© UCL 2004

17TH IEEE/LEOS Conference

Puerto Rico, 7-11 of November, 2004

Modeling Of Optical Coupling To Multimode Polymer Waveguides: Axial And Lateral

Misalignment Tolerance

Guoyu Yu and David R. SelviahDepartment of Electronic and Electrical Engineering

University College London

Outline• Modelling strategy• VCSEL modelling • Coupling optics• Receiver modelling • Results and Discussion

2© UCL 2004

Modeling Diagram

0110

PRBS Driver VCSEL Guide Receiver

Eye

Power

Power meter reading varies with relative lateral and axial misalignment between VCSEL and waveguide

Time information such as eye diagram and thus system BER obtained to meet general specification

BER

3© UCL 2004

Spatial Field Distribution

Polarisation direction

LG00 LG10

LG11 LG01

843 843.5 844 844.5 845 845.5 846

-70

-65

-60

-55

-50

-45

-40

10 Gb/s VCSEL Spectrum at Drive Current i=2.5 mA

Wavelength (nm)P

ow

er

(dB

m)

VCSEL active area

diameter=7 µm

4© UCL 2004

Polar Plot of 4 modes

LG00 LG10

LG11 LG01

5© UCL 2004

Weighted 4 modes

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VCSEL Output

0 2 4 6 8 100

1

2

3

4

5

constant output power

Rdiff

=50

typicalbias current range

90°C

13°C

optic

al p

ower

(mW

)

current (mA)

0

2

4ULM002Q02S3066100

vol

tage

(V)

Small-signal transfer function at 25 oC, bias

of 5 and 10 mA

Transient response of single-mode VCSEL

Simulated (left) VCSEL LI output

compared with data from manufacture

(right)

7© UCL 2004

Spatial Output

8© UCL 2004

Spatial Output

9© UCL 2004

Results

Single Mode Four Modes

10© UCL 2004

Power Contour at -1 dB

• The lateral and axial tolerance increase monomatically with the increased guide width (10-60 µm).

• For guide of 100 µm width, tolerance is not improved due to modal noise.

• The lateral and axial tolerance increase monomatically with the increased guide width (10-60 µm).

• Axial tolerance is not as good as single mode due to mode divergence.

Single Mode Four Modes

From inner most, guide with=10, 20, 30, 40, 50, 60, 70 micron

From inner most, guide with=10, 20, 30, 40, 50, 60, 70 micron

11© UCL 2004

0 100 200 300 400 500 600 700 800 900 1000-50

-40

-30

-20

-10

0

10

20

30

40

50

Larger Guides

0 100 200 300 400 500 600 700 800 900 1000-50

-40

-30

-20

-10

0

10

20

30

40

50

0 100 200 300 400 500 600 700 800 900 1000-50

-40

-30

-20

-10

0

10

20

30

40

50

0 100 200 300 400 500 600 700 800 900 1000-50

-40

-30

-20

-10

0

10

20

30

40

50

Guide Width=80m Guide Width=100m

Guide Width=80m Guide Width=100m

1 mode 1 mode

4 modes 4 modes

12© UCL 2004

Experiment

0 10 20 30 40 50 60 70-14

-12

-10

-8

-6

-4

-2

0

Model: w=50 µm, xi=100 µm, zi=100 µm.

Experiment: x scan range: 0-62 µm.

13© UCL 2004

Conclusion

Acknowledgement

•Increased guide width result in improved lateral and axial misalignment tolerance if the guide width is less than receiver aperture size.

•Modal noise will affect the tolerance level when guide width is greater than receiver aperture size.

•EPSRC and Xyratex for financial support

•Anibal Fernandez and Frank Tooley for useful discussion

14© UCL 2004

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15© UCL 2004

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