Reflectometric frequency-modulation continuous-wave distributed fiber-optic stress sensor with forward coupled beams

Coherence analysis of optical frequency-modulated continuous-wave interference

I analyze the coherence of optical frequency-modulated continuous-wave (FMCW) interference. With a simple model modified from the classical coherence theory, I successfully derive the relationships among the frequency bandwidth, coherence length, and coherence time of the practical optical source, and the contrast of the beat signal in optical FMCW interference.

Continued analysis of optical frequency-modulated continuous-wave interference

I continue to analyze systematically the theory of optical frequency-modulated continuous-wave (FMCW) interference. Two special cases, multiple-beam optical FMCW interference and multiple-wavelength optical FMCW interference, are discussed in detail. Multiple-beam optical FMCW interference generates a signal with multiple frequencies because of mutual interference among the waves. Multiple-wavelength optical FMCW interference produces a signal whose amplitude is modulated by a synthetic wave. The applications of both types of optical FMCW interference are also discussed.

All-fiber single-mode fiber frequency-modulated continuous-wave Sagnac gyroscope

An all-fiber single-mode fiber unbalanced Sagnac gyroscope is described. The gyroscope is based on optical frequency-modulated continuous-wave interference and consists primarily of four Y-type single-mode fiber directional couplers and a single-mode fiber coil. The rotational velocity of the fiber coil is determined simultaneously by detection of the phase shift of the beat signal. The advantages and limitations of the gyroscope are discussed.

Analysis of optical frequency-modulated continuous-wave interference

I systematically analyze the theory of optical frequency-modulated continuous-wave (FMCW) interference. There are three different versions of optical FMCW interference, discussed in detail: sawtooth-wave optical FMCW interference, triangular-wave optical FMCW interference, and sinusoidal-wave optical FMCW interference. The essential concepts and technical terms are clearly defined, the necessary simplifications are introduced according to the characteristics of optical waves, and the formulas used to calculate the signal intensities under two different situations (static and dynamic) are properly derived. Advantages and limitations of each version of optical FMCW interference are also discussed.

Optical time-of-flight chemical detection: spatially resolved analyte mapping with extended-length continuous chemically modified optical fibers

We theoretically evaluate and experimentally verify a novel strategy for spatially resolved analyte mapping over extended remote areas. The approach combines a method for the fabrication of continuous extended-length sensors with optical time-of-flight chemical detection (OTOF-CD). The use of OTOF-CD makes it possible to locate the zones in the fiber where attenuation or fluorescence takes place, to determine the magnitude of these variations, and to relate the magnitude of the variations to the local concentration or concentrations of a single analyte or several analytes. Simulation experiments suggest that OTOF-CD should provide spatial resolution close to its theoretical limit by deconvolution of the returned wave form with all time-dependent experimental variables (laser pulse width, reagent fluorescence lifetime, etc.). The signal-processing technique should be useful for a wide variety of sensors based on absorption, refractive index, or statically and dynamically quenched fluorescence. Experimental results with a model system (a 48-m-long oxygen sensor) compare favorably with those predicted by numerical simulations. Possible experimental difficulties in the realization of these novel sensors are discussed as are ways to overcome them.