Optical sensing device containing fiber Bragg gratings

An interrogating system for a fiber optical sensor having fiber Bragg gratings comprising:

• a scanning filter optically coupled to the fiber optical sensor;
• an interferometer optically coupled to an output port of the scanning filter;
• a first photodetector optically coupled to the interferometer;
• a second photodetector optically coupled to the interferometer;
• and
• a third photodetector optically coupled to the interferometer.

A method for measuring a change in an environment comprising the steps of:

• irradiating a fiber having a plurality of fiber Bragg gratings with different center wavelengths with a broadband light to generate a reflected light from each of the Bragg gratings, wherein each of the reflected lights is reflected from a specific fiber Bragg grating and has a wavelength which is the sum of the center wavelength characteristic of the specific fiber Bragg grating and a wavelength shift based on the change in the environment;
• filtering one of the reflected lights through a scanning filter at a time;
• encoding the wavelength of the reflected light from the scanning filter into a phase signal embedded in at least three interference lights using an interferometer;
• converting the at least three interference lights into at least three voltage signals using at least three photodetectors;
• demodulating the at least three voltage signals to obtain the phase of the phase signal;
• calculating the wavelength shift of the reflected light from the phase of the phase signal;
• and
• determining the change in the environment from the wavelength shift.