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We present the operating range of Raman wavelength converters based on silica nanofibers immersed in liquids for the design of all fibered wavelength converters that can be inserted in optical networks with very low losses.

Optical nanofibers are highly attractive tools that are used in an increasing number of applications. However, at these radii typically smaller than the wavelength, the optical field is highly sensitive to dusts that rapidly degrade the optical transmittance, which is an issue for their use and storage. In this work we propose and characterize simple and efficient solutions. The chosen nanofiber radius is 500 nm. Firstly, we make systematic and long-term measurements (over several months) of nanofiber optical transmittance at 1.5 μ m in two protected environments that can be easily found in almost any laboratory and differing by their levels of cleanliness. We show that the rate of decrease of the optical transmittance is very low when the nanofiber is put in a simple protection box and ten times lower when the nanofiber is put in an airtight box. Secondly, the repetition of these measurements gives a mean value of this rate of −5.2 × 10−2%/day in the protection box and −6.3 × 10−3%/day in the airtight box. Thirdly, we perform the optical transmittance measurements on two nanofiber lengths (2 cm and 7 cm) and show that there is no significant difference on the rate of degradation between the two lengths. These results also enable to predict the value of the optical transmittances after several months or even years, which is a key parameter for most of the applications using nanofibers.

International audience; We demonstrate, build and optimize evanescent Raman converters at the sub-nanosecond regime based on a silica nanofiber immersed in ethanol. Two different standard silica fibers (SMF28, 460HP) are tested and compared. The converters are pumped at 532 nm and deliver pulses at 630 nm, which is the first Stokes order wavelength of ethanol. They present highly reproductible performances. A maximum output Stokes energy of 0.29 μJ is usually reached with an external conversion efficiency of 60%. Lowering the Raman threshold and pushing up the nanofiber breakdown allow a higher conversion operating range, that is the conception key of these converters.

Raman-scattering noise in silica has been the key obstacle toward the realisation of high quality fiber-based photon-pair sources. Here, we experimentally demonstrate how to get past this limitation by dispersion tailoring a xenon-filled hollow-core photonic crystal fiber. The source operates at room temperature, and is designed to generate Raman-free photon-pairs at useful wavelength ranges, with idler at the telecom, and signal at a visible range. We achieve a coincidence-to-accidentals ratio (2) as high as 2740 combined with an ultra low heralded g H (0) = 0.002, indicating a very high signal to noise ratio and a negligible multi-photon emission probability. Moreover, by gas-pressure tuning, we demonstrate the control of photon frequencies over a range as large as 13 THz, covering S-C and L telecom band for the idler photon. This work demonstrates that hollow-core photonic crystal fiber is an excellent platform to design high quality photon-pair sources, and could play a driving role in the emerging quantum technology., 9 pages, 5 figures, 1 supplementary

After presenting a theoretical modelling based on the heat equation, we show two different experiments to measure the laser induced temperature variation in silica nanofibers in air, a direct one and an indirect one based on Brillouin scattering, leading to an estimated value of the convective parameter h.

We present experimental results demonstrating the possibility to tune the wavelength of the photon pair emitted through four wave mixing in a nanofiber, using the pressure of a gas surrounding the nanofiber. Using Argon, a shift of idler wavelength of -1.1nm/bar is measured demonstrating fine adjustment possibility of emission wavelength, allowing to choose between different WDM channels.

We present the operating range of Raman wavelength converters based on silica nanofibers immersed in liquids for the design of all fibered wavelength converters. This range is bounded on the lower limit by the pump energy necessary to reach the Raman threshold and on the upper limit by the laser induced breakdown of the nanofiber. These breakdown energies are measured in the ns regime for different liquids (water, ethanol, isopropanol) and for air. We finally define guidelines that open the way to a new family of low-cost compact and efficient all-fibered Raman converters that can be directly inserted in optical fibered networks with very low losses.

The emerging interest in integrated optical technologies raises the need for precise characterisation techniques for waveguides presenting nonlinearities. Here we propose a non-interferometric measurement to accurately characterise the Kerr contribution in hybrid waveguides and illustrate its performances using SiN waveguides with a GSS chalcogenide top-layer. The sensitivity of our technique in terms of nonlinear phase reaches 10 mrad and its accuracy makes possible to extract the nonlinear contributions from the top-layer.

International audience; Background: Liquid filled hollow core fiber Raman wavelength converters are devices enabling to red-shift the wavelength of laser beams delivered by either fixed wavelength or tunable lasers. Most of the reported converters operate in a pulsed regime with pulse durations comprised between a few hundreds of picoseconds and up to a few nanoseconds, and energy of a few micro-Joules. However, and depending on the pulse duration, the optimization of Raman converters turns to be rather challenging since the desired forward Raman scattering may compete with counter-propagating nonlinear effects like Raman and Brillouin back-scatterings. The Brillouin back-scattering is especially hard to cancel since the Brillouin gains are usually larger than the Raman gains. Techniques have already been investigated but are not fully satisfactory. Our aim in this paper is to propose a technique to optimize the Raman forward scattering and to minimize these back-scattering effects.Methods: We compare the interaction lengths in the forward and backward directions in the above-mentioned temporal regimes. If the fiber length is higher that the backward effective length of interaction then the backward effects should decrease at the benefit of the forward Raman scattering. Numerical simulations enable to estimate more precisely how long the fiber should be to get large Raman conversion efficiency and negligible Brillouin scattering.Results and discussion: To validate this technique we build two identical Raman converters differing only by the fiber lengths (0.5 m and 1.5 m). We present the experimental setup. The experimental results are confronted to the numerical simulations. As expected increasing the fiber length strongly decreases the Brillouin scattering.Conclusions: We have proposed a simple and efficient solution to minimize Brillouin back-scattering in Raman wavelength converters by optimizing the fiber length. The experimental demonstration was conducted with low energy (≈ 6 μJ) but the energies should scale with the fiber effective area if more energy is needed, without affecting the conversion efficiencies.

International audience; We present highly efficient and reproducible Raman converters built with a silica nanofiber immersed in ethanol. The converters

International audience

Photon-pair states, whether spectrally correlated or separable, can all be very useful in quantum technology applications. For example, the former are used for improving the security of quantum key distribution, whilst the latter are the backbone in heralded single photon sources. It has been shown that the amount of spectral correlations is well-described by the shape of the Joint Spectral Amplitude function (JSA), which mostly depends on the relative group velocity relation between the pump, signal and idler photons within the source medium [1].

International audience; We describe a technique that allows increasing the resolution of optical microscopes for nanofiber measurements. We demonstrated it by measuring the diameter of tapered fibers for radii ranging from 0.2 to 1.5 μm.

We present a Raman converter emitting at 583 nm on the second Stokes order of propan-2-ol pumped by a microlaser at 532 nm in the sub-nanosecond regime with an internal conversion efficiency of 67%.

International audience; We describe a technique that allows the improvement of the resolution of optical microscopes for nanofiber measurements beyond the diffraction limit. It can be readily implemented on any microscope. We demonstrated it by measuring tapered fibers radii from 0.4 to 4 µm with a resolution below the diffraction limit, from a few nanometers up to 50 nm in the worst case, depending on the radii. This technique is a non-contact measurement with the microscope objective placed a few centimeters from the nanofiber. We acquire the experimental diffraction pattern by scanning the object plane of the microscope system, upstream and downstream the nanofiber. We compare this experimental diffraction pattern to a bank of all the simulated patterns for all the radii. The radius of the simulated diffraction pattern that best matches to the experimental one is the sought radius.

In this paper, we present a design of an all-fiber source of correlated photon pairs based on standard telecommunications tapered fibers. We examine the generation of correlated photon pairs using parametric process χ ( 2 ) in silica tapered optical fibers. This nonlinear process is ensured thanks to surface dipole and bulk multipole nonlinearities. The process of photon creation is modeled by taking into account the vector aspect of the propagation of the optical field in a silica nanofiber. The phase matching is provided by propagating the pump field in one spatial mode while generating a photon pair in another spatial mode. The generation efficiency of photon pairs depends on diameter uniformity of the nanofiber after the manufacturing process. We size this nanofiber for a good optimization of photon pair generation efficiency, and we report that the tolerance in diameter uniformity is Δ d = 2 n m for a generation rate of photon pairs estimated to N ph ≈ 22 000 p a i r s / s , for 1 W power pump and a nanofiber length of 1.1 mm. Deposits on the nanofiber can be used in order to relax the manufacturing constraints on diameter to maximize the generation rate of photon pairs. As an example, the use of polytetrafluoroethylene on the nanofiber applied as a cladding whose thickness is infinite makes it possible to relax the constraints on the nanofiber diameter. For the same Δ d = 2 n m , a generation rate of photon pairs estimated to N ph ≈ 78 000 p a i r s / s for 1 W power pump and a nanofiber length of 2.4 mm is predicted.

International audience; Nanofibers enable exploring evanescent nonlinearities. In this context, we aim to characterize a nanofiber immersed in ethanol. A single mode fiber at 532 nm is used and the nanofiber diameter is increased. Designed tapers are adiabatic in ethanol helping to investigate the stimulated Raman effect.

International audience; We present a Raman converter emitting at 583 nm on the second Stokes order of a line of propan-2-ol pumped by a microlaser at 532 nm in the sub-nanosecond regime. We used a mixture of liquids to adapt the transmission band of a photonic bandgap fiber. The internal conversion efficiency is 67% in photon numbers, and the output power is 1.06 mW, corresponding to a maximum peak power of 338 W. The beam delivered by the converter presents a Gaussian spatial structure and a high spectral brightness, typically more than five times higher than supercontinuum sources in this spectral range.

National audience; Les fibres optiques étirées, appelées nanofibres, sont des guides d'ondes obtenus par étirage de fibres optiques standard. Le contrôle des mélanges d'onde non linéaires dans ces nanofibres nécessite de connaitre leur profil à quelques nanomètres près. Nous décrivons une technique de super-résolution, applicable sur tout microscope optique, qui permet de mesurer ce profil à quelques nanomètres près.

International audience; We experimentally show how multiband dispersion properties of inhibited-coupling hollow-core fibers allow to control the spectral correlations of photon pairs generated through four-wave-mixing in a fiber filled with non-linear gas.

International audience; A simple and accurate determination of the diameters of tapered optical fibers is essential for the development of new optical components. For this purpose, we propose a technique to increase by more than 10 the resolution of optical microscopes. This technique can be readily implemented on any microscope. We demonstrated it by measuring the diameter of a tapered optical fiber with a resolution better than 100 nm with a x10 optical microscope whose aperture is 0.28.

International audience; Nanofibers are nowadays attracting attention as an interesting tool to explore evanescent nonlinearities. In this context, we propose a full optical characterization of a nanofiber immersed in a Raman liquid in order to control the backward Raman and Brillouin beams that limit the forward Raman effect. Simulations are performed determining the parameters of the nanofibers to be fabricated on this issue for different vectorial modes. An experimental setup is presented enabling us to investigate such a characterization. Further experimental results will be gotten and are expected to lead to novel applications in nonlinear optics.

International audience; Fibered sources of photon pairs can be easily integrated into future quantum communication networks. However, in silica-core fibres, the broadband spectrum of spontaneous Raman scattering strongly contributes to uncorrelated noise photons degrading the quality of the source. To overcome the problem of the silica Raman scattering, a new architecture was recently proposed, with hollow-core photonic crystal fibers (LF-HCPF) whose core and cladding are filled with a non-linear liquid. As opposed to the Raman scattering spectrum of silica, which is broadband and continuous, the Raman scattering spectrum of liquids is composed of narrow lines. Thus, generating photon pairs between these narrow lines permits to avoid the spectral overlap between the SFWM pairs and the Raman photons. A near infra-red LF-HCPCF photon pair source has been demonstrated, featuring a three order of magnitude suppression of the Raman noise [1]. We have also demonstrated the first non-linear LF-PCF with a transmission band and a zero-dispersion-wavelength (ZDW) in the telecom wavelength range combined with a non-linearity of the same order of magnitude as the one of silica, as a first step towards a Raman-free photon pair source in the telecom band [2]. Injecting light on both sides of this fiber in a Sagnac loop configuration can then be used to obtain entanglement.

Raman wavelength converters based on hollow core microstructured fibres filled with gases or liquids have been widely studied in the last few decades [1, 2]. In these converters the wavelength of a laser pump beam is red-shifted by stimulated Raman scattering in the material filling the core of the fibre, giving rise to new discrete wavelengths that can be used in many domains of applications (biophotonics, environment …). The possibility to strongly confine the pump light over long distances is an asset to get a high conversion efficiency. However if no particular care is taken unwanted non linear effects can occur at the expense of the stimulated forward Raman scattering. These effects are the Raman and Brillouin back-scatterings. In this work we are interested in the optimization of liquid-core Raman converters operating with pulses of a few nanoseconds or less. In these temporal regimes competition between the abovementioned effects are known to be very strong. We validate here a solution to minimize Raman and Brillouin back-scatterings by an appropriate choice of the fibre length. The effective length of interaction L eff in the backward direction is estimated to be cΔt / 2n, where At is the pulse width duration and n the refractive index. In the forward direction, as the dispersion is negligible, this effective length is the length of the fibre L. In liquids, as backward and forward Raman gains are nearly the same, L has just to be slightly higher than L eff to avoid Raman back-scattering. In most liquids and for long pulses Brillouin gain is much higher than Raman gain (typically one order of magnitude). To decrease Brillouin scattering L has to be subsequently higher than Leff. We demonstrate experimentally these trends by building two Raman converters differing only by their lengths. Our initial aim was to realize a Raman converter emitting in the near IR range. The pump source is a microlaser at 532 nm delivering 900 ps pulses at a repetition rate of 4.5 kHz. We choose ethanol as the Raman liquid. When pumped at 532 nm, the first Stokes order of ethanol is at 630 nm and the second Stokes order is at 772 nm, i.e the near IR wavelength we want to generate. A Kagome fibre was used to realize the two converters. When empty this fibre guides in the near IR range over a 1 μm wide transmission band. When filled with ethanol this transmission band is blue-shifted and then covers the pump and the Stokes wavelengths. In our configuration L eff =0.1 m. The lengths of the two converters are 0.5 m and 1.5 m. The results are shown in figure 1. As expected we observed no Raman backscattering in both cases and Brillouin effect is strongly attenuated for the longer fibre. For instance at the critical point (when the output Raman Stokes energy equals the transmitted pump energy), the Brillouin energy is 66% of the forward Raman energy for the 0.5 m fibre and is only 9% for the 1.5 m fibre. As a consequence, the output energy at 772 nm is highly improved and we obtain an output energy of 0.9 μJ at 772 nm for an injected energy of 5.8 μJ.

International audience

Photon pair generation through four-wave mixing in photonic crystal fibers is highly sensitive to cladding pitch-induced fluctuation of the phase matching along the fiber. Our model describes its consequence on the pair spectrum.

We report on the experimental characterization of a novel nonlinear liquid-filled hollow-core photonic-crystal fiber for the generation of photon pairs at telecommunication wavelength through spontaneous four-wave-mixing. We show that the optimization procedure in view of this application links the choice of the nonlinear liquid to the design parameters of the fiber, and we give an example of such an optimization at telecom wavelengths. Combining the modeling of the fiber and classical characterization techniques at these wavelengths, we identify, for the chosen fiber and liquid combination, spontaneous four-wave-mixing phase matching frequency ranges with no Raman scattering noise contamination. This is a first step toward obtaining a telecom band fibered photon-pair source with a high signal-to-noise ratio., Comment: 5 pages, 5 figures, journal

International audience; We demonstrate theoretically and experimentally a high level of control of the four-wave mixing process in an inert gas–filled inhibited-coupling guiding hollow-core photonic crystal fiber. The specific multiple-branch dispersion profile in such fibers allows both correlated and separable bi-photon states to be produced. By controlling the choice of gas and its pressure and the fiber length, we experimentally generate various joint spectral intensity profiles in a stimulated regime that is transferable to the spontaneous regime. The generated profiles may cover both spectrally separable and correlated bi-photon states and feature frequency tuning over tens of THz, demonstrating a large dynamic control that will be very useful when implemented in the spontaneous regime as a photon pair source.

The enhanced nonlinear interaction in a silicon microcavity under coherent excitation is studied under different conditions. By controlling the pulse frequency drift, we guarantee, at every instant, the coincidence with the frequency resonance of the cavity that in the nonlinear regime suffers from a blue shift in time. This limiting shift effect is caused by the free carriers generated by the strong silicon two-photon absorption. Owing to the linear time-frequency relation of the pulse, the coupling efficiency to the drifted resonance can be maintained, further increasing the blue-shift. We study the input power effect after using different pulse durations.

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International audience; We present an experimental demonstration of stimulated Raman scattering in a hollow core photonic crystal fibre filled with ethanol. By combining the original transmission properties of these fibres with a highly nonlinear liquid we have realized a very efficient Raman generator. This technique can be applied to other nonlinear mechanisms and opens the way towards the realisation of new fibered components for optical systems

International audience; Combining the propagation engineering of hollow core photonic crystal fibres with the large variety of possible liquids filling the fibre core allows for a delicate tuning of new devices. Here, we illustrate the optimisation of such liquid filled hollow core fibres with two devices: efficient wavelength Raman converters and high purity sources of correlated photon pairs.

National audience; L’émission Raman stimulée dans le coeur liquide de fibres à cristal photonique est un moyen efficace pour décaler en fréquence un faisceau laser. Néanmoins les décalages en fréquence possibles sont nécessairement inférieurs à la bande passante de ces fibres,bande passante limitée dans le cas des fibres à cristal photonique. Nous démontrons ici que l’emploi de fibres de type Kagome remplies de liquide permet d’atteindre des décalages beaucoup plus grands que ceux obtenus avec des fibres à cristal photonique.

We present a new fibered architecture for generation of correlated photon pairs, in which the deleterious influence of Raman photons has been highly reduced by filling the core of a microstructured fiber with a liquid

International audience; The large field enhancement that can be achieved in high quality factor and small mode volume photonic crystal microcavities leads to strengthened nonlinear interactions. However, the frequency shift dynamics of the cavity resonance under a pulsed excitation, which is driven by nonlinear refractive index change, tends to limit the coupling efficiency between the pulse and the cavity. As a consequence, the cavity enhancement effect cannot last for the entire pulse duration, limiting the interaction between the pulse and the intra-cavity material. In order to preserve the benefit of light localization throughout the pulsed excitation, we report the first experimental demonstration of coherent excitation of a nonlinear microcavity, leading to an enhanced intra-cavity nonlinear interaction. We investigate the nonlinear behavior of a Silicon-based microcavity subject to tailored positively chirped pulses, enabling to increase the free carrier density generated by two-photon absorption by up to a factor of 2.5 compared with a Fourier-transform limited pulse excitation of equal energy. It is accompanied by an extended frequency blue-shift of the cavity resonance reaching 19 times the linear cavity bandwidth. This experimental result highlights the interest in using coherent excitation to control intra-cavity light-matter interactions and nonlinear dynamics of microcavity-based optical devices.

International audience; A new method to determine complex amplitudes of index and absorption gratings in photorefractive multiple quantum wells is presented. In usual method to evaluate these parameters, spectral measurement of absorption change due to the applied field over a wide wavelength range is required and the index change is calculated through the Kramers-Krönig's relationship. In our method, only a set of measured data for photorefractive two-wave mixing set-up with small sinusoidal phase modulation for fixed wavelength is needed. This is thus well adapted to insitu characterization of systems that operate at a given wavelength. Real and imaginary part of the gains owing to the index and the absorption gratings are calculated from the output signals of the system. We apply this method to our photorefractive multiple quantum devices operating at 1064 nm, and obtain consistent results

We present an experimental investigation of the photorefractive properties of rhodium-doped barium calcium titanate (BCT) crystals of the congruent melting composition Ba0.77Ca0.23TiO3. Considering the results previously obtained on these crystals in the visible region and at 850 nm wavelength, it should be a good alternative to BaTiO3:Rh. Besides, the rhodium doping has the effect of making this material sensitive up to the wavelength of 1.06 µm—a very technologically significant wavelength, because of the existence of high-power lasers. Therefore we present a study of rhodium-doped BCT crystals at 1.06 µm. These crystals are characterized by two-wave-mixing experiments. Two-beam coupling gain factors of up to 7.5 cm−1, with ordinary polarization and a response time of the order of 1 s at an incident power of 10 W cm−2, have been obtained. All properties are explained by a three-centre charge transport model, together with the existence of an iron impurity which masks the influence of rhodium at low doping concentrations.

International audience; The photonic bandgap of microstructure fibers allows a perfect engineering of the linear propagation characteristics of optical beams. Total control over the nonlinear properties is nevertheless limited by the silica from which they are drawn. To gain over this control, we previously proposed to fill the hollow core of photonic bandgap fibers with selected nonlinear liquids. On the one hand, the transmission band and the dispersion are optimized through the photonic structure and the liquid refractive index, while, on the other hand, the non-linear coefficients are governed by the liquid choice. To further enhance the fine tuneability of such devices, mixtures of liquids are used. We will present our latest results for the optimization of such liquid filled hollow core fibers taking two applications as examples: efficient wavelength Raman converters, high purity parametric generation of pairs of photons.

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International audience; We report the excitation of non-steady-state photoelectromotive force and two-wave mixing signals using uniformly accelerated motion of the recording light pattern. Such illumination is created by linear frequency modulation of the interfering light beams. The pulse response is predicted theoretically and observed experimen- tally in GaAs and Bi12TiO20 crystals at λ 633 nm. The evolution of the pulse shape versus sweep rate is demonstrated and explained in the frames of the developed theory. The application of the effects in laser Doppler velocimeters and accelerometers is discussed as well.

Photoexcited carrier and space charge field subnanosecond dynamics has been investigated in bulk vanadium-doped and Cl- (or As-) co-doped CdTe crystals by using a degenerate four-wave mixing technique. Time-resolved measurements of picosecond grating decay at various illumination intensities revealed peculiarities of defect transformation with doping or under illumination. Novel features in carrier generation and dynamics were observed for the first time and allowed parameters of the defects to be extracted. A fast electron capture and its saturation with increasing intensity of illumination were observed in CdTe:V and attributed to a Cd divacancy, which is known as a deep double acceptor. Numerical modelling by using the two-deep-trap model allowed us to extract the concentration and recombination activity of Cd divacancies. An enhanced electron generation rate by factor of 3-4 was found in Cl-co-doped CdTe:V crystals in spite of a decreased density of donor vanadium states after the co-doping. We attribute this additional channel of electron generation to photoexcitation of the DX centre, which activation energy of 1-1.2 eV is close to a quantum energy of the YAG:Nd laser used ( eV).

Nous presentons les premiers resultats experimentaux de diffusion Raman stimulee dans une fibre a cristal photonique a coeur creux rempli d'un liquide a fort gain Raman d'indice inferieur a celui de la silice. Cette etude preliminaire ouvre la voie vers de nombreuses perspectives pour des applications en traitement du signal optique.

Ce travail vise a l'elaboration d'un systeme d'amplification faible bruit de signaux hyperfrequences sur porteuse optique. Nous avons mene une etude experimentale de l'amplification Raman dans des fibres optiques monomodes a 1550nm. La configuration contra-propageante –la moins bruitee– permet d'atteindre des gains nets de plus de 25dB, elle s'est aussi montree plus performante en termes de RIN (relative intensity noise) qu'un EDFA commercial. Une analyse theorique de l'amplification Raman a ete conduite dans le domaine spectral afin de quantifier le transfert de RIN de la pompe vers le signal. L'analyse a montre une decroissance de ce transfert a hautes frequences que l'on considere un laser de pompe monochromatique faiblement module ou, a l'oppose, pseudo-incoherent. Par contre, a basses frequences, le laser de pompe monochromatique faiblement module apporte un exces de bruit qui n'est pas present avec la pompe pseudo-incoherente. Ce type de source de pompe peut donc presenter un interet tout particulier pour le developpement d'amplificateurs Raman faible bruit pour les liaisons opto-hyperfrequences. Une autre piste envisagee est la reduction du bruit d'emission spontanee amplifiee. Nous avons etudie les moyens a mettre en œuvre pour parvenir a diminuer ce bruit. L'utilisation de deux lasers de pompe de meme puissance presentant un faible decalage spectral (devant la largeur de la transition Raman) doit permettre d'atteindre ce resultat. Les descriptions holographique, "optique non lineaire" ou quantique de la diffusion Raman bifrequence indiquent que pour une reduction effective du bruit d'emission spontanee, il faut que les deux pompes soient opposees en amplitude.

International audience; We present the experimental investigation of a photorefractive ring phase modulation amplifier, that is not resonant and that can work with distorted beams. We show that with this geometry an amplification by a factor 5 of a phase modulation signal is possible. We also show that this strong amplification is alleviated by the presence of losses in the ring. These losses lead to a real gain in signal to noise ratio of a factor 3, that nevertheless expresses that with such a system the photon noise limit of laser ultrasonics system can be overpassed. The losses are also responsible for the strong sensitivity of the system to the vibrations, which puts a strong limitation of the ring amplifier