BROADBAND & OPTICAL NETWORKING
BROADBAND & OPTICAL NETWORKING ECSE 6660
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This 273 page Class Notes was uploaded by Miss Damien Crooks on Monday October 19, 2015. The Class Notes belongs to ECSE 6660 at Rensselaer Polytechnic Institute taught by Staff in Fall. Since its upload, it has received 27 views. For similar materials see /class/224786/ecse-6660-rensselaer-polytechnic-institute in ELECTRICAL AND COMPUTER ENGINEERING at Rensselaer Polytechnic Institute.
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Date Created: 10/19/15
ECSE6660 Label Switching and MPLS httgwww gdergiedu Or h p prep rni Shivkumar Kalyanaraman Rensselaer Polytechnic Institute shivkumaecserpiedu Based m part on shdes from Prof Raj Jam osuy Ktreett KompeHa Jumpernetworks PeterAShWoodySmtth an mousst V e 0 5 V aI yamraman J lPoverATM to MPLS History of IP Switching u MPLS generalization of labels decoupling of control plane u Label distributionsetup protocols RSVP LDP Cl Introduction to Traffic Engineering Shivkumar Kalyanaraman lP BestEffort Philosophy 1 Well architected not necessarily worked out in detail 1 Realization can t predict the future 1 Architectural decisions 1 Make it reasonable 1 Make it flexible 39r k u Make it extensible stuff belo Shivkumar Kalyanaraman lP Control Plane Evolution 4 Again just good enough besteffort 4 But again flexible extensible Distance Vector routing was fine for quite a while 1 Just in time along came link state OSPF and ISIS 3 Now a burning question in OSPFlSIS is J Convergence in a few seconds is not good enough u See NANOG June 2002 for interesting videos and papers on how to fix LSrouting for fast convergence El L Goal Business IP for service providers i Make me money new services 608 D Don t lose me money uptime SLAs u OSPFBGP not originally designed to support QoS or multiple services eg VolP VPNs ATM Perfectionist s Dream C Connectionoriented 1 Does everything and does it well 1 Anticipated all future uses and factored them in Philosophical mismatch with IP D Shivkumar Kalyanaraman UU L E L Overlay Model for lPoverATM Internetworking Goal Run IP over ATM core networks Why ATM switches offered performance predictable behavior and services CBR VBR GFR ISPs created overlay networks that presented a virtual topology to the edge routers in their network Using ATM virtual circuits the virtual network could be reengineered without changing the physical network Bene ts 1 Full traffic control 1 Percircuit statistics 1 More balanced ow of traf c across inks Shivkumar Kalyanaraman voriay Moo oi Comm 1 ATM core ringed by routers l PVCs overlaid onto physical network Physical View Logical View Shivkumar Kalyanaraman lssue l Mapping lP data plane to ATM Address Resolution Woes l A variety of serverbased address resolution servers 3 ATMARP RFC 1577 LANE server BUS server MPOA server NHRP server 0 Use of separate ptpt and ptmpt VCs with servers J Multiple servers backup VCs to them needed for fault tolerance a Separate servers needed in every LOGICAL domain eg LIS J Mismatch between the notion of IP subnet and ATM network sizing l Cutthrough forwarding between nodes on same ATM network hard to achieve Shivkumar Kalyanaraman Issue 2 Mapping lP controlplane eg OSPF to ATM a Basic OSPF assumes that subnets are ptpt or offer broadcast capability a ATM is a NonBroadcast Multiple Access NBMA media J NBMA segments support multiple routers with ptpt VCs but do not support datalink broadcastmcast capability 1 Each V0 is costly gt setting up full mesh for OSPF Hello messages is prohibitively expensive 1 Two ooding adi39acencz models in OSPF a NonBroadcast Multiple Access NBMA model a PointtoMultipoint ptmpt Model 1 Different tradeoffs Shivkumar Kalyanaraman Pam a M hz A Figure 52 rum mm m puma rvc mesh mplmm 11 Neiqhbordiscoverg manually configured u2 Di39kstra SPF views NBMA as a full mesh Partial Mesh 2 mt model Frame Fleiay suhnst Figure 510 NBMA vs PtMpt Subnet Model a Key assumption in NBMA model 1 Each router on the subnet can communicate with every other same as IP subnetmodel l But this requires a full mesh of expensive PVCs at the lower layer l Many organizations have a hubandspoke PVC setup aka partial mesh u Conversion into NBMA model requires multiple IP subnets and complex con guration see g on next slide 1 OSPF s ptmpt subnet model breaks the rule that two routers on the same network must be able to talk directly Cl Can turn partial PVC mesh into a single IP subnet Shivkumar Kalyanaraman QSPF Destgna ted Reuters DRs NMA Case R4 4 J thure 1217 naming a LAN like n3 links Fignx ms mating the LAN Ike 1 nmk mm H mm Instead of sending a separate routerLSA for each router one esignated router can create a networkLSA for the subnet OSPF Designated Router DR NBMA Case One router elected as a designated router DR Each router in subnet maintains ooding adjacency with the DR le sends acks of LSAs to DR DR informs each router of other routers on LAN 7 39 2 A 2 39 l a on subnet s behalf after synchronizing with all routers Complex election protocol for DR in case of failure Figure 54 Hauling adjacammiwn m4 7 3 and 10471 are Designated Rnuirr and Backup Designated Rome n39spetlivelja V 39 DR and BDR in OSPF NBMA model 1 In NBMA model u DR and BDR only maintain VCs and Hellos with a routers on NBMA El Flooding in NBMA always goes through DR l Multicast not available to optimize LSA flooding u DR generates networkLSA Shivkumar Kalyanaraman Summary lPtoATM Overlay Model Drawbacks i lPtoATM controlplane mapping issues 3 Need a full mesh ofATM PVCs for mapping IP routing u Both NBMA and PtMpt mapping models have drawbacks Ll lPtoATM dataplane mapping issues 1 Address resolution eg LANE RFC 1577 MPOA NHRP requires a complex distributed server and multicast VC infrastructure D segmentation and Reassembz SAR of IP packets into ATM cells can have a multipliereffect on performance even if one cell in a packet is lost 3 ATM SAR has trouble scaling to 0048 and 00192 speeds a PacketoverSONET POS emerged as an alternative at the link layer D ATM AAL5 overhead 20 deemed excessive Shivkumar Kalyanaraman Reexamining Basics Routing vs Switching I l Routing Based on address lookup Max pre x match 2 Search Operation Complexity 0log3n J Switching Based on circuit numbers 2 Indexing operation d Complexity 01 Fast and Scalable for large networks and large address spaces J These distinctions apply on all datalinks ATM Ethernet SONET Sliile umar Kalyanaraman IP Routing vs IP Switching ATM Host DUE Router Switch DEIEIEI On ATM networks 1 IP routers use IP addresses gt Reassemble P clatagrams from cells ATM Host l IP Switches use ATM Virtual circuit numbers gt Switch cells gt Do not need to reassemble IP datagrams MPLS Best of Both Worlds PACKET CIRCUIT ROUTING HYBRID SWITCHING A L E MPLS ATM TDM IP Caveat one cares about combining the best of both worlds only for large ISP networks that need both features Note the hybrid also happens to be a solution that basses lPoverATM mapping woes H sfcowz ps ongs UP Switehmg Conoept w Developed by psilon C Routing software in every ATM switch in the network packets are reassembled by the routing tardecl to the next hop 4 Long term ow e transferred to separate quotC s Mapping of VC Is in the switch gt No re ssembly Hybrid VP muting confirm plane A TM switching data Mame Ipsilon s IP Switch39ng l J F low oriented traf c FTP Telnet HTTP Multimedia 1 Traf c DNS query SMTP NTP SNMP use I claimed that 80 of packets and 9 12 of bytes 3 2 J lpsilon claimed their Generic Switch Management Protocol GSMP to be 2000 lines and lpsilon Flow Management Protocol 1F MP to be only 10000 lilies of code J Runs as added software on an ATM switch Sluvkumar Kalyanaraman Issues with Ipsilon s IP switching J VCI eld is used as ID VPlVC I change at switch gt Must run on i 39 39 ATM switch gt non 1P switches not allowed between P switches gt Subnets limited to one switch J Cannot support VLANs J Scalability Number of VC 2 Number of ows gt 39 I V 39 quot 1000 setupssec J Quality of service determined implicitly by the flow class or by RSVP J ATM On Tag Switching I Proposed by CISCO Similar to VLAN tags I Tags can be explicit or implicit L2 header L2 Header I lngress routerhost puts a tag Exit router strips it off Untagged El l Packet Ke difference tags can be setup in the background using IP routing protocols e cont l 39 Alphabet Soup J CSR Cell Switched Router J SR Integrated Switch and Router J LSR Label Switching Router J TSR Tag Switching Router J Multi layer switches Swoters J Directh J Fasth J PowerIP Shivkumar Kalyanaraman MPLS Bmad C mep z R ut amt Edge Switch rm C r P mg MES WW Shivkumar Kalyanaraman MPLS Terminology U LDP Label Distribution Protocol II LSP Label Switched Path 1 FEC Forwarding Equivalence Class 1 LSR Label Switching Router Ll LER Label Edge Router Useful term not in standards 1 MPLS is multiprotocol both in terms ofthe protocols it supports ABOVE it and BELOW it in the protocol stack MPLS Header D IP packet is encapsulated in MPLS header and sent down LSP I I IP Packet C 32bit MPLS Header El IP packet is restored at end of LSP by egress router El TTL is adjusted by default M PLS Label Stack Concept 1 Labels Explicit or implicit L2 header J TTL Time to live J Exp Experimental I SI Stack indicator L2 Headerl Label Stack Entry Label Stack Entry I l 20b 3b lb 8b 39 Allows nested tunnels that are opaque e do not know or care what protocol data they carry aka m It39 oto ol MPLS Header ma 1 Label u Used to match packet to LSP u Experimental bits 1 Carries packet queuing priority COS I Stacking bit can build stacks of labels u Goal nested tunnels u Time to live u Copied from IP TTL Shivkumar Kalyanaraman Multiprotocol operation The abstract notion of a label can be mapped to multiple circuit or VCoriented technologies ATM label is called VPIVCI and travels with cell Frame Relay label is called a DLCI and travels with frame TDM label is called a timeslot its implied like a lane w a label is an LCN Proprietary labels TAG in tag switching etc Frequency or Wavelength substitution where label is a light frequencywavelength idea in GMPLS Shivkumar Kalyanaraman Label Encapsulation ATM Ethernet m VCI MPLS Encapsulation is specified overvarious media types Top labels may use existing format lower abes use a new shim label format Shivkumar Kalyanaraman M PLS Encapsulation ATM ATM LSR constrained by the cell format imposed by existing ATM standards l 5 Dctets ATM Header VPI VCI PT cu HEC DEClOI39I l LabelJ LabeJ Option 2 ECombined L I g abe Option 3 ATM VPI Tunnel Label AAL I 1 II ATM Generic Label Encap Wm Layer Header SAR PPPILAN format AALS Trailer and Packet eg IP l ATM Header ll A11Vl Payload 39 39 39 Top 1 or 2 labels are contained in the VPINCI elds ofATM header one in each or single label in combined eld negotiated by LDP Further felds in stack are encoded with shim header in PPPLA ormat must be a least one with bottom label distinguished with explicit NULL TTL is carried in top label in stack as a proxy for ATM header that lacks TTL MPLS Encapsulation Frame Relay Generic Encap PPPILAN Format Layer3 Header and Packet 1 c1 E BE E DL DLCI SIZE 10 17 23 Bits Current label value carried in DLCI eld of Frame Relay header Can use either 2 or 4 octet 0922 Address 10 17 23 bytes Generic encapsulation contains n labels for stack of depth n top label contains TTL which FR header lacks explicit NULL label value ulation PPP amp LAN Data Link MPLS Shim Headers 1 n H n 1 Layer2 Header Network Layer Header eg PPP 3023 and Packet eg IP A Dctets Label Stack Entry Format Label l Exp l s l TTL Label Label Value 20 bits 046 reserved Exp mentor 3 bits was Class ofSerVrce 5 Bottom ofStack ibrt 1 last entry rrrlabelstack TTL Trmeto we 8 bits Network layer must be inferable from value of bottom label of the stack TTL must be set to the value ofthe IP TTL eld when packet is rst labelled When last label is popped off stack MPLS TTL to be copied to IP TTL eld Pushing multiple labels may cause length offrame to exceed layer2 MTU LSR must support Max IP Datagram Size for Labellingquot parameter any unlabelled datagram greater in size than this parameter is to be fragmented MPLS on PPP links and LANs uses Shim Header Inserted B etween Layer 2 and Layer 3 Headers MPLS Forward mg Examp e D An IP packet destined to 1341121532 arrives in SF 3 San Francisco has route for 13411216 1 Next hop is the LSP to New York 13411216 New York Francisco Santa Fe MPLS Forwarding Examp e E San Francisco prepends MPLS header onto IP packet and sends packet to first transit router in the path 13411216 New York Santa Fe Shivkumar Kalyanaraman MPLS Forwarding Exampie a Because the packet arrived at Santa Fe with an MPLS header Santa Fe forwards it using the MPLS forwarding table D MPLS forwarding table derived from mpls0 switching table 13411216 New York Francisco Santa Fe Shivkumar Kalyanaraman MPLS Forwarding Example U Packet arrives from penultimate router with label 0 Egress router sees label 0 and strips MPLS header Egress router performs standard lP forwarding decision DU 13411216 New York Francisco Santa Fe Shivkumar Kalyanaraman Label SetupSignaling MPLS Using IP Routing Protocols Destination based forwarding tables as built by OSPF ISIS RIP et 1 471 P47111 39 2 P47111 E IP 47111 IP destination address unchanged in packet header MPLS Label Distribution Intf Label Intf Label In In Out Out 1 Label Switched Path LSP Intf Intf In Out 4 IP 47111 A General Vanilla LSP A Vanilla LSP is actually part of a tr from every source to that destination unidirectional Vanilla LDP builds that tree using existing IP forwarding tables to route the control messages Explicitly Routed ER LSP ERLSP follows route that source chooses In other words the control message to establish the LSP label request is source routed Explicitly Routed ER LSP Contd Intf Label Intf Label In Out Out LSP advamtag 22 Operator has routing flexibility policybased QoSbased Can use routes other than shortest path Can compute routes based on constraints in exactly the same manner as ATM based on distributed topology database traffic engineering Shivkumar Kalyanaraman ER LSP a discord Two signaling options proposed in the standards CRLDP RSVP extensions CRLDP LDP Explicit Route RSVP ext Traditional RSVP Explicit Route Scalability Extensions Not going to be resolved any time soon market will probably have to resolve it Shivkumar Kalyanaraman Traffic Engineering TE that aspect of Internet network engineering dealing with the issue of performance evaluation and 39 i 7 Two abstract sub groblems 1 Define a or ATM PVCs 2 Map the traffic aggregate 1 exp Cannot do this in OSPF or BGP4 today OSPF and BGP4 offer only a SINGLE path eg 00 or Tcarrier hierarchy EE ID L s af id Da3 fz39i i d Why not TE with OSPFBGP a Internet connectionless routing protocols designed to find only E route a The connectionless approach to TE is to tweak le change link weights in IGP OSPF lSIS or EGP EGP4 protocols u Assumptions Quasistatic traffic knowledge of demand matrix 3 Limitations 3 Performance is fundamentally limited by the single shortestpolicy path nature i All flows to a destination prefix mapped to the same path 1 Desire to map traffic to different route eg for loadbalancing reasons gt the single default route MUST be changed Ll Changing parameters eg OSPF link weights changes routes changes the traffic mapped to the routes Ll Leads to extra control traf c eg OSPF floods or BGP 4 update message convergence problems and routing instability Cl Summary Traffic mapping coupled with route availability in OSPFBGP D MPLS decoupestraffic trunking from path Traffic Engineering w MPLS Step I Engineer unidirectional paths through your network without using the IGP s shortest path calculation r IGP shortest path W New York Traf c Engineering WI MPLS Part DH 1 IP prefixes or traffic aggregates can now be bound to MPLE Label Switched Paths LSPs 192168124 Shivkumar Kalyanaraman Traffic Aggregates Forwarding Equivalence Packets are destined for different address pre xes but can be mapped to common path A subset of packets that are all treated the same way by a router The concept of FECs provides for a great deal of flexibility and scalability In conventional routin a packet is assigned to a FEC at each ho ie L3 lookup in MPLS it is onl done once at the network39 ress Signaled TE Approach eg MPLS J Features L In MPLS the choice ofa route and its setup is orthogonal to the problem of traf c mapping onto a route u Signaling maps global IDs addresses path specification to local IDs labels u FEC mechanism for de ning traf c aggregates label stacking for multiIevel opaque tunneling q Issues u Requires extensive upgrades in the network u Hard to internetwork beyond area boundaries u Very hard to go beyond AS boundaries even in same organization u Impossible for interdomain routing across multiple organizations gt interdomain TE ha 9 97 HopbyHop vs Explicit Routing HopbyHop Routing Distributes routing of control traffic Builds a set of trees either fragment by fragment like a random fill or backwards orforwards in organized manner Reroute on failure impacted by convergence time of routing protocol Existing routing protocols are destination prefix based Difficult to perform traffic engineering QoS based routing Explicit Routing Source routing of control traffic Builds a path from source to dest Requires manual provisioning or automated creation mechanisms LSPs can be ranked so some reroute very quickly andor backup paths may be preprovisioned for rapid restoration Operator has routing flexibility policy based QoS based Adapts well to traffic engineering Explicit routing shows great promise for tra 39 RSVP Resource reSerVation Protocol 1 A generic QoS signaling protocol 1 An Internet control protocol uUses IP as its network layer Ll Originally designed for hosttohost 1 Uses the IGP to determine paths a RSVP is not Li A data transport protocol a A routing protocol Cl RFC 2205 Shivkumar Kalyanaraman Ll L L LE Recall Signaling ideas Classic scheme sender initiated SETUP SETUPACK SETUPRESPONSE Admission control Tentative resource reservation and confirmation Simplex and duplex setup no multicast support l t lilmli l39 39 Kalyanaraman RSVP Internet Signaling u Creates and maintains distributed reservation state D Decoupled from routing amp also to support IP multicast model J Multicast trees setup by routing protocols not RSVP unlike ATM or telephony signaling a Key features of RSVP 1 Receiverinitiated scales for multicast 1 Softstate reservation times out unless refreshed 1 Latest paths discovered through PATH messages forward direction and used by RESV mesgs reverse direction D Again dictated by needs of decoupling from IP routing and to support IP multicast model RSVP Path Signa ing Examp e D Signaling protocol sets up path from San Francisco to New York reserving bandwidth along the way Seattle New York Egress Francisco Ingress RSVP Path Signaling Example 1 Once path is established signaling protocol assigns label numbers in reverse order from New York to San Francisco Seattle New York Egress Francisco Ingress Call Admission a Session must rst declare its QOS requirement and characterize the traffic it will send through the network a Rspec de nes the Q08 being requested 1 Tspec de nesthe traffic characteristics 1 A signaling protocol is needed to carry the Rspec and T spec to the routers where reservation is required RSVP is a leading candidate for such signaling protocol Shivkumar Kalyanaraman Call Admission Call Admission routers will admit calls based on their Rspec and Tspec and base on the current resource allocated at the routers to other calls 1 Request specify traffic Tspec guarantee Rspec 3 Reply whether or not request can be satisfie 2 Element considers unreserved resources re uired resources Summary asic RSVP Path Signaling D Reservation for simplex unidirectional flows D lngress router initiates connection a Soft state u Path and resources are maintained dynamically D Can change during the life of the RSVP session D Path message sent downstream 1 Resv message sent upstream MPLS Extensions to RSVP CI Path and Resv message objects a Explicit Route Object ERO Ll Label Request Object 1 Label Object u Record Route Object U Session Attribute Object u Tspec Object 1 For more detail on contents of objects daftietf mpls rsvp lsp tunnelO4txt Extensions to RSVP for LSP Tunnels Shivkumar Kalyanaraman Explicit Route Object L Used to specify the explicit route RSVP Path messages take for setting up LSP 1 Can specify loose or strict routes uLoose routes rely on routing table to find destination uStrict routes specify the directlyconnected next router u A route can have both loose and strict components Shivkumar Kalyanaraman ERO Strict Route Next hop must be directly connected to previous hop Ingress LSR ERO Loose Route Consult the routing table at each hop to determine the best path similar to IP routing option concept Ingress LSR ERO StrictLoose Path Strict and loose routes can be mixed Ingress LSR Label Objects 1 Label Reguest Ob39ect uAdded to PATH message at ingress LSR uRequests that each LSR provide label to upstream LSR Cl Label Ob39eot aCarried in RESV messages along return path upstream 1 Provides label to upstream LSR Shivkumar Kalyanaraman Record Route Object PATH Message 1 Added to PATH message by ingress LSR 1 Adds outgoing IP address of each hop in the path L In downstream direction a Loop detection mechanism LISends Routing problem loop detected PathErr message 1 Drops PATH message Shivkumar Kalyanaraman Session Attribute Object 1 Added to PATH message by ingress router 1 Controls LSP a Priority El Preemption L Fastreroute Cl Identifies session DASCII character string for LSP name Shivkumar Kalyanaraman Adjacency Maintenance Hello Message 1 New RSVP extension leverage RSVP for hellosl u Hello message a Hello Request CI Hello Acknowledge Li Rapid node to node failure detection Li Asynchronous updates L 3 second default update timer D12 second default dead timer Shivkumar Kalyanaraman Path Maintenance Refresh Messages 1 Maintains resenation of each LSP 1 Sent every 30 seconds by default Cl Consists of PATH and RESV messages Shivkumar Kalyanaraman RSVP Message Aggregation 1 Bundles up to 30 RSVP messages within single PDU 1 Controls El Flooding of PathTear or PathErr messages JPeriodic refresh messages PATH and RESV Cl Enhances protocol efficiency and reliability Cl Disabled by default Shivkumar Kalyanaraman Traffic Engineering Qanstrained Routing Shivkumar Kalyanaraman Signaled vs Constrained LSPs Common Features 1 Signaled by RSVP L MPLS labels automatically assigned 1 Con gured on ingress router only 1 Signaled LSPs J CSPF not used le normal IP routing is used L1 User con gured ERO handed to RSVP for signaling 1 RSVP consults routing table to make next hop decision 1 Constrained LSPs I CSPF used a Full path computed by CSPF at ingress router C1 Complete ERO handed to RSVP 39 n 39 n I Shivkumar Kalyanaraman J J D Constrained Shortest Path First Algorithm Modi ed shortest path first algorithm Finds shortest path based on IGP metric while satisfying additional QoS constraints Integrates TED Traf c Engineering Database El IGP topology information 1 Available bandwidth 1 Link color Modi ed by administrative constraints El Maximum hop count D Bandwidth 1 Strict or loose routing Cl Administrative groups Shivkumar Kalyanaraman Computing the ERO a lngress LSR passes user de ned restrictions to CSPF u Strict and loose hops D Bandwidth constraints El Admin Groups LI CSPF algorithm 1 Factors in user de ned restrictions 1 Runs computation against the TED u Determines the shortest path u CSPF hands full ERO to RSVP for signaling Shivkumar Kalyanaraman Summary Key Benifits of MPLS 4 Goal Lowoverhead virtual circuits for IP D Originally designed to make routers faster by leveraging ATM switch cores bypasses lPoverATM overlay problems a Fixed label lookup faster than longest match used by IP routing a Caveat Not true anymore D IP forwarding has broken terabits speeds through innovative datastructures next class i PPPoverSONET POS provides a link layer B Value of MPLS is now purportedly in raf c engineering a Same forwarding mechanism can support multiple new services eg VolP VPNs etc i Allows network resource optimization at the level of routing eg constrained based routing D Allow survivability and fastreroute features i Can be generalized for optical networks 6 39 EC E 60 Availability Survivability PrutectionRestoratiun Fast Re Route htlwwwvn mu atquot 7 m g uwww ecsu durHamegrshtmunar n if mute Availability Impact of Outages Market Drivers for Survivability Szrvlce Outage Impact Newark Sur u39r39e Types amp Other Motivations wrm 5 1 a w e Network Survivability Architectures Nebunrk Survivability Architectures Remmtinn Pmuu39nn mu Selthza ng RerCun unhlz hm mink N quotk SWIM N mi Pmlecllnn rung Prnle lnn n Mesh Reslnmtlnn magnum Archlle ums Archlle ures 5min MlnVr sun eriVr 5n MlnNr 5 MlnNr EMlHYr Services Determine the Requirements on Network Availability Network mummy Hm Servlce RehabMy High Ntwk a ramquot es N Maw Fremlelvcy Mk K A W m H A7 Sums 1min Service 3 ms 5 outage Durations Brow5lii aman Network Availability 8 Survivability Availability is the probability that an item will be able to perform its designed functions at the stated performance level within the stated conditions and in the stated environment when called upon to do so Reliab ty Reliability Recovery Availability PQTN The Yardstick I Individual elements have an availability of 9999 One cutoff all in 8000 calls 3 min for average call Five ineffective calls in every 10000 calls A AN on Faullly m a um LE Em Em um E L ca Exchari nun5 n l ant5 Distance to Long Luz AN Amy Network Measuring Availabil The Port Method The Port Method Example quot Fm quotUm W it 10000 active access ports Network An Access Router with 100 access ports fails for 30 minutes Total Available PortHours 39100003924 40000 Total Down PortHours 100 0 Availability for a Single Day 2400005024000039100 99979166 A The Bandwidth Method The Bandwidth Method Example Based on Amount of Bandwidth available in Network x1 n lime amount m 9W x Sample Period M um m 9E lmva m xumazeduralunl l m p Takes into accountthe Bandwidth of ports Good for Core Routers Defects Per Million Defects Per Million Example PSTN networks de ned as numbe of blocked lls per one million calls averaged over one ye Basic Ideas Working and Protect Fibers Protection Topologies Linear i UUWF with two UV Protection Topologies Ring Mesh r Topologies Rings Fibers Directionality SDNET Automatic Protection Switching APS LInE anmm Wilkhl a Pam Pmm mn Swlkhl a quotmm I t Accssllm panmu nupncm mm Sun on mm M mmzhli Prmethm Swl ih R v m Re Restasz TImEs 5 ms K1 K2 BYmSSImzl change Protection Switching Terminology 11 vs 1n ma sFsu Damion Uni irectional Path Switched Ring UPSR UPSR discussion Bidirectional Line Switched Ring LSRZ 2Fiber ELsR Anaess mgslUVSWl Bidirectional Line Switched Ring BLSRZ Bidirectional Line Switched Ring BLSRZ Iuv bmux Ildvrmnamm Bidirectional Line Switched Ring BLSR4 Bidirectional Line SNitched Ring Mm nmmm SR Discussion Mesh Resturatiun Rmum gurm elur aummgl Rawmawe Resoratmn kchnacture u named EommHa Mesh Restoration Mesh Restorat H vs 1 mm mu De nhzedcr ugnmed mmcmmm mphde mm an y t w mmquot Wynn mm mumquot mm mm Rummy mg m Fast Reroute Fast Rem te 2 Fast Rem t MPLS vs IF39 Fast Rero te vs IP Routing 1r mm mw MPL devour w B ECSE6660 Optical Networking Components Part httgwww gdergiedu Or h p prep rni Shivkumar Kalyanaraman Rensselaer Polytechnic Institute shivkumaecse rpi edu Basedin pat on textbooks of SVKa1talopoulos DWDM and H Dutton Understanding Optical communications and slides of Partha Dutta shjvkumar Kalyanaraman D LLl D Couplers Splitters lsolators Circulators Filters Gratings Multiplexors Optical Ampli ers Regenerators Light Sources Tunable Lasers Detectors Modulators Chapter 2 and 3 of RamaswamiSivaraj n L LDLL L Optical Couplers e 1 Inpmz wuplmgleng l Output Combines amp splits signals Wavelength independent or selective Fabricated using waveguides in integrated optics or coupling ratio PowerOutput1 or Powerlnput1 PowerOutput2 1 0c Powerlnput1 a Power splitter if oc12 3dB coupler 394 Tap ifoc close to 1 a kselective ifocdepends upon 7v u 39 I A Couplers contd 1 Light couples from one waveguide to a closely placed waveguide because the propagation mode overlaps the two waveguides J Identical waveguides gt complete coupling and back periodically coupled mode theory a Conservation of energy constraint 1 Possible that electric fields at two outputs have same magnitude but will be 90 deg out of phase u Lossless combining is not possible Shivkumar Kalyanaraman Couplers Contd Propagahon Constant conlroi Ampiihed Signal on Drrectrona coup er Absorbed Signal UH Coupler LUJ Phase comrm Amplified slgnz d39 aCh Zehnder coumer Absorbed srgnaL Coupler Diffraction device Drmacrrun coupler Absorbed srgnak DH39 Drifracted srgrral39 quoto 1quot 8port Splitter Made by Cascading Y Couplers Figure 109 An 9Port Splitter Mal1 by Cusmding YCnuplmis 8x8 Star Coupler 1 an muplm Power from all inputs equally split among outputs lsolators and Cireula tors Nonreciprocal gt will not work same way if inputs and outputs reversed lsolator allow transmission in one direction but block all transmission eg re ection in the other Circulator similar to isolator but with multiple ports Shivkumar Kalyanaraman Recall Polarization Polarization Time course ofthe direction of the electric eld vector Linear Elliptical Circular Nonpolar Polarization plays an important role in the interaction of light with matter Amount of light reflected at the boundary between two materials LightAbsorption Scattering Rotation Refractive index of anisotropic materials depends on polarization Brewster s law P Uar z mg F tmg Pnlarmng hlt DIFECUDH of propaganon vzed light Polar U gh mter Kt V D recuon m ohrza mn Unpolan d Mgl u h p z I belore entenng f11er Figure 223 Polarlzmg v xher Done using crystals called dichroz39cs Rotating Polarizat omg DH 7 vpmpa V DHDrImn 01 pommuhun Unnnla belore m s Figure 224 An mb y g e um and a votuxmg pomrmng We 0 mule me rm man du echan Crystals called Faraday Rotators can rotate the polarization without loss Optical Isolator Figure 231 F39u 13I172vIZJEEi Elf an DTC l iE I t 39 Tranami ed wave 1155 339 Re ected incident 3 E 7 I r We J Palarizer A x T Fahrizer E y Faraday mtatur Palarlzer A P Dar zati m p m mt U Hat r Limitation Requires a particular SOP for input light signal Shivkumar Kalyanaraman Polarizationinde endent Isolators Favaday WEEK1 pBEE SW 19 9 Famday man 1 plane SW GD Multiplexers Filters Gratings Wavelength selection technologies vkumar Kalyanaraman EC LLL L Applioa tions Wavelength band selection Static wavelength crossconnects WXCs OADMs Equalization of gain Filtering of noise ldeas used in laser operation Dispersion compensation modules L l Shivkumar Kalyanaraman E L U C Li D haracteristics of Filters Low insertion inputto output loss Loss independent of SOP geometry ofwaveguides Filter passband A independent of temperatur Flat passbands Sharp skirts on the passband amp crosstalk rejection Cost integrated optic waveguide manufacture Usually based upon interference or diffraction Shivkumar Kalyanaraman ratings LI Device using interference among optical signals from same source but with diff relative phase shifts le different path lengths D Constructive interference at wavelength 9 and grating pitch a if asin9i sin9d m 9 I m order of the grating Shivkumar Kalyanaraman Grating at U IN Uniting mum plum Narrow slits tx vs narrow re ection surfaces rx 1 Majority of devices are latter type rX 1 Note etaon is a device where multiple optical signals generated by repeated traversals of a single cavity Shivkumar Kalyanaraman Diffrmtimu Gratimgg k 39 v Figure 212 A h rachon gratmq Figure 213 A passrthrough glaung di racts each wavelength In dmerem angle Grating principlee centch a Blazing concentrating the refracted energies at a different maxima otherthan zeroth order 1 Reflecting slits are inclined at an angle to the grating plane Shivkumar Kalyanaraman raung Gratings A ll lllllllll Re ections 3 Periodic perturbation eg of RI written in the propagation medium a Bragg condition Energy is coupled from incident to scattered wave ifwavelength is 10 2 ne A where A is period ofgrating i If incident wave has wavelength 10 this wavelength is reflected by Bragg grating Bragg Grating Princ39ples SemImlrror Semilmwrror RT Semi mrrror F T Semigym I HI Outgoan hghi Re ecled reson Frequency Figure 217 Princ ples of me Bragg grating J L I ragg Gratings contol Uniform vs apodized index pro le Apodized side lobes cut off but width of main lobe increased Reflection spectrum is the Ftransform of RI distribution Bw of grating 1 nm inversely proportional to grating length few mm Note Lasers use Bragg g gratings to achieve a single frequency operation Fiber Gratings D Very lowcost low loss ease of coupling to other fibers polarization insensitivity low temp coeffand simple packaging a Writing Fiber Gratings 1 Use photosensitivity of certain types of bers eg Silica doped with Ge hit with UV light gt RI change a Use a phase masK diffractive optical element 1 Shortperiod aka Bragg 05pm or longperiod gratings upto a few mm a Shortperiod Fiber Bragg low loss 01dB 7 accuracy 005nm u Longperiod ber gratings used in EDFAs to provide gain compensation Fiber Bragg Grating uv Ime erence patlem Fmergrazmg Claddng Carcrn Figure 218 A ber Bragg grahng 15 made by exposyng lhe core wim a UV pattern and a mnnohnw one 5 made wnh muugmed mGaAsP aver lnP subsnate OADM Elements with FB Gratings Fiber Bragg Chirgeei reting Fiber i i 7 Graiing Ciadding linearly vanabie i Coren Figure 219 A fiber Bragg chir 9 re ects dispersed wavelengths oi a channei at different depths thus restoring the spectra u Used in dispersion compensation it tightens the pulse width Shivkumar Kalyanaraman Longperiod Fiber Gratings Principle of operation slightly different from fiber Bragg Energy after grating interaction is coupling into instead of being fully re ected as in Fiber Bragg Cladding modes very lossy and quickly attenuated gt Couple energy M ofa desired wavelength band Faloryuperot FF Filters a FabryPerot lter also called FP interferometer or etaon 3 Cavity formed by parallel highly reflective mirrors D Tumble w cavity length or RI within cavity 1 Eg Piezoelectric material can compress when voltae is a lied Input signal Shivkumar Kalyanaraman ipr Hnte erome e Semi mirror 2 Semimirror 1 Air or Dielectric I I Ouigofng light Figure 24 Princrples of a FabryiPeroi imerferorneter l The outgoing ks for which d k M2 add up in phase resonant ks Shivkumar Kalyanaraman Interferometer Sharpness amp Line Width Re ectivin increase l 2n Unit Figure 27 As re ectivin increases the interferometer sharpness increases Different DWDM As can coincide with the passbands FSR freespectraIrange between the Filter Parameters Inpul power level dBm 100 absoluie Peak transmxsswon a Insertion loss v 1 dB F I Output power levei dBm BODQ a r 0 peak FWHM FullWidth haltmaximum Figure Fll er parammer de nition 4 LC Spm m Width L mw d h Lam Spacing Figure 25 m IO 0mm cnannel spam 9 Sp39zhum hequency hresho d aI Kalyanaraman Figure 20 Defmdmn at 9mm 5 Anal charnsl and spacing wmh 2527 unu zny MuxlDemux Using Cascaded TFMFs 13911 is Narrow band ller Glass substrulu Each lter passes one A and reflects the other As Very flat top and sharp skirts agaadald TFMFS Qm c Inctdenl beam k Reflected beam High Index Low Index Mundayer H hundex v Lo Index quh dex Transmitted 39L A Figure 211 A dwe ecim Interference lter is made With a tematmg ayers of hm 1 CW reiractlve ma e each W mxck A Usmg such iers at One side of a nwrored plate a demumplexer is bum B MachZehnder FilterInterferometer MZI Figure 220 Principies of a MachZehnder ner Shivkum Kalyanaraman Machiehnder Central u Reciprocal device 1 Phase lag I39Mlld C 39 interference I l Used for W2 broadband ltering hum M o will Crosstalk non at mm of m e um spectrum large skirts WW 1 Tunability by 39 varying Wm temperature SvaI alyanaraman ThwmwTumab g MZ Fi m b sputter i g Figure 221 Princsmes of a thermoitunab e Mach Zehnder filter Multistae MZI Transfer Function Arrayred Waveguide rating AWGil Generalization of MZI several copies of signal phase shifted differently and combined gt 1xn nX1 elements Lower loss atter passband compared to cascaded MZI 39 Active temperature control needed Tnpuc cough grating Arrayced Wavegu de Grafting I A N Figure 222 Prlncxples 01 an arrayed waveguide grahng Shl kumar Kalyanaraman Acousto ptic Tunable Filter ACDJTF 1 Interaction between sound and light Sound is used to create a Bragg grating in a waveguide 1 Acoustic wave in opposite direction to optical signal 1 Density variations depend on acoustic RF freq lead to RI variations RF frequency can be easily tuned Polarization dependent or independent designs Acou 5m transducer Acoustic wave Output polarizcr output I 1 Input pol an39zer I Input 2 Dynamic Wavelength Crossconnects Autumn optic tunable l lcr Acousm oplic tumble ller Multiple acoustic waves can be launched simultaneously The Bragg conditions for multiple As can be sa s ed simultaneously gt Dynamic crossconnects Lots of crosstalk amp High Channel Count Multiplexers Multistage Banded multiplexers l x HHHH lizuull 9 16 HHHH l w 0 In l 21 5 3 r mun HHHHHlllllllllllllllllllll Hand Band 3 Hand Hand gtl quot Guard 55mm 4 b 17 24 Hllllll and WDM Mgnul 15 31 1 l l l l l l Band 4 Multistage Interleaving Filters in the last stage can be much wider than each channel width I35 31 HHHHH1 HH 123 12 HIHHHHHHR HHHHH WDM Igm 1quot quot 3 11 11quot111139111 l Operaung powel mnge Minimum operating level i Amphher Ampli er Figure 266 Signal atlenuatmn and amplification action Optical Amplifiers 5 Regenerators 1 4A v1 vvq LTemnman V N Vi 4 m M J 4 TBTWBHHZUJ egenerator 7 3R Reamplify Reshape and Re me 120 km 1 Termian i ia a i i at 1 DFA 7 1R Reamplify OEO Regenerator Transler hmchon mum Output Amplmer Ophcal recevver Opncal ransnmter 77 gt47 gt4 7 Pnommc regme Elemvomc regxme Phommc rcgvme Figure 265 The mode a a regenerazor and me three major unclxons opncm recewer e ectrcmc amphhen and opucm Iransmltten 1R 2R and 3R Regeneration MM Mgm Ru Mm HEN Regenerators vs OAmplifiers U Regenerators speci c to bit rate and modulation format used OAmps are insensitive le transparent a A system with optical ampli ers can be more easily upgraded to higher bit rate wo replacing the ampli ers u Optical amplifiers have large gain bandwidths gt key enabler of DWDM a Issues 1 Ampli ers introduce additional noise that accumulates u Spectral shape of gain atness output power transient behavior need to be carefully designed Shivkumar Kalyanaraman EDFA Enables DWDM EDFAs amplify all As in 1550 window simultaneously Key performance parameters include Saturation output power noise figure gain flatnesspassband Optical Ampli ier Varieties 53 P E E c a O U 93 S E U 1400 Wavelength nm Figure 166 Optical ampli ers are many each suiiabie for a dx ereni spectral range Optical Ampllfler Flat Gain Region H H ff m gls m m lmiif m f m nm quot k r 739 4397 U 150 8 WWW 67W mm m HHh H il H HHIHH HHIH I 1550 l39 BHKN UAFLKHHHYHPUH39V lt man ltsa5 man x59 mun Exxmulm L n ma 4 els1OC lllllllllllllllllllll QOCV ZWE 5 z separauon 200 GHz sepamnon mu reierence llequency 93 w Tsz Figure 417 Ophca amphher at gem reqwon m Crband Principles Stimulated Emission Transitions between discrete energy levels of atoms accompanied by or of photons E2 gt E1 can be stimulated by an optical signal Resulting photon has i 7 i coherent If stimulated emission dominates absorption then we have ampli cation of signal Need to create a population inversion N2 gt N through a pumping process Stimulated Stimulated Cllli hlilll Alasurplmn Spontaneous Emission 1 E2 gt E1 transitions can be spontaneous le independent of external radiation E The photons are emitted in random directions polarizations and phase le incoherent J Spontaneous emission rate or its inverse spontaneous emission lifetime is a characteristic of the system L Ampli cation of such incoherent radiation happens along with that of incident radiation J Aka ampli ed spontaneous emission ASE appears as noise 1 ASE could saturate the ampli er in certain cases Shivkumar Kalyanaraman Optical Amplification mechanics hwput sxgnal Oulpul sxgnm o o O O o 000 Low energy veservmr 0 ms absorb pump energy and are excued 10 a higher energy resewmr N O Ions relurnmg to owev energy euher by sllmulahon Nq ov sponlancously NED Flgure 268 For susxamed amn mc hnn me ra e of exmlahon should be Mass or anm in the vale 0v summon He rale m sponmm zous em ssKm Erbiuma oped Fiber Amplifier EDPQt u Length of ber core doped with rare earth erbium ions 3 D Fiber is pumped with a laser at 980 nm or 1480nm 1 Pump is coupled in and out using a kselective coupler a An isolator is placed at the end to avoid re ections else this will convert into a laser EDFA success factors 1 1 Availability of compact and reliable highpower semiconductor pump lasers 1 2 EDFA is an allfiber device gt polarization independent amp easy to couple light inout L 3 Simplicity of device 1 4 No crosstalk introduced while amplifying Shivkumar Kalyanaraman EDFA Qperation 11 When Er3 ions introduced in silica electrons disperse into an energy band around the lines E1 E2 E3 Stark splitting u V thin each band the ion distribution is nonuniform thermalization 1 Due to these effects a large 7 range 50 nm can be simultaneousl amlified amp luckil it is in the 1530nm range V V V V H Fluoride L glass only 9amp0 nm HM nun EDFA peration CGontoi 1 980 nm or 1480nm pumps are used to create a population inversion between E2 and E1 a 980 nm pump gt E1 gt E3 absorption amp E3 gt E2 spontaneous emission a 1480 nm pump gt E1 gt E2 absorption less efficient 1 Lifetime in E is 1us whereas in E it is 10ms 300 nrr 580 um i i Ma um 153wquot EDFA Pumping Issues 391 ppquot quot1480nm pumps compared to 980 nm pumps Higher power 1480nm pumps may be 39 4 l Degree of population inversion with 1480nm is lesstgt Fluoride fiber EDFFAs produce 39 ii 1 15 ut they must be pumped at 1480nm see pic earlier due to excited state absorption E gt E l up to 70 km Erbium DO d K of fibre l Fibre Sect t 4 Remote Amplifier Fignrz 124 Remote Pumping Towards Flat EDFA Gain Long period bergrating l0 um the peaks of the curve I54 ISM Vmclcnglh mm H LbiJm ler 3 dm mg Grain Rims1 EDFA gain Flher Transfer iunc W Inverse Finer Oquut power M Wavelength 0 Figure 414 hwerse fi ters reduce EDFAs gain ripme Shl kumar Kalyanaraman EDFA Summary Figure 271 An EDFA amplmer c 515 of an erbiumrdo silwca ber an otcapun1pa summer and isnla ors 3 both ends Signa emission Pump abscrp on 4 50 500 1 ECU yamraman Figure 272 Pumps rptwonandsana I wanna Semicon uctor Optical Amplifiers SOA Termini Am lied omcai om m Weak optical mpul D i D Tammi 7 Figure 257 Semiconducior optical amphliers 150A are devices based on cunveniianai iasai pnnmpies C onducmn Hand n Valancehand ab SOAs have seve But used in switches etc Remll and Raman Amplifiers Ill rlmnncl ci nuulmn THJ Power transferred from channels about 100nm Eg 14601480nm pump gt amplification at 1550 1600nm Gain can be provided at ANY wavelength all you need is an appropriate Pump Multiple pumps can be used and gain tailored Lumped or distributed designs possible Used today to complement EDFAs in ultr Shivkumar Kalyanaraman Ramam Amp f m mm Weak Signal In coupler Amplified Signal out 21540 nm a l 39 lsofator Pump signal lsolator lter Figure 278 Princip es of Raman amplification Shl kumar Kalyanaraman Raman Amplification contd m o E u u E g o u E 9 a O A A o l 1530 1535 1540 1545 1550 1555 1550 Wavelengm nm Figure 230 Typicai Fiaman amphhcatmn over a 35 nm range nouce me peakrtorpeak amphlude variauon Counterpumped Raman Amplification m ampmmanon a E E a u g u 40 Fiber ienmh mm Figure 233 Com ilerrpmmjad Harman ampiiiicalion LLL l Distributed Raman Amplifiers Complement EDFAs in ultralonghaul systems Challenge need highpower pumps Pump power uctuation gt crosstalk noise Counterpumping dominant design pump power uctuations are averaged out over the propagation time of ber other crosstalk sources also reduced Anmlilier silc Shlvkumar Kalyanaraman Practica Raman Pumps Li Use a conveniently available eg 1100 nm pump and use Raman effect itself in combination with a series of FPresonators created through kselective mirrors e matched Bragg gratings Eg1100nm gt1155nm gt1218nm gt1288nm a1366nm gt 1455 nm The final stage 1455nm has owre ectivitygt output pump at 1455nm which produces gain at 1550nm 39 80 of the power comes to the output tuglmnmimy mm Bragg gratings Mk i initle mum l m 5 not izsx ms H55 i155 i118 my ilh 1455 Han S v aIK L Li Recall Optical Ampli ier Varieties 53 P E E c a O U 93 S E U 1400 Wavelengm nm Figure 166 Optical ampli ers are many each suilable for a dx erenl spectral range Churuclcl Ni Raman vs OFAs Table 42 Qualitative camparison between Ramaquot and OFAs Rumun 1 111p11391c111i1111 lmml Guln BW H 521111 HW lulu 111 V1 1i w Pump 1 clcng1h Pump pmwr Sunnulinn mm or DlI L L IlUIl unxu Other Simpllcll lcpcmlx 1111 pump UI IKL39I 10750 11111 per pump l5 20 um umphl lungcr Ax murc llmn slllll lL l39 hut i ndjuslublc Rumun wullur Llnuhlc R39 by 110 11111 ltl1nl391c139 l1z1n ampli ed Hgnul 111 c r 3110 111W pmxcr of 111 mp Suppunx hiLIiruulinnul lgllLLlN Fulunliul L l Uhrl lk among 0015 nlhcr nunlinmnliux sllnplul 111x xpcclull lihcr neudud tlcpcndx 1111 dulmnl Hr Y l39lH 0 11111 clc111lcd 1111gu1 umplil39 Ion 1l11111 lmrlcr Huell more LSUlnlb39l 11111 or Erbium 3 W depends on dopum 11nd gain largely hunmgcnvmu mlurulmn cl1ur11c1crix11cx Unidirccliunul Potential crossilulk lmlc burning 111011 complu EDFA unwind L mg au AHE pt aH Amp f wtmm v39 Photomc regwme 160 as or more f9 Protecuon path d End TErmmal E DOM Equahzahon E EDFA gt Raman Termmal 0E0 OED Figure 446 AH optical mphhualmn EDFA v Hamanj and dispersxon compensauon modmas tDCM I enach the optlca swgnal m reach qua ong distances 000 mm between and lermmals Optical Regenerator Figure 418 Model of an optical regeneraior R g mera m Figure 420 ODlx39 mini Regen w Dispersion Compensation and Gain Equalization Hburspa39i i swan cnmpcnsaimn murime m moduie anable GEM C 7 s GEM G i merging f t x Mon Conlroi v lMon Raman BOOSTER PREAMPLIFIER Flgure 425 vchHumiur mm dispmSion Lompu umuh mu 5mm qnnimwou mum Light Sources LEDs Lasers VCSEL5 Tunable Lasers Shivkumar Kalyanaraman Lasers Key Target Characteristics 2 Laser an optical ampli er enclosed in a re ective cavitv that causes it to oscillate via positive feedback 1 High output power 110 mW normal 100200mW EDFA pumps few Ws for Raman pumps u Threshold Current drive current beyond which the laser emits power 1 Slope Efficiency ratio of output optical power to drive current a Narrow spectral width at speci ed X a Sidemode suppression ratio D Tunable laser operating its k stability drift over lifetime needs to small relative to WDM channel spacing a Modulated lasers low accumulated chromatic disper50n Shivkumar Kalyanaraman D Recall Energy Levels amp Light Emission LevelS Level 4 Level 3 Level 4 Level 3 Level 2 Level 3 Level 2 I quot Level 2 Level 1 Level 1 Level 1 deenergy level syslem C senergy level system Mullienergy level system Figure 251 A four three and multIenergy level system Spontaneous Emission MetaStable States Figure 63 Slmumneam Emixsmn mm mm Eminent Phamn Enmyy Tm AAAr atsomn Vgt Level mama summaan SwLa rIthon mm mm ws mvs waugod 39 w w rkPmuquot v A me I Igurr a Energv sum n v 39ml Ham Mamm v quotg f g n A mmo id mm 111747 My momum rm loving m acew W 521 w quotW a 39 a J 1 I A v mm m wwl kr wwwmn t d xram A J vel mm H MW my rmlmhu39 nmuw mmm m mm w Kim u Id39m m39 Minnemquot mmk39 K413111141 1111311 RecallStimuated Emission 1 Atom in quotgroundquot low 2 Energy is supplied from energy state outside and atom enters excited state Original Photon VVVVV MAW Emitted Photon 4 Atom emits additional photon and returns to the ground state Amving Photon r 3 Photon arrives and interact with excited atom Figure 62 Stimulated L mixsion a Fabqumm Eta m Laser vs LEDs l E FonNardbiased pnjunction low R etalon u Recombination of injected minority carriers by spontaneous emission produces light u Broad spectrum upto gain bw of medium 4 Low power 20dBm a Low internal modulation rates 1005 of Mbps max 1 LED slicing LED lter power loss a Laser 0 Higher power output 0 Sharp spectrum coherence l chromatic dispersion u lnternal or External modulation T distance T bit rates a Multilongitudinal mode MLM larger spectrum 10 ofnm with discrete lines unlike LEDs Shivkumar Kalyanaraman Simple LEDs pn junction bandgap Elsclruns 5 Conduction Band Energy LU 2V Laval Reverse Bxas Fcnlvald BIBS device msulates dewce conducts Ivigum 54 Kur39dgap Ener pv Irzgm ii l nrrmm PMquoter WW kn mintum prn Juncuon regwon psemmondumor n semiconductor Figure 55 Simple PN Ium lilm Mil oulol inleterojunction LE 3 Light produced in a Mammal more localized area in double heterojunction LEDs Hetero39unction junction between two semiconductors with different bandgap energies Charge carriers attracted to lower vatmm bandgap restricts 5quot 95 quot 39 region of ehole e 57 May b39 mm 54 Dulllie Hrmmjumriw LED i E Energy Level v ar ya man Ef fcacgt off T mp ra m cm A 81m 1 Relative mensuy m i I nm Figure 249 Effeck of temperature on wave1englh and optical mtensily of solid Mate hgm sources LED Temperaturedependent Wavelength Drift Max optv power 31 laser output Receiver threshold uncerlarnty LU Iau clled pulses m her Ungraded nurses one G larr39roeramrr Brwa ue uv cerramry m reculver LE5 Meefu Em Freenegcaeem pt a Grammum cat cm Output Optical Power P 7 Output Optical Power P 1 17 wavelength I 7 Input Electrical Current Output Optical Spectral Width W In 726a 23 5 7quot M p Shivkumar Kalyanaraman l L L C Lasers vs Optical Amplifiers As reflectivity ofthe cavity boundaries aka facets T the gain is high only for the resonant is of the cavity u All resonant is add in phase D Gain in general is a function ofthe 7v and re ectivity If re ectivity R and gain is suf ciently high the ampli er will oscillate e produce light output even in the absence ofan input signal LI This lasing threshold is where a laser is no longer a mere amplifier but an oscillator 1 Wo input signal stray spontaneous emissions are ampli ed and appear as light output Output is coherent it is the result of stimulated emission LASER Light Ampli cation by Stimul n u 39 n 0 Radiationquot Figure 65 Iming gitudinal Modes Lateral Modes Figure 68 RywnanLg Modes in he Cavity ufu Fabr Pmnl Lawl M d 5 Sp tfa Width and Limwid h gm M m Sp Kral39l lld h L n m FWHM aquot M In Wavelength Figtm S I WMIU39 und mm W Xv u u Umqu mm d Jmquotfirnmrumm I39Iulwnphmda vlwmyrwmzmum 11 ml L Fabryu gmt Lama S ur s Cleaved edges at both ends of the hghlgmde Terminal act mirm F W 3 quotL Termma Isolanon bartiers Opiical Output Figure 254 Fundamentals of a F39 Perot 3 er source Laser Output Behavior vs Applied Power Below Just Aha FullPower Threshold Threshold Figure 7 uqu Swarm Chaupm m Power is Appml ym39z39 illuxlmm r P lam An unguile FP Imm at full power prmlurex us many as mm inc Wm a gain guided deme rypimlb39 pmducex Ihree gnml 1111ain IllFGUILJFJ A Sam GmJau ase39 lnusx Gmcsd Laser ngm amth Dr v3 curvenz nnvu cmmm mm 71 Fish175211inJan39r zmrw mm mm mm Dirmt ng the Light n a Fabrympem Lamaquot a Unguided aI Kalyanaraman Longitudinal Modes SLM and mum u k within the bw of the gain medium inside the cavity u Cavity length should be integral multiple OfQMZ u Such is are called longitudinal modes Li FP laser is a multiplelongitudinal mode MLlVl laser Large spectral width 10 nm or 13 Thzl Li Desired singlelongitudinal mode SLM 1 Add a lter to suppress other is by 30dB A low nunnmclcn 4 A e A I L cub Innizm39niillz a Laser cavi1y e modes Mw im d utg u f Lagw Cw ty Laser gain curve Laser output spectrum Figure 252 Multimode output of a laser cavity Kalyanaraman Recall History of SLMMLM Usage T chcnurum Mulmnndr mm a MLM as 139 V I 3 An M V W V V x mm 0 MM P IL y Trnnmmtcr A onucm anmh cr II WDM mnlliplncr d k DM demuuimmr istrilouted Feedback DP Lasers u Idea Provide a distributed setof reflections feedback by a series of closelyspaced reflectors u Done using a periodic variation in width of cavity of Bragg condition satis ed for many ks only the 1 st the corrugation period is M2 is preferentially ampli ed 1 Corrugation inside gain region called DFB laser 3 Corrugation outside gain region called DBR distributed Bragg re ector laser Bragg Laser Achve raglan Terminal Optical waveguide From quot2 Opucar Outpm Back rage 1 r ellrphcal Output 75 or power r Terminar Bragg gra ngs Re ector amp frrter Figure 255 Fundamentals of a Bragg laser rnotlce the 5 laser Irght from rhe back face Ta ered Frbre 9m a i i Fibre Bragg Grat ng Lens Mirror mm H mm Bragg Grming mum Figure 90 Srubr limriun ome nvl mo Lam39 6 UmnF bm Lagm raging Pum 980a F39bre B39a G39a m Erb um Duper me Seaman F We Bra Gram put gt 100 Mirror 53477809 Mirror at seiscted wavelenglh at sebected wavehangm Figure 93 InAFibre Laser Using lBGs Depending on the detailed In gquot the mil mirror migh have my rtf ertiv quot at the SIM ml wavelz nglh benryen 111ml I am 3917 External Cavity Lasers a Only those is which are resonant for both primary and external cavities are transmitted 391 Diffraction grating can be used in external cavity with X selective reflection at grating and antireflection coating outside ofthe primary cavity facet 1 Used in test equipment cannot modulate at high speed Antlrc ccunn cuanng Jain Cavity waill VCSELs Vertical Cavity SurfaceEmitting Lasers J l L L Frequency longitudinal mode spacing c2nl If is made small mode spacing increases beyond cutoff of gain region bandwidth gt SLM Thin active layer deposited on a semiconductor substrate gt vertical cavity amp surface emitting For high mirror re ectivity a stack ofalternating low and highindex dielectrics le dielectric mirrors are used Issues Large ohmic resistance heat dissipation problem a Roomtemperature 13um VCSELs recently shown Lgt Shivkumar Kalyanaraman VCSELs Su ace emitted aser In a curcular narrow cone Terminal 0 piype mmtllayer DER re ecior lsolatnon 7 W ACUVC regxon quantle WCHS layers 4 Termlnal O Figure 256 ofa 7 VCSEL Structure Passivehon 902 M Prawn bombarded fewquot in mung A Insulallng Reglon Top View 7 5 Ac r Regan Conductwg EQIOH MI Prawn bumbarded not re ion xnsmatm stack 9 g lt 2O microns gt Figure 92 VCSEL Slrm rm p WavelengthSelective VCSEL Array 1 High array packing densities possible with VCSELs compared to edgeemitting lasers silicon fabrication l Used a tunable laser by turning on required laser D Harder to couple light into ber 3 Yield problems if one laser does not meet spec the whole array is wasted Combining VCSELs I i i m 1 g 1 Lens VCSE Sysen1 mamx Figure 259 Manv VCSELS on he same substlatc nouemwew mamas me iota Output power to hng wmeus ly ooleallockeol Lasers 1 Match the phase of the longitudinal modes gt regular pulsing in time domain aka mode locking Used in OTDM Achieved by using longer cavities eg I illMAM WW ber laser or modulating the gain of cavity EC 2n m H h Shivkumar Kalyanaraman Mode Locking by Amplitude Modulation of Cavit Gain Gaussian Beams Gausswan quotilsmljulmn Cross eunou Cucmar EHlplIcal Crassrsechon crossrseclion C Figure 260 Crvaraclenshcs of a Gaussxan beauLA crossrsecnunm msmbuhous of prachca beams B and carrecnve acnon Tunable Lasers 1 Tunable lasers key enabler of recon gurable optical networks 1 Tunability characteristics a Rapid lt ms ranges El Wide and continuous range of over 100 nm J Long lifetime and stable over lifetime u Easily controllable and manufacturable 1 Methods D Electrooptical changing RI by injecting current or applying an E eld approx 1015 nm D Temperature tuning 1 nm range may degrade lifetime of laser D Mechanical tuning using MEMS gt Tunable Two amp Threesection DBR Lasers Lmrsururmrc imn rrgmn mng I gt 39m My quotmm vlnclungm Enclcnglh M IV Power a Bragg adumun anclcngm Wm clcngth Lnulcngxh Tumab g DER Lagers Clm idj Active Sectiun Bragg Secllon I v execmcaw Gama Isma on regian Figure 84 Tunable ZrSem un DBR Lam Active Sectmn Phase Secllon Bragg Secllon 6am MSOLum Elecmca Comm so a on reglons Figure 5 5 Tunable JSw39n39nn DER Lum Sampied rating u Goal largertuning range by combining tuning ranges at different peaks aka combs may macs Lnulcngih Samniu graimg 1 alyanaraman Wm cicngih Samp m Grating BR C mt Grating Structure Iv vv Gramg Elanxec 5 Figure 86 Samme Sr39lmrmzm amneer 5 mar V laueleugl v m Gva m 7 39gtxm x7 nymph A 17 1 Ea h gnaw r u g t Mmmm en Mm m mum vu39xHIS m39umr A mm rnxvvu mvq hc ulhe vgrating Tim 39Im bananaIvy11mm mmA Sn Shlvkumar Kalyanaraman pt a Rrgm ve grgz Bash H as Conduction band Ltlcclron Photon H019 Photoconductive Detector Electrical Contact Electrical Contact t 7 undo ad Amvm Photon F 9 Semiconductor Material meamrmn cams a c w non a nu clown and mm gf ll Figure 97 lelm39umluuii39u Dm39vmr 7 Prim iplz Application of external bias gt absorbed photons lead to electronhole pairs and a current aka photocurrenf Energy ofincident photon atleast the bandgap energy gt largest k cutoffk Si GaAs cannot be used InGaAs InG yanaraman Pramicca Ph t m u t ms l H 7 Semiconductor Material Mela Comacis Figure 98 Practical letm39mzduclive Detector Sn39lema t Shivkumar Kalyanaraman The Many Uses of 3 PN Junction Diode Lasers 7 kAcmZ Light Emission Light Emitgling Diodes mAAcm Light Detection Solar Photovoltaic 20 50mAcm2 Photodiodes mAAlcmz Thennophotovoltaic llOAcmz Power Production Avalanche Photodiods mA Acmz 9 espou ue v ry Ratio of electric current owing in the device to the incident optical power 3 S Photoelectric detectors responds to photon ux rather than optical power unlike thermal detectors Responsivity vs 9 Shivkumar Kalyanaraman l L U E Photoconductor vs Photodiode Photoconductor Le a single semiconductor slab is not very ef cient in Many generated electrons recombine with holes before reaching the external circuit Need to sweep the generated conductionband electrons rapidly OUT ofthe semiconductor Better use a pnjunction and reversebias it positive bias to ntype a Aka photodiode Drift current eh pairs in the depletion region rapidly create external current Diffusion eh pairs created OUTSIDE the depletion region move more slowly and may recombine reducing efflcuencv RVr laf ad PM ph kumar Kalyanaraman Ph t di deg Reverse biased p n or p in junctions Elenmc raid 4 Photodiodes are faster than photoconductors PlN Photodiode a To improve ef ciency use a lightly doped intn39nsic semiconductor between the p and ntype semiconductors u Much of light absorption takes place in the region increases ef ciency and responsivity 1 Better make the p and ntype transparent e above cuttoff k to desired x double heterojunction u Eg cuttoff for InP is 092 um transparent in 1316 um range and cuttoff for InGaAs is 1 65um Shivkumar Kalyanaraman Avalanche Photodiode a Photogenerated electron subjected to high electric field le multiplication region may knock off more electrons le force ionization a Process avalanche multiplication 1 Too large a gain G can lead to adverse noise effects Electrical Reflection Coating Ring Guard Rxng 7 n doped 397 multiplication region 9 absorption r tngfl Electrical I Contact quot395 Si D Figure 101 Arulum39hz39 lelmlimle lAPDl Shivkumar Kalyanaraman Avalanche Process Electrical contacts Electrical comad Entering Light n region Figure 102 Al ulum hc Amplf mlion Prm39mx The H egimz hm been enlarged IU shmr m39almn39lw prm39m v Electric Field Strengths in APD l Electric 18 Strength Avalanan regmn lt W newsman ream Figure I03 Elertrir Field StrengIIS in an APD Nate the may vmall avalanche regimz Wmcmanmmm m Electronic vs Photonic Regime F7hi 17 0 r 43 71 NRzr gt Emery Gala OOK NRZ RZ j 7 A quotK m phase Change m 7 arequency chamge EMF 7 Id Figure 4 11 Optical moclulaiion memods Issues in Optical Modulation a OnOff keying 00K is the simplest 1 Direct modulation vs External modulation u Extinction ratio ratio ofoutput power for bit1 to output power for bit0 u Some lasers cannot be directly modulated 4 Direct modulation adds chirp e time variation of frequency within the pulse u Chirped pulses are more susceptible to chromatic dispersion a Combat chirp by increasing the power of bit0 so that lasing threshold is not lost uReduction of extinction ratio down to 7dB 391 Solution external modulation for higher speeds longer distancedispersionIimited regimes Shivkumar Kalyanaraman External Modulation Pcnndlc pulses External R R R A modulation IzmwculNchuu onestage U U I designs if a Mmqu nu m modelocked mm t t o t 7 X r quot l quot lasers used 1 t or 7 two stage designs External Modulation contd a Light source is continuoust operated le not modulated 1 External modulation turns light signal ON or OFF 1 They can be integrated in same package as laser eg electroabsorption or EA modulators 1 EA applying E eld shrinks bandgap gt photons absorbed Stark effect Moulation CW source SBCliO seamquot V Modulated Modulator Modulated light i Isolation 39 barrier unit and mo Lithium Nioloate External llulloolullatcors 1 MZI or directional coupler configuration 394 Voltage applied gt change RI and determine coupling or invert phase in MZI 391 MZI design gives good extinction ratio 1520dB and precise control of chirp but is polarization dependent alyanaraman Exi ama Mm u amrg meaJ LIND03 Contact uida Phase contra gun123 u culh39wn h IL 4 hmmuurdxllmml L t Mudn WNW comacl kumar Kalyanaraman Optical Modulators E Qcmca 1 mm m mammum MOW mod 0 E tCir l mumamr Mach nude mLHlHILlaHlLHH weH CrossGain amp CrossPhase Modulation npm dam m quota Dmpm dam on A mam mm qu I m p Te ed am an A Figure 287 quot P one pump 51m wave enqih gene39a39ea m meme Hecombmer gt Modmaled A Flgure zsa Pv nm aa 15a artsmass mna m deuce Eye Diagrams Badly stoned eye I gt a 3 0 ll 1 7 V Declswon Samphng H 8 Lb eve pow A Figure 293 Eye dwagrnms prowde a qmck and quahlzmve measure of the quamy and megmy oi the swgnal at me receiver ophca has afready been convened to elecmcall Eye Diagrams contd Eye anram H31 39 mm quotm u mm Figure 294 BER Estimation w Eye Diagrams 0 max 4 39 1 Measurey estlmate Variance for 0quot Var Variance or Vary an std deviation ior O 2 Calcmale E rye 11mm leax 2 2 O Ernax 51 quot 70 Jar std deviatiun for 1quot BER 2 arts 0 U2 an E E nm Em Penalty EON2 E M Figure 295 BER and penany esnma on based on eye dlagram BER Estimation contd SQ cu 5 9 gt J C CL 3 U 9 LL Spaces I 1 Marks Amphiude mmnx mm Figure 296 BER and penalty estlmahon based on the histogram diaaram Wmcmanmmm m Multiplexing Willi 1 TDM Time Division Multiplexing u 1OGbs upper limit a WDM Wavelength Division Multiplexing u Use multiple carrier frequencies to transmit data simultaneously Mu tip exersg Fi tergg Routers J Filter se ects one wave ength and re ects 31W others J Multiplexor combines different wavelengths Router exchanges wave engths from one input to a different output Li Shivkumar Kalyanaraman Switch Parameters 4 Extinction Ratio ratio ofoutput power in ON state to the power in the OFF state a 1025 dB in external modulators u Insertion loss fraction of power lost u Different losses to different outputs gt larger dynamic range gt may need to equalize esp for large switches u Crosstalk ratio of power at desired vs undesired output 1 Low polarization dependent loss PDL D Latching maintain switch state even if power turned off Readout capability to monitor current state Reliability measured by cycling the switch through its states a few million times EU Switch Considerations J Number of switch elements complexity of switch 1 Loss uniformitydifferent losses to different outputs esp for large switches Ll Number of crossovers waveguide crossovers introduce power loss and crosstalk not a problem for freespace switches J Blocking Characteristics Any unused input port can be connected to any unused output port u Widesense nonblocking without requiring any existing connection to be rerouted gt make sure future connections will not block D Strictsense nonblocking regardless of previous connections D Rearrangeaby nonblocking connections may be re routed to make them nonblocking rossbar Sw toh Widesense non blocking Shortest path length 1 vs longest 2n1 Fabricated wo any crossovers Shivkumar Kalyanaraman ch Architecture Strictsense nonblocking used in large portcount sws N mk k m X p switches in rstlast stages p kx k switches in middle stage Nonblocking ifp gt 2m 1 Lower number of crosspoints than crossbar n2 3 Spanke Alrclmitectu re Strictsense nonblocking Only 2 stages 1xn and nX1 switches used instead of 2X2 Switch cost scales linearly with n Lower insertion loss and equal optical p h le Shivkumar Kalyanaraman Benee Amh tee wre 8 Rearrangeably nonblocking Ef cient in number of 2X2 components ves not WSnonblocking and requires crossovers Shlvkumar Kalyanaraman ltltma no r it wt 3 ante Be esArchec re 1 8 Rearrangea y non oc Ing Ef cient in number of 2X2 components Eliminates waveguide crossovers nsta anaMl aI alyanaraman MENUS M rmr Sw mh ng Qmpnm Hinge jninl Hingcjoml Acumch Iranslalion sings Shivkumar Kalyanaraman NXN Swimming with MEMS MEMO Armquot315 Mirror array Mirror an ay NH H ENS quot11 a 439 AMP 1112 Nu mm 5 II II quot wjis EHE quot Htquot Mg 1 l I I gt 1 N l Murorl E s sm M o a o a 0 o 0 0 0 o Anselm Bgam S egcermg MWTQU Innur framu 0mm fmmc Flcxurc Shivkumar Kalyanaraman P anar Wawguidra Sw mh Air bubble causes ligln m be rc cclcd 8 through P anar Wawagu dQ Sw mh llhah Shivkumar Kalyanaraman EXZ Liqu d Crysta Sw mh Pt mmlmn hcun quot I ulanzallon bcnm wmhincr Fiber m l Ibcr m ECSE6660 Introduction to Optical Networking amp Relevant Optics Fundamentals httgwww gdergiedu Or prep rni 39 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute shivkumaecse rpiedu Based in pelt on textbooks ofSVKa1talopoulos DWDM and H Dutton I quot 39 39 J Optical ulu slides of Partha Dutta ShleumaI Kalyanaraman 3 Quick History u Relevant Properties of Light 1 Components of Fiber Optic Transmission and Switching Systems Cl Chapter 2 of RamaswamiSivarajan Shivkumar Kalyanaraman Quick History of Optical Networking 1958 Laser discovered Mid60s Guided wave optics demonstrated 1970 Production of lowloss fibers in Made longdistance optical transmission possible 1970 invention of semiconductor laser diode 1 Made optical transceivers highly refined 70s80s Use of fiber in telephony SONET El Mid80s LANsMANs broadcastandselect architectures 1988 First transatlantic optical fiber laid Late80s EDFA optical amplifier developed u Greatly alleviated distance limitations Midlate90s DWDM systems explode Late90s Intelligent Optical network Li J U UL L EU Big Picture Optical Transmission System Pieces 111 Optical Transmission System Concepts Transmittera lt Receiverigt Connector Connector GlassiFibre y aModulator V r gt iAmrplifierii V iii Light Source Light Sensor Detector Detector i Electricity gt Light N 7 Electricity gt Figurc l OptiLal Transmim39ion Srlmmalic Big Picture DWDM Optical components EQUAL D SPC OADM EQUAL DISPVC I a r Twi g AN gt RE Recerver Laser Dwode Modulator w DM Opncal ampli er DISPC WDM Dispersmn compensauon EQUAL WDM E ualiza on OADM Optical AddDrop Muitxmexer Figu e iii A broad range of optical componems has made ll possible for WDM networks to transpnn severe Terabus per second MLNH P L5 Law mumrme lm zrcwcr mum umpl m WDM nmlummu m WDM dcmuu mum Immu ry n electromagnetic 39 can be transmmea wllhaul distorhcn iqlerferance due to eleclncal siolms etc Non nle erence of MD or Unlike alec39 cal signals optical more Crossedheams gnuls can crass each Other wilhou 7 a lonlan High parallelism rwcdlmensxonal Inlormuhcn can 39 be sen nnG received mgn speedrhigh Bandwiqlh i Foven al bundwicllhs for optical communicalion systems exceed 10 3 blfs per second for recon gurable nee space connecnons allow versume arcnnacmre lor fnfurmaflon admrsfee g Drocesslng nrsr qnhecrs Sbeciulfuncllongevices lnierlerence ma tract n a gm 39 39 can be used lo Speclul applica ons W39ave nalure or gh 1m special a iCES Moqunear materials New Io devices can be crauiecl Fhoionic eleihunus coup ng The best of elecllanics and 39 phobnics can be exploited by np39oelech39onlc devlces Electromagnetic Spectrum Frequency Wavetengtr meters m 12045 Gamma Rays XHays Ultraviolet Visible L39 quot 39 0 2 Infrared 0 Microwaves Ha in Frequency Figure 2A The Elgarmm nelit s ecuMu r p E 3 3 F a E 3 Fe 9 3 53 63 E 613 3 1 E 3 F5 Quantum optics Electromagnetic antics Wave optics Ray optics Historical Development What is Light l Wave nature 1 Re ection refraction diffraction interference polarization fading loss J Transverse EM TEM wave a Interacts with any charges in nearby space a Characterized by frequency wavelength phase and propagation speed D Simpli ed Maxwell s equationsanalysis for monochromatic planar waves D Photometric terms luminous flux candle intensity illuminance Luminance 1 Particle nature LI Number of photons min energy E hu 1 Free space gt no matter OR EM fields u Trajectory affected by strong EM fiel Light Attributes of Interest 3 Dual Nature EM wave and particle 3 Many its wide amp continuous spectrum L Polarization circular elliptic linear affected by elds and matter 1 Optical Power wide range affected by matter I Propagation L Straight path in free space L In matter it is affected variously absorbed scattered through a In waveguides it follows bends 1 Propagation speed diffks travel at diff speeds in matter El Phase affected by variations in elds and matter Shivkumar Kalyanaraman Table 110 Cause and effect Calm inicracls vilh A inkram Kilil maucr l rmullcril imuruuliun Nonnmnuchmnwuc channel Rci39raclivu indcx arialiun in Tramparcnc arialiun altering Rc cclhil Inn in mailer Inlcrl39crrnci Linear and nonlinear cl39i39cclx uhxnrpzion scattering bircl ringcncc phaxc min rc cclimL refraction dii i39raciiun pnlarizalioiL ularizalinn xhil39l Pl nmdulalinn selliphuxe mmluialmn clc FWM iwucs SRS 583 017A ulxe broadening nilc number of channel within amilahlu han Al39i39cch propagation of light Affu anmunl uI39 Iighl lhruugh man up al puwcr loss alicnuulionl Al l cclg polarization of re ected optical wave Aliens phase of re ected optical wave Diphlcs inlcrucling xclurlivcly with M Em ahmrplinn ur uxchangc Ailcul rcl39racliw imiev Goal Light Transmission on Optical Fiber Cladding Core Li m R Ingm Refractive index Figure 11 BISiL39 Pl im39ipM afngu Trum39mixsiwz m pliml Fibre eed to understand basic ideas ofl interacts Fit 1 and with matter Light interaction with Other 7L5 and interaction with matter Shivkumar Kalyanaraman lmtera retimt with Marthaquot R ly pti When light waves propagate through and around objects whose dimensions are much greater than the wavelength the wave nature of light is not readily discerned s that its behavior can be adequately described by rays obeying a set of geometrical rules This model of light is called ray optics Strictly speaking ray optics is the limit of wave optics when the wavelength is in nitesimally small Light rays travel in straight lines Shivkumar Kalyanaraman R f g n Light P ane o1 mmdence m xrmr 0 52 m The rg mrted my figs in the plane of incidence the magic of re ection equals the angle of incidsnce Shivkumar Kalyanaraman RQf eemmn App mtmng M rrmg amp MEIRES Plane Spherical P7 xi 4 Shivkumar Kalyanaraman R fra ti n Light quotI sin 939 112 Sin 02 The nj mcrcd my Ha if the plane of incidence the angle ofquot refraction 63 is related 0 the angle of incidence at by SneU s law S vkumar Kalyanaraman by Wieme a re D Q n at A gyy DR H e angle 0f lde eenon l r l Hl I u Composite beam 2 L7 3 n M A2 39 quot39 Ml 1 Base of prism n2 2 nl Newton s Rainbow Deflection angle dependent on the wavelength Used in optical multiplexers and de multiplexers Optical Multiplexer amp DeMultiplexer Mu tp exac new A x3 gt x 6 Lens Hm ema 8 Exicwma RQEHQQ39EEQWS Exiemal refractlon Internal reilacilon Critical Angle for Total Internal Reflection Totai intermi Re ection Total internal reflection forms the back bone for fiber optical communication
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