NEW YORK CITY COLLEGE of TECHNOLOGY

Transcription

1 NEW YORK CITY COLLEGE of TECHNOLOGY THE CITY UNIVERSITY OF NEW YORK DEPARTMENT OF ELECTRICAL AND TELECOMMUNICATIONS ENGINEERING TECHNOLOGY Course : TCET 4102 Fiber-optic communications Module 9: Components for optical networks Prepared by: Professor Djafar K. Mynbaev Spring 2008 D. Mynbaev TCET 4102,Module 9,Spring

2 Module 9: Components for optical networks Optical networks review Components for optical networks Wavelength-division multiplexing (WDM) Long-distance, metro- and access networks Components Switches Optical cross connects (OXCs) Optical add-drop multiplexers (OADMs) Splitters and couplers Repeaters and optical amplifiers Textbook: Djafar K. Mynbaev and Lowell L. Scheiner, Fiber-Optic Communications Technology, Prentice Hall, 2001, ISBN Notes: The figure numbers in these modules are the same as in the textbook. New figures are not numbered. Always see examples in the textbook. Key words Wavelength-division multiplexing (WDM) Long-distance networks Metro-are networks Access networks Switches Optical cross connects (OXCs) Optical add-drop multiplexers (OADMs) Splitters and couplers Repeaters (regenerators Optical amplifiers Erbium-doped fiber amplifier (EDFA) Raman amplifier Semiconductor optical amplifier D. Mynbaev TCET 4102,Module 9,Spring

3 Optical networks - introduction Optical networks: point-to-point link and network. Physical and intelligent levels. Optical fiber Information Electronic domain Tx Optical domain Rx Information Electronic domain Figure 4.1 Block diagram of a fiber-optic communications system Note: As usual, black and white figures are borrowed from the textbook and color figures are added to these modules. Figure numbers placed in such a box are valid for this module only. D. Mynbaev TCET 4102,Module 9,Spring

4 Optical networks - introduction Node 2 Node 4 Node 1 Node 3 1 Can I send you the first packet of my message? Node N Node 5 Internet Figure 4.2 Network. Yours computer Yes, you can send up to 65 kbit. I received the first packet; now you can send the second up to 65 kbit. 2 3 Your friend s computer Figure 4.3 Communications between two computers through the Internet. D. Mynbaev TCET 4102,Module 9,Spring

5 Optical networks - introduction First, the network must provide physical connections among all communicating parties; secondly, communication is possible if and only if the communicating parties follow the certain rules (protocols). But connections are something physical, tangible while protocols are something logical, intelligent. Therefore, telecommunications network are built on two aspects (sides): physical and logical (intelligent). Clearly, physical side is given by the network s physical facilities such as transmitters, receivers, switches, links, etc. What devices support logical (intelligent) work? The general answer is, computers. Specifically, we refer to electronic machines that are able to perform arithmetic and logic operations, such as processors. What if the nodes of a telecommunications network would not be able to perform switching? There would be no network, just a set of point-to-point links. Therefore, switching (routing) ability is the main feature of a logical (intelligent) aspect of a telecommunications network. A word about terminology: Switching is a general term that refers to operation of relaying messages through a network. However, in telecommunications we use term switching to describe transferring signals from one circuit to another; in other words, switching refers to circuit-to-circuit connections within a network. Routing is also a general term that refers to switching among networks; however, in regards to the Internet communications, routing means forwarding packets through network. D. Mynbaev TCET 4102,Module 9,Spring

6 Optical networks - introduction PSTN public switched telephone network Switches Switches Circuit switching implies establishing temporary physical connections throughout the entire network between two terminals. Example: Public Switched Telephone Network (PSTN). D. Mynbaev TCET 4102,Module 9,Spring

7 Optical networks - introduction Packet switching implies breaking a message into a set of small packets and sending these packets through a network by different routes. At Overview the destination, of optical these packets networks-- are assembled back into the original message. No special connections are established for a specific transmission through the network. Packet switching: block diagram Example: the Internet. Packet switching Switch Internet D. Mynbaev TCET 4102,Module 9,Spring

8 Optical networks IP over WDM As optical communications has migrated from point-to-point links to optical networks, switching and routing problems ideal solution: optical packet switching. Optical (fiber/lambda) circuit switching Internet Data packets O/E conversion Electronic packet switching Data packets Optical packet switching D. Mynbaev TCET 4102,Module 9,Spring

9 Optical networks - introduction Control plane and data plane: Separation of control and transport functions Control messages Optical network node Control plane (router) Interface Control messages Traffic Data plane (OXC) Traffic Figure 5-1 Control plane and data plane of an optical network node. Control plane and data (forwarding) plane: Several cornerstone steps have been made in this direction. First, the well-known concept of separation transport and control of transportation was introduced into optical domain. This introduction was made in from of separation of control and data planes at every network node. These planes are shown in Figure 5-1. D. Mynbaev TCET 4102,Module 9,Spring

10 Optical networks - introduction Control plane is a set of software and/or hardware residing in a network node that executes control and management functions. Implementation of control plane depends on protocols. An example of hardware is a router. Examples of control plane protocols include signaling system seven (SS7) protocol stack in voice transmission, open shortest path first (OSPF) routing protocol in data transmission and generalized multiprotocol label switching (GMPLS) protocol. Data (information, or forwarding) plane is a set of hardware and software that provides transportation of voice, data, and video traffic. An example of hardware is an optical cross-connect (OXC) and an example of protocols is IP suite. Control and data plane interaction: Control plane at a node generates routing and label tables and exchange this information with peers. This information is used by data (forwarding in IP routers) plane for transportation [2]. In other words, control plane protocols (OSPF and others) enable IP to forward traffic correctly [3]. Separation of control and data planes makes data plane protocol-independent. Today, control plane interact with data (forwarding) plane through open interface, which constitute the third (current) generation of the network element architecture. Control planes residing in nodes of any given subnetwork make up a control domain of this subnetwork. Control planes enable traffic transportation within and between their subnetworks. The main functions of an optical control plane are targeted solving the problem of find, route, and connect, which requires the follows: Naming and addressing scheme (find) A routing process to handle the network resources usage and route calculation (route), including routing and wavelength assignment (RWA) and topology and resources discovery A signaling network that provides communication between entities requesting services and those provision these services A signaling protocol for the setup, maintenance, and tear down of optical trails, including lightpath signaling and maintenance In addition, control plane has to support network survivability based on fault monitoring and protection and restoration. D. Mynbaev TCET 4102,Module 9,Spring

11 Optical networks - introduction Figure 5-2 Control domains and transport domains of optical networks. Figure 5-2 shows how control planes of different subnetworks interact through a network-network interface (NNI). This figure also shows how data traffic flows through different optical subnetworks. The main concept of this architecture is separation of control and transport domains. D. Mynbaev TCET 4102,Module 9,Spring

12 Optical networks - introduction IP router = labelswitched router (LSR) Two separate control planes: One in OTN and the other in the LSRs. Advantage: It is easily to deploy since transport and clients are independent. Disadvantage: data and control traffic are combined limited number of LSRs can participate in the network [4]. UNI OXC Control traffic Data traffic Lightpath OXC IP router = labelswitched router (LSR) Optical transport network (OTN) UNI UNI user-network interface; OXC optical cross-connect (switch) Figure 5-3 Transmission IP traffic over the optical transport network. D. Mynbaev TCET 4102,Module 9,Spring

13 Optical networks - introduction Control plane and data plane (continued) D. Mynbaev TCET 4102,Module 9,Spring

14 Optical networks - introduction In conclusion, we need to stress where optical networks were yesterday and where they are today: Initially optical fibers were used as pipes to transport large volume of traffic while all processing (intelligent) work was relegated to electronics. Thus, multiplexing, switching and routing were done in electronic domain. Optical transport was simply the sets of point-to-point links. Today optical networks have reached the point where the need arise for execution of all transport tasks in optical domain. Now we are in the transition stage. This is the trend to watch in the development of optical networks. D. Mynbaev TCET 4102,Module 9,Spring

15 Optical networks - introduction References: 1. Djafar K. Mynbaev, Next-generation optical networks from network layer and physical layer perspectives, Tutorial presented at the 11th International Conference on Telecommunications, Fortaleza, Brazil, August Manasi Deval et al, Distributed Control Plane Architecture for Network Elements, Intel Technology Journal, November 14, 2003, pp Uyless Black, Optical Networks, Prentice Hall, Yinghua Ye and Sudhir Dixit, Surviavibility in IP-over-WDM Networks, in IP over WDM edited by Sudhir Dixit, Hoboken, N.J.: Wiley Interscience, Rajiv Ramaswami and Kumar N. Sivarajan, Optical Networks A Practical Perspective, 2 nd ed., San Francisco: Morgan Kaufmann, Vivek Alwayn, Optical Network Design and Implementation, San Jose, CA: Cisco Press, Arun K. Somani, Survivability and Traffic Grooming in WDM optical Networks, New York: Cambridge University Press, John R. Vacca, Optical Networking Best Practices Handbook, Hoboken, N.J.: Wiley Interscience, D. Mynbaev TCET 4102,Module 9,Spring

16 Optical networks components general From point-to-point link to WDM networks Basic point-to-point fiber-optic link Info Electrical Tx Optical fiber Optical Rx Info Electrical Tx-Transmitter Rx-Receiver REG- Regenerator Link with regenerator Tx O/E/OREG Rx Block diagrams of a fiber-optic link D. Mynbaev TCET 4102,Module 9,Spring

17 Optical networks components general From point-to-point link to WDM networks In the middle of the 1990s, network operators started to experience a lack of fiber capacity ( fiber exhaust ). WDM has become the solution to this problem MUX DE- MUX MUX-WDM Multiplexer DEMUX-WDM Demultiplxer Basic wavelength-division multiplexing (WDM) link D. Mynbaev TCET 4102,Module 9,Spring

18 Optical networks components - general Network classification component requirements CPE access CPE access metro access metro Long-distance, metro and access networks: Traffic aggregation metro access access access Long-distance CPE access CPE-Customer premises equipment D. Mynbaev TCET 4102,Module 9,Spring

19 Optical networks components - general By the end of the 1990s, new long-haul (backbone) optical networks had been massively deployed and the use of WDM technology had dramatically increased the capacity of these networks. These developments have placed major demands on metro networks. In response, major research and development efforts in the optical communications industry have been concentrated in this area As a result, metro networks today are able to carry all required traffic. Because of a continuous increase in traffic growth, access networks have become the bottleneck in the global communications infrastructure. All these advances are reflected in the progress of components development and the equipment requirements for these networks. Long-haul metro access components D. Mynbaev TCET 4102,Module 9,Spring

20 Optical networks components - general Components for different types of networks-- Example: Transmitters Long-haul networks Dense WDM (DWDM) expensive cooled lasers. 160 channels within nm (EDFA) bandwidth requires 0.4 nm spacing minimal wavelength drift. Metro networks Coarse WDM. (CWDM) less expensive uncooled lasers. 18 wavelengths within nm bandwidth allows 20 nm spacing no strict requirements on wavelength drift. PON Very coarse WDM inexpensive uncooled lasers Three wavelengths: 1310 nm, 1490 nm and 1550m Wavelength drift is not the issue. D. Mynbaev TCET 4102,Module 9,Spring

21 Optical networks components - general Each type of network requires specific types of components Variety Quality Cost Long-haul All existing Best High Metro All existing Best possible for the price Access Restricted Not a priority Moderate Lowest D. Mynbaev TCET 4102,Module 9,Spring

22 Optical networks components - switches Couplers/Splitters are devices that couple or split optical signal among several optical fibers. Types of couplers/splitters: Regular (50:50) singlemode and multimode Tap (1:99), including low polarization tap splitters. WDM power couplers/splitters for EDFAs and EDWAs. Polarization beam combiners/splitters for EDFAs and Raman amplification, including PM couplers/splitters. Couplers/splitters for transceiver modules: Couple and split light into/from Tx and Rx (e.g., PON OLTs and ONUs). Splitters for PON networks: 1:4, 1:8, and 1:32 splitters. PLC-based programmable splitters for PON applications that allow for switching paths, connecting ingress port to multiple egress ports and providing weighted multicast (split power in a required ratio). D. Mynbaev TCET 4102,Module 9,Spring

23 Optical networks components - switches D. Mynbaev TCET 4102,Module 9,Spring

24 Optical networks components - switches Switches - introduction Two types: Optical/Electrical/Optical (O/E/O) Optical/Optical/Optical (O/O/O) Current situation: Most switches are O/E/O types. Migration to 40 Gbit/s and higher channel count will require O/O/O switches. IP over WDM requires new approaches: burst and packet switching and label switching. D. Mynbaev TCET 4102,Module 9,Spring

25 Optical networks components - switches Nonblocking switch: Every input can be connected with every output No interference among switched signals Strictly nonblocking: New connections don t affect existing connections. D. Mynbaev TCET 4102,Module 9,Spring

26 Optical networks components - switches Approach Free space Guided optics Main features Collimating optics + moving switch element Technologies Design concerns MEMS, opto-mechanical, liquid crystal, Electroholography, acousto-optical, etc. Gaussian beam coupling and diffraction effects within the switch Semiconductor or dielectric waveguide + change of refractive index of the waveguide material Thermo-optical, electrooptical, MZI, TIR, etc. Efficient coupling of light between waveguide and optical fiber outside the switch. D. Mynbaev TCET 4102,Module 9,Spring

27 Optical networks components - switches 3D MEMS optical switch concept Micromirrors fabricated on a silicon substrate semiconductor manufacturing technology. 2D and 3D mirrors. Precise analog electrical control. Large number of ports. D. Mynbaev TCET 4102,Module 9,Spring

28 Optical networks components - switches Operation of 3D MEMS optical switch: Micromirrors direct light from one fiber to another. Mirror array Mirror i Mirror k Mirror array Mirror j Port i Fibers Port k Port j D. Mynbaev TCET 4102,Module 9,Spring

29 Optical networks components - switches 2D MEMS optical switch concept and operation D. Mynbaev TCET 4102,Module 9,Spring

30 Optical networks components - switches MEMS optical switch: discussion Advantages: Easy manufacturing. Protocol independent. Wavelength independent covers entire spectrum from 1280 nm to 1625 nm. Can be made in 2D and 3D configurations. Scalability: small-, intermediate-, and large-port switches can be built. Problems: Conceptual: Digital operation vs. analog implementation. Specific: Precise analog electronic control is needed. Aging regular tuning is required. Relatively big insertion loss (from 3 db). Relatively slow switching time (several ms). D. Mynbaev TCET 4102,Module 9,Spring

31 Optical networks components - OXC Optical cross connect (OXC) λ 1 Fiber 1 Fiber 1 λ 2 λ Fiber 2 Fiber 2 2 λ 1 Fiber switch (FXC). (Automated fiber patch panel.) λ 1 Fiber 1 Fiber 1 Fiber 2 Fiber 2 λ 2 λ 2 λ 1 Fiber 1 Fiber 1 Fiber 2 Fiber 2 λ 2 λ 4 λ 1 λ 3 Wavelength-selective cross-connect (WSXC). OXC with wavelength conversion. (Wavelength interchanging XC, WIXC.) Basic types of OXCs. (After P.Perrier/S.Thompson.) D. Mynbaev TCET 4102,Module 9,Spring

32 Optical networks components - OADM Optical add/drop multiplexer (OADM) Node B Node A Optical through traffic Node C Drop traffic Add traffic OADMs may be opaque (O/E/O) and transparent (all-optical). D. Mynbaev TCET 4102,Module 9,Spring

33 Optical networks components - OADM Reconfigurable Optical add/drop multiplexer (OADM) with filter and variable optical attenuator (VOA). D. Mynbaev TCET 4102,Module 9,Spring

34 Optical networks components - network OXCs and OADMs in network OADM OXC OXCs are used in mesh networks and for ring interconnections; OADMs are used in nodes of ring and linear spans. Source: J. Lacey D. Mynbaev TCET 4102,Module 9,Spring

35 Optical networks components repeaters and amplifiers Regenerator (repeater) generates a fresh copy of a received signal by doing O/E and E/O conversions and electronic signal processing [1]. (See (a) and (b).) Optical amplifiers just amplify the optical signal without O/E conversion. (See ( c).) D. Mynbaev TCET 4102,Module 9,Spring

36 Optical networks components repeaters and amplifiers REG 1 λ 1 λ 1 λ N DE MUX MUX λ 1 λ N REG N λ N Regenerators are sensitive to the bit rate and format of a signal. Most importantly, a regenerator can work with one wavelength only. Therefore, to use regenerators in WDM network, we need to demultiplex the input optical signal, regenerate every individual wavelength, and multiplex the output signal again. D. Mynbaev TCET 4102,Module 9,Spring

37 Optical networks components repeaters and amplifiers We need regeneration to support high bit rate. However, regeneration presents the following main problems: It is the most costly operation in optical transport network. It causes delay in transmitting traffic. Regeneration sites have the highest failure rate in the network because of heavy concentration of high-speed electronic and optical components. Regeneration solutions: Avoid regeneration by all means. Specifically: Employ dispersion management strategy (the most practical) Make use of hybrid Raman/EDFA amplification (the most practical) Put into practice the new coding techniques (FEC, DPSK, etc.) Use new pre-compensation [6] and electronic compensation[7], [8] techniques Example: One of the new ULH network will have up to 2,000 km of unregenerated links with 40 Gb/s x 80 channels (scalable to 160 channels). All these solutions translate into the need for development of new components. Examples: inexpensive E/0 converters and dispersioncompensation modules. D. Mynbaev TCET 4102,Module 9,Spring

38 Optical networks components - optical amplifiers Classification of optical amplifiers (OAs) Rare-earth-doped fiber based amplifiers Semiconductor-based amplifiers Transmission fiber-based amplifiers Erbium-doped fiber amplifier (EDFA) Erbium-doped waveguide amplifier (EDWA) Praseodymium-doped (PDFA) and thuliumdoped fiber amplifiers (TDFA) Semiconductor optical amplifier (SOA) Linear optical amplifier (LOA) Gain-clamped semiconductor optical amplifier (GC-SOA) Raman Parametric Source: Gerlas van den Hoven, Alternative amplifiers, Paper ThJ3, OFC 04.) D. Mynbaev TCET 4102,Module 9,Spring

39 Attenuation (db/km) C-band EDFA L-band EDFA Optical networks components - optical amplifiers O E S C L U SOAs and Raman Wavelength (nm) Gain bandwidth of various optical amplifiers. D. Mynbaev TCET 4102,Module 9,Spring

40 Erbium-doped fiber amplifier (EDFA) is the workhorse of WDM networks. Main advantages: Cover C band from 1530 to 1565 nm and L band from 1560 to 1610 nm. Can amplify wavelength-division multiplexed signal in any transmission format, bit rate, and wavelength. High gain (> 30 db) and low noise figures (< 6 db). Fiber-based optical amplifiers easy coupling. Insensitive to signal polarization. Drawbacks: Optical networks components - optical amplifiers Multi-component unit high cost and sophisticated control + difficult to integrate with other components. Sensitive to dropping and adding channels (transient problem) dynamic gain equalization is required. D. Mynbaev TCET 4102,Module 9,Spring

41 Optical networks components - optical amplifiers EDFA module (JDS Uniphase). D. Mynbaev TCET 4102,Module 9,Spring

42 Optical networks components - optical amplifiers EDFA: basic block diagram D. Mynbaev TCET 4102,Module 9,Spring

43 Optical networks components - optical amplifiers Raman amplification: principle of operation Pump high light power (0.5-1 W) into regular fiber and get optical signal amplified. Active medium: transmission fiber. Gain mechanism: transferring pump power to optical signal. Pumping: Amplified wavelength is about 100 nm longer than a pump wavelength.for example, pumping at 1450 nm provides gain around 1550 nm with about 30-nm bandwidth. Physics: Stimulated Raman scattering high-energy-pump photons scatter off the fiber core s lattice matrix and cause appearance of wavelength-shifted photons that coherently add to lower energy (longer wavelength) signal photons gain. D. Mynbaev TCET 4102,Module 9,Spring

44 Optical networks components - optical amplifiers Discrete Raman amplifier and pump laser for Raman amplification. D. Mynbaev TCET 4102,Module 9,Spring

45 Raman amplification: block diagram Coupler Input signal Transmission fiber WDM Output signal PBC (Polarization-beam combiner) PBC PBC λ 1 λ 2 λ 3 λ 4 Pump Pump Pump Pump laser laser laser laser Control electronics D. Mynbaev TCET 4102,Module 9,Spring

46 Raman gain coefficient, (m/w) Raman amplification pump and gain spectra 1.0 Raman pump Total gain Raman gain 0.5 λ 1 λ 2 λ 3 λ Wavelength (nm) D. Mynbaev TCET 4102,Module 9,Spring

47 Optical networks components - optical amplifiers Raman amplification: components Active medium: Transmission fiber for distributed amplification. Raman gain coefficient varies for different fibers (SMF, NZDSF, DSF, etc.) within 20%. Pump sources:laser diodes (most common), Raman fiber lasers (noisy). WDM multiplexer: Must keep up to 1 W optical power. Dielectric (bulk optics) and fused-fiber coupler. Optical monitoring: Provides control of the whole operation and eye-safety control..polarization-beam splitter: Provides mixing of two polarized beams depolarized pump source. D. Mynbaev TCET 4102,Module 9,Spring

48 Signal power Raman amplification application Optical networks components - optical amplifiers Signal EDFA EDFA Total gain Raman pump Raman gain EDFA gain Amplifier site Distance Raman small-signal gain ~ exp(g R P pump L eff/ /A eff ); Effective (differential) noise figure ranges from 3 db to 3 db. D. Mynbaev TCET 4102,Module 9,Spring

49 Optical networks components - optical amplifiers Operation of a semiconductor optical amplifier (SOA) [1]. D. Mynbaev TCET 4102,Module 9,Spring

50 Optical networks components - optical amplifiers Module of a SOA operating at 1550 nm by QPhotonics, L.L.C. D. Mynbaev TCET 4102,Module 9,Spring

51 Optical networks components See reading assignment and homework problems in the course s outline. After study this module you must be able to: Explain the operation of point-to-point and WDM links. Describe local, metro and long-distance networks and the volume of their traffic. Describe why different types of network require different types of components. Explain operation of a coupler/splitter and its main characteristics. Explain the optical switch operation and list the main types of optical switches. Describe operation of MEMS switches and their applications. Explain operation of OXC and OADM and their applications in optical networks. Explain the difference between repeater and optical amplifier and list drwabacks of a repeater. Discuss classification of optical amplifiers and their bandwidths. Explain operation of EDFA and its application. Explain operation of Raman amplifier and its application. Explain operation of SOA and its application. References: 1. Djafar K. Mynbaev, The physical layer of the optical networks: Devices and subsystems, IEEE Communications Society, online tutorial, Djafar K. Mynbaev and Lowell L. Scheiner, Fiber-Optic Communications Technology, Prentice Hall, D. Mynbaev TCET 4102,Module 9,Spring