多模光纤和单模光纤的区别是什么

对的,纤芯与包层的材料一致,只是掺杂的物质略有不同,二者的折射率差非常小,但包层一定比纤芯小,否则光就发生折射,无法将光约束在纤芯内传送了

The first semiconductor lasers into practical,the lasing wavelength 0.83鍒?.85 um.This corresponds to the fiber loss spectrum of a window,multi-mode optical fiber loss of 2 dB / km.Centered on improving the capacity of optical fiber communication systems,in the 1970s-period.1.3 um wavelength in the loss was smaller (0.4 dB/km3,close to zero coefficient of dispersion single mode optical fiber.Soon after to develop further reduce the wear and tear 1.55um single-mode optical fiber
Window.Back in the late 1960s began to study the long-wavelength (1.3 ym) InGaAsP / InP laser also with single-mode optical fiber into the development of practical systems.1.55 uPm lasing wavelength of the laser diode was quick to practical use.To further to achieve the low threshold lasers,good dynamic single-frequency,high temperature and the characteristics of the work of the long-term stability,and have a lot of different structures,high-performance semiconductor lasers,such as the hidden bar buried heterojunction (BH ) Laser,distributed feedback (DFH) laser,sub-Bubu Bragg reflector (DBR) laser,cleavage coupled lasers and quantum well lasers,and so on.
Visible development of the momentum from semiconductor laser discs,optical-times the income copying and processing technology development.As early as 1974 the Netherlands,Philips Research experimental laser-start digital audio recording (DAD) Study.Okazaki in the record store data on the number of inverse laser beam focus will be on the spot diameter and the diameter is proportional to the wavelength of the laser.Therefore,in order to improve access to the information DAD density,to use the laser wavelength as short as possible sources.The first is the use of the He-Ne laser,but because of their size greenhouses limited life,the 1982 listing of the CD (CompactDisk) jukebox on a wavelength of 780 nm semiconductor laser.In recent years.A shorter wavelength such as the 30 nm semiconductor lasers have become commodities.Small size,low price and long life in the semiconductor laser optical information storage and processing has been the largest market.shan of laser research to promote a high-power laser diode (including the array of lasers) development.For there were iron-doped solid medium,such as Nd:YAG,Nd; YVO,such as the wavelength of 808 nm-effective around the peaks,with small size,lasing wavelength of 808 nm semiconductor laser instead of the usual-pumped solid-state laser materials,Can be small in size,Su Pu high efficiency (up to 70%) for dim light of the solid.
With REE-doped fiber amplifier,used as the source of pumping high-power laser diode was also another important application.For example,using wavelength of 980 nm or 1480 nm,for the tens of milliwatts of power semiconductor laser pump fiber,can get high-gain coefficient,so that optical signals are more than 30 dB gain.Fiber amplifier in the optical fiber communication has been critical applications.
In short,the need for a variety of applications,semiconductor laser beam is to improve the quality of development,reducing the beam divergence angle to enhance the coherence of space,increasing the high-speed modulation of the so-called dynamic single-model; pressure narrow spectral line width to improve beam The time coherence; further enhance the stability of temperature (that is,high temperature on the strength of the levy),the application of the laser diode is continuously expanding.
5,the band works so that semiconductor lasers generate a new leap forward with the molecular beam epitaxy (MBE) and metal organic compounds chemical vapor deposition (MOCVD) technology development and improvement,can grow to atomic size of the order of ultra-thin layer,which can Formation of the carrier into a holding it is the nature of quantum wells and superlattices.This is a band semiconductor and massive (often referred to as material) Semiconductor completely different shape and structure,and can,if necessary,by changing variables should be ultra-thin layer of the band structure change.The so-called "band project" or "band cutting project" to semiconductor laser with a new vitality,its device performance a big leap.For example,the quantum well semiconductor laser output power for up to tens of watts; temperatures as high as several characteristics of Baidu; laser threshold current of less than 1 mA; multiple quantum modulation doped laser relaxation oscillation frequency of up to 30 GHz,as usual Double-heterojunction semiconductor laser five times in the high-speed modulation than the width of the semiconductor laser is usually a low number
Order of magnitude,and so on.As quantum well (especially strained quantum well) structure emerges,the visible light laser diode increase the life span,the lasing wavelength further shortened.Have proven that the band works to fundamentally change the face of the semiconductor laser.In the near future,its continuous power output may reach several hundred watts and watts in order to enable it is not only a technical school in the field of information,but also in material processing,and to play an important role.

光纤的性能特点
光纤与前面介绍的电缆完全不同,它不再是用电子信号来传输数据,而是使用光脉部来传输传输信号.正是这种特殊的材质,使它拥有电缆无法比拟的优点：
频带极宽：拥有极宽的频带范围,以GB位作为度量；
抗干扰性强：由于光纤中传输的是光束,光束是不会受外界电磁干扰影响；
保密性强：由于传输的是光束,所以本身不会向外幅射信号,有效地防止了窃听；
传输速度快：光纤是至今为止传输速度最快的传输介质,能轻松达到1000Mbps；
传输距离长：它的主减极小,在较大的范围内是一个常数,在许多情况下几乎可以忽略不计的,在这方面比电缆优越很多.
多模光纤与单横光纤
光纤有单模光纤和多模光纤之分；
单模光纤采用窄芯线,使用激光作为发光源,所以其地散极小；另外激光是发一个方向射入光纤,而且仅有一束,使用其信号比较强,可以应用于高速度、长距离的应用领域中,便也合得它的成本相对更高.
而多模光纤则更广泛地应用于短距离或相对速度更低一些的领域中,它采用LED 作为光源,使用宽芯线,所以其散较大；在加上整个光纤内有以多个角度射入的光,所以其信号不如单模光纤好,但相对低的价格是它的优势.

按传输模式分
按光在光纤中的传输模式可分为：单模光纤和多模光纤.
多模光纤的纤芯直径为50~62.5μm,包层外直径125μm,单模光纤的纤芯直径为8.3μm,包层外直径125μm.光纤的工作波长有短波长0.85μm、长波长1.31μm和1.55μm.光纤损耗一般是随波长加长而减小,0.85μm的损耗为2.5dB/km,1.31μm的损耗为0.35dB/km,1.55μm的损耗为0.20dB/km,这是光纤的最低损耗,波长1.65μm以上的损耗趋向加大.由于OHˉ的吸收作用,0.90~1.30μm和1.34~1.52μm范围内都有损耗高峰,这两个范围未能充分利用.80年代起,倾向于多用单模光纤,而且先用长波长1.31μm.
多模光纤
多模光纤(Multi Mode Fiber)：中心玻璃芯较粗(50或62.5μm),可传多种模式的光.但其模间色散较大,这就限制了传输数字信号的频率,而且随距离的增加会更加严重.例如：600MB/KM的光纤在2KM时则只有300MB的带宽了.因此,多模光纤传输的距离就比较近,一般只有几公里.
单模光纤
单模光纤(Single Mode Fiber)：中心玻璃芯很细(芯径一般为9或10μm),只能传一种模式的光.因此,其模间色散很小,适用于远程通讯,但还存在着材料色散和波导色散,这样单模光纤对光源的谱宽和稳定性有较高的要求,即谱宽要窄,稳定性要好.后来又发现在1.31μm波长处,单模光纤的材料色散和波导色散一为正、一为负,大小也正好相等.这就是说在1.31μm波长处,单模光纤的总色散为零.从光纤的损耗特性来看,1.31μm处正好是光纤的一个低损耗窗口.这样,1.31μm波长区就成了光纤通信的一个很理想的工作窗口,也是现在实用光纤通信系统的主要工作波段.1.31μm常规单模光纤的主要参数是由国际电信联盟ITU－T在G652建议中确定的,因此这种光纤又称G652光纤.

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在光纤通信理论中,光纤有单模、多模之分,区别在于：x0d1. 单模光纤芯径小（10m m左右）,仅允许一个模式传输,色散小,工作在长波长（1310nm和1550nm）,与光器件的耦合相对困难x0d2. 多模光纤芯径大（62.5m m或50m m...