Optical Technologies and Lightwave Networks
This presentation is the property of its rightful owner.
Sponsored Links
1 / 35

Optical Technologies and Lightwave Networks PowerPoint PPT Presentation


  • 61 Views
  • Uploaded on
  • Presentation posted in: General

Optical Technologies and Lightwave Networks. Outline: Optical Technologies Optical Fibers, Fiber Loss and Dispersion Lightwave Systems and Networks Multiplexing Schemes Undersea Fiber Systems Lightwave Broadband Access Optical Networks. Need for Optical Technologies.

Download Presentation

Optical Technologies and Lightwave Networks

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Optical technologies and lightwave networks

Optical Technologies and Lightwave Networks

  • Outline:

  • Optical Technologies

    • Optical Fibers, Fiber Loss and Dispersion

  • Lightwave Systems and Networks

    • Multiplexing Schemes

    • Undersea Fiber Systems

    • Lightwave Broadband Access

    • Optical Networks


Optical technologies and lightwave networks

Need for Optical Technologies

  • huge demand on bandwidth nowadays

    •  need high capacity transmission

  • electronic bottleneck:

    • speed limit of electronic processing

    • limited bandwidth of copper/coaxial cables

  • optical fiber has very high-bandwidth (~30 THz)

    •  suitable for high capacity transmission

  • optical fiber has very low loss (~0.25dB/km @1550 nm)

    •  suitable for long-distance transmission


Optical technologies and lightwave networks

amplitude

position/distance

wavelength

Light Wave

  • electromagnetic wave

  • carry energy from one point to another

  • travel in straight line

  • described in wavelength (usually in mm or nm)

  • speed of light in vacuum = 3108 m/s


Optical technologies and lightwave networks

 > 

 > c

Incident light

Reflected light

Medium 1

 

Medium 2

 

Reflecting surface

Reflection and Refraction of Light

Reflection

Refraction

  • medium 1 is less dense (lower refractive index) than medium 2

  • light path is reversible

  • If incident light travels from a denser medium into a less dense medium and the incident angle is greater than a certain value (critical angle c)  Total Internal Reflection

Incident angle= reflected angle


Optical technologies and lightwave networks

cladding

light beam

core

Optical Fiber

  • made of different layers of glass, in cylindrical form

  • core has higher refractive index (denser medium) than the cladding

  • light beam travels in the core by means of total internal refraction

  • the whole fiber will be further wrapped by some plastic materials for protection

  • in 1966, Charles K. Kao and George A. Hockham suggested the use of optical fiber as a transmission media for information


Optical technologies and lightwave networks

Optical Fiber (cont’d)

  • Fiber mode describes the path or direction of the light beam travelling in the fiber

  • number of fiber modes allowed depends on the core diameter and the difference of the refractive indices in core and cladding

Single-mode Fiber

Multi-mode Fiber

  • smaller core diameter

  • allow only one fiber mode

  • typical value: 9/125mm

  • larger core diameter

  • allow more than one fiber modes

  • typical value: 62.5/125mm


Optical technologies and lightwave networks

Optical Fiber (cont’d)

  • Advantages of optical fiber:

  • large bandwidth  support high capacity transmission

  • low attenuation  support long-distance transmission

  • small and light in size  less space

  • low cost

  • immune to electromagnetic interference


Optical technologies and lightwave networks

Fiber Attenuation

  • optical power of a signal is reduced after passing through a piece of fiber

  • wavelength-dependent

low loss wavelength ranges: 1.3mm (0.4-0.6 dB/km), 1.55mm (0.2-0.4 dB/km)

 suitable for telecommunications


Optical technologies and lightwave networks

Fiber Dispersion

  • Inter-modal dispersion (only in multi-mode fibers):

    • different fiber modes takes different paths

    •  arrived the fiber end at different time

    •  pulse broadening  intersymbol interference (ISI)  limit bit-rate

  • Intra-modal dispersion (in both single-mode and multi-mode fiber):

    • different frequency components of a signal travel with different speed in the fiber

    •  different frequency components arrived the fiber end at different time

    •  pulse broadening  limit bit-rate


Optical technologies and lightwave networks

20

10

0

-10

-20

Standard

Dispersion-flattened

Dispersion (ps/(km•nm))

Dispersion-shifted

1.1 1.2 1.3 1.4 1.5 1.6 1.7

Wavelength (mm)

Fiber Dispersion

Typical values:

standard fiber:

~ 0 ps/(km• nm) @1300 nm

~17 ps /(km• nm) @1550 nm

dispersion-shifted fiber:

~0.5 ps /(km• nm) @1550 nm


Optical technologies and lightwave networks

System Capacity

  • fiber attenuation  loss in optical power limit transmission distance

  • fiber dispersion  pulse broadening  limit transmission bit-rate


Optical technologies and lightwave networks

Input electrical data

optical power (photons)

output optical power

wavelength

l

input electric current

threshold current

optical power (photons)

photo-current

Laser Source and Photodetector

  • Laser source

  • generate laser of a certain wavelength

  • made of semiconductors

  • output power depends on input electric current

  • need temperature control to stabilize the output power and output wavelength (both are temperature dependent)

  • Photodetector

  • convert incoming photons into electric current (photo-current)


Optical technologies and lightwave networks

A2

A2

C2

B2

B1

C2

C1

A1

A1

C1

B1

B2

A

time

B

l

C

Multiplexing Schemes

Multiplexing: transmits information for several connections simultaneously on the same optical fiber

Time Division Multiplexing (TDM)

  • only require one wavelength (one laser)

  • if channel data rate is R bits/sec, for N channels, the system data rate is (R  N) bits/sec


Optical technologies and lightwave networks

fA fB fC

fA

freq

freq

A

fB

freq

B

fC

l

freq

C

Multiplexing Schemes

Subcarrier Multiplexing (SCM)

  • multiple frequency carriers (subcarriers) are combined together

  • only require one wavelength (one laser) (optical carrier)

  • suitable for video distribution on fiber


Optical technologies and lightwave networks

lA

lA lB lC

A

lB

wavelength

B

lC

C

wavelength multiplexer

Multiplexing Schemes

Wavelength Division Multiplexing (WDM)

wavelength spacing: 0.8 nm (100-GHz)

  • one distinct wavelength (per laser) per sender

  • wavelength multiplexer/demultiplexer are needed to combine/separate wavelengths

  • if channel data rate per wavelength is R bits/sec, for N wavelengths, the system data rate is (R  N) bits/sec

  • suitable for high capacity data transmission


Optical technologies and lightwave networks

TDM/WDM

lA lB lC

lA lB lC

SCM/WDM

f1 f2 f3

f1 f2 f3

f1 f2 f3

wavelength

wavelength

TDM stream

A

A

TDM stream

B

B

TDM stream

C

C

wavelength multiplexer

wavelength multiplexer

Multiplexing Schemes

Hybrid Types (TDM/WDM, SCM/WDM)  higher capacity

lA

lA

lB

lB

lC

lC


Optical technologies and lightwave networks

132 Ch

1 Ch TDM

Transmission System Capacity


Optical technologies and lightwave networks

G

Optical Amplifier

  • no Electrical-to-Optical (E/O) or Optical-to-Electrical (O/E) conversion

  • can amplify multiple wavelengths simultaneously

  • Semiconductor Optical Amplifier

  • Fiber-Amplifier

    • Erbium-doped fiber amplifier (EDFA) : operates at 1550 nm transmission window (1530-1560 nm) (mature and widely deployed nowadays)

    • Pr3+ or Nd3+ doped fiber amplifier: operates at 1310 nm transmission window (not very mature)

    • ultra-wideband EDFA: S-band (1450-1530 nm), C-band (1530-1570 nm), L-band (1570-1650 nm)


Optical technologies and lightwave networks

Low-Rate Data Out

Low-Rate Data In

E

MUX

E

D MUX

REG RPTR

REG RPTR

XMTR

RCVR

Opto-Electronic Regenerative Repeater

EQ

DEC

LASER

DET

AMP

AMP

TMG REC

Lightwave Systems

Traditional Optical Fiber Transmission System

  • Single-wavelength operation, electronic TDM of synchronous data

  • Opto-electronic regenerative repeaters, 30-50km repeater spacing

  • Distortion and noise do not accumulate

  • Capacity upgrade requires higher-speed operation


Optical technologies and lightwave networks

Data In

Data Out

O

MUX

O

D MUX

l1

l1

XMTR

l2

RCVR

l2

XMTR

RCVR

OA

OA

OA

lN

XMTR

lN

RCVR

Lightwave Systems

Optical Fiber Transmission System

  • Multi-channel WDM operation

  • Transparent data-rate and modulation form

  • One optical amplifier (per fiber) supports many channels

  • 80-140 km amplifier spacing

  • Distortion and noise accumulate

  • Graceful growth


Optical technologies and lightwave networks

Undersea Fiber Systems

Design Considerations

  • span distance

  • data rate

  • repeater/amplifier spacing

  • fault tolerance, system monitoring/supervision, restoration, repair

  • reliability in components: aging (can survive for 25 years)

  • cost


Optical technologies and lightwave networks

Undersea Fiber Systems

AT&T


Optical technologies and lightwave networks

SYSTEMTIMEBANDWIDTH/NUMBER OF COMMENTS

BIT-RATE BASIC CHANNELS

TAT-1/21955/590.2 MHz48

HAW-11957COPPER COAX

TAT-3/41963/65ANALOG

HAW-219641.1 MHz140VACUUM TUBES

H-G-J1964

TAT-51970

HAW-319746 MHz840Ge TRANSISTORS

H-G-O1975

TAT-6/71976/8330 MHz4,200Si TRANSISTORS

TAT-81988OPTICAL FIBER

HAW-41989280 Mb/s8,000DIGITAL

TPC-31989l = 1.3 mm

TAT-9199116,000

TPC-41992560 Mb/s24,000 l = 1.55 mm

TAT-10/111992/93

TAT-1219955 Gb/s122,880OPTICAL AMPLIFIERS

TPC-51995 l = 1.55 mm

TAT: Trans-Atlantic Telecommunications TPC: Trans-Pacific Cable

Undersea Fiber Systems


Optical technologies and lightwave networks

Undersea Fiber Systems

FLAG: Fiberoptic Link Around the Globe (10Gb/s SDH-based, 27,000km, service in 1997)

  • Tyco (AT&T) Submarine Systems Inc., & KDD Submarine Cable Systems Inc.

  • 2 fiber pairs, each transporting 32 STM-1s (5-Gb/s)


Optical technologies and lightwave networks

Undersea Fiber Systems

Africa ONE: Africa Optical Network

(Trunk: 40Gb/s, WDM-SDH-based, 40,000km trunk, service in 1999)

  • Tyco (AT&T) Submarine Systems Inc. & Alcatel Submarine Networks

  • 54 landing points

  • 8 wavelengths, each carries 2.5Gb/s

  • 2 fiber pairs


Optical technologies and lightwave networks

Passive Optical Network (PON)

Remote Node

passive optical splitter

electrical repeater

Headend

Coaxial Cable

Fiber

Lightwave Broadband Access

  • Remote Node performs optical-to-electrical conversion

  • Hybrid Fiber-Coax (HFC), Fiber-to-the-Curb (FTTC), Fiber-to-the-Home (FTTH)

  • Distribution system: video, TV, multimedia, data, etc.

  • Two-way communications: upstream and downstream

  • Subcarrier multiplexing (single wavelength)


Optical technologies and lightwave networks

WDM-PON

Remote Node

l1

l1, … , lN

l2

electrical repeater

Headend

lN-1

multi-wavelength source

lN

wavelength demultiplexer

Lightwave Broadband Access

  • WDM-PON: Wavelength Division Multiplexed Passive Optical Network

  • use multiple wavelengths, each serves a certain group of users

  • higher capacity


Optical technologies and lightwave networks

  • Transmission

  • Multi-access

  • Channel add-drop

  • Channel routing/ switching

Lightwave Networks

Optical Networks


Optical technologies and lightwave networks

  • Tunable transmitter and tunable receiver (TTTR)

    • most flexible, expensive

  • Fixed transmitter and tunable receiver (FTTR)

    • each node sends data on a fixed channel

    • receiver is tuned to receiving channel before data reception

    • have receiver contention problem

  • Tunable transmitter and fixed receiver (TTFR)

    • each node receives data on a fixed channel

    • transmitter is tuned to the receiving channel of the destination node before sending data

T

T

T

T

R

R

R

R

Lightwave Networks

  • connection between two hosts via a channel  need to access channel

  • Channel: Wavelength (in WDM network), Time Slot (in TDM network)

A

B

C

D


Optical technologies and lightwave networks

l1, l2, l3

l1, l2*, l3

Add-drop Multiplexer (ADM)

l2

l2*

DROP

ADD

l1

l1, ..., lN

l1*, ..., lN

lN

l1*

l1

Lightwave Networks

Channel add-drop

Wavelength ADM:

ADD

DROP


Optical technologies and lightwave networks

l11, l12, l13, …, l1M

l11, lN2, … , l3(N-1), l2N

l21,l22, l23, …, l2M

l21, l12, lN3, … , l3N

l31,l32, l33, …, l3M

l31, l22, l13, lN4, ...

lN1, lN2, lN3, …, lNM

lN1, … , l3(N-2), l2(N-1), l1N

Lightwave Networks

Static Optical Cross-Connect: Channel routing

(fixed wavelength routing pattern)


Optical technologies and lightwave networks

l1

#1

#1

l11 , l12 , ... , l1M

l21 , l12 , ... , lNM

l2

#2

#2

l21 , l22 , ... , l2M

l11 , lN2 , ... , l2M

lM

#N

#N

lN1 , lN2 , ... , lNM

lN1 , l22 , ... , l1M

Routing control module

Lightwave Networks

Dynamic Optical Cross-Connect: Channel switching


Optical technologies and lightwave networks

l1 with data

l2 with data

Wavelength Converter

l2 no data (continuous-wave)

l1

l1

l1

l1

l2

l-converter

Lightwave Networks

Wavelength Conversion

Resolve output contention of same wavelength from different input fibers

l1 , l2

output contention


Optical technologies and lightwave networks

Lightwave Networks

Common optical networks: SDH, SONET, FDDI

  • “All-Optical” Networks

  • reduce number of O/E and E/O interfaces

  • transparent to multiple signal format and bit rate

     facilitates upgrade and compatible with most existing electronics

  • manage the enormous capacity on the information highway

  • provide direct photonic access, add-drop and routing of broadband full wavelength chunk of information


Optical technologies and lightwave networks

Lightwave Networks


  • Login