Patrick Labbe

New electro-optic modulator based on polymer waveguide and loop structure

Photonics devices based on polymer optical waveguides are widely studied now and some commercial announcements have already been published. Nevertheless they are not been followed by really available products and it is still necessary to improve such kind of devices. The aim of this paper is to present a new structure for a polymer electro-optic modulator. The electro-optic polymer material is PMMA-DR1. This electro-optic polymer is well known by its high frequency bandwidth of modulation and its functional robustness. Nevertheless, its half-wave voltage remains relatively high, that is why a new configuration is proposed decreasing the half-wave voltage. The new device, which is fully described, is based on the classical Mach-Zehnder optical modulator structure, to which a completely new loop structure is added. Thus the optical waveguides are designed in order to increase the active length and so reducing the half-wave voltage. Otherwise the device is designed for a complete planar realization. The RF strip lines are also designed according to the loop structure with 50Ω characteristic impedance. A device has been realized and its optical are checked at 1.55μm wavelength. Electronic characteristics should be determined by the way of spectrum and network analyzers at frequencies up to 2GHz. All the measurements should show the feasibility and efficiency of the new structure.

Stabilization of the bias point of an electro-optic modulator based on polymer material

Electro-optic modulators based on polymer material are very promising devices because of the expected very high modulation rate and low cost fabrication process. These modulators are mainly based on Mach-Zehnder structure, but phase modulators associated to polarizer and analyzer can also be used. Until now there are no real devices commercially available. One of the problems concerns the temperature stability. Because of the optical power of the laser beam and the absorption of the polymer material used for the optical waveguide there is a slight temperature evolution of the modulator leading to a change in the bias point of the modulator and then to a slow drift of the bias point leading to a dissymmetry of the optical modulated signal. This evolution can be compensated by adding a small DC value to the voltage applied to the electrodes. A control loop has been designed and tested in order to stabilize the bias point of the modulator. This loop acts as a synchronous detection with a low frequency modulation at 500 Hz and a practical detection at 1 kHz. By this way it is in fact the first order derivative of the signal which is stabilized leading to the signal symmetry control. This low frequency signal can be added without any problem to the informative modulating signal. By using this control loop the modulator can be used for a very longer time than without it. Of course a temperature control of the modulator by a Peltier effect module should also be implemented for a better and complete stabilization.

Design of a new photomixer based on electro-optic polymer

A new photomixer based on the nonlinear behavior of an electro-optic polymer material is proposed here. The microwave frequency is generated by mixing two optical signal waves propagating simultaneously inside an optical waveguide made of the crosslinked PMMA-DR1 electro-optic copolymer; the cladding layers are made of NOA material and the microwave signal is collected on a microstrip line. By matching the velocities of the microwave signal and of the optical signals it is possible to create constructive mixing in a traveling-wave configuration at more than 60 GHz. If one of the optical waves is modulated by an informative signal, the microwave signal will infer the modulation

Fractal-spiral antenna for UWB standard

We claim a new approach for UWB antennas taking advantages from the classical and the fractal techniques by applying a log spiral transformation to a fractal design. Stricto senso, this antenna loose its mathematical fractal properties but keeps the physical advantages of a real fractal pattern. A concrete realization of this concept on a twisted Sierpinsky carpet is presented in this paper. To cancel potential additional resonance deserving UWB pulse system, we also propose to use different iterations of the pattern or different fractal initiator for each arm of this antenna. Based upon the simulation of a dipolar twisted Sierpinski carpet, several advantages related to this concept have been emphasized and are detailed here.