high speed transmission over mmf and pf-pof using mimo ... · two mmf detection points ¾two...

Lehrstuhl fürNachrichten- und Übertragungstechnik

Technische Fakultät derChristian-Albrechts-Universität zu Kiel

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S.Schöllmann, 9.1.07

1

Stefan Schöllmann

High Speed Transmission over MMF and PF-POF using MIMO

Approach



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Motivation

Initial Point: High speed transmission over short distances (< 300m)

Easier handling compared to SMF

Multi Mode Fibre & Plastic Optical Fibre

• Bending

• Connectors

• Cheaper components

Short reach at high speed

• Low bandwidth distance product

• Coarse (C)WDM

• Equalization

• Mode Group Diversity Multiplexing

Research Topic: Increase of bandwidth distance product

Existing Alternative



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Outline

• Motivation

• Introduction

– Multi Mode Fibre (MMF) and Plastic Optical Fibre (POF)

– Optical Multi Input Multi Output (MIMO) system

• Experimental Investigations

– Intensity distributions for different launching positions

– Mode dispersion

– Crosstalk

– Equalization

• Conclusion and outlook



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Introduction (1)

• Large core diameter

(MMF:50 – 62,5 μm; POF: 62,5 -1000 μm)

• Multi mode character

• Mode dispersion

• Mode coupling

1

0( ) ( )

M

m mm

h t P tδ τ−

== −∑

MMF and POF

M = Number of excited mode groupsPm = Power of mode group m

r

Signal 1

Sign

al 2

Signal 3

Impulse Response

τm = Time delay of mode group m

With the effect of mode coupling

,

1

0m n m

N

nn

P Pγ−

== ⋅∑



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Assignment of different

signals to different mode groups

Separation of different

mode groups

Introduction (2)

Principle of Mode Group Diversity Multiplexing as MIMO approachTransmitter Receiver

high order modes

low order modes

Multiplexing De-Multiplexing

rest

ricte

d la

unch

ing

spot

s

core

OLP

CLP

Intensity [a.u.]

Radius [um]

0

Power distribution in MMF/POF

CLP OLP



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Experimental Setup

VOA

VOA

GI-MMF/POF

Mode Mux

Mode DeMux

SMFMMF

OLP

a)

SMF

MM

F

b)

c)1540 nm

5.35 Gb/sData

CLP

CLC

OLC

2 x 1Coupler

Micro-positionerx

y

BER

SMF

xy

SMF

d)Fixed MMF/POF Moveable

SMF

d =

62.5

um

d= 9 um

5.35 Gb/sData

s1(t)

s2(t)

y1(t)

y2(t)

h11

h21

h12

h22



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Intensity distributions for different launching positions on MMF

Experimental Results (1)

-10

-20

-30

-40

-50

60 μm

60 μm

[dBm]

Centre Launch Position

Concentration of power

in the centre of the core

Offset Launch Position

Power is distributed over complete core radius (closer to core cladding)

-10

-20

-30

-40

-50

60 μm

60 μm

[dBm]

CLP OLP 20 um



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Intensity distribution after 300 m GI-MMF


OLP, 20 umCLP, 0 um

-10

-20

-30

-40

-50

-60

[dBm]-25

-30

-40

-50

-60

[dBm]

60um

60um

60um60

um

No significant change for intensity distributions at CLP and OLP



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Demultiplexing of the signals (MMF)


Completely distorted eye based on mode dispersion

No error free transmission reduction of mode dispersion,

3020100-10-20-30

30

20

10

0

-10

-20

-30

boun

dary

e) area 1

area 2

200 ps

200 ps

f)

g)

2 x 5.35 Gb/s with MGDM

Overfilledlaunch

position

MM

F's c

ore

Transmitter Receiver

Completedetection

area

MM

F's c

ore

1 x 10.7 Gb/s

500ps

Wide open eyes error free transmission is possible

Reduced influence of mode dispersion

Widened one level higher influence of crosstalk



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10-1

10-12

10-10

10-8

10-6

10-4

10-2

-34 -32 -30 -28 -26 -24 -22

BER

Received input power [dBm]

Detection Area 2

Detection Area 1

only s2(t) transmittedonly s1(t) transmitted

6 dB

10-1

10-12

10-10

10-8

10-6

10-4

10-2

BER

-32 -30 -28 -26 -24

ΔPdB=(P2 -P1)dB

ΔP=0dB

ΔP=3

ΔP=6dB

ΔP=9dB

Only detection Area 2for varying ΔP

both, s1(t) & s2(t)transmitted

300m GI-MMF 300m GI-MMF

Received input power [dBm]

Strong mode coupling from low order modes to high order modes for equal power levels

Equalization

Significant reduction for increasing ΔP = P2-P1

Performance analysis: MGDM with different power levels for s1(t) and s2(t)

Unequal power levelsEqual power levels



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Intensity distributions after 10m GI-POF


CLP

No significant change in intensity distributions for CLP and OLP

-10

-20

-30

-40

-50

100 μm

100 μ m

[dBm]

-10

-20

-30

-40

-50

100 μm

100 μm

[dBm]

OLP, 20 um



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Restricted detection point 1

200 ps

Demultiplexing of the signals (POF)


Wide open eye for CDP

low influence of mode dispersion

low interference from second channel

Restricted detection point 9

200 ps

ODPWide open eye for ODP

more distorted due to

Mode dispersion

High crosstalk from second signal

CDP



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Influence of slight variations at CLP

Revised Experimental Setup

10.7 Gb/sData

VOA

VOA

SMFMMF

OLP

SMF

MM

Fb)

c)1540 nm

10.7 Gb/sData

CLPCLC

OLC

2 x 1Coupler

xy

Micropositioner

Moveable SMF

Only Centre Launch Position is varying

Realized with a second micropositioner

Variation from 0 um to 6 um offset

Crosstalk is measured by BER measurements in the second channel



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Influence of slight variations at CLP


0 um to 3 um offset

no significant performance change

4 um and 5 um offset

significant performance reduction to a BER of 10-4

6 um offset

BER of 3*10-3 Correction by standard FEC is not possible

Equalization

10-1

10-12

10-10

10-8

10-6

10-4

10-2

0 1 2 3 4 5 6

BER

offset [um]

10 m GI-POF



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Equalization

Until now: Assumption h = 0 und h =012 21

Reduction of crosstalk by zero forcing in a 2 x 2 MIMO system

1 11 1 21 2( ) ( ) ( )y t h x t h x t= ⋅ + ⋅

2 12 1 22 2( ) ( ) ( )y t h x t h x t= ⋅ + ⋅

New approach:Determination of transmission coefficients h11, h12, h21 and h22

1 12 2 112

12 21 22 11

( ) y h y hx th h h h

⋅ − ⋅=

⋅ − ⋅

1 22 2 211

11 22 12 21

( ) y h y hx th h h h

⋅ − ⋅=

⋅ − ⋅



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Experimental Equalization Setup

Two MMF detection points

Two detection points with different power influence of the signals (Distance:10 um)

Determination of the transmission coefficients (h11, h12, h21, h22)

Sampling the bit sequences with the oscilloscope at both points (y1 and y2)

Offline equalization

10 Gb/sData

VOA

VOA

GI-POF

Mode MuxSMF

MMF

OLP

a)

SMFM

MF

b)

c)1540 nm10m

10 Gb/sData

CLP

CLC

OLC

2 x 1Coupler

Mode DeMux

x

MMF

Fixed MMFMoveableMMF

d)

Fibre 1: 62.5 um

y

MMFDetektor Sampling the bit

sequence with 4050points



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Both eye diagrams show four different power levels (00, 01, 10 11)

Completely distorted eye due to crosstalk

Two MMF detection points

Detection point 2Detection Point 1

0 0

0 11 0

1 1

s1 s2



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Determination of the transmission coefficients by detecting only one signal

Only power influence is measured

Determination of transmission coefficients

Detection point 1 Influence of signal 1

Influence of signal 2

h11

h21



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Without equalization

200 ps 200 ps

200 ps 200 ps0

0

3

3

[mV

][m

V]

[mV

][m

V]

0

0

1.2

1.2

With equalization

Successful equalization

of crosstalk

Detection Point 1

Detection Point 2




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Conclusion & Outlook

Experimental investigations of MIMO approach using MMF/POF

Experimental realization of a 2 x 2 MIMO setup based on MGDM

Reduction of the mode dispersion influence

Investigation of crosstalk between the channels

Dependant on the power levels in the channels

Dependant on the exact launching positions

Successful equalization of crosstalk by zero forcing method

Investigation of modal noise in optical MIMO systems

high speed transmission over mmf and pf-pof using mimo ... · two mmf detection points ¾two...

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