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In recent years, bimaxillary rotation advancement (BRA) has become the method of choice for surgical treatment of obstructive sleep apnea (OSA). As dislocation of the jaw bones affects both, airways and facial contours, surgeons are facing the challenge of finding an optimal jaw position that allows for the reestablishment of normal airway ventilation and esthetic surgical outcome. Owing to the complexity of the facial anatomy and its mechanical behavior, individual planning of surgical OSA treatment under consideration of functional and esthetic aspects presents a challenge that surgeons typically approach in a non-quantitative manner using subjective evaluation and clinical experience. This paper describes a framework for individual planning of OSA treatment using bimaxillary rotation advancement, which relies on computational modeling of hard and soft tissue mechanics. The described framework for simulation of functional and esthetic post-surgery outcome was used in 10 OSA patients. Comparison of the simulation results with post-surgery data reveals that biomechanical simulation provides a reliable estimate for post-surgery facial tissue behavior and antero-posterior airway extension, but fails to accurately describe a surprisingly large lateral stretch of the velopharyngeal region. This discrepancy is traced back to anisotropic effects of pharyngeal muscles. Possible approaches to improving the accuracy of model predictions and defining sharp criteria for optimizing combined OSA planning are discussed.

The influence of absorption or gain on the Bragg diffraction efficiency of intracavity refractive index gratings is analyzed. Losses drastically reduce the diffraction efficiency of the device which can nevertheless be optimized in order to limit their inauspicious influence. On the contrary, in amplifying intracavity media very large diffraction efficiencies are obtained even with small integrated refractive index modulations. The optimization of the device for maximum diffraction efficiency or vanishing reflectivity could find applications in tunable lasers and in high contrast amplifying optical signal processing.

We investigate the influence of thermally induced higher order aberrations on the fundamental mode of a rod solid-state laser. The perturbations of the laser due to the most common aberrations (spherical aberration and astigmatism) are studied for several sizes of the fundamental mode. Results concerning the additional losses and beam quality degradation induced by these aberrations are also presented and demonstrate that for a large overlapping of the beam size and the laser rod, the spherical aberration amplitude must not exceed 0.5λ for the cavity to oscillate. The influence of gain saturation also analyzed in the model is shown to be of less importance.

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.

We consider the Raman amplification problem for silicon waveguides in the regime in which both the pump and signal pulses are relatively short but wide enough that their duration exceeds the phonon lifetime (about 3 ps in silicon). We use the coupled pump-signal equations for numerical simulations that include all competing nonlinear effects such as self- and cross-phase modulations, two-photon and free-carrier absorptions, and changes in the refractive index induced by the free carriers. However, numerical simulations do not provide much physical insight. For this reason, we also develop an approximate analytic approach for solving the Raman amplification problem. We introduce the concept of an effective Raman gain and show analytically how it depends on the pump bandwidth. As the pump spectrum broadens inside the silicon waveguide, the effective Raman gain is reduced considerably. We obtain an analytical form of the nonlinear phase accumulated during propagation inside a silicon waveguide and use it to calculate the total spectral broadening experienced by a pump pulse. Using this result, we can predict changes in the effective Raman gain as a function of pump pulse energy. A comparison of our predictions with the recent experimental data shows that our model is reasonable and captures the essential physics.

The giant Faraday rotation (larger than 90°) photoinduced in ZnMnTe or CdMnTe by picosecond duration pump pulses is analysed by the time-resolved pump and probe technique. Slow thermal and fast photocarrier-induced processes are found to occur depending on the choice of the semimagnetic semiconductor sample.

We experimentally show that the self-phase modulation of picosecond pump pulses, induced by both the optical Kerr effect and free-carrier refraction, has a detrimental effect on the maximum on-off Raman gain achievable in silicon on insulator nanowaveguides, causing it to saturate. A simple calculation of the Raman gain coefficient from the measured broadened output pump spectra perfectly matches the saturated behavior of the amplified Raman signal observed experimentally at different input pump powers., Accepted for publications in Applied Physics Letters

We present a Raman generator based on a 35 cm long hollow core photonic crystal fiber entirely filled with ethanol emitting on a nearly-Gaussian beam. The power conversion efficiency from the pump at 532 nm to the first Stokes order of ethanol at 630 nm is 67%. Temporal profiles, mode patterns and power stability are also analyzed.

High-efficiency pulse compression has been obtained by using an externally pumped intracavity Raman oscillator. Through stimulated Raman scattering, the energy of a primary, long-pulse-duration omega(L) laser is downconverted and stored at the first Stokes frequency omega(1s) in a high-Q cavity containing the Raman medium. Then this electromagnetic energy is quickly extracted at the second Stokes frequency. This technique, which uses hydrogen gas as the Raman medium, permits a 25-nsec-duration ruby-laser pulse shortening by a factor of 12.5 with a near 50% quantum efficiency. Contrary to the case of intracavity Raman oscillators or amplifiers, this method can also be used with absorbing laser media.

Very-high-efficiency (80%) Raman amplification of a narrow-band injected Stokes signal has been achieved in the case in which pump and Stokes linewidths are both narrower than Raman transition width. Under such conditions, the Stokes-beam amplification is obtained without line broadening, permitting the creation of widely tunable powerful monochromatic sources when tunable lasers are used. With fixed-frequency pump lasers, tunability within the Raman linewidth has also been demonstrated. With a pump linewidth much broader than that of the injected Stokes signal, a spectral compression rate up to 16 has been achieved by using this Raman amplification technique.

A new filtering technique is proposed that associates the high dispersion of standard reflection gratings with the tuning speed of acousto-optic cells. Tuning is performed by adjusting the grating period so that the chosen wavelength is at Bragg resonance. In this way, the selected wavelength always experiences a maximum diffraction efficiency, ensuring good uniformity. Using a commercial acousto-optic modulator, a wavelength selectivity of 0.075 nm is demonstrated together with a uniformity of ±0.2 dB on a tuning range of 2.2 nm corresponding to N = 30 resolvable frequencies. N > 600 could be obtained with an acousto-optic cell specially designed for this device.

In recent years, a significant amount of attention has been drawn towards all-optical semiconductor switching. To that respect, exploitation of light localization, in slow light photonic crystal waveguides (PCWs) or in microcavities, is of considerable interest because it enables enhancement of optical nonlinearities. Recently, we observed experimental and theoretical enhancement of optical Kerr effect, two-photon absorption (TPA) and free-carrier index changes (FCI) in GaAs PCWs, which demonstrated the important role of group velocity [1].

International audience; A very simple model has been developed to describe the diffractive properties of a crossed grating structure of the refractive index formed by a thin transmission grating recorded in a Bragg reflector. When the Bragg condition of the transmission grating coincides with the band edge of the reflection grating seen as a one dimensional photonic crystal, the diffraction efficiency and wavelength selectivity of the transmission grating are highly enhanced and a Bragg diffraction regime can be obtained, even in very thin samples. The model can be used to design micrometric very efficient new diffracting devices for optical signal processing

Recent developments in the field of nonlinear optics with photonic crystal fibers have led to the realization of supercontinuum spectra or parametric sources of correlated photons. However the nonlinearities were still limited by the use of silica. Hollow core photonic crystal fibers (HCPCF) filled with highly nonlinear liquids or gases enable the implementation of more performing nonlinear devices and open the scope of potential applications thanks to the large variety of usable liquids and gases. Moreover liquid and gas filled HCPCF present several original propagation properties such as transmission bands that can be tailored to favor or prevent a given nonlinear mechanism. In this work we will show that the on-purpose limited transmission band enables a high conversion efficiency towards a single Stokes component even at high pump intensities. Moreover such Raman converters generate single spatial mode at specific wavelengths that can be determined to fit desired applications.

Nonlinear propagation experiments in GaAs photonic crystal waveguides (PCW) were performed, which exhibit a large enhancement of third order nonlinearities, due to light propagation in a slow mode regime, such as two-photon absorption (TPA), optical Kerr effect and refractive index changes due to TPA generated free-carriers. A theoretical model has been established that shows very good quantitative agreement with experimental data and demonstrates the important role that group velocity plays. These observations give a strong insight into the use of PCWs for optical switching devices., Comment: 6 pages

Non-linear Faraday processes occurring at high laser intensities are experimentally demonstrated in a Cd 0.75 Mn 0.25 Te alloy. Both the polarization direction and the phase of the incident beam are modified through the non-linear interaction. The large non-linear susceptibilities measured for the material show that non-linear Faraday processes overcome two-photon absorption and Kerr effects for magnetic field of the order of few teslas.

Nonlinear Faraday processes occuring at high laser intensities are experimentally demonstrated in a Cd 0.75 Mn 0.25 Te alloy. Both the polarization direction and phase of the incident beam are modified through the nonlinear interaction. The large nonlinear susceptabilities measured for the material show that nonlinear Faraday processes are expected to overcome two-photon absorption and Kerr effects for magnetic field of the order of few Tesla.

International audience; Highly improved diffraction properties are demonstrated in a two-dimensional [2D] grating consisting of a transmission grating optically recorded in a semiconductor one-dimensional photonic crystal (1D-PC). Near unity internal diffraction efficiency, high wavelength selectivity, and Bragg diffraction regime operation are demonstrated when the read beam is set at Bragg incidence on the transmission grating while its wavelength corresponds to the band edge of the 3 um thick 1D-PC. When the 2D grating is grown on a Bragg mirror, a single diffracted beam is obtained, which makes the device promising for optical signal processing

5 pages; International audience; An optical parametric oscillator for the infrared region pumped by a picosecond Ti:Sapphire laser is demonstrated. Fourier transform limited pulses of 15 and 10 ps, for signal and idler wavelengths respectively, have been obtained using a periodically poled stoechiometric lithium tantalate nonlinear crystal, without any spectral filtering. A complete experimental study of the influence of the cavity length detuning on the spectral and temporal dynamic of the output radiation is discussed.

International audience; Raman amplification of optically carried RF signals is shown to be a good alternative to erbium-doped-fiber amplification. In the case of continuous RF signal, RIN levels as low as -160 dB/Hz, limited by the laser source, are obtained. Moreover, when the RF signal is no more continuous, such as real radar waveforms, we evidence that Raman amplification overcomes erbium-doped-fiber amplification. Improvement of the pulse-to-pulse RF phase stability of 17 dB is observed. This result is attributed to the nature of Raman amplification, which does not involve transient variations of the population inversion across the whole spectral range covered by radar waveforms.

Optical limitation in resonant Faraday media sandwiched between crossed polarizers is analyzed both theoretically and experimentally. In this technique resonant Faraday rotation permits a net transmission at low intensity levels, whereas the setup transmission is quenched at higher intensities when the active transition is completely saturated. This technique offers many advantages, such as a very low fluence threshold (~12 nJ/cm(2) in cesium vapor), a high intensity range (more than 4 orders of magnitude for polarizer losses of 10(-5)), and quasi invulnerability to optical damage, which make this technique attractive for the protection of fixed-wavelength operated detectors.

International audience; We report the results of an experimental investigation of the diffractive properties of a thick index grating embedded in a Fabry-Perot resonator, the so-called intracavity Bragg grating. We compare the performance of this device with that of a bare Bragg grating with same thickness and the same index modulation and establish the improvement in performance with the resonator. The experimental data also fit predictions calculated from a theoretical model.

We realized an efficient single spatial mode Raman generator that uses an ethanol filled HC-PCF. Despite the non optimized nature of the commercial fiber used, good performances have been obtained and the technique presents interesting opportunities for the realization of Raman amplifiers and generators able to operate in the CW regime using optimized fibers.

Singlemode Raman generation in an ethanol filled photonic band gap fiber is demonstrated. Due to the limited fiber transmission band a high conversion efficiency towards the first Stokes is achieved even at high pump intensities.

Intracavity gain gratings are theoretically demonstrated to exhibit diffraction efficiencies larger than unity at pumping powers below lasing threshold. Experiments performed using a Nd- YVO4 microlaser demonstrate huge enhancements of diffraction efficiency and angular selectivity.

International audience; Intracavity gain gratings are theoretically demonstrated to exhibit diffraction efficiencies that are 100 times larger than unity at pump powers substantially below the lasing threshold. Experiments performed using a Nd:YVO4 microlaser pumped below threshold by two interfering Ti:sapphire laser beams are described. Huge enhancement of the diffraction efficiency (5000x) and a large increase of the angular selectivity (10x) are demonstrated despite the angular reduction of the Fabry-Perot cavity finesse. Much better results are expected using gain gratings with larger areas or thinner cavities such as vertical cavity surfaceemitting lasers. Such large fan-out values could be very interesting for applications to optical signal processing.

International audience; We experimentally and theoretically analyze an original method based on two-wave mixing in an erbiumdoped fiber amplifier for optical carrier reduction of microwave signals. 75% optical carrier attenuation has been observed, and a 10 dB modulation depth increase of the microwave signal is experimentally demonstrated. Moreover, calculated results are in good agreement with measurements and predict that up to 80% carrier attenuation is easily possible.

One way to realize such a light localization is to structure the material at the wavelength size level creating thus a photonic crystal that may present a photonic band gap that prevents propagation of light in it for a given frequency bandwidth. Near its band edge such a structure becomes transparent and presents a low group velocity connected to a very pronounced light localization inside the structure or, equivalently, a high local intensity that favors the nonlinear phenomena. To study such an effect we develop a four wave mixing experiment based on a tunable picosecond laser source that allows to perform a spectroscopic study of the phase conjugate reflectivity

We present here an experimental and theoretical study of two wave mixing by gain saturation in a diode pumped erbium doped polarisation maintaining fiber amplifier. Application to modulation depth enhancement of optically carried microwave signals is proposed and demonstrated.

We demonstrated experimentally the feasibility of a fast tuning high resolution filter with a good flatness. The device could easily be adapted to applications in spectroscopy or in DWDM communications (tunable lasers or filters for instance). Acousto-optic filtering has been extensively studied because its tuning rapidity makes it very useful for many applications. Nevertheless, its resolution is often not sufficient in the fields of telecommunication or spectrometry. The proposed grating-assisted acousto-optical filtering technique combines the high resolution of diffraction gratings (/spl sim/10 pm) and the tuning swiftness of acousto-optics (/spl mu/s).

In this paper, we propose to investigate the case when both the incident beam and the main diffraction order are Fabry-Perot resonant, at Bragg incidence on a thin unslanted grating. We calculate the intensities of the most important diffraction orders and show what conditions must be fulfilled to obtain a Bragg diffraction regime where all diffracted energy is concentrated in a single diffraction order

We present a theoretical study and an experimental demonstration of stimulated Raman effect in a hollow core photonic crystal fiber filled with a low index nonlinear liquid (ethanol).

International audience; A theoretical analysis of the Raman amplification in optical fibers and the pump-to-signal relative intensity noise (RIN) transfer has been performed in the spectral domain. An efficient Raman amplification of a monochromatic signal beam by a large-bandwidth pump beam has been demonstrated for a pump bandwidth much smaller than the Raman linewidth. Under the same approximation the pump-to-signal RIN transfer has been calculated in both cases of copropagating and counterpropagating beams in the two limiting cases of modulated monochromatic and smooth-profile large-bandwidth pump beams. At low frequencies the excess of noise evidenced in the case of a modulated monochromatic pump beam did not exist in the case of large-bandwidth pseudoincoherent sources. As this noise reduction can be as large as 13 dB for a 40 dB net gain of the amplifier, such incoherent pumping sources must be considered for the purpose of low-noise Raman amplifiers

International audience; We have investigated a three-dimensionally periodic (3D) photonic crystal structure based on an epitaxial periodic GaAs/Al0.93Ga0.07As multilayer structure that was designed for non-linear optical interactions. The 3D photonic crystal structure consisted of a two-dimensionally periodic planar photonic crystal hole pattern etched into the one-dimensionally periodic multilayer structure designed for a centre wavelength of lambda = 1.6 µm. Numerical simulations on the 3D PhC structure have shown that it should exhibit slow group velocity modal features near the edge of the photonic bandgap.

International audience; Stimulated Raman amplification of optically carried microwave signals in optical fibers is experimentally investigated. In the backward configuration which is shown to be less noisy than the forward one, net amplification factors larger than 20 dB are demonstrated in the low signal regime with better relative intensity noise (RIN) values than using erbiumdoped fiber amplifiers. Due to the RIN flatness with respect to the gain of the stimulated Raman amplifier high quality variable gain amplification of optically carried microwave signals could be implemented using optimized Raman amplifiers

International audience; We present a modeling of a degenerate four-wave-mixing nonlinear process in one-dimensional photonic crystals. The model is based on the nonlinear extension of the transfer-matrix description of propagation in the structure. The influence of light localization, near the band edge of the structure, on the enhancement of the phase-conjugate reflectivity is studied. The phase-conjugate reflectivity is shown to increase as the eighth power of the number of layers with an additional large dependence on the index contrast of the structure. In both cases the enhancement is accompanied by a strong reduction of the resonance width, which may lead to some limitation of the enhancement when ultrashort pulses are used. A strong influence of the losses on the nonlinear efficiency of the structure is also predicted with a great importance of scattering losses at the multiple interfaces of the structure

International audience; We show that high efficiency stimulated Raman scattering can be obtained using hollow core photonic crystal fiber with the core filled with a low refractive index nonlinear liquid. This new architecture opens new perspectives in the development of nonlinear functions as any kind of nonlinear liquid media can now be used to implement them, with original properties not accessible with silica core fibers

We present the implementation and characterization of a four wave mixing experimental set-up for the characterization of third order nonlinearities in photonic crystals. This set-up allows us to perform a first experimental demonstration of the enhancement of the efficiency of the phase conjugate reflectivity, due to light localization at the band edge of the photonic crystal.

Large polarization rotations and ellipticity changes are photoinduced at room temperature in semiconductor microcavities containing manganese. Two contributions of different physical origins are identified thanks to a time resolved spectral analysis. A short lived contribution only occurs for circularly polarized pump beams, due to the polarization dependent saturation of the excitonic transition. A nanosecond duration pump-polarization independent contribution is also reported which is presumably due to a photoinduced magnetization mediated by free holes due to the trapping of electron on manganese ions. A simple model based on transfer matrices confirm the experimental results. These room temperature processes could be useful for fast high contrast optical signal processing.

In this paper, we present single-mode SBS laser, based on an all-fiber short cavity, simultaneously resonant for pump and Stokes waves for radiofrequency applications. All-fiber stimulated Brillouin scattering (SBS) lasers can be good candidates to fulfill both of these requirements.

International audience; We theoretically analyze a high-efficiency single-frequency Brillouin all-fiber ring laser at 1.5 mm wavelength, taking pump depletion into account. The output pump and Stokes intensities are calculated as functions of the cavity coupling coefficient and of the input pump intensity. Lasing threshold and pump-to-Stokes conversion efficiency are predicted. Furthermore, we demonstrate good agreement between model results and measurements. Applications to the improvement of optoelectronic links for radio-frequency signals by use of stimulated Brillouin scattering fiber lasers are also presented.

International audience; We experimentally demonstrate efficient optical carrier reduction of microwave signals with a single-mode 1.5-mm wavelength Brillouin all-fiber ring laser. Because of the tunable optical coupling, the lasing threshold of the short-length (20-m) fiber cavity is lower than 5 mW, and high conversion efficiencies (up to 60%) are obtained at any pump power up to _200 mW. Using the single-mode Stokes beam as a seed for the stimulated Brillouin scattering process allows up to 40-dB optical carrier depletion with almost no added noise for an optically carried microwave signal at 6 GHz. In addition, using this resonator, we provide evidence of generation of high-spectral-purity beatnotes.

Summary form only given. Amplification of the intracavity medium hugely enhances the diffraction efficiency of intracavity Bragg gratings. The device can be optimized for optimum diffraction efficiency (with diffracted intensity 1000 times larger than the incident one) or for null reflected signal (with diffraction efficiencies larger than 1000%). This could be of importance for tunable lasers and optical signal processing.

Summary form only given. The diffraction efficiency of refractive index modulation can be increased by using a Fabry-Perot resonator. We present here a detailed analytical study of diffraction by such a structure and show that it offers some more advantages.

Summary from only. Optical signal processing requires very high diffraction efficiencies and angular selectivities. These parameters are well known to increase with index modulation and material thickness but we study an alternative solution: the insertion of the grating in a Fabry-Perot resonator.

We investigate the influence of thermally induced spherical aberrations on the fundamental mode of a rod solid-state laser. Results concerning the additional losses and beam quality degradation are presented and point outthat for a large volume fundamental mode resonator, a spherical aberration greater than O.5X dramaticallydeteriorates the laser performances. To control the resonator performances, we present a new phase control technique with an intracavity opticallyaddressed liquid-crystal spatial light modulator. The presented Nd:YAG resonator is able to deliver beams withvarious spatial profiles, as flattop super-Gaussian or square-shaped beams, and is thus potentially able tocompensate for the thermally induced aberrations of the laser medium.Keywords : thermal aberrations, laser rod resonator, beam shaping, liquid-crystal devices 1. INTRODUCTION With the recent development of high-brightness, high-power solid-state lasers, requiring up to kWatts ofpumping power, the analysis of the influence of the higher order aberrations of the laser rod thermal lens on theperformances of the resonator is becoming a crucial point in the development of high-brightness sources 2 Therealization of an efficient TEM00 resonator implies an optimized overlap of the fundamental mode of the cavitywith the gain region in order to increase the volume of the active material involved in the laser action

International audience; The grating thickness limit lFP between the Raman-Nath and the Bragg diffraction regimes is calculated for an index grating placed in an asymmetric Fabry-Perot resonator with a totally reflecting back mirror and compared with that which was obtained for the same grating with no cavity lM . Owing to the increase of the effective interaction length inside the Fabry-Perot cavity, the stronger the front mirror reflectivity R1 of the cavity, the smaller the thickness above which the whole diffracted intensity can be concentrated into one unique diffracted beam: lFP=[(1−√R1)/(1+√R1)]lM/2.

Summary form only given. Optical signal processing through Bragg diffraction requires high diffraction efficiencies and angular selectivities. We present experimental results showing how the diffraction properties of an index grating can be enhanced by using a Fabry-Perot resonator. In order to demonstrate the actual performances of intracavity Bragg gratings, we used an organic dye dissolved in ethanol as the nonlinear medium filling the Fabry-Perot cavity.

Summary form only given. We present a case with instantaneous recording of microsecond duration gratings in CdMnTe semimagnetic semiconductors when the laser frequency is tuned near the band edge of the semiconductor medium. In such a case the photo-generated carriers are very efficiently trapped on Mn/sup 2+/ sites, which allows the generation of a grating of fixed negative charges if an interference pattern illuminates the crystal. Neutrality requires the existence of a hole grating, which then creates a hole induced refractive-index grating.