Frédéric Lecoche

Two electric-field components measurement using a 2-port pigtailed electro-optic sensor

Based on an isotropic electro-optic crystal, a two-port pigtailed electro-optic sensor has been built. The probe allows to measure two orthogonal components of the ambient electric field. The sensor intrinsically presents a temperature-dependent free response. The two measured electric field components are orthogonal to the sensor revolution axis, leading to a transverse electro-optic probe. Magnitude and orientation of the electric field are measured simultaneously with an accuracy of 0.5 dB and 2°, respectively. The rejection of orthogonal components to the electric field vector reaches 30 dB.

A Nonperturbative Electrooptic Sensor for in Situ Electric Discharge Characterization

Pulsed power and intense electric field now apply to a large variety of domains for which the need of in situ nonperturbative measurements remains a challenge. The main requirements that sensors should fulfill for that purpose are nonmetallic composition, small size, ultrawide bandwidth, compatibility with liquids and gases, possibility for remote measurements at long distances, true vectorial (field direction) time-domain measurements, capability of measuring electric fields up to the electric breakdown of air, and a large dynamic range. Obviously, all these requirements cannot be achieved by a unique sensor. However, most of them are fulfilled by pigtailed electrooptic (EO) sensors. In this paper, after recalling the principle of the EO effect and its use for electric field measurement, we deal with the measurement linearity and selectivity of the EO sensor. Associated with the nonperturbative behavior of the EO sensor, the measurement dynamics of EO sensors exceeds 100 dB. Furthermore, EO sensors present an intrinsic flat response from quasi d.c. (10 Hz) up to a few tens of gigahertz. Thanks to their composition of high dielectric strength materials and their optical pigtail, EO sensors are completely immune to the electromagnetic environment except on a very small volume (≅ 10 mm3) corresponding to the transducer element of the sensor. This leads to a very high spatial resolution. We finally illustrate the capabilities of this technology through in situ measurement of the electric discharge transients and vectors.

Single Shot and Vectorial Characterization of Intense Electric Field in Various Environments With Pigtailed Electrooptic Probe

In this paper we illustrate the ability of electrooptic sensors to perform electric (E)-field vectorial measurements. Thanks to their frequency response spreading over nine decades and to their measurement dynamics reaching 120 dB, these sensors are of high interest for some applications (near field mapping, energy line monitoring, electromagnetic compatibility, and so on). Furthermore, due to their fully dielectric structure and millimetric size, almost no perturbation is induced on the E-field to be measured, even in the near field region. This paper is focused on high-intensity pulsed E-field characterization in different environments such as air, water (bioelectromagnetism applications), or plasmas (in situ assessment of the E-field associated to an electric discharge and to the induced plasma). The use of such a technology for electrical equipment and energy line monitoring is also investigated.

Contactless, Real Time, and Vectorial Inspection of a Multiwire Power Cable Voltage Using an Electro-Optic Technique

Here, we demonstrate the suitability of the electro-optic technique for contactless monitoring of a power cable composed of several conductors. We have developed an electrometer performing real-time characterization of the field surrounding the cable. The electrometer gives the transient evolution of the field strength as well as the field orientation. The actual transverse field vector associated with a three-phase cable follows ellipses. These ellipses have been assessed with an analytical approach, finite difference time domain simulations, and also experimentally with the electro-optic electrometer.

Single shot measurements of electric field vector in various environments with pigtailed electro-optic probes

We here illustrate the ability of electro-optic sensors to perform electric field vectorial measurements. Thanks to their frequency response that remains flat over nine decades and to their measurement dynamics reaching 120 dB, these sensors are of key interest for many applications. Furthermore, due to their fully dielectric structure and to their millimetric size, almost no perturbation is induced on the electric field to be measured, even in the near field region. This paper is focused on high intensity pulsed electric field characterization in different environments such as water (bioelectromagnetism applications) or plasma (in-situ assessment of the electric-field associated to an electric discharge). The use of such technology for electrical equipments and energy lines monitoring is also investigated.

Optical Sensor for the diagnostic of high voltage equipment

We present the potentialities of electro-optic sensors to perform non-invasive and vectorial electric field measurement. The realized optical probes are dedicated to the diagnostic of high voltage equipment regardless of magnetic field and temperature variations. The performances of such a technique are characterized and are compared to more commonly used sensors. The optical and pigtailed transducer is here used to perform the non invasive electric field mapping within a coaxial structure. Latest improvement concerning sensitivity enhancement are also investigated.

Optical sensor for the vectorial analysis of the plasma induced electric field

Summary form only given. We here present recent developments related to electro-optical (EO) sensors dedicated to vectorial characterization of intense electric (E) field. This technique is based on the Pockels effect, which results in the linear modification of the refractive indices of a crystal, induced by the E-field. A typical EO measurement system involves a pigtailed E-field probe (the transducer itself) and an optoelectronic unit. This latter one feeds optically the transducer. It also ensures the optical treatment of the useful signal (optical modulation) in order to deliver electrical signals proportional to the E-field vector components.This EO system has already demonstrated unprecedented performances: a dynamic range exceeding 120 dB from less than 1 V/m up to more than 1 MV/m, a frequency bandwidth covering more than 9 decades from 30 Hz to several tens of GHz, the adaptation of the measurement both to time-and frequency-domain. Due to the millimeter size of the dielectric transducer, the disturbance on the field to be measured remains very weak. These properties fulfill the requirements of intense E-field assessment. Indeed, measurement within a plasma jet or in the closest vicinity of an electrical discharge has already been demonstrated. Moreover, the analysis includes the actual transient evolution of the each component o, the E-field vector2. Latest advances concern the spatio-temporal characterization of the E-field vector ,or the diagnostic of the plasma source. The field contribution of the ionization potential, together with the plasma itself, are thoroughly investigated. Measurement results have demonstrated that the plasma source behavior can be disrupted by parasitic discharges linked to plasma gas pollution.

Spatio-temporal and vectorial analysis of the electric field vector with an optical sensor

The ability of an electro-optic system is here demonstrated for the mapping of the electric field vector over a wide bandwidth. Thanks to their dielectric structure, such sensors are intrinsically very low invasive and allow to perform near field analysis. Even in the reactive area of radiative devices, the probe allows to characterize the field vector distribution with a dynamics exceeding 120 dB. The associated spatial resolution is weaker than 500 μm and the measurement bandwidth reaches more than 10 GHz.

Contactless real-time voltage monitoring of multi-conductors cables with electro-optic sensor

We present herein a original concept of contactless electrometer based on an electro-optic technique. The developed device embeds an electro-optic crystal ensuring the real-time analysis of the transverse electric field vector surrounding a multiwires power cable. The field behaviour has been theoretically investigated, numerically computed, and experimentally characterized with the realized electrometer.

Single shot measurements of the E-field vector with pigtailed optical probes

Summary form only given. Over the variety of available sensors dedicated to electric (E)-field characterization, the use of antennas constitutes the most widespread technique. While such probes are convenient and provide a good sensitivity, they remain invasive and bandwidth limited. At the opposite, fibered electro-optic transducers1 are fully dielectric, millimeter sized and allow to perform measurements of the E-field vector from DC to several gigahertz and even up to terahertz frequencies using equivalent-time sampling. Furthermore, recent developments lead to a simultaneous characterization of 2 transverse E-field vector components with a single EO probe2. Based on polarization state modulation, the EO transducer is linked to a remote (up to 30 meters) optoelectronic set-up including a ultra low noise laser feeding the probe and a real time optical set-up to manage the modulation treatment. The automated and servo controlled measurement bench is temperature dependent free. The available measurement dynamics exceeds 100 dB, ranging from less than 1 V. m-1. Hz-1/2 up to the breakdown electric field in air.An exhaustive comparison between BO sensors and other technologies will be firstly given during the conference. This analysis will be based on intrinsic sensor properties, such as sensitivity, frequency bandwidth, vectorial selectivity, spatial resolution and induced perturbation on the field to be measured. After recalling the principles of the BO effect, the optical arrangement of the optical probes will be described. The characterization of the BO system will be presented together with experimental results illustrating the potentialities of BO sensors. Among these examples, measurements of pulsed B-field in air (pulsed power), water (specific absorption rate evaluation in pulsed regime) or in plasma (real time evolution of the electrical discharge associated B-field) will be shown.