Optical waveguides – Optical waveguide sensor
Reexamination Certificate
1999-09-10
2001-08-21
Ben, Loha (Department: 2873)
Optical waveguides
Optical waveguide sensor
C385S013000, C385S037000, C250S227110, C250S227140, C356S032000
Reexamination Certificate
active
06278810
ABSTRACT:
TECHNICAL FIELD
An optical fiber Bragg grating sensor, a method and an apparatus employing the same for measuring distributed strain and temperatures at the same time, are disclosed.
BACKGROUND
Optical fiber sensors capable of simultaneously measuring distributed strain and temperature have generated significant interest in the technical community. Current technologies have two limitations. They are either difficult to manufacture because they require multi-step manufacturing procedures or they have limited multiplexing potential. For example, the cascaded Bragg grating/extrinsic Fabry-Perot and intrinsic Fabry-Perot/extrinsic Fabry-Perot have excellent numerical stability, have proven very effective in measuring strain and temperature in combined thermomechanical fields, and satisfy the condition of having the same or similar gage lengths for the strain and temperature components of the sensor. However, the extrinsic Fabry-Perot component of the sensor is not always easy to manufacture, and has limited multiplexing potential (maximum of approximately 5 sensors). The other sensor configuration that is promising is the superposed grating configuration proposed by Xu et al.,
Electronic Letters
, 30 (13), pp. 1085-1087, 1994. This technology does not enable cost effective manufacturing. Superposing two gratings is simply not compatible with present day Bragg grating mass production facilities available at Bragg grating manufacturers.
The concept of a two-Bragg condition grating sensor was recently proposed by Brady et al.,
IEEE Proc.—Optoelectrons
, Vol. 144, No. 3, June 1997, pages 156-161. However, Brady et al. did not attempt to make simultaneous measurements of strain and temperature. They were only able to achieve ~0.1 percent reflectivities of second order Bragg condition. The small reflectivity of the second order Bragg condition of the grating necessitated the use of overly complex method of monitoring the two Bragg wavelengths.
SUMMARY
An improved Bragg grating sensor of the present invention for measuring distributed strain and temperature at the same time comprises an optical fiber and a saturated, higher order Bragg grating therein having first and second order Bragg conditions. The optical fiber is selected to have a single mode operating wavelength region and, below a cutoff wavelength of the fiber, a multimode operating wavelength region. A Bragg grating is fabricated in this optical fiber such that the first order Bragg resonance wavelength of the Bragg grating is within the single mode operating wavelength region of the optical fiber and the second order Bragg resonance wavelength is below the cutoff wavelength of the fiber within the multimode operating wavelength region. Further, the higher order Bragg grating is fabricated with controllable second order reflectivity such that the reflectivities at the first and second order Bragg conditions are less than two orders of magnitude of one another. The improved sensor with this combination of features advantageously has a high degree of multiplexability so that large structural systems can be monitored with minimal instrumentation and at much lower cost as compared with prior art systems.
REFERENCES:
patent: 5208877 (1993-05-01), Murphy et al.
patent: 5696863 (1997-12-01), Kleinerman
patent: 5698848 (1997-12-01), Belk
patent: 5760391 (1998-06-01), Narendran
Xu et al.,Electronic Letters,30 (13), pp. 1085-1087, 1994.
Brady et al.,IEEE Proc.-Optoelectrons,vol. 144, No. 3, pp. 156-161, Jun. 1997.
Brady et al., “Recent Developments in Optical Fiber Sensing Using Fiber Bragg Gratings,”SPIE Proceedings,Colorado, 1996, vol. 2839, pp. 8-14.
Faustini and Martini, “Bend Loss in Single Mode Fibers”,J. Lightwave Tech.,vol. 15, No. 4, pp. 671-679, Apr. 1979.
Sirkis James S.
Sivanesan Ponniah
Venkat Venki S.
Antonelli Terry Stout & Kraus LLP
Ben Loha
University of Maryland
LandOfFree
Measurement of distributed strain and temperature based on... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Measurement of distributed strain and temperature based on..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Measurement of distributed strain and temperature based on... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2467467