Determining quasi-static measurands without a receiving interferometer using a simple dual-wavelength technique

A technique using dual-wavelength interferometry which permits the demodulation of quasi-static measurands from very short cavities is introduced. It requires the optical path difference of the sensor to be perturbed and a careful choice of the two wavelengths. Under these conditions comparable resolution and range to conventional dual- wavelength white-light interferometry is obtained. A remote receiving interferometer is not required. Experimental verification of this technique using a fiber Mach-Zehnder under conditions of natural drift are presented. A resolution of 0.2 nm (corresponding to 1.5 mrad at 827 nm) over an effective wavelength of 114.8 micrometer was achieved. Multiplexing using this demodulation technique is also presented. A network of eight sensors is demonstrated with the same resolution and range as the single Mach- Zehnder.