Proceedings Article | 20 February 2017
KEYWORDS: Optically addressed spatial light modulators, Liquid crystals, Holography, Wavefronts, Light valves, Holographic interferometry, Optical sensing, Interferometers, Optical components, Digital holography, Phase modulation, Signal to noise ratio, Multimode fibers, Phase shift keying, Optical fibers, Holographic interferometers
Dynamical holography is an interferometric method that allows the measurements of phase modulations in the presence of environmental low-frequency fluctuations. The technique is based on the use of a nonlinear recombining medium that performs the dynamic hologram through a beam-coupling process. In our work, as the nonlinear medium, we use an optically addressed spatial light modulator operating at 1:55 μm. The beam coupling process allows obtaining a phase modulation sensitivity of 200 μrad= √Hz at 1 kHz. The interferometer behaves as an optical high pass filter, with a cutoff frequency of approximately 10 Hz, thus, filtering slow phase disturbances, such as due to temperature variations or low frequency fluctuations, and keeping the detection linear without the need of heterodyne or active stabilization. Moreover, owing to the basic principles of holography, the technique can be used with complex wavefronts, such as the speckled field reflected by a highly scattering surface or the optical field at the output of a multimode optical fiber. We demonstrate, both theoretically and experimentally, that using a multimode optical fiber as sensing element, rather than a single mode fiber, allows improving the interferometer phase sensitivity. Finally, we present a phase-OTDR optical fiber sensor architecture using the adaptive holographic interferometer.
