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Introduction to optical networks – Light propagation X – Polymer Optical Fibres. Marc Wuilpart, Véronique Moeyaert, Patrice Mégret : FPMs, [email protected] Our main reference. Polymer Optical Fibers for Data Communication W. Daum, J. Krauser, P.E. Zamzow and O. Ziemann

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Introduction to optical networks – Light propagation

X – Polymer Optical Fibres

Marc Wuilpart, Véronique Moeyaert, Patrice Mégret : FPMs, [email protected]


Our main reference

Polymer Optical Fibers

for Data Communication

W. Daum, J. Krauser,

P.E. Zamzow and O. Ziemann

Springer, 2005


POF fibres are designed for short range optical transmission

  • Increase of the necessity of installing optical systems in local environment (100 m).

  • For example : - Company (LAN)

  • - Vehicle (multimedia system, safety system)

  • - Home (FTTH, domotic, lighting technology)

  • - Aerospace (sensing)

  • Development of cheaper optical systems and, in particular,

    a cheaper optical fibre.

  • POF fibres (Polymer Optical Fibres)

  • Advantages : - Insensible to electromagnetic interferences.

  • - light, easy to install

  • - more cumbersome


POF fibres is a solution to increase bit rates in LAN

From http://www.physics.iitm.ac.in/~labs/iitmspie/Nampoori.pdf


POF fibres are used in car manufacturing

BMW : "We are using two bus systems, one for all multimedia applications and one for connecting all of the sensors in the safety devices. There is no price advantage for using POF instead of copper. The advantages for us are high data rates, reduced weight, less packaging and no problems with electromagnetic interference.“ (Optics.org)

From http://www.physics.iitm.ac.in/~labs/iitmspie/Nampoori.pdf

From the BMW 7 booklet



POF fibres in domotic: system centralization

From http://www.physics.iitm.ac.in/~labs/iitmspie/Nampoori.pdf


POF fibres are used for lighting technology

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


POF are also used for optical sensing

From http://www.physics.iitm.ac.in/~labs/iitmspie/Nampoori.pdf


POF dimensions are big compared to glass fibres

POF fibres are characterized by - a high numerical aperture : (0.50 to 0.90)

- a high core diameter (1 mm)

 Less demanding for connection technology and easier to manufacture

 The cost is reduced compared to glass fibres

  • Multimode fibres

  • Ray optics can be

    used

N=4380000 for =520nm, NA=0.50 and d=980m

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.



The theory developed for glass fibres is still applicable

The mode calculus is identical to glass fibre

In particular, two phenomena are not negligible in POF fibres :

  • Mode coupling : energy transfer between propagation modes

  • Mode conversion : a mode can convert into another mode when propagating


In POF a coupling between modes is possible

Diffusion center in the fibre core can change the light direction (other mode)

 Influence on the attenuation

Not perfect core/cladding interface at the sub-nanometric level generates new angles

 Mode coupling depends on the propagtion angle

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Bending generates mode conversion in POF

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.



POF fibres are designed for short range optical transmission

Losses are 400 times greater than glass fibre

 Short distances (loose 50% after 38m)

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Losses are due to intrinsic and extrinsic phenomena

Intrinsic losses

  • Absorption through electronic transition (UV)

  • Absorption through molecular vibrations (C-H in POF, IR)

  • Rayleigh scattering (proportional to 1/4)

Extrinsic losses

  • Absorption by doping atoms/molecules

  • Scattering at impurities in the fibre and imperfections at the core/cladding interface


Three windows appear in the attenuation spectrum

  • Visible sources

  • LED’s are available at 520, 570 and 650 nm

  • LD at 650 nm allows to reduce the extra attenuation due to the large spectrum of LED

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


POF are characterized by mode dependent attenuation

Two mechanisms:

1. In POF, the NA is high compared to glass fibres

 The path difference between the fundamental mode and propagation angle close to the critical angle can reach 6% (std POF, NA=0.50)

 Attenuation is higher for high order modes

 Mode-dependent attenuation

2. At the core/cladding interface, the light projects into the cladding by a distance in the order of magnitude of the wavelength

 The number of reflection depends on the mode

 Mode-dependent attenuation

 Mode conversion generates additional attenuation

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.



POF intermodal dispersion is larger compared to silica fibres

For a standard POF (NA=0.50 and n2=1.456)

 T = 290 ns/km

> 67 ns/km for glass fibres

  • In practice, T does not vary linearlywith L because of the mode dependent attenuation

  • Lk dependence for L>Lc

    0.5 < k < 0.8

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


POF chromatic dispersion is also larger compared to silica fibres

At 650 nm, D = 300ps/(nm.km)

 20x larger compared to silica fibres at 1550 nm

Moreover : use of LED (20-40nm spectral width) which increases the dispersion

But : short distances which decreases the total dispersion

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Influence of chromatic dispersion in POF fibres

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.



The bending loss depends on two parameters fibres

Sensitivity of POF to bending is of special significancedue to their fields of application (car, home,…)

Two parameters influence the bending losses: NA and the core diameter

Influence of NA

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.

from Keiser, "Optical Fiber Communications"


The bending influence can be explained by ray optics fibres

When NA increases, the angle variation effect is less damaging because the critical gets smaller

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


POF are characterized by mode dependent attenuation fibres

Influence of the core diamteter

The smaller the core diameter, the smaller the bending losses

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.

When the core radius decreases, the number of modes decreases as well as the power fraction in the cladding.


Bending losses do not vary linearly with the number of bends fibres

During the propagation, there is less and less energy present in the highest modes

=650nm

R=32mm

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.

The NC fibre is a low-NA POF

 Care during installation


GI-POF are characterized by larger bending loss fibres

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.



The transfer function gives the bandwidth of POF fibres

Amonochromatic wave is modulated and the output power is measured in the electrical domain  transfer function

std POF, NA=0.50, L=30m

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


POF with lower NA give a larger bandwidth fibres

Lower NA decreases the number of modes the intermodal dispersion is reduced The bandwidth is increased

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Bandwidth evolution with the fiber length fibres

Due to mode dependent attenuation, the real bandwidth are larger than foreseen by the theory: higher-order modes responsible of high intermodal dispersion attenuates faster than low-order modes.

  • The bandwidth decreases when L increases

  • The bandwidth does not decrease linearly with L due to the presence of mode coupling, mode conversion and mode dependent attenuation

  • The bandwidth is approximately identical for the three windows

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Four main methods are possible to increase the bandwidth fibres

  • Launching light with a effective NA lower than the fibre NA

  • Reducing the number of modes detected at the receiver

  • Using pre-distorsion by means of a high pass filter (peaking)

  • Using high pass filter for dispersion post-compensation

3 1 2 4

  • 500 Mbits/s over 100m (NA=0.11)

  • 1Gbit/s over 10m (Daimler-Chrysler)

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Several methods exist for mode filtering fibres

Injection system using lenses

Bending based system

 50 to 80% BW increase

 Loss of 3dB

Figures from « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


The “peaking” modifies the temporal signal fibres

The higher frequencies are relatively increased

Figures from « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Nowadays system performances fibres

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Types of POF fibres


Nowadays system performances fibres

  • The first POF was manufactured by DuPont at the end of the 60’s (1000 dB/km).

  • During the 70’s: reduction to 125 dB/km

  • Meanwhile, silica fibres (1 dB/km) have been developed for long-range transmission. Short-range transmission was adequatly operated with copper wires up to 10 Mbit/s  POF without interest for long-rang transmission.

  • During the 90’s, the increasing demand of bandwidth for short-range networks (home, company, cars,…) generated a market for POF fibres

  • POF fibres have continuously been upgraded to meet the increasing demand of bandwidth


The first POF was a step-index fibre (SI-POF) fibres

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.

+ NA = 0.50  easy for injection and reduction bending losses

d =  1mm  easy for connection technology

- NA = 0.50  low bandwidth due to high intermodal dispersion

 BW = 40 MHz over 100m (sufficient until the necessity of replacing copper wires for 155 Mbit/s bit rates over 50m (ATM)


Low-NA POF fibres increase the bandwidth fibres

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.

+ NA = 0.30 (n < 2%) easy for injection and reduction bending losses

 bandwidth is larger compared to standard POF

d =  1mm  easy for connection technology

- NA = 0.30  high sensitivity to bending

 BW = 100 MHz over 100m (sufficient until the necessity of replacing copper wires for 155 Mbit/s bit rates over 50m (ATM))


The bending sensitivity can be reduced using double-step index POF (DSI-POF)

NA = 0.30  easy for injection and reduction bending losses

+

DSI configuration alleviates the bending losses

Figures from « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Multicore POF fibres also alleviate the bending losses (MC-POF)

The fibre core can also be reduced to decrease the bending sensitivity but the advantage of easy and cheap connection technology is lost.

 Solution: MC-POF fibre: a high number (19 to 200) of core+clading structures are put together to give an effective diameter of  1mm

NA = 0.30

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


DSI-MC POF fibres also exist (MC-POF)

The bandwidth is also increased in MC-POF by reducing the index difference

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Higher bandwidth can be achieved by graded index POF fibres (GI-POF)

The bandwidth can be 2 or 3 times larger with the GI configuration

but it is rather difficult to manufacture and the profile deteriorates with time

Figures from « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


A comparable profile can be obtained usong multi step POF fibres (MSI-POF)

  • More stable with time

  • Increase of bandwith compared to standard POF but less than GI-POF

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Nowadays system performances fibres (MSI-POF)

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Materials used for POF fibres (MSI-POF)


The most used material is PMMA fibres (MSI-POF)

PMMA

Polymethylmethacrylate

« plexiglass »

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Characteristics of existing PMMA-POF fibres (MSI-POF)

GI

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.

SI


Nowadays system performances fibres (MSI-POF)

  • PMMA-POF cannot be used in high temperature environment (up to 85°C)

  • New material for agressive environment (ex.: car engine)

  • Polycarbonate or silicon elastomere

BUT higher attenuation

and higher NA  lower BW

Figures from « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


The maximum temperature is now 800°C fibres (MSI-POF)

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


Deuterium can be used to increase the power budget fibres (MSI-POF)

A significant reduction in the absorption losses of polymers can be axhieved by substituting the hydrogen with deuterium

Practical problem:

water vapor present in the atmosphere slowly replace the deuterium and a special protection coating would be too expensive. Let’s no forget that the main advantage of POF is to be cheap !

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


The fluorine is a potential solution fibres (MSI-POF)

Fluorinated POF fibres can theoretically reach 0.2 dB/km

15 dB/km in practice

Practical difficulties of manufacturing (research in progress !)

Impossiblities to realize SI-POF. PF have a very low n (1.340 at 650nm)  difficult to find a material for the cladding

From « Polymer Optical Fibers for Data Communication », Daum, Krauser, Zamzow and O. Ziemann, springer 2005.


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