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ISBN 978-1-943580-84-2; International audience; We propose a new scheme of quasi-phase matching based on the negative first-order of the spatial modulation of the sign of the second-order optical nonlinearity. The experimental validation is done in a periodically-poled Rubidium-doped KTiOPO4 crystal.

Established waveguide fabrication technologies on lithium niobate (LN) and potassium titanyl phosphate (KTP) were revisited, and a comparative analysis of their performance for type-0 quasi-phase matched second-harmonic generation at 1.55 µm was provided based on literature data and our simulations. This analysis aided identifying gaps where the waveguide performance is below the theoretical predictions, and the possible reasons are discussed. It provides the reader with a roadmap for choosing the most appropriate waveguide type and material choice between LN and KTP for desired performance of targeted applications.

The waveguiding properties of high-resistivity float zone silicon slab waveguides are characterized over the spectral range from 0.5 to 7.5 THz. Waveguide modes and dispersion are observed for lengths of 1.2 cm and silicon thicknesses from 40 to 300 µm. The influence of core thickness and cladding glass attenuation is characterized, and modeled transmitted pulse shapes compare well to the measured signals. Fused silica cladding allows propagation in the 40 µm thick wafer, demonstrating the feasibility of developing flexible semiconductor core fibers for THz transmission. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

We present the fabrication of channel waveguides in PPRKTP crystals for QPM SHG in the blue region. Our waveguides reached a normalized conversion efficiency of 119 %/Wcm2 and showed low loss (0.51dB/cm).

International audience; We worked on a new scheme of Quasi-Phase-Matching (QPM) based on the negative first-order of the spatial modulation of the sign of the second-order nonlinearity. Applying this scheme in the case of Angular-Quasi-Phase-Matching (AQPM) in a biaxial crystal reveals new directions of propagation for efficient parametric frequency conversion as well as "giant" spectral acceptances. The experimental validation is performed in a periodically-poled Rubidium-doped KTiOPO4 biaxial crystal. This new approach naturally extends to other periodically-poled uniaxial crystals such as periodically-poled LiNbO3. Phase-matching is the privileged way to optimize the performance of nonlinear optical frequency conversion. Usually, it can be obtained by using the birefringence of anisotropic crystals, which corresponds to birefringence phase-matching (BPM) [1,2]. However, BPM conditions are strongly limited by the refractive indices of the material and they usually forbid the exploitation of the highest coefficient of the second-order electric susceptibility tensor. To overcome this limitation, quasi-phase matching (QPM) is a powerful alternative. It is based on a periodical modulation of the sign of the second-order optical nonlinear coefficient of anisotropic or isotropic non-centrosymmetric crystals [3,4]. We propose here the development and the experimental validation of a new scheme of QPM that allows us to enlarge the spectral range of phase-matched generation and to get access to giant spectral acceptances. For that purpose, we studied Second-Harmonic Generation (SHG) in the ferroelectric periodically-poled Rubidium-doped KTiOPO4 crystal (PPRKTP) [5]. The key parameter of QPM is the periodicity Λ of the spatial modulation of the second-order nonlinearity along the direction of propagation of three interacting waves such as their wavelengths fulfil: 1/λ ! − 1/λ " − 1/λ # = 0. Actually, the goal is to compensate the #% ' , is the grating vector oriented along the propagation direction, and m is the order of the Fourier series. Usually, m is chosen as a positive integer (m ≥ 1), as it is the case for instance while targeting the largest nonlinear coefficient χ !! (#). It is shown in Fig. 1 (left) in the optimal case, i.e. for the lowest QPM positive order m = 1. This is the classical scheme of QPM that we called QPM-A. However, it is also possible to consider propagation directions where m ≤-1. This configuration has been previously theoretically considered, but without any phenomenological interpretation or experimental verification [6]. We called here this new scheme QPM-B. As for the case of positive orders, the lowest QPM-B order (namely m =-1) shown in Fig. 1 (right) leads to the best efficiency compared to higher

International audience

We describe a simple, narrow-linewidth, tunable fiber-based laser with a high degree of tuning accuracy. A polarization independent semiconductor optical amplifier (SOA) is used as the gain medium in a unidirectional fiber ring cavity with a circulator connected to a 6-meter long chirped fiber Bragg grating (CFBG). The laser wavelength is chosen by setting the modulation frequency of the SOA the same as the harmonics of the fundamental repetition rate of the light reflected at a specific point on the CFBG. Careful management of the drive current and pulse width helps to generate laser light of narrow linewidth (less than 0.03 nm) with low power variation (1.46 dB) over a tuning range of 40 nm. QC 20190610

The strict momentum conservation constraints for backward-wave optical parametric oscillators (BWOPOs) gives an inherently narrowband backward-generated wave, even with broadband pumping. Unfortunately, the limited tuning range of this wave restricts potential applications. Here we demonstrate a method to circumvent this restriction and increase the tuning range by more than one order of magnitude. A linearly chirped pump modulation is transferred to the forward-generated BWOPO wave, which is then mixed with an identically chirped pump in a conventional optical parametric amplifier to obtain narrowband (38 GHz), broadly tunable, infrared radiation around 1.86 µm, with an output energy of 19 µJ.

Semiconductor-core optical fibres have potential applications in photonics and optoelectronics due to large nonlinear optical coefficients and an extended transparency window. Laser processing can impose large temperature gradients, an ability that has been used to improve the uniformity of unary fibre cores, and to inscribe compositional variations in alloy systems. Interest in an integrated light-emitting element suggests a move from Group IV to III-V materials, or a core that contains both. This paper describes the fabrication of GaSb/Si core fibres, and a subsequent CO2 laser treatment that aggregates large regions of GaSb without suppressing room temperature photoluminescence. The ability to isolate a large III-V crystalline region within the Si core is an important step towards embedding semiconductor light sources within infrared light-transmitting silicon optical fibre., Semiconductor-core optical fibres are of interest for their non-linear optical and electro-optical properties. Here, GaSb/Si composite-core optical fibres were fabricated and a CO2 laser was used to facilitate controlled GaSb segregation within the silicon. This has implications for embedding light sources in IR-transmitting fibers

Atmospheric dual-band Scheimpflug lidar is demonstrated at 980 and 1550 nm. Signals are compared during three weather conditions, and the spatio-temporal resolution of the atmospheric structure is considered. The potential for aerosol classification is evaluated, and future directions are discussed.

We report the first experimental validation of angular quasi-phase-matching (AQPM) theory in a biaxial crystal by performing second-harmonic generation (SHG) in the periodically-poled Rb-doped KTiOPO4 (PPRKTP) crystal cut as a sphere. Both AQPM and birefringence phase-matching (BPM) angles were measured thanks to a Kappa circle.

Flow cytometry is currently the gold standard for analysis of cells in the medical laboratory and biomedical research. Fuelled by the need of point-of-care diagnosis, a significant effort has been made to miniaturize and reduce cost of flow cytometers. However, despite recent advances, current microsystems remain less versatile and much slower than their large-scale counterparts. In this work, an all-silica fibre microflow cytometer is presented that measures fluorescence and scattering from particles and cells. It integrates cell transport in circular capillaries and light delivery by optical fibres. Single-stream cell focusing is performed by Elasto-inertial microfluidics to guarantee accurate and sensitive detection. The capability of this technique is extended to high flow rates (up to 800 µl/min), enabling a throughput of 2500 particles/s. The robust, portable and low-cost system described here could be the basis for a point-of-care flow cytometer with a performance comparable to commercial systems.

We present a numerical method for studying fiber-based ultra-short pulse amplification at high repetition rates. Validation of the simulations, by comparison with experimental results, are also presented. QC 20160712

We present a CW and polarized 946 nm laser based on Nd:YAG single-crystal fiber. The output power at 946 nm reaches 11.5 W with a 60W diode ; the beam quality was measured below 1.7 and the ouput power was stable for hours. This high power source was then used to study the frequency doubling properties of periodically poled, rubidium-doped KTP (PPRKTP) in a continuous, extracavity configuration. We show that while we can obtain up to 800 mW of blue power, residual absorption hinders the obtainable stable power

Summary form only given. Quasi-phase-matching (QPM) is a method to get tailored efficient second order nonlinear interactions [1]. Several techniques exist for fabrication of periodic domain structures in ferroelectric crystals for QPM frequency conversion. By far, electric field poling using lithographically patterned electrodes on the z-face of the crystal is the most common one [2]. High-quality periodically inverted ferroelectric domain structures in flux grown KTiOP 4 (KTP) crystals were fabricated already in the late 90's using this technique [3], and recently periodic domain sizes of few hundred nanometers were fabricated in 1 mm thick samples thanks to the quasi-one dimensional structure of KTP. It has recently also been shown that a slight Rb doping of the KTP crystal (RKTP) facilitates the periodic poling [4]. However, fabrication of two-dimensional (2D) domain structures in RKTP has not yet been investigated. A disadvantage with the lithographic patterning is that each sample needs to be patterned individually, which is tedious and time consuming. Moreover, when it comes to the small domain features, which are required by the next generation of nonlinear optical devices, a more versatile poling technique has to be developed due to the limitations of conventional photolithography. Structured silicon has been investigated as an alternative electrode for formation of 1D domains by contact poling in LiNb 3 [5]. However, these electrodes were fabricated by wet etching and the sample thickness was limited to ~200 μm.In this work we present a new technique for 2D domain inversion in 1 mm thick RKTP and demonstrate the densest 2D lattice in a KTP isomorph. First, 2D periodic arrays of silicon pillars were constructed using isotropic dry etching (Fig.1 (a)). The silicon substrate was p-type with orientation and a resistivity of 0.005-0.02 Ωcm. Second, the silicon arrays of pillars were used as contact electrode to periodically pole the RKTP crystal (Fig.1 (b)). A regular and homogeneous domain pattern with a 5x5 gm' period was obtained, as can be seen in Fig.1 (c). A high normalized conversion efficiency of 1.27 %W-1cm-1 was obtained for frequency doubling of a CW Ti-Sapphire laser at 894 nm. The measured temperature bandwidth was 4.25 °C, from which we estimated an effective crystal length of 5.4 mm, which is very close to the physical structure length of 6 mm.This novel poling technique has several advantages. First, the silicon electrode is reusable and there is no need for patterning each sample individually. Second, the crystalline structure of silicon provides high accuracy and reproducibility in the electrode fabrication. Finally, Si-pillar array electrodes can be designed for any desirable period or electrode geometry. Therefore, we believe that contact electrode poling can be a more convenient, flexible and suitable method for making small feature domain patterns, and it also can reduce the fabrication costs.

International audience; Periodically-poled ferroelectric crystals show unprecedented efficiency and properties otherwise impossible to obtain. Unfortunately, the sample thickness obtainable today limits their use to low and moderate power application. With the aim of increasing the size of periodically domain-structured crystals with a controlled and regular grating period, we proposed an epitaxial growth process using seeds made of thin plates domain engineered by electric field poling. We demonstrated this process with the ferroelectric crystal KTiOPO4 (KTP) which is one of the most promising candidate materials for that purpose. The poling step requires a sample exhibiting (001) and (00 (1) over bar) faces, so that the growth step has to be performed onto these faces. This constraint is a difficulty to circumvent as these faces are not present in the standard equilibrium morphology. It is then necessary to find the growth conditions enabling to work below the roughening temperature of these faces. By using a high temperature solution method, the so-called "flux method", and by choosing an appropriate chemical composition of the flux solution, we obtained periodically domain-structured KTP layers with thicknesses up to 800 mu m and regular periodicity onto (001) and (00 (1) over bar) faces of the initial PPKTP seeds.

We theoretically and experimentally investigate multistep parametric processes in broadband optical parametric generators (OPGs) based on periodically poled 1 mol. % MgO-doped stoichiometric LiTaO3. We demonstrate that parametric collateral processes may deplete or enhance spectral portions of the OPG output, depending on pump pulse duration. QC 20120618This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-37-10-1727 . Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.

Spectral requirements for the first stage OPO used to pump a tandem ZGP mid-infrared OPO are theoretically investigated. Based on these requirements we demonstrate a singly-resonant type-I OPO including periodically poled KTiOPO4 and volume-Bragg gratings as output couplers. Singly resonant oscillation is demonstrated very close to degeneracy, where signal and idler spectra are not well separated. Investigations of the longitudinal mode spectrum and the idler spectrum with high resolution using a scanning Fabry-Perot interferometer show the essential role played by the phase correlations of the multi-longitudinal mode Q-switched pump laser in formation of the nonresonant idler spectrum. QC 100517

Proton exchange was observed to increase the poling voltage for congruent lithium niobate. Patterned proton exchange was then used to control domain nucleation and inhibit broadening of reversed domains. Periodically proton exchanged samples were used to form domain gratings by electric field poling just using planar electrodes and without need for poling current control. The reversed domain gratings had a duty cycle faithfully reproducing that of the proton exchanged pattern with straight domain walls parallel to the x face, thus demonstrating that high-fidelity reversed domain patterning is possible to obtain by a relatively simple process.

A continuous-wave (CW) master oscillator-power amplifier (MOPA) fiber source, tunable around 978 nm, was frequency-doubled to 488.7 nm. Both the laser and the amplifier were made with cladding-pumped jacketed air-clad Yb-doped fibers. The MOPA generated up to 2.7 W of power in an output beam with an M/sup 2/ value of 1.8. This was frequency-doubled in a periodically poled potassium titanyl phosphate crystal at room temperature, in a single-pass configuration. The generated blue light had a CW power of 18.1 mW, a nearly Gaussian spatial intensity profile, and an M/sup 2/ value of 1.7.

We report on a diode-pumped Er:Yb laser able to generate a single-frequency output power in excess of 200 mW at both 1.53 /spl mu/m and 1.56 /spl mu/m and over 300 mW in multimode operation. The tuning characteristics of the source are reported and discussed. The relative intensity noise presents in all configurations a peak value lower than -92 dB/Hz and its level decreases below -160 dB/Hz for frequencies higher than 8 MHz.