Depolarized light source for fiber optic sensors

An apparatus comprising a depolarized light source, said depolarized light source comprising:

• a first laser for generating a first beam at a first frequency, said first beam having a linear polarization state, said first laser being tunable to produce said first beam at a desired first frequency;
• a second laser for generating a second beam at a second frequency, said second beam having a linear polarization state, said second laser being tunable to produce said second beam at a desired second frequency such that the frequency difference between said desired first and second frequencies is between 1 and 100 gigahertz (GHz) and said depolarized composite beam contains components having a frequency difference of between 1 and 100 GHz;
• means for rotating the polarization state of said second beam so that said first and second beams have orthogonal linear polarization states with respect to each other;
• and
• means for combining the first beam with the polarization-rotated second beam to obtain a composite beam which is depolarized.

An apparatus comprising:

• a source of depolarized light having orthogonal linear polarization states, said source comprising
• two tunable lasers with each of said tunable lasers being tuned to a frequency different from that of the other said tunable laser and being capable of producing a beam having a linear polarization state and
• means for merging said laser beams to obtain said depolarized light having orthogonal linear polarization states;
• integrated optic modulator means for receiving a modulator drive signal said integrated optic modulator means selected from the group consisting of a single polarization waveguide device and a fiber polarizer coupled to an integrated optic modulator;
• a first low-birefringence fiber for conveying said depolarized light from said depolarized light source to said integrated optic modulator means, said integrated optic modulator means modulating only one linear polarization state in said depolarized light as a function of said modulator drive signal to produce a modulated beam;
• a photodetector;
• and
• a second low-birefringence fiber for conveying said modulated light to said photodetector, said photodetector being responsive to said modulated light for developing an electrical signal proportional to said modulator drive signal.