Shivkumar KalyanaramanRensselaer Polytechnic Institute
1
ECSE-6660
Introduction to Optical Networking
& Relevant Optics Fundamentals
http://www.pde.rpi.edu/
Or
http://www.ecse.rpi.edu/Homepages/shivkuma/
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
shivkuma@ecse.rpi.edu
Based in part on textbooks of S.V.Kartalopoulos (DWDM) and
H. Dutton (Understanding Optical communications), and
slides of Partha Dutta
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Overview
Quick History
Relevant Properties of Light
Components of Fiber Optic Transmission and
Switching Systems
Chapter 2 of Ramaswami/Sivarajan
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Quick History of Optical Networking
1958: Laser discovered
Mid-60s: Guided wave optics demonstrated
1970: Production of low-loss fibers
Made long-distance optical transmission possible!
1970: invention of semiconductor laser diode
Made optical transceivers highly refined!
70s-80s: Use of fiber in telephony: SONET
Mid-80s: LANs/MANs: broadcast-and-select
architectures
1988: First trans-atlantic optical fiber laid
Late-80s: EDFA (optical amplifier) developed
Greatly alleviated distance limitations!
Mid/late-90s: DWDM systems explode
Late-90s: Intelligent Optical networks
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Big Picture: Optical Transmission
System Pieces
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Big Picture: DWDM Optical components
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Evolution of Fiber Transmission Systems
Bigger Picture: Key Features of Photonics
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Electromagnetic Spectrum
What is Light? Theories of Light
Historical
Development
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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What 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 equations-analysis 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
Trajectory affected by strong EM fields
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Light 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 KalyanaramanRensselaer Polytechnic Institute
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Interaction of Light with Matter
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Goal: Light Transmission on Optical Fiber
Need to understand basic ideas of  interacts with s and with matter
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Light interaction with other s and
interaction with matter
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· Light rays travel in straight lines
Interaction with Matter: Ray Optics
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Reflection of Light
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Reflection Applications: Mirrors & MEMS
Plane
Paraboloidal
Spherical
Elliptical
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Refraction of Light
Ray Deflection by Prism
· Newton's Rainbow: Deflection angle
dependent on the wavelength;
· Used in optical multiplexers and de-
multiplexers !
Optical Multiplexer & DeMultiplexer
Internal & External Reflections
· Critical Angle for Total
Internal Reflection:
Total Internal Reflection
· Total internal reflection forms the back-
bone for fiber optical communication
Light (Wave) Guides: Reflection vs
Total Internal Reflection
Light Guiding: Concept of Optical Fiber
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Geometrical Optics: Fiber Structure
Fiber Made of Silica: SiO2 (primarily)
Refractive Index, n = cvacuum/cmaterial
ncore > ncladding
Numerical Aperture:
Measures light-gathering
capability
n~1.45
n~1.43
Light Coupling into a fiber
Effect of numerical
aperture...
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Light Coupling is Polarization
Dependent
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Geometrical 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 KalyanaramanRensselaer Polytechnic Institute
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Total Internal Reflection & Modes
Impacts
how much a
fiber can be
bent!
Micro-bends
can eat up
energy, kill
some modes!
Modes are
standing
wave patterns
in wave- or
EM-optics!
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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EM Optics: Optical Electromagnetic Wave
Linear polarization assumed ...
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Amplitude Fluctuations of TEM Waves
Speed 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 optics!
Diffraction Pattern from a Circular
Aperture
Diffraction Patterns at Different Axial
Positions
Diffraction Grating
· Periodic thickness or refractive index variation ("grooves")
* Diffraction also occurs w/ pin hole of size of ~
* In polychromatic light, different wavelengths diffracted
differently
Diffraction Grating as a Spectrum Analyzer
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Interference: Young's Experiment
Interference is simple superposition, and a wave-phenomenon
Interference of Two Spherical Waves
Interference of Two Waves
Multiple Waves Interference (Equal
Amplitude, Equal Phase Differences)
Sinc-squared function
Application: Bragg Reflection & Interference
High Intensity, Narrow Pulses from
Interference between M
Monochromatic Waves
· Used in Phase locked lasers
Propagation of a Polychromatic Wave
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Optical Splicing Issues: Speckle Patterns
Speckle patterns are
time-varying and
arise from solution
of Maxwell's
equations
(> geometric optics)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Recall: Interaction of Light with Matter
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Optical Transmission: More Light-
Matter Interaction Effects
Attenuation
Dispersion
Nonlinearity
Waveform after 1000 kmTransmitted data waveform
Reflectance
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Absorption 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 KalyanaramanRensselaer Polytechnic Institute
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Absorption and Attenuation: Absorption
Spectrum
Material absorption (Silica)
0.2 dB/km
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Fiber:Transmission Windows
Lucent's new AllWave Fiber (1998) eliminates absorption peaks
due to watervapor in the 1400nm area!
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Transmission Bands
Bandwidth: over 35000 Ghz, but limited by bandwidth of EDFAs
(optical amplifiers): studied later...
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Optical Amplifier: Limitations on
Practical Bandwidths
EDFAs popular in C-band
Raman: proposed for S-band
Gain-shifted EFDA for L-band
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Fiber Attenuation
Two windows:
1310 & 1550 nm
1550 window is
preferred for long-
haul applications
Less attenuation
Wider window
Optical amplifiers
1190.5 0.486417271 Lucent SMF28 clone fiber spool
1190.999 0.487290677
1191.499 0.488428184 fiber Spool ID : 021V14645A1CVC
1191.998 0.489291309
1192.498 0.489196919
1192.998 0.487617079
1193.497 0.484524638
1193.997 0.480520733
1194.496 0.476593948
1194.996 0.473623898
1195.496 0.471936705
1195.995 0.471200314
1196.495 0.470722289
1196.994 0.469923294
1197.494 0.46863602
1197.994 0.467056305
1198.493 0.465486474
1198.993 0.4641438
1199.492 0.463158704
1199.992 0.462656083
1200.492 0.462743335
1200.991 0.463378013
1201.491 0.464281553
1201.99 0.465049286
1202.49 0.465362492
1202.99 0.465060732
1203.489 0.464032079
1203.989 0.462164558
0.2
0.3
0.4
0.5
0.6
1310
window

1550
window
1190 0.486098221 obtained by measuring about 50 km of
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Fiber Anatomy
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Fiber 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 KalyanaramanRensselaer Polytechnic Institute
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Single vs. Multimode Fiber
Silica-Based Fiber Supports 3 Low-Loss "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
Single-mode Fibers Propagate One Mode Only
core diameters from 8 to 10 m
chromatic dispersion limitations
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Summary: Single-mode vs Multi-mode
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Multimode vs Single mode: Energy
distributions
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Single 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 KalyanaramanRensselaer Polytechnic Institute
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Single Mode Light Propagation
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Dispersion
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
Degradation scales as (data-rate)2
Was not important for < 2.5Gbps, < 500km SMF fibers
Modal dispersion limits use of multimode fiber to short
distances
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Effects of Dispersion
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Pulse-Widening Effect on ISI & BER
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Combating Modal Dispersion in Multimode
Fiber: Refractive Index Profiles
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Graded Index (contd)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Graded 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 1-5ns/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 KalyanaramanRensselaer Polytechnic Institute
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Chromatic Dispersion
Different spectral components of a pulse travel at
different velocities
Also called group-velocity-dispersion (GVD),
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Chromatic Dispersion
Different spectral components of a pulse travel at different
velocities
Also called group-velocity-dispersion (GVD), aka 2
Sub-components:
Material dispersion: frequency-dependent 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 (2) > 0 => normal dispersion (1.3m)
GVD parameter (2) < 0 => anomalous dispersion (1.55m)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Pulse 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 c-dispersion in normal 1.55 um fibers
(2< 0), and negative chirping ( < 0, natural for semi-
laser outputs), the pulse broadening effects are
exacerbated (next slide)
Key parameter: dispersion length (LD)
@1.55um, LD = 1800 km for OC-48 and LD = 155 km
for OC-192)
If d << LD then chromatic dispersion negligible
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Chromatic Dispersion effect on
Unchirped/Chirped Pulses
Unchirped
(Negatively)
Chirped
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Chirped Pulses May Compress (I.e. not broaden)!
* Depends upon chirping
parameter () and GVD
Parameter (2), I.e  2<0
* Pulse may compress upto a
particular distance and
then expand (disperse)
* Corning's metrocor fiber:
positive 2 in 1.55 um band!
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Combating Chromatic Dispersion: Dispersion
Shifted Fiber
Though material
dispersion cannot be
attacked, waveguide
dispersion can be
reduced (aka "shifted")
=> DSF fiber
Ïeployed a lot in Japan
ØI profile can also be
varied to combat residual
C-dispersion
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Dispersion Shifted Fiber (contd)
* Waveguide dispersion may be reduced by changing the
RI-profile of the single-mode fiber from a step-profile to a
trapezoidal profile (see below)
* This operation effectively "shifts" the zero-chromatic
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 KalyanaramanRensselaer Polytechnic Institute
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Fiber Dispersion
Wavelength
l
Dispersionps/nm-km
18
0
1310 nm 1550nm
Normal fiber
Non-dispersion shifted fiber (NDSF)
>95% of deployed plant
Reduced dispersion fibers
Dispersion shifted fiber (DSF)
Non-zero dispersion shifted fibers (NZDSF)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Dispersion Compensation Modules
Instead of DSF fibers, use dispersion compensation modules
Eg: In-fiber chirped bragg gratings (carefully reflect selected
s and make then travel a longer path segment) to
compensate for C-dispersion
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Residual Dispersion after DCMs
Role of Polarization
· Polarization: Time course of the direction of the electric
field vector
- Linear, Elliptical, Circular, Non-polar
· 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 Light
Circularly Polarized Light
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Polarizing Filters
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Rotating Polarizations
Optical Isolator
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Single 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 circular-symmetric fiber, the modes should
have the same velocity
Practical fibers have a slight difference in these velocities
(birefringence): separate un-polarized light into two rays
with different polarizations
This leads to pulse-spreading called Polarization Mode
Dispersion (PMD)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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AnIsotropy 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 KalyanaramanRensselaer Polytechnic Institute
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Birefringence
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Polarization Mode Dispersion (PMD)
Most severe in older
fiber
Caused by several
sources
Core shape
External stress
Material properties
Note: another issue is
polarization-dependent
loss (PDL)
Both become dominant
issue at OC-192 and OC-
768
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Polarization Mode Dispersion
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Non-linear Effects
Linearity: a light-matter 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)
Non-linearity:
 bit rates (10 Gbps) and  power => non-linearities
 channels (eg: DWDM) => more prominent even in
moderate bit rates etc
Two categories:
A) -phonon interaction & scattering (SRS, SBS)
B) RI-dependence upon light intensity (SPM, FWM)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Non-linearity 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 high-power 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 KalyanaramanRensselaer Polytechnic Institute
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SRS: Photon Emission Mechanics
Photons interact with atoms: eg: May be absorbed to reach
an "excited" state ("meta-stable", 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
Photon-Atom vs Photon-Atom-Photon interactions
Most of these effects are "third order" effects
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Stimulated 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 KalyanaramanRensselaer Polytechnic Institute
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Raman Scattering
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Stimulated 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 (5-10 mW)
Limits launched power per channel, but may be used in
amplification
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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SBS: Threshold Variation
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Electro-Optic RI Effects
Electro-optic effects:
Refractive index (RI) depends upon amplitude
(and hence intensity) of electric field (E)
Result: induced birefringence, dispersion
Pockels Effect: n = (a1)E
Kerr Effect: (second order) n = (K)E2
The second order magnification in Kerr effect
may be used to create ultra high speed
modulators (> 10Gbps)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Intensity-dependent RI Effects
Self-phase Modulation (SPM), Cross-Phase Modulation
(CPM) & Four-wave 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
In-band and out-of-band crosstalk
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Self-Phase Modulation
Example of (positive) chirp or frequency fluctuations
induced by self-phase modulation
Modulation instability or self-modulation: In the
frequency domain, we see new sidelobes
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Four-Wave Mixing (FWM)
Creates in-band 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 KalyanaramanRensselaer Polytechnic Institute
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Four-Wave Mixing Effects
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Fiber Dispersion (revisited)
Wavelength
l
Dispersionps/nm-km
18
0
1310 nm 1550nm
Normal fiber
Non-dispersion shifted fiber (NDSF)
>95% of deployed plant
Reduced dispersion fibers
Dispersion shifted fiber (DSF)
Non-zero dispersion shifted fibers (NZDSF)
* Dispersion-shifted (DSF) is good for chromatic dispersion
but bad for non-linear effects.
* NZ-DSF: puts back a small amount of C-dispersion!
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Non-Zero Dispersion Shifted Fiber
· NZ-DSF: puts back a small amount of C-dispersion!
· Note: The goal of RI-profile shaping is different here than
graded-index in multimode fiber
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Fibers: chromatic dispersion story...
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Latest Fibers & Bands
LEAF fibers
have larger
effective
area=> better
tradeoff for
non-linearities
Fiber Bands:
O-band: (Original) 1260-1360nm
E-band: (Extended) 1360-1460nm
S-band: (Short) 1460-1530nm
C-band: (Conventional): 1530-1565nm
L-band: (Long) 1565-1625nm
U-band: (Ultra-long): 1625-1675nm
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Terrestrial 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 KalyanaramanRensselaer Polytechnic Institute
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Fiber Dispersion (contd)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Solitons
Key idea: SPM induced chirping actually depends upon
the time-domain 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/cross-section 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 KalyanaramanRensselaer Polytechnic Institute
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Solitons (contd)
Family of pulse shapes which undergo no change or
periodic changes
Fundamental solitons: no change in shape
Higher-order 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)!
Dispersion-managed solitons:
An approximation of soliton pulse, but can operate on
existing fiber
This can be used for DWDM: 25-channel, 40 Gbps,
1500km has been shown in lab (2001)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
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Summary: Fiber and Optical Amplifier Trends
Bandwidth-span 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: 40-160)...
Fiber amplifiers:
Erbium doped (EDFA): 1550 nm range
Praseodymium-doped flouride fiber (PDFFA): 1310 nm
Thorium-doped (ThDFA): 1350-1450nm
Thulium-doped (TmDFA): 1450-1530 nm
Tellerium-erbium-doped (Te-EDFA): 1532-1608 nm
Raman amplifiers: address an extended spectrum using
standard single-mode fiber... (1150 ­1675 nm!)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
109
Optical Amplifier: Limitations on
Practical Bandwidths
EDFAs popular in C-band
Raman: proposed for S-band
Gain-shifted EFDA for L-band
Shivkumar KalyanaramanRensselaer Polytechnic Institute
110
Future: Hollow Nano-tube
Waveguides
Perhaps carbon nanotubes developed at RPI could be used? 
Shivkumar KalyanaramanRensselaer Polytechnic Institute
111
Summary: Interaction of Light with Matter
Shivkumar KalyanaramanRensselaer Polytechnic Institute
112
Metrics and Parameters in Optics