Lithium Niobate Optical Waveguides and Microwaveguides

Lithium niobate has attracted much attention since the 1970s due to its capacity to modify the light by means of an electric control. In this chapter, we review the evolution of electro-optical (EO) lithium niobate waveguides throughout the years, from Ti-indiffused waveguides to photonic crystals. The race toward ever smaller EO components with ever-lower optical losses and power consumption has stimulated numerous studies, the challenge consisting of strongly confining the light while preserving low losses. We show how waveguides have evolved toward ridges or thin film-based microguides to increase the EO efficiency and reduce the driving voltage. In particular, a focus is made on an easy-to-implement technique using a circular precision saw to produce thin ridge waveguides or suspended membranes with low losses

Lithium niobate micromachining for the fabrication of microfluidic droplet generators

In this paper, we present the first microfluidic junctions for droplet generation directly engraved on lithium niobate crystals by micromachining techniques, preparatory to a fully integrated opto-microfluidics lab-on-chip system. In particular, laser ablation technique and the mechanical micromachining technique are exploited to realise microfluidic channels in T-and cross junction configurations. The quality of both lateral and bottom surfaces of the channels are therefore compared together with a detailed study of their roughness measured by means of atomic force microscopy in order to evaluate the final performance achievable in an optofluidic device. Finally, the microfluidics performances of these water-in-oil droplets generators are investigated depending on these micromachining techniques, with particular focus on a wide range of droplet generation rates

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

RACE3 project : Electro-optic, piezoelectric, ferroelectric single-crystal thin films

International audience&nbsp

Efficient wavelength-tunable deep-diced ridge waveguide lasers in bulk Yb3+:CaF2 crystal

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Efficient Broadly Tunable Waveguide Lasers in Yb3+:CaF2 Produced by Deep Diamond Saw Dicing

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Arrays of millimeter-sized glass lenses for miniature inspection systems

SPIE Photonics Europe 2014, Microoptics Conference Bruxelles (Belgique), du 14/04/2014 au 17/04/2014In this paper, we adapt a technique employed for glass microlenses fabrication in order to obtain matrices of millimeter size lenses having high quality. The use of microfabrication processes and Micro ElectroMechanical Systems (MEMS) compatible materials allow the integration of lenses larger than usual in microsystems. Since the presented lenses can have 2 mm in diameter or more, some aspects apparently irrelevant when diameters are lower than 500 µm must be reviewed and taken into account. Indeed, when the lenses are in the millimeter range, problems such as size non-uniformities within a matrix and asymmetric shapes of each lens are dependent on parameters such as mask design, depth of the silicon cavities, enclosed vacuum control after anodic bonding, reflow temperature and even position of the lenses on the substrate. In the fabrication process, a mask formed of circular shapes is patterned with positive photoresist on a silicon wafer by standard UV photolithography. Then, cylindrical cavities about 300 µm deep are obtained in silicon by deep reactive ion etching (DRIE). After removing the photoresist mask, the silicon cavities are sealed under vacuum with a borosilicate glass wafer by anodic bonding. When placing the silicon-glass stack inside a furnace at high temperature, the glass melts with spherical shape by getting aspired into the cavity thanks to the pressure differences between the sealed cavity and the outer environment. After melting, the glass backside is polished in order to obtain a flat surface with optical quality. Silicon can be afterwards selectively removed by dry or wet etching and the plano-convex lenses are then released. Issues related to this fabrication flow-chart are addressed in this paper and few solutions are proposed. Results consecutive to optimization are shown to prove the pertinence of this technique to fabricate MEMS-compatible millimeter-sized lenses to be integrated in miniature microscopes

Autofocalisation Rapide Contrôlée par Effet Pyroélectrique dans un Film de LiNbO3

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Comparison of Anodic and Au-Au Thermocompression Si-Wafer Bonding Methods for High-Pressure Microcooling Devices

International audienceSilicon-based microchannel technology offers unmatched performance in the cooling of silicon pixel detectors in high-energy physics. Although Si–Si direct bonding, used for the fabrication of cooling plates, also meets the stringent requirements of this application (its high-pressure resistance of ~200 bar, in particular), its use is reported to be a challenging and expensive process. In this study, we evaluated two alternative bonding methods, aiming toward a more cost-effective fabrication process: Si-Glass-Si anodic bonding (AB) with a thin-film glass, and Au-Au thermocompression (TC). The bonding strengths of the two methods were evaluated with destructive pressure burst tests (0–690 bar) on test structures, each made of a 1 × 2 cm2 silicon die etched with a tank and an inlet channel and sealed with a plain silicon die using either the AB or TC bonding. The pressure resistance of the structures was measured to be higher for the TC-sealed samples (max. 690 bar) than for the AB samples (max. 530 bar), but less homogeneous. The failure analysis indicated that the AB structure resistance was limited by the adhesion force of the deposited layers. Nevertheless, both the TC and AB methods provided sufficient bond quality to hold the high pressure required for application in high-energy physics pixel detector cooling

Channel waveguide lasers in bulk Tm:LiYF 4 produced by deep diamond-saw dicing

International audienceWe report on a novel approach to fabricate channel (ridge) waveguides (WGs) in bulk crystals using precision diamond saw dicing. The channels feature a high depth-to-width aspect ratio (deep dicing). The proof-of-the-concept is shown for a Tm3+:LiYF4 fluoride crystal. Channels with a depth of 200 µm and widths of 10–50 µm are diced and characterized by confocal laser microscopy revealing a r.m.s. roughness of the walls well below 100 nm. The channels obtained possess waveguiding properties at ∼815 nm with almost no leakage of the guided mode having a vertical stripe intensity profile into the bulk crystal volume and relatively low propagation losses (0.20-0.43 dB/cm). Laser operation is achieved in quasi-CW regime by pumping at 780 nm. The maximum peak output power reaches 0.68 W at ∼1.91 µm with a slope efficiency of 53.3% (in σ-polarization). The proposed concept is applicable to a variety of laser crystals with different rare-earth dopants