fiber optics workshop dr feng zhou department of physics indiana university of pennsylvania

72
Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Upload: harriet-sims

Post on 22-Dec-2015

212 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Fiber Optics Workshop

Dr Feng ZhouDepartment of Physics

Indiana University of Pennsylvania

Page 2: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Biography

PhD in Optics in 1989 5 years postdoc in the UK (Strathclyde U.,

Glasgow U., and Imperial College) 5 years lecturer at Nanyang Technological

U in Singapore (teaching & research); 5 years of working experience with

industry in the US (Corning Applied Tech, Nanovision, Phosistor, ESI Newwave Research).

Joined IUP since 2003, the new EO program supported by OP-TEC

2

Page 3: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Workshop Outline

This course consists of 2 sessions. This afternoon session is 4 hours (1-5 pm) and tomorrow morning is 1.5 hours (from 8:30-10:00 am).

This lecture is condensed from a 30 hr training course for Certified Fiber Optics Technician.

Sequence ->History -> basic concepts -> optical fibers -> light sources -> detectors -> other components such coupler and optical amplifier

3

Page 4: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Objectives

After completing this workshop, participants will be able to: Define the basic technical differences

between optical, wired, and wireless communications systems.

Discuss applications of optical, wired, and wireless communications systems.

Explain some of the factors that can impact optical, wired, and wireless communications systems.

4

Page 5: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

5

The Textbook

We will cover all the content except the fiber sensors.

Page 6: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

6

Fiber Optic Installation Standard

ANSI/NECA/FOA 301 Written for installers Defines installation

in a “neat and workmanlike manner”

Covers premises and outside plant

Free online

Page 7: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

7

Lennie Lightwave’s Guide

http://www.lennielightwave.com

Page 8: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Session 1:

Basics of Fiber Optics

This session provides • A historical review of Fiber Optics

development• Refractive index, total internal reflection• An understanding of the basics of optic

fiber.

Page 9: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

9

What is Fiber Optics

Transmitting communications signals using light over hair thin glass or plastic fibers

Concept over a century old

Technology used commercially for 25 years

Page 10: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

10

History

Interest in the use of light as a carrier for information grew in the 1960's.

As Corning made the first low loss glass fiber in 1970 (<20dB/km), it became feasible to use optical fibers as a practical transmission medium. The high loss was due to impurities.

Charles Kao 2009 Nobel price By 1980 world wide installation of fiber

optic communication systems had been achieved.

By 1990, erbium doped fibers were used as optical amplifiers.

Page 11: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

11

Future Trends

Fiber is already used in: >90% of all long distance telephony and

>50% of all local telephony; Most CATV networks and LAN backbones; Many video surveillance links.

Fiber is the least expensive, most reliable method for high speed and/or long distance communications

While we already transmit signals at GB/s speeds, we have only started to utilize the potential bandwidth of fiber.

Page 12: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

12

Advantages of Fiber Optic Comm

What are the advantages?

Page 13: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

13

Advantage 1

Capacity - Optical fibers carry signals with much less energy loss than copper cable and with a much higher bandwidth. This means that fibers can carry more channels of information over longer distances and with fewer repeaters required. Bandwidth: A measure of the maximum

frequency by which light intensity can be modulated [MHz/km]. The greater the bandwidth, the greater the information carrying capacity .

Page 14: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

14

Advantage 2 Size and Weight - Optical fiber cables

are much lighter and thinner than copper cables with the same bandwidth. This means that much less space is required in underground cabling ducts. Also they are easier for installation engineers to handle.

 

Page 15: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

15

Advantage 3

Security – difficult to tap information; a great

advantage for banks and security installations.

immune to Electromagnetic (EM) interference from radio signals, car ignition systems, lightning etc. They can be routed safely through explosive or flammable atmospheres.

Page 16: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

16

Advantage 4

Running Costs - The main consideration in choosing fiber when installing domestic cable TV networks is the electric bill. Although copper coaxial cable can handle the bandwidth requirement over the short distances of a housing scheme, a copper system consumes far more electrical power than fiber, simply to carry the signals.

Page 17: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

17

Application Areas of Fiber Optics

Telecom - telephones and the Internet (capacity)

LANs - local area networks (weight/size)

CATV (cable TV) - for video, voice and Internet connections (low running cost)

Security - CCTV (closed circuit TV) and intrusion sensors (security)

Military - everywhere! (immune to EM & security)

Page 18: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

18

Basic Fibre Optic System

Electrical

Signal In

Driver

O/pCircuit

Source Detector

Electrical

Signal Out

Transmitter Receiver

FO cable plant

Transmitter: uses laser or LED, etc to covert an electrical signal to an optical signal.

Receiver: uses a photodiode to convert optical to electric signal.Physical plant: Fiber (SM or MM); Cable (application specific); Connectors; Splices; Panels; and Closures.

FO cable plant

Page 19: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

19

How to make glass fibers

Three methods:(1) MCVD(2) OVD(3) VAD

Page 20: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

20

Deposition by MCVD process

Page 21: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

21

Consolidation When deposition is complete, the tube with

the soot is placed into a consolidation furnace.

During the consolidation process, the tube changes into a solid, dense, transparent glass blank which is called preform.

After the preform cools, it is ready for drawing.

Which part will be the cladding? The core?

Page 22: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

22

Fiber Drawing Tower

1900-2500oC

Diameter controlbuffer coating

buffer coating

10-20 m/s

Page 23: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Video

How to make a preform How to draw fiber from a preform

23

Page 24: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

24

Optics - Reflection of Light

Consider the light strikes a flat mirror at the point P and is then reflected.

How do you describe the reflected beam?

Page 25: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

25

Law of Reflection

The surface normal is a line perpendicular to the surface at the point the light ray hits

The normal and the incident ray form the plane of incidence.

p

surface normal

reflecting surfaceplane of incidence

Angle of incidence = angle of reflection

The incident ray, normal, and the reflected ray all lie in the incidence plane perpendicular to the reflecting surface.

Page 26: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

26

Speed of Light

In vacuum: The speed of light c = 3x108 m/s

Light/Matter Interaction Think about the speed of light in air, in

water and in a solid, which speed is fastest? Which speed is slowest? Why?

Page 27: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

27

Index of refraction, n

Index of refraction, a way to indicate the speed of light in a medium

n = c/v n<1, ~ 1, or > 1? Slow down the speed of light with a huge

n?

Page 28: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

28

Index of Refraction n

In vacuum, the speed is highest. c = 3x108 m/s.

In traveling through all matter, the velocity is slower, depending on material properties.

Page 29: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

29

Refractive Indices of Materials

Material nair 1.00027

water 1.33glass 1.5

diamond 2.4

ngas < nliquid < nsolid. Higher refractive index means

more dense of the material.

Page 30: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

30

Light at a Boundary

“Different refractive indexes” form boundaries.

At a boundary, some light is reflected, some transmitted, and some absorbed depending on material

properties which form the boundary

n1

n2

Page 31: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

31

Law of refraction

How about the direction of the refracted light?

Amount of bending depends on refractive indexes n1, n2 of the two materials, as given by Snell’s law.

n1sinq1 = n2sinq2

Page 32: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

32

Two possible cases exist

n1 < n2 n1 > n2

q1

q2

q1

q2

When traveling from less dense to more dense medium, light is bent toward the normal.

When traveling from more dense to less dense medium, light is bent away from the normal.

n1Less denseAir n = 1.0

More densen2glass n = 1.5

n1More denseGlass n = 1.5

Less densen2Air n = 1.0

Page 33: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

33

Total Internal Reflection (TIR)

From more dense to less dense medium, light is bend away from the normal => So q2 > q1.

What will it happen if we increase q1?

q1

q2

qc

n2 = 1

n1 = 1.5

2n2sin 1n1sin

Page 34: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

34

Critical angle

At the point when q2 = 90o, q1 has reached a value called the critical angle (q1 = qc ).

n1sinqc = n2sin90o

sinqc = n2/n1qc = arcsin (n2/n1) = sin-1(n2/n1)

Once q1 >= qc, there is no transmitted ray and all the light energy is reflected.

This phenomenon is called Total Internal Reflection (TIR).

Page 35: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

35

Examples – qc at Interfaces

Ex 1: Given: n1 = 1.49 for glass fiber core and n2=1.47 for the cladding. Find: critical angle qc

Solution

deg60.80)49.1/47.1arcsin( c

Ex 2: For a glass-air interface, n1 = 1.5, n2 = 1.0, and the critical angle is given byqc = sin–1 (1.0/1.5) ≈ 41.8°

Page 36: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

In the 1840s, people noticed that the light cold be guided in a jet of water flowing from a tank.

This is now known as total internal reflection (TIR).

Light propagates through fibers by the principle of TIR. 36

Demonstrations of TIR

More TIR examples:• Light pipes• Right angle prisms

Page 37: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

37

For TIR to Occur

The refractive index of the 1st medium is greater than the refractive index of the 2nd one. e.g.., glass to air

The incident angle is large. TIR causes 100% reflection (no energy loss).

In no other situation in nature, where light is reflected, does 100% reflection occur. So TIR is unique and very useful.

Page 38: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

38

Is a dielectric waveguide. Core refractive index is higher than the

cladding refractive index. Light is confined within the optic fiber

by TIR.

Optic Fiber

Page 39: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

39

Attenuation vs wavelength

v1 O–Si–O bending mode; v13 O–H stretching mode

Page 40: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

40

Transmission Windows

Fiber Type/ Wavelength

850 nm 1300 nm 1550 nm

Multimode 3 dB/km 1 dB/km NA

Singlemode 1 dB/km 0.4 dB/km 0.25 dB/km

Page 41: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

41

Structure of an Optics Fiber

Core refractive index is higher than the surrounding material’s refractive index.

Light is confined within the optic fiber by Total Internal Reflection (TIR). Core and cladding are

both made of glasses of different refractive indexes and can not be separated.

Page 42: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

42

Fiber Technology

Page 43: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

43

Fiber Core/Cladding Sizes

Here are the three most widely used fiber types:

• 50/125 microns;• 62.5/125 microns; • 8-10/125 microns.

• The buffer has a diameter of 250 microns.

• Human hair has a typical diameter of 75 microns.

Page 44: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

44

Cross Section of a Bare Fiber

Bare fiber

Page 45: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

45

Cross Section of a Fiber Cable

Fiber Cable

Page 46: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Metric Units

46

Fiber optics uses the metric systems as the standard form of measurement.

Several of the more common terms are: Meter (m): 39.37 inches, or just slightly

larger than a yard. Kilometer (km): 1,000 meters (3,281

feet) or approximately 0.62 of a mile. Micron (m): One millionth of a meter. Nanometer (nm): One billionth of a

meter.

Page 47: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

47

Numerical Aperture

Numerical Aperture is the “light gathering ability”

The numerical aperture is defined as NA = (n1

2 – n22) = sinqA

It is a measure of the light gathering power of the fiber.

Example: Calculate NA and the acceptance angle of a fiber with a core refractive index of 1.53 and cladding of 1.50.

Page 48: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

48

About NA

It lies between 0 and 1. A numerical aperture of 0 means that

the fiber gathers no light (corresponding to qA = 0o). A numerical aperture of 1 means that the fiber gathers all the light that falls onto it (corresponding to qA = 90o).

Page 49: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

49

High NA vs low NA

Page 50: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

50

The Fiber Loss - Decibel (dB)

A logarithmic unit describing the ratio of two powers.

dB = 10 log10 (Pout/Pin) dB = 10 log10 (power remaining)

CircuitInput power, Pin Output power, Pout

• Used to measure losses (or attenuations).

Page 51: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Example – power ratio and dB

Power remaining dB Ratio 100% 0 1 95% -0.22 0.95 90% -0.46 0.9 80% -0.97 0.8 70% -1.55 0.7 60% -2.22 0.6 50% -3.01 0.5

51

Page 52: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Example – power ratio and dB

52

Power remaining dB Ratio

40% -3.98 0.4 30% -5.22 0.3 20% -6.99 0.2 10% -10 0.1 5% -13 0.05 2% -17 0.02 1% -20 0.01 0.1% -30 0.001 0.01% -40 0.0001

Page 53: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

53

dBm

Definition: dBm = 10 log10 (P/1 mW), P –power

Decibels referenced to a milliwatt dBm gives an absolute value dB measures the ratio of two power

Page 54: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Example – dBm and Power in mW

Power in W Power in mW dBm 100W 100,000 50 60W 60,000 47.8 1W 1,000 30 0.5W 500 27 0.1W 100 20 0.02W 20 13 0.01W 10 10 0.001W 1 0 0.0001W 0.1 -10 0.00001W 0.01 -20 54

Page 55: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

55

Power Budget

System design RX Power = TX Power –aL– Nspliceηsplice –

Nconnectotηconnector - System margin

TX RXOptical fiber

Transmitter Receiver

Express received and transmitter power in dBm, losses in dB.

2 – 10 dB(aging)

Average splicinginsertion lossLoss

Average connectorinsertion loss

Page 56: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

56

Example

Perform a link budget analysis to determine the margin, and sketch a power budget graph.

Given: Transmitter output: -14 dBmReceiver sensitivity: -35 dBm

Fiber loss: 2.2 dB/kmCable length: 4 kmConnector/splice: 1 pair with 1.5dB loss/pair

(Do not forget the 2 connector pairs needed for the transmitter and receiver)

Page 57: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Answers

1. Fiber loss _4km x 2.2 dB/km = 8.8 dB_____

2. Connector Loss__1.5x(2) = 3 dB ____3. Fusion splice loss _1.5x1 = 1.5 dB

________

4. Total cable plant loss (1+2+3) _13.3 dB ____

5. Maximum allowable loss (with excess margin factored in)_-14 – (-35) = 21 dB __________

6. Link loss margin_ 21 – 13.3 = 7.7 dB ______

57

Page 58: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

58

Power Budget Graph

-35

-25

-15

-5

1km 2km 3km 4km 5km

T R

margin

Page 59: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

59

Fiber Types

Page 60: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

60

Fiber Classification

MATERIAL MAKEUP

REFRACTIVE INDEX AND MODE

glass, pcs, plastic, etc

Step-index

Multi-mode

Single-mode

graded-index, etc

Page 61: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

61

Fiber Classification – glass fiber

Glass fiber – most common made of ultrapure silicon dioxide or fused

quartz. If sea-water were as clear as a fiber, you could

see to the bottom of the deepest trench ~ 11 km-deep Marianas Trench in Pacific (7 miles)

Impurities are added to change the refractive index

Germanium or phosphorus increases the index Boron or fluorine decreases the index

Page 62: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

62

PCS fiber means plastic-clad silica fiber Glass core and plastic cladding Performance is not as good as glass

fiber No buffer coating needed

Fiber Classification – PCS fiber

Page 63: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

63

Plastic core and plastic cladding Disadvantage – high loss and low

bandwidth Advantages – low cost and easy to use Applications – loss or bandwidth is not a

concern No buffer coating needed

Fiber Classification – Plastic fiber

Page 64: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

Mode

64

A path. Singlemode fibers have a single path at a single wavelength. Multimode fibers have multiple light paths at a single wavelength. The number of modes in a fiber will increase as the fiber core increases, or the wavelength decreases.

Page 65: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

65

Modes in optic fibers

Optical fibers can sustain as few as one mode to greater than 100,000 modes.

n n

Page 66: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

66

Fiber types

• In defining fiber types, we will not use physical materials for classification.

• Fiber types are classified according to the type of mode structure and light passage paths in the fiber.

• The three fiber types are• step-index (multimode step-index fiber)• graded-index (multimode graded-index

fiber)• single-mode (single-mode step-index

fiber)

Page 67: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

67

Step-index (SI) Fiber

Step-index fiber was the first fiber developed and the simplest of the three types.

It has many modes depending on the core size and the refractive index differences between the core and cladding.

The different modes travel different distances along the fiber as they bounce down the optical fiber.

It suffers from having the lowest bandwidth.

Page 68: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

68

Graded-index Fiber

This construction is similar to having many concentric cylinders or tubes of optical material.

The outer layers have a lower refractive index to "speed up" these light rays, compensating for the greater distance traveled.

n To overcome the

lengthening effect, a graded refractive index core was developed.

Page 69: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

69

Single-mode Fiber

• A fiber only allows a single mode to pass efficiently.

• For a fiber to behave as a single mode, the diameter of the core must be very close to the size of the wavelength of the optical carrier. The core is ~ 8 to 10 µm in diameter.

• A single-mode fiber at 1300 nm may not be single-mode at 820 nm. Most commonly available single-mode fibers are for 1300 and 1500 nm systems.

Page 70: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

70

Review Advantages of Optic Fiber

1. High Capacity/Large bandwidth 10 Gbps x 160 channels x 108 fibers

2. Low running costo Low loss (attenuation ~ 0.2dB/km)

3. Light weight & Small size 9 times lighter than coaxial cable 10 times smaller than coaxial cable

4. Safety & Security (dielectric, no fire, chemical, etc

hazard) (no radiation leakage) Electromagnetic immunity (no EM

interference)

Page 71: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

71

Review

The simplest fiber optic cable consists of two concentric layers. The inner portion, the ____, carries the

light. The outer covering is the ______.

The cladding must have a (higher, lower) ______ refractive index than the core.

therefore, the core and cladding material (is, isn’t) _____ exactly the same.

n1 (>, <) _______ n2. n1

n2

Page 72: Fiber Optics Workshop Dr Feng Zhou Department of Physics Indiana University of Pennsylvania

72

Review