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 <i>μm</i>. The beam coupling process allows obtaining a phase modulation sensitivity of 200<i> μrad= √Hz </i>at 1 <i>kHz</i>. The interferometer behaves as an optical high pass filter, with a cutoff frequency of approximately 10 <i>Hz</i>, 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.
Due to its remarkable properties, graphene-based devices are particularly promising for optoelectronic applications. Thanks to its compatibility with standard silicon technology, graphene could compete III-V compounds for the development of low cost and high-frequency optoelectronic devices. We present a new optoelectronic device that consists in a coplanar waveguide integrating a commercially-available CVD graphene active channel. With this structure, we demonstrate high-frequency (30 GHz) broadband optoelectronic mixing in graphene, by measuring the response of the device to an optical intensity-modulated excitation and an electrical excitation at the same time. These features are particularly promising for RADAR and LIDAR applications, as well as for low-cost high-speed communication systems.
Photo-addressed liquid crystal media allow realizing optical phase detection based on self-adaptive holographic processes. Examples are reported of adaptive holographic systems based on optically addressed liquid crystal spatial light modulators. Owing to the physical mechanisms involved, such liquid crystal based adaptive interferometers adapt to slow phase variations, thus filtering out low frequency noise while transmitting the phase modulations at higher frequencies. This method permits measuring small phase modulations in noisy environments and with distorted and speckled wavefronts. The basic principles of the adaptive interferometer are presented, then, the association with an optical fiber is shown to realize a new class of distributed optical fiber sensors.
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.
We report on the use of an adaptive holographic interferometer, based on a liquid crystal light valve, to achieve phase shift measurements in an optical fiber. Owing to the physical mechanisms involved, the interferometer adapts itself to slow phase variations. As a consequence, it is possible to use a multimode fiber for sensing, which improves the sensitivity. Moreover, a distributed architecture relying on phase-OTDR principle is presented and a localization experiment is performed.
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.
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.
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.
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.
Adaptive interferometers based on dynamic holography within a nonlinear medium allow to precisely measuring phase modulations in noisy environments. Thanks to its adaptive behavior, the hologram follows slow external perturbations cancelling the low frequency phase mismatches between the two arms of the interferometer, while it appears static at high frequencies, hence, converting phase into intensity modulation. As a holographic medium, we use a liquid crystal light valve combining a photoconductor with a liquid crystal layer. The effective refractive index and, thus, the phase shift, depend both on the incident optical intensity and the bias voltage. By characterizing the response of the light valve, we show that low frequency noise can be filtered out within a voltage-controlled frequency bandwidth. This feature can be useful for applications where the signal of interest is limited by external noise such as temperature fluctuations and/or vibrations.
For underwater surveillance applications, an all-optical acoustic array technology allows enhanced capabilities compared to conventional piezoelectric antenna in terms of compactness, robustness and large distance remote interrogation through small diameter optical cable. This paper presents the results obtained on a first full optical antenna panel based on an innovative wideband pressure and temperature compensated fiber laser hydrophone. The presented mock-up includes 12 fiber-laser optical hydrophones interrogated through a 4 km lead optical cable.
We demonstrate the feasibility of detection of the nature (laminar/turbulent/transitional) of the aerodynamic boundary
layer of a profile of a wing aircraft model, using a Distributed FeedBack (DFB) Fiber Laser as optical fiber sensor.
Signals to be measured are pressure variations : ΔP~1Pa at few 100Hz in the laminar region and ΔP~10Pa at few kHz in
the turbulent region. Intermittent regime occurring in-between these two regions (transition) is characterized by turbulent
bursts in laminar flow. Relevant pressure variations have been obtained in a low-speed research-type wind tunnel of
ONERA Centre of Toulouse. In order to validate the measurements, a "classical" hot film sensor, the application and use
of which have been formerly developed and validated by ONERA, has been placed at the neighborhood of the fiber
sensor. The hot film allows measurement of the boundary layer wall shear stress whose characteristics are a well known
signature of the boundary layer nature (laminar, intermittent or turbulent) . In the three regimes, signals from the fiber
sensor and the hot film sensor are strongly correlated, which allows us to conclude that a DFB fiber laser sensor is a
good candidate for detecting the boundary layer nature, and thus for future integration in an aircraft wing. The work
presented here has been realized within the framework of "Clean Sky", a Joint Technology Initiative of the European
A new concept of optical fiber dynamic strain sensor has been experimentally characterized. It is based on two wave
mixing by gain saturation in an erbium doped optical fiber. The main feature of this sensor is insensitivity to slow
varying perturbations, which is of major interest for underwater acoustic applications for instance. Its multiplexing
capabilities are also investigated.
A new concept of optical fiber dynamic strain sensor has been theoretically studied and its proof-of-the-principle
experimentally demonstrated. It is based on two wave mixing by gain saturation in an optically pumped erbium
doped optical fiber. The main feature of this sensor is insensitivity to slow varying perturbations, which is of
major interest for underwater acoustic applications for instance.