Fabrication and Analysis of Etched SMF for the use as chemical sensor

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“Fabrication and Analysis of Etched Single Mode Fiber for the use as chemical sensor Based on Evanescent field leakage theory” Dept. of Optoelectronics Syam Mohan P.M. M.Tech IVth Semester Roll no: OPE/MTECH-09-06-14 Dept. of Optoelectronics University of Kerala Project Supervisor Dr.Tarun K Gangopadhyay Principal Scientist (E II) OSA Senior member FOP Division CGCRI, Kolkata-32 INDIA

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Outline Dept. of Optoelectronics 1. Introduction 2. Advantage of fiber optic Chemical sensing. 3. Fabrication of etched single mode fiber (Sensor element). 4. Chemical Etching: A method of accessing Evanescent field 5. Theoretical and Experimental Analysis of sensor element. 6. Fluid –Cuvette Spectrometry 7. Application of sensor element in fiber ring resonator. 8. Conclusion. University of Kerala

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Dept. of Optoelectronics University of Kerala Advantage of fiber optic chemical sensing. 1 ) No coupling optics are required in the sensing region because the interrogating light remains guided 2) Considerable miniaturization is possible 3) Enhanced sensitivity Distributed sensing is possible 5) Significant cost reduction 6) No electrical interference 7) Can be used for accurate absorption measurements.

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Dept. of Optoelectronics University of Kerala Fabrication of etched single mode fiber (sensor element) Chemical Etching Using Hydrofluoric Acid. SiO 2 (s) + 3H 2 F 2 (l) = H 2 SiF 6 (l) + 2H 2 O(l)

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Dept. of Optoelectronics University of Kerala Experimental setup used for chemical etching.

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Dept. of Optoelectronics University of Kerala 1) HF acid with 16M concentration is used for etching 2) The fiber is connected to IL1 quartz halogen lamp, which is a general purpose light source for the use in the UV, visible and IR spectral regions from 350nm to 2500nm. 3) The detector station which comprises two detection ports, (і) a silicon detector for the spectral region 350-1100nm (іі) an InGaAs detector for the spectral range 1000-1700nm and the power is continuously monitored.

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Dept. of Optoelectronics University of Kerala Concentration of HF Vs Final diameter of fiber

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Dept. of Optoelectronics University of Kerala Chemical Chamber

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Dept. of Optoelectronics University of Kerala In the first step we used standard fiber (SMF 28). Then striped out the polymer jacket at appropriate length and clean it by alcohol. The fiber is connected from broad band source to detector via the etching setup and placed the stripped portion in the chemical chamber shown in above figure Setting of total etching time and stepup time in the bentham software. Filling the chemical chamber with HF of 16M, at the same time started the scanning with respect to time using bentham software. When the scanning stops then the acid is removed carefully from the chamber and cleaned it with water and alcohol. Started another time scan to package the sensor element carefully. Hence the fluctuation for any perturbation in the output power can be recorded on the online scanning. The fiber sensor element then imaged using a calibrated optical microscope fitted with CCD camera.

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Dept. of Optoelectronics University of Kerala Digital image of Etched Single mode fiber ( 11 micron diameter)

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Dept. of Optoelectronics University of Kerala 13 mm etched portion length of a sensor element

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Dept. of Optoelectronics University of Kerala Power variation during 1hr 10 min and 1hr 20 min HF etching

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Dept. of Optoelectronics University of Kerala Change in Typical graphical behavior

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Dept. of Optoelectronics University of Kerala Power fluctuation during sensor element packaging.

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Dept. of Optoelectronics University of Kerala When there are only two modes (LP 01 and LP 02 ), the relative phase between them is expressed as where Δ β is the difference in propagation constants of the two modes and L 0 is the length of the etched portion. For efficient recoupling of power from LP 02 mode to LP 01 mode, the length of the etched portion must be To achieve the minimum loss etched single mode fiber the phase shift of LP 01 and LP 02 modes should be 2π.

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Dept. of Optoelectronics University of Kerala Optimized length with fiber diameter of an etched fiber.

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Dept. of Optoelectronics University of Kerala Refractive index sensor using etched single mode fiber Transmission spectra of the etched fiber with and without chemical Cobalt Sulphate

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Dept. of Optoelectronics University of Kerala Light attenuation spectra of air, water, isopropanol as the external mediums

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Dept. of Optoelectronics University of Kerala

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Dept. of Optoelectronics University of Kerala Effect of cladding modes

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Dept. of Optoelectronics University of Kerala Fluid Cuvette Spectrometry Spectrometers are analytical instruments implementing absorption of light energy by chemical in a cuvette. The cuvette is a small, transparent square vessel typically made from a high transmission polymer or quartz to hold a solution for analysis The molar absorptivity is ε ; the path length is L, molar concentration c. Absorption spectroscopy is used to measure the absorption radiation, due to its interaction with chemical. The chemical absorbs the energy ie , photon from the radiating field. Absorbance is defined as,

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Dept. of Optoelectronics University of Kerala Schematic for fluid-cuvette spectrometry

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Dept. of Optoelectronics University of Kerala Schematic of the spectroscopic experiment performed at CGCRI

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Dept. of Optoelectronics University of Kerala Absorption Spectrum of Nickel Sulphate at 390nm wavelength

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Dept. of Optoelectronics University of Kerala Absorption Spectrum of Cobalt sulphate Sulphate at 520nm wavelength

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Dept. of Optoelectronics University of Kerala Fiber Loop Resonator Fiber-loop resonator 1560-nm Extended cavity diode Laser EAB Variable ratio coupler PC PZT amplifier RF Splitter Detector L P F 2 MHz Oscillator Servo Schematic of the fiber ring resonator. PC: polarization controller; EAB: evanescent access block(Etched sensor element); LPF : low pass filter .

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Dept. of Optoelectronics University of Kerala Glycerol Diluted with 5% of D2O having refractive index 1.467 has been used as the index matching oil. Glycerin+D2O (93%+7%) solution is used as the chemical. It has strong absorption around 1550 nm. The cavity resonance signal before and after applying chemical is recorded using an oscilloscope. A specific shift in the cavity resonance is obtained a degradation in finesse which is expected because of the absorption of light by the chemical.

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Dept. of Optoelectronics University of Kerala The cavity resonance signal before and after applying chemical .

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Dept. of Optoelectronics University of Kerala Conclusion In this scope of the work it is tried to make etched fiber after removing the cladding part. In CGCRI, HF acid of 16M is used for etching Single mode fibers (SMF28). The total etching time is optimized 1 hour 10 minutes to achieve a 11 μm diameter fiber. After etching, the same element has been used to observe the RI changes of some chemicals such as cobalt nitrate, nickel sulphate etc. It is proved that the sensor element is primarily able to act as a sensor element on the fiber loop for chemical sensing The theoretical study has been done on etched single mode fiber then optimized the length and diameter of the sensor element to achieve minimum loss.

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Dept. of Optoelectronics University of Kerala The effect of cladding modes on the chemically etched portion of the sensor element has been proved. Fluid cuvette spectroscopic experiment has been carried out for the back up for our measurements. The mechanism to integrate HF etched single mode fiber into the fiber loop and the preliminary experiments on Fiber loop resonator has been carried out in CGCRI .

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Dept. of Optoelectronics University of Kerala Journal Article Linslal C.L., Syam Mohan P.M ., Arintham Haldar, Tarun Kumar Gangopadhyay, “Eigen Value Equation and Core-mode Cutoff of Weakly Guiding Tapered Fiber as Three Layer Optical Waveguide and used as biochemical sensor”, Journal of Light wave Technology, (Under Review) Conference Presentation Linslal C.L., Syam Mohan P.M ., Arintham Haldar, M.C. Paul, Tarun Kumar Gangopadhyay ‘ Effect of cladding modes in Evanescent field absorption Sensor ’ National Conference for Communication Networks and Sensors (NCCNS) Hindustan University Chennai India. May 17-18, Linslal C.L., Syam Mohan P.M ., Tarun Kumar Gangopadhyay, ” Analysis of evanescent access block and its application in fiber loop resonator for chemical sensing ” International Conference on specialty Glass and optical Fiber (ICGF-2011) August 4-6, Central Glass and Ceramic Research Institute, Kolkata, India.

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Dept. of Optoelectronics University of Kerala References D.J. Monk, D.S. Soane , R.T. Howe,"A review of the chemical reaction mechanism and kinetics for hydrofluoric acid etching of silicon dioxide for surface micromachining applications," Thin Solid Films, 232, 1-11 (1993). C.A. Rowe- Taitt et al “Fiber Optic Biosensors; Handbook of optical fiber sensing technology”, Edited by J. M. Lopez- Higuera , John Wiley & Sons Ltd. 2001; 687-700. G.Gagliardi et al , ”Optical fiber sensing based reflection laser spectroscopy”, Sensors, Vol.10, 2010, pp.1823-1845. C.Wang et al,” High -sensitivity fiber-loop ringdown evanescent field index sensors using single-mode fiber”, Optics letters, Vol.35, 2010, pp.1629-1631. C.Herath et al ,”Fiber loop ringdown DNA and bacteria sensor”, Journal of bio-medical optics, Vol. 16(5), 2011, pp. 050501(1)-050501(3)

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Dept. of Optoelectronics University of Kerala What is next in Fiber optic sensing?

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Dept. of Optoelectronics University of Kerala THANK YOU