Introduction to Silicon Photonics.

Transcription

1 Introduction to Silicon Photonics 周治平 Zhiping (James) Zhou Peking University, China For PKU Summer School, June 25, 2012

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3 信息科学技术学院电子学系区域光纤通信网与新型光通信系统国家重点实验室 State Key Laboratory (SKL) on Advanced Optical Communication Systems and Networks (Peking University) Optical Transmissions Optical Networks Silicon Photonics 硅基光电子及微系统实验室 2

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5 SPM team at PKU, February,

6 Research Goals To develop the next generation of compactly integrated low cost optoelectronic systems that may be used for real time sensing/detection, high-density data communications, and high-speed control/actuation Research Funding Two 973 projects, one 863 project, six NSFC projects, one provincial project, two industrial projects, and projects from the SKL. 5

7 Outline Introduction Fundamentals for Silicon Photonics Development in Silicon Photonics Conclusions

8 Why Silicon Photonics? To meet the challenges in high-density data communications, real time sensing/detection, and high-speed control/actuation 7

9 离 ( Gb b/s km m) 距离 速率 高速光通信的发展 光通信每一次的飞跃发展都依赖于光电子器件的突破 光子集成 10 9 波分复用 高锟光放 10 6 大器 10 5 半导体 10 4 激光器 10 3 光纤 阿尔费罗夫 光电子集成是解决容量和能耗问题的关键技术

10 高速计算机网络的发展 高速并行光传输 infiniband QDR 40Gb/s 高速率 小型化 低能耗需要光电子集成 9 9

11 What is Silicon Photonics? Chip size optical solutions with strong interaction between photons and electrons 10

12 Silicon Photonics Studies the principles and technologies of merging electronics and photonics into the silicon platform. It is considered a more efficient and lower cost optical solution o for high density data communications cat o in optical fiber system and computer system. It is expected that a successful monolithic integration of silicon based nanophotonic devices and microelectronic devices will lead to a more significant "micro optoelectronics revolution" than the well-known "microelectronics revolution". 11

13 Components for Siliconizationi 1) Light Source 2) Guide Light 3) Fast Modulation External Cavity Laser Light Source Waveguides Tapers Silicon Modulator Splitters Switches, Couplers, & others 4) Detect Light 5) Low Cost Assembly 6) Intelligence Passive Alignment CMOS Photo-Detector 12

14 Difficulty in Silicon Photonics Silicon has low absorption coefficient in optical communication wavelengths, therefore, good waveguide property. But, 1. It is indirect bandgap material: light emission efficiency is very low; 2. It has highly symmetric crystal structure, therefore, the linear EO effect is zero; 3. It uses photons as information carriers: the connections and processing compatibility with ICs need a lots of work. 13

15 涉及的研究领域涉及的研究领域 衍射超快表面半导半导材料集成纳米微纳和纳米速光通等离子体器件体器件能带工传感技科学与加工及光学信体理物理工艺程术技术集成论与技术技术14 14

16 关键问题 微纳米范围之内的光电相互作用及影响 微纳光电器件的计算机模拟 微纳光电器件的耦合 微纳传感器件的集成光电 微弱信号的探测与放大 微纳薄膜技术 电子束光刻, 纳米压印技术 聚焦离子束加工, 高精度等离子体工艺 15

17 Outline Introduction Fundamentals for Silicon Photonics Development in Silicon Photonics Conclusions

18 Theoretical Bases for Silicon Photonics 1. Wave Theory: Transmission 2. Semiconductor Science: Interaction 3. Integration: High speed and low cost 17

19 Optics When and how was the photon introduced? 1. Light consists of particles called photons. (Planck's law on Blackbody) 2. A photon has zero rest mass and carries electromagnetic energy and momentum. 3. It also carries an intrinsic angular momentum (or spin) that governs its polarization properties. 4. The photon travels at the speed of light in vacuum (C 0 0); its speed is retarded in matter. 5. Photons also have a wavelike character that determines their localization properties in space and the rules by which they interfere and diffract. 18

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21 Wave and Photon Wave Photon Frequency Energy Wavelength Phase Polarization Interference Position Momentum Polarization Interference Diffraction Uncertainty 20

22 Wave Nature of Light 1 Light Waves in a Homogeneous Medium 2 Refractive Index 3 Group Velocity and Group Index 4 Multiple Interference and Optical Resonators 5 Diffraction Principles 21

23 1. Light Waves in a Homogeneous Medium A. Plane Electromagnetic et c Wave 1. EM wave traveling in z direction: Phase Propagation Constant or Wave Number Monochromatic plane wave Wavefront E x and B y (same ωand k) Optical field => E x Exponential Expression 22

24 2. Refractive Index The EM wave and the induced molecular dipoles become coupled; The polarization mechanism delays the propagation of the EM wave. For an EM wave traveling in a nonmagnetic dielectric medium of relative premittivity, i i ε r, the phase velocity is Vacuum Medium Note: In noncrystaline materials, n is isotropic; In crystals, n is anisotropic ε r is frequency dependent 23

25 3. Group Velocity and Group Index No perfect monochromatic waves in practice. +? E max E max k Wave packet Two slightly different wavelength waves travelling in the same direction result in a wave packet that has an amplitude variation which travels at the group velocity. 24

26 3. Group Velocity and Group Index Group Velocity: The speed the energy and information is propagated In vacuum, v=c and is independent of frequency, therefore, 25

27 3. Group Velocity and Group Index Group Index: When in medium, we have By differentiating the equation, we have Or Where Group Index of the medium Dispersive medium causing Dispersion 26

28 3. Group Velocity and Group Index N g n Wavelength (nm) Refractive index n and the group index N g of pure SiO 2 (silica) glass as a function of wavelength. Around 1300nm, Ng is minimum, which means that for wavelengths close to 1300nm, Ng is wavelength independent. Thus, the waves travel with the same group velocity and do not experience dispersion. 27

29 4. Multiple Interference and Optical Resonators Electrical Resonator (LC) and Optical Resonator (FP) --store energy and filter frequency-- M 1 M 2 m = 1 A B m = 2 Relative intensity 1 f R ~ 0.8 R ~ 0.4 L m = 8 m -1 m m +1 (a) (b) (c) m Schematic illustration of the Fabry-Perot optical cavity and its properties. (a) Reflected waves interfere. (b) Only standing EM waves, modes, of certain wavelengths are allowed in the cavity. (c) Intensity vs. frequency for various modes. R is mirror reflectance and lower R means higher h loss from the cavity. 28

30 4. Multiple Interference and Optical Resonators Applications of the Optical Resonator Partially reflecting plates Transmitted light Filter Input light Output light Laser L Fabry-Perot etalon m - 1 m Tuning Transmitted light through a Fabry-Perot optical cavity. Transmitted Mode Intensities 29

31 4. Multiple Interference and Optical Resonators Applications of the Optical Resonator Transmission Reflection eff m 2 R Single Round Phase shift φ Filter Laser Sensor Tuning 30

32 5. Diffraction Principles B. Diffraction grating y Incident light wave a y One possible diffracted beam Single slit diffraction envelope m = 2 Second-order m = 1 First-order m = 0 Zero-order d dsin z m = -1 m = -2 First-order Second-order Diffraction grating Intensity (a) (b) (a) A diffraction grating with N slits in an opaque scree. (b) The diffracted light pattern. There are distinct beams in certain directions (schematic) Grating Equation 31

33 5. Diffraction Principles B. Diffraction grating Blazed Grating Normal to Can be used as a high efficient optical coupler First order Normal to face grating plane d Blazed d( (echelette) hltt) grating. 32

34 Binary Blazed Grating (BBG) Coupler Grating length: 14μm Coupling efficiency: 70% 3dB bandwidth: ~70nm 33

35 Semiconductor Science 1. Brief Introduction 2. Energy Bands and Charge Carriers 3. Electron and Hole Concentrations 4. Interactions of Photons with Electrons Band-to-Band Absorption and Emission Rates of Absorption and Emission Refractive Index 5. Optical modulation in Silicon 34

36 Brief Introduction: Semiconductors Electronics is the technology of controlling the flow of electrons whereas photonics is the technology of controlling the flow of photons. Electronics and photonics have been joined together in semiconductor optoelectronic devices where photons generate mobile electrons, and electrons generate and control the flow of photons. The compatibility of semiconductor optoelectronic devices and electronic devices has, in recent years, led to substantive advances in both technologies. Semiconductors are used as optical detectors, sources (LEDs and lasers), amplifiers, waveguides, modulators, sensors, and nonlinear optical elements l t Silicon Photonics 35

37 Brief Introduction: Semiconductors Two processes are fundamental to the operation of almost all semiconductor optoelectronic devices: The absorption of a photon creates an electron-hole pair. The resulting mobile charge carriers can alter the electrical properties of the material. This process is responsible for the operation of photodetectors. The recombination of an electron and a hole results in the emission of a photon. This process is responsible for the operation of semiconductor light sources. Spontaneous radiative electron-hole recombination: light generation in the light-emitting diode. Stimulated electron-hole recombination: source of photons in the semiconductor laser. 36

38 Semiconductors: Energy Bands The solution of the Schrödinger equation for the electron energy, in the periodic potential ti created dby the collection of atoms in a crystal lattice, results in a splitting of the atomic energy levels l and dthe formation of energy bands. 37

39 Semiconductors: Charge Carriers In the absence of thermal excitations, the valence band of Si and Ge is completely l filled and the conduction band is completely empty: the material cannot conduct electricity. As the temperature increases, some electrons will be excited into the empty conduction band. Each electron excitation will create a free electron in the conduction band and a free hole in the valence band. The two charge carriers are free to drift under the effect of the applied electric field and thereby to generate an electric current. The conductivity of a semiconductor increases sharply pywith temperature as an increasing number of mobile carriers are thermally generated. 38

40 Semiconductors: Energy-Momentum Relations The energy E of an electron in a crystal can be obtained by solving the Schrödinger equation: V(x) () = V(x+ma), m=1,2,3, The solutions, Bloch wavefunctions, are of the form: Each such a function will correspond to a particular k value and represents a state with an energy E k.the dependence of the energy E k on the wavevector k forms the E- k diagram in crystal, which is similar to the curve for electron in free space. 39

41 Semiconductors: Energy-Momentum Relations The E-k Diagram E k The Energy Band Diagram Conduction Band (CB) E g e - E c Empty k h E c CB E v E v e - h Valence v v Band (VB) h + Occupied h + k VB š /a The E-k diagram of a direct bandgap semiconductor such as GaAs. The E-k curve consists of many discrete points with each point corresponding to a possible state, wavefunction k (x), that is allowed to exist in the crystal. The points are so close that we normally draw the E-k relationship as a continuous curve. In the energy range E v to E c there are nopoints ( k (x) solutions). š/a k 40

42 Semiconductors: Direct- and Indirect-Gap The E-k diagrams take different shapes depending on materials, e.g.: E E E Direct Bandgap k E g CB VB E c E v Photon k k VB k vb CB Indirect Bandgap, E g E c k cb E v k k E r VB CB E c Phonon E E v k (a) GaAs (b) Si (c) Si witha recombination center (a) In GaAs the minimum of the CB is directly above the maximum of the VB. GaAs is therefore a direct bandgap semiconductor. (b) In Si, the minimum of the CB is displaced from the maximum of the VB and Si is an indirect bandgap semiconductor. (c) Recombination of an electron and a hole in Si involves a recombination center. 41

43 Semiconductors: Direct- and Indirect-Gap A transition ta sto between the etopo of the evae valence ceband dand dthe bottom of the conduction band in an indirect-gap semiconductor o requires es a substantial change in the electron s momentum. Si is an indirect-gap semiconductor, whereas GaAs is a direct-gap gpsemiconductor. Direct-gap gpsemiconductors such as GaAs are efficient photon emitters, whereas indirect-gap gpsemiconductors such as Si cannot be efficiently used as light emitters. 42

44 Interactions of Photons with Electrons - Band-to-Band Absorption and Emission - Rates of Absorption and Emission - Refractive Index 43

45 Interactions of Photons with Electrons : Examples of absorption and emission of photons in a semiconductor. (a) Band-to-Band (Inter-band) Transitions in GaAs. (b) Impurity-to-Band Transitions in Ge:Hg. (c) Free-Carrier (Intraband) Transitions. 44

46 Interactions of Photons with Electrons : Si is relatively Intrinsic GaAs transparent in is relatively the band λ = transparent in 1.1to12μm. 12 the band λ = 0.87 to 12 μm. Observed optical absorption coefficient α versus photon energy for Si and GaAs in thermal equilibrium at T = 300 K. 45

47 Interactions of Photons with Electrons : 46

48 Interactions of Photons with Electrons : Direct-gap semiconductors have a more abrupt absorption edge than indirectgap gpmaterials. Absorption coefficient versus photon energy for Ge, Si, GaAs, and selected other III-V binary semiconductors at T = 300 K. 47

49 Interactions of Photons with Electrons : Band-to-Band Absorption and Emission Direct band-to-band absorption and emission can take place only at frequencies for which the photon energy hv > E g. The minimum frequency v necessary for this to occur is v g = E g /h, so that the corresponding maximum wavelength is λ g = c 0 /v g = hc 0 /E g, or the bandgap wavelength * The bandgap wavelength λ g can be adjusted over a substantial range (from the infrared to the visible) by using III-V ternary and quaternary semiconductors of different composition. 48

50 Interactions of Photons with Electrons : Band-to-Band Absorption and Emission Conditions for Absorption and Emission Conservation of Energy: E 2 E 1 = hv. Conservation of Momentum: p 2 - p 1 = hv/c = h/λ, or k 2 k 1 = 2π/λ. Absorption/Emission in an Indirect-Gap Semiconductor: Phonons can carry relatively large momenta but typically have small energies so their transitions appear horizontal on the E-k diagram. Emission is Not easy Absorption is Easier 49

51 Interactions of Photons with Electrons : Rates of Absorption and Emission Three factors determine these probability densities (Rates): The occupancy probabilities, The transition probabilities, and The density of states. 50

52 Interactions of Photons with Electrons : Rates of Absorption and Emission Occupancy Probabilities Emission condition: A conduction-band state of energy E 2 is filled and a valence-band state of energy E 1 is empty. Thus the emission probability f e (v) of a photon of energy hv is Absorption condition: A conduction-band state of energy E 2 is empty and a valence-band state of energy E 1 is filled. Similarly, the absorption probability f a (v) is 51

53 Interactions of Photons with Electrons : Rates of Absorption and Emission Overall Emission and Absorption Transition Rates Where, τ r the radiative electron-hole recombination lifetime, Φ v the mean photon-flux spectral density at frequency v. These rate equations describe the operation of the lightemitting diode (LED), semiconductor optical amplifiers and dinjection lasers, and semiconductor photon detectors. t 52

54 Interactions of Photons with Electrons : Refractive Index The refractive index is dependent on the materials, wavelength, temperature, and doping level. And, more important, the carrier injections Refractive index for high-purity, p-type, and n-type GaAs at 300 K, as a function of photon o energy e (wavelength). e 53

55 Optical Modulation in Silicon 54

56 Absorption loss in semiconductor Photon energy (ev) Band edge absorption Wavelength dependent (m -1 ) Si Ge In 0.7 Ga 0.3 As 0.64 P 0.36 In 0.53 Ga 0.47 As GaAs InP a-si:h Free carrier absorption Carrier concentration dependent Wavelength ( m) Absorption coefficient ( ) vs. wavelength ( ) for various semiconductors (Data selectively collected and combined from various sources.) 55

57 Kramers-Kronig K Relation Differential Kramers-Kronig Dispersion Relation 56

58 Franz-Keldysh effect The effect is due to distortion of the energy bands of the semiconductor under an electric field. This shifts the bandgap energy, resulting in a change in the absorption properties of crystal, particularly at wavelengths close to the bandgap, and hence a change in the complex refractive index. Plasma dispersion effect (carrier injection or depletion) Changing the concentration of free carriers can change the refractive index of materials (Semiconductor) 57

59 Electric Optic effect in Silicon a. Pockels effect (Symmetry 0) b. Kerr effect (small) 10-4 c. Franz-keldysh effect (smaller 0 at 1.3 and 1.53 m) 58

60 d. Plasma dispersion effect (large) ~10-3 For N=5x10 o =1.3 m, e 17 n=-6.2x10-22 (5x10 17 )-6.0x10-18 (5x10 17 ) 0.8 =-1.17x10-3 Therefore, it is widely used for optical modulation in silicon 59

61 Thermo-optic effect The refractive index of silicon is varied by applying heat to the material. The thermo-optic coefficient i in silicon is: It indicates that 6 degree temperature change will vary index by 1.1X10-3. The challenges are: how to deliver and localize the thermal energy to a small area. 60

62 Integration 61

63 Integration ti 62

64 Front-end dintegration ti Approaches A. Transistor and technology selection: Fully Depleted Transistor Technology on SOI But, Si=50nm is too thin for optical waveguide; therefore, the double-stack SOI wafer is needed, which brings in additional cost and development effort. Its performance is slightly superior than the partially depleted devices. 63

65 Front-end dintegration ti Approaches A. Transistor and technology selection: Partially Depleted Transistor Technology on SOI (Si=>250nm, kink effect) Digital is OK, but analog and RF circuitry is a problem 64

66 Front-end dintegration ti Approaches B. Waveguide Near Active CMOS Devices: All CMOS processes should not leave anything to degrade the performance of the waveguide; waveguide insertion should not change the CMOS processing flow 65

67 Front-end Integration Approaches C. Edge-coupling vs Surface-coupling and Reliability: The edge-coupling: require cutting, polishing, destroying anti-crack ring, The surface-coupling: good for wafer-level testing, but need to consider the interferences from the multilayers of back-end processing 66

68 Front-end dintegration ti Approaches D. Germanium Integration: Electrically: higher mobility from Ge improving transport properties and shorten transit time of minority carriers Optically: smaller bandgap enable application in optical communication wavelengths Normal incidence Ge-on-Si PD vs waveguide PD The Ge thickness for absorbing 1.55um light is about 2 um, but the thickness of the poly gate lines are about 0.2um. Photocarriers traveling perpendicular to photons 67

69 Outline Introduction Fundamentals for Silicon Photonics Development in Silicon Photonics Conclusions

70 1. More conferences and publications 2. Better devices and processing 69

71 Group IV conference history London (2011) Antwerp (2005) Belgium Sorrento (Italy2008) Beijing (2010) Tokyo (2007) Hong Kong (2004) San Diego (2012) Ottawa (2006) San Francisco(2009) 1st International Conference on Group IV Photonics 70

72 Welcome to 2010 Workshop on Frontiers in Silicon Photonics Conference Co Chairs: Zhiping g( (James) Zhou, Peking University, China Jurgen Michel, Massachusetts Institute of Technology, USA August, 2010 Jadepalace Hotel Beijing, China wfsp.html 71

73 Silicon Photonics has been very frequently appeared in IEEE, OSA, SPIE conferences and publications 72

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75 Electronics Letters Vol. 45, No. 12, 4th June, Special Supplement: Advance in Silicon Photonics (Guest Editor Zhiping ZHou) The content t includes: 1. Two Landmark Letters from the 1980s, showing the pioneering work of Soref and Petermann and their colleagues. 2. Six Insight Letters written by leading experts across the globe presenting their personal viewpoints of silicon photonics and their predictions of the future challenges selected recently published Letters which demonstrate some of the latest advances. 4. Contemporary features including an interview with the field s pioneer, Richard Soref, and an article on the first silicon plasmonic devices demonstrated by David Miller s group at Stanford University. 74

76 Focus issue: August 2010 Volume 4 No 8 Commentaries Towards fabless silicon photonics - Michael Hochberg & Tom Baehr-Jones Mid-infrared photonics in silicon and germanium - Richard Soref Interview Integrating silicon photonics -Interview with Mario Paniccia Progress article Recent progress in lasers on silicon - Di Liang & John E. Bowers Reviews Silicon optical modulators - G. T. Reed, G. Mashanovich, h F. Y. Gardes & D. J. Thomson High-performance Ge-on-Si photodetectors - Jurgen Michel, Jifeng Liu & Lionel C. Kimerling Nonlinear silicon photonics - J. Leuthold, C. Koos & W. Freude 75

77 1. More conferences and publications 2. Better devices and processing 76

78 1. Light Emitters 2. Optical Modulators 3. Photodetectors t t 4. Integrations 77

79 Si based light source P. Ball, Nature, 409, (2001) Erbium Doping Si emitters (Ennhen, APL 43, (1983) 943) Porous Silicon emitters (Canham et al. APL 57, (1990) 1046) Si Nano-crystals emitters ( Pavesi et al. Nature 408, (2000) 440) Si Raman laser (Rong et al. Nature 433, (2005) 292) III-V laser bonding on Si (Fang et al, Opt. expr. 14, (2006) 9203) GeSi laser (Liu, et al, Opt. Lett. 35, (2010) 679) 78

80 Er Yb silicate optical amplifiers 3mm Experiment showed a 5.5dB 55dBsignal enhancement in a 7.8-mm-long 78 waveguide pumped by 1480nm laser. The signal is not saturated and can be further enhanced by increasing pumping power and decreasing waveguide loss. R. Guo, X. Wang, K. Zang, B. Wang, L. Wang, L. Gao, Z. Zhou, Appl. Phys. Lett., 99, ,

81 Optical gain and stimulated emission in periodic nanopatterned crystalline silicon The sub-bandgap b emission i at 1278 nm can be attributed t to the so-called A-centre mediated radiative recombination. Cloutier et al. Nature Materials 4, 887(2005) 80

82 A continuous wave Raman silicon laser Rong et al, Nature 433, 725 (2005). 81

83 Ge-on-Si laser operating at room temperature Reported the first observation of optical gain 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 nm. Liu et al. Opt. Lett. 35: 679 (2010) 82

84 III-V Vlaser bonding Si Fang, et al, OPTICS EXPR 14,9203 (2006) Campenhout, et al OPTICS EXPR (2007) Hong et al, PHOTON. TECHN. LETT.22,1411(2010) 83

85 1. Light Emitters 2. Optical Modulators 3. Photodetectors t t 4. Integrations 84

86 Optical Modulator 85

87 Towards silicon modulator LiNbO3 modulator silicon modulator Key differences from conventional modulators: Small footprint Silicon platfom --- Compatible with CMOS Integration to build PIC 86

88 Electro-optic ti modulation in Silicon Electric Optic effect in Silicon a. Pockels effect (Symmetry, 0) b. Kerr effect (small,10 4 ) c. Franz keldysh kld effect (smaller,0 at and μm) d. Plasma dispersion effect (large, ~10 3) For λ=1.55μm, Δn = Δn e +Δn h = [ ΔN e (ΔN h ) 0.8 ] Δα = Δα e +Δα h = ΔN e ΔN h If ΔN e = ΔN h = , then Δn = Therefore, it is widely used for optical modulation in silicon 87

89 Mechanisms of Carrier modulation a) Carrier accumulation: MOS capacitance high charge on/off speed Small overlay of optical mode and carrier concentration change area low modulation efficiency b) Carrier injection: Diffusion and recombination low speed Large overlay high modulation efficiency c) Carrier depletion Not limited by Diffusion and recombination high switch on/off speed Large overlay low modulation efficiency G. T. Reed et al. Nature Photonics. 10,1038(2010). 88

90 Comparison of different structure t modulators FP and MZI: large footprint, large power cost; broad optical bandwidth; (a) (b) Ring: small footprint, low power temperature sensitive Narrow bandwidth; (c) (d) (a) FP;(b) MZI;(c)Ring;(d)EA EA: difficult to integrate with silicon platforms 89

91 Progress: Intel s 40Gb/s Modulator Performances: Bandwidth:30 GHz Data rate:40 Gb/s ER: 11dB 1.1dB IL: 4dB Liao, L. et al. Electron. Lett. 43, (2007). 90

92 Progress: G. T. Reed s group MZ modulator Performances: Data rate: 40Gb/s ER: 6.5dB IL: 6.7dB VπLπ: 14V cm Features : Suitable for TE and TM CMOS compatible: no epitaxial growth Self aligned photolithographic steps Gardes, F.Y., et al., Optics Express, (12): p

93 Progress: Kutora s MZ modulator based on offset structure Performances: 3dB Bandwidth:12GHz (1mm) 30GHz (0.25mm) Data rate: 12.5Gb/s Vπ Lπ: 1.4 V cm IL: 2.5dB ER: >4dB Features: Lateral PN junction Using offset structure to improve modulation efficiency Ning-Ning Feng et. al. OPTICS EXPRESS, 2010,18(8),

94 Progress: 30GHz Ge EA modulator Performances: 3dB Bandwidth: 30GHz Data rate: 12.5Gb/s Vπ Lπ: 1.4 V cm IL: 2.5 5dB ER: 475dB 4 7.5dB Features: Integrated with 3μm SOI waveguide Butt coupled with a deep etched silicon waveguide Feng, N., et al.. Optics Express, (8): p

95 Oracle Labs: 25Gbps Microring Modulator Modulation Performance: Speed: 25Gbps Extinction ratio: Power consumption: 7fJ/bit Tuning efficiency: 0.19nm/mW Operating wavelength range: 12.6nm Footprint: 400μm2 Tuning Key: 1. Low drive voltage 2. Thermal tuning 3. Thicker Si slab, smaller waveguide height and small(7.5um) radius minimize RC Guoliang Li,* Xuezhe Zheng, Jin Yao, et al. OE Oct

96 1. Light Emitters 2. Optical Modulators 3. Photodetectors t t 4. Integrations 95

97 Photodetectors Conventional Ⅲ-Ⅴ group photodetectors. Intel s high performance APD in 2007 Silicon based photodetectors : small footprint, compatibility with silicon CMOS circuits, low cost, low power consumption.

98 Ge on Si Photodetector In order to sensitively detect t the near infrared light (such as 1.31μm,1.55μm),researchers are paying attention to the Ge on Si photodetectors. Advantages: excellent optoelectronic properties, Absorption coefficients for Ge, Si and (In)GaAs. high responsivity from visible to nearinfrared wavelengths, high bandwidths, compatibility with silicon CMOS circuits, low cost and low power consumption.

99 Ge on Si Photodetector (a) (b) (a) Schematic cross section view of a normal incident (free space) photodetector Hai Yun Xue, Chun Lai Xue, Bu Wen Cheng,et al 2010 IEEE Electron device letters (b) Schematic figure of a Ge photodetector integrated in a passive waveguide. Yin, T. et al. Optics Express 2007,15, The trade-off between quantum efficiency, bandwidth, and a relatively high dark current for free-space detectors can be overcome by using the Ge detector as part of a waveguide.

100 A germanium/silicon APD with 340 GHz gain bandwidth product It demonstrates a gain bandwidth product of 340 GHz, ak eff of and a sensitivity of -28 db m at 10 Gb s -1. Schematic (a) and SEM (b) cross-sections of a germanium/silicon APD. This work paves the way for the future development of low-cost, CMOS-based germanium/silicon APDs operating at data rates of 40 Gb s -1 or higher. Kang et al. Nature photonics 3:59 (2008)

101 A butt-coupled waveguide photodetector (a) Schematic view of Ge photodetector integrated with SOI waveguide. (b) Cross-section view of the Ge p-i-n region. The photodetector has an active area of only 0.8*10μm 2. The measured optical bandwidths are 32.6, and 36.8 GHz at bias of -1, and -3 V, respectively. It demonstrates a responsivity of 1.1A/W at a wavelength of 1550 nm. Dazeng Feng et al. Applied Physics Letters 95,(2009)

102 An evanescently-coupled coupled photodetector (b) (a) 3D schematic view of a vertical pin Ge waveguide photodetector integrated on top of an SOI waveguide. (b) Cross-sectional view of the device. It considers the influence of the electrodes. By increasing the thickness of the intrinsic Ge and narrows the width of the electrodes. The detector has an 3dB bandwidth of 36 GHz at the bias of -1V and a responsivity of 0.95 A/W over the wavelength range of 1520nm to 1550nm. Shirong Liao et al. Optics Express (2011)

103 Future research and development elopment consideration Photodetecors with ideal responsivity, higher bandwidth, lower dark current and lower noise will be needed. The challenge for Ge-on-Si detectors will be to achieve high performance without relying on the benefits of epitaxy.

104 1. Light Emitters 2. Optical Modulators 3. Photodetectors t t 4. Integrations

105 Integration: Bottlenecks and Approaches Still low integration level Integration level can be improved by novel structures (photonic crystals, SPP, nanowire, on-chip light source ) Ideal material platform All silicon approach (Intel, IBM) Promotion of hybrid integration Tight fabrication tolerance New patterning technology (deep UV, imprint lithography) Tunability brings more flexibility Efforts to reduce sizes and power consumption Device efficiencies 104

106 50 Gbit/s Wavelength Division i i Multiplexing l i using Silicon Microring Modulators Demonstrated 50 Gbit/s modulation using four silicon microring modulators within a footprint of 500 μm2. This is the highest total modulation capacity shown in silicon using compact micro-ring modulators. (Michal Lipson et al. Cornell University) 105

107 Luxtera Integrated CMOS Photonics Silicon 10G Modulators driven with on-chip circuitry highest quality signal low loss, low power consumption Flip-chip bonded lasers wavelength 1550nm passive alignment non-modulated = low cost/reliable Silicon Optical Filters - DWDM electrically tunable integrated w/ control circuitry enables >100Gb in single mode fiber Complete 10G Receive Path Ge photodetectors trans-impedance amplifiers output t driver circuitry it Fiber cable plugs here Ceramic Package The Toolkit is Complete 10Gb modulators and receivers Integration with CMOS electronics Cost effective, reliable light source Standard d d packaging technology 106

108 107

109 Intel transceiver---50gb/s (2010) III-V laser bonding Si Mario Paniccia, Nature Photonics 4, (2010) 108

110 Power consumption roadmap 5Gb/s, Tuning efficiency: 90 pm/mw 5Gb/s, Receiver: 690 fj/bit 5Gb/s, Transmitter: 320 fj/bit 20Gb/s, 50 fj/bit Guoliang Li et al, Proc. of SPIE, 7607 (2010)

111 Outline Introduction Fundamentals for Silicon Photonics Development in Silicon Photonics Conclusions

112 Conclusions 所谓硅基光电子学, 就是结合光的极高带宽 超快速率和高抗干扰特性以及微电子技术在大规模集成 低能耗 低成本等方面的优势低成本等方面的优势, 研究和开发以光子和电子为信息载体的硅基大规模光电集成技术 其核心内容就是研究如何将光电子器件 " 小型化 " 硅片化 并与纳米电子器件相集成, 即利用硅或与硅兼容的其他材料, 应用硅工艺平台, 在同一硅衬底上同时制作若干微纳量级, 以光子和电子为载体的信息功能器件, 形成一个完整的具有综合功能的新型大规模光电集成芯片 虽然硅材料在光电效应方面存在着 先天不足, 而光子器件在尺寸方面也 衍射受限, 但通过能级工程 量子调控 以及纳米技术, 这些传统观念已被一一突破 新的硅基光电子器件与技术不断出现, 硅基光电子学正以井喷式的速度蓬勃发展 将微电子和光电子结合起来, 开发硅基大规模光电子集成技术, 已经成为信息技术发展的必然和业界的普遍共识 111

113 Thank you for your attention 112