Fiber optic sensing systems and method of use thereof

A method of sensing a parameter comprising:

• providing a fiber optic measuring sensor having measuring optical output;
• providing a birefringent fiber optic reference sensor having a reference optical output;
• and
• comparing said measuring optical output with said reference optical output, wherein said measuring and reference sensors have substantially the same nominal operating wavelength.

A method of sensing using:

• at least two passive π-phase shifted FBG sensors written into respective fibers, at least one of which is a birefringent fiber;
• and
• detecting instrumentation;
• the method comprising:
• measuring a frequency splitting between said two resonances of the birefringent fiber;
• and
• said detecting instrumentation using said splitting to derive a reference signal.

A method of deriving an output signal indicative of at least one parameter comprising:

• providing at least two fiber optic sensors providing optical outputs with substantially the same nominal operating wavelength, at least one of said outputs having birefringent components;
• receiving and analysing said optical outputs;
• and
• comparing said optical outputs to derive said output signal indicative of the at least one parameter.