Download Fiber Systems : Dense Wavelength Division Multiplexing

Fiber Systems
Dense Wavelength Division
Multiplexing (DWDM)
Alpina Kulkarni
Optical Communications (EE566)
Dr. Paolo Liu
Electrical Engineering @ UB
Brief Overview
► Problems
with increasing network demands
► Solutions proposed & their limitations
► Evolution of DWDM
► Technical details
► Drawbacks
► Ongoing Research
► Conclusion
Growing Network Usage Patterns
► Issues
 Exponential increase in user demand for bandwidth
► Doubling
of bandwidth requirement every 6-9 months
 Consistency in quality of services provided
 Keeping the cost of solutions at bay
► Solutions
 Increase channel capacity: TDM, WDM
 Statistical multiplexing of users: Multiple optical fibers
Another glimpse at the solutions
► TDM
(Time Division Multiplexing)
 Slotting of channels  simultaneous users
 Increasing bit rate to maximize utilization of given
bandwidth
► WDM




(Wavelength Division Multiplexing)
Use of optical fibers to achieve higher speeds
Utilize wavelengths to multiplex users
Allow continuous channel allocation per user
Increases the effective bandwidth of existing fiber
Limitations of current solutions
► TDM
 Dependency of Mux-Demux on bit rate
 Limitations on bit rates
► how
fast can we go? (Decides how small the time slots can be)
► WDM
 Inefficient usage of full capacity of the optical fiber
 Capability of carrying signals efficiently over short distances only
►
Improvements in optical fibers and narrowband lasers
 Birth of Dense WDM (DWDM)
Evolution of DWDM
Late
1990’s
1996
DWDM
Early
1990’s
Narrowband WDM
1980’s
Wideband WDM
64+ channels
25~50 GHz spacing
16+ channels
100~200 GHz spacing
2~8 channels
200~400 GHz spacing
2 channels
1310nm, 1550nm
What is DWDM?
►
Definition
 Dense wavelength division multiplexing (DWDM) is a fiber-optic
transmission technique that employs light wavelengths to
transmit data parallel-by-bit or serial-by-character
How does DWDM fair better?
► No
O-E-O required
► Protocol & Bit Rate independence
► Increased overall capacity at much lower cost
 Current fiber plant investment can be optimized by a
factor of at least 32
► Transparency
 Physical layer architecture  supports both TDM and
data formats such as ATM, Gigabit Ethernet, etc.
► Scalability
 Utilize abundance of dark fibers in metropolitan areas
and enterprise networks
Capacity Expansion
Basic Components & Operation
►
Transmitting Side
 Lasers with precise stable
wavelengths
 Optical Multiplexers
►
On the Link
 Optical fiber
 Optical amplifiers
►
Receiving Side
 Photo detectors
 Optical Demultiplexers
►
Optical add/drop
multiplexers
Optical Amplifier
►
►
►
►
►
Eliminates O-E-O conversions
More effective than electronic repeaters
Isolator prevents reflection
Light at 980nm or 1480nm is injected via the pump laser
Gains ~ 30dB; Output Power ~ 17dB
Drawbacks
► Dispersion
 Chromatic dispersion
 Polarization mode dispersion
► Attenuation
 Intrinsic: Scattering, Absorption, etc.
 Extrinsic: Manufacturing Stress, Environment, etc.
► Four
wave mixing
 Non-linear nature of refractive index of optical fiber
 Limits channel capacity of the DWDM System
Ongoing Developments
► Nortel
Networks
 Metro DWDM
 OPTera Long Haul 5000 Optical Line System
► Cisco
Systems
 ONS 15200 Metro DWDM Solution
► Lucent
Technologies
 LambdaXtreme Transport
 WaveStar OLS 1.6T
► Agility
Communications & UC Santa Barbara
 Tunable Lasers used for multiple wavelengths
Conclusion
► Robust
and simple design
► Works entirely in the Optical domain
► Multiplies the capacity of the network many fold
► Cheap Components
► Handles the present BW demand cost effectively
► Maximum utilization of untapped resources
► Best suited for long-haul networks
References
[1] Introducing DWDM
http://www.cisco.com/univercd/cc/td/doc/product/mels/dwdm/dwdm_fns.htm
[2] Fundamentals of DWDM Technology
http://www.cisco.com/univercd/cc/td/doc/product/mels/dwdm/dwdm_ovr.htm
[3] Dense Wavelength Division Multiplexing (DWDM)
http://www.iec.org/online/tutorials/dwdm
[4] Dense Wavelength Division Multiplexing (DWDM) Testing
http://www.iec.org/online/tutorials/dwdm_test
[5] “Fiber-Optic Communications Technology” by D.K. Mynbaev, L.L. Scheiner, Pearson
Education Asia, 2001 edition
[6] “Dense wave nets' future is cloudy” by Chappell Brown, EETimes
http://www.eetimes.com/story/OEG20011221S0035
[7] Cisco Systems
http://www.cisco.com/en/US/products/hw/optical/ps1996/products_quick_reference_gui
de09186a00800886bb.html
[8] Lucent Technologies
http://www.lucent.com/products/subcategory/0,,CTID+2021-STID+10482LOCL+1,00.html
[9] Nortel Networks: “OPTera Long Haul” & “Metro DWDM”
(http://www.nortelnetworks.com/products/01/optera/long_haul/dwdm/) &
(http://www.nortelnetworks.com/products/library/collateral/12001.25-03-02.pdf)
[10] Agility Communications
http://agility.com/intervals/index.phtml?ID=93&f_code=1