1. © 2005, it - instituto de telecomunicações. Todos os direitos reservados. This tutorial is licensed under the Creative Commons http://creativecommons.org/licenses/by-nc-sa/3.0/ António Teixeira, Paulo André, Rogério Nogueira, Tiago Silveira, Ana Ferreira, Mário Lima, Ferreira da Rocha, G. Tosi Beleffi, J. Prat, J. A. Lazaro, C. Bock, João Andrade 2B- Optical Technologies E-Photon One Curriculum Coordinator: António Teixeira, Co-Coordinator: K. Heggarty

2. 2 E1- 2b Optical technologies Jan 2006 Program 1. Basic Photonic Measurements 2. Material growth and processing 3. Semiconductor materials 4. Transmission systems performance assessment tools 5. Optical Amplifiers a)Semiconductor Optical Amplifiers (SOAs) b)Erbium Doped Fiber Amplifiers (EDFAs) c)Fiber Amplifiers- Raman d)Other Amplifiers 6. Emitters a)Semiconductor b)Fiber 7. Receivers a)PIN b)APD 8.Modulators a)Mach Zehnder b)Electro-absorption c)Acoust-optic 9.Filters a)Fiber Bragg gratings b)Fabry Perot c)Mach-Zehnder 10.Isolators 11.Couplers 12.Switches a)Mechanical b)Wavelength converters c)Multiplexers/ Demultiplexers

3. © 2005, it - instituto de telecomunicações. Todos os direitos reservados. This tutorial is licensed under the Creative Commons http://creativecommons.org/licenses/by-nc-sa/3.0/ 2B- Optical Amplifiers António Teixeira, Tiago Silveira, José da Rocha, Sérgio Junior, Paulo André, Giorgio Tosi Beleffi Coordinator: António Teixeira, Co-Coordinator: K. Heggarty

4. 4 E1- 2b Optical technologies Jan 2006 5. Optical AmplifiersOptical Amplifiers 1.Optical AmplifiersOptical Amplifiers 1.1. Previous Art (1) 1.2. Advantages in their use (1) 1.3. Main Types (2) 1.4. Basis (9) 1.5. Applications (1) 1.6. Scenarios (1) 1.7. Amplifiers- Measuring Performance (4) 1.8. Amplifiers - Transients (1) 1.9. Concepts (3) 2. Semiconductor Optical Amplifiers (SOAs)Semiconductor Optical Amplifiers (SOAs) 2.1. Introduction (2) 2.2. Historical Development (2) 2.3. SOA vs. Fiber Amplifiers (3) 2.4. Principle of operation (3) 2.5. Radiative Processes 2.5.1. Absorption (1)

5. 5 E1- 2b Optical technologies Jan 2006 5. Optical AmplifiersOptical Amplifiers 2.5.2. Stimulated Emission (1) 2.5.3. Spontaneous Emission (1) 2.6. Types of SOA (1) 2.6.1. Fabry-Perot (1) 2.6.2. Traveling Wave (1) 2.7. Basic Amplifier Characteristics 2.7.1. Gain (2) 2.7.2. Polarization Dependence (1) 2.7.3. Amplified Spontaneous Emission (4) 2.7.4. Amplifier Design (13) 2.7.5. Special SOA (6) 2.7.6. SOA vs. Fiber Amplifiers (3) 2.8. SOA Dynamics (17) 2.8.1. Intraband and Inter-band effects (4) 2.8.2. Response to an Optical Pulse (6) 2.8.3. Modeling (7) 2.9. Applications (20) References

6. 6 E1- 2b Optical technologies Jan 2006 5. Optical AmplifiersOptical Amplifiers 3. Erbium Doped Fiber Amplifiers 3.1. Basics (12) 3.2. Pumping (15) 3.3. Characteristics 3.3.1. Gain (4) 3.3.2. Working Principle (1) 3.3.3. Bandwidth (2) 3.3.4. Typical gain curve (1) 3.4. Issues (2) 3.5. Equalizing the EDFA Gain (1) 3.6 Characterization (2) 3.7. Rate Equations (8) 3.8. Transient Regime (5) 3.9. Cross- Saturation (3) 3.10. Noise (10) 3.11. Key specifications (2)

7. 7 E1- 2b Optical technologies Jan 2006 5. Optical AmplifiersOptical Amplifiers 4. Fiber Amplifiers - RamanFiber Amplifiers - Raman 4.1. Introduction (3) 4.2. Physical principle (5) 4.3. Configurations and Setups (4) 4.4. Propagation 4.4.1. Power, Field and Gain (8) 4.5. Noise and Multi Path Interference (6) 4.6. Raman fiber Lasers (1) 4.7. Amplification and Spectral Considerations (10) 4.8. New Raman and Fibers (1) 4.9. Raman Amplifiers 5. Other Amplifiers (11)Other Amplifiers References

8. 8 E1- 2b Optical technologies Jan 2006 Optical Amplifiers – Previous Art  Full optical device for optical signal amplification  An alternative to the optical-electrical-optical (OEO) regenerators used previously  OEO were formed by: photodiode, electronic regenerator and optical source

9. 9 E1- 2b Optical technologies Jan 2006 Optical Amplifiers – Advantages in their use  Optical amplifiers eliminates the double opto-electric conversion  Independent of the link bit rate, modulation format, detection type and…  All channels are simultaneously amplified -> WDM

10. 10 E1- 2b Optical technologies Jan 2006 Optical Amplifiers – Main Types  Erbium Doped Fiber Amplifier (EDFA): is the most deployed fiber amplifier as its amplification window coincides with the third transmission window (1530nm – 1570nm) of silica-based optical fiber  Semiconductor Optical Amplifiers (SOA): typically group III-V semiconductors (GaAs/AlGaAs, InP/InGaAs,…) From 850 nm to 1600 nm  Raman Amplifiers: unlike the EDFA and SOA the amplification effect is achieved by a nonlinear interaction between the signal and a pump laser within an optical fiber

11. 11 E1- 2b Optical technologies Jan 2006 Optical amplifiers Input Power = P External source Output Power = G  P Amplifier Gain = G G Noise Similar to electrical amplifiers Used by permission from VPIphotonics, a division of VPIsystems, the Photonics Curriculum version 4.0 (copyright) 2007 Jan 2006

12. 12 E1- 2b Optical technologies Jan 2006 Excited Fundamental state State Population N 1 Population N 0 Optical Amplifiers - Basics One should cause “population inversion”; normal regime, N 1 is the number of carriers on the fundamental state population inversion regime, N 1 > N 0 Used by permission from VPIphotonics, a division of VPIsystems, the Photonics Curriculum version 4.0 (copyright) 2007

13. 13 E1- 2b Optical technologies Jan 2006 N1N1 N0N0 Along the amplifier  One photon enters in the amplifier,  An atom is stimulated in order to decay to the fundamental state, emitting a photon identical to the one which gave rise to it;  This process is repeated and the signal gets amplified (gain). Optical amplifiers - Gain Used by permission from VPIphotonics, a division of VPIsystems, the Photonics Curriculum version 4.0 (copyright) 2007

14. 14 E1- 2b Optical technologies Jan 2006 The decay can occur spontaneously; Emitting photons with random phase, polarization and wavelength. Called “spontaneous emission”. N1N1 N0N0 Optical Amplifiers - Basics Used by permission from VPIphotonics, a division of VPIsystems, the Photonics Curriculum version 4.0 (copyright) 2007

15. 15 E1- 2b Optical technologies Jan 2006 Optical Amplifiers - Basics Most of the spontaneously emitted photons are Lost; Only a fraction is transmitted: only the ones that become guided modes in the amplifier. N1N1 N0N0 Used by permission from VPIphotonics, a division of VPIsystems, the Photonics Curriculum version 4.0 (copyright) 2007

16. 16 E1- 2b Optical technologies Jan 2006 The photons emitted spontaneously can be amplified; Amplified Spontaneous Emission (ASE); Noise source. N1N1 N0N0 Optical amplifiers - Basics Used by permission from VPIphotonics, a division of VPIsystems, the Photonics Curriculum version 4.0 (copyright) 2007

17. 17 E1- 2b Optical technologies Jan 2006 A signal entering the amplifier will be submitted to gain and noise (ASE). Signal + N1N1 N0N0 ASE Optical amplifiers - Basics Used by permission from VPIphotonics, a division of VPIsystems, the Photonics Curriculum version 4.0 (copyright) 2007

18. 18 E1- 2b Optical technologies Jan 2006 Optical Amplifiers - Basics

19. 19 E1- 2b Optical technologies Jan 2006 Gain Input power Output power Pre-AmpLineBooster Optical amplifiers - Basics

20. 20 E1- 2b Optical technologies Jan 2006 P signal_out P signal_in G(dB)= 10 log 10 Optical amplifiers - Basics

21. 21 E1- 2b Optical technologies Jan 2006 Optical Amplifiers - Applications Pre-amplifier. Located before the receiver. Low signal => low noise –Typically pumped from the output to avoid losses in the coupler of an already small signal. –High pumping, and no saturation Power Amplifier. Located at the transmitter. Targets the compensation of the loss of the modulation devices and the lack of power in the lasers –100mW Line Amplifiers. Should provide high gain, high output power and low noise –Should be similar to the cascade of a pre-amplifier and a power amplifier.

22. 22 E1- 2b Optical technologies Jan 2006 Optical amplifiers - Scenarios - Pre-Amplifier Booster power Amplifier Line Amplifier SOA Distributed Raman EDFA TDFA DiscreteRaman OA TxN Tx3 Tx2 Tx1 A W G OAOA A W G Raman pumpLD RxN Rx3 Rx2 Rx1 Raman pumpLD Raman pumpLD OA

23. 23 E1- 2b Optical technologies Jan 2006 Amplifiers – Measuring performance - gain Used by permission from VPIphotonics, a division of VPIsystems, the Photonics Curriculum version 4.0 (copyright) 2007

24. 24 E1- 2b Optical technologies Jan 2006 Amplifiers – Measuring performance – saturation Used by permission from VPIphotonics, a division of VPIsystems, the Photonics Curriculum version 4.0 (copyright) 2007

25. 25 E1- 2b Optical technologies Jan 2006 Amplifiers - Noise  As any other amplifier, optical amplifiers produce noise that degrades the optical signal  Measured as Optical Signal to Noise Ratio (OSNR)

26. 26 E1- 2b Optical technologies Jan 2006 Amplifiers – performance – G, NF Signal is better than in the beginning since the gain is distributed and the signal is improved at a ratio higher than the noise is added Used by permission from VPIphotonics, a division of VPIsystems, the Photonics Curriculum version 4.0 (copyright) 2007

27. 27 E1- 2b Optical technologies Jan 2006 Amplifiers - transients Ô Amplifiers are subject to changes in the “optical power load”. Ô This leads to changes in the operation conditions. Ô The effects of adding and dropping of several channels at different time result in the change of output average power of each of the channels.

28. 28 E1- 2b Optical technologies Jan 2006 Concepts - 3R Regeneration Through its optical path a data signal gets corrupted, therefore all optical 3R is required: 1. Reamplification – the power of the signal is increased, can be performed through simple optical amplification

29. 29 E1- 2b Optical technologies Jan 2006 Concepts - 3R Regeneration 3R is required: 2. Reshaping – The Inter Symbol Interference (ISI) and the noise are reduced.

30. 30 E1- 2b Optical technologies Jan 2006 Concepts - 3R Regeneration 3R is required: 3. Retiming – The Jitter of the signal is reduced.

31. © 2005, it - instituto de telecomunicações. Todos os direitos reservados. This tutorial is licensed under the Creative Commons http://creativecommons.org/licenses/by-nc-sa/3.0/ Semiconductor Optical Amplifiers

32. 32 E1- 2b Optical technologies Jan 2006 Outline Introduction Historical Development SOA vs. Fiber Amplifiers Principle of operation Radiative Processes Absorption Stimulated Emission Spontaneous Emission Types of SOA Fabry-Perot Traveling Wave

33. 33 E1- 2b Optical technologies Jan 2006 Outline Basic Amplifier Characteristics Gain Polarization Dependence Amplified Spontaneous Emission SOA Dynamics Intraband and Interband effects Response to an Optical Pulse Modeling Amplifier Design The Double Heterostructure Suppression of Resonances

34. 34 E1- 2b Optical technologies Jan 2006 Outline Amplifier Design Polarization Insensitive Structures Structures of the active region Special SOA Gain Clamped SOA Reflective SOA Multi Electrode SOA Applications Linear amplifier Modulator Detector

35. 35 E1- 2b Optical technologies Jan 2006 Outline Applications All Optical Wavelength converter 3R Regeneration Optical Logic Gates Pulse Generator and Clock Recovery Recommended Bibliography

36. 36 E1- 2b Optical technologies Jan 2006 Introduction A Semiconductor Optical Amplifier (SOA) is basically a Semiconductor Laser (SL) with very low (negligible) facet feedback. A signal injected into the SOA is amplified through stimulated emission. SOA are also known as: Laser Diode Amplifier (LDA) Semiconductor Laser Amplifier (SLA) Traveling Wave Amplifier (TWA) Fabry-Perot Amplifier (FPA)

37. 37 E1- 2b Optical technologies Jan 2006 SOA - Introduction  Based on recombination of electron-hole pairs  Very compact devices http://www.covega.com/pdfs/COVEGA%20Catalog%202007.pdf

38. 38 E1- 2b Optical technologies Jan 2006 Historical Development In first times SOA were SL driven bellow threshold. The first demonstration of a SOA dates back to 1964. In 1966 Anti-Reflection Coating (ARC) was proposed to reduce the optical feedback. The arrival of the double heterostructure in 1969 led to significant improvements in SOA. Whilst early studies concentrate in the 830nm range, in the 80’s decade, InP/InGaAsP SOA are developed for the 1300 nm and 1550 nm range.

39. 39 E1- 2b Optical technologies Jan 2006 Historical Development First transmission tests using SOA were reported in late 1980’s. The EDFA is invented in 1987 and competes with SOA for in-line amplification In 1989 true Traveling Wave (TW) amplifiers are enabled with further developments on the anti-reflection coating technology. TW SOA lead to lower polarization sensitivity. In the mid 90’s SOA were available featuring: Low Polarization dependence High Gain High Saturation Power

40. 40 E1- 2b Optical technologies Jan 2006 SOA – One example of a multi-electrode SOA E:\IMG_6546_1.jpg

41. 41 E1- 2b Optical technologies Jan 2006 SOA - One Example – Reflective SOA 1 mm x 0.4 mm x 0.2 mm

42. 42 E1- 2b Optical technologies Jan 2006 SOA – Coupling with Fiber I Anti-reflection coatings fiber

43. 43 E1- 2b Optical technologies Jan 2006 Principle of operation The operation of a semiconductor laser and, thus, of a SOA requires a p-n junction. A n-type semiconductor has a valence electron in excess. A p-type semiconductor has less a valence electron.

44. 44 E1- 2b Optical technologies Jan 2006 Principle of operation In thermal equilibrium an electrical field prevents diffusions of electrons and holes across the p-n junction. No free electrons or holes are present in the depletion region

45. 45 E1- 2b Optical technologies Jan 2006 Principle of operation By applying an external voltage, the built-in electrical field is reduced. This reduction results in diffusion of electrons and holes across the junction (depletion region). When an electron and a hole are present in the same region they recombine and can produce a photon.

46. 46 E1- 2b Optical technologies Jan 2006 Radiative Processes Absorption If a photon of suitable energy insides on the semiconductor, it may stimulate a carrier from the VB to the CB and cause absorption. Absorption is a loss process, since the photon is extinguished.

47. 47 E1- 2b Optical technologies Jan 2006 Radiative Processes Stimulated Emission An incident photon can also provoke the recombination of a carrier in the CB with a hole in the VB and a photon is originated through stimulated emission. The new photon is identical to the incident photon. If the injection current is enough for the carrier population in the CB to exceed that of the VB, the stimulated emission exceeds the absorption: the semiconductor exhibits optical gain.

48. 48 E1- 2b Optical technologies Jan 2006 Radiative Processes Spontaneous Emission A photon can also be emitted through spontaneous emission when a carrier at the CB spontaneously recombines with a VB hole The new photon has random phase and frequency, therefore spontaneously emitted photons are noise and reduce the carrier population available for optical gain.