Ultrahigh-sensitivity fiber-optic strain and temperature sensor.

We report ultrahigh-sensitivity static strain sensing (noise equivalent strain

Fiber-optic Bragg grating strain sensor with drift-compensated high-resolution interferometric wavelength-shift detection.

The operation of a fiber Bragg grating strain sensor system that uses interferometric determination of strain-induced wavelength shifts and incorporates a reference channel to compensate for random thermal-induced drift in the output is described. This system is shown to be capable of resolving sub-microstrain changes in the quasi-static strain applied to a grating and has a resolution of ~6 x 10(-3) microstrain/ radicalHz at a strain perturbation frequency of 1 Hz.

Reflective fiber ring resonator with polarization-independent operation.

A polarization-insensitive fiber-optic ring-resonator configuration based on a reflective mode of operation with a Faraday rotator mirror for birefringence compensation is reported. An output resonant-dip transfer function that is independent of the input polarization to the system is obtained, which is shown to produce a stable scale factor of the system.

In-line fiber étalon for strain measurement.

A description and demonstration of a fiber interferometer that uses a short segment of silica hollow-core fiber spliced between two sections of single-mode fiber to form a mechanically robust in-line cavity are presented. The hollow-core fiber is specifically manufactured to have an outer diameter that is equal to the outer diameter of the single-mode lead fibers, thereby combining the best qualities of existing intrinsic and extrinsic Fabry-Perot sensors. A dynamic strain resolution of ~22 nepsilon/ radicalHz at frequencies of >5 Hz with a sensor gauge length of 137 microm is demonstrated.

Polarization diversity detection for fiber interferometers using active feedback control of output polarization-mode selection.

The application of an adaptive polarization diversity detection technique in an interferometric fiber sensor system is described. The approach utilizes feedback control of the polarization modes selected at the sensor output and produces the optimum level of total interference signal while allowing the states of polarization of the light in the signal and reference arms of the interferometer to vary randomly.

Cross talk in a fiber-optic Fabry-Perot sensor array with ring reflectors.

We demonstrate a fiber-optic interferometric sensor array based on the in-line Fabry-Perot configuration, which uses fiber ring reflectors to effect the low-reflectivity elements required between each sensor section. The intrinsic optical cross talk that occurs between the sensor sections owing to multiple reflections is analyzed and compared with experimental results obtained with a four-sensor system.

Dependence of visibility on input polarization in interferometric fiber-optic sensors.

We present an analysis of the effects of input polarization on the output fringe visibility of two-beam interferometric fiber-optic sensors, which predicts the existence of interferometer input-polarization eigenmodes for which optimum visibility is obtained. Experimental results that verify this are also presented.

Observation of input-polarization-induced phase noise in interferometric fiber-optic sensors.

It is shown that polarization fluctuations in the input fiber to an interferometric sensor can result in the generation of excess phase noise in the output. Experimental observations of this phenomenon are compared with theoretical models, and the impact of this noise source in interferometric sensors is briefly discussed.

Time-division multiplexing of interferometric fiber sensors using passive phase-generated carrier interrogation.

The multiplexing and demodulation of interferometric sensors using a time-division/phase-generated carrier approach is described. The scheme uses slightly unbalanced interferometers and laser frequency modulation to effect the interrogation of the sensors, while the time-division multiplexing allows individual sensors to be addressed. Phase sensitivities of ~20 microrad/ radicalHz and cross-talk levels of <-47 dB are demonstrated for a three-sensor network.