Spectral Phase Shift Interferometry for Refractive Index Monitoring in MicroCapillaries In this work, we demonstrate spectral phaseshift interferometry operating in the nearinfrared wavelength range for refractive index (RI) monitoring of fluidic samples in microcapillaries. A detailed theoretical model was developed to calculate the phasesensitive spectral reflectivity when lowcost rectangular glass microcapillaries, filled with samples with different refractive indices, are placed at the end of the measurment arm of a Michelson interferometer. From the phasesensitive spectral reflectivity, we recovered the cosineshaped interferometric signal as a function of the wavelength, as well as its dependence on the sample RI. Using the readout radiation provided by a 40nm wideband light source with a flat emission spectrum centered at 1.55 xc2xb5m and a 2 xc3x97 1 fiberoptic coupler on the common inputoutput optical path, experimental results were found to be in good agreement with the expected theoretical behavior. The shift of the microcapillary optical resonances, induced by RI variations in the filling fluids (comparing saline solution with respect to distilled water, and isopropanol with respect to ethanol) were clearly detected by monitoring the positions of steep phase jumps in the cosineshaped interferometric signal recorded as a function of the wavelength. By adding a few optical components to the instrumental configuration previously demonstrated for the spectral amplitude detection of resonances, we achieved phasesensitive detection of the wavelength positions of the resonances as a function of the filling fluid RI. The main advantage consists of recovering RI variations by detecting the wavelength shift of xe2x80x9csharp peaksxe2x80x9d, with any amplitude above a threshold in the interferometric signal derivative, instead of xe2x80x9cwide minimaxe2x80x9d in the reflected power spectra, which are more easily affected by uncertainties due to amplitude fluctuations.

SignaltoNoise Ratio of Brillouin Grating Measurement with MicrometerResolution Optical Low Coherence Reflectometry Signaldependent specklelike noise was the dominant noise in a Brillouin grating measurement with micrometerresolution optical low coherence reflectometry (OLCR). The noise was produced by the interaction of a Stokes signal with beat noise caused by a leaked pump light via squarelaw detection. The resultant signaltonoise ratio (SNR) was calculated and found to be proportional to the square root of the dynamic range (DR) defined by the ratio of the Stokes signal magnitude to the variance of the beat noise. The calculation showed that even when we achieved a DR of 20 dB on a logarithmic scale, the SNR value was only 7 on a linear scale and the detected signal tended to fluctuate over xc2xb114% with respect to the mean level. We achieved an SNR of 24 by attenuating the pump light power entering the balanced mixer by 55 dB, and this success enabled us to measure the Brillouin spectrum distributions of mated fiber connectors and a 3dB fused fiber coupler with a micrometer resolution as examples of OLCR diagnosis.