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ELEKTRONIKOS ĮTAISAI 2009 VGTU EF ESK 1 OPTOELECTRONIC SEMICONDUCTOR DEVICES

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ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

1

OPTOELECTRONIC

SEMICONDUCTOR DEVICES

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

2

• Optical effects in fibers

• Structure and types of optical fibers

• Dispersion in single mode fibers

• Attenuation

• Communication windows

• Optical cables

Optical fibers

• 1. In vacuum rays travel at velocity of 3⋅108 m/s. In any other medium rays travel at a slower speed given by v = c / n. The factor n is the index of refraction or refractive

index of the medium.

• 2. If any power crosses the boundary, the transmitted ray direction is given by Snell’s

law:

• 3. If n2 < n1 , the transmitted ray is bent away from the normal when traveling from

media having a high refractive index into a media with a lower refractive index.

• 4. At the critical incident angle, the transmission angle becomes π/2. For , the total internal reflection occurs..

•5. At a plane boundary between two media a ray is reflected at

an angle equal to the angle of incidence.

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

3

t2i1 sinsin ϕϕ nn =

crϕϕ >

Optical fibers

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

4

At n2<n1:

t2i1 sinsin ϕϕ nn =

12cr /sin nn=ϕ

reflection total:krϕϕ >

Optical fiber is round

cross-section waveguide.1966 m.: 1000 dB/km.

K.C.Kao : 20 dB/km.

1975 m.: 2 dB/km, 1979 m.: 0,2 dB/km.

• Why are only certain optical wavelengths used

in telecommunication systems?

• What are reasons of attenuation? How can we

reduce attenuation?

• What materials are used for optical fibers?

• What are reasons of distortions of optical

pulses?

SiO2

Optical fibers

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

5

In 1965, Charles K. Kao and George A. Hockham of the British company

Standard Telephones and Cables were the first to recognize that

attenuation of contemporary fibers was caused by impurities, which could

be removed, rather than fundamental physical effects such as scattering.

They demonstrated that optical fiber could be a practical medium for

communication, if the attenuation could be reduced below 20 dB per

kilometer.

The first practical optical fiber for communications was invented in 1970

by researchers Robert D. Maurer, Donald Keck, Peter Schultz, and Frank

Zimar working for American glass maker Corning Glass Works. They

manufactured a fiber with 17 dB optic attenuation per kilometer by doping

silica glass with titanium.

On 22 April, 1977, General Telephone and Electronics sent the first live

telephone traffic through fiber optics, at 6 Mbit/s, in Long Beach,

California.

http://en.wikipedia.org/wiki/Optical_fiber

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

6

Step-index fiber

c// 11 lnvlt ==

cnlnlnt 221cr12 /sinc/ == ϕ

c2

1 n

n

n

l

t ∆∆=

nn

n

t

lBl

∆∆c

1

2=≅t

B∆1

↓↓

==

−==

−=

−=

=

==

↓↑

0

20

22

21ma

a22

21m

122

21cr

12cr

cr1m1ma

,

)( ,cos)(

sin

sin

cos

/sin

cossinsin

if ,

ΦΦ∆

ΦΦθθ

α

α

ϕ

ϕ

ϕθα

/n

NA/I

nnNAn

nnn

nnn

nn

nnn

nBl

How can we reduce dispersion?

SiO2

Pulse

out.

Multipath (delay) time dispersion,… bit-rate,…

n1 = 1.5, n2 = 1, … Bl = 0.4 (Mb/s)km

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

7

t = 0 X

Initially the density of runners

can be approximated by δ

function.

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

8

t = 4 min

X

After some time the pulse

characterizing density of

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

9

( )

[ ]( )

18

,8cc8

),2(1 If

2 ,)/()(

if ,)(21)(

:ionApproximat

...5,01cosh)(

02

0

20

22

20

2/10

2200

<<≅=

−≅

−==

≤⋅−=

+−≅=

δδδδ∆

δα

δ

δ

αα

α

nn

l

t

nnnarrf

arrfnrn

rnrnrnThe axial ray follows the most direct path

through the fiber, but travels through the

most refractive part of the medium and

therefore travels most slowly.

The oblique rays travel further but much of

their path lies in a medium of lower

refractive index, in which they travel faster.

Due to this the multipath time dispersion is

less.

The refractive index decreases

continuously with distance from the

fiber axis.

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

10

• If α = 2, dispersion is minimal.

• The refractive index profile

must be precise.

µm 102 ,π

405,22

22

21

<−

< ann

wm ,/ DDDDlt +== λ∆∆

Multimode and single mode fibers

Propagation of light can be considered as

propagation of electromagnetic waves.

SI and GRIN fibers are multimode

fibers. Many types of electromagnetic

waves can propagate along the fibers as

dielectric waveguides. Then the

dispersion is due to different phase

velocities of the waves.

We can reduce the number of the

waves that can propagate and

reduce the mode dispersion

reducing the core diameter.

Dispersion is minimal in the

single-mode fibers. The core

diameter of a single-mode fiber is

less than 10 µm.

Chromatic dispersion

α

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

11

A typical single-mode optical fiber,

showing diameters of the

component layers.

Single-mode fiber

Dispersion is minimal in

the single-mode fibers.

The core diameter of a

single-mode fiber is less

than 10 µm.

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

12

Dispersion in the single-mode fibers

( )αβω

jc

'j* +=+= nnn

n is dependent on λ and Npr

2

2

m

m2

2g

d

d

c

,d

d

c

λ

λ

λ∆λ∆λ

λ∆

nD

Dn

l

t

−=

=−≅

Visible light

Infrared rays

Ultraviolet rays

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

13

2wwm)π2(c

,an

DDDDλ

−≅+=

The chromatic dispersion is

minimal at λ = 1300 nm.

In DSF (dispersion shifted fibers):

dispersion is minimal at λ = 1550 nm

In DFF (dispersion flattened fibers)

dispersion is small in the range from

1300 to 1700 nm.

Dispersion in the single-mode fibers

ELEKTRONIKOS ĮTAISAI 2009

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14

Attenuation

zWW dd α=−

)exp()0()( zWzW α−=

)/exp()/exp(

)/exp()/exp(

uvuvuvuvuv

iririririr

λλα

λλα

AWWA

AWWA

==

−=−=

Attenuation in glass is

caused by

absorption and

scattering of light.

Slopes of ...

Rayleigh scattering...

4RR /λα A=

Attenuation is minimal at

wavelength of 1.55 µm.

Attenuation

Rayleigh scatteringAbsorption

Impurities cause increase

of attenuation.

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

15

• Glass (silicon dioxide, also called silica) is used

usually for optical fibers.

• An optical fiber consists of core and cladding,

having less refractive index.

• In multi-mode fibers light propagates reflecting from

• To reduce distortions of optical pulses, we must

reduce dispersion and attenuation.

• In the single mode fibers minimal dispersion is

achieved at wavelength of 1.3 µµµµm, minimal attenuation is at wavelength of 1.55 µµµµm.

Optical fibers

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

16

• Three communication windows are used in

practice.

• The first communication window is at the

wavelength of 0.85 µm. It is related to GaAs light sources.

• The second window is at 1.3 µm. At this wavelength attenuation is small and dispersion is minimal.

• The third window is at 1.55 µm. At this wavelength attenuation in a glass fiber is minimal.

• Minimal dispersion at 1550 nm is achieved using the

dispersion-shifted fibers. Small dispersion in

the range 1300–1600 nm is achieved in the

dispersion-flattened fibers.

Optical fibers

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

17

Optical cable

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

18

Optical cable

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

19

Indoor/Outdoor Breakout Cable

Armored Cable

Optical cables

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

20

Optical cable

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

21

Optical cable

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

22

202020102000199019801970

Year

Transmission Capacity (b/s)

1011

1010

109

108 100 M

400 M

2.5 G

1.6 G

10 G

1.3 µm SMF

FP-LD

HIC

: Under Development

1.55 µm DS-SMF

DFB-LD

Si-MIC

Optical Amplifier

External Modulator

Si-/GaAs-MIC

Soliton Transmission

Optical FDM

Quantum Effect Devices

OEIC

Evolution of Technology (T. Miki, IEEE Proc. Nov. 1993, pp 1594-1609)

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

23

In mathematics and physics, a soliton is a self-reinforcing solitary

wave (a wave packet or pulse) that maintains its shape while it

travels at constant speed; solitons are caused by a delicate balance

between nonlinear and dispersive effects in the medium.

The soliton phenomenon was first described by John Scott

Russell (1808-1882) who observed a solitary wave in the Union

Canal, reproduced the phenomenon in a wave tank, and named it

the "Wave of Translation".

In 1973, Akira Hasegawa of AT&T Bell Labs was the first to

suggest that solitons could exist in optical fibers, due to a balance

between self-phase modulation and anomalous dispersion. He

also proposed the idea of a soliton-based transmission system to

increase performance of optical telecommunications.

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

24

Solitons

In mathematics and physics, a soliton is a self-reinforcing solitary

wave (a wave packet or pulse) that maintains its shape while it

travels at constant speed; solitons are caused by a delicate balance

between nonlinear and dispersive effects in the medium.

The soliton phenomenon was first described by John Scott Russell

(1808-1882) who observed a solitary wave in the Union Canal,

reproduced the phenomenon in a wave tank, and named it the

"Wave of Translation".

In 1973, Akira Hasegawa of AT&T Bell Labs was the first to

suggest that solitons could exist in optical fibers, due to a balance

between self-phase modulation and anomalous dispersion. He also

proposed the idea of a soliton-based transmission system to increase

performance of optical telecommunications.

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

25

In 1988, Linn Mollenauer and his team transmitted soliton pulses over 4,000

kilometers using a phenomenon called the Raman effect, named for the

Indian scientist Sir C. V. Raman who first described it in the 1920s, to

provide optical gain in the fiber.

In 1991, a Bell Labs research team transmitted solitons error-free at 2.5

gigabits over more than 14,000 kilometers, using erbium optical fiber

amplifiers (spliced-in segments of optical fiber containing the rare earth

element erbium).

In 1998, Thierry Georges and his team at France Télécom R&D

Center, combining optical solitons of different wavelengths

(wavelength division multiplexing), demonstrated a data

transmission of 1 terabit per second.

In 2001, the practical use of solitons became a reality when

Algety Telecom deployed submarine telecommunications

equipment in Europe carrying real traffic using John Scott

Russell's solitary wave.

In 1988, Linn Mollenauer and his team transmitted soliton

pulses over 4,000 kilometers using a phenomenon called the

Raman effect, named for the Indian scientist Sir C. V. Raman

who first described it in the 1920s, to provide optical gain in

the fiber.

In 1991, a Bell Labs research team transmitted solitons error-

free at 2.5 gigabits over more than 14,000 kilometers, using

erbium optical fiber amplifiers (spliced-in segments of optical

fiber containing the rare earth element erbium).

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

26

Solitons

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

27

In 1998, Thierry Georges and his team at France Télécom

R&D Center, combining optical solitons of different

wavelengths (wavelength division multiplexing),

demonstrated a data transmission of 1 terabit per second.

In 2001, the practical use of solitons became a reality when

Algety Telecom deployed submarine telecommunications

equipment in Europe carrying real traffic using John Scott

Russell's solitary wave.

Solitons

ELEKTRONIKOS ĮTAISAI 2009

VGTU EF ESK [email protected]

28

The refractive indices of the core and cladding are 1.45

and 1.43 respectively. Light wavelength is 1.55 mm.

Find the maximal core diameter of the single-mode fiber.

Optical fibers