Teching Methodology Presentation-OfC
description
Transcript of Teching Methodology Presentation-OfC
Presented By Shuchi A. ParkhaniSneha P. Sawarkar
Swati R. JambhulkarSnehal K. Gaikwad
M. Tech. III sem. (Communication Engineering)
Department Of Electronics & Telecommunication EngineeringG. H. Raisoni College of Engineering, Nagpur
(An autonomous Institute under UGC act 1956 & Affiliated to Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur)
Session 2015-2016
A Seminar On
Optical Fiber Communication
CONTENTSIntroduction to optical fiber
networkOptical fibersOptical sourcesOptical detectorsOptical amplifiers
• High Speed Data Transmission (Tb/sec)
• Low Loss of Signal due to lack of Radiation And Conduction
• Low Dispersion and Attenuation Properties
• Better Electrical Isolation
• Small size and light weight
• Huge bandwidth
Advantages of Optical Networks
Major Elements of an optical fiber link
Introduction to Optical Fiber
An optical fiber is essentially a waveguide for light It consists of a core and cladding that surrounds the coreThe index of refraction of the cladding is less than that of the
core, causing rays of light leaving the core to be refracted back into the core
A light-emitting diode (LED) or laser diode (LD) can be used for the source
Advantages of optical fiber include:◦ Greater bandwidth than copper◦ Lower loss◦ Immunity to crosstalk◦ No electrical hazard◦Flexibility
Areas of application of Optical Fiber
TelecommunicationsLocal Area NetworksCable TVCCTVOptical Fiber Sensors
Optical Fiber & Communications System
Optical Fiber
Optical fiber is made from thin strands of either glass or plastic
It has little mechanical strength, so it must be enclosed in a protective jacket
Often, two or more fibers are enclosed in the same cable for increased bandwidth and redundancy in case one of the fibers breaks
It is also easier to build a full-duplex system using two fibers, one for transmission in each direction
Total Internal Reflection (TIR)
Optical fibers work on the principle of total internal reflection
With light, the refractive index is listedThe angle of refraction at the interface between
two media is governed by Snell’s law:
n1 sin1 n2 sin2
Reflection law: angle of incidence=angle of reflection
Snell’s law of refraction:
2211 sinsin nn
Total internal reflection, Critical angle
1
2sinn
nc
1
1
2sinn
nc
n 2
n 1 > n2
Incidentlight
Transmitted(refracted) light
Reflectedlight
kt
TIR
Evanescent wave
ki
kr
(a) (b) (c)
Light wave travelling in a more dense medium strikes a less dense medium. Depending onthe incidence angle with respect to , which is determined by the ratio of the refractiveindices, the wave may be transmitted (refracted) or reflected. (a) (b)
(c)
and total internal reflection (TIR).
2
1 c
902
c 1
cc 1 c 1
c 1
Critical angle
Launching optical rays to slab waveguide
1
21
12
22
1max0 2sinNA
n
nn
nnnn
Numerical aperture:
Different Structures of Optical Fiber
According to the Fiber Material◦ Glass◦ Plastic
According to the number of modes◦ Single mode◦ Multimode
According to the refractive index profile◦ Step index ◦ Graded index
Types of Optical Fibers
Transmission Windows in Optical Fiber
1st window is at 850nm◦Low loss◦Silica fibers◦10 Km repeater spacing◦Multimode fibers were
used◦140 Mbps◦Higher attenuation◦Short distance
Transmission Windows in Optical Fiber
2nd window is at 1310nm◦Low loss◦Silica fibers◦40 Km repeater spacing◦Single mode as well as Multimode fibers were used◦2.5Gbps◦Comparatively less attenuation◦ long distance
Transmission Windows in Optical Fiber
3rd window is at 1550nm◦Low loss◦Silica fibers◦90 Km repeater spacing◦Single mode and Multimode fibers were used◦Up to 10 Gbps◦lowest attenuation◦long distance
Attenuation Characteristics of an Optical Fiber
Types of Optical Sources
Monochromatic incoherent source:◦ Light emitting diode (LED)
Large wavelength content Incoherent Limited directionality
Monochromatic coherent source:◦ Laser diode (LD)
Small wavelength content Highly coherent Directional
Source CharacteristicsImportant Parameters
◦Electrical-optical conversion efficiency◦Optical power◦Wavelength◦Wavelength distribution (called linewidth)◦Cost◦Compact
Basic Light Emission Processes
Pumping (creating more electron-hole pairs)◦ Electrically create electron-hole pairs◦ Optically create electron-hole pairs
Emission (recombination of electron-hole pairs)◦ Spontaneous emission ◦ Simulated emission
Semiconductor Light Sources
A PN junction (that consists of direct band gap semiconductor materials) acts as the active or recombination region.
When the PN junction is forward biased, electrons and holes recombine either radiatively (emitting photons) or non-radiatively (emitting heat). This is simple LED operation.
In a LASER, the photon is further processed in a resonance cavity to achieve a coherent, highly directional optical beam with narrow linewidth.
LED vs. laser spectral width
Single-frequency laser (<0.04 nm)
Standard laser (1-3 nm wide)
LED (30-50 nm wide)
Wavelength
Laser output is many timeshigher than LED output
Types of LED
The basic LED types used for fiber optic communication systems are
Surface-emitting LED (SLED) Edge-emitting LED (ELED)
LED performance LED performance differences help link designers decide
which device is appropriate for the intended application.
For short-distance (0 to 3 km), low-data-rate fiber optic systems, SLEDs and ELEDs are the preferred optical source.
Typically, SLEDs operate efficiently for bit rates up to 250 megabits per second (Mb/s). Because SLEDs emit light over a wide area (wide far-field angle), they are almost exclusively used in multimode systems.
LED performance For medium-distance, medium-data-rate systems,
ELEDs are preferred. ELEDs may be modulated at rates up to 400 Mb/s.
ELEDs may be used for both single mode and multimode fiber systems.
Both SLDs and ELEDs are used in long-distance, high-data-rate systems. SLDs are ELED-based diodes designed to operate in the superluminescence mode.
SLDs may be modulated at bit rates of over 400 Mb/s.
April 18, 2023 Optical Fiber Communication 27
Surface-emitting LED
April 18, 2023 Optical Fiber Communication 28
Edge-emitting LED
Quantum Efficiency
Internal quantum efficiency is the ratio between the radiative recombination rate and the sum of radiative and non-radiative recombination rates
For exponential decay of excess carriers, the radiative recombination lifetime is n/Rr
and the nonradiative recombination lifetime is n/Rnr
)/(int nrrr RRR
Drawbacks
Large line width (30-40 nm)Large beam width (Low coupling to the fiber)Low output power Low E/O conversion efficiency
AdvantagesRobust Linear
The LASER
Light Amplification by ‘Stimulated Emission’ and Radiation (L A S E R)
Coherent light (stimulated emission)Narrow beam width (very focused beam)High output power (amplification)Narrow line width because only few
wavelength will experience a positive feedback and get amplified (optical filtering)
Fundamental Lasing OperationAbsorption: An atom in the ground state might
absorb a photon emitted by another atom, thus making a transition to an excited state.
Spontaneous Emission: Random emission of a photon, which enables the atom to relax to the ground state.
Stimulated Emission: An atom in an excited state might be stimulated to emit a photon by another incident photon.
Optical light sources convert electrical signals into optical signals and launch them.
Commonly used light sources include LEDs, ELEDs, SLEDs, and LDs.
LEDs produce incoherent light whereas a Laser Diode produces coherent light.
Incoherent light sources used in multimode systems and Laser Diodes/Tunable Lasers are used in single mode systems
Laser diodes must operate above their threshold region to produce coherent light, otherwise operating as ELED.
Laser diodes are much faster in switching response than LEDsTunable laser is able to produce coherent light output with
controlled variable wavelength Tunable laser is used in multi wavelength systems by replacing a
system where many sources are coupled into a multiplexing device system
Introduction to the Photodetectors
Three steps for the operation of a photodetector:
◦(i) carrier generation by incident light absorption and generation
◦(ii) carrier transport (and/or multiplication) by current gain mechanism photocurrent
◦(iii) interaction of current with the external circuits to provide the output signal current collection
Simple point-to-point link
System Requirements1. Transmission Distance2. The data rate or channel
bandwidth3. The bit-error rate (BER)
Elements of Link/ Network Design
• Transmitter : Operating wavelength (),
Linewidth (), Rise time, Bit-rate, Line format, Power level
• Fiber : SMF/MMF, Fiber type – SMF28,
DSF, etc, Cable loss
• Rx : PSEN, PSAT, Rise time
Elements of Link/ Network Design (cont.)
• Connection: No. of splice, Splice lossNo. of connectors, Connector
Loss
• In Line Devices: Splitter, Filter, Attenuator,
Amplifier Insertion loss, Gain
Optical Amplifiers
•An optical amplifier is a device which amplifies the optical signal directly without ever changing it to electricity. The light itself is amplified.
•Reasons to use the optical amplifiers: ReliabilityFlexibilityWavelength Division Multiplexing (WDM)Low Cost
•Variety of optical amplifier types exists, including:Semiconductor Optical Amplifiers (SOAs)Erbium Doped Fibre Amplifiers (EDFAs) (most common)
Basic Concepts
Most optical amplifiers use stimulated emission
An optical amplifier is basically a laser without feedback
Optical gain is realized when the amplifier is pumped optically (or electrically) to achieve population inversion
Gain depends on wavelength, internal light intensity and amplifier medium
Two types: semiconductor optical amplifiers and fiber doped amplifiers
OFAs in the Network
Relatively simple construction
Reliable, due to the number of passive
components
Allows easy connection to external fibers
Broadband operation > 20 nm
Bit rate transparent
Ideally suited to long span systems
Integral part of DWDM systems
Undersea applications for OFAs are now
common
In-line Amplifier
PowerAmplifier
Preamplifier
Transmitter
Transmitter
Transmitter
Optical Amplifiers
Optical Amplifier
Fiber Link
Optical Amplifier
Fiber Link
Optical Receiver
Optical Receiver
Optical Receiver
Optical Amplifier Applications
Fiber Link
Type GainMaximum Output
power Noise figure
Power Amplifier
High gain High output power moderate
In-line Medium gain Medium output
powermoderate noise
figure
Preamplifier Low gain Low output powerLow value < 5 dB
essential
Selecting Amplifiers
Semiconductor Optical Amplifiers
Similar to Laser diodes but the emission is triggered by input optical signal
Work in any wavelength.Have high integration, compact and low
power consumption .Gain fluctuation with signal bit rate .Cross talk between different
wavelengths .Two types: Fabry-Perot or Traveling Wave
Amp.
Erbium Doped Fiber Amplifier
A pump optical signal is added to an input signal by a WDM coupler Within a length of doped fiber part of the pump energy is transferred to the
input signal by stimulated emission For operation 1550 nm the fiber dopant is Erbium Pump wavelength is 980 nm or 1480 nm, pump power 50 mW Gains of 30-40 dB possible
Working of an EDFA
Characteristics of EDFA
Efficient pumpingLow insertion lossHigh output power Low noiseVery high sensitivityLow distortion, minimal interchannel crosstalk
Advantages
Low crosstalkHappen to operate in most transparent region
of the spectrum for glass fiberExtremely long excited state lifetime (on the
order of 10 ms)
Disadvantages
Can only work at wavelengths where Er+3 fluoresces
Requires specially doped fiber as gain medium
Requires long path length of gain medium (tens of meters in glass)
Gain very wavelength-dependent and must be flattened
Gain limited by cooperative quenching
Thank you