A. Peigné

Adaptive holographic interferometer at 1.55 μm based on optically addressed spatial light modulator

We report the realization of an adaptive holographic interferometer based on two-beam coupling in an optically addressed liquid crystal spatial light modulator operating at 1.55-μm. The system allows efficient phase demodulation in noisy environment and behaves as an optical high-pass filter, with a cut-off frequency of approximately 10 Hz, thus filtering slow phase disturbances (due to, for example, temperature variations or low frequency fluctuations) and keeping the detection linear without the need of heterodyne or active stabilization.

Self-adaptive vibrometry with CMOS-LCOS digital holography

A self-adaptive interferometer based on digital holography is here reported for applications involving measurements of very small amplitude vibrations. The two-beam coupling gain is optimized through an electronic feedback, while the dynamic character of the hologram allows reaching a high sensitivity of the interferometric measurements even in unstable environments and with strongly distorted wave-fronts. The frequency bandwidth of the adaptive interferometer and its spatial resolution are determined, respectively, by the maximum frame rate and the pixel size of the camera and of the spatial light modulator used to build the digital holographic setup.

Adaptive Interferometry for High-Sensitivity Optical Fiber Sensing

Adaptive holographic interferometry is a promising method for high-sensitivity phase modulation measurements in the presence of slow perturbations from the environment. This technique is based on the use of a nonlinear recombining medium. Here, we report the use of an adaptive holographic interferometer based on an optically addressed spatial light modulator. Owing to the physical mechanisms involved, the interferometer adapts to slow phase variations within a range of 5–10 Hz. Moreover, owing to the basic principle of holography, this technique can be used with complex wave fronts 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 using the adaptive holographic interferometer.

Phase modulation detection with liquid crystal devices

Self-adaptive interferometry allows measuring small optical phase modulations even in noisy environments and with strongly distorted optical wavefronts. We report two examples of self-adaptive interferometers based on liquid crystals, one obtained by using an optically addressed spatial light modulator, the second one realized by adopting adopting digital holography a CCD-LCOS scheme.

Acoustic fiber laser array architecture with reduced optical feedback limitations

Many sensing applications would benefit of multiplexing a maximum number of Distributed FeedBack Fiber Lasers (DFB FLs) on the same optical fiber. However, in such configurations, some physical mechanisms may impact DFB FLs stable operation, limiting, for instance, the number of DFB FLs spliced on the same fiber and the distance between them. The aim of this experimental study is to investigate the impact of optical feedback on DFB FLs stability. The results of our study are used to propose possible associated architectures.

Dynamical holography and wavefront control with liquid-crystal light valve

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.

Adaptive holographic interferometer based on optically addressed spatial light modulator for high-sensitivity optical fiber sensing

Abstract Adaptive holographic interferometry is a promising method for high-sensitivity phase-modulation measurements in the presence of slow perturbations from the environment. This technique is based on the use of a nonlinear recombining medium. We report the realization of an adaptive holographic interferometer relying on an optically addressed liquid crystal spatial light modulator operating at 1.55 μm. The beam-coupling process that occurs in a GaAs-liquid crystal device, allows obtaining a phase-modulation sensitivity of 200 μrad/sqrt (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 principle of holography, this technique can be used with complex wave fronts 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 a sensing element, rather than a single-mode fiber, allows improving the interferometer phase sensitivity. Finally, we present a phase-optical time domain reflectometry (OTDR) optical fiber sensor using the adaptive holographic interferometer.

Adaptive holography for optical sensing applications

Adaptive holography is a promising method for high sensitivity phase modulation measurements in the presence of slow perturbations from the environment. The technique is based on the use of a nonlinear recombining medium, here an optically addressed spatial light modulator specifically realized to operate at 1.55 μm. Owing to the physical mechanisms involved, the interferometer adapts to slow phase variations within a range of 5-10 Hz, thus filtering out low frequency noise while transmitting higher frequency phase modulations. We present the basic principles of the adaptive interferometer and show that it can be used in association with a sensing fiber in order to detect phase modulations. Finally, a phase-OTDR architecture using the adaptive holographic interferometer is presented and shown to allows the detection of localized perturbations along the sensing fiber.

Liquid crystal based adaptive holography for optical sensing applications

Adaptive holographic interferometry allows measuring small optical phase modulations even in noisy environ- ments and with strongly distorted optical wavefronts. We report examples of adaptive holographic systems based on liquid crystals, such as optically addressed liquid crystal spatial light modulator and digital holography with an LCOS spatial light modulator.

Nonlinear holography for acoustic wave detection

A liquid crystal medium is used to perform nonlinear dynamic holography and is coupled with multimode optical fibers for optical sensing applications. Thanks to the adaptive character of the nonlinear holography, and to the sensitivity of the multimode fibers, we demonstrate that the system is able to perform efficient acoustic wave detection even with noisy signals. The detection limit is estimated and multimode versus monomode optical fiber are compared. Finally, a wavelength multiplexing protocol is implemented for the spatial localization of the acoustic disturbances.