Introductory Lecture on Photonic Networks

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Hugh Austin
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1 Introductory Lecture on Photonic Networks

Motivation and Objectives The idea behind the all-optical networking is to maximize the transmission distance and deliver transparent and flexible connections.

2 Motivation and Objectives The idea behind the all-optical networking is to maximize the transmission distance and deliver transparent and flexible connections. Keeping it all optical will result in cost reduction both in capital as well as in operations. It will lead to an ultimate realization of the Optical Internet. Limiting Optical-Electrical-Optical (OEO) conversions to mainly the ingress and egress points of the network, and thus reducing the amount of equipment that needs to be installed to add capacity to the network, should achieve the economic gains. A number of Ultra-Long- Haul (ULH) system vendors have promoted such a benefit but none to date have fulfilled the promise.

3 Some History Optical Communication is not new! Alexander Graham Bell s Photophone, 1880

4 The Network Life Cycle. Telegraph Network Messaging VF Telex Manual Telephone Network Magneto Audio Amplifiers Switchboard Sleeve Control Switched Analog Telephone Network Electrical Exchange Coax Systems VF Signaling Digital Network ISDN PCM Intelligent Network #7 Signaling SONET/SDH Broadband Network DWDM. IP ATM *Source: From Bell to Broadband, Professor Keith Ward of University College London

5 Transmission Media Transmission Medium, or channel, is the actual physical path that data follows from the transmitter to the receiver. Copper cable is the oldest, cheapest, and the most common form of transmission medium to date. Optical Fiber is being used increasingly for high-speed applications. Fiber Replaces Copper

6 Fiber Optics

7 . Fiber Optic Transmission Bands. Frequency Wavelength C=νλ /n Near Infrared (vacuum) UV THz µm Longhaul Telecom Regional Telecom Local Area Networks 1550 nm 1310 nm 850 nm HeNe Lasers 633 nm CD Players 780 nm

8 Why Optical? Growing demand for faster and more efficient communication systems Internet traffic is tripling each year It enables the provision of Ultra-high bandwidth to meet the growing demand Increased transmission length Improved performance etc.

9 Demand for Bandwidth Bandwidth Demand 20,000 x Typical data bandwidth requirement Raw text = Mb Word document = Mb Word document with picture = 0.12 Mb Radio-quality sound = 0.43 Mb Low-grade desktop video = 2.6 Mb CD-quality sound = 17 Mb Good compressed (MPEG1) video = 38 Mb

10 Light Provides more Bandwidth Bandwidth is the range of frequencies employed to transmit (communicate) a signal (information) More bandwidth = more information. Typical Signals: Audible Sound-waves (20 to 20,000 cycles/s) AM radio uses 10kHz FM radio uses 100kHz TV uses 6MHz range Signals: sound = a variation in air pressure loudness = the amplitude of the variation pitch = the frequency of the variation wavelength = speed of propagation pitch Λ s : 1100ft/sec = 2.5 ft. 440Hz

11 Bandwidth Evolutionary Landmarks Bandwidth TDM (Gb/s) Enablers EDFA + Raman Amplifier Dense WDM/Filter High Speed Optoelectronics Advanced Fiber EDFA All-Optical Network (Terabits Petabits) 40Gb/s 40 Gb/s EDFA + Raman Amplifier Mb/s Mb/s (1310 nm, 1550 nm) 1.2 Gb/s 810 Mb/s 1.8 Gb/s Gb/s 2.4 Gb/s TDM After Shoa-Kai Liu Director - Network Technology Development; WorldCom DWDM

12 Point-to-Point Optical Link a building block for backbone and all-optical networks. E Tx/Rx DLaser Thresh APDF A Mod DLaser Thresh APDF A Mod E Tx/Rx

13 The Need for Photonic Networks Node A Circuit Path Node C Media Node B Regenerator or amplifier Node J Optics is used only for point to point links All other functionality is in the electronics frequent switching enables high utilisation of transmission link

14 The Need for Photonic Networks Increasing transmission capacity by Wavelength Division Multiplexing (WDM) Transmitter Transmitter Transmitter Transmitter Receiver Receiver Receiver Receiver WDM + amps saves regenerators + fibre Transmitter Transmitter Transmitter Transmitter Receiver Receiver Receiver Receiver

15 The Need for Photonic Networks Growth of transmission capacity with time 128λ 64λ 1 Tb/s 32λ 16λ Capacity (log scale) 2.5Gb/s 10Gb/s 4λ 8λ TDM WDM now WDM soon 565Mb/s 140Mb/s 34Mb/s 8Mb/s 2Mb/s Year

16 The Need for Photonic Networks Capacity of existing or announced WDM products Capacity per fibre (Gb/s) x2.5 32x2.5 40x2.5 16x10 80x2.5 32x10 40x10 OADM and optical protection features also available 64x10 40Gb/s systems around the corner? Compiled from information in vendor web sites

17 Bandwidth and Capacity First Generation 35nm; 80ch Wideband 80nm; 200ch Enables Terabit Systems! Ultra-Wideband

18 Optical Technology - Advantages High data rate, low transmission loss and low bit error rates High immunity from electromagnetic interference Bi-directional signal transmission High temperature capability, and high reliability Avoidance of ground loop Electrical isolation Signal security Small size, light weight, and stronger 62 mm 21mm 648 optical fibres 363 kg/km 448 copper pairs 5500 kg/km

19 Importance of Optical Networks The services provided by Optical Technology are: Next Generation Internet Internet 2 IPTV Video Conferencing Online Gaming And many more

20 Applications Electronics and Computers Broad Optoelectronic Medical Application Instrumentation Optical Communication Systems High Speed Long Haul Networks (Challenges are transmission type) Metropolitan Area Network (MAN)? Access Network (AN)? Challenges are: -Protocol - Multi-service capability -Cost Optics is here to stay for a long time.

21 Evolution of Photonic Networks Further increase in transmission capacity of TDM lines to 40 Gb/s (ETDM) and above (OTDM) Further increase in number of wavelengths above 100 Intelligent electrical at border of transparent optical core Wavelength switching devices introduced in network core IP routers with optical interfaces deployed IP routers combined with OADMs and OXCs equipped with optical interfaces enabling optical bypass

22 Evolution of Photonic Networks New kinds of network elements optimized for packet switching/routing. UNI between electronic routers and optical network elements and NNI between optical network elements with control and signalling capability Integrated protocols and algorithms for traffic engineering, path establishment, protection and restoration in the optical layer coordinated with IP layer will be developed

Evolution of Photonic Networks Increasing resolution Subwavelength level Wavelength channel level Fibre level Digital crossconnect Fibre patch panels

23 Evolution of Photonic Networks Increasing resolution Subwavelength level Wavelength channel level Fibre level Digital crossconnect Fibre patch panels Tbit router Opaque Oparent packet router Oparent Transparent photonic packet router Transparent Manual provisioning Remote provisioning Dynamic provisioning

24 Network Evolution WDM/Point-to-Point Transport High Capacity Transmission Fixed WDM/Multipoint Network Fixed Sharing Between Multiple Nodes Passive Access of Wavelength Channels Photonic XC and WADM Reconfigured WDM Network Automated Connection Provisioning Flexible Adjustment of Bandwidth Network Self-Healing/Restoration Fiber Amplifier Wavelength Mux/DMux Wavelength Add/Drop Wavelength Cross-Connect

25 WDM Adds a New Dimension. EDFA ASE EDFA gain Crosstalk 4W mixing Raman FS Brillouin BS Wavelength Power. Laser power EDFA bandwidth Central wavelength stability BW stability Fiber attenuation Component and system losses Modulation Self-phase mod. BER Cross-phase modulation Time Fiber PMD Fiber dispersion Jitter Transmission rate Laser chirp Chromatic dispersion DGD

26 .

27 Anatomy of a DWDM system

28 All Optical Network IP IP ATM ATM SDH ATM IP Other SDH SDH Open Optical Interface Challenges ahead: Network protection All Optical Networks Network routing True IP-over-optics

29 Undersea Cables

30 System Block Diagram

31 Architecture of Photonic Networks Network devices: transmitters wavelength defined, high speed? Tx-1 Tx-2 Tx-N m u x multiplexer gratings, couplers, filters fibre disp compensation? nonlinearities? optical amplifier EDFA? gain flattened? OADM optical add-drop multiplexer: couplers, filters, circulators optical cross - connect couplers, amplifiers, filters, switches OXC d e m u x demux gratings, couplers, filters receivers Rx-1 Rx-2 Rx-N

32 Key Functional Blocks Transceivers (LD, PD, Mod.) DFBs, VCSELs Optical Amplifiers (EDFAs, SOAs, Raman) DWDM (Sources, Mux/ de-mux) OA Mux E Tx/Rx Tunable Filters / OADM FBGs, FPs Switching/Routing Optical Circulators 1 2 3

33 Transceivers Crucial building blocks Transmitters (LDs, LEDs, Drivers/ Modulators) (Precision Tunable Laser arrays needed for DWDM) Modulators (External, data source) Receivers (PDs, Pre-Amp, Filters) Data in D Thresh Laser A Mod APD F signal out signal in

34 Source Source coding Modulation Analogue Digital Multiplexing Frequency Time Modulation External Internal Pulse shaping Channel coding Encryption etc.

35 Receiver 1 st -stage amplifier 2 nd -stage amplifier Pre-detection filtering Sampler & detector Demultiplexer Equalizer Demodulator Decoder Decryption Output signal

36 Light Sources Semiconductor lasers, LEDs and particularly VCSEL s remain an important area for further work.

37 Communication Window and Er Absorption Gain Nature s gift to optical communications: Erbium gain spectrum and transmission fiber minimum loss wavelengths coincide.

38 EDFA: A Key Enabler for WDM High power Low noise figure Bit-rate transparent No cross-talk Wide bandwidth Excellent mech. property and more Data In XMTR XMTR XMTR λ 1 λ 2 λ N O M U X OA OA OA WDM Point-to-Point OA O D M U X λ 1 λ 2 λ N RCVR RCVR RCVR Data Out

39 Optical Amplifiers (EDFA) Erbium doped fiber amplifiers permit the boosting of optical signals within the fiber, without the o- e-o conversion that limits bit rates! These work exactly in the range of frequencies, nm, cover whole third window! This technology permits long haul transmission and, more importantly, enables: Wavelength Division Multiplexing (WDM) Today EDFAs Exist in S-band, C-band and L-band

40 Optical Isolators and Circulators. P i 0 o 45 o 45 o P T 90 o Faraday Rotator P R Combination of Isolators make up a Circulator 1 2 3

41 Fiber Bragg Gratings (FBG).. Optical circulator 1-λ OADM Optical circulator In FBG 1 Out λ Bragg = λ 3 Drop Add

42 Example

43 OADM Technologies

44 Basics of Optical Mux/De-Mux Prism based λ 1 λ 2 λ 1 + λ 2 +..λ n.. λ n Grating based

45 . Sub-Multiplexing and Multiplexing

46 DWDM. Components. MEMS Switch Technology

Optical Space Switch λ 1 Optical Layer X- connect Optoelectronic Output Fibers Optical Space Switch λ 2

47 Optical Cross Connects (OXCs) Transponders nm Optical Switching Fabric Transponders Transparent Optical Switching Fabric without λ Conversion Optical Space Switch λ 1 Optical Layer X- connect Optoelectronic Output Fibers Optical Space Switch λ 2 Output Fibers Input Fibers Input Fibers Optical Space Switch λ n Add traffic Drop traffic Opaque / Translucent Optical Switch Transparent Optical Switch Architecture

48 Fiber Related Problems Chromatic dispersion PMD Non-linear effects Dispersion and non-linear effects P λ

49 Chromatic Dispersion It causes pulse distortion, pulse "smearing" effects Higher bit-rates and shorter pulses are less robust to Chromatic Dispersion Limits "how fast and how far data can travel 10 Gbps 60 Km SMF-28 t 40 Gbps 4 Km SMF-28 t

50 Polarization Mode Dispersion (PMD) Ey n x Ex Input pulse n y Spreaded output pulse The optical pulse tends to broaden as it travels down the fibre; this is a much weaker phenomenon than chromatic dispersion and it is of some relevance at bit rates of 10Gb/s or more

51 Challenges Ahead Modulation and detection and associated high speed electronics Multiplexer and demultiplexer Fibre impairments:. Loss. Chromatic dispersion. Polarization mode dispersion. Optical non-linearity. etc. Optical amplifier. Low noise. High power. Wide bandwidth. Longer wavelength band S

52 Challenges Ahead Dedicated active and passive components Optical switches management All optical regenerators Network protection Instrumentation to monitor QoS

53 Optical Transport Network Global Network < km < 10 Tbit/s Wide Area Network < 100 km < 1 Tbit/s Metropolitan/Regional Area Optical Network Client/Access Networks Cable modem Networks SDH/ SONET ISP ATM FTTB Gigabit Ethernet < 20 km 100M - 10 Gbit/s ATM Cable FTTH PSTN/IP Mobile Corporate/ Enterprise Clients

54 Types of MPLS Nodes There are three types of MPLS nodes as shown in diagram and perform the following functions. Transit LSR User Ingress LSR Transit LSR Transit LSR Egress LSR User Transit LSR Ingress LSR receives native-mode traffic (e.g. IP datagram) and classifies into FEC. It then generates Generates MPLS header and assign it initial label. IP datagram encapsulated into MPLS packet with MPLS header attached to datagram. Integrated with QOS operations (if applicable). Transit, Interior, or core LSR receivers the packet and use MPLS header to make forwarding decision. It processes label header only and performs label swapping. Egress LSR receives performs decapsulation operations (it removes the MPLS header).

55 Resources & NIIT Optsim Access to vast online digital data IEEE (Comm Magazine, Comm letters, Photonic Technlogy Letters (PTL), Journal of Lightwave Technology (JLT), Journal of Selected Areas in Communications (JSAC), etc ACM Focussed Networking Research group with strong international Collaborations (Stanford (PNRL), UNCC (Center for optoelectronics and optical communications), North Carolina Research Triangle, TTU, US Participation in International GLIF project HONET Workshop/Symposia

56 Concluding Remarks We have given a selective overview of Optical Networks architecture from physical layers perspective Optical components technologies will undergo a major revolution for next generation all-optical internet!! Demand for low-cost high-quality active and passive components and modules,e.g. DWDM Interleavers, ROADMs, Optical Circulators, Mux/de-mux, Dispersioncompensating elements, OAs and Dynamic gain-flattening filters, and so on...is felt GMPLS supports the evolving OTN that will accommodate all type of traffic with a high level of reliability and transparency

Introduction To Optical Networks Optical Networks: A Practical Perspective

Introduction To Optical Networks Optical Networks: A Practical Perspective Galen Sasaki Galen Sasaki University of Hawaii 1 Galen Sasaki University of Hawaii 2 Galen Sasaki University of Hawaii 3 Telecommunications