Compact laser sensors and monitoring systems including such sensors

A seismic or sonar monitoring system comprising:

• a fiber optic transmission line;
• a seismic or sonar sensor array comprising at least two laser sensors, wherein each of said at least two laser sensors comprises:
• a doped lasing crystal arranged to generate a light at two different frequencies with two orthogonal polarizations, said light exhibiting a beat frequency between said two different frequencies which varies in accordance with a force incident upon the lasing crystal;
• a pump diode generating an excitation light to drive said lasing crystal, said pump diode adjacent to and directly coupled to a first end of said lasing crystal by a direct butt-coupling integrated optic;
• a photodetector directly coupled to a second end of said lasing crystal by a direct butt-coupling integrated optic;
• a dense wavelength division multiplexing laser in communication with said photodetector, said dense wavelength division multiplexing laser generating an output modulated by output current from said photodetector and exhibiting frequency shifts proportional to said force;
• and
• a fiber optic cable connected to said dense wavelength division multiplexing laser for transmitting said output, wherein said fiber optic cable is in communication with said fiber optic transmission line;
• and
• a receiving unit arranged to process said output, said receiving unit comprising:
• an optical demultiplexer connected to said fiber optic transmission line to demultiplex output light from said at least two laser sensors and to produce demultiplexed outputs;
• and
• optical receivers in communication with said optical demultiplexer and arranged to process said demultiplexed outputs from said optical demultiplexer, wherein each of said optical receivers includes a photodiode for converting light into an electrical signal and an analog-to-digital converter for converting an output of said photodiode to digital data.