NIST delivers high accuracy calibration instrument for Navy optical fiber sensors.

A NIST scientist designed, characterized, and recently delivered a calibration instrument for optical fiber Bragg grating (FBG) strain and temperature sensors to the Naval Research Laboratory (NRL). This instrument will be used to calibrate the Navy's strain sensor read out units that will be deployed throughout the Navy fleet. The project was funded by the Navy's Coordination and Calibration Group.

FBGs are a periodic modulation of refractive index written directly into the core of optical fiber. This periodicity causes a narrow spectral bandwidth of the light traveling in the fiber to be selectively reflected from the FBG. The center wavelength of the reflected light changes as the FBG is subjected to strain and temperature changes, making FBGs attractive as small, lightweight, networkable sensors.

The calibration instrument delivered to the NRL contains four stabilized FBGs whose center wave-lengths were accurately measured using both a tunable laser measurement system and low-coherence inter-ferometry. Careful uncertainty analysis on both techniques yielded a 2 pm expanded uncertainty on the calibration instrument. It was found that the "stabilized" FBGs actually drift slightly with time (a few picometers per year). This instability illustrates the need for accurate metrology related to FBG characteristics. FBG sensors have potential uses in medical applications and as strain sensors to measure the structural integrity of buildings, bridges, and aircraft. NIST researchers are investigating FBG metrology needs for these applications.

CONTACT: Shellee Dyer, [phone]; [e-mail].