9078 Leslie St., Unit 11, Richmond Hill, ON L4B 3L8 Canada

19078 Leslie St., Unit 11, Richmond Hill, ON L4B 3L8 Canada

Phone 905-326-5040 Fax 905-326-5041 [email protected] www.spectral.ca

Single mode fibre transmission apparatus

Chris F. Dimas, Anthony Knottenbelt, Peter SinclairSpectral Applied Research

June 17, 2014

Measuring light where it counts



Company profile

•High-tech manufacturing facility located in Richmond Hill, Ontario

•Manufacture laser engines, specialized microscope systems (confocal, TIRF)

•Manufacture other fiber optic systems for biomedical OEM customer

•35 Employees

•Large R&D department

•Last year was purchased by Andor Technology, and later by Oxford Instruments



405nm laser+single mode fibre 405nm laser

A Single mode Fiber - designed to carry light only directly down the fibre - the transverse mode

•Most common biophotonics applications:

•Fluorescence microscopy

•Therapeutics

•Etching, micromachining



Problem

•Light transmission degrades rapidly in single mode fibre when exposed to 405nm light, 0.01-0.5%/hr (0.3 - 11%/day)

•Light is cw laser, and below the damage threshold for fiber: 1MW/cm2 as opposed to 1GW/cm2

•Possible causes:, • LIPSS Gonshior, C. P., et al, (2013). Generation of periodic surface structures on silica fibre surfaces

using 405nm CW diode lasers. Journal of Non-Crystalline Solids, 361(1), 106-110

• Contamination on end of fibre• Solarization of fibre • Defective AR coating• Burning of input due to improper alignment

•Need to measure the degradation•Precisely: +/-0.02%/hr •Over a shorter period of time: 17 hrs., not 1000hrs•Without damaging product



Techniques

laser •Detector is underfilled

•Detector is underfilled at beginning…

•Can measure light at the focus, off focus, and beamshape

laser

laser

1.

2.

3.

fibre

fibre

fibre

Detector (thermopile)

Detector (integrating sphere)

Lens

Lens

Camera



Technique 1. Directly at fibre

laser

•Measuring rates of < -0.1%/hr +/- 0.02%/hr, linear decay

•Concluded rate after 17 hour test

•Realized that detector needed to be thermally controlled, laser needed to be thermally controlled, and that continuous monitoring of laser input power (to provide closed loop feedback) is, unfortunately, not possible

y = -0.0206x + 99.932

R2 = 0.9259

99.40

99.50

99.60

99.70

99.80

99.90

100.00

100.10

100.20

0 2 4 6 8 10 12 14 16 18

Time (hr)

Po

wer

Regression statisticsslope: -0.0000089std error: 0.0000000321

Detector (thermopile)

fibre



Techniques 2. At output of relay lens

laser

•Corrected for laser thermal, detector thermal, rig dependency

•Measured higher degradation rates, not linear, but with quadratic component as well

•Beam profiles at fibre end showed widened beams for contaminated fibre ends (-0.5%/hr)

•Perhaps something similar going on even though surfaces were clean

y = -0.0002x2 + 0.0306x + 99.909

R2 = 0.8423

y = -0.0002x2 + 0.0222x + 100.19

R2 = 0.986650.00

60.00

70.00

80.00

90.00

100.00

0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00 900.00 1000.00

Total Time on Burn-in (hrs.)

Po

wer

ou

tpu

t (n

orm

aliz

ed)

25.00

30.00

35.00

40.00

45.00

50.00

Po

wer

ou

tpu

t n

orm

aliz

ed (

scal

e fo

r C

3 50

% p

ow

er o

nly

)

Relay lens

Detector (integrating sphere)

Cannot test every production unit for 1000hrs!

More investigation required!!!



Beam profiles; before and after cleaning fibre

Before After cleaning

R



Beam profiles, cont..

•In this instance, the change to the beam profile was more severe, did not have significant power degradation rate, and furthermore cleaning the end of the fibre did not improve the beam profile



White light profilometry



Technique 3. Using beam profiles

laser

•Measuring the beam profile periodically throughout the test

Camera

Relay lens Detector (integrating sphere)

Collimating lens

fibre



Beam profile vs. Power out

E

C



Beam profile vs. Power out

•Shape of beam profile has a close correspondence to % power degradation

•Knowing the hours of exposure, know the % deg/hr, one shot-measurement

y = 0.0003x + 0.9568

R2 = 0.9125

0.8

0.9

1

1.1

1.2

1.3

1.4

0 200 400 600 800 1000 1200

Time (hrs.)

E/C

(R

atio

, ed

ge

to c

entr

e)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

c v, (C

oef

fici

ent

of

vari

atio

n i

n c

entr

e o

f p

rofi

le,

%)



Failure mode diagnosis

Rate of Degradation

(Transmission)

Rate of Increase of

Edge to Centre Ratio

Failure Mode

0.5%/hr >30%/1000hr Contamination of output

0.1%/hr 30%/1000hr Burning of input

0.01%/hr 30%/1000hr Pit formation/ LIPSS



Conclusions

•Prolonged exposure to 405nm laser light in single mode fibre in our case causes depression in fibre core

•The rate of power degradation and beam profile degradation can diagnose the root cause of failure in a fibre

•A beam profile gives a more application specific rate of degradation, in addition to allowing for a non-destructive and immediate diagnosis if the number of hours of exposure is known.



Thank you!

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9078 Leslie St., Unit 11, Richmond Hill, ON L4B 3L8 Canada

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