Development of a miniature, multichannel, extended Fabry-Perot fiber-optics laser interferometer system for low frequency SI-traceable displacement measurement

摘要

The goal of this work was to build a directly SI-traceable laser interferometer displacement sensor with a sensor head no bigger than a single optical fiber diameter (0.125 mm). The sensor was designed and built specifically to serve as the primary displacement and force gauge sensor in an SI-traceable precision nanoindentation platform. The sensor is based on a fiber-optic, homodyne, low finesse, single detector Fabry-Perot cavity that is set up between a reflective surface and the cleaved end of an optical fiber whose laser wavelength is modulated sinusoidally. By modulating wavelength while cavity length is being changed, the signal measured by the detector has a spectrum consisting of responses at the modulation frequency and its harmonics. Those signals can be used to extract target displacement. This approach extends the working distance to well beyond 25 mm, while still maintaining sub-nanometer performance.