Non-intrusive, wide bandwidth and spatial resolution are terms often heard in electric field sensing. Despite of the fact that conventional electromagnetic field probes (EMF) can exhibit notable functional performances, they fail in terms of perturbation of the E-field due to their loaded metallic structure. In addition, even though electro-optical technology offers an alternative, it requires large interaction lenghts which severely limit the sensing performances in terms of bandwidth and spatial resolution. Here, we focus on miniaturizing the interaction volume, photon lifetime and device footprint by taking advantage of the combination of lithium niobate (LN), Lab-on-Fiber technologies and photonic crystals (PhC). We demonstrate the operation of an all-dielectric E-field sensor whose ultra-compact footprint is inscribed in a 125 μm-diameter circle with an interaction area smaller than 19 μm × 19 μm and light propagation length of 700 nm. This submicrometer length provides outstanding bandwidth flatness, in addition to be promising for frequency detection beyond the THz. Moreover, the minituarization also provides unique features such as spatial resolution under 10 μm and minimal perturbation to the E-field, accompanied by great linearity with respect to the E-field strength. All these specifications, summarized to the high versatibility of Lab-on-Fiber technology, lead to a revolutionary and novel fibered E-field sensor which can be adapted to a broad range of applications in the fields of telecommunications, health and military.

The measurement of microwave electric-field (E-field) exposure is an ever-evolving subject that has recently led the International Commission on Non-Ionizing Radiation Protection to change its recommendations. With frequencies increasing toward terahertz (THz), stimulated by 5G deployment, the measurement specifications reveal ever more demanding challenges in terms of bandwidth (BW) and miniaturization. We propose a focus on minimally invasive E-field sensors, which are crucial for the in situ and near-field characterization of E-fields both in harsh environments such as plasmas and in the vicinity of emitters. We browse the large varieties of measurement devices, among which the electro-optic (EO) probes stand out for their potential of high BW up to THz, minimal invasiveness, and ability of vector measurements. We describe and compare the three main categories of EO sensors, from bulk systems to nanoprobes. First, we show how bulk-sensors have evolved toward attractive fibered systems that are advantageously employed in plasmas, resonance magnetic imagings chambers or for radiation-pattern imaging up to THz frequencies. Then we describe how the integration of waveguides helps to gain robustness, lateral resolution, and sensitivity. The third part is dedicated to the ultra-miniaturization of components allowing ultimate steps toward electromagnetic invisibility. This review aims at pointing out the recent evolutions over the past 10 years, with a highlight on the specificities of each photonic architecture. It also shows the way to future multi-physics and multi-arrays smart sensing platforms. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

On account of the micro-scale building components manipulation and high precision demands, the interest is oriented toward automated robotic micro-manipulation and micro-assembly to provide low-cost, high performances, notably for integrated optical devices. The paper proposes a novel strategy for high precision fully automated robotic alignment. This strategy permits high accurate and fast automated alignment of two optical building structures (optical fiber, optical component) with optimal optical function in a known referencing between the robotic manipulator and the optical axis. The strategy allows to identify and to compensate the optical component misalignment angles and the robot translation error angles yielded from the robotic manipulator. The approach relies on robotic positioning combined with the use of Fabry-Perot interferometry of the reflected light irradiance for closed loop control. Fabry-Perot interference principle is especially used to give a rapid and high precision measurement. A photo-robotic positioning model is proposed that relates the optical component misalignment angles and robot translation error angles with the Fabry-Perot measurements. A 6 Degree-Of-Freedom (DOF) robotic platform is used to relatively align an optical component to an optical fiber for experimental validation. The obtained results leads to robotic positioning uncertainty of about 0.0021 • and alignment time of less than 12 s.

Lab-on-fiber technology is an emerging topic for sensing cutting-edge technologies due to the high versatility and functionality that it offers when it is combined with different sensitive materials. A particular configuration, which consists of the integration of nanophotonic structures into the tip of a pigtailed fiber, allows the exploitation of light localization performances to produce high-performing sensors. However, integrating such tiny structures into the fiber facet requires complex and expensive procedures. In this work, we report a novel high precision assembly procedure that ensures the parallelism between the photonic chip and the fiber surface, in addition to the alignment with the light injection into the nanostructure. The integrated structure consists of an ultra-compact (19 μm × 19 μm) Photonic Crystal Slab (PCS) structure based on a 700 nm thin film of lithium niobate (LN) which is sensitive to external E-fields via the electro-optic effect. Thus, the assembled sensor detects electric fields, presenting great linearity and a sensitivity of 170 V/m. This technique shows a way to assemble compact planar nanostructures into fiber facets keeping high throughput, high precision, and relatively low costs.

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Le niobate de lithium (LiNbO3) suscite un vif intérêt en photonique depuis des décennies en raison de ses fortes propriétés électro-optiques et non-linéaires. L’opportunité récente de l’usiner en couches minces a élargi le spectre des applications déjà nombreuses du matériau. Les enjeux actuels concernent la miniaturisation des composants tout en préservant de faibles pertes optiques.

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