? ? 1917年，Einstein發(fā)表題為"論輻射量子理論 (On the quantum theory of radiation)" 的論文，提出激光的兩條物理原理:
a.原子的發(fā)射和吸收機(jī)理 (Emmision and absorption of atoms)
b.原子能級(jí)占有數(shù)反轉(zhuǎn)的實(shí)現(xiàn) (Realizing the inversion of occupation number of atomic level)
即，論文中的三種條件原子的自發(fā)輻射 (Spontaneous radiation)、受激吸收 (Simulated absoption)、受激輻射 (Simulated radiation)。
? ? "光和熱輻射能量一樣量子化"這一輻射理論觀念在物理學(xué)中立即起到導(dǎo)火索的作用，Quantum Mechanics 這門新學(xué)科迅速發(fā)展起來(lái)，然而在非理論物理界的四十年后它才開(kāi)始被廣泛應(yīng)用，人們制造出強(qiáng)"泵浦 (Pump)"和適當(dāng)反饋的光學(xué)諧振腔發(fā)射可資利用的激光 (Light Amplification by Stimulated Emission of Radiation, ie. LASER)。
? ? 當(dāng)然最不科幻的應(yīng)用就是在通信中了，激光源的出現(xiàn)，再加上自然界送給光纖通信的禮物: "鉺"元素，用它制造出的光纖"摻鉺光纖"具備了奇跡性的巧合:
Er離子的增益譜與光纖傳輸最低損耗窗口重合。
? ? 這些因素直接促成了所謂"全光通信網(wǎng)"的產(chǎn)生，吊足胃口之后下面也該進(jìn)入正題了。。。╮( ??ω?? )╭? ?﹏?
? ? The theses is simple at the first sight but not as easy as it seems, the topic as Optical Amplifier has rich and broad content in it, and, the most important thing it has, the votality.
? ? The picture below just want to make you clear with the problem "What can Amplifier mainly help us to do?"
? ? The Optical Amplifier, with the simple reason with "Easily breaking through the electronic bottle neck", has become a nova in Optical-fiber communication, which directly leads to the emergence of all-optical communication network, that means, provide us dozens of Tbits/s information capacity, however, in this active family, the most famous and has been put into use to get great benefits one is named "Erbium-doped fiber amplifiers (Abbreviation for EDFA)".
? ? ? ? All the reason is made by the creature, ie. the miracle, that the erbium atom has its gain spectrum coincide with the energy level of the lowest minimum loss window (In optical-fiber telecommunitation).
? ? There are two important portion of the Amplifier made by Erbium:
。。。。。。
。。。。。。
? ? I will explain what the Er-doped fiber（摻鉺光纖EDF） in the following statement.
? ? Easily speaking, EDF is a special form of optical fiber, and has a same structure as single mode fiber, the main difference is that it is made by .
? ? As you can learn from the figurre of "EDF Structure", erbium ions are located at the center of the fiber, which allows themto absorb maximum pump and signal energy for better amplification. The glass cladding witn low refractive index is used to perfect the waveguide structure, besides, providess the properties to the fiber, and the coating is used to increase the diameter of the light.
Principle of EDFA function and course of EDFA work?
The pumped light source emits a laser (
) which excites erbium ions
to transition from the ground state to the excited state (ie. the pumped energy band).
The excited state of the excited ion is very unstable and rapidly decays to metastabe states (Approximately to
), and release the excess energy as phonons.
Metastable particle accumulation will gradually forms the reversed particle number distribution, hence
will have transition from the metastable state to the bottom (
).
If can find the pump source formed
of laser, electron will jump from ground energy level to the metastable state level, and then it will form the reversed particle number distribution again. (Maybe there will also exist the signal light to excites the electron)
The metastable state will soon jump back to the ground level with the corresponding photon of signal, and the laser it gives out will possess the same phase (That means, have good coherence proporties) of the signal.
Structure! Let's have a look of it!
? ? The figures below gives you explamation of how these two components form the Amplifier as EDFA and how to install it into the Optical-fiber communication Net.
Advantages of it! (I'll be less rigorous to neglect the disadvantages)
? ? 1. It's oprating band is just at the lowest dissipation. 1525-1565nm
? ? 2. It's boardband can amplifier more WDM signal at the same time.
? ? 3. The sufficient interaction between light and matter greatly improves the efficiency of energy convertion.
? ? 4. High gain and low noise.
? ? Of course, If can get multiple light source to excite fibers, the advantages will shine through better.
? ? 摻鉺光纖放大器是大自然贈(zèng)予光纖通信的禮物ヾ(′?｀。ヾ)。。我?guī)е鵂I(yíng)業(yè)式的表情這樣復(fù)述到。。。
