lecture:3 lightwave/optical systems
DESCRIPTION
Lecture:3 Lightwave/Optical Systems. Ajmal Muhammad, Robert Forchheimer Information Coding Group ISY Department. Outline. Optical Networks Core, metro, and access networks Optical Access Networks Optical Amplifiers Doped fibers, semiconductor optical amplifiers (SOAs) Modulation - PowerPoint PPT PresentationTRANSCRIPT
Lecture:3 Lightwave/Optical Systems
Ajmal Muhammad, Robert ForchheimerInformation Coding Group
ISY Department
Outline
Optical Networks Core, metro, and access networks
Optical Access Networks Optical Amplifiers
Doped fibers, semiconductor optical amplifiers (SOAs) Modulation
Direct intensity, external modulation Demodulation
Telecom Network Hierarchy
Long haul- 100s-1000s km- Mesh
Metro (interoffice)- 10s of km- Rings
Access- a few km- Hubbed rings
The “Last” Mile “First”
✕
Part of core Network – Submarine Optical CablesThe longest submarine cable is the Southeast Asia—Middle East—Western Europe (SEA-ME-WE 3) system stretching 39,000 km from Norden, Germany, to Keoje, South Korea
Metropolitan-Area Networks (MANs)
MAN is connected to a WAN at egress nodes (EN) MAN is connected to LANs at access nodes (AN). ADM stands
for add-drop multiplexer Several MANs can be interconnected with a ring to form a
regional network Regional rings provide protection against failures
The First Mile :: Access Networks
Telephone companies: xDSL (Digital Subscriber Line) - DSL data rate 128kb/s - 1.5Mb/s
- Maximum subscriber distance from central office 5.5 km-Other flavors: ADSL (asymmetric DSL) 12Mb/s, VDSL (very-high-bit-rate) 50Mb/s-0.5 km, HDSL(high-bit-rate DSL)
Cable TV companies: CM (Cable Modem) -Dedicated radio channel for data
Problems with today’s access technologies (xDSL, CM)- Originally designed and built for voice and TV, respectively
- Retrofitting for data not working well
- Limitations in Reach, Bandwidth, Scalability, Flexibility, Cost
Fiber Access Network
Fiber-to-the-x (FTTx) where x = {H,B,C,P,BS,AP,…}
Platform for triple play service, i.e., voice, data and videoLong reach: 0-20 kmFiber plant has long life span (~20 years)Able to scale and incorporate new technologies without digging new trenchesLeverage long reach to facilitate broadband wireless access over shorter distance
Optical Fiber Based Access Networks
Power in the field required
Passive Optical Network (PON)
- Point-to-multipoint topology- Low cost implementation- Relative ease of deployment- Future-proof
OLT: Optical line terminalONU: Optical network unit
Passive Splitter
Optical Line Terminal (OLT)
Optical Network Unit (ONT)
ONT for FTTH outdoor unit
ONT for FTTH (Home)
1G PON - Ethernet PON(EPON)
Shared medium network for downstream traffic
Broadcasting
1 Gb/s1490-nm wavelength
1G PON - Ethernet PON(EPON)
Point-to-point network for upstream traffic
Time Division Multiplexing
1 Gb/s1310-nm wavelengthLow cost FP lasers
OLT Structure
Service adaptation provides the translation between the signal format required for client equipment connection and the PON signal format
Service Network Interface (SNI)
Physical Media Dependent defines the optical transceiver & the wavelength demulplexer
Media Access Control schedules the right to use physical medium
ONU Structure
User to Network Interface (UNI)
Typical PON Configuration
WavelengthDual fiber 1310 nmSingle fiber upstream (downstream) on 1310 (1490) nm
TransceiverONU Fabry-Perot (upstream), PIN (downstream)ONT APD(upstream), DFB(downstream)
Transceiver Assumptions
Upstream(@1310 nm) power budget = 30 dBDownstream(@1490 nm) power budget= 22 dB
Second Generation PON:: Line-Rate Upgrade
10G-PON: Suppose symmetric 10-Gb/s downstream and upstream, and asymmetric 10-Gb/s downstream and 1-Gb/s upstream
GPON: Suppose asymmetric 2.488-Gb/s downstream and 1.244-Gb/s upstream
XG-PON: Suppose coexistence with GPON on the same fiber plant. Downstream 10-Gb/s and upstream 2.5-Gb/s
High upstream capability (symmetric approach) require more expensive ONU devices
Candidate Technologies for the NG-PON
Wavelength division multiplexing (WDM) PON
State-of-the-art experimental WDM PON support 100Mb/s – 2Gb/s symmetric communication per wavelength channel with 32 ONUs
Wavelength-routed WDM PON
Migration requirements:- Change the power splitter with the AWG- Coexistence with previous generations of deployed devices not possible
Hybrid (TDM/WDM) PON
Pareto principle80% of the traffic is generated by only 20 % of the users
Utilize network resources (wavelengths) efficiently
Optical Amplifiers
Typical fiber loss around 1.5 um is ~0.2 dB/kmAfter traveling ~100 km, signals are attenuated by ~20dBSignals need to be amplified or signal-to-nose (SNR) of detected signals is too low and bit error rate (BER) becomes too high (typically want BER <10-9)
Different functions of an optical amplifier
Optical Amplifiers :: Characteristics
An optical amplifier is characterized by:
Gain: ratio of output power to input power (in dB)Gain efficiency: gain as a function of input power (dB/mW) Gain bandwidth: range of wavelengths over which the amplifier is effectiveGain saturation: maximum output power, beyond which no amplification is reachedNoise: undesired signal due to physical processing in amplifier
Optical Amplifiers :: Types
Rare-earth doped fiber amplifiers:Erbium Doped (EDFA) – 1,500 – 1,600 nm bandPraseodymium Doped (PDFA) – 1,300 nm band
Raman amplifiers – 1,280 – 1,650 nm band
Semiconductor Optical Amplifiers (SOAs) – 400 – 2,000 nm band
Erbium Doped Fiber :: Amplification Process
Erbium Doped Fiber :: Operation
Absorption and gain spectra for 1480 nm pump
Raman Amplifier
Raman Amplifier :: Operation
Semiconductor Optical Amplifier
SOA :: Amplification Process
SOA :: Design
Optical Amplifiers : Comparison
Modulation
The process transmitting information via light carrier (or any carrier signal)
Direct Intensity (current) 1310 nm transmittersInexpensive light emitting diode (LED)Laser diode (LD): suffer from chirp up to 1nm (wavelength variation due to variation in electron densities in the lasing area)Distance < 30 km, no EDFA
1310 nm
External Modulation
1550 nm transmitters Expensive but can cover distance up to 120 km by using EDFA
Optical Receiver To extract the optical signal (low level) from various noise
disturbances To reconstruct original information correctly
Selection criteria Optical sensitivity for a given SNR and BER, operating wavelength Dynamic range, simplicity, stability
Photodetector :: Types
The most commonly used photodetectors in optical communications are:
Positive-Intrinsic-Negative (PIN)No internal gainLow bias voltage [10-50 V @ Lambda=850 nm, 5-15 V @Lambda= 1300-1550 nm]Highly linear, low dark current
Avalanche Photo-Detector (APD)Internal gain (increased sensitivity)Best for high speed and highly sensitive receiversStrong temperature dependenceHigh bias voltage [250 V @ Lambda=850 nm, 20-30 V @Lambda= 1300-1550 nm]Costly
Photodiode (PIN) :: Structure
• No carrier in the I region• No current flow
• Reverse-biased• Photons generated electron-hole • Current flow through the diode