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In this paper, the field-induced residual ferroelectricity in antiferroelectric lead zirconate thin films has been studied by impedance measurements together with a hyperbolic law analysis, which permits us to extract the different contributions to the material’s complex permittivity. By measuring the Rayleigh coefficient αr, it appears that the residual ferroelectricity is considerably enhanced when the sample has been previously exposed to an electric field close to the antiferroelectric to ferroelectric transition field. This indicates that a part of the material remains ferroelectric after the antiferroelectric–ferroelectric backward transition, which constitutes an additional contribution to polarization. Consequently, a higher domain wall density and mobility can be observed. Measurements after exposition to thermal treatment show that this ferroelectric response is metastable.

International audience; The weak ferroelectric contribution to the polarization of antiferroelectric lead zirconate (PZO) thin films has been investigated using PUND (Positive Up Negative Down) pulse measurements and hysterons decomposition by First Order Reversal Curves (FORC) technique. The PUND allows decomposing the measured current, obtained from the polarization-electric field loop measurements, into a switching and a non-switching contribution. We show that the weak ferroelectric phase is enhanced when a large electric field has been previously applied to the material, in order to switch from the antiferroelectric to the ferroelectric phase. Using the PUND measurement at fields below the antiferroelectric to ferroelectric phase transition, the polarization loop corresponding only to the ferroelectric switching contribution has been determined revealing that this contribution to the overall polarization is small. FORC measurements, however, indicate that the ferroelectric phase is present at different fields. At low fields, a quite homogeneous distribution of hysterons exists and at large field, a high concentration of hysterons at a field near to the antiferroelectric to ferroelectric phase transition can be seen. Moreover, when changing the delay between pulses of the PUND and the FORC measurements, we show that this weak ferroelectricity contribution is metastable and decreases with time.

International audience

International audience; We hereby present a new equivalent circuit model including both lumped and distributed elements for GCPW-MS transitions (GCPW for Grounded CoplanarWaveguide and MS for Microstrip). In order to validate the modelling results, such transitions have been fabricated on a 20 μm-thick BCB (Benzocyclobutene resin) substrate using grounding pads including via-holes of different diameters. The study focused on the impact of the via-hole diameter on the performance of the transition and more specifically on its bandwidth. The transitions were made using a simple technological process based on photosensitive polymer. ADS simulation data of the new equivalent circuit model were in very good agreement with measured S-parameters. Both theoretical and experimental results have shown that the bandwidth of such a transition can reach up to 100 GHz using via-holes of 900 μm diameter.

A broadband via-hole less transition from a conductor-backed coplanar waveguide (CBCPW) to a parallel coupled microstrip line (CMS) via microstrip section (MS) is reported in this paper that is realized on a MCL FX-2 substrate (100 μm thick). This transition should find a wide variety of applications due to its demonstrated broadband (from 4.5 GHz up to 39.5 GHz) behavior, ease of fabrication, and low manufacturing cost. In addition, utilization of the MS section between the CBCPW and CMS sections allows putting ground electrode in a different plane than the signal electrodes. This exibility made possible by electromagnetic field coupling between the bottom and top ground planes simplifies the transition manufacturing and facilitates the characterization of optical components driven with CMS line using coplanar probes.

Generation of microwave, millimetre-wave even THz signals by optical means is currently a favoured technique for a lot of system applications such as: high bit-rate wireless telecommunications, local oscillator or radar signal distribution within satellites, video signal distribution, automotive communications, THz security systems, etc.... We report here the fabrication and the characterization of an ultra-compact optical source made of semiconductor material. It allows generating two optical modes that are separated by the frequency that is requested at the photodetector level. This source is composed of two DFB lasers constituting a dual-mode laser emitting in the 1.55μm wavelength range. The device has been fabricated at Alcatel-Thales III-VLab using a proprietary DFB technology and the work has been supported under the "IPHOBAC" European project. Several targets were fixed for this device: tunability of intermodal spacing up to 300GHz, optical linewidth close to the MHz as well as horizontal and vertical divergences around 10°. The first goal has been achieved by using two DFB structures with a 0.3nm difference in the grating pitch and tuning the drive current of each section. The second goal has been globally achieved by using a quantum well based active layer. A new version including quantum dot based active layer should answer positively to this target. Last objective was partially obtained by the design and the integration of a spot size converter. The divergence has been measured as 10°x17° (HxV). Concerning the vertical divergence, the target of 10° was not obtained mainly linked to the device structure and the limitations we fixed on the overall length of the device.; La génération de signaux microondes, millimétriques, voire THz par voie optique est actuellement une solution technique privilégiée pour la réalisation de systèmes de (télé)communications mobiles haut débit mais encore, les réseaux de distribution d'oscillateurs locaux et de signaux d'observation ou de radar intra- satellitaires, la distribution de signaux vidéo, la communication automobile, les systèmes de visualisation THz pour la sécurité, etc..... Nous reportons ici la réalisation et la caractérisation d'une source optique ultra-compacte en matériau semiconducteur permettant de générer deux modes optiques séparés de la fréquence que l'on désire créer au niveau de la photodétection. Cette source prend la forme d'un laser DFB bi-longueur d'onde émettant dans la gamme de longueurs d'onde autour de 1,55μm. Le composant a été fabriqué chez Alcatel- Thales III-VLab à partir d'une technologie propriétaire de laser DFB et dans le cade du projet Européen IPHOBAC. Différents objectifs avaient été fixés pour ce composant: accordabilité de l'écartement intermodal jusque 300 GHz, largeur de raie de l'ordre du MHz et divergence dans le plan horizontal et vertical de 10°. Le premier objectif a été atteint par la réalisation de deux lasers DFB dont l'écart de pas de réseau est différent de 0,3nm et par la variation des courants d'injection de chaque section. Le second a été globalement atteint par l'utilisation d'une structure active à puits quantiques, une nouvelle version du composant utilisant des boites quantiques devrait remplir complètement cet objectif. Le dernier objectif a été partiellement atteint par la conception et l'adjonction d'un adaptateur de mode en sortie de composant, la divergence obtenue est de 10°x17° (HxV). Dans le plan vertical, les 10° de divergence n'ont pas pu être obtenus principalement à cause de la structure du composant et des limitations que l'on s'était imposées sur la longueur totale de celui-ci.

Generation of microwave, millimetre-wave even THz signals by optical means is currently a favoured technique for a lot of system applications such as: high bit-rate wireless telecommunications, local oscillator or radar signal distribution within satellites, video signal distribution, automotive communications, THz security systems, etc.... We report here the fabrication and the characterization of an ultra-compact optical source made of semiconductor material. It allows generating two optical modes that are separated by the frequency that is requested at the photodetector level. This source is composed of two DFB lasers constituting a dual-mode laser emitting in the 1.55μm wavelength range. The device has been fabricated at Alcatel-Thales III-VLab using a proprietary DFB technology and the work has been supported under the "IPHOBAC" European project. Several targets were fixed for this device: tunability of intermodal spacing up to 300GHz, optical linewidth close to the MHz as well as horizontal and vertical divergences around 10°. The first goal has been achieved by using two DFB structures with a 0.3nm difference in the grating pitch and tuning the drive current of each section. The second goal has been globally achieved by using a quantum well based active layer. A new version including quantum dot based active layer should answer positively to this target. Last objective was partially obtained by the design and the integration of a spot size converter. The divergence has been measured as 10°x17° (HxV). Concerning the vertical divergence, the target of 10° was not obtained mainly linked to the device structure and the limitations we fixed on the overall length of the device.; La génération de signaux microondes, millimétriques, voire THz par voie optique est actuellement une solution technique privilégiée pour la réalisation de systèmes de (télé)communications mobiles haut débit mais encore, les réseaux de distribution d'oscillateurs locaux et de signaux d'observation ou de radar intra- satellitaires, la distribution de signaux vidéo, la communication automobile, les systèmes de visualisation THz pour la sécurité, etc..... Nous reportons ici la réalisation et la caractérisation d'une source optique ultra-compacte en matériau semiconducteur permettant de générer deux modes optiques séparés de la fréquence que l'on désire créer au niveau de la photodétection. Cette source prend la forme d'un laser DFB bi-longueur d'onde émettant dans la gamme de longueurs d'onde autour de 1,55μm. Le composant a été fabriqué chez Alcatel- Thales III-VLab à partir d'une technologie propriétaire de laser DFB et dans le cade du projet Européen IPHOBAC. Différents objectifs avaient été fixés pour ce composant: accordabilité de l'écartement intermodal jusque 300 GHz, largeur de raie de l'ordre du MHz et divergence dans le plan horizontal et vertical de 10°. Le premier objectif a été atteint par la réalisation de deux lasers DFB dont l'écart de pas de réseau est différent de 0,3nm et par la variation des courants d'injection de chaque section. Le second a été globalement atteint par l'utilisation d'une structure active à puits quantiques, une nouvelle version du composant utilisant des boites quantiques devrait remplir complètement cet objectif. Le dernier objectif a été partiellement atteint par la conception et l'adjonction d'un adaptateur de mode en sortie de composant, la divergence obtenue est de 10°x17° (HxV). Dans le plan vertical, les 10° de divergence n'ont pas pu être obtenus principalement à cause de la structure du composant et des limitations que l'on s'était imposées sur la longueur totale de celui-ci.

In this paper we present the different type of laser diodes that are developed at Alcatel-Thales III–V Lab in order to fulfil different functions required for radio over fibre and radar systems. The first device that is presented is a directly modulated laser with a bandwidth exceeding 20 GHz and good linearity that is used for analog wideband link. This kind of device is precious for remote delivery and distribution of wide bandwidth signals with very low attenuations. The second device we will present is a passive mode-locked quantum dash lasers that has sufficiently good phase noise performances to be used as a carrier for 60 GHz wireless transmission links. The third device we will present is a dual wavelength laser. It can be used for a wide and potentially fast tuning of the frequency generated by heterodyning two optical wavelengths on a photodetector, the photodetector behaving as a photomixer.