LiNbO3 ridge waveguides realized by precision dicing on silicon for high efficiency second harmonic generation

Nonlinear periodically poled ridge LiNbO3 waveguides have been fabricated on silicon substrates. Components are carved with only use of a precision dicing machine without need for grinding or polishing steps. They show efficient second harmonic generation at telecommunication wavelengths with normalized conversion reaching 204%/W in a 15 mm long device. Influence of geometrical non uniformities of waveguides due to fabrication process is asserted. Components characteristics are studied notably their robustness and tunability versus temperature.Comment: 10 pages, 10 figure

PPLN ridge waveguides for frequency conversion of high power CW beams

International audienceLiNbO3 has one of the highest quadratic nonlinear optical coefficients that makes it a material of choicefor the development of frequency conversion systems and more generally nonlinear optical functions.This crystal can be periodically poled (PPLN) to allow quasi‐phase matching for various combinationsof wavelengths mixing in its wide transparency window (0.4‐5 μm). In addition, efficient nonlinearconversion can be reached even with moderate power CW beams taking advantage of the lightconfinement provided by LiNbO3‐based optical waveguides. However, waveguides made byconventional fabrication techniques such as titanium in‐diffusion or proton exchange still suffer fromunstable behavior due to photorefractive optical damage especially when visible wavelengths areconcerned. In this study, we present recent developments of ridge PPLN waveguides with promisingcharacteristics even when operating at high average power.More specifically, the design, fabrication and characterization of nonlinear PPLN waveguides forsecond harmonic generation (SHG) of telecommunication wavelengths are presented. Fabrication isbased on wafer bonding, grinding‐polishing steps and carving with use of a precision dicing saw. Thecomponents show efficient SHG with normalized conversion over 200%/W. The componentsperformances will be presented along with their long‐term stability when pumped with Watt‐leveloptical signals. Optical damage threshold of the input face is also investigated to determine themaximum usable power. Undoped and MgO doped LiNbO3 are considered. We will also emphasizethe specificity of the ridge waveguides that allows stable frequency conversion at high power. Theperspectives offered by this specific waveguide geometry will also be tackled

Optical cavity-less 40-GHz picosecond pulse generator in the visible wavelength range

International audienceHigh-repetition-rate optical frequency-comb sources emitting picosecond pulses play important roles in variousscientific researches and industrial applications. Such ultrafast pulse sources are mostly generated in opticalcavities or microresonators. By means of the wavelength-conversion techniques, it is possible to transfer thecavity-based near-IR robust and compact sources to the mid-IR or to the visible wavelength regions [1-2], forwhich there is an increasing demand, for biophotonics and other applications. Here we demonstrate the generationof high-repetition-rate picosecond pulses in the visible wavelength range by using a fully optical cavity-lessconfiguration. First, we developed a tunable C-band picosecond pulse generator whose high-repetition-rate is alsotunable from 20 to 40 GHz. This near-IR optical cavity-less system makes use of high reliability componentsdeveloped for telecommunications [3]. Next, it was used to directly pump a nonlinear periodically poled ridgeLiNbO3 (PPLN) waveguide fabricated on silicon substrate [4]. This highly efficient χ(2)-type nonlinear material,which performs ultrafast-response of second harmonic generation (SHG), will offer us the opportunities to developfiber-coupled frequency doubling modules for fiber-integrated picosecond pulse sources in the visible. Figure 1(a)presents the experimental setup, where the generation of stable 40-GHz pulse trains is obtained through thenonlinear compression of an initial beat-signal in a cavity-less optical-fiber-based device. The initial sinusoidalbeating is generated by using a commercial LiNbO3 intensity modulator driven by a half repetition-rate externalRF clock and then amplified by means of Er-doped fiber amplifier. Moreover, we imposed a RF phase modulationto suppress Brillouin backscattering into the 2.2-km-long compression fiber. High-quality 6-ps Gaussian pulses ata repetition rate of 40 GHz are then obtained with an average power of 400 mW at the fiber output as shown inFig. 1(c1-1). The corresponding spectrum is reported in Fig. 1(b1) with a FWHM bandwidth about 100 GHz. Thispulse source is then injected into the fundamental mode of our PPLN waveguide by means of a lensed fiber. Thecenter wavelength and state of polarization of the near-IR pulse train is set to match the optimum SHG conversionof the PPLN waveguide whose temperature is stabilized near room temperature. The 20mm long SHG waveguidegives a normalized conversion coefficient of 40%/W. After beam collimation at the waveguide output, an opticalprism and an optical diaphragm are used to efficiently filter out the SHG signal and reject the residual pump andspectra generated by other nonlinear processes. The SHG signal is then collected into a multimode fiber andanalyzed by means of an optical spectrum analyzer (~15 GHz resolution) and our 45-GHz photodiode –oscilloscope system. As shown in Fig. 1(b2), the SHG spectrum exhibits a 40-GHz frequency-comb profilecentered at ~771 nm whose bandwidth is ~100 GHz. The SHG average power is measured to be about 30 mW.The temporal profile of our 40-GHz pulse train converted into the visible is shown in Fig. 1(c2) and exhibits a 40-GHz sinusoidal waveform due to the limitations of our detection system. The same behaviour and pulse durationis obtained when applying the same detection device to the measurement of our initial near-IR picosecond pulsetrain (see Fig. 1(c1-2))

Step-index LiNbO3 waveguides for frequency conversion

International audience&nbsp

Guides ridges multimodes en LiNbO3 non dopé pour la génération de second harmonique haute puissance

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Accent 3"/&gt <w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 3"/&gt <w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 3"/&gt <w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 3"/&gt <w:LsdException Locked="false" Priority="70" Name="Dark List Accent 3"/&gt <w:LsdException Locked="false" Priority="71" Name="Colorful Shading A

Watt-level SHG in undoped high step-index PPLN ridge waveguides

International audienceNonlinear quadratic waveguides are key components to obtain efficient frequency conversion. In this paper we present the performances of highly multimode periodically poled lithium niobate (PPLN) ridge waveguides for high power CW SHG are presented. We report the generation of 1 W of second harmonic on the fundamental guided mode with a conversion efficiency of 56% at telecom wavelengths. A stable nonlinear process is obtained despite use of an undoped congruent LiNbO<sub&gt3</sub&gt crystal. The input damage threshold of the ridge waveguide is found to set the maximum usable power

Nonlinear elasticity of silica nanofiber

International audienceOptical nanofibers (ONFs) represent versatile nanophotonic platforms for important photonic applications such as optical sensing and quantum and nonlinear optics. The attractiveness of ONFs arises from the tight optical confinement, their wide evanescent field in the subwavelength limit, their surface acoustic properties, and their high tensile strength. Here we investigate Brillouin light scattering in silica-glass ONFs under high tensile strain and show that the fundamental properties of elastic waves dramatically change due to elastic anisotropy and nonlinear elasticity for strain larger than 2%. This yields to unexpected Brillouin strain coefficients for all Brillouin resonances including surface and hybrid waves, followed by a nonlinear evolution at high tensile strength. We further provide a complete theoretical analysis based on third-order nonlinear elasticity of silica that agrees well with our experimental data. These new regimes open the way to the development of compact tensile strain optical sensors based on nanofibers

Microsystèmes intégrés en niobate de lithium

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Diameter and tensile strain measurements of optical nanofibers using Brillouin reflectometry

International audienceWe demonstrate a simple and efficient technique that allows for a complete characterization of silica-based tapered optical fibers with sub-wavelength diameters ranging from 0.5 μm to 1.2 μm. The technique is based on Brillouin reflectometry using a single-ended heterodyne detection. It has a high precision sensitivity down to 1% owing to the strong dependence of the Brillouin spectrum on the taper diameter. We further investigate the tensile strain dependence of the Brillouin spectrum for an optical microfiber up to 5% of elongation. The results show strong dependences of several Brillouin resonances with different strain coefficients ranging from 290 MHz/% to 410 MHz/% with a specific nonlinear deviation at high strain. Those results therefore show that optical micro and nanofibers could find potential application for sensitive strain optical sensing

Brillouin fiber spectrometer for metrology of tapered silica optical fiber

International audienceWe report a technique based on Brillouin scattering measurement to characterize precisely the geometry and the mechanical properties of tapered silica fiber. Our method relies on the Brillouin backscattering spectrum analysis that directly depends on the waveguide geometry