agilent back to basics in optical communication

8/3/2019 Agilent Back to Basics in Optical Communication

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Back to Basics

in Optical Communications

Technology


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Back to Basics in Optical Communications TechnologyCopyright Agilent Technologies, 2002 2

Back to Basics in Optical Communications

Technology

Today . . .

The innovations that enable 2.5 10 40 1000 Gb/ s

The science that drives the technologyThe science that drives the technology

Recipe:(1) Review the physical foundation of the technology(2) Derive the technology from the science(3) The major issues in development of the technology(4) Characterization and test of the technology


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The Science: Four Easy Pieces

1. Geometric Optics- How fibers work

2. Physical Optics- Properties of electromagnetic waves- Optical filters and spectrum analyzers

3. Atomic Physics- How transmitters, receivers, and amplifiers work

4. Electrodynamics of continuous media

- How the index of refraction affects the system- Dispersion


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But first, a word from our sponsors. . .

ssss

Agilent Technologies Lightwave Training

Understanding Lightwave Technology

Understanding Optical Passive DeviceCharacterization

Understanding Optical Transmitters andReceivers and Their Characterization

Understanding DWDM

Optical Spectrum Analysis/ OSA UsersCourse

Characterizing Polarization Effects

Eye Diagram Analysis

TDR in High-Speed Digital DesignBit Error Rate Analysis

Digital Communications Analyzer UsersCourse

Back to Basics in OpticalCommunications Technology

Understanding Optical Networking

The Elements of Lightwave Technology

TodaysPresentationApre-requisiteforothercourse

s


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Todays Presentations

Geometric Optics: The optic fiber as a waveguide

Physical Optics and Passive Component Characterization

Light Transmission, Reception and Modulation: Active ComponentCharacterization

Optical Signal Amplification and DWDM Dispersion: The evolution of the index of refraction with wavelength

and polarization

Characterizing the Optical Network


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High Speed Networking

Why were all here. . .


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Networking at High Speed

Pulses of infrared lightguided through glass fibers

move huge blocks of data

long or short distances

insensitive to electrical interference

cheap and light weight

Telephone Data Cable TV

Long distances WAN - Wide Area NetsShort Distances LAN - Local Area Nets

In between MAN - Metro Area Nets


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High Speed Networking is Accelerating

1995 2000 2005 2010 Year

10

20

30

40

50

RelativeLoad

1990

Total: 35%/year

Voice: 10%/yearSource:


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Optical Networking - The DWDM Forest

Dispersion

Compensator

DispersionCompensator

Other

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Data

1

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demultiplexer

multiplexer


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Geometric Optics

The index of refraction

Total internal reflection

The optic fiber as a waveguide

Single and multi mode fibers

Cladding

Primary coating(e.g., soft plastic)

Core

SiOGlas

s2


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Fibers



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Optic Fibers and the Index of Refraction, n()

The index of refraction of a dielectric is given by

At the boundary of two media, incident light isreflected or transmitted (a.k.a., refracted),

The relationship between the angles of incidence

and transmission is given bySnells Law:

)sin()sin( transcladdinginccore nn =trans

cladding

n

ncore

inc

medium

vacuum

ccn )(


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Optic Fibers Contain Light by

Total Internal ReflectionAt incident angles larger than a critical angle, all light is reflected - contained:

Typical values:

Bending cables losses

Only light injected in a cone of some angle smaller than NAwill be contained by the fiber

The spec for this is numerical aperture, NA:

claddingcore nn >

22sin cladcoreNA nnNA =

transinc


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Conducting Waveguide Analogy

Optic Fibers are dielectricwaveguidesFirst, consider conductingwaveguides:

Conducting

wave guide

Boundary Conditions:ETcond = 0 and B cond = 0

give . . .

The cutoff wavelengths, or frequencies, determine

the modes of propagationSingle Mode (SM) a< < 2aMulti Mode (MM) < a

For a given range of wavelengths there areSingle and Multi Mode waveguides

- single mode doesnt mean single wavelength

a

1 = 2a

2 = a

3 = 2a/3

Cutoff

wavele

ngth

s


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Modal Dispersion:

Waveguide dispersion arises from the dependence of the group velocityon the frequency, , and the mode-cutoff frequency cutoff= 2c/cutoff.

Modal dispersion occurs when a pulse is composed of waves of morethan one mode.

The different modes travel at very different, speeds Modal Dispersion

21

2cutoff

= cgroup

0

0.5

1

Vgroup/c

1

2

3

Conductin

g

waveguide


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Optic Fibers are Dielectric Waveguides

Boundary conditions:Smooth decay of the electric field atthe core/ cladding boundary

Claddingd

dCore

1 > 2dCore

2 > dCore

3 > 2 dCore /3

Single Mode: 1 < < 2

e.g., for 1.5 m,

dCore 10 m.

Single mode cutoffwavelength is larger than

the fiber core diameter

2

2

0022

tn

= EE

)(

)(ztj

erEE

=

Transverse

standingw

ave Longitudin

al

travelingwa

ve


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Multi Mode Fibers

Modal Dispersion In Multi Mode fibers suffer Modal Dispersion from

Bitrate x Distance product is severely limited!

100/ 140 m Silica Fiber: ~ 20 Mb/ s km0.8/ 1.0 mm Plastic Optical Fiber: ~ 5 Mb/ s km

Single mode fibers do not suffer modal dispersion!

2

2

mode

1~

cvgroup


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Fiber Structure

Multi-mode: 100/ 140 or 200/ 280 m

Single Mode: 9/ 125 or 10/ 125 m

n

r

1.465

1.460

RefractiveI ndex ( n)

Diamet er ( r )

Cladding

Primary coating

(e.g., soft plastic)

Core

1.480

1.460

100m

140m

SiOGlas

s2

NA = 0.24TIR= 80

NA = 0.12

TIR

= 85


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Couplers

The solution includes the smooth decay of E in the cladding This evanescent wave travels along with the guided wave Energy travels along the cladding and it s easy to get it out

Join two fibers together - a double wave guide

Light can tunnel from one core to the other - a coupler

This is how couplers work Waves tunnel from one core to the next

Core CoreCladding Cladding


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The Directional Coupler

Single Waveguide with Two Cores

Solving the wave equation with two single mode

cores gives . . .A transverse wave that oscillates between cores

End Side

d

Incident signal power oscillates back

and forth between the two cores as thelight propagates the length of thecoupler

The distance along the fiber where the signal is in a given core depends on . . .

Wavelength

The distance between the cores

The geometry of the two original single mode fibers


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Wave Coupling Splitters

The length of a directional coupler can be tuned so that incident light of agiven wavelength will exit the coupler in a specific core

L

1, 2

2

1

a

b

c

d

Couplers can be designed to

demultiplex incoming signals In reverse the demultiplexer is a

multiplexer

With different single mode fibersand geometry couplers can bevery selective with narrowchannel spacing.

The wavelength dependence canalso be reduced over ~ 100 nm togive a wavelength independent3 dB coupler.


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Fibers



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Physical Opticsand

Passive Component

Characterization


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Physical Optics

Electromagnetic waves


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Electromagnetic Spectrum

Frequency

RFRadar

InfraredLight

VisibleLight

Ultraviolet

X-Rays

Wavelength1 Mm 1 km 1 m 1 mm 1 nm1 m

1 kHz 1 MHz 1 GHz 1 THz 1 EHz1 PHz

| U | L | C | S | E | O | LAN

Frequency

Wavelength1600

300

1000 800nm

4001400 1200

THz200 250 400

Networking wavelength bands


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Waves

Describe light with = wavelength, = frequency 1500 nm 200 THz

= c = 299,792,458 m/ s

30 cm/ ns (1 ft/ ns)

and reserve

f= modulation frequency

Magnetic Field

Strength, B

Electric Field

Strength,E


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The relationship between

optical frequency bandwidth, andwavelength linewidth,

Let frequency bandwidth beand wavelength linewidth be

Then since

or

The relationship between

bandwidth and linewidth is

or, equivalently

c=

c=

= 2c

=2

c


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Recipe for creating electromagnetic waves:

= CA dddtd

n lBSE

00

2

=CA dddt

dlES

B

The strength of the magnetic field is small sowe only consider the electric field.

Changing Electric

Field, E

Changing Magnetic

Field,B

2

2

0022

tn

= EE

2

2

00

22

tn

=

BB

Electromagnetic Waves

Induction


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Electric Field Components

Ey

Ex An E-Field is the vector sumof the components Ex and Ey

I t d ti t P l i ti


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Introduction to Polarization

Linear PolarizationProjection of E is a line

Circular PolarizationProjection of E is a circle

Ey

Ex

Ey

Ex


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Poincar Sphere

Representation of PolarizationGraphical representation of stateof polarization using Stokesparameters (S1, S2, S3)

Left-handcircularpolarization

(0,0,-1)

S1axis

S2axis

S3

axis

45 degree linearpolarization (0,1,0)

Right-handcircular

polarization(0,0,1)

Vertical linearpolarization (-1,0,0)

C h


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Coherence

Coherence the phase relationship of waves

Lc

Lc

Coherent wavescomponents of coherent waves havewell defined phase relationships.

Incoherent waves

components of incoherent waveshave random indeterminatephaserelationships.

C h Ti d C h L th


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Coherence Time and Coherence LengthCoherence time (T

C)

Average time for the wave train to lose its phase relationships

Coherence length (LC)

Average distance over which superposed waves lose their phase relationships

There is a Fundamental Relationship between Coherence and Bandwidth

1. The bandwidth determines the coherence length and time,Tc 1/(4), Lc c/(4)

2. A minimum optical bandwidth is required for a pulse of duration T, 1/(4T)Restricts the spacing of DWDM signals for given rates

CC TcL =

41

CT

Short coherence length broadband source

Coherence and Optical Bandwidth


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Coherence and Optical Bandwidth

ExamplesLight Bulb:

LED:

DFB Laser:

m5

ps02.0

THz50

nm500WidthLineSpectral

C

C

OpticalL

T

BW

m50

ps2.0

THz5

nm50WidthLineSpectral

C

C

Optical L

T

BW

m30

ns100

MHz10

pm1.0WidthLineSpectral

C

C

Optical L

T

BW

Interference


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Interference

Interference = effect of adding waves from different sources

Constructive Interference Destructive Interference

Conditions for interference:

waves must be coherent andhave the same polarization

coherent sources add in phase

Incoherent sourcesadd in power: [ ] +==

kkk

kk

tEtPtP2

Total)sin()()(

2

Total )sin()(

+= kkk tEtP

+ =

+ =

Ph i l O i


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Physical Optics

Interference and Diffraction

Interference Based Technologies


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Interference Based Technologies

Interference

Fiber Bragg Grating

Optical Mux/ Demux

Optical Spectrum Analyzer

dd'

n n'

Thin Film filters

Wavelength Meter



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p g

PassiveComponents



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Interference Between Two Sources


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Interference Between Two Sources

Constructive Destructive

Waves

Interference in One Dimension


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Interference in One DimensionThe Michelson Interferometer

Inputbeam

Fixed referencemirror

Movingmirror

Interferencefringe pattern

When the mirror moves,the interference pattern alternates

light (constructive fringes) anddark (destructive fringes) on the detector.

The distance between fringes is related tothe wavelength of light

1/ 2 silveredmirror

The Wavelength Meter


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The Wavelength Meter

With a reference beam the Michelson interferometer can measureabsolutewavelengths

with an accuracy of 300 fm and resolution bandwidth of 30 pm

e.g., Agilent 86122

Wavelength

Reference

UnknownSignals Fixed Mirror

Signal

Processing

Moving Mirror

FFT the fringe pattern signal spectrum

The Fabry Perot Etalon d


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The Fabry Perot Etalon d

/2 /4

A resonant cavity containingmultiple reflections/ transmissions

If d= / 2 thenreflections and transmissionsinterfere constructively

If d= / 4 theninterference is destructive

Which makes a filter

Its also the foundation for a LASER, as well see soon.

Thin Films


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Thin Films

Series of Fabry-Perot Etalons with different properties

Anti-reflective coatings- must be centered at some wavelength

Selective transmission/ reflective coatings

Many possibilities:

d

d'

n n'

Layers Substrate

IncomingSpectrum

Reflected

Spectrum

TransmittedSpectrum

Tunable Fabry-Perot Filters


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Tunable Fabry Perot Filters

Filter shape

Repetitive passband with Lorentzian shapeFree Spectral Range FSR= c/ 2 n L (L: cavity length)Finesss F = FSR/ BW (BW: 3 dB bandwidth)

Typical specifications for 1550 nm applications

FSR: 4 THz to 10 THz, F: 100 to 200, BW: 20 to 100 GHzInsertion loss: 0.5 to 35 dB

Fiber

Piezoelectric-actuators

Mirrors

Optical Frequency

FSR

1 dB

30 dB

The In-Fiber Bragg Grating (FBG)


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e be agg G at g ( G)

A simple filter and a cornerstone of the Optical Revolution

To make a stretch of fiber into a grating:

scratch the fiber with ultra-violet light

Waves are transmitted and reflected at each scratch

Regular intervals between gratings reflect one wavelength- a notch filter

Cladding

Primary coating(e.g., soft plastic)

Core

SiOGlas

s2

In Fiber Bandpass and Chirped Filters


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p p

Band Pass Filters

Combine simple Fiber Bragg Gratings (FBG) to form Etalons tuned to

different wavelengths and make in fiber Fabry-Perot bandpass filter

Overlap gratings tuned to different wavelengths - Moire filter

L

Chirped Filters

Uneven grating spacing can be used in different applications

- e.g., compensation of Chromatic Dispersion (more later)

Interferometric Filters


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Combined Technology: Coupler + Interferometer + FBG

2 is reflected by the gratings

The Coupler is chosen so that the 2 couples to 2 on reflection

Only 2 emerges from 2

The second coupler is wavelength-independent to form a Mach-Zehnderband pass filter.

Make mux/ demux, add-drop node, etc

1

2

3

2

1,

3, . . .

1,

2,

3, . . .

Arrayed Waveguide Grating


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y g gGeneralized Mach-Zehnder Interferometric Filter

An MZI filter with wavelength dependent coupling

1 x n mux/ demux

Lower loss, flatter passband

+ + +

Multiport coupler Multiport coupler

Array of waveguides shifts the relative phases of each wavelength resulting in constructiveand destructive interference of different wavelengths at different outputs

Polarization Based Technology


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Low loss in forward direction - 0.2 to 2 dBHigh loss in reverse direction - 20 to 80 dB

Reflectedlight

gyThe IsolatorMain application:

To protect lasers and optical amplifiers from reflections thatcan cause instabilities

Input light is polarized and transmitted through a series of polarizors Series of polarizors reject light of all polarizationsin the back direction

Input l ight

Add Drop Nodes and Circulators


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Combined Technology: Coupler + Isolator + FBG

Circulator based Add Drop Node (ADN)

Add iDrop i

Three isolated ports:

Port 1 port 2 Port 2 port 3 Port 3 port 1

Filter reflects iAdd / Drop

Common Passband

Thin film based ADN

Monochromators and Optical Spectrum Analyzers


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Two Dimensional Gratings

Transmission grating

Reflection grating

Interference From Gratings


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Detector

Detector

Two Slits

Five Slits

More slits

more interference

With more interferencepurple red and blue

Spectrum is Resolved


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-3 -2 -1 0 1 2 3

-3 -2 -1 0 1 2 3sin() in units of /b

Increasing the number of slits

50 slits

1000 slits

Increases the spectral resolution

Wavelengths can be resolved withamazing accuracy: 60 pm

Grating Based Technologies


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Gratings are the basis for many tools and components: Monochromators

Notch/ passband filters,

Multiplexers/ demultiplexers Optical Spectrum Analyzers

Transmitting gratingsand

reflecting gratings

Grating Based Optical Spectrum Analyzer

S i M h t


56/178


Rotate grating to shinedifferent color, ,

through aperture

Grating angle, , determines spectralline shining through aperture

ADC Processor

Amplifier

Display

Input

Photodiode

Aperture

Sweeping Monochromator

Optical Spectrum AnalysisE l


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Examples

Optical Amplifier TestingGain, Noise Figure, tiltet cetera

WDM Components50 GHz Mux, Filters,Add/ Drop Components

WDM SignalsSignal to noise for

channel spacingsas low as 50 GHz

Source Testing

FP, DFB lasersAmplitude, SMSR

PerformanceAccuracy, = 0 10 pmResolution, ~ 40 pmDynamic range ~ 70 dB

Physical Optics


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Physical Optics

Component Characterization

Filter Characteristics


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i-1 i i+1

PassbandCrosstalk Crosstalk

Passband

Insertion loss

Ripple Wavelengths

(peak, center, edges)

Bandwidths (0.5 db, 3 db, ..)

Polarization dependence

Stopband

Crosstalk rejection

Bandwidths (20 db, 40 db, ..)

Total Insertion Loss


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A measure of the loss of light within an optical component.

DUTWithout

DUTWith

P

PIL 10log10)dB( =

Devi ce

Reference

Source DeviceUnderTest

PowerMeter

Reference Path

Filter Transmission Spectrum (Insertion Loss)OSA M th d


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OSA Method:Broadband Source + -Selective Detector

Fast Sweep High Dynamic Range Good Sensitivity Incoherent Light

Notch Filter

Source spectrum Detector sensitivityand resolution

Transmitted spectrum

Test Solution


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8614x Optical Spectrum Analyzer series

Built in applications to characterize

Sources, DWDM signals,Passive Components,Amplifiers

Built in Broadband Sources

10 pm absolute accuracy

2 pm repeatability

60 pm resolution bandwidth

70+ dB dynamic range

600 nm 1700 nm

Filter Transmission Spectrum (Insertion Loss)TLS Method: Selective Source + Broadband Detector


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TLS Method: -Selective Source + Broadband Detector

Notch Filter

P

Parameters to Test Center 3 dB Bandwidth Ripple

Isolation

Devi ce

Reference

)(

)(log10 10

DUTWithout

DUTWith

P

PIL =

Test Solutions


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86082Wavelength DomainComponent Analyzer

Tunable Laser System/Power Meter

+ Photonic Foundation Library

Fast filter characterization resolution: < 1 pm

Speed: > 2 sweeps/ s Range: 1260 1640 nm Vertical accuracy 0.06 dB

Configurable to perform all

parameter tests Scaleable to multi-channels resolution 0.1 pm Low SSE

Insertion Loss as a Function of WavelengthSwept Insertion Loss


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Swept Insertion Loss

Two standard approaches:

1.Use a Tunable Laser Source (TLS)

Worry about back scattering interference issues

2.Use a Broadband source and an OSA Short coherence length of source no interference issues

Must calibrate and subtract baseline spectrum Need high spectral density (energy at each wavelength)

Reference p/ n 5980-1454E:

State of the art characterization of optical components for DWDM applications

Return Loss


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Total Return loss

A measure of the light reflected by a componentreference

reflected

P

PRL 10log10=

Device Termination

LightInput

Attenuator

Power Detector

Angled

OutputDirectionalCoupler

DUT

Return Loss MeterModule (81534A)

Insertion/ Return Loss Measurement Subtleties


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Beware of multiple reflections!! If multiple reflections occur within a distance less than LC

then there will be interference fringes on the detector

uncertainty in RL up to 100%

Avoid using coherent beams

LED or Tungsten lamp ideal, but too low spectral energy density

for most cases

But RL() may be desired and may depend on and

a narrow source has a large LC Common to use a Fabry-Perot laser

high power, with sidebands to mit igate interference,

still . . . LC~ meters

Understand the device and the source

Polarization Dependent Loss


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Recall Polarization describes theorientation of the electric field

The attenuation of light in fibers and network elements variesaccording to polarization.

Polarization Dependent Lossthe variation of attenuation with polarization.

Monitor output power of DUT while varying polarization to get

min

max10log10)dB(

P

PPDL =

Polarization Dependent Loss


69/178


Insertion loss with polarization control:

Source

Device

UnderTest

(DUT)

Power Meteror

OSA

OpticalIsolator

PolarizationController

(PC)

Reference Path

Need: Constant power into DUT Polarization Controller (PC)

either provide all states,or use a Mller matrix technique

Polarization independent power meter/ OSA

Look for PDL < 0.1 dB

8169 Polarization

Controller

min

max10log10)(

P

PPDL =dB


Passive1


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Passive

Components



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demultiplexer

multiple

xer


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LightTransmission, Reception,and

Modulation:

Active ComponentCharacterization


72/178


Modulation

Putting information into pulses of lightInternal and external modulators

1

r


Modulators


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xer

ModulationEncoding Data into Light Pulses


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g g

Extinction ratio: typically, about 10 dB.

Average power:

,"0"

"1"

Logic

Logic

P

PE=

"0""1"2

1

LogicLogicAvg

PPP +=

"0"

"1"

10log10)(Logic

Logic

P

PE =dB

0 1 1 0 0 1

Time

Plogic "1"

Plogic "0"

Pavg

P (mW)

NRZ - Non Return to Zero and RZ - Return to Zero Modulation

Modulation Techniques

Encoding data into binary pulses


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Encoding data into binary pulses

Direct modulation:modulate LASER input power

LASER chirp

1.5 Mb/ s - 2.5 Gb/ s

Indirect modulation:

Indirect or phase modulation Modulation with absorption or

Modulate with interference

Constructive 1, destructive 0

AM sidebands dominate line width

Can approach = 1/(4bit)

10 Gb/ s - 40 Gb/ s 200 Eb/ s

DC

RF

DC MOD

RF

Indirect ModulationMach-Zehnder Principle


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p

Split the beam and vary the optical path lengths to get:

Logic 0 - destructive interference - optical path length difference of (2n-1) / 2

Logic 1 - constructive interference - optical path length difference of n

Vary path lengths tochange relative phase

Split beam

Merge beam

Destructive interferencelogic 0

The relative phasechanges!

An external electric field applied to some crystals, e.g., LiNbO3, changes the index

of refraction, n = n(E)1. Use an RF modulation signal to apply a voltage across the crystal2. Varies the index of refraction of each path3. Change the path lengths to get desired interference

Modulate the light signal!

Indirect ModulationElectro-Absorptive Modulation


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p

A solid-state based shutter

Pass a continuous wave through a diode

Logic 1 - No applied bias,larger band gap

light transmits through

Logic 0 - High reverse bias,smaller band gap

light is mostly absorbed

Energy

Conduction Bands

Valence Bands

Continuous wave input

gapEh > gapEh


78/178


Lasersection

Modulation

section

DFB laser with externalon-chip modulator

Polarization sensitive, need correct launch

Mach-Zehnder Modulator

Electro-Absorptive Modulator

Atomic Physics:


79/178


Light Generation

Electromagnetic radiation

Light Emitting Diodes (LED)

Light Amplification by Stimulated Emission ofRadiation (LASER)

1r


Optical


80/178




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Transmitters

The Premise for Radiation

All radiation results from the acceleration of a charge


81/178


An LRC circuit An oscillating dipole:

An atomic transition

+

-

+

+

2p state

to a

1s state1s

2p

Spontaneous Emission


82/178


Light is spontaneously emitted when an electron decays from ahigher to a lower energy state.

In an atom In a semiconductor

Energy

Conduction Bands

Valence Bands

Energy

Light Emitting Diode (LED)


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Datacom through air & multimode fiberInexpensive(laptops, airplanes, LANs)

Key characteristicsMost common for 780, 850, 1300 nmTotal power up to a few WSpectral width 30 to 100 nmCoherence length 0.01 to 0.1 mmNo specific polarization

P -3 dB

P peak

BW

Energy

SpontaneousEmission

Conduction Bands

Valence Bands

Data in

LASERLight Amplification by Stimulated Emission of Radiation


84/178


Requirements for LASER:

Confine light in a resonant cavity toset up standing waves

Excite more electrons to higher energy levels

More photons from stimulated emission thanfrom spontaneous emission

population inversionStimulated Emission will resonate in the cavity

amplification

Mirrors confine s to2L/n& also reject non-perpendicular light

L

Stimulated Emission light that ismonochromatic (same wavelength)coherent (in phase)polarized

Fabry-Perot (FP) Laser


85/178


Reflective coatings along cavity allow onlyn/ 2 wavelengths through

Multiple longitudinal mode (MLM) spectrum Classic semiconductor laser

First fiberoptic links (850 or 1300 nm)Today: short & medium range links

Key characteristicsMost common for 850 or 1310 nm

Total power up to a few mWSpectral width 3 to 20 nmMode spacing 0.7 to 2 nmHighly polarizedCoherence length 1 to 100 mmGood coupling into fiber

P peak

I

PThreshold

Distributed Feedback (DFB) Laser


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Sidemodes filtered out Single longitudinal mode (SLM) spectrum High performance telecommunication laser

Most expensive (difficult to manufacture)Long-haul links & DWDM systems

Key characteristicsMostly around 1550 nmTotal power 3 to 50 mwSpectral width 10 to 100 MHz

(0.08 to 0.8 pm)Sidemode suppression ratio

SMSR > 50 dBCoherence length 1 to 100 mSmall NA ( good coupling into fiber)

Ppeak

SMSR

Comparison of FP and DFB Lasers


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1300 13101305 nm

REF: 0.00 dBm

-90

-70

-50

-30

-10

10

dBm

1540 15501545 nm

REF: 0.00 dBm

-90

-70

-50

-30

-10

10

dBm

Power versus wavelength

Fabry-Perot Laser DFB Laser

Vertical Cavity Surface Emitting Lasers

Di t ib t d B R fl t (DBR) Mi


88/178


Distributed Bragg Reflector (DBR) Mirrors

Alternating layers of semiconductor material

40 to 60 layers, each / 4 thick

Key properties

Wavelength range 780 to 1310 nm Gigabit ethernet

Spectral width < 1 nm

Total power > -10 dBm

Coherence length: 10 cm to 10 m

Numerical aperture: 0.2 to 0.3

active

n-DBR

p-DBR

External Cavity/ Tunable LasersLow Source Spontaneous Emission(SSE) output

A il t M i


89/178


High Poweroutput

Adjust angle to choosereflected wavelength

Adjust cavity length to chooseresonant wavelengths

Agilent Magic

n/2

Grating

High Power

Low SSE

Tunable Laser System

The Agilent TLS systems for the 8164 mainframe


90/178


1260 < < 1640 nm in three different modules Two Power outputs:

+5 dBm peak (high power output)

- 6 dBm peak (low SSE output)60 dB signal to SSE ratio

10 pm absolute wavelength accuracy 2-3 pm typical relative wavelength accuracy, mode-hop free

0.1 pm wavelength resolution

Other Light Sources


91/178


Need for small coherence length high power light sources:

White light source Specialized tungsten light bulb Wavelength range 900 to 1700 nm, Power density 0.1 to 0.4 nw/ nm (SM), 10 to 25 nw/ nm (MM)

Amplified spontaneous emission (ASE) source Noise of an optical amplifier without input signal Wavelength range 1525 to 1570 nm Power density 10 to 100 w/ nm

SummarySemiconductor Light Sources

Data in


92/178


Stimulated Emission(monochromatic & in-phase)

LASERs

Lasers Require Stimulated Emission Population Inversion ConfinementE

nerg

y

LEDs

Spontaneous

Emission

I

PThreshold

More electrons in upper energylevel than lower(more photons emitted thanabsorbed)

Mirrors confine s to2L/ n & also rejectnon-perpendicularlight

L

Parameters to TestCharacterization of Transmitters

Output Power


93/178


Output Power Power meter

Wavelength

Optical Spectrum Analyzer, accuracy ~ 15 pm, 50 pm Interferometer-based wavelength meter, accuracy ~ 5 pm, 0.3 pm

Linewidth, chirp, modulation effects, ultra DWDM structure High Resolution Spectrometer,

accuracy

~ 15 pm, 8 fm

Distortion, Relative Intensity Noise (RIN), harmonic noise,Spontaneous emission/ recombination relaxation effects

Lightwave Signal Analyzer

Electrical-Optical Response, BandwidthRecombination time scale affects modulation properties

Lightwave Component Analyzer

Transmitter Linewidth MeasurementWith a High Resolution Spectrometer

O i l H d


94/178


Optical Heterodyne

Measure transmitter linestructure with terrificdetail

resolution: 8 fm

Transmitter

Reference

Interferometer

Chirp/ FM MeasurementWith an HRS

Chirp A change in the optical


95/178


Chirp = A change in the opticalfrequency caused by directmodulation of the laser

Direct Modulation

Transmitter

Reference

Interferometer

Modulator

Chirp/ FM MeasurementWith an HRS

Indirect Modulation with a


96/178


Indirect Modulation with aMach Zehnder modulator

Transmitter

Reference

Interferometer

Modulator

(0.2 nm span)

High Resolution Optical SpectrometerAgilent 83452A

Optical Heterodyne and high resolution spectrum analysis


97/178


Optical Heterodyne and high resolution spectrum analysis

Linewidth, laser spectral symmetry, modulation spectrum,relaxation oscillations, close-in sidebands, UltraDWDM spectra

Resolution: better than 80 fm (10 MHz)Dynamic Range: 60 dB

Ultra DWDM spectrum

Lightwave Signal Analyzer

Essentially a wide-bandwidth calibrated OE + Electrical SpectrumAnalyzer


98/178


Essentially a wide bandwidth, calibrated OE + Electrical SpectrumAnalyzer

Measures average optical power vs frequency, (over modulationfrequency range!)

Harmonic Noise

Relative Intensity NoiseNoise from the Transmitter

Relative Intensity Noise [ ]12)(1 P


99/178


Relative Intensity Noise(Incidental Amplitude Modulation)

Measures laser fluctuations at modulation frequencies

The power variance spectral density , (P)2/BW, is the fluctuation of

power observed in the interval fmodto fmod+dfmodper unit modulationbandwidth, dfmod.

After electrical conversion (recall (optical power)2 (electrical power) ),measure RIN from the electrical spectrum analyzer:

[ ]1-HzRIN2

)(1

avgP

P

BW

=

BWRINii avgRIN

Measuring Relative Intensity NoiseWith an LSA

[ ]dB/ HPRIN 1)(l102


100/178


DFB Laser

[ ]dB/ HzBWP

PRINavg

1)(log102

Agilent 71400

Atomic Physics:Light Detection


101/178


Solid state photon countersresponsivity

Photo Diodesefficiency, gain, dark current

Light Detection

Data

1

2.

multiple

xer


Optical

Receivers


102/178




OtherSegment

OtherSegment

Other

Segment

OtherSegment

LAN

CrossConnect

(Switch)

.

.

n

Data

1

2.

.

.

n

demultip

lexer

m Receivers

Light Detectors

C d ti Photons are absorbed in an


103/178


Valence

Bands

Conduction

Bands

Energ

y

Photons are absorbed in anintrinsic layer of semiconductor create e - hole pairs

Apply a reverse-bias potential photocurrent

Quantum Efficiency = number of electrons created per photon, ()

Responsivity = photocurrent per unit of optical power (A/ W)

hc

e

P

iR

)(

)(

)()( ==

Optical

Photo

Photo Diodes

PIN (p-layer, intrinsic layer, n-layer)Highly linear low dark current


104/178


(p y , y , y )Highly linear, low dark currentDetector is followed by a Transimpedance

Amplifier

Avalanche photo diode (APD)Intrinsic gain up to x100 lifts the optical signal

above electrical noise of receiver

Strong temperature dependence

Main characteristics

Quantum efficiency (electrons/ photon)Dark currentWavelength dependence, responsivity

n+

Bias Voltage

A

PD

Gain

Material Aspects of PIN Diodes


105/178


Silicon (Si)Least expensive

Germanium (Ge) Classic detector

Indium gallium arsenide (InGaAs)Smooth responsivityHigh speed

Notice the sharp wavelength rolloff- due to E

band gap

> h= hc/

0.7 0.9 1.1 1.3 1.5 1.7

90%

70%

50%

30%

10%

Quantum

efficiencies

Si

InGaAs

Ge

Wavelength (m)

Responsivity(A/W)

hc

eR

)()( =

Quantum efficiency

Noise

Thermal (Johnson) Noise is the intrinsic noise from the load resistor in

the photodiode circuit


106/178


R = Load resistancek= Boltzmanns constant = 1.38 10-23 J/ KTin Absolute,B = modulation bandwidth

R

BkTi rmsTherm

=

4

Dark current, id, is the current generated in the absence of light

Thermally or spontaneous diffusion generated charge in the photodiode.Typical values at T= 300 K, Si: 1 - 10 nA, Ge: 50 - 500 nA, InGaAs: 1 - 20 nA

Shot Noise, (quantum noise) is from the random arrival time of electronsin the detector- Shot noise causes the photo-current to fluctuate about amean, iavg and includes the dark current.

- Trouble with small signals in noisy environments- Shot noise limited means shot noise > thermal noise

Biiei davgrmsshot )(2 +=

Receivers:Sensitivity and Modulation Bandwidth

Hi h i i i i l / d d


107/178


High sensitivity requires a large/ deep detector Need to detect each photon = increase quantum efficiency

create more electron-hole pairs and catch each one

Large Bandwidth requires a small/ shallow detector Need to finish detection process fast to accommodate a short pulse

Larger the detector the longer the relaxation time of the detection process

Tradeoff between sensitivity and bandwidth:Larger bandwidth, lower sensitivity

Example: Sensitivity Modulation rateLightwave Clock/ Data Receivers: Agilent 83446A -28 dBm 2.5 Gb/ s

Agilent 83434A -16 dBm 10 Gb/ s

Typical Power Levels

Transmitter:

6 to +17 dBm (0.25 to 50 mW)Optical Amplifier:


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Optical Amplifier:+3 to +20 dB (gain of 2 to 100 times input)

Difference between optical and electrical power:Optical power is converted to photocurrent,

iphoto = PopticalG, G = conversion gain, typically 0.4 - 0.9 A/ W,so

in dB, a change in Poptical means twice that change in Pelectric

RGPPRiP opticalelectric22 )(==

(dB)(dB) opticalelectric PP = 2

iOptical

fOptical

ielectric

felectric

electricP

P

P

PP

(dB) log20log10 ==

Active Component CharacterizationTransmitters, Receivers, Regenerators

Measure Electro-optic response


109/178


Fixed wavelength, measure response vs fmod

Vector network analyzer with precisely calibrated optical interface

Measures E/ O, O/ O, O/ E, E/ E devices

Gives 3 dB bandwidth

Flatness of frequency response

RF Receiver& Display

O/ O

O/ EE/ OE/ ERF

Lightwave Component AnalysisSource Responsivity = Optical power

produced (W)/ electrical currentsupplied (A)

Receiver Responsivity = Electrical

current produced (A)/ optical powersupplied (W)


110/178


pp ( ) pp ( )

Modulation Rate

Modulation Rate

W/ A A/ W

=

in

out

s

I

PR 10log20(dB)

=

in

out

r

P

IR 1020log(dB)

Typical Laser Frequency Response Typical Photodiode Frequency Response

Frequency Response and Modulation BandwidthLightwave Component Analyzers


111/178


8702300 KHz - 3 or 6 GHz 870350 MHz - 20 GHz 8603045 MHz - 50 GHz

Data

1

2.

.multiple

xer


Active

ComponentsModulators


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OtherSegment

OtherSegment

Other

Segment

OtherSegment

LAN

CrossConnect

(Switch)

.

n

Data

1

2.

.

.

n

demultiplexer

Modulators,Transmitters,Receivers

Optical Signal


113/178


Optical SignalAmplification

andDWDM

Atomic Physics:Optical Amplification


114/178


Raman scattering

Optical pumping

Optical Amplification

Signal Attenuation

OH absorption

O-band

E-band

S-band

C-band

L-band

U-band

Networking wavelengthbands


115/178


P

owerAbsorbed(dB/

km)

1200 1400 16001000 1800

(nm)

UV-absorption

IR-absorption

RayleighScattering

Typical fiber attenuation 0.2 dB/ km

amplification every 25 - 50 km(Not very good fiber)


116/178

Spontaneous and Stimulated Emission

Spontaneous emissionLight is spontaneously emitted

h l d

Stimulated emissionIncident light stimulates the decay of an electron.

Li h i i d h i id i l i id li h


117/178


when an electron decays to a

lower energy state.

Light is emitted that is identicalidenticalto incident light.

Same wavelength, direction, polarization, and phase

Twice as much lightoutgoing as incident gain of two

Raman Scattering

When a bound electron is excited to some energy Eex and

decays by emitting light of energy Elight , with


118/178


Elight Eex it is called Raman scattering

E

lightE

ex

Lifetime of the excited state is the relaxation time~ 1 ms - metastable (Erbium)< 1 ns - unstable (SiO2)

Optical Amplifiers - Erbium Doped Fiber Amplifier

1. Dope a fiber with erbium 2. Pump energy into the fiber


119/178


3. Transmit and amplify the signal

Amplified signalSignal

Pumplight

Amplified Spontaneous Emission(ASE) noise!

Erbium Doped Fiber Amplifiers

Erbiumdoped fiber

LASER pumping energyinto Er doped fiber


120/178


p

Incoming

signal

Outgoing amplified signal

plus

Coupler

ASE noise

Two major characteristics:GainNoise

Amplifier Input/ Output Spectra

Signal spectrum Amplifier Spectrum

Amplified Signal

Spectrum(Amplified Signal +


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Signal spectrum Amplifier Spectrumwith noinput

Reduced ASE +Amplified Source noise)

Output Spectrum

+10 dBmAmplified signal

spectrum- the input signal


122/178


ASE spectrumwith noinput

1575 nm

-40 dBm

1525 nm

saturatestheamplifier)

The relaxation time of Er causes a ~ 1 ms time scale for the ASEbackground to shift between levels with and without a signal

Other Optical Amplifier TechnologySemiconductor and Raman Optical Amps

Same physical principle but different energy structure


123/178


Other Dopants: xDFA

50 nm3 dB

Wavelength

Gain(dB)

Raman AmplifierUse vibrational energy states of SiO2 instead of atomic states of a dopant

Raman scattering among vibrational statesPump laser through the whole fiber- pump energy is very high- states are not metastable

Gain region over ~ 100 nm centered about 13 THz above the pump frequency

Semiconductor Optical Amplifier (SOA)- Stimulated emission in of the signal as ittraverses an excited semiconductor

- Pump to high energy states by bias current orexternal pump laser

- Tend to be very noisyGain region can be tuned with band gap

Optical Amplifiers - Summary


124/178


EDFA- Material is doped with Erbium- Material is pumped with

1480 or 980nm- Good for 1550nm signals

Pump Light

Signal (pre-amp)Signal (post-amp)

Raman Amplifier- Whole undoped fiber is pumped- Wide signal -range- Amplification throughout fiber length- High pump power required

DWDMDense


125/178


DWDMDenseWavelength

DivisionMultiplexing

Introduction toDense Wavelength Division Multiplexing

Use many different wavelengths on one fiber


126/178


single mode or multi-mode fibers

Combine different wavelengths to increase data rate

e.g., 125 s at 40 Gb/ s each 5 Tb/ s (Alcatel, Feb-2002)

New and growing technology requiring

mux/ demux and optical switch technologies

peculiar dispersion properties

worry about noise at different s

worry about optical crosstalk - four wave mixing

RL +0.00 dBm

Amplified Dense Wavelength Division MultiplexSpectrum


127/178


1565 nm

5.0 dB/ DIV

1545 nm

Amplified

SpontaneousEmission (ASE)

Channels: 16

Spacing: 100 GHz (~ 0.8 nm)

Basic DWDM Design

WavelengthsPower levels

RS RS


128/178


Signal-to-noise ratios

2

n

1

n-1

2

n

1

n-1

S

Rm1

Sdn Rn

S1

RS R

R1Sd1

Sn Rmn

Amplified DWDM SpectrumParameters to Test


129/178


P

Parameters to Test

Channel Gain Noise Figure

Center

Span Tilt Gain Flatness

Channel Spacing

Amplifier Characteristics

Signal

Signal

out

P

PG =


130/178


out

in

SNR

SNRFigureNoise =

inP

Gain = 0 50 dB

Noise Figure = 3.5 12dB= Output Spectrum of Amplifier without input

= Input spectrum to Amplifier= Output spectrum from Amplifier

Interpolated Source Subtraction (ISS) Method

Gain & Noise Figure

1. Measure a constant wave input spectrum

2. Measure the amplified constant wave output spectrum


131/178


EDFA

Optical Spectrum Analyzer

Power Meter

Calibration Path

Laser Source

3. Interpolate across the signal to estimate the background at the signal

wavelength separate signal and noise

Time Domain Extinction (TDE) Method

SignalSpectrum

Gain & Noise Figure

1. Measure output withsignal gated off


132/178


EDFA

Optical SpectrumAnalyzerDFB/ TLS

Gate

Gating ofSignal

Calibration Path

signal gated off

2. Long relaxation time (metastability) of the Erbium excited states allow

direct measurement of the spontaneous emission curve

Gain Compression

Total output power: Amplified signal + ASE

EDFA is in saturation if almost all Erbium


133/178


EDFA is in saturationif almost all Erbiumexcited states are consumed by

amplification

Total output power remains almostconstant

Lowest noise figure

Preferred operating point

Power levels in link stabilize automaticallyPin (dBm)

Total Pout

-3 dBMax

-20-30 -10

Gain

Span Tilt and Peak to Peak Deviation

dB

nm

Peak-to-PeakDeviation


134/178


Span Tilt

Deviation


135/178

Standard Amplifier Test SetupEDFA, Semiconductor, and Raman Amplifier

OA(DUT)

DFB

SWITCH SWITCH


136/178


(DUT)

DFB

DFB OSA +

OA-TestRoutine

ATT

SWITCH SWITCH

WDM

TLS PowerMeter

OSA separates signals from broadband spontaneous emission

Amplifier characteristics depend on input power, wavelength, polarization Sources simulate operation (multichannel, adjustable power)

The Complete EDFA Test Solution

Time Domain Extinction Method Interpolated Source Subtraction

MethodN i G i P fil M th d


137/178


Noise Gain Profile Method

Issues in DWDMSM fiber can tolerate up to 50 mW (+17 dBm)

Nonlinear effects start causing trouble around 10 dBm About 100 kW/ m2 ! limits available channel power to Power/ channel < 50 mW/Nchannels


138/178


Optical Amplifiers have limited effective range e.g., EDFA: 1525 < < 1565 (roughly)

High power densities cause nonlinear scattering e.g., Kerr effect: n= n(E)

Four Wave Mixing (FWM), self-phase modulation, . . ., noise

Trends:Higher capacity

160 wavelengths 12.5 GHz spacing

All optical network (the grail)


EDFAData

1

2...

n

multiplexer EDFA

Optical

Amplification


139/178




EDFA

OtherSegment

OtherSegment

Other

Segment

OtherSegment

ADN

LAN

CrossConnect

(Switch)

Data

1

2...

n

demu

ltiplexer

Dispersion:


140/178


Dispersion:The evolution of the index of

refraction w ith wavelength and

polarization

Electrodynamics ofContinuous Media


141/178


Continuous Media

Chromatic dispersion

Polarization mode dispersion

x

Optical Networking - The DWDM ForestDispersionCompensators

Data

1

2...

n

multiplexer


142/178




OtherSegment

OtherSegment

OtherSegment

OtherSegment

LAN

CrossConnect

(Switch)

Data

1

2...

n

demultiplexer

Color: Index of refraction

Why is a ruby red?

White Light

+ Only red is


143/178


Because the nRuby() has a resonance at red.

For pigments, e.g., red paint, the other colors are absorbed in the mess of organic molecules that have manyavailable energy states resulting in heat.

+

+

+

Only red is

absorbed

Red is emitted at

random angles

Ruby "atom"

Excitedruby "atom"

The Index of Refraction

The index of refraction

of a dielectric is given by The energy carried by light is determined by the frequency, not the

wavelength, so the frequency of light in media doesnt change, but the

media

vacuum)(c

cn =


144/178


wavelength does.

The index of refraction varies with wavelength, different colors travel at different speeds chromatic dispersion.

The index of refraction can also vary with polarization birefringence polarization mode dispersion

The heart of these phenomena is the response of the media to theelectric and magnetic fields that compose the light.

media

vacuum

media

vacuum

media

vacuum)(

===

c

cn

vacuum

mediavacuummedia )(

cc =

Chromatic Dispersion Spreads Pulses Increases the Bit Error Rate

Recall from coherence:

the minimum frequency/ wavelength spread of a pulse of light is


145/178


n = n() narrower the pulse, the larger the chromatic dispersion Modulation sidebands and chirp also increase pulse wavelength content

41

CT

PulsePulse cTT

44

1 2orthus

T T+T

The Cause of Chromatic Dispersion

Two causes:

1. Material Dispersion

The response, permittivity , of the media:

x


146/178


2. Waveguide Dispersion

ncore() and ncladding() vary differently with

different boundary conditions for different wavelengths

different solutions to the wave equation

===

000media

vacuum)(ccn

Dielec

tricco

nstant

Chromatic Dispersion - Definitions

Define

describes how the propagation time varies with wavelength in ps/ nm

d

d g )(

dispersionchromatic


147/178


where g() is the propagation time along a fiber of length L.

Factor out the length and get the

The pulse spreads by an amount

d

d

L

Dg )(1t,coefficiendispersionchromatic

DLT

T T+T

Chromatic Dispersion Observables

)(g

Group

cg


148/178


Delay (ps)

0

Chromatic dispersion coefficient(ps/ nmkm)

d

d

L

Dg )(1

Zero dispersionwavelength,

typically 1300 nm

0

Typical CD value: 10 ps/ nmkm

Tolerable Levels of Chromatic Dispersion

Require with B= bit rate in Gb/ s

since and so

Bg

1


149/178


and

For 1 dB penalty:

2

1Bd

dDLg =

2

510

B

DL


150/178


Optical

Modulator

DUT

Tunable

Laser

TunableRF Source

Phase

Detector

Signal

Processing

Data

g() = /2f

4. Fit curve to g() and calculate

d

d

LD

g )(1

Chromatic Dispersion Compensation

Dispersion compensating fiber: Follow a segment of dispersing fiber with a segment of dispersion

compensating fiber

DispersingDispersion compensating


151/178


There are also compensating components, e.g., the chirped FBG

Dispersing

fiberfiber


152/178

Principle States of Polarization

Fibers and components have distinctslow and fast polarization axis

nx

ny


153/178


TT+T

PMD in fibers is a Random Process

Small random variations in fiber geometry and media cause unpredictable

changes in polarization states and principal states of polarization For fiber length much larger than the correlation length, (L >> LC)

The Differential Group Delay, , follows a Maxwellian distribution


154/178


The Differential Group Delay, , follows a Maxwellian distribution

Since contributions from different segments are independent, theycombine to a total in quadrature (i.e., like the sides of a right triangle):

The mean DGD, , increases with

For components, e.g., filters, (L >> LC) PMD is deterministic

2

2

23

22)(

= ef

22

2

2

1 Ntotal +++= L L

N

Tolerable Levels of Polarization Mode Dispersion

PMD is a random processdepending on temperature and geometry

PMD combines like the legs of a right triangle:

Define the 1st order PMD Coefficient:L

P

=2

iTotal


155/178


1st order PMD is wavelength independent

2nd order PMDdepends on wavelength, but is very small

Typical good quality fiber:

Older, poor quality fiber:

Tolerate

L

km/ps2.0

km/ps21

BTotal1.0


156/178


p

low quality 2 ps/km

The graph is forthe average,

Fear the tail!

1

100

10,000

1,000,000

Le

ngth( k

m)

Data Rate (Gb/s)

0.01 0.1 1 10 100

OC-1 OC-3 OC-12

OC-48 OC-192 OC-768

Poor quality fiber

Measuring Polarization Mode DispersionJones Matrix Eigenanalysis method:

Measure DUT Transfer matrix

at three known polarizationsat a set of wavelengths, J(): J() Pin = Pout

Extract T() by diagonalizing J()


157/178


Polarization

Synthesizer

Polarization Analyzer

S0 S1 S2 S3

TunableLaser

TransferMatrix

O1

O2

I1

I2

J11 J12

J21 J22

J() Pin = Pout

Jones Matrix Eigenanalysis (JME) Result


158/178


Cannot compensate PMD with a passive device

Must have feedback to monitor PMD and actively compensate

Also measure PMD with Modulation phase shift and interferometric techniques

Complete Dispersion Test SetAgilent 86038

Modulation Phase Shift MethodSingle connection measurement ofChromatic Dispersion and


159/178


Polarization Mode DispersionExcellent for

Broadband device characterization

e.g., spools of fiber

Narrowband device characterizatione.g., filters, mux/ demux, etc.


160/178

Optical Networking - The DWDM ForestDispersionCompensators

OtherSegment

Data

1

2.

.

.

n

multiplexer


161/178




OtherSegment

OtherSegment

Segment

Other

Segment

LAN

CrossConnect

(Switch)

Data

1

2.

.

.

n

demultiplexer

Characterizing the

SystemOptical Time Domain Reflectometry


162/178


Optical Time Domain ReflectometryNoiseBit Error Rate MeasurmentsEye diagram analysis

Extinction ratioJitterMask tests

Optical Time Domain Reflectometry:Link Characterization

Optical Time-Domain Reflectometer(with Power Meter, Visual Fault


163/178


Finder, and Laser Source)

Optical radar

Measures loss vs. distance

10 m - 200 km range

Key tool in installation and

maintenance MM and SM modules

FusionSplice

Bend Connector Crack FiberEnd

MechanicalSplice

Los

s

Distance

Bit Error Ratio

Bit error ratio,

BER = # of bits received in error/ # of bits received

Gives a good indication of the performance of acomponent, link or entire network

BER


164/178


Typical BER spec: 1.0 10-12

Tradeoff between

minimum input power andacceptable bit error rate

Larger the powerless effect of dispersion,

less noise from optical amplifiers, etc.

Pi (dBm)


165/178

BERTs


166/178


86130 Bitalyzer (up to 3.6 Gb/ s)

71612 HSBERT (up to 12.5 Gb/ s)

81250 ParBERT (up to 43 Gb/ s)

Pulse Parameters

Overshoot On Logic 1

b180%

Fall Time

Half-Period Of

Ringing Freq.

Undershoot On Logic 1

Rise Time


167/178


50%

20%

b0bdark

Pulse Width

Overshoot On Logic 0

Undershoot On Logic 0Jitter

Eye Diagram Analysis

Standard compliance verification(SONET / SDH, G-Ethernet, Fibre Channel, ..)

Mask


168/178


Pulse ParametersExtinction Ratio

Signal capture of patternscausing bit errors

Eye-line measurements

1 0 0

0 1 0

0 0 0

The Eye Diagram


169/178


0 0 1

0 1 1

1 0 1

1 1 0

1 1 1

Superimposed Bit Sequences

Eye Diagrams

Power(mW)

Time (ns)

Digital Communications AnalyzerA sampling oscillosc

agilent back to basics in optical communication

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