Basic introduction Chinese name: optical fiber technology application fields: communication, electronics, electric power, etc. Definition: Examples of new basic materials: optical fiber transmission to complete power transmission function, widely used, plastic optical fiber, composition principle, optical signal transmitter, optical signal receiver, transmission optical fiber to complete power transmission function. American Lalian Company successfully used optical fiber to complete the power transmission function, which opened up a brand-new road in the power field. At the transmitting end, they use semiconductor laser diode to convert electric energy into laser and transmit it in optical fiber, and use solar cell as the receiving device. The device uses 300 micron thick gallium arsenide as an insulating substrate, which is covered with 20 micron thick solar cells. Divided into six independent areas, connected in series by gold-plated air bridges. When the laser from the optical fiber irradiates the solar cell, the light energy immediately becomes electric energy. The voltage generated by each area is exactly 1V, and the voltage of six areas in series is 6V, which is enough for the control circuits of most sensors. Widely used If the power of laser diode is continuously improved, coupled with a complete power transmission system, optical fiber power transmission can be widely used in military, industrial, commercial and other aspects. Borgen laboratory in France specializes in computer, electronic equipment, signal processing and image technology, which can realize lossless transmission in optical fiber by using solitons and short pulses of light. This technology can solve the problems of dispersion and nonlinear effect, and it is not necessary to set up multiple regeneration devices along the optical cable. When working, just set an amplifier every100km. Solitary wave wavelets can cross each other without interference. It is said that this new technology can be used on submarines within the range of 6450- 12900 km, which can solve the problem of communication difficulties. An irregular carrier signal optical fiber communication technology developed by American communication security experts is specially used to deal with the increasingly rampant and sophisticated eavesdropping experts. This technology first converts useful information such as voice into digital pulse signals, and then encodes these digital pulse signals and modulates them on random microwave carriers with irregular changes. When transmitting, the laser transmitter transmits an irregular carrier signal carrying information to the receiver through the optical fiber communication system. The receiver's laser receiver works synchronously and dynamically with the laser emitting device with special technology, and finally completes the task of demodulating useful signals from irregular carriers. Using this technology, eavesdroppers will never be able to use it again, they will only hear chaotic noise. Lin Bao recently developed an optical fiber scale, which can weigh trucks with optical fiber and laser. This optical fiber scale uses an optical fiber with very special resistance characteristics. When it is subjected to pressure or tension, the optical fiber will be slightly deformed, resulting in changes in the characteristics of the laser. At this point, the detector will immediately learn this change and convert it into an electrical signal change. So as to be reflected on the display panel of the instrument. Because optical fiber is made of glass, it has moisture-proof and radiation-resistant properties. More importantly, it is convenient to install and maintain, and it is suitable to be installed around urban main roads, factories, airports and runways, warehouses and ports for 24-hour continuous work. Therefore, in addition to weighing, it can also play the role of monitoring, and the accuracy far exceeds the existing electronic equipment. Plastic optical fiber According to a recent report in American magazine, a plastic optical fiber developed by Boston Optical Fiber Company in Massachusetts, USA, is 30 times faster than the current standard copper wire, lighter, more flexible and lower in cost than glass fiber. This kind of optical fiber uses the refraction of light or the jumping of light in the fiber to achieve higher transmission speed, and can transmit data at a speed of 3 megabytes per second within 100 meters. At present, 370,000 kilometers of submarine optical cables have been laid in the world, which is almost around the earth 10. Moreover, because lasers are used at both ends, there is no need for repeaters to amplify signals during transmission, which will greatly reduce the cost and the call cost. It is reported that the world's largest submarine optical cable connecting Europe and America will be opened this year. This submarine communication cable connecting the whole world is being laid, which is the most magnificent project in the communication field in the 20th century and has been supported by 30 international telecommunication organizations all over the world. It spans the Atlantic Ocean, the Mediterranean Sea, the Red Sea and the Indian Ocean, and enters the Pacific Ocean through the Straits of Malacca. With a total length of nearly 320,000 kilometers, it connects 175 countries and regions, and can make 2.4 million telephone calls or transmit hundreds of thousands of compressed pictures at the same time. The whole project costs $654.38+0.4 billion and is expected to be completed in 2003. Composition principle Optical fiber technology generally consists of three parts: optical signal transmitter, optical fiber for transmitting optical signal and optical signal receiver. The function of the optical signal transmission end is to convert the electric signal to be transmitted into an optical signal through an electro-optical conversion device. At present, the electro-optical conversion device at the transmission end generally adopts light emitting diode or semiconductor laser tube. The output light power of light-emitting diodes is small, the signal modulation rate is relatively low, but the price is cheap. Its output light power is basically linear with the driving current in a certain range, which is more suitable for short-distance, low-speed and analog signal transmission. Laser diode has high output power, high signal modulation rate, but high price, which is suitable for long distance, high speed and digital signal transmission. The function of optical fiber is to transmit the optical signal at the transmitting end to the optical signal receiving end with as little attenuation and distortion as possible. At present, optical fiber is generally used in 0.84-:micro near infrared band; m、 1.3 1 & amp； Microscopic; m、 1.55 & amp； Microscopic; M multimode or single mode optical fiber with good transmittance. The function of the optical signal receiver is to restore the optical signal to the corresponding electrical signal through photoelectric conversion devices, which generally adopt semiconductor photodiodes or avalanche photodiodes. The luminous wavelength of the light source constituting the optical fiber transmission system must be matched with the band where the transmission fiber presents a low loss window and the peak reverberation band of the photoelectric detection device. The electro-optical conversion device at the transmitting end adopts 0.84 &: micro； The central emission wavelength of; M high-brightness near-infrared semiconductor light-emitting diode, transmission fiber adopts multimode synchronous fiber, and photoelectric conversion device at receiving end adopts peak reverberation wavelength of 0.8&: micro； M to 0.9&; Microscopic; M silicon photodiode. The following sections are further introduced. The driving and modulating circuit of LED in the optical signal transmission system is shown in Figure 2. The signal is modulated by light intensity modulation. The transmitted light intensity adjusting potentiometer is used to adjust the static driving current flowing through the LED, so as to change the emitted light power of the LED accordingly. The set static driving current adjustment range is 0-20mA, which drives the display value of 0-2000 units corresponding to the light transmission intensity of the panel. When the driving current is small, the emitted light power of LED is basically linear with the driving current. The audio signal is isolated from the operational amplifier through the capacitor and resistor network, and then coupled to the negative input end of another operational amplifier, which is superimposed with the static driving current of the led, so that the LED emits an optical signal varying with the audio signal, and this optical signal is coupled to the transmission optical fiber through the optical fiber coupler. The low end of the frequency of the transmittable signal can be determined by the capacitor and resistor network. The low frequency reverberation of the system is not more than 20Hz. The optical signal receiving end is the working principle diagram of the optical signal receiving end. The transmission optical fiber couples the optical signal sent by the sending end to the photoelectric conversion device photodiode through the optical fiber coupler, and the photodiode converts the optical signal into a current signal proportional to it. Photodiode should be reversed biased when used, and the photocurrent signal is converted into a voltage signal proportional to it through the current-voltage conversion of operational amplifier. The audio signal contained in the voltage signal is converted into a voltage signal through a capacitor. The frequency response of photodiode is generally high, and the high frequency response of the system mainly depends on the response frequency of operational amplifier. Transmission optical fiber At present, optical communication generally adopts timely optical fiber. It is covered by a cladding with a relatively large refractive index n2, and the light is totally reflected at the interface between the core and the cladding, so that it is confined to propagate in the core. As shown in fig. 5, the optical fiber is actually a dielectric waveguide, and the light is locked in the optical fiber and can only be transmitted along the optical fiber. According to the mode of transmitting light, the core diameter of optical fiber usually ranges from several microns to several hundred microns. Refractive index step fiber contains two kinds of circularly symmetric coaxial media, which are uniform in texture but different in refractive index, and the refractive index of the outer layer is lower than that of the inner layer. Gradient refractive index fiber is a kind of fiber whose refractive index changes gradually along the cross section of the fiber. The purpose of changing the refractive index is to make the group velocities of various modes similar, thus reducing the mode dispersion and increasing the communication bandwidth. Multimode index step fiber has limited transmission bandwidth because of the different group velocities of each mode transmission. Multi-mode graded index fiber increases the bandwidth of signal transmission because of its special refractive index distribution, which makes the group velocity of each mode the same. Single-mode fiber is an optical fiber that only transmits a single optical mode, and single-mode fiber can transmit the highest signal bandwidth. At present, single-mode optical fiber is widely used in long-distance optical communication. The main technical indexes of time-sensitive optical fiber are attenuation characteristics, numerical aperture and dispersion. Numerical aperture: Numerical aperture describes the characteristics of optical fiber when it is coupled with optical devices such as light source and detector. Its size reflects the ability of optical fiber to collect light. As shown in fig. 5, the light incident on the fiber end face within the solid angle range of 2θmax is totally reflected and transmitted at the fiber inner interface, while the light incident on the fiber end face outside the range of 2θmax is not totally reflected at the fiber inner interface, but transmitted to the cladding and immediately attenuated. The numerical hole of optical fiber is defined as: NA=Sinθmax. Its value is generally between 0. 1 ~ 0.6, and the corresponding θmax is between 90 and 330. The numerical aperture of multimode fiber is relatively large, while that of single-mode fiber is relatively small, so the general single-mode fiber needs LD semiconductor laser as its light source.