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Introduction to Optical Networking & Relevant Optics Fundamentals

Introduction to Optical Networking & Relevant Optics Fundamentals 6
Introduction to Optical Networking Relevant Optics Fundamentals Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Quick History  Relevant Properties of Light  Components of Fiber Optic Transmission and Switching Systems  Chapter 2 of Ramaswami/Sivarajan Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2Quick History of Optical Networking  1958: Laser discovered  Mid60s: Guided wave optics demonstrated  1970: Production of lowloss fibers  Made longdistance optical transmission possible  1970: invention of semiconductor laser diode  Made optical transceivers highly refined  70s80s: Use of fiber in telephony: SONET  Mid80s: LANs/MANs: broadcastandselect architectures  1988: First transatlantic optical fiber laid  Late80s: EDFA (optical amplifier) developed  Greatly alleviated distance limitations  Mid/late90s: DWDM systems explode Shivkumar Kalyanaraman  Late90s: Intelligent Optical networks Rensselaer Polytechnic Institute 3Big Picture: Optical Transmission System Pieces Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Big Picture: DWDM Optical components Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Evolution of Fiber Transmission Systems Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6Bigger Picture: Key Features of PhotonicsElectromagnetic Spectrum Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8What is Light Theories of Light Historical DevelopmentWhat is Light  Wave nature:  Reflection, refraction, diffraction, interference, polarization, fading, loss …  Transverse EM (TEM) wave:  Interacts with any charges in nearby space…  Characterized by frequency, wavelength, phase and propagation speed  Simplified Maxwell’s equationsanalysis for monochromatic, planar waves  Photometric terms: luminous flux, candle intensity, illuminance, Luminance…  Particle nature:  Number of photons, min energy: E = hu  “Free” space = no matter OR EM fields Shivkumar Kalyanaraman  Trajectory affected by strong EM fields Rensselaer Polytechnic Institute 10Light Attributes of Interest  Dual Nature: EM wave and particle  Many s: wide continuous spectrum  Polarization: circular, elliptic, linear: affected by fields and matter  Optical Power: wide range; affected by matter  Propagation:  Straight path in free space  In matter it is affected variously (absorbed, scattered, through);  In waveguides, it follows bends  Propagation speed: diff s travel at diff speeds in matter  Phase: affected by variations in fields and matter Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Interaction of Light with Matter Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12Goal: Light Transmission on Optical Fiber Need to understand basic ideas of  interacts with s and with matter Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13Light interaction with other s and interaction with matter Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14Interaction with Matter: Ray Optics • Light rays travel in straight lines Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15Reflection of Light Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16Reflection Applications: Mirrors MEMS Plane Paraboloidal Elliptical Spherical Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17Refraction of Light Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18Ray Deflection by Prism • Newton’s Rainbow: Deflection angle dependent on the wavelength; • Used in optical multiplexers and de multiplexers Optical Multiplexer DeMultiplexerInternal External Reflections • Critical Angle for Total Internal Reflection:Total Internal Reflection • Total internal reflection forms the back bone for fiber optical communicationLight (Wave) Guides: Reflection vs Total Internal ReflectionLight Guiding: Concept of Optical FiberGeometrical Optics: Fiber Structure  Fiber Made of Silica: SiO (primarily) 2  Refractive Index, n = c /c vacuum material  n n core cladding n1.43 n1.45  Numerical Aperture: Measures lightgathering capability Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 25Light Coupling into a fiber Effect of numerical aperture… Light Coupling is Polarization Dependent Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 27Geometrical Optics Applied to Fiber  Light propagates by total internal reflection  Modal Dispersion: Different path lengths cause energy in narrow pulse to spread out T = time difference between fastest and slowest ray Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 28Total Internal Reflection Modes  Impacts how much a fiber can be bent  Microbends can eat up energy, kill some modes  Modes are standing wave patterns in wave or EMoptics Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 29EM Optics: Optical Electromagnetic Wave Linear polarization assumed … Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 30Amplitude Fluctuations of TEM Waves Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 31Speed of Light in a Medium As a monochromatic wave propagates through media of different refractive indices, its frequency remains same, but its velocity, wavelength and wavenumber are altered.Diffraction or Fresnel Phenomenon Cannot be explained by ray opticsDiffraction Pattern from a Circular ApertureDiffraction Patterns at Different Axial PositionsDiffraction Grating • Periodic thickness or refractive index variation (“grooves”) Diffraction also occurs w/ pin hole of size of  In polychromatic light, different wavelengths diffracted differentlyDiffraction Grating as a Spectrum AnalyzerInterference: Young’s Experiment Interference is simple superposition, and a wavephenomenon Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 38Interference of Two Spherical WavesInterference of Two WavesMultiple Waves Interference (Equal Amplitude, Equal Phase Differences) Sincsquared function Application: Bragg Reflection InterferenceHigh Intensity, Narrow Pulses from Interference between M Monochromatic Waves • Used in Phase locked lasersPropagation of a Polychromatic WaveOptical Splicing Issues: Speckle Patterns Speckle patterns are timevarying and arise from solution of Maxwell’s equations ( geometric optics) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 45Recall: Interaction of Light with Matter Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 46Optical Transmission: More Light Matter Interaction Effects Attenuation Dispersion Nonlinearity Reflectance Transmitted data waveform Waveform after 1000 km Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 47Absorption vs Scattering Both are linear effects that lead to “attenuation”. Rayleigh scattering effects dominate much more than absorption (in lower Wavelengths, but decreases with wavelength) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 48Absorption and Attenuation: Absorption Spectrum Material absorption (Silica) 0.2 dB/km Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 49Fiber:Transmission Windows Lucent’s new AllWave Fiber (1998) eliminates absorption peaks due to watervapor in the 1400nm area Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 50Transmission Bands Bandwidth: over 35000 Ghz, but limited by bandwidth of EDFAs (optical amplifiers): studied later… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 51Optical Amplifier: Limitations on Practical Bandwidths EDFAs popular in Cband Raman: proposed for Sband Gainshifted EFDA for Lband Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 52Fiber Attenuation  Two windows: 1310 1550 nm  1550 window is 1550 preferred for long window haul applications 1310 window  Less attenuation  Wider window   Optical amplifiers Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 53Fiber Anatomy Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 54Fiber Manufacturing  Dopants are added to control RI profile of the fiber (discussed later)  Fiber: stronger than glass  A fiber route may have several cables  Each cable may have upto 1000 fibers  Each fiber may have upto 160 wavelengths  Each wavelength may operate at 2.5Gbps or 10 Gbps Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 55Single vs. Multimode Fiber  SilicaBased Fiber Supports 3 LowLoss “Windows”: 0.8, 1.3 , 1.55 m wavelength  Multimode Fibers Propagate Multiple Modes of Light  core diameters from 50 to 85 m  modal dispersion limitations  Singlemode Fibers Propagate One Mode Only  core diameters from 8 to 10 m  chromatic dispersion limitations Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 56Summary: Singlemode vs Multimode Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 57Multimode vs Single mode: Energy distributions Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 58Single Mode Characteristics (contd)  It (almost) eliminates delay spread  More difficult to splice than multimode due to critical core requirements  More difficult to couple all photonic energy from a source into it; light propagates both in core and cladding  Difficult to study propagation w/ ray theory; requires Maxwell’s equations  Suitable for transmitting modulated signals at 40 Gb/s and upto 200 km w/o amplification  Long lengths and bit rates = 10 Gbps bring forth a number of issues due to residual nonlinearity/birefringence of the fiber  Fiber temperature for long lengths and bit rates 10 Gbps becomes significant. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 59Single Mode Light Propagation Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 60Dispersion Interference  Dispersion causes the pulse to spread as it travels along the fiber  Chromatic dispersion important for single mode fiber  Depends on fiber type and laser used 2  Degradation scales as (datarate)  Was not important for 2.5Gbps, 500km SMF fibers  Modal dispersion limits use of multimode fiber to short distances Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 61Effects of Dispersion Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 62PulseWidening Effect on ISI BER Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 63Combating Modal Dispersion in Multimode Fiber: Refractive Index Profiles Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 64Graded Index (contd) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 65Graded Index MultiMode Characteristics (contd)  Minimizes delay spread (modal dispersion), but it is still significant at long lengths  One percent index difference between core/cladding amounts to 15ns/km delay spread  Step index has 50 ns/km spread  Easier to splice and couple light into it  Bit rate is limited (100 Mbps etc) for 40 km.  Higher bit rates for shorter distances  Fiber span w/o amplification is limited  Dispersion effects for long lengths, high bit rates is a limiting factor Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 66Chromatic Dispersion  Different spectral components of a pulse travel at different velocities  Also called groupvelocitydispersion (GVD), Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 67Chromatic Dispersion  Different spectral components of a pulse travel at different velocities  Also called groupvelocitydispersion (GVD), aka  2  Subcomponents:  Material dispersion: frequencydependent RI  Waveguide dispersion: light energy propagates partially in core and cladding.  Effective RI lies between the two (weighted by the power distribution).  Power distribution of a mode between core/cladding a function of wavelength  GVD parameter ( ) 0 = normal dispersion (1.3m) 2  GVD parameter ( ) 0 = anomalous dispersion (1.55m) 2 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 68Pulse Shaping: Chirped Gaussian Pulses  Since chromatic dispersion affects pulse shape, we study how pulse shaping may affect the outcome  Gaussian: envelope of pulse  Chirped: frequency of launched pulse changes with time  Semiconductor lasers + modulation, or nonlinear effects also lead to chirping  With anomalous cdispersion in normal 1.55 um fibers ( 0), and negative chirping ( 0, natural for semi 2 laser outputs), the pulse broadening effects are exacerbated (next slide)  Key parameter: dispersion length (L ) D  1.55um, L = 1800 km for OC48 and L = 155 km D D for OC192)  If d L then chromatic dispersion negligible D Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 69Chromatic Dispersion effect on Unchirped/Chirped Pulses Unchirped (Negatively) Chirped Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 70Chirped Pulses May Compress (I.e. not broaden) Depends upon chirping parameter () and GVD Parameter ( ), I.e  0 2 2 Pulse may compress upto a particular distance and then expand (disperse) Corning’s metrocor fiber: positive  in 1.55 um band 2 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 71Combating Chromatic Dispersion: Dispersion Shifted Fiber Though material dispersion cannot be attacked, waveguide dispersion can be reduced (aka “shifted”) = DSF fiber •Deployed a lot in Japan •RI profile can also be varied to combat residual Cdispersion Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 72Dispersion Shifted Fiber (contd) Waveguide dispersion may be reduced by changing the RIprofile of the singlemode fiber from a stepprofile to a trapezoidal profile (see below) This operation effectively “shifts” the zerochromatic dispersion point to 1550nm the average value in the band is 3.3 ps/nm/km Alternatively a length of “compensating” fiber can be used Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 73Fiber Dispersion Normal fiber Nondispersion shifted fiber (NDSF) 95 of deployed plant 18 Wavelength 0 l 1310 nm 1550nm Reduced dispersion fibers Dispersion shifted fiber (DSF) Nonzero dispersion shifted fibers (NZDSF) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 74 Dispersion ps/nmkmDispersion Compensation Modules Instead of DSF fibers, use dispersion compensation modules Eg: Infiber chirped bragg gratings (carefully reflect selected s and make then travel a longer path segment) to compensate for Cdispersion Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 75Residual Dispersion after DCMs Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 76Role of Polarization • Polarization: Time course of the direction of the electric field 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 Light Absorption, Scattering, Rotation Refractive index of anisotropic materials depends on polarization (Brewster’s law)Linearly Polarized LightCircularly Polarized LightPolarizing Filters Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 80Rotating Polarizations Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 81Optical IsolatorSingle Mode Issues: Birefringence, PMD  Even in single mode, there are 2 linearly independent solutions for every  (to maxwell’s equations)  State of polarization (SOP): distribution of light energy between the (two transverse) polarization modes Ex and Ey  Polarization Vector: The electric dipole moment per unit volume  In perfectly circularsymmetric fiber, the modes should have the same velocity  Practical fibers have a slight difference in these velocities (birefringence): separate unpolarized light into two rays with different polarizations  This leads to pulsespreading called Polarization Mode Dispersion (PMD) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 83AnIsotropy and Birefringence Silica used in fiber is isotropic Birefringence can also be understood as different refractive indices in different directions It can be exploited (eg: Lithium niobate) for tunable filters, isolators, modulators etc Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 84Birefringence Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 85Polarization Mode Dispersion (PMD)  Most severe in older fiber  Caused by several sources  Core shape  External stress  Material properties  Note: another issue is polarizationdependent loss (PDL)  Both become dominant issue at OC192 and OC 768 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 86Polarization Mode Dispersion Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 87Nonlinear Effects  Linearity: a lightmatter interaction assumption  Induced dielectric polarization is a convolution of material’s susceptibility () and the electric field (E)  Linearity: low power (few mW) bit rates (2.4 Gbps)  Nonlinearity:  bit rates (10 Gbps) and  power = nonlinearities  channels (eg: DWDM) = more prominent even in moderate bit rates etc  Two categories:  A) phonon interaction scattering (SRS, SBS)  B) RIdependence upon light intensity (SPM, FWM) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 88Nonlinearity Scattering Effects  Stimulated Raman or Brillouin Scattering (SRS or SBS)  Energy transferred from one  to another at a longer  (or lower energy)  The latter wave is called the “Stokes wave”  Former wave is also called the “pump”  Pump loses power as it propagates and Stokes wave gains power  SBS: pump is signal wave Stokes is unwanted wave  SRS: pump is highpower wave, and Stokes wave is signal wave that is amplified at the expense of the pump  Parameters:  g: gain coefficient (strength of the effect) f: Spectral width over which the gain is present Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 89SRS: Photon Emission Mechanics  Photons interact with atoms: eg: May be absorbed to reach an “excited” state (“metastable”, I.e. cant hang around)  In the excited state, certain photons may trigger them to fall back, and release energy in the form of photons/phonons  PhotonAtom vs PhotonAtomPhoton interactions  Most of these effects are “third order” effec St hs ivkumar Kalyanaraman Rensselaer Polytechnic Institute 90Stimulated Raman Scattering (SRS)  Power transferred from lower to higher channels  Can be used as basis for optical amplification and lasers  Photons of lower have higher energy (aka “pump”) that excite atoms and lead to stimulate emission at higher  Effect smaller than SBS, but can affect both forward and reverse directions  Effect is also wider: I.e a broadband effect (15 Thz) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 91Raman Scattering Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 92Stimulated Brillouin Scattering (SBS)  Triggered by interaction between a photon and an acoustic phonon (I.e. molecular vibrations)  Affects a narrowband: 20 Mhz (compare with 15 Thz effect in SRS)  Can combat it by making source linewidth wider  The downshifted wavelength waves propagate in the opposite direction (reverse gain): need isolation at source  Dominant when the spectral power (brightness) of the source is large and abruptly increases beyond a threshold (510 mW)  Limits launched power per channel, but may be used in amplification Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 93SBS: Threshold Variation Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 94ElectroOptic RI Effects  Electrooptic effects: Refractive index (RI) depends upon amplitude (and hence intensity) of electric field (E) Result: induced birefringence, dispersion  Pockels Effect:n = (a )E 1 2  Kerr Effect: (second order) n = (K)E  The second order magnification in Kerr effect may be used to create ultra high speed modulators ( 10Gbps) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 95Intensitydependent RI Effects  Selfphase Modulation (SPM), CrossPhase Modulation (CPM) Fourwave mixing (FWM)  SPM: Pulses undergo induced chirping at higher power levels due to RI variations that depend upon intensity  In conjunction with chromatic dispersion, this can lead to even more pulse spreading ISI  But it could be used to advantage depending upon the sign of the GVD parameter  CPM: Multiple channels: induced chirp depends upon variation of RI with intensity in other channels  FWM: A DWDM phenomena: tight channel spacing  Existence of f1, … fn gives rise to new frequencies 2fi – fj and fi + fj – fk etc  Inband and outofband crosstalk Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 96SelfPhase Modulation Example of (positive) chirp or frequency fluctuations induced by selfphase modulation Modulation instability or selfmodulation: In the frequency domain, we see new sidelobes Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 97FourWave Mixing (FWM)  Creates inband crosstalk (superposition of uncorrelated data) that can not be filtered  Signal power depletion  SNR degradation  Problem increases geometrically with  Number of s  Spacing between s  Optical power level  Chromatic dispersion minimizes FWM ()  Need to increase channel spacing and manage power carefully Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 98FourWave Mixing Effects Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 99Fiber Dispersion (revisited) Normal fiber Nondispersion shifted fiber (NDSF) 95 of deployed plant 18 Wavelength 0 l 1310 nm 1550nm Reduced dispersion fibers Dispersion shifted fiber (DSF) Nonzero dispersion shifted fibers (NZDSF) Dispersionshifted (DSF) is good for chromatic dispersion but bad for nonlinear effects. NZDSF: puts back a small amount of Cdispersion Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 100 Dispersion ps/nmkmNonZero Dispersion Shifted Fiber • NZDSF: puts back a small amount of Cdispersion • Note: The goal of RIprofile shaping is different here than gradedindex in multimode fiber Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 101Fibers: chromatic dispersion story… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 102Latest Fibers Bands LEAF fibers have larger effective area= better tradeoff for nonlinearities Fiber Bands: Oband: (Original) 12601360nm Eband: (Extended) 13601460nm Sband: (Short) 14601530nm Cband: (Conventional): 15301565nm Lband: (Long) 15651625nm Shivkumar Kalyanaraman RenU sse laba er Pond: (U lytechnic Inlt stitr uta elong): 16251675nm 103Terrestrial vs Submarine Fibers Positive (chromatic) dispersion fibers (CDF) used in terrestrial, and negative CDF used in submarine apps. Due to modulation instability (interaction between SPM and chromatic dispersion at high power levels) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 104Fiber Dispersion (contd) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 105Solitons  Key idea: SPM induced chirping actually depends upon the timedomain envelope of the pulse  If pulse envelope right, SPM induced chirping will exactly combat the chromatic dispersion (GVD) chirping  Soliton Regime: input power distribution shape, effective area/crosssection of fiber core and fiber type  DWDM with pure solitons not practical since solitons may “collide” and exchange energy over a length of fiber Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 106Solitons (contd)  Family of pulse shapes which undergo no change or periodic changes  Fundamental solitons: no change in shape  Higherorder solitons: periodic changes in shape  Significance: completely overcome chromatic dispersion  With optical amplifiers, high powers, the properties maintained = long, very high rate, repeaterless transmission  Eg: 80 Gb/s for 10,000km demonstrated in lab (1999)  Dispersionmanaged solitons:  An approximation of soliton pulse, but can operate on existing fiber  This can be used for DWDM: 25channel, 40 Gbps, 1500km has been shown in lab (2001) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 107Summary: Fiber and Optical Amplifier Trends  Bandwidthspan product:  SMF: 1310 nm, 1983 = 2.5Gbps for 640 km w/o amplification or 10 Gbps for 100 km  Recent SMF: 2.5 Gbps for 4400 km; 10 Gbps for 500 km  Multiply these by of DWDM channels (eg: 40160)…  Fiber amplifiers:  Erbium doped (EDFA): 1550 nm range  Praseodymiumdoped flouride fiber (PDFFA): 1310 nm  Thoriumdoped (ThDFA): 13501450nm  Thuliumdoped (TmDFA): 14501530 nm  Telleriumerbiumdoped (TeEDFA): 15321608 nm  Raman amplifiers: address an extended spectrum using standard singlemode fiber… (1150 –1675 nm) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 108Optical Amplifier: Limitations on Practical Bandwidths EDFAs popular in Cband Raman: proposed for Sband Gainshifted EFDA for Lband Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 109Future: Hollow Nanotube Waveguides Perhaps carbon nanotubes developed at RPI could be used  Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 110Summary: Interaction of Light with Matter Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 111Metrics and Parameters in Optics Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 112