-scale cable television system to adopt optical fiber transmission. Due to the abundant sources of materials (quartz) for making optical fibers, with the advancement of technology, the cost will be further reduced; and the copper raw materials required for cables are limited, and the price will be higher and higher. Obviously, in the future, optical fiber transmission will have an absolute advantage and become the most important transmission method for the establishment of cable television networks in the whole province and even the whole country.
SSD 240GB 240 GB SMI2258XT TLC Hard Disk Solid State Drive
>High R/W Speed Supports
Solid State Disk,Solid State Drive,Solid State Hard Drive,Solid State External Hard Drive,SSD MICROBITS TECHNOLOGY LIMITED , http://www.microbitstrade.com
Max. read speed up to 560 MB/s
>3D NAND
Adopts 3D NAND flash to optimize capacity, performance and stability
>Shockproof
No mechanical structure Adopts electronic chips control High data security
>SATA 2.5-inch Interface
Note
Capacity: 1GB=1,000,000,000 bytes by IDEMA. Performance test is performed in a specific testing environment. Any change of computer system, operation system, hardware, software, or functions will influence the test result.
Interface: 2.5", SATA 3 6Gb/s(compatible with SATA2 , SATA1,to drop speed )
Performance in the specifications is tested based on CrystalDiskMark.
Power consumption may differ according to flash configuration and platform. Power consumptions are measured by using CrystalDiskMark 1000 MB to test sequential R/W 5 times.
The TBW value is calculated based on Workload of JEDC 218B/219A standard.
The MTBF value is calculated based on the functional failure rate of JEDC 218B/219A standard.