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OUTLINE

OUTLINE. 1. Introduction 2. Main Characteristics of SOAs Gain, Gain Saturation, Gain Bandwidth, Polarization Characteristics, Noise Figure 3. Application of SOAs 4. Summary. 1. INTRODUCTION.  Types of Optical Amplifiers for Lightwave Systems.

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OUTLINE

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  1. OUTLINE 1. Introduction 2. Main Characteristics of SOAs Gain, Gain Saturation, Gain Bandwidth, Polarization Characteristics, Noise Figure 3. Application of SOAs 4. Summary

  2. 1. INTRODUCTION Types of Optical Amplifiers for Lightwave Systems • Rare Earth Doped Fiber Amplifier • Active Ions in Glass Host • Optically Powered • Dopents Include Er (1550nm) • Nd (1330nm)and Pr (1320nm) Signal  Doped fiber Pump

  3. Types of Optical Amplifiers for Lightwave Systems • Fiber Amplifiers • Raman Gain: Coupling of Signal and Pump • Beams through Molecular Vibrations in Glasses • Brillouin Gain: Coupling of Signal and Pump • Beams through Acoustic Phonons • Four-wave Mixing: Coupling of Signal and Pump • Beams through Kerr Effect Signal  Transmission fiber Pump

  4. Types of Optical Amplifiers for Lightwave Systems • Semiconductor Amplifiers • Light Coupling into Active Semiconductor • Waveguide. Optical Gain Results from • Electron-Hole RecombinationInduced by • Stimulated Emission. Current Injection Fiber Fiber

  5. 1. INTRODUCTION • EDFA Characteristics Important for • System Applications • ADVANTAGES : • Gain at 1550nm ( 30 - 50 db) • Nearly Ideal noise performance ( 4db) • Low signal distortion, Low Cross Talk • High output power ( 20 - 28 dbm) • High efficiency • No polarization dependence • Pump LD commercially available ( 980, 1480nm) • Large Optical Bandwidth ( 40 - 80 nm ) • Simple Design

  6. 1. INTRODUCTION • EDFA Characteristics Important for • System Applications • DISADVANTAGES : • No Gain at 1300nm • Non-Uniform Gain Profile • Unpumped Amplifier Attenuates • Very Short Lengths not Possible

  7. 1. INTRODUCTION SOA

  8. 1. INTRODUCTION • Types of Semiconductor Optical Amplifiers • FP-SOA (FPA) biased under Ith (0.9 ~ 0.95Ith ) • high gain • ripples of the gain spectrum • reduce BW • sensitive to temperature • TW-SOA (TWA) AR coating for cleaved facets • single pass gain • G.BW 103 higher the FPA • fair temperature stability • lower niose figure • IL-SOA biased above Ith • injection locked by input high • stabilitylightwave

  9. 1. INTRODUCTION Types of Semiconductor Optical Amplifiers Classification of SOAs by their Gain spectrum Practical SOA ---- NTWA Near Travelling- Wave Amplifier

  10. 1. INTRODUCTION Comparison between TWA and FPA Amplifier Charact. TWA FPA Amplifier Gain 20db (R=0.1%) 20 - 40 db 30db (R=0.01%) Gain Bandwidth 20 THz 8 - 43 GHz Saturation output 5 - 10 dbm -7 to - 12dbm Noise: sig.- spon.beating low high spon. - spon. beating high low Application: preAmp. (with filter)  repeater  (with filter)  booster Amp.  post Amp. 

  11. 2. Main Characteristics of SOAs 2-1 Gain (1) Absorption Photon with h is absorbed (2) Spontaneous Electron returns from excited state emmission emitting a photon with h (3) Stimula ted An externalphoton causes an electron returns emmission from excited state emitting a second photon (4) Nonradiative f.I. Recombination of one electron and hole where recombination the energy is transferred to another electron (Auger)

  12. 2. Main Characteristics of SOAs Condition for optical Gain Net Gain of stimulated emission: Rst= R21stim –Rabs= B21 ·D(E) [ fc (E) –fv (E)] with B21 , D(E) > 0follows Rst > 0, if fc (E) > fv (E) Inversion condition: 1/ fv – 1/ fc > 0 The inversion condition gives the energy levels necessary to provide optical Gain : Ec– Ev = Efc– Efv Only a photon having an energy of E with Ec– Ev < E < Efc– Efv can be amplified !

  13. 2. Main Characteristics of SOAs Condition for optical Gain Population inversion state is achieved by forward biasing a PN junction . The material composition should be chosen a particular band gap corresponding to the desired laser wavelength.

  14. 2. Main Characteristics of SOAs Fabry - Perot cavity Gain: (1 – R1) (1 – R2) GS G =  (1–  R1R2 GS)2 + 4 R1R2 GS sin2   = 2 n L /  , R1R2: facet reflectivities When R = R1 = R2 : (1 – R)2 GS Single pass Gain: G =  GS= exp [  (gm– )L] (1– RGS)2 confinement factor, gmmaterial gain coefficient loss coefficient 10 ~ 50 cm-1, L amplifier length

  15. 2. Main Characteristics of SOAs Gain Saturation Gsat = exp (gm L) = exp [ g0 / (1+ Iout/ISat )] gm material gain coefficient g0 unsaturated value of gm Iout output light intensity

  16. 2. Main Characteristics of SOAs Gain Bandwidth 2 1 –  R1R2 GS B3db =  sin-1   (4 GS  R1R2)1/2 Gmax, Gmin: Gain at the F-P maximum & F-Pminimum Gmax 1 +  R1R2 GS 2  =  Gmin  1 –  R1R2 GS

  17. 2. Main Characteristics of SOAs Polarization Characteristics Different confinement factor TE>TM Different propagation constant

  18. 2. Main Characteristics of SOAs Polarization Characteristics

  19. 2. Main Characteristics of SOAs Polarization Characteristics

  20. 2. Main Characteristics of SOAs Polarization Characteristics

  21. 2. Main Characteristics of SOAs Noise Figure Pout = G Pin + PASE , F = (S/N)in / (S/N)out out2 = G <nin> + (G – 1)nspmt  f1 + 2G(G–1)nsp  <nin> + (G –1)2 nsp2 mt f2 + G2( <nin2> – <nin>2 – <nin> ) 1. 放大器信号散粒噪声 2. 自发发射散粒噪声 3. 信号-自发发射间拍频噪声 4. 自发发射-自发发射间拍频噪声 5. 信号的过量噪声

  22. 2. Main Characteristics of SOAs Noise Figure ------ R , + filter out2 SOA 输出中单位时间光子数起伏的方差值 <nin>单位时间内入射光子平均数 mt 有效横模数 nsp 放大介质的粒子数反转参数  信号 - 自发发射拍频噪声系数  f1， f1自发发射散粒噪声和自发发射-自发发射拍频 噪声的等效噪声带宽 N  gm(1 – R1) (1 – R2) (GS –1) nsp =  ·   =  N – N0  (gm– ) (1 – GS R1R2 )2 (G–1) For TWA with R1 =R2 =0, GS = G,  = 1, and G >>1 F = 2 nsp  , when nsp = 1, F = 3 db

  23. 3. Application of SOAs

  24. 3. Application of SOAs •  Main Applications • Long distance Application: When fiber • transmission is attenuation limited, SOA may • replace O/E/O repeaters, up to 20 optical • SOA can be cascaded on an amplifier chain • and provide for instance an increased • transmission span of 1000km (=1.55m) for • simultaneous transmission of 100 optical • signal channels.

  25.  Main Applications Long distance Application Item Unit Short-haul Middle-haul System Length km 1000 3000 Repeater spacing km 85 60 Signal wavelength nm 1558.5 1558.5 Transmission bitrate Gb/s 5.3 5.3 Fiber Loss db/km 0.21 0.21 Repeat Output Level dbm +4 +4 Repeat Input Level dbm -14.5 -14.5 Repeat Gain db 18.5 13 Repeat Noise Figure db < 6 <6

  26. 3. Application of SOAs

  27.  Main Applications • Local Network Application: • The gain of 20 - 30 db can be used to • compensate coupling and distribution • losses. (  = 1.31 or 1.55m) • Switching Networks: • As nonlinear optical device capable to • provide all - optical switching ( 1×N • lossless switcher , N×N OXC & OADM) • and all-optical wavelength conversion • over a range of 40 nm.

  28.  Main Applications • OTDM System : •  Extraction of optical clock signals: • PLL utilized SOA •  DMUX : NALM based on SOA • Other Applications: •  Electronically controlled optical gate •  Pulse shape •  Optical bistable element •  Optical receiver preamplifier •  Optical booster amplifier

  29. 3. Application of SOAs

  30. 4. SUMMARY • ADVANTAGES : • Direct optical amplification with a minimum • of electronics • Commercially available laser anti-reflection • coated on both facet • Reflectivity < 10-3 • Bandwidth > 40 nm • Gain ~ 30 db • Multy function • High potential to be monolithically integrated • with Optoelectronic & Photonic Devices: LD, • PD, MUX, DMUX…...

  31. 4. SUMMARY •  SOA - Functional Elements • Linear Mode : repeater, power booster, • preamplifier, external cavity laser • Electro-optical Mode: optical switching, • switching matrices, tunable DFB-filter, • PD with internal gain, phase modulator • Nonlinear optical Mode: all- optical switch, • bistable device, wavelength converter, • optical mixer, • High power optical source with broad • emission spectrum

  32. 4. SUMMARY •  Desired improvements of future SOA • Higher saturation output power • Lower spontaneous emission • Lower polarization sensitivity • Improved AR coating • Optimized amplifier - fiber • interconnection

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