OSA's Digital Library

Optics Express

Optics Express

  • Editor: J. H. Eberly
  • Vol. 4, Iss. 11 — May. 24, 1999
  • pp: 457–466
« Show journal navigation

Applications of long-period gratings to single and multi-parameter sensing

Vikram Bhatia  »View Author Affiliations


Optics Express, Vol. 4, Issue 11, pp. 457-466 (1999)
http://dx.doi.org/10.1364/OE.4.000457


View Full Text Article

Acrobat PDF (132 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

Photoinduced long-period gratings are shown as versatile sensors for temperature, axial strain and index of refraction measurements. The principle of operation of such devices is discussed and the application to simultaneous temperature and strain is demonstrated.

© Optical Society of America

1. Introduction

Over the past decade optical fiber-based sensors have found numerous applications to environmental sensing [1

1. J. Dakin and B. Culshaw, Optical Fiber Sensors: Principles and Components (Artech House, Boston, 1988).

,2

2. D. A. Krohn, Fiber Optic Sensors (Instrument Society of America, North Carolina, 1992).

]. We demonstrate that long-period gratings written in the core of a photosensitive optical fiber can be used for temperature, strain and index of refraction sensing. The basic functionality of such devices is discussed and the dependence on the host fiber parameters, the grating periodicity and the order of the cladding mode is outlined. It is also shown that long-period gratings can be implemented using a simple intensity demodulation scheme. Finally, the multiple bands of a single grating are use for simultaneous measurement of temperature and axial strain.

2. Long-period gratings

Gratings are fabricated by exposing the core of a photosensitive optical fiber to a spatially varying ultra-violet beam [3

3. G. Meltz, W. W. Morey, and W. H. Glenn, “Formation of Bragg gratings in optical fibers by transverse holographic method,” Opt. Lett. 14, 823 (1989). [CrossRef] [PubMed]

]. Typically the impinging UV beam is periodic in space and results in a regular pattern of index of refraction modulation in the fiber core. The periodicity and amplitude of this refractive index variation determines the coupling of light between the guided mode(s) and the non-guided modes through the phase-matching condition [4

4. K. O. Hill, Y. Fujii, D. C. Johnson, and B. S. Kawasaki, “Photosensitivity in optical fiber waveguides: Applications to reflection filter fabrication,” App. Phy. Lett. 32, 647 (1978). [CrossRef]

,5

5. F. Bilodeau, K. O. Hill, B. Malo, D. Johnson, and I. Skinner, “Efficient narrowband LP01>-<LP02 mode convertorsfabricated in photosensitive fiber: Spectral response,” Elect. Lett. 27, 682 (1991). [CrossRef]

].

For standard telecommunication optical fiber, grating periodicity of the order of 0.5 μm causes the fundamental guided more to couple light to the reverse propagating guided mode over a narrow range of wavelength [4

4. K. O. Hill, Y. Fujii, D. C. Johnson, and B. S. Kawasaki, “Photosensitivity in optical fiber waveguides: Applications to reflection filter fabrication,” App. Phy. Lett. 32, 647 (1978). [CrossRef]

]. This coupling of light shows up as a loss in transmitted intensity through the Bragg grating. The phase-matched wavelength is reflected back and can be retrieved using an input coupler or an optical circulator. Such gratings are typically several millimeters long and any external perturbation that varies the effective index or the periodicity in the localized region causes the coupling wavelength to shift. For example, for a 100 °C change in ambient temperature, a fiber Bragg grating at 1550 nm undergoes a shift of 1 to 1.3 nm to longer wavelengths [6

6. G. Meltz, J. R. Dunphy, W. H. Glenn, J. D. Farina, and F. J. Leonberger, “Fiber optic temperature and strain sensors,” in Conf. on Fiber Optic Sensors II, Proc. SPIE 798, 104 (1987).

]. A similar shift corresponds to about 1% axial strain on the grating [6

6. G. Meltz, J. R. Dunphy, W. H. Glenn, J. D. Farina, and F. J. Leonberger, “Fiber optic temperature and strain sensors,” in Conf. on Fiber Optic Sensors II, Proc. SPIE 798, 104 (1987).

]. To demodulate this wavelength shift optical spectrum analyzers are commonly utilized. For higher sensitivities complex unbalanced interferometer's have been demonstrated in the past [7

7. A. D. Kersey and T. A. Berkoff, “Fiber-optic Bragg-grating differential-temperature sensor,” IEEE Phot. Tech. Lett. 4,1183 (1992). [CrossRef]

]. Although Bragg gratings present an attractive sensing platform, these are limited by either sensitivity to strain or temperature, or by expensive demodulation schemes. Additionally, index of refraction sensors using Bragg gratings require the user to etch the cladding to gain access to the evanescent filed of the guided mode [8

8. G. Meltz, W. W. Morey, S. J. Hewlett, and J. D. Love, “Wavelength shifts in fiber Bragg gratings due to changes in the cladding properties,” in Topical Meeting on Photosensitivity and Quadratic Nonlinearity in Glass Waveguides, OSA Proceedings Series (Optical Society of America, Washington, D.C., 1995), paper PMB4, 225

]. Since the Bragg grating-based sensor is sensitive to both strain and temperature, separating these parameters requires multiple co-located gratings [9

9. M. G. Xu, J. L. Archambault, L. Reekie, and J. P. Dakin, “Discrimination between temperature and strain effects using dual wavelength fiber grating sensors,” Elect. Lett. 30, 1085 (1994). [CrossRef]

], adding to the system cost.

A long-period grating is formed by using a ultra-violet beam that has a spatial intensity variation with periods ranging from tens to several hundred micrometers [10

10. A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, J. E. Sipe, and T. E. Ergodan, “Long-period fiber gratings as band-rejection filters,” J. Lightwave Tech. 14, 58 (1996). [CrossRef]

]. For these gratings, the energy typically couples from the fundamental guided mode to discrete, forward-propagating cladding modes. The cladding modes are quickly attenuated and this results in series of loss bands in the transmission spectrum of the grating. Each of these attenuation bands corresponds to coupling to a distinct cladding mode that has an effective index that is a strong function of the host fiber parameters. For an unglazed long-period grating with periodicity Λ, the wavelength λ(m) at which the mode coupling occurs is given by:

λ(m)=(neffncl,m)Λ
(1)

3. Single-parameter sensing

3.1 Temperature

The sensitivity of a long-period grating to temperature T can be examined by expanding Eq. (1) to yield:

dT=d(δneff)(dneffdTdncldT)+ΛdΛ1LdLdT
(2)

where L is the length of the grating, δneff=neff-ncl is the differential effective index, and the ordinal m has been dropped for the sake of simplicity.

Fig. 1. Shift in a band of a long-period grating with temperature. The spectra correspond to temperatures of 22.7 °C, 49.1 °C, 74.0 °C, 100.9 °C, 127.3 °C and 149.7 °C from left to right [14]. The resonant wavelength shifts from 1607.8 nm at 22.7 °C to 1619.6 nm at 149.7 °C.

The two terms on the right hand side of Eq. (2) separated by the + sign represent the contributions to the grating thermal sensitivity due to the change in the differential effective index and the grating periodicity, and will henceforth be referred to as the material and waveguide effects, respectively [13

13. J. B. Judkins, J. R. Pedrazzani, D. J. DiGiovanni, and A. M. Vengsarkar, “Temperature-insensitive long-period fiber gratings,” in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1996), postdeadline paper PD1.

]. The material contribution arises from the change in the indices of refraction of the core and the cladding due to temperature and is a function of the composition of the fiber. The waveguide contribution has its basis in the thermal sensitivity of the grating periodicity and can be negative or positive depending strongly on the slope dλ/dΛ of the characteristic curve corresponding to the appropriate cladding mode [14

14. V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia1996).

]. The wavelength shift due to the material effect can similarly have either polarity and its magnitude is a function of the relative change between the effective indices of the guided and cladding modes. For standard long-period gratings with periodicity of hundreds of micrometers, the material effect typically dominates the waveguide contribution to the temperature-induced shift. The strong dependence of the material effect on the order of the cladding modes results in the distinct wavelength shifts of the individual loss bands of a long-period grating. Moreover, since the period of the grating dictates the order of the coupled cladding mode, the temperature response for a given fiber can vary considerably with periodicity.

To study the effect of temperature, a long-period grating with Λ=280 μm was fabricated in Corning SMF-28 fiber using a continuous-wave UV laser [14

14. V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia1996).

]. Fig. 1 illustrates the thermally-induced shift in the loss band from 1607.8 nm at 22.7 °C to 1619.6 nm at 149.7 °C. A linear fit to the wavelength shift data yields a slope of 0.093 nm/°C and that is almost an order of magnitude higher than that observed in a fiber Bragg grating. In Fig. 1 the intensity variation with temperature at a particular wavelength is very significant. This will be used to implement a simple demodulation scheme for long-period gratings in Section 4.

Fig. 2. Shift in the peak loss wavelengths (with respect to that at 31.2 °C) with temperature for various resonance bands of a long-period grating [14]. The location of the bands A, B, C and D are 1608.6 nm, 1332.9 nm, 1219.7 nm and 1159.6 nm, respectively at 31.2 °C. The experimental data (symbols) are and approximated by linear curve fits. The dashed line (E) is the shift for a Bragg grating at 1550 nm with a temperature coefficient 1.3 nm/100 °C.

Fig. 2 shows the wavelength shifts in the four resonance bands of the long-period grating described above. The distinct spectral displacement of the four bands is clearly visible. Also shown is the temperature sensitivity of a standard Bragg grating. The non-linearity in the wavelength shift for the long-period grating bands can be attributed primarily to the temperature dependence of the thermo-optic coefficients of the core and the cladding. For this particular grating the sensitivity to temperature increases with the order of the cladding mode due to the different material contributions for distinct cladding modes. The thermal sensitivity is a strong function of the grating period, the order and the coupling wavelength of the cladding mode and the host fiber parameters [14

14. V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia1996).

]. It has been shown recently that the wavelength shift can be further enhanced by using appropriate coating around the grating [15

15. A. A. Abramov, A. Hale, R. S. Windeler, and T. A. Strasser, “Temperature-sensitive long-period fiber gratings for wideband tunable filters,” in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1999) ThJ5.

]. It has also been demonstrated that the temperature sensitivity can be suppressed by tailoring the fiber profile [13

13. J. B. Judkins, J. R. Pedrazzani, D. J. DiGiovanni, and A. M. Vengsarkar, “Temperature-insensitive long-period fiber gratings,” in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1996), postdeadline paper PD1.

] or by coupling to specific cladding modes in standard fibers [16

16. V. Bhatia, D. Campbell, T. D’Alberto, G. Ten Eyck, D. Sherr, K. A. Murphy, and R. O. Claus, “Standard optical fiber long-period gratings with reduced temperature-sensitivity for strain and refractive index sensing,” in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1997) paper FB1

].

3.2 Axial strain

As with temperature, the sensitivity of a long-period grating to axial strain ε can be studied by expanding Eq. (1) and re-arranging to yield:

=d(δneff)(dneffdncl)+ΛdΛ
(3)

where the two terms on the right-hand side can again be divided into material (first term) and waveguide (second term) contributions. In this case the two contributions can have either polarity depending on the grating period and the order of the cladding mode. The waveguide effect can be significant and is a function of the local slope dλ/dΛ for a particular cladding mode [14

14. V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia1996).

]. Moreover, the two contributions can be equal in magnitude but opposite in polarity, resulting in a strain-insensitive grating that can be employed as a pure temperature sensor [17

17. V. Bhatia, D. K. Campbell, D. Sherr, T. G. D’Alberto, N. A. Zabaronick, G. A. Ten Eyck, K. A. Murphy, and R.O. Claus, “Temperature-insensitive and strain-insensitive long-period grating sensors for smart structures,” Opt. Eng. 36, 1872 (1997). [CrossRef]

].

Fig. 3. Shift in the peak loss wavelengths with strain for various resonance bands of a long-period grating [14]. The dashed line (E) is the shift for a Bragg grating with coefficient 11.55 nm/%ε.

Fig. 3 depicts the axial strain-induced shift in the resonance bands of the long-period grating written in SMF-28 fiber (with Λ=280 μm). The dependence on the order of the cladding mode is clearly evident from the fact that the resonance bands corresponding to curves A and D have linear fits of 19.42 nm/%ε and -0.32 nm/%ε, respectively. Figs. 2 and 3 also reveal the cross-sensitivity of long-period gratings to strain and temperature. The strong dependence of this cross-sensitivity on the order of the cladding mode will be employed for simultaneous strain and temperature sensing in Section 5.

3.3 Index of refraction

The influence of variation in the index of refraction n3 around the cladding of a long-period grating can be explained by arranging Eq. (1) to produce:

dn3=dncldncldn3
(4)

For each cladding mode, the term dncl/dn3 is distinct and hence a long-period grating is expected to have a strong dependence on the order of the coupled cladding mode. The shift with refractive index changes, for a given fiber and cladding mode, may be positive or negative depending on the local slope of the characteristic curve dλ/dΛ [14

14. V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia1996).

].

Fig. 4. Experimental shift in the four resonance bands of a long-period grating as a function of the index of the ambient medium [14]. The bands at 1496.6 nm (A), 1329.3 nm (B), 1243.8 nm (C) and 1192.1 nm (D) were used for the experiment. The shifts are measured with respect to the locations at n3=1.0. The indices of the oils are calculated at the corresponding resonant wavelengths of the bands.

Fig. 4 shows the wavelength shifts in the resonance bands (with respect to n3=1.0) for a long-period grating written in Corning SMF-28 fiber with Λ=320 μm [13

13. J. B. Judkins, J. R. Pedrazzani, D. J. DiGiovanni, and A. M. Vengsarkar, “Temperature-insensitive long-period fiber gratings,” in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1996), postdeadline paper PD1.

]. For this particular grating, the shift is negative for all bands and increases with the order of the cladding mode. At approximately n3=1.444 the distinct loss bands disappear since the cladding modes get converted to radiation mode losses. Wavelength shifts as large as -66.9 nm were measured for one of the resonance bands. The sensitivity to index of refraction changes can be enhanced or reduced by manipulating the fiber parameters and choosing the appropriate grating period for coupling to specific cladding modes [14

14. V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia1996).

].

4. Demodulation

The demodulation of long-period gratings is typically implemented by detecting the wavelength shift using an optical spectrum analyzer. The spectrum analyzers are expensive and are additionally limited by resolution. The wavelength shift of the broad resonance bands can be converted into an intensity variation by using a laser source centered on either side of the grating center wavelength. A simple photodetector can then be used to determine the applied perturbation for a calibrated sensor [11

11. V. Bhatia and A. M. Vengsarkar, “Optical fiber long-period grating sensors,” Opt. Lett. 21, 692 (1996). [CrossRef] [PubMed]

]. Alternatively, a broadband source can be used as the input and an optical filter can be employed at the output end with the photodetector. The demodulation technique is potentially low cost, offers improved sensitivity and can be used for applications where the parameter to be measured is varying rapidly. Typically the shift in the wavelength of a resonance band under an applied perturbation is accompanied by a variation in the amplitude of the loss. This can easily be accounted for during the calibration of the sensor assuming the change in the amplitude is repeatable. For applications to index of refraction sensing the variation in amplitude can be significant around the value n3=1.444 for conventional fibers and might limit the system performance.

Fig. 5. Change in transmission through a grating for increasing (circles) and decreasing (squares) temperature [14]. The resonance band for the grating under test is centered at 1294 nm (50 °C) while the laser diode is located at 1312 nm. The transmission is normalized to 0 dB at 50 °C. Inset shows the grating spectra in steps of 50 °C.

Fig. 5 shows the effectiveness of this demodulation scheme [14

14. V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia1996).

]. The resonance band of a long-period grating was subjected to temperature variation. The inset in Fig. 5 illustrates the shift in the band due to temperature. A laser diode at 1312 nm was used at the light source while the transmission through the grating was monitored using a photodetector. Once calibrated, the transmitted intensity can be used for determining the local temperature at the grating.

5. Simultaneous strain and temperature sensing

As discussed in Section 3, the wavelength shift for a particular band of a long-period grating due to axial strain or temperature is a strong function of the host fiber parameters and the order of the corresponding cladding mode. The differential shift in two or more resonance bands of a long-period grating can be utilized for multi-parameter sensing [12

12. V. Bhatia, D. Campbell, R.O. Claus, and A. M. Vengsarkar, “Simultaneous strain and temperature measurement with long-period gratings,” Opt. Lett. 22, 648 (1997). [CrossRef] [PubMed]

]. As a simple analysis, let us consider two bands of a grating centered at λ1 and λ2. Let A and B be the temperature and axial strain coefficients of wavelength shift for the first band and let C and D be the corresponding coefficients of the second band. The shifts in the wavelengths of the two bands due to concurrent temperature change ΔT and strain change Δε, assuming a linear system, are given by:

AΔT+BΔε=Δλ1
(5)
T+DΔε=Δλ2
(6)

Assuming A, B, C and D are known, the two simultaneous equations can be solved for ΔT and Δε. The non-linearity in the four coefficients requires that they be expanded in higher order terms [14

14. V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia1996).

]. Additionally, the cross-sensitivity between strain and temperature causes the linear and higher order coefficients of B and D to be functions of temperature [14

14. V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia1996).

]. If the non-linearity and cross-sensitivity can be appropriately characterized, the grating can be used for simultaneous strain and temperature measurements.

Fig. 6. Comparison between measured (symbols) and actual (lines) values of (a) temperature (b) strain using a long-period grating [14]. The average rate of temperature change was -1.08 °C/min.

To test this concept an experiment was performed, the details of which can be found elsewhere [12

12. V. Bhatia, D. Campbell, R.O. Claus, and A. M. Vengsarkar, “Simultaneous strain and temperature measurement with long-period gratings,” Opt. Lett. 22, 648 (1997). [CrossRef] [PubMed]

]. Fig. 6 shows the simultaneous variation in the applied temperature and axial strain on the long-period grating as a function of time. The corresponding calculated values of the perturbations are also plotted. The maximum errors in strain and temperature were found to be 42 με and 0.6 °C, respectively. This system may be extended to include index of refraction measurements also. Moreover, the simple intensity demodulation technique proposed in Section 4 can be used with multiple laser sources and optical filters to improve sensitivity and speed.

6. Conclusions

Acknowledgments

The author wishes to thank Ashish Vengsarkar at Bell Laboratories, Lucent Technologies, for his technical support. Acknowledgments are also extended to Dave Campbell, Dan Sherr and Rick Claus at the Fiber & Electro-Optics Research Center at Virginia Tech, and Tiffanie D’Alberto and Mary Burford at Corning Inc.

References and links

1.

J. Dakin and B. Culshaw, Optical Fiber Sensors: Principles and Components (Artech House, Boston, 1988).

2.

D. A. Krohn, Fiber Optic Sensors (Instrument Society of America, North Carolina, 1992).

3.

G. Meltz, W. W. Morey, and W. H. Glenn, “Formation of Bragg gratings in optical fibers by transverse holographic method,” Opt. Lett. 14, 823 (1989). [CrossRef] [PubMed]

4.

K. O. Hill, Y. Fujii, D. C. Johnson, and B. S. Kawasaki, “Photosensitivity in optical fiber waveguides: Applications to reflection filter fabrication,” App. Phy. Lett. 32, 647 (1978). [CrossRef]

5.

F. Bilodeau, K. O. Hill, B. Malo, D. Johnson, and I. Skinner, “Efficient narrowband LP01>-<LP02 mode convertorsfabricated in photosensitive fiber: Spectral response,” Elect. Lett. 27, 682 (1991). [CrossRef]

6.

G. Meltz, J. R. Dunphy, W. H. Glenn, J. D. Farina, and F. J. Leonberger, “Fiber optic temperature and strain sensors,” in Conf. on Fiber Optic Sensors II, Proc. SPIE 798, 104 (1987).

7.

A. D. Kersey and T. A. Berkoff, “Fiber-optic Bragg-grating differential-temperature sensor,” IEEE Phot. Tech. Lett. 4,1183 (1992). [CrossRef]

8.

G. Meltz, W. W. Morey, S. J. Hewlett, and J. D. Love, “Wavelength shifts in fiber Bragg gratings due to changes in the cladding properties,” in Topical Meeting on Photosensitivity and Quadratic Nonlinearity in Glass Waveguides, OSA Proceedings Series (Optical Society of America, Washington, D.C., 1995), paper PMB4, 225

9.

M. G. Xu, J. L. Archambault, L. Reekie, and J. P. Dakin, “Discrimination between temperature and strain effects using dual wavelength fiber grating sensors,” Elect. Lett. 30, 1085 (1994). [CrossRef]

10.

A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, J. E. Sipe, and T. E. Ergodan, “Long-period fiber gratings as band-rejection filters,” J. Lightwave Tech. 14, 58 (1996). [CrossRef]

11.

V. Bhatia and A. M. Vengsarkar, “Optical fiber long-period grating sensors,” Opt. Lett. 21, 692 (1996). [CrossRef] [PubMed]

12.

V. Bhatia, D. Campbell, R.O. Claus, and A. M. Vengsarkar, “Simultaneous strain and temperature measurement with long-period gratings,” Opt. Lett. 22, 648 (1997). [CrossRef] [PubMed]

13.

J. B. Judkins, J. R. Pedrazzani, D. J. DiGiovanni, and A. M. Vengsarkar, “Temperature-insensitive long-period fiber gratings,” in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1996), postdeadline paper PD1.

14.

V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia1996).

15.

A. A. Abramov, A. Hale, R. S. Windeler, and T. A. Strasser, “Temperature-sensitive long-period fiber gratings for wideband tunable filters,” in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1999) ThJ5.

16.

V. Bhatia, D. Campbell, T. D’Alberto, G. Ten Eyck, D. Sherr, K. A. Murphy, and R. O. Claus, “Standard optical fiber long-period gratings with reduced temperature-sensitivity for strain and refractive index sensing,” in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1997) paper FB1

17.

V. Bhatia, D. K. Campbell, D. Sherr, T. G. D’Alberto, N. A. Zabaronick, G. A. Ten Eyck, K. A. Murphy, and R.O. Claus, “Temperature-insensitive and strain-insensitive long-period grating sensors for smart structures,” Opt. Eng. 36, 1872 (1997). [CrossRef]

OCIS Codes
(050.0050) Diffraction and gratings : Diffraction and gratings
(280.0280) Remote sensing and sensors : Remote sensing and sensors

ToC Category:
Focus Issue: Sensing

History
Original Manuscript: April 5, 1999
Published: May 24, 1999

Citation
Vikram Bhatia, "Applications of long-period gratings to single and multi-parameter sensing," Opt. Express 4, 457-466 (1999)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-4-11-457


Sort:  Journal  |  Reset  

References

  1. J. Dakin and B. Culshaw, Optical Fiber Sensors: Principles and Components (Artech House, Boston, 1988).
  2. D. A. Krohn, Fiber Optic Sensors (Instrument Society of America, North Carolina, 1992).
  3. G. Meltz, W. W. Morey and W. H. Glenn, "Formation of Bragg gratings in optical fibers by transverse holographic method," Opt. Lett. 14, 823 (1989). [CrossRef] [PubMed]
  4. K. O. Hill, Y. Fujii, D. C. Johnson and B. S. Kawasaki, "Photosensitivity in optical fiber waveguides: Applications to reflection filter fabrication," Appl. Phy. Lett. 32, 647 (1978). [CrossRef]
  5. F. Bilodeau, K. O. Hill, B. Malo, D. Johnson and I. Skinner, "Efficient narrowband LP 01 <->LP 02 mode convertors fabricated in photosensitive fiber: Spectral response," Elect. Lett. 27, 682 (1991). [CrossRef]
  6. G. Meltz, J. R. Dunphy, W. H. Glenn, J. D. Farina and F. J. Leonberger, "Fiber optic temperature and strain sensors," in Conf. on Fiber Optic Sensors II, Proc. SPIE 798, 104 (1987).
  7. A. D. Kersey and T. A. Berkoff, "Fiber-optic Bragg-grating differential-temperature sensor," IEEE Phot. Tech. Lett. 4, 1183 (1992). [CrossRef]
  8. G. Meltz, W. W. Morey, S. J. Hewlett and J. D. Love, "Wavelength shifts in fiber Bragg gratings due to changes in the cladding properties," in Topical Meeting on Photosensitivity and Quadratic Nonlinearity in Glass Waveguides, OSA Proceedings Series (Optical Society of America, Washington, D.C., 1995), paper PMB4, 225
  9. M. G. Xu, J. L. Archambault, L. Reekie and J. P. Dakin, "Discrimination between temperature and strain effects using dual wavelength fiber grating sensors," Elect. Lett. 30, 1085 (1994). [CrossRef]
  10. A. M. Vengsarkar, P. J. Lemaire, J. B. Judkins, V. Bhatia, J. E. Sipe and T. E. Ergodan, "Long-period fiber gratings as band-rejection filters," J. Lightwave Tech. 14, 58 (1996). [CrossRef]
  11. V. Bhatia and A. M. Vengsarkar, "Optical fiber long-period grating sensors," Opt. Lett. 21, 692 (1996). [CrossRef] [PubMed]
  12. V. Bhatia, D. Campbell, R.O. Claus and A. M. Vengsarkar, "Simultaneous strain and temperature measurement with long-period gratings," Opt. Lett. 22, 648 (1997). [CrossRef] [PubMed]
  13. J. B. Judkins, J. R. Pedrazzani, D. J. DiGiovanni and A. M. Vengsarkar, "Temperature-insensitive long-period fiber gratings," in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1996), postdeadline paper PD1.
  14. V. Bhatia, Properties and sensing applications of long-period gratings (Ph.D. Dissertation, Virginia Tech, Blacksburg, Virginia 1996).
  15. A. A. Abramov, A. Hale, R. S. Windeler and T. A. Strasser, "Temperature-sensitive long-period fiber gratings for wideband tunable filters," in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1999) ThJ5.
  16. V. Bhatia, D. Campbell, T. DAlberto, G. Ten Eyck, D. Sherr, K. A. Murphy and R. O. Claus, "Standard optical fiber long-period gratings with reduced temperature-sensitivity for strain and refractive index sensing," in Optical Fiber Communication, (Optical Society of America, Washington, D.C., 1997) paper FB1
  17. V. Bhatia, D. K. Campbell, D. Sherr, T. G. DAlberto, N. A. Zabaronick, G. A. Ten Eyck, K. A. Murphy and R.O. Claus, "Temperature-insensitive and strain-insensitive long-period grating sensors for smart structures," Opt. Eng. 36, 1872 (1997). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited