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Fundamental limits in fiber Bragg grating peak wavelength measurements



Shellee D. Dyer, Paul A. Williams, Robert J. Espejo, Jonathan Kofler, Shelley M. Etzel


We discuss the fundamental limits of fiber Bragg grating (FBG) wavelength metrology. High-accuracy wavelength measurements are critical for FBG strain sensors, because wavelength measurement uncertainties even as small as 1 pm lead to an uncertainty of nearly 1 microstrain. We discuss the measurement uncertainties for several common wavelength measurement systems, including tunable laser, optical spectrum analyzer (OSA), and interferometric measurements. We show that when using an OSA it is difficult to achieve a measurement uncertainty better than 10 pm, and if the OSA is not accurately calibrated to a known wavelength reference, then the wavelength measurement uncertainty can be as large as 1 nm. We describe the uncertainties involved in determining peak and/or centroid wavelength from a measured data set. We also discuss calibration references for FBG sensor interrogation units. Wavelength references that are based on molecular absorption lines are often an excellent choice for FBG sensor calibration. However, some interrogation units require a wavelength reference unit based on narrow reflection lines rather than absorption lines. We investigated the application of athermally packaged FBGs as wavelength references, but we found that their wavelengths will drift with time and can undergo large jumps. We concluded that it is difficult to achieve stability better than 4 pm/year in athermally packaged FBGs.
Proceedings Title
Proc. of SPIE
Conference Dates
May 23-27, 2005
Conference Location
Bruges, 1, BE
Conference Title
17th International Conference on Optical Fiber Sensors


calibration, fiber Bragg gratings, fiber-optic sensors, wavelength metrology


Dyer, S. , Williams, P. , Espejo, R. , Kofler, J. and Etzel, S. (2005), Fundamental limits in fiber Bragg grating peak wavelength measurements, Proc. of SPIE, Bruges, 1, BE, [online], (Accessed April 21, 2024)
Created December 31, 2004, Updated October 12, 2021