Dual-wavelength quadrature phase-shifted demodulation of low-finesse short F-P cavity

An improved two-wavelength quadrature-shifted demodulation approach of low-finesse Fabry-Perot (F-P) interferometer is reported. An optical passive device, dense wavelength division multiplexer (DWDM), is used to generated two quadrature phase-shifted output signals in the design scheme. The filtering wavelength of DWDM is calculated by the optimization design method. The F-P cavity phase change is then extracted by using the Arctan algorithm The scheme test is implemented by using F-P cavity whose gauge length ranges from 0 to 0.8μm. Besides being totally passive and flexible, this modulation technique is potential to be used in the interrogation of low-finesse short F-P cavities with a sensitivity of 0.468°/nm and the small nonlinearity of 1.2%.