Abstract
An interferometric-fiber-optic sensor and an efficient fringe-detection scheme are described. The fiberoptic interferometer consists of two fibers; they are labeled the reference fiber and the sensing fiber. The reference fiber is arranged in a circular pattern, whereas the sensing fiber is arranged in an ‘S’ pattern. These fibers are exposed to the same strain field and each experiences a strain-induced phase shift. A difference in the phase shift between the two fibers indicates a change in strain.
The strain-induced phase difference causes the interferometrically produced fringes to shift spatially. Analysis shows that the number of fringes passing an arbitrary point on a screen (the detection point) is linearly related to the strain in the fiber. In this analysis, the strain sensor is assumed to be perfectly bonded so that the fibers experience the same strain field as the specimen. It is further assumed that the sensor covers a sufficiently small area so that the strain can be considered constant over the entire strain sensor. Also, the phase change produced by transverse strain components (with respect to the fiber) induced by the specimen is assumed negligible compared to the phase changes attributable to the axial strain components. A cantilever beam was used as a specimen. Experimentally determined strains correlated well with the strains predicted by beam theory.
The fringe-detection scheme described is a high-speed fringe counter. The speed of this counter is necessary to detect vibrational phase noise which is invisible to the human eye. Two photodiodes detect the fringes, and a logic circuit counts the fringe shifts, both strain and noise induced. Since noise is random in nature, it can be averaged out. This fringe detector exhibits good sensitivity and is the key to moving the sensor from the laboratory to the field.
Similar content being viewed by others
References
Hocker, G.B., “Fiber-Optic Sensing of Pressure and Temperature,”Appl. Opt.,18 (9),1445–1448 (May 1979).
Giallorenzi, T.G., Bucaro, J.A., Dandridge, A.D., Siegel, G.H., Cole, J.H., Rashleigh, S.C. andPriest, R.C., “Optical Fiber Sensing Technology,”IEEE J. Quantum Elec. QE-18 (4),626–665 (April 1982).
Jones, B.E. and Spooner, R.C., “Photoelastic Pressure Sensor with Optical Fibre Links Using Wavelength Characterization,” Proc. First Int. Conf. on Opt. Fiber Sensors, IEE Pub. 221 (1983).
Spillman, W.B. and McMahon, D.H., “Multimode Fiber Optic Sensors,” Proc. First Int. Conf. on Opt. Fiber Sensors, IEE Pub. 221 (1983).
Kashyap, R. and Nayar, B.K., “A Single Mode Fibre Michelson Interferometer Sensor,” Proc. First Int. Conf. on Opt. Fiber Sensors, IEE Pub. 221 (1983).
Paolantonio, A.N., “Fiber Optic ‘Half Life’,”, Electro Optical System Design, 33–41 (Aug. 1982).
Tebo, A.R., “Sensing With Optical Fibers: An Emerging Technology,” Electro Optical System Design, 39–45.2 (Feb. 1982).
Page, R.P., A Fibre Optic Multiplexing System for Use on a Motor Car,” ed. L.R. Baker, Fibre Optics 85, SPIE 522 (1985).
Butter, C.D. andHocker, G.B., “Fiber Optics Strain Gauge,”Appl. Opt.,17 (18),2867–2869 (Sept 1978).
Seiler, M.K. andLeach, E.R., “Analysis of Thermal Phase Noise in Fiber-Optic Sensors,”J. Appl. Phys.,53 (8),5498–5508 (Aug. 1982).
Hughes, R. andPriest, R., “Thermally Induced Optical Phase Effects in Fiber Optic Sensors,”Appl. Opt.,19 (9),1477–1483 (May 1980).
Musha, T., Kamimura, J. andNakazow, M., “Optical Phase Fluctuations Thermally Induced in A Single-Mode Optical Fiber,”Appl. Opt.,21 (4),694–698 (Feb. 1982).
Jenkins, F.A. andWhite, H.E., Fundamentals of Optics, 7th Ed., McGraw Hill, New York (1965).
Jeunhomme, L.B., Single Mode Fiber Optics, Marcel Dekker, Inc., New York (1983).
Stowe, D.W., Moore, D.R. andPriest, R.G., “Polarization Fading in Fiber Interferometric Sensors,”IEEE J. Quantum Electronics,QE-18 (10),1644–1646 (Oct. 1982).
Smith, A.M., “Birefringence Induced by Bends and Twists in Single-Mode Optical Fiber,”Appl. Opt.,19 (15),2606–2611 (Aug. 1980).
Rashleigh, S.C., “Polarimetric Sensors: Exploiting the Axial Stress in High Birefringence Fibers,” Proc. 1st Int. Conf. on Optical Fiber Sensors, IEE Publ. 221 (1983).
Nye, S.F., Physical Properties of Crystals, Oxford Press, London (1954).
Martinelli, M., “The Dynamical Behavior of a Single-Mode Optical Fiber Gage,”IEEE J. Quantum Elec.,QE-18 (4),666–670 (April 1982).
Fields, J.N. andCole, J.H., “Fiber Microbend Acoustic Sensor,”Appl. Opt.,19 (19),3265–3267 (Oct. 1980).
Bush, I.J. andPhillips, R.L., “Synchronous Phase Detection for Optical Fiber Interferometric Sensors,”Appl. Opt.,22 (15),2329–2336 (Aug. 1983).
Cole, J.H., Danver, B.A. andBucaro, J.A., “Synthetic-Heterodyne Interferometric Demodulation,”IEEE J. Quantum Elec.,QE-18 (4),694–696 (April,1982).
Dandridge, A., Tveten, A.D., andGiallorenzi, T.G., “Homodyne Demodulation Scheme for Fiber Optic Sensors Using Phase Generated Carrier,”IEEE J. Quantum Elec.,QE-18 (10),1647–1652 (Oct. 1982).
Shajenko, P. andGreen, E.L., “Signal Stabilization of Optical Interferometric Hydrophones by Tuning the Light Source,”Appl. Opt.,19 (12),1895–1897 (June 1980).
Sheem, S.K., Giallorenzi, T.G. andKoo, K., “Optical Techniques to Solve the Signal Fading Problem in Fiber Interferometers,”Appl. Opt.,21 (4),689–693 (Feb. 1982).
Dandridge, A. andTveten, A.B., “Noise Reduction in Fiber Optic Interferometer Systems,”Appl. Opt.,20 (14),2337–2339, (July 1981).
Giles, I.P., Uttam, D., Culshaw, B. andDavis, D.E.N., “Coherent Optical-Fiber Sensors with Modulated Laser Sources,”Elec. Let.,19 (1),14–15 (Jan. 1983).
Olsson, A., Tang, C.L. andGreen, E.L., “Active Stabilization of a Michelson Interferometer by an Electroptically Tuned Laser,”Appl. Opt.,19 (12),1897–1899 (June 1980).
Koo, K.P. andCarome, E.F., “Active Stabilization of a Optical Interferometer Systems,”Elec. Let.,17 (11),330–332 (May 1981).
Timoshenko, S. andGoodier, S.H., Theory of Elasticity, McGraw Hill, New York, 213 (1951).
Marcuse, D., “Influence of Curvature on the Losses of Doubly Clad Fibers,”Appl. Opt.,21 (23),4208–4213 (Dec. 1982).
Marcuse, D., “Microdeformation Losses of Single-Mode Fibers,”Appl. Opt.,23 (7),1082–1091 (April 1984).
Sharma, A.B., Al-Ani, A.H. andHalme, S.J., “Constant Curvature Loss in Monomode Fibers: An Experimental Investigation,”Appl. Opt.,23 (19),3297–3301 (Oct. 1984).
Durelli, A.J. andRiley, W.F., Introduction to Photomechanics, 1st Ed., Prentice-Hall, Englewood Cliffs, NJ, Chapt. 3, 160 (1965).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Sirkis, J.S., Taylor, C.E. Interferometric-fiber-optic strain sensor. Experimental Mechanics 28, 170–176 (1988). https://doi.org/10.1007/BF02317568
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF02317568