Hanoi 4-2013

Class: Materials Science EngineeringTeacher : Nguyễn Tuyết NgaStudent: Hoàng Văn Tiến

contents

- Introduction- General structures and properties- Case study : fiber optics

- Introduction- Optical Fiber & Communications System- Modes and materials- Optical fibers processing- Applications

- Applications- Conclusions and References

Introduction

Optical ceramics

Materials with special light reflecting, transmitting or other optical properties include a wide range of glass compositions, glass ceramics, and selected ceramics. 

Classification: Transparent ceramics : glass,  optical fibers,

opticalswitches, laser amplifiers and lenses… Glass coloring Luminessence ceramics…

-REFRACTION

Light that is transmitted from one medium into another, undergoes refraction.

Refractive index, (n) of a material is the ratio of the speed of light in a vacuum (c = 3 x 108 m/s) to the speed of light in that material.

n = c/v

5

6

Snell principal:

OPTICAL PROPERTIES OF CERAMICS

Callister, W., D., (2007), Materials Science And Engineering, 7th Edition, 7

12.04.23

OPTICAL PROPERTIES OF CERAMICS

ABSORPTION

•Color in ceramicsMost dielectric ceramics and glasses are colorless.

By adding transition metals (TM)Ti, V, Cr, Mn, Fe, Co, Ni

Carter, C., B., Norton, M., G., Ceramic Materials Science And Engineering, 8

Case study: fiber optics (optical fibers )

Introduction

An optical fiber is essentially a waveguide for light

It consists of a core and cladding that surrounds the core

The index of refraction of the cladding is less than that of the core, causing rays of light leaving the core to be refracted back into the core

A light-emitting diode (LED) or laser diode (LD) can be used for the source

Optical Fiber & Communications System

Optical Fibers

It has little mechanical strength, so it must be enclosed in a protective jacket

Often, two or more fibers are enclosed in the same cable for increased bandwidth and redundancy in case one of the fibers breaks

It is also easier to build a full-duplex system using two fibers, one for transmission in each direction

- Fiber optics ( optical fibers) is a flexible, transparent fiber made of glass (silica) or plastic, slightly thicker than a human hair. It functions as a waveguide, or “light pipe”,to transmit light between the two ends of the fiber

Types of Fiber Both types of fiber described earlier are known as step-index fibers

because the index of refraction changes radically between the core and the cladding

Graded-index fiber is a compromise multimode fiber, but the index of refraction gradually decreases away from the center of the core

Graded-index fiber has less dispersion than a multimode step-index fiber

Why are fiber-optic systems revolutionizing telecommunications?

Compared to conventional metal wire (copper wire), optical fibers are……….

Less costSeveral miles of optical cable can be made cheaper than equivalent lengths of copper wire. This saves your provider (cable TV, Internet) and you money.

Smaller-Thinner

Optical fibers can be drawn to smaller diameters than copper wire.

Higher carrying capacity

Because optical fibers are thinner than copper wires, more fibers can be bundled into a given-diameter cable than copper wires. This allows more phone lines to go over the same cable or more channels to come through the cable to your tv.

Less Signal Degradation

- The loss of signal in optical fiber is less than in copper wire, so there is far less “bleeding” on the lines.

Light signals

Unlike electrical signals in copper wires, light signals from one fiber do not interfere with those of other fibers in the same cable. This means clearer phone conversations or TV reception.

Low power Requirement

Because signals in optical fibers degrade less, lower-power transmitters can be used instead of the high-voltage electrical transmitters needed for copper wires. Again, this saves your provider and you money.

Digital signals

Optical fibers are ideally suited for carrying digital information, which is especially useful in computer networks.

Non-flammable

Because no electricity is passed through optical fibers, there is no fire hazard.

Lightweight

An optical cable weighs less than a comparable copper wire cable. Fiber-optic cables take up less space in the ground.

how do we make an optical fiber?

Materials : glass (silica) or plastic

Making optical fibers requires the following steps: Making a preform glass

cylinder Drawing the fibers from

the preform Testing the fibers

Making a preform glass cylinder

Purifying silica Mine sand (raw silica) React with chlorine to produce SiCl4 and

other metals from the impurities in the sand (FeCl3, etc.)

Heat this mixture (essentially distilling) Collect SiCl4 vapors only

Condense the pure SiCl4 vapors

modified chemical vapor

deposition (MCVD). Prepare a silica tube (glass extrusion). Heat the tube

Inject SiCl4 and O2 into the tube

At the heated portion, the SiCl4 is oxidized

The lathe turns continuously to make an even coating and consistent blank UItra pure SiO2 is deposited on the

inner walls of the tube Draw the tube through the furnace,

continuously coating the inner walls. SiO2 particles deposit and sinter along

the tube, leaving a hollow core [for now].

2224 2ClSiOOSiCl heat

modified chemical vapor deposition (MCVD).

This technique can be used to manufacture very long fibres (50 km). It is used for both step-index and graded-index fibres.

Plasma-Enhanced Modified Chemical Vapour Deposition (PMCVD)

Fiber drawing and protecting Anneal the multiwalled tube to the glass softening temperature.

The tube and inner coating collapse to a solid, multilayered rod.

Fire the rod at an even higher temperature softening it further. Draw the fiber through a nozzle, thinning the fiber dramatically. Core diameters from <5 to 500 um are used.

Polymer coatings must also be applied. Fibers are finally bundled.

Fiber drawing

- The tip of the preform is heated to about 2000 oC in a furnace.

- As the glass softens, a thin strand of softened glass falls by gravity and cools down.

- As the fiber is drawn its diameter is constantly monitored

- A plastic coating is then applied to the fiber, before it touches any components.

- The fiber is then wrapped around a spool.

Continuous production Fibers are drawn at 30

to 60 feet per second. Multiple polymer

coatings may be applied Thermoplastic (buffer) Aramid (strength) PVC of fluoride co-

polymer Spools of up to several

kilometers are wound.

2000 °C

Fiber optic diameter Plastic fiber has a core diameter

of up to 900 micrometer. 20-30 feet max length. Easy to work with. Cheap.

Glass fibers have cores from 8 to 62.5 micrometer across. Connecting two fibers end-to-

end is the hardest par—requires a microscope or an automatic connection of some kind.

Fiber testing

Fibers must generally pass the following tests Tensile strength greater than 100,000

lb/in2

Dimensional tolerance Temperature dependence Optical properties

Importance of Fiber Purity This complicated procedure is necessary due to the incredible

sensitivity of optical fiber communications to impurities and flaws.

Fiber optics only became a reality in 1970, when Corning figured out how to make fiber optics with less than 99% loss/km.

Light transmission through 1 km of fiber drops to 1% of the input intensity if there are only: 2 Co atoms per billion 20 Fe atoms per billion 50 Cu atoms per billion

Transmission in modern fibers is still limited to: 60 to 75 percent/km for light with a wavelength of 850 nm.

Transmission losses <1% have been achieved over >3000 miles.

Repeating Stations Repeating stations are generally placed at regular

distances along a fiber network to detect and amplify the signals since loss will occur over km, or hundreds of km, of fiber. When light drops to 95% of transmission, a

repeating station is required. Since the cost of the repeaters is high compared to

fiber, tremendous effort goes into making pure, flaw free optical fibers.

Repeating stations today are generally 100 km apart for major fiber bundles (trans-oceanic, etc).

http://www.telebyteusa.com/foprimer/foch2.htm

disadvantages

difficult to install and test optical fibers

 fiber is a less familiar technology and requires skills

Fibers can be damaged easily if bent too much

 fiber interfaces cost more than electrical interfaces

Future fiber optic manufacturing? Why bother purifying Si and the trouble of making pure

and flaw-free fiber optics when a spider does it naturally?

http://www.newscientist.com/article.ns?id=dn3522

APPLICATIONS

- Optical fiber communication : telecommunication and computer networking

- Fiber optic sensors ( remove sensing )

- Other uses…

Optical fiber communication

Fiber optic sensing systems (optical sensors )

Two types :-Intrinsic sensor : the sensors are internal or embedded into the

fibers-Extrinsic sensors : the transducer is external to the fiber 

how the environmental signal is detected

  Informations (in terms of intensity, phase, frequency, polarization, spectral content, etc.) are printed into the light beam and is carried through the optical fiber to an optical and/or electronic processor.

The environmental signal is perceived by the fiber optic itself ( as the light modulator )

-intrinsic sensor can be classified as a distributed sensor, since it allows the measurement to take place in any point along the optic fiber.

Properties of Fiber Optic Sensing

- Highly sensitive (more than other technologies) - Configuration versatility - point and distributed configurations

possible - Dielectric construction (can be used with high voltages, high

temperatures, and stressed environments) - Wide dynamic range - Multiplexing capabilities - Freedom from electromagnetic interface (fibers carry no

current) - Chemically passive - Provide real-time feedback - Resistant to corrosion - Multi point measurement (intrinsic sensors) or specific

location sensing (extrinsic sensors)

- Ability to measure a wide range of different properties (wide range of applications)

- High resistance to extreme environments due to their robustness and immunity to both electromagnetic and radio frequency interference (intrinsic sensors).

- They do not conduct electricity which means that the measurements are not easily affected by external causes (intrinsic sensors).

- Extremely small size - Remotely powered - Ability to measure direct physical strain. - Sensors can placed upon the optic fiber

Input and Output Input: Light beam that carries the information Output:

-Extrinsic: 1. encoder plates/disks: linear and angular position 2. Evanescence: temperature, strain 3. reflection and transmission: pressure, flow, damage 4. Laser Doppler velocimetry: flow measurement 5. total internal reflection: liquid level, pressure 6. absorption Band edge: temperature 7. Gratings: Pressure, Acoustics, vibrations 8. Photo elastics effects: pressure, acceleration, vibration, rotatory, position. 9. Fluorescence: temperature, viscosity, chemical analysis. 10. Pyrometers: temperature.

- Intrinsic: 1. Microbends sensors: strain, pressure, vibration. 2. blackbody sensors: temperature 3. interferometryc sensors: rotation acceleration, acoustics, magnetic fileds,

electric fields, strain, temperature, pressure, current.

Uses of Fiber optic sensing systems testing machinery monitoring conditions in bridges or

wind turbines. used for industrial automation, biomedical technologies for digital

diagnostic imagery, Endoscopy… military, space, and automotive

applications.

Example: Uses of Fiber optic sensing systems in Endoscopy

SUMMARY Optical Fiber

Processing Initial tube CVD of core Sintering and

annealing coating applications

references Callister, W., D., (2007), Materials Science And Engineering, 7th

Edition, http://www.laserfocusworld.com/articles/2011/01/

medical-applications-of-fiber-optics-optical-fiber-sees-growth-as-medical-sensors.html

http://en.wikipedia.org/wiki/Optical_fiber http://www.ofsoptics.com/fiber/ http://www.madehow.com/Volume-1/Optical-

Fiber.html#b [4] John Crisp, Barry Elliott, Introduction to Fiber

Optics, 3rd edition, Newnes, 2005 http://www.fiberopticproducts.com/ http://www.fiber-optics.info/ ………………………..