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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 19 — Sep. 13, 2010
  • pp: 19951–19956
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An interferometric current sensor based on optical fiber micro wires

Mohammad Belal, Zhang-qi Song, Yongming Jung, Gilberto Brambilla, and Trevor Newson  »View Author Affiliations


Optics Express, Vol. 18, Issue 19, pp. 19951-19956 (2010)
http://dx.doi.org/10.1364/OE.18.019951


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Abstract

In this paper we demonstrate a compact current sensor using the optic fiber micro wire, based on the idea of interferometrically measuring the thermally induced optical phase shifts as a result of heat produced due to the flow of electric current over short transit lengths. A responsivity of 1.28 x 10-4 rad/I2 at 50Hz of current signal has been shown, with capability of measuring alternating current signals up to 500Hz.

© 2010 OSA

1. Introduction

Current sensor is a typical application of optical fibers [19

19. B. Lee, “Review of the present status of optical fiber sensors,” Opt. Fiber Technol. 9(2), 57–79 (2003). [CrossRef]

,20

20. R. I. Laming and D. N. Payne, “Electric Current Sensors Employing Spun Highly Birefringent Optical Fibers,” J. Lightwave Technol. 7(12), 2084–2094 (1989). [CrossRef]

]. All fiber optical current sensors are typically divided into two categories, where one is based on Faraday effect and the other is based on thermal effect. The former is limited by the extremely small Verdet constant of silica, so in order to increase the device responsivity lots of turns of fibers are needed. A long fiber is necessary to increase the device responsivity because the minimum bend radius of normal optical fiber is a couple of centimeters. The latter needs a short length of fiber but requires complex manufacturing techniques to coat fibers with metals [21

21. A. Dandridge, A. B. Tveten, and T. G. Giallorenzi, “Interferometric current sensors using optical fibres,” Electron. Lett. 17(15), 523–525 (1981). [CrossRef]

23

23. G. L. Tangonan, D. I. Persechini, R. J. Morrison, and J. A. Wysocki, “Current sensing with metal coated multimode optic fibers,” Electron. Lett. 16(25-26), 958–959 (1980). [CrossRef]

].

In this paper we demonstrate a compact optical current sensor using an 80mm-long optical fiber micro wire (OFM) with a diameter of 5μm. The OFM was wound for 25 times directly on a 5mm-long, 1mm-diameter copper wire coated with a very thin Teflon film to prevent light coupling. To our knowledge, this is the first time such a miniature optical fiber current sensor is reported.

2. Sensor fabrication and theoretical considerations

Sensor fabrication comprises two-steps. A conventional single mode optical fiber (Corning SMF-28) is tapered into an OFM with a diameter of 5 micrometers using the modified flame-brushing technique [1

1. G. Brambilla, “Optical fibre nanowires and microwires: a review,” J. Opt. 12(4), 043001 (2010). [CrossRef]

], with 80mm length of the central uniform taper region. The taper is then wound on a copper wire of length 5mm and diameter 1mm. Two ends of the copper wire are soldered on two pieces of copper plate to facilitate the assembly in an electric circuit with low contact resistance. Before winding, a very thin Teflon layer is coated on the copper wire to prevent leakage losses due to optical coupling from the OFN into the copper wire. The OFM is carefully wound on the copper wire with a large pitch to eliminate optical coupling between adjacent turns. 25 turns were wound on the copper wire with an 80mm-long OFM. The sensor is then packaged with a UV-curable acrylate polymer (Luvantix PC-373). During the fabrication process, the OFM transmission is measured in situ to ensure low insertion loss. Figure 1(a)
Fig. 1 (a) Experimental results on the fabrication of current sensor. Transmission spectra were recorded before tapering, after tapering and after packaging. (b) Photograph of the packaged OFM coil on the copper wire.
shows the transmissions of the OFM as a function of wavelength before and after packaging with a total loss of 1.5dB at 1550nm, while Fig. 1(b) shows the packaged sample.

3. Experiment Results

The experimental layout as shown in Fig. 2
Fig. 2 Diagram of the experimental set-up used to test the sensor. LD stands for laser diode, PZT for piezoelectric transducer, FRM for Faraday rotating mirror, and D for detector.
, comprises a Michelson interferometer, current transformer and a digital signal processing system. Light from a laser diode (LD) at 1550nm with a linewidth of 0.01nm travels through the optical circulator and is split into two arms of the Michelson interferometer by the 3dB coupler. One arm comprises the current sensor, while the other forms a fiber wrapped round a PZT in order to control the phase by locking at the quadrature point. In order to minimise the polarization dependent noise, both the arms of the interferometer are terminated in Faraday rotating mirrors (FRM). The interferometer output is sampled by an A/D convertor and recorded by a computer. Due to electromagnetic induction, passage of alternating current through the coil results in a high current being induced in the frame at the same frequency. .

The current in the frame is measured by a current meter. The interferometer output is sampled by one of A/D convertor channels of National Instrument USB-6221 multifunction data acquisition board. Data is sent to a computer for signal processing. The computer is also used to control the phase bias of the interferometer by adjusting PZT phase modulator through an analog output channel on the USB-6221.

Figure 3
Fig. 3 Output of the current sensor with 90A@50Hz input. The top waveform represents the 50Hz input, while the bottom one is the sensor output.
shows the output of the interferometer when a 50Hz, 90A rms alternating current passes through the sensor. Waveform 1 is the detector output, while waveform 2 is the input signal. The frequency of the output signal was measured to be 100Hz, which is in agreement with Eq. (4).

Responsivity was measured in two different ways. For currents in the range 0 to 40A rms, phase bias control was used. From 45 to 120A rms, harmonics were used to calculate the amplitude of phase modulation [24

24. K. Böhm and K. Petermann, “Signal processing schemes for the fiber-optic gyroscope,” Proc. SPIE 719, 36–44 (1986).

], and results are shown in Fig. 4
Fig. 4 Amplitude of AC phase measured as a function of square of alternating electric current passing through the copper wire at frequency 50Hz
. Linear relationship (R2 = 0.98) between the amplitude of phase modulation and the square of alternating current (1.2A to 120A rms) passing through the copper wire was obtained. Nearly same slopes achieved for the linear fits carried on the data (ref. Fig. 4) corresponding to two different tests suggests repeatability of interferometer phase change measurements with input current. The responsivity of the sensor is 1.28×104rad/I2 at 50Hz. The resistance of the copper wire is 107μΩ. Assuming a minimum-detectable phase change of 10−6 rad [25

25. D. A. Jackson, “Recent progress in monomode fibre-optic sensors,” Meas. Sci. Technol. 5(6), 621–638 (1994). [CrossRef]

], the observed responsivity at 50Hz corresponds to a minimum detectable current variation of 88mA rms.

The sensor response to frequency is presented in Fig. 5
Fig. 5 AC response (rad/I2)of interferometer as a function of driving frequency for heating current sensor
. A digital function generator was used to supply currents with different frequencies. The current flowing through the sensor was kept at 9A rms and the current sensor response was recorded. Figure 5 shows that the sensor reponsivity decays for increasing frequencies and is found to be 3.57×106rad/I2at 500Hz.

4. Conclusion

In conclusion, we have demonstrated the sensing capabilities of an interferometric current sensor based on optical fiber micro wires. The current sensor comprised an optical fiber micro wire wrapped round a 1mm-diameter copper wire over a length of 5mm. Success with such compact designs opens possibilities for even smaller copper support rods, carrying current. The sensor was tested in an optical fiber Michelson interferometer configuration with a phase responsivity of 1.28×104rad/I2at 50Hz with an input impedance of 107μΩ. However, the responsivity was found to vary inversely with increasing frequencies, and was shown to be 3.57×106rad/I2 for a frequency of 500Hz. Responsivity can be increased by reducing the diameter of the copper wire or increasing the material electrical resistivity.

Acknowledgments

GB gratefully acknowledges the Royal Society (London, U.K.) for his research fellowship. The authors thank the Engineering and Physical Sciences Research Council (EPSRC) for financial support. Z. Song is grateful to CSC for his academic visitor scholarship.

References and links

1.

G. Brambilla, “Optical fibre nanowires and microwires: a review,” J. Opt. 12(4), 043001 (2010). [CrossRef]

2.

L. Tong, “Brief introduction to optical microfibers and nanofibers,” Front. Optoelectron. China 3(1), 54–60 (2010). [CrossRef]

3.

J. Lou, L. Tong, and Z. Ye, “Modeling of silica nanowires for optical sensing,” Opt. Express 13(6), 2135–2140 (2005). [CrossRef] [PubMed]

4.

J. Villatoro and D. Monzón-Hernández, “Fast detection of hydrogen with nano fiber tapers coated with ultra thin palladium layers,” Opt. Express 13(13), 5087–5092 (2005). [CrossRef] [PubMed]

5.

L. Zhang, F. Gu, J. Lou, X. Yin, and L. Tong, “Fast detection of humidity with a subwavelength-diameter fiber taper coated with gelatin film,” Opt. Express 16(17), 13349–13353 (2008). [CrossRef] [PubMed]

6.

F. Gu, L. Zhang, X. Yin, and L. Tong, “Polymer single-nanowire optical sensors,” Nano Lett. 8(9), 2757–2761 (2008). [CrossRef] [PubMed]

7.

F. Xu, P. Horak, and G. Brambilla, “Optical microfiber coil resonator refractometric sensor,” Opt. Express 15(12), 7888–7893 (2007). [CrossRef] [PubMed]

8.

F. Xu and G. Brambilla, “Demonstration of a refractometric sensor based on optical microfiber coil resonator,” Appl. Phys. Lett. 92(10), 101126 (2008). [CrossRef]

9.

P. Polynkin, A. Polynkin, N. Peyghambarian, and M. Mansuripur, “Evanescent field-based optical fiber sensing device for measuring the refractive index of liquids in microfluidic channels,” Opt. Lett. 30(11), 1273–1275 (2005). [CrossRef] [PubMed]

10.

C.-Y. Chao and L. Jay Guo, “Design and Optimization of Microring Resonators in Biochemical Sensing Applications,” J. Lightwave Technol. 24(3), 1395–1402 (2006). [CrossRef]

11.

N. Vukovic, N. G. R. Broderick, M. N. Petrovich, and G. Brambilla, “Novel method for the fabrication of long optical tapers,” IEEE Photon. Technol. Lett. 20(14), 1264–1266 (2008). [CrossRef]

12.

L. M. Tong, R. R. Gattass, J. B. Ashcom, S. L. He, J. Y. Lou, M. Y. Shen, I. Maxwell, and E. Mazur, “Subwavelength-diameter silica wires for low-loss optical wave guiding,” Nature 426(6968), 816–819 (2003). [CrossRef] [PubMed]

13.

G. Brambilla, V. Finazzi, and D. J. Richardson, “Ultra-low-loss optical fiber nanotapers,” Opt. Express 12(10), 2258–2263 (2004). [CrossRef] [PubMed]

14.

F. Xu and G. Brambilla, “Embedding optical microfiber coil resonators in Teflon,” Opt. Lett. 32(15), 2164–2166 (2007). [CrossRef] [PubMed]

15.

F. Xu and G. Brambilla, “Preservation of Micro-Optical Fibers by Embedding,” Jpn. J. Appl. Phys. 47(8), 6675–6677 (2008). [CrossRef]

16.

N. Lou, R. Jha, J. L. Domínguez-Juárez, V. Finazzi, J. Villatoro, G. Badenes, and V. Pruneri, “Embedded optical micro/nano-fibers for stable devices,” Opt. Lett. 35(4), 571–573 (2010). [CrossRef] [PubMed]

17.

Y. Jung, S. R. Han, S. Kim, U. C. Paek, and K. Oh, “Versatile control of geometric birefringence in elliptical hollow optical fiber,” Opt. Lett. 31(18), 2681–2683 (2006). [CrossRef] [PubMed]

18.

Y. Jung, G. Brambilla, K. Oh, and D. J. Richardson, “Highly birefringent silica microfiber,” Opt. Lett. 35(3), 378–380 (2010). [CrossRef] [PubMed]

19.

B. Lee, “Review of the present status of optical fiber sensors,” Opt. Fiber Technol. 9(2), 57–79 (2003). [CrossRef]

20.

R. I. Laming and D. N. Payne, “Electric Current Sensors Employing Spun Highly Birefringent Optical Fibers,” J. Lightwave Technol. 7(12), 2084–2094 (1989). [CrossRef]

21.

A. Dandridge, A. B. Tveten, and T. G. Giallorenzi, “Interferometric current sensors using optical fibres,” Electron. Lett. 17(15), 523–525 (1981). [CrossRef]

22.

W.-W. Lin, “Fiber-optic current sensor,” Opt. Eng. 42(4), 896–897 (2003). [CrossRef]

23.

G. L. Tangonan, D. I. Persechini, R. J. Morrison, and J. A. Wysocki, “Current sensing with metal coated multimode optic fibers,” Electron. Lett. 16(25-26), 958–959 (1980). [CrossRef]

24.

K. Böhm and K. Petermann, “Signal processing schemes for the fiber-optic gyroscope,” Proc. SPIE 719, 36–44 (1986).

25.

D. A. Jackson, “Recent progress in monomode fibre-optic sensors,” Meas. Sci. Technol. 5(6), 621–638 (1994). [CrossRef]

OCIS Codes
(060.2310) Fiber optics and optical communications : Fiber optics
(060.2370) Fiber optics and optical communications : Fiber optics sensors

ToC Category:
Sensors

History
Original Manuscript: June 24, 2010
Revised Manuscript: August 30, 2010
Manuscript Accepted: August 30, 2010
Published: September 3, 2010

Citation
Mohammad Belal, Zhang-qi Song, Yongming Jung, Gilberto Brambilla, and Trevor Newson, "An interferometric current sensor based on optical fiber micro wires," Opt. Express 18, 19951-19956 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-19-19951


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References

  1. G. Brambilla, “Optical fibre nanowires and microwires: a review,” J. Opt. 12(4), 043001 (2010). [CrossRef]
  2. L. Tong, “Brief introduction to optical microfibers and nanofibers,” Front. Optoelectron. China 3(1), 54–60 (2010). [CrossRef]
  3. J. Lou, L. Tong, and Z. Ye, “Modeling of silica nanowires for optical sensing,” Opt. Express 13(6), 2135–2140 (2005). [CrossRef] [PubMed]
  4. J. Villatoro and D. Monzón-Hernández, “Fast detection of hydrogen with nano fiber tapers coated with ultra thin palladium layers,” Opt. Express 13(13), 5087–5092 (2005). [CrossRef] [PubMed]
  5. L. Zhang, F. Gu, J. Lou, X. Yin, and L. Tong, “Fast detection of humidity with a subwavelength-diameter fiber taper coated with gelatin film,” Opt. Express 16(17), 13349–13353 (2008). [CrossRef] [PubMed]
  6. F. Gu, L. Zhang, X. Yin, and L. Tong, “Polymer single-nanowire optical sensors,” Nano Lett. 8(9), 2757–2761 (2008). [CrossRef] [PubMed]
  7. F. Xu, P. Horak, and G. Brambilla, “Optical microfiber coil resonator refractometric sensor,” Opt. Express 15(12), 7888–7893 (2007). [CrossRef] [PubMed]
  8. F. Xu and G. Brambilla, “Demonstration of a refractometric sensor based on optical microfiber coil resonator,” Appl. Phys. Lett. 92(10), 101126 (2008). [CrossRef]
  9. P. Polynkin, A. Polynkin, N. Peyghambarian, and M. Mansuripur, “Evanescent field-based optical fiber sensing device for measuring the refractive index of liquids in microfluidic channels,” Opt. Lett. 30(11), 1273–1275 (2005). [CrossRef] [PubMed]
  10. C.-Y. Chao and L. Jay Guo, “Design and Optimization of Microring Resonators in Biochemical Sensing Applications,” J. Lightwave Technol. 24(3), 1395–1402 (2006). [CrossRef]
  11. N. Vukovic, N. G. R. Broderick, M. N. Petrovich, and G. Brambilla, “Novel method for the fabrication of long optical tapers,” IEEE Photon. Technol. Lett. 20(14), 1264–1266 (2008). [CrossRef]
  12. L. M. Tong, R. R. Gattass, J. B. Ashcom, S. L. He, J. Y. Lou, M. Y. Shen, I. Maxwell, and E. Mazur, “Subwavelength-diameter silica wires for low-loss optical wave guiding,” Nature 426(6968), 816–819 (2003). [CrossRef] [PubMed]
  13. G. Brambilla, V. Finazzi, and D. J. Richardson, “Ultra-low-loss optical fiber nanotapers,” Opt. Express 12(10), 2258–2263 (2004). [CrossRef] [PubMed]
  14. F. Xu and G. Brambilla, “Embedding optical microfiber coil resonators in Teflon,” Opt. Lett. 32(15), 2164–2166 (2007). [CrossRef] [PubMed]
  15. F. Xu and G. Brambilla, “Preservation of Micro-Optical Fibers by Embedding,” Jpn. J. Appl. Phys. 47(8), 6675–6677 (2008). [CrossRef]
  16. N. Lou, R. Jha, J. L. Domínguez-Juárez, V. Finazzi, J. Villatoro, G. Badenes, and V. Pruneri, “Embedded optical micro/nano-fibers for stable devices,” Opt. Lett. 35(4), 571–573 (2010). [CrossRef] [PubMed]
  17. Y. Jung, S. R. Han, S. Kim, U. C. Paek, and K. Oh, “Versatile control of geometric birefringence in elliptical hollow optical fiber,” Opt. Lett. 31(18), 2681–2683 (2006). [CrossRef] [PubMed]
  18. Y. Jung, G. Brambilla, K. Oh, and D. J. Richardson, “Highly birefringent silica microfiber,” Opt. Lett. 35(3), 378–380 (2010). [CrossRef] [PubMed]
  19. B. Lee, “Review of the present status of optical fiber sensors,” Opt. Fiber Technol. 9(2), 57–79 (2003). [CrossRef]
  20. R. I. Laming and D. N. Payne, “Electric Current Sensors Employing Spun Highly Birefringent Optical Fibers,” J. Lightwave Technol. 7(12), 2084–2094 (1989). [CrossRef]
  21. A. Dandridge, A. B. Tveten, and T. G. Giallorenzi, “Interferometric current sensors using optical fibres,” Electron. Lett. 17(15), 523–525 (1981). [CrossRef]
  22. W.-W. Lin, “Fiber-optic current sensor,” Opt. Eng. 42(4), 896–897 (2003). [CrossRef]
  23. G. L. Tangonan, D. I. Persechini, R. J. Morrison, and J. A. Wysocki, “Current sensing with metal coated multimode optic fibers,” Electron. Lett. 16(25-26), 958–959 (1980). [CrossRef]
  24. K. Böhm and K. Petermann, “Signal processing schemes for the fiber-optic gyroscope,” Proc. SPIE 719, 36–44 (1986).
  25. D. A. Jackson, “Recent progress in monomode fibre-optic sensors,” Meas. Sci. Technol. 5(6), 621–638 (1994). [CrossRef]

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