Fiber-coupled, Littrow-grating cavity displacement sensor

Abstract

We have demonstrated a compact, optical-fiber-fed, optical displacement sensor utilizing a Littrow-mounted diffraction grating to form a low-finesse Fabry–Perot cavity. Length changes of the cavity are read out via the Pound–Drever–Hall rf modulation technique at $925\mathrm{MHz}$. The sensor has a nominal working distance of $2\mathrm{cm}$ and a total dynamic range of $160\mathrm{nm}$. The displacement noise floor was less than $3\times {10}^{-10}\mathrm{m}∕\sqrt{\mathrm{Hz}}$ above ${10}^{-2}\mathrm{Hz}$, limited by the frequency drift of the reference laser. A frequency-stabilized laser would reduce the noise floor to below ${10}^{-12}\mathrm{m}∕\sqrt{\mathrm{Hz}}$. The use of a $925\mathrm{MHz}$ modulation frequency demonstrates high-precision readout of a low-finesse compact resonant cavity.

© 2010 Optical Society of America