Overview of Optical Communications

8/2/2019 Overview of Optical Communications

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Slide 1

An Overview of the Fundamentals of Fiber Optic Communications


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Slide 2

Topics

What are Optical Communications? Wavelengths of Light

Common Transmission Wavelengths Optical Fiber Types Dispersion in Optical Fiber Link and Loss Budget Wave Division Multiplexing

Commonly Used Optical Equipment Example Network


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Slide 3

What Are Optical Communications?

Optical communications can be described as thetransmission of information by modulation of a carrier frequency that is generated by an optical source, andthe recovery of that information by means of an opticallysensitive receiver.


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Slide 4

What Are Optical Communications?

Although todays topic is centered around opticalcommunication through fiber, there are many freespace applications of optical communications in usetoday.


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Slide 5

Wavelengths Of Light

Chromatic dispersion is the result of change of theindex of refraction with wavelength. For example, bluelight travels slower than red light in the same material,causing a separation of colors in a prism


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Slide 6

Wavelengths Of Light

Light refracted in water droplets



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Slide 7

Common Transmission Wavelengths

Optical fiber wavelengths used in communications have been

divided into several bands. These bands simply partition thefiber wavelengths into 6 segments. The most commonly usedband in the United States is the C (Common) band,covering the spectrum from about 1525-1565nm.

Band Wavelength (nm)

O band 1260 to 1360

E band 1360 to 1460

S band 1460 to 1525

C band 1525 to 1565

L band 1565 to 1625

U band 1625 to 1675



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Slide 8

Common Transmission Wavelengths

Frequency (thz) Wavelength (nm) Channel Frequency (thz) Wavelength (nm) Channel191.7 1563.86 17 194.0 1545.32 40191.8 1563.05 18 194.1 1544.53 41191.9 1562.23 19 194.2 1543.73 42192.0 1561.42 20 194.3 1542.94 43192.1 1560.61 21 194.4 1542.14 44

192.2 1559.79 22 194.5 1541.35 45192.3 1558.98 23 194.6 1540.56 46192.4 1558.17 24 194.7 1539.77 47192.5 1557.36 25 194.8 1538.98 48192.6 1556.55 26 194.9 1538.19 49192.7 1555.75 27 195.0 1537.40 50

192.8 1554.94 28 195.1 1536.61 51192.9 1554.13 29 195.2 1535.82 52193.0 1553.33 30 195.3 1535.04 53193.1 1552.52 31 195.4 1534.25 54193.2 1551.72 32 195.5 1533.47 55193.3 1550.92 33 195.6 1532.68 56193.4 1550.12 34 195.7 1531.90 57193.5 1549.32 35 195.8 1531.12 58193.6 1548.51 36 195.9 1530.33 59193.7 1547.72 37 196.0 1529.55 60193.8 1546.92 38 196.1 1528.77 61193.9 1546.12 39

100GHzC bandGrid



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Slide 9

Optical Fiber Types

Optical fiber can be divided into two basic types, singlemode and multi-mode. Single mode fibers (SMFs) havea core diameter of about 9m. Multi-mode fiber has acore diameter of 50 or 62.5 m.

Because of the longer distances an optical signal cantravel in single mode fiber, WDM networks are generallybased on single mode fiber.


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Slide 11

Optical Fiber Types

Multi-mode mode fiber cross section

Quick note: A yellow jacket is generally used for single-mode fiber, andorange for multi-mode fiber



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Slide 12

Dispersion In Optical Fiber

Chart of dispersion vs. wavelength for differing fiber types


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Slide 14

Link Budget And Loss

Loss in single mode fiber depends on the fiber type, but is linear withthe length of the fiber link. For example, for an 80km link of SMF-28Efiber with a loss of 0.25dB/km, the loss would be:

80km * 0.25dB/km = 20dB

For a given fiber link, the maximum loss that can be incurred withoutlink failure can be calculated as follows:

Link Budget = Transmitter power minimum receiver power

The loss budget would be:

Link Loss = Mux loss + Fiber loss + dispersion Loss + DeMux loss + margin



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Slide 15

Wave Division Multiplexing

Wave Division Multiplexing (WDM) is meansmultiplexing different wavelengths onto a single fiber,then de-multiplexing them at the other end of the link.

East

West

Mux

MuxDeMux

DeMux



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Slide 16

Commonly Used Optical Equipment

If the links are long, or if the loss is high, we can ErbiumDoped Fiber Amplifiers (EDFAs)

East

West

Mux

MuxDeMux

DeMuxEDFA

EDFA



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Slide 17


In some links, a regenerator is required to Retime,Reshape and Retransmit the signal (a 3R regenerator)

East

West

Mux

MuxDeMux

DeMuxEDFA

EDFA

Regen

Regen


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Slide 19


Node C in a unidirectional ring using passive add/drop muxes

DeMux

Node C

Mux



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Slide 20


Node C in a unidirectional ring using a ROADM

Node C

Mux

WSS



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Slide 21

Example Network

A customer who well call RSTC (Real Smart Telephone Company)wanted to integrate two networks into one.

They had some WDM and fixed add/drop node and were looking for flexibility and room to grow.

They asked us to make it work within our budget.



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Slide 22

Example Network

E

F

B

A C

D

Simplified view of original network(s)

OADM OADM

OADM

OADMOADM


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Slide 23

Example Network

The we had a list of things to do:

Shift the wavelengths so they wouldnt conflict Connect the networks

Add a ROADM to node B for additional drops Add wavelength shifting at the new nodes for 1310nmequipment support

Add redundancy


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Slide 24

Example Network

E

F

BA C

D

Simplified view of original networks

OADM

OADM

OADMOADM

ROADM

R OADM

R OADM


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Slide 25

Example Network

Node B is added to the mix and any wavelength or combination of wavelengths can be dropped.

Next we have to connect the two networks, but they use some of thesame wavelengths, and the customer wants to add new wavelengths

between the two networks


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Slide 26

Example Network

E

F

B

A C

D

OADM

OADM

ROADM

R OADM

R OADM

OADMOADM


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Slide 27

Example Network

E

F

B

A C

D

OADM

OADM

ROADM

R OADM

R OADM

OADMOADM

East West


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Slide 28

Example Network

DCF

EDFA

Node D East


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Slide 29

Example Network

DCF

EDFA

DeMux

Mux

From Link AD

To Link DE

Node D East


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Slide 30

Example Network

DCF

EDFA

DeMux

Mux

From Link AD

To Link DE

WavelengthShifter

Node D East


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Slide 31

Example Network

E

F

B

A C

D

OADM

OADM

ROADM

R OADM

R OADM

OADMOADM

Channel 30 in use

Channel 30 availableat Node E

Node D East


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Slide 33

Example Network

E

F

B

A C

D

OADM

OADM

ROADM

R OADM

R OADM

OADMOADM

East West


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Slide 34

Example Network

MuxDeMux

To Link EF

From Link EF

Node E Redundancy

To Client Premises Equipment

OADM

DeMuxMux

From Link DE

To Link DE


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Slide 35

Example Network

EF

BA C

D

A1508A1508

A1508

A1508

EDFA

(2) A1508 A1508

(2) A1508

A1508

A1508

A1508

AM2554 =>

AM2580 =>

(1) A2050 Chassis

(2) A2050 Chassis

(1) A2050 Chassis

(1) A2050 Chassis

(2) A2050 Chassis

EDFA

EDFA

EDFA


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Overview of Optical Communications

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