王興軍--2015 暑期學校PPT-光發(fā)射1 硅基集成中的光發(fā)射技術

1、http:/ Emission in Silicon Photonics王興軍王興軍 Beijing 2015.7.13 http:/ Emission and detector http:/ Photonic Integration and Microsystems:Combining electrical and optical components on the same silicon-based substrates used in the fabrication of a semiconductor chip, which employs numerous integrated o

2、ptics devices, including lasers, photodetectors, splitters, isolators, filters, modulators, switches, et. al.Silicon photonicsIntroduction (Intel and IBM)http:/ 硅基光源是硅基光電子學元器件中的重中之重。l 由于硅是間接帶隙的半導體，發(fā)光效率不高，內量子效率約為10-5-10-6。l 因此硅一直以來被認為不適合制作光源材料。 http:/ 上世紀90年代，多孔硅的室溫發(fā)光 2000年，納米硅的增益 2004年，鉺摻雜微環(huán)激光器 2005

3、年，硅拉曼激光器 2006年，III-V族-硅混合激光器 2010年，鍺硅激光器http:/ l=hc/Eg=1.24eV/EgLight emissionhttp:/ 一個電子或空穴吸收另一電子與空穴復合時放出的能量，躍遷到更高的能量狀態(tài)的過程稱為俄歇復合過程。 這種過程的幾率與復合的載流子濃度和接受能量的載流子濃度乘積成正比，所以載流子濃度高的材料俄歇復合過程更容易。l自由載流子吸收l多聲子復合 晶體中電子和空穴復合時可以發(fā)射多個聲子來釋放能量稱之為多聲子復合。http:/ 自發(fā)輻射是指處于激發(fā)態(tài)的原子中的電子在激發(fā)態(tài)能級上只能停留一段很短的時間，就自發(fā)地躍遷到較低能級中去，同時輻射出一個

4、光子。l受激輻射 當原子處于激發(fā)態(tài)E2時，如果恰好有能量等于（E2-E1）的光子入射進來，在入射光子的影響下，原子會發(fā)出一個同樣的光子而躍遷到低能級E1上去，這種輻射叫做受激輻射。這種方式就是產生激光的基本原理。http:/ 1917年 愛因斯坦在“關于輻射的量子理論”論文中提出，解釋黑體輻射現(xiàn)象光子與原子的三種相互作用：自發(fā)輻射、受激輻射、受激吸收自發(fā)輻射、受激輻射、受激吸收 自發(fā)輻射：自發(fā)輻射：電子-空穴對復合時產生的光在波長、相位等特性彼此互不關聯(lián)，自發(fā)性的行為。光譜較寬，相位不一致，沒有偏振性，光輸出功率較弱，例：發(fā)光二極管 受激輻射：受激輻射：已有的傳播光子誘發(fā)產生一個光子能量、相位

5、、偏振等特性與前一個光子完全相同。這個輻射復合過程為受激輻射。光譜窄、相位一致、有偏振方向、光輸出功率大。例：激光器 EcEvSpontaneous emissionStimulated emissionhttp:/ 在正常狀態(tài)下，電子處于基態(tài)E1，在入射光作用下，它會吸收光子的能量躍遷到激發(fā)態(tài)E2上，這種躍遷稱為受激吸收。電子躍遷后，在基態(tài)留下相同數(shù)目的空穴。受激吸收是受激輻射的逆過程。 設在單位物質中，處于E1和E2的原子數(shù)分別為N1和N2。當系統(tǒng)處于熱平衡狀態(tài)時，存在下面的分布 http:/ Emission Rate and Einstein Coefficients The upwa

6、rd transition depends on the number of atoms N1 and the energy density in the radiation:Need to determine the controlling factors for the rates of stimulated emission, spontaneous emission, and absorption in two energy system.E1E2h(a) Absorptionh(b) Spontaneous emissionh(c) Stimulated emissionInhOut

7、hE2E2E1E1Absorption, spontaneous (random photon) emission and stimulatedemission. 1999 S.O. Kasap, Optoelectronics (Prentice Hall)B12, A21, and B21 are the Einstein coefficients for absorption, spontaneous emission and stimulated emission.The downward transition depends on the number of atoms N2 and

8、 the energy density in the radiation:http:/ Emission Rate and Einstein Coefficients At the thermal equilibrium, we can assume up and down transitions are equal and the atom numbers at energy levels are determined by Boltzmann statistics:Also at the thermal equilibrium, the radiated photon energy den

9、sity from atoms must follow the Plancks black body radiation distribution law:http:/ Emission Rate and Einstein Coefficients Based on above assumptions and equations, the Einstein coefficients can be determined as:The ratio of stimulated to spontaneous emissions can be determined as:orhttp:/ Emissio

10、n Rate and Einstein Coefficients The ratio of stimulated emission to absorption can be determined as:From above equations, two requirements need to be met to have stronger stimulated emission over spontaneous emission and absorption (Lasing): (1) large photon concentration (optical cavity) and (2) N

11、2 N1 (population inversion). http:/ (wnr+wr)之比。因此，只有當nrr，才能獲得高效率的光子發(fā)射。l 對間接復合為主的半導體材料，一般既存在發(fā)光中心，又存在其他復合中心，通過前者產生輻射復合，后者產生非輻射復合。因此，要使輻射復合占優(yōu)勢，必須使發(fā)光中心濃度遠大于其他雜質濃度。發(fā)光效率http:/ 光的放大主要由材料的增益譜決定，對于半導體材料，它是由態(tài)密度（(h)）、費米函數(shù) (fg(h)和輻射壽命r決定的。L.Pavesi, Review Article:Silicon-Based Light Sources for Silicon Integrat

12、ed Circuits Advances in Optical TechnologiesVolume 2008 其中，drstim or drabs是一定光子能量h下的受激發(fā)射和受激吸收率，g(h)是增益系數(shù)，d是光子流量的變化。 fe和和fh是電子是電子-空穴對的熱分布函數(shù)，空穴對的熱分布函數(shù)，是光子流密度，是光子流密度，EFe和和 EFh是電子和空穴的準費米能是電子和空穴的準費米能級，當沒有外泵浦的情況下，費米級，當沒有外泵浦的情況下，費米函數(shù)函數(shù)減少到簡單的費米態(tài)，也就是對于一個空的導帶和減少到簡單的費米態(tài)，也就是對于一個空的導帶和填滿的價帶，增益系數(shù)小于吸收系數(shù)，填滿的價帶，增益系數(shù)小

13、于吸收系數(shù)，fgh，滿足粒子數(shù)反轉條件，滿足粒子數(shù)反轉條件，fg0。這意味上面的公式為正值，。這意味上面的公式為正值，因此系統(tǒng)也顯示正的增益。從上面公式可以看出，輻射壽命因此系統(tǒng)也顯示正的增益。從上面公式可以看出，輻射壽命r也是一個關鍵的參數(shù)也是一個關鍵的參數(shù),壽命越壽命越短，增益越大。短，增益越大。 http:/ http:/ I=I0egx, g=Jm, g為增益系數(shù)，J為電流密度，為增益因子，對于同質m=1，異質m=2.8。光傳輸公式： I=I0e(g-)x R1R2e2(g- )L=1 g= +ln(1/R1R2)/2L左邊光吸收引起的損耗包括體內所有損耗：本征光吸收,自由載流子吸收等

14、右邊為端面透射損耗.http:/ 閾值的物理意義：閾值的物理意義：在激光物質中，要實現(xiàn)受激輻射的光放大，必須其內部增益足夠大。 g= +ln(1/R1R2)/2Ll盡量提高電注入效率，使增益盡可能大，受激輻射盡可能高。l通過高質量的外延生長獲得高質量的晶體，使內部吸收非常低。l通過鍍反射膜來提高反射率，減少透射損耗。http:/ 能產生激光的物質 直接帶隙的半導體發(fā)光效率比間接帶隙高3個數(shù)量級，一般只有直接帶隙才能制備激光器，對比：GaAs：0.5；Si：10-5(2) 粒子數(shù)反轉 光照、電流注入、化學反應等泵浦方式（p-n結電注入載流子是最簡單方式，效率高）(3) 諧振腔 對頻率一定、方向一

15、致的光產生正反饋，使其獲得足夠大的增益，克服內部和端面的損耗，從而發(fā)生諧振，產生激光。 直接帶隙材料、電注入實現(xiàn)粒子數(shù)反轉和諧振腔直接帶隙材料、電注入實現(xiàn)粒子數(shù)反轉和諧振腔三大要素構三大要素構成了成了半導體激光器半導體激光器的基本支柱。的基本支柱。http:/ 1.1 eV 兩個強非輻射躍遷過程： 俄歇復合 自由載流子吸收。http:/ limits: 1l 在硅中，電子-空穴對的輻射壽命長（毫秒量級），一個電子-空穴對需要毫秒才能復合，典型的非輻射壽命是納秒量級，因此內量子效率約為10-5-10-6。 在此期間，電子和空穴移動的體積達到10m3。這樣他們很容易遇到缺陷或俘獲中心，載流子就會發(fā)

16、生非輻射復合。int = wr/(wnr+wr)=nr /(nr + r )=1-r /(nr + r )http:/ limits: 2硅的俄歇復合 一旦多的載流子被激發(fā)，這種機理就非常嚴重。一個俄歇復合的概率是和激發(fā)的載流子數(shù)n的平方成正比，和禁帶寬度成反比。因為半導體中有很多的載流子，所以俄歇復合是很強的。l其中C為常數(shù),和材料的摻雜濃度有關。對于硅，為10-30cm6s-1,當n為1019cm-3，非輻射復合壽命為10ns。因此，對于高載流子注入硅，俄歇復合是非輻射復合的主要機制。http:/ limits: 3自由載流子吸收l自由載流子吸收系數(shù)是和硅的自由載流子濃度nfc以及光波長有

17、關an 10-18 nfc 2 當nfc=1019cm-3, =1.55m，n為24cm-16。對于重摻雜硅，這也是產生激光的主要限制，然而對于本征硅，除非nfc非常高，否則這種貢獻比較小。 http:/ process:The anodization of Si wafers at low current densities in HF-based solution can be used to generate an array of extremely small holes that run orthogonal to the surface.Porous silicon (PL) T

18、hey observed strong visible PL at room temperature. The have been interpreted as arising from free standing Si quantum wires wherein two-dimensional Quantum confinement of carriers has appreciably widened the Si band gap.1990, Canham et al. APL 57, 1046http:/ The demonstration of bright and efficien

19、t EL from porous silicon layers at low bias voltages is very encouraging. It shows that electron-hole pairs can be created electrically with subsequent radiative recombination. 1992, Canham et al. APL 61, 2583Porous silicon (EL)http:/ nanocrystal fabricationPavesi et al. Advances in Optical Technolo

20、gies 2008 Beat the indirect band gap and avoid non-radiative recombinationshttp:/ 目前對低維納米硅基材料發(fā)光機理的研究出現(xiàn)了各種各樣的物理模型，各有優(yōu)缺點，總體上看，目前主要存在以下3種發(fā)光機理解釋的模型。l量子限制發(fā)光模型l與氧有關的缺陷發(fā)光模型l量子限制效應-發(fā)光中心發(fā)光模型http:/ Xe 4f n n=1-14 .4f n 5s2 5p66s2Optical doping with lanthanide ionshttp:/ levels of lanthanide ions1.5 mEgap(Si)h

21、ttp:/ dopingEnhanced co-doping Er silicate(a) Si:Er( ) (N1018cm-3)(b) Si:Er( )/O( ) (N1019cm-3)(e) Er2SiO5 (N1022cm-3) Er-O polyhedra SiOx crystalline matrix(c) SiO2:Er( ) (N1019cm-3)(d)SiO2:Er( )ncSi( )(N1020cm-3)Schematics of related light source materials embedded with Er ionsSchematics of relate

22、d light source materials embedded with Er ions Er concentration 10dB gainEDFA 1018cm-3 10mEDWA 1020cm-3 3cmEr2SiO5 1022cm-3 1 mm ?!G(dB)=4.43 (s semN2-s sabsN1)L s semNEr Ls sem: emission cross sections sabs: absorption cross section: optical confinement factorL: waveguide lengthDoping Constitutiona

23、l elementEDFAhttp:/ Erbium Doping SiliconPLELhttp:/ processEr ion implantation bulk SiIon implantation process(能量為100keV-10MeV量級) Advantage: ion implantation is a materials engineering process by which ions of a material can be implanted into another solid, thereby changing the physical properties o

24、f the solid. 1. pure doping 2. enlarge solubility of Er doping 3 controlling Er ion concentration and deep 4. large areahttp:/ and EL PropertiesPL Ion implantation350KeV, 1*1017-5*1018 Er ions/cm3EL Ion implantation20 KeV, 5.6*1018 Er ions/cm3 http:/ dependent on microstructure 1400 1450 1500 1550 1

25、600 1650 1700 654nm30mWRT PL intensity arb. unitsWavelength nmEr2SiO5 Er2O3 Er:Al2O3http:/ (Edge X-ray Absorption Fine Structure) Local structure around Er in glassesM.A. Marcus et al., J. of Non-Cryst. Solids 136, 260 (1991) http:/ Erbium Doping and Er CompoundsIntroduction to about rare earth ions

26、Si based Er light source historyEr + Silicon (si nanocrystal) riched silicon oxide Er compoundEr doping Al2O3 materialsSome new structure conclusionshttp:/ + Silicon (si nanocrystal) riched silicon oxide http:/ of Er2SiO5 structure 0.86nmHR-TEM of Er2SiO5 crystal 0.86 nmHRTEM050100150200250300020406

27、080100 O, Si, Er atomic%Depth nm O Si Erhttp:/ of Er2SiO5 structure at 300K PL at RT1400 1450 1500 1550 1600 1650 1700 654nm30mWRT PL intensity arb. unitsWavelength nm1528 nmhttp:/ mW4I13/24I15/2Er3+87PL at different measurement temperaturehttp:/ J F et al. Opt. Exp. 15: 11272 (2007)Energy band engi

28、neering of Ge136 meV115 meVGeSi 0.25%的張應變會使的張應變會使與與L谷的帶隙差減小到谷的帶隙差減小到115meV，這一差別可，這一差別可以通過以通過n型摻雜來進一步彌補。型摻雜來進一步彌補。1019的的n摻雜可以填滿摻雜可以填滿L谷并使電子谷并使電子開始填充開始填充谷，從而獲得直接帶隙躍遷發(fā)光和顯著的增益，谷，從而獲得直接帶隙躍遷發(fā)光和顯著的增益，鍺的帶隙結構：(a)體材料；(b)0.25%張應變；(c)0.25%張應變加n摻雜http:/ resultshttp:/ 實現(xiàn)其高效率和高穩(wěn)定度的發(fā)光。二是從器件實用化角度考慮,如何實現(xiàn)硅-LED 在室溫下的電致

29、發(fā)光。l人們已嘗試了三種硅基納米材料用于高效率硅-LED 的制作, 即高純體單晶硅，硅納米量子點和摻Er硅。http:/ Si light-emitting diodes M. A. Green, et al, Nature, 412: 805, 2001.以區(qū)熔法生長的具有晶格完整以區(qū)熔法生長的具有晶格完整性好的硅單晶作為基底性好的硅單晶作為基底, 利用利用適宜的蝕刻技術使表面加以構適宜的蝕刻技術使表面加以構型型, 把硅表面設計成鋸齒狀光把硅表面設計成鋸齒狀光學圖形，使入射角小于全反射學圖形，使入射角小于全反射角，光的輸出效率可以達到角，光的輸出效率可以達到99%以上以上并對其進行高質量的熱

30、氧化和并對其進行高質量的熱氧化和表面鈍化表面鈍化, 以有效地減少載流以有效地減少載流子的非輻射復合速率子的非輻射復合速率,可使量子可使量子效率得以明顯提高效率得以明顯提高, 其室溫下其室溫下的電注入有效量子效率可達的電注入有效量子效率可達1 %以上，開啟電壓小于以上，開啟電壓小于1V。http:/ silicate-V+p-SiErYb/Y silicaten-Sip-SiErYb/Y silicateITO臺階結構臺階結構p-i-n結構結構MIS結構結構鉺鐿鉺鐿/釔硅酸鹽薄膜容易擊穿，釔硅酸鹽薄膜容易擊穿，電流無法與鉺離子作用電流無法與鉺離子作用http:/ C C退火退火11001100

31、C C退火退火直接帶隙吸收擬合直接帶隙吸收擬合12gEaww 5gEeV絕緣體絕緣體電流注入困難電流注入困難http:/ silicateSiNx/SiONITO加入加入SiNx/SiON限流層限流層防止硅酸鹽薄膜的破壞性擊穿防止硅酸鹽薄膜的破壞性擊穿 FN隧穿產生熱載流子，碰撞激發(fā)鉺離子隧穿產生熱載流子，碰撞激發(fā)鉺離子Alp-SiErYb/Y silicateITOhttp:/ -Fowler-Nordheim隧穿隧穿2expJBAEEAlp-SiErYb silicate 60nmSiNx 60nmITO2expJBAEEAlp-SiErYb silicate 60nmITOAlp-SiS

32、iNx 60nmITO限流層輔助實現(xiàn)了限流層輔助實現(xiàn)了FN隧穿，隧穿，有可能產生熱載流子有可能產生熱載流子http:/ EL-V-IAlp-SiErYb silicate 60nmSiNx/SiON 60nmITO1.53um EL譜譜http:/ SiON做限流層做限流層Alp-SiErYb silicate 60nmSiON 60nmITO1.53m EL壽命壽命1.5ms1.53m EL碰撞激發(fā)截面碰撞激發(fā)截面ErYb silicate: 310-14cm2Er-doped SiO2: 110-14cm211risedecaysErYb silicate 的碰撞激發(fā)截面較大！的碰撞激發(fā)截

33、面較大！http:/ 硅基激光器的研制是硅基光電子學領域中的一個最具有魅力、最富挑戰(zhàn)性的前沿課題。制備出具有光增益、光放大和受激輻射的有源區(qū)材料或結構,能夠實現(xiàn)粒子數(shù)的反轉,具有適宜結構形式的光學諧振腔,能夠實現(xiàn)電注入條件下的受激輻射。http:/ et al. Nature materials 4: 888 (2005) 刻蝕了一種周期性的納米孔陣列結刻蝕了一種周期性的納米孔陣列結構，孔直徑為構，孔直徑為110nm。在連續(xù)。在連續(xù)1.5W的的514.5nm Ar離子激光泵浦下獲得離子激光泵浦下獲得了了1.278m的連續(xù)光。這是由于周的連續(xù)光。這是由于周期性的納米孔陣列產生了高密度的期性的納米

34、孔陣列產生了高密度的A型陷阱中心，這些缺陷中心作為光型陷阱中心，這些缺陷中心作為光激活中心發(fā)生反轉產生受激發(fā)射和激活中心發(fā)生反轉產生受激發(fā)射和光增益。但主要缺點是只有在低于光增益。但主要缺點是只有在低于80K的溫度才能產生受激發(fā)射的溫度才能產生受激發(fā)射Nanopatterned siliconhttp:/ Although these experimental observations strongly suggest that significant optical gain and stimulated emission can be achieved in periodic nanopa

35、tterned crystalline silicon, a complete understanding or analysis of the observed phenomena is not readily available at this early stage. For one, the sub-bandgap emission at 1278 nm can be attributed to the so-called A-centre mediated radiative recombination. It has been established that an A-centr

36、e defect state, located 0.17 eV below the conduction band edge of silicon, allows direct (phononless) recombination between trapped electrons and free holes. The exact nature and origin of the A-type trapping centres have remained a subject of inquiry, but are more often attributed to silicon vacanc

37、ies.http:/ Raman scattering is an inelastic light scattering process, whereby the energy of an incident photon is modified by an inelastic interaction with a molecule.http:/ Raman spectrumhttp:/ Raman laser級聯(lián)拉曼光纖激光器是利用光纖的非線性效應,產生紅外激光的一種新型激光器。在光纖通信中，可作為拉曼光纖放大器和遠程摻鉺光纖放大器的泵浦光源。在其他領域也有廣泛應用。原理上只要泵浦功率足夠強，

38、就可以在紅外范圍實現(xiàn)高功率、高質量激光光束輸出，應用前景廣泛。http:/ Another nonlinear optical effect that is particularly strong in semiconductor. The effect results in pump depletion and generation of the free carriers. TPA-induced free-carrier absorption depends on the free carriers concentration through the relation a=1.45*10

39、-17(l/1.55)2N N=Ip2eff/(2hv) hv is pump photon energy, eff is effective recombination lifetime for free carriers; Ip: pump intensityTwo photon absorption (TPA)http:/ approacheslOne method for diminishing these losses is to reduce the free carrier lifetime through lateral scaling of waveguide modal a

40、rea. lAnother approach for reducing free carrier losses is to use pulsed pumping.l Using a reverse biased p-i-n diode embedded in a silicon waveguide to remove the carriershttp:/ main challenge in Raman laser is TPA that competes with Gainhttp:/ Bulk Si: Several tens ns. SOI: blow several ns. lThe l

41、ifetime is determined by the combination of diffusion and interface/surface recombination currents between top Si and buried oxide layer in a bare SOI waveguide, the geometry of the waveguide plays a significant role in determining the carrier lifetimes.http:/ Raman silicon laser based on a ring-res

42、onator-cavity configuration. (2007-Intel) A cascaded silicon Raman laser (2008- Intel)Si Raman laser developmenthttp:/ silicon laser pulses with lifelGain: Raman amplificationlLoss: free carrier absorption due to TPAlSolution 1: pulsed operationlPulse width carrier pulse periodO. Boyraz and B. Jalal

43、i, “Demonstration of a silicon Raman laser,” Opt. Express 12, 5269 (2004).Pulsed Si Raman laserhttp:/ 25ps Pulsed pumping. To the extent that the pulse width is much less than the carrier lifetime and the pulse period is much larger than the lifetime.http:/ Threshold: 9 W pump pulse powerhttp:/ Puls

44、e operation is necessary in order to avoid accumulation of free carriers that are generated due to TPA. The results show that free carrier induced limitations can be solved by using pulsed pumping. http:/ TPA-induced FCA in silicon can be significantly reduced by introducing a reverse biased p-i-n d

45、iode embedded in a silicon waveguide. The laser cavity is formed by coating the facets of the silicon waveguide with multilayer dielectric films.rib width: 1.5 m; height (H):1.55 m; etched depth (h):0.7 m. The waveguide was formed in an S-shaped curve with a total length of 4.8 cm and a bend radius

46、of 400 mRong et al, Nature 433, 725 (2005).http:/ a reverse bias voltage is applied to the p-i-n diode, the TPA-generated electronhole pairs can be swept out of the silicon waveguide by the electric field between the p- and n-doped regions. Thus the effective carrier lifetime, representing the lifet

47、ime of the free carriers interaction with the optical mode in the waveguide region, reduces with increased bias voltage. At a reverse-bias voltage of 25 V, the effective carrier lifetime is reduced to 1ns.http:/ the parameterslThe performance of this silicon Raman laser could be further improved by

48、optimizing cavity mirror and cavity length design. lThe threshold power could be reduced by using a waveguide with smaller cross-sectional dimensions and/or by introducing a larger cavity enhancement for the pump beam.lThe fibre to waveguide coupling efficiency could be improved by adding a mode con

49、verter in the waveguide. lIn addition, with optimization of the p-i-n diode design, it may be possible to further reduce the effective carrier lifetime to below 1 ns. http:/ silicon laser based on a ring-resonator-cavity configuration A racetrack-shaped ring laser cavity. A bus waveguide is connecte

50、d to the ring cavity through a directional coupler, which couples both pump and signal laser light into and out of the cavity. The coupling ratio depends on the wavelength and polarization and can be varied by changing the gap or length of the coupler or both to achieve the desired coupling ratios f

51、or pump and lasing wavelengths. The gap (d) between the two waveguides in the coupler was 0.7 mm, Rong et al, Nature Photonics 1, 235 (2007).http:/ reducing the linear loss to 0.2 dB cm-1 and the carrier lifetime to 0.4 ns.http:/ The realization of low-threshold and zero-power-consumption silicon Ra

52、man lasers represents a major leap towards producing practical silicon-based lasers. Threshold can be reduced to 16 mW.http:/ cascaded silicon Raman laser (2008- Intel)Rong et al, Nature Photonics 2, 170 (2008).http:/ The pump power reaches a threshold of 80 mW, first-order lasing takes place and th

53、e laser output power continues to increase with increasing pump power. When the coupled pump power is increased to 120 mW, the intracavity power of the first-order laser becomes high enough to generate sufficient optical gain at the second-order Stokes wavelength, and second-order Raman lasing begin

54、s.http:/ applications Methane, one of the major greenhouse gases, and water vapour, which needs to be controlled tightly in high-yield semiconductor manufacturing processes. These molecules have characteristic absorption patterns in the regions covered by the cascaded silicon Raman laser.http:/ summ

55、ary, cascaded Raman lasing in silicon has been demonstrated. Using a pump beam of 1,550 nm. A stable, single-mode, first- and second-order continuous-wave lasing at 1,686 nm and 1,848 nm, respectively was observed. lThey have been able to resolve the rotationalvibrational IR absorption spectra of me

56、thane and water vapour molecules in two separate spectral regions over 160 nm apart.l The realization of the second-order silicon Raman laser paves the way towards higher-order cascaded Raman lasing, and opens a new path to producing low-cost, compact, room temperature, high-performance mid-IR laser

57、s http:/ Hybrid laserA novel laser that utilizes a silicon waveguide bonded to AlGaInAs quantum wells is demonstrated. r using low temperature oxygen plasma-assisted wafer bonding. The optically pumped1538 nm laser has a pulsed threshold of 30 mW and an output power of 1.4 mW.John E. Bowers, et al.

58、Opt. Exp. 13, 9460 (2005)http:/ laser The fabrication is done in four major parts. First, the silicon waveguides are formed on the SOI wafer. Next, the III-V epitaxial layer structure is transferred to the SOI wafer through oxide plasma assisted wafer bonding. The III-V layers are then processed to

59、control the flow of current to the optical mode. Finally the devices are diced and polished to create high quality mirror facets and define the cavity length. Browers et al. 4th International Conference on Group IV Photonics, Tokyo Japan, Sep. 2007http:/ Reported the first observation of optical gai

60、n and laser in epitaxial Ge-on-Si at room temperature by using tensile strain and n-type doping for band engineering. Absorption spectra of the n+ Ge mesa sample under 0 and 100 mW optical pumping. Negative absorption coefficients corresponding to optical gain are observed in the wavelength range of