Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM...

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Fiber Optic Communications Lecture 9: Wavelength Division Multiplexing WDM Principles WDM Hardware Hybrid packet/optical networks

Transcript of Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM...

Page 1: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Fiber Optic CommunicationsLecture 9: Wavelength Division Multiplexing

• WDM Principles

• WDM Hardware

• Hybrid packet/optical networks

Page 2: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Recap: Multiplexing schemes

• FDM – each channel is assigned to a different

frequency

• TDM – each channel is transmitted in a different time

interval

• CDM – each channel is encoded differently

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Page 3: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Wavelength Division Multiplexing

Also known as

frequency division

multiplexing (FDM).

Demultiplexing is

performed by

spectral filtering.

Total bandwidth is

sum of each

wavelength

contribution

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original extended short

conventional

long ultralong

Page 4: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Bandwidth

• Total bandwidth is sum of each wavelength’s

contribution:

�� =������

• Available channels depends on spacing Δ�• Spectral efficiency � = �/Δ�• Should be maximized for best performance

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Page 5: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Channel Spacing

• Spacing Δ� must be large enough to minimize

crosstalk

• Traditionally, this is taken to mean Δ� ≥ 2�• This implied Δ� = 100 GHz (WDM, now deprecated)

• Can now find Δ� = 50 GHz (original DWDM),

Δ� = 25 GHz (DWDM) or even 12.5 GHz (UDWDM)

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Page 6: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Amplification Bandwidth

• Total bandwidth for DWDM extends over EDFA

amplification range: 1525-1565 nm and/or 1570-

1610 nm (~5 THz)

• Ideally, could extend over the full low-loss range of

fibers, 1260-1610 nm (~50 THz)

• Approx. number of channels available listed below

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Wavelength range WDM (50 GHz) DWDM (25 GHz) UDWDM (12.5 GHz)

C-band (1525-1565 nm) 80 160 320

L-band (1570-1610 nm) 80 160 320

O-band (1260-1360 nm) 200 400 800

All (1260-1610 nm) 800 1600 3200

Page 7: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Fiber Optic CommunicationsLecture 9: Wavelength Division Multiplexing

• WDM Principles

• WDM Hardware

• Hybrid packet/optical networks

Page 8: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

DWDM Hardware

Key components include:

• Tunable optical filters

• Multiplexers & demultiplexers

• Add-drop multiplexers

• Star couplers

• Wavelength routers

• Optical cross-connects

• Wavelength converters

• Transmitters

• Receivers

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Page 9: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Tunable optical filters

• Desired features: wide tuning, low crosstalk,

fast tuning, low-loss, environmental stability,

low cost

• Four common types:

– Fabry-Perot: � < ��– Mach-Zender: � � = ∏ cos� �����– Bragg grating: �� = 2� sin !– Acousto-optic filters: �� = Δ" · Λ%

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Page 10: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Multiplexers & demultiplexers

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Can use filter elements discussed above to combine and separate

multiple wavelengths – e.g., a hierarchical Mach-Zender filter

Allows one to create multiple point-to-point links through a single

channel, as illustrated below

�&

��

�'

�(

�&,��

�',�(�&,��, �',�(

Page 11: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Add-drop multiplexers

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• Most easily implemented as series of MZ interferometers with

equal delays (a resonant coupler)

• Alternates include gratings and grating/circulator strategies

Page 12: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Star couplers

• Aim to divide inputs among � outputs equally, regardless of wavelength

• Can be made from 2x2 couplers or fused biconicaltapers

• Used for hierarchical transmission of videos and similar

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)

Star

coupler

() + �)/�

() + �)/�

() + �)/�

() + �)/�

() + �)/�

Page 13: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Wavelength routers

• Combines star coupler with multiplexing

• Complex design; usually made from Si or

InGaAsP/InP

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Idris et al., Opt. Express 24, 672 (2016).

Page 14: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Optical cross-connects

• Allows for dynamic routing of wavelengths across a network

• Often implemented using MEMS mirrors or MZ interferometers

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Page 15: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Wavelength converters

• Converts between wavelengths while

preserving data

• Needed to extend cross-connect capabilities

• Four implementations:

– Optoelectronic regeneration

– Semiconductor laser amplifier (SLA)

– Phase modulation in SLA

– Four-wave mixing in SLA

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Page 16: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

WDM Transmitters

• Few channels: DFB lasers with calibrated

frequencies

• Many channels: tunable or multimode lasers

(potentially using arrayed waveguide gratings),

or supercontinuum sources

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Page 17: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

WDM Receivers

• Photodiode array with filters to provide

broadband detection + differentiation by

wavelength (a planar concave-grating

demultiplexer or a WGR)

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Page 18: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Fiber Optic CommunicationsLecture 9: Wavelength Division Multiplexing

• WDM Principles

• WDM Hardware

• Hybrid packet/optical networks

Page 19: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Optical Transport Network (OTN)

• Physical implementation of a series of DWDM-

connected nodes

• Topologies can be any of a number discussed

earlier: e.g., bus; ring; star; or hierarchy

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Page 20: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Synchronous optical networking (SONET)

• Standardized protocol for transporting multiple bit streams over fiber optics

• Significant advance over predecessor, Plesiochronous Digital Hierarchy (PDH)

• Uses atomic clocks for synchronization

• Agnostic regarding specific communications protocol

• As a result, SONET and its variants (SDH) now used worldwide

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Page 21: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Synchronous optical networking (SONET) topology

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Page 22: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Synchronous transport signal 1 (STS-1) frame

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Page 23: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

OTNs vs. SONET

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OTN SONET/SDH

Timing Synchronous with

clients

Internally

synchronous

Multiplexing Fixed multiplexing Flexible multiplexing

Frame properties Frame size fixed Frame rate fixed

Bandwidth

efficiency

Can be bandwidth

inefficient

Very bandwidth

efficient

Error correction Forward error

correction

None

Page 24: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

OTN+SONET Example: Internet2

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Page 25: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

General Relation to TCP/IP

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Page 26: Fiber Optic Communications Lecture 9: Wavelength Division ...... · • WDM Principles • WDM Hardware • Hybrid packet/optical networks. Recap: Multiplexing schemes • FDM –each

Hybrid Packet/Optical Network Architecture

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Courtesy Dr. John S. Graham (Indiana University)