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Fiber Fabry-Perot cavity for interferometric displacement measurement: an experimental study



Bartosz K. Nowakowski, Douglas T. Smith, Stuart T. Smith


This paper presents an experimental study of a fiber-based Fabry-Perot interferometer comprising two reflecting surfaces (the end of a cleaved fiber and a plane mirror) for the measurement of displacement. Displacement is based on interferometric phase measurement using a frequency stabilized, frequency modulated laser source. The phase signal is derived from intensity measurement of the light reflected from the cavity at both the modulation frequency, f , and its harmonic at 2 f . The resulting signals, while periodic, are neither harmonic nor of constant shape. Simple quadrature detection results in phase errors corresponding to displacement deviations of up to 50 nm. Using compensation algorithms discussed in this paper, these inherent non-linearities can be reduced to below 3 nm over limited measurement distances. When the cavity is held to a constant gap, a noise of 0.106 nm/√Hz is measured with a displacement stability of better than 1 nm per 24 hour period being observed. During all measurements, the center frequency of the modulated laser under closed loop stabilization control showed a 2σ deviation of less than 0.002 nm. Wavelength tuning capability enables the absolute measurement of the mirror separation. This is limited by the available modulation depth for small separations (<20 m) and increasing uncertainties for longer separations. A further limit on the range is the loss of signal at mirror separations greater than around 25 mm. This is affected by the external mirror (material and surface texture) and its alignment to the face of the fiber. These last two variables appear to have little influence on performance with mirrors ranging from ceramics to metals and plastics providing adequate signal strengths, while reasonable signal to noise is measured for mirror misalignments of up to 10 degrees.
Review of Scientific Instruments


interferometry, fiber-optic, Fabry-Perot, displacement sensing, dimensional metrology


Nowakowski, B. , Smith, D. and Smith, S. (2016), Fiber Fabry-Perot cavity for interferometric displacement measurement: an experimental study, Review of Scientific Instruments, [online], (Accessed June 9, 2023)
Created October 31, 2016, Updated October 12, 2021