Downhole fiber optic sensors with downhole optical interrogator

An apparatus for sensing a parameter beneath a surface of the earth, the apparatus comprising:

• an optical fiber disposed beneath a surface of the earth and comprising at least one fiber Bragg grating sensor configured to sense the parameter, wherein the at least one fiber Bragg grating is pressure compensated and the at least one fiber Bragg grating is immersed in a compressible fluid for the pressure compensation;
• a flexible membrane coupled to the optical fiber and configured to sense acoustic wave amplitude;
• a wide-band light source disposed beneath the surface of the earth and configured to emit light in a wide band of wavelengths, the light source being in optical communication with the optical fiber in order to illuminate the at least one fiber Bragg grating;
• an optical interrogator disposed beneath the surface of the earth and configured to receive light reflected by the at least one fiber Bragg grating sensor and to transform a shift in wavelength of the reflected light into a variation of light intensity,
• a photo-sensor disposed beneath the surface of the earth and configured to measure intensity of light received from the optical interrogator;
• and
• electronics coupled to the photo-sensor and configured to measure a voltage representing the light intensity at the photo-sensor to sense the parameter.