1. Diaphragm Etching in Extrinsic Fabry-Perot InterferometricFiber Optic Pressure Sensors[CLEO - Europe, 2013]Sven Poeggel, Daniele Tosi, Gabriel Leen, Elfed LewisUniversity of Limerick, IrelandOptical Fibre Sensors Research Centre (OFSRC)

2. Extrinsic FPInterferometerDaniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of LimerickEFPI: Fiber-optic Fabry-Perot interferometric sensor based on all-silica glass structure: (1) launch fiber, (2) diaphragm, (3) capillaryCapillaryLaunch SMfiberDiaphragmMM fiberAIR-GAPdL

3. dDaniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of LimerickEFPI principleL

4. PressureL0 - Sp PDaniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of LimerickEFPI principleL

5. White light systemASE sourceASE sourceSpectrometerSpectrometer1530-1600 nm1520-1596 nm CouplerCoupler3 dB1x4 switchServerServerEFPIEFPIEFPIDAQDAQ(LabVIEW)(LabVIEW)Daniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of LimerickS pre-loadingpre-loadingEFPId estimationOnline QAHF bath(argon-ion source)

6. SensitivityDaniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerickd = diaphragm thicknessa = fiber inner diameterE = Possons ratio = Youngs modulussP =3(1 )2a416Ed3

7. SensitivityDaniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerickd = diaphragm thicknessa = fiber inner diameterE = Possons ratio = Youngs modulusTrade-offTiltFlatnessProblem:- etch the diaphragm to lowest d- preserve air-gap sealing and FPI- independently on etching speed

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

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

10. SimulationDaniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of LimerickEtching rate:period = 0.495 mSpectrum (as on spectrometer)Q-point vs diaphragm length ( m)

11. Real-time dataDaniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of LimerickAcceleratedetching in HF48%Breakpoint

12. QA analysisDaniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of LimerickLow-quality probeHigh-quality probe

13. Pressure testDaniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of Limerick18pm/mmHgSP = 2.3 nm/kPaAccuracy ~0.4 mmHg

14. Daniele Tosi - Optical Fibre Sensors Research Centre - project portfolio - UL2013ConclusionsOptimization of EFPI sensitivity for eachindividual sensorAchievement of 1-10 nm/kPa sensitivity,leading to accuracy below 1 mmHgResults independent on air-gap length, etchingtype and speed, geometryQA > 70% for maximum sensitivity

15. AcknowledgmentsDaniele Tosi - Optical Fibre Sensors Research Centre (OFSRC) - University of LimerickResearch support Financial supportUL, Material and SurfaceScience InstituteScience Foundation Ireland(RFP/ECE2898)UL, Chemical andEnvironmental ScienceEnterprise Ireland (IP-2012-0166-Y)Galway-Mayo Institute ofTechnologyFP7-People Marie Curie(299985 Probesens)