University of Limerick - Presentation at Conference on Lasers and Electro-Optics Europe 2013 - Diaphragm etching

1. Diaphragm Etching in Extrinsic Fabry-Perot Interferometric
Fiber Optic Pressure Sensors
[CLEO - Europe, 2013]
Sven Poeggel, Daniele Tosi, Gabriel Leen, Elfed Lewis
University of Limerick, Ireland
Optical Fibre Sensors Research Centre (OFSRC)

2. Extrinsic FP
Interferometer
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
EFPI: Fiber-optic Fabry-Perot interferometric sensor based on all-
silica glass structure: (1) launch fiber, (2) diaphragm, (3) capillary
Capillary
Launch SM
fiber
Diaphragm
MM fiber
AIR-GAP
dL

3. d
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
EFPI principle
L

4. Pressure
L0 - Sp PΔ
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
EFPI principle
L

5. White light system
ASE sourceASE source
SpectrometerSpectrometer
1530-1600 nm
1520-1596 nm CouplerCoupler
3 dB
1x4 switch
ServerServer
EFPI
EFPI
EFPI
DAQDAQ
(LabVIEW)(LabVIEW)
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
S pre-loadingpre-loading
EFPI
d estimation
Online QA
HF bath
(argon-ion source)

6. Sensitivity
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
d = diaphragm thickness
a = fiber inner diameter
E = Posson’s ratio
μ = Young’s modulus
sP =
3(1− μ)2
a4
16Ed3

7. Sensitivity
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
d = diaphragm thickness
a = fiber inner diameter
E = Posson’s ratio
μ = Young’s modulus
Trade-off
Tilt
Flatness
Problem:
- etch the diaphragm to lowest d
- preserve air-gap sealing and FPI
- independently on etching speed

8. Wet etching
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
Hydrofluoric acid (HF), 5-48%
- Low BOM cost
- Easy setup fume hood
- Speed/concentration
- Chemically dangerous
- Non-constant rate
- Remove residual HF

9. Dry etching
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
- Multiple probe etching
- Etching rate ~constant
- Dry, chemical-free
- Preserve surface quality
- Expensive
High power argon-ion etching
Femtosecond laser etching
~mm/s etching rate!

10. Simulation
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
Etching rate:
period = 0.495 mμ
Spectrum (as on spectrometer)
Q-point vs diaphragm length ( m)μ

11. Real-time data
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
“Accelerated”
etching in HF
48%
Breakpoint

12. QA analysis
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
Low-quality probe
High-quality probe

13. Pressure test
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
18pm/mmHg
SP = 2.3 nm/kPaAccuracy ~0.4 mmHg

14. Daniele Tosi - Optical Fibre Sensors Research Centre - project portfolio - UL2013
Conclusions
Optimization of EFPI sensitivity for each
individual sensor
Achievement of 1-10 nm/kPa sensitivity,
leading to accuracy below 1 mmHg
Results independent on air-gap length, etching
type and speed, geometry
QA > 70% for maximum sensitivity

15. Acknowledgments
Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick
Research support Financial support
UL, Material and Surface
Science Institute
Science Foundation Ireland
(RFP/ECE2898)
UL, Chemical and
Environmental Science
Enterprise Ireland (IP-2012-
0166-Y)
Galway-Mayo Institute of
Technology
FP7-People Marie Curie
(299985 Probesens)