A polymer optical leaky waveguide in view of realizing an all-optical analog-to-digital converter operating over 40 Giga Samples/s – ADC Poly

Analog to digital converters (ADC) are essential components to enhance performance of numerous equipment and systems, for both civilian and military applications. As the sampling rate of electronic ADCs will be particularly capped by sampling signal jitter (100 fs to the state of the art), optical approaches are studied to take advantage of much lower jitter obtained using laser pulses (fs or less).
This ADC Poly proposal aims to demonstrate the feasibility of an innovative solution based on the use of an optical deflector, realized by using integrated optics technology. The deflector is the central component of an all-optical ADC that, ultimately, could be capable to sample at a very high rate of 40 Giga samples per second with a resolution of 6 bits or more, which could be then one of the best performances obtained with photonic ADCs. The demonstrator aimed in this project will consist of a deflector, based on an optical leaky waveguide made of electro-optic polymers (EO), capable of addressing a coding mask with 8 resolved lines (3 bits). The leakage angle is controlled by the voltage to be digitized which is applied to the driving electrodes.
Active integrated optical components based on EO polymers, modulators for example, usually operate with a microstrip electrode on the EO polymer guide, ensuring an optimal overlap integral between optical and electrical waves. In the case of the deflector, the light leaks from the top of the optical waveguide, making this topology inoperative, so the driving electrode must be located laterally, on both sides of the optical waveguide, and additionally buried, to optimize this overlap. The first challenge of the project is therefore to develop a new technological fabrication process, more complex than those commonly used and to validate the behavior of the EO structure. The buried and laterally placed poling electrodes requested by our design do not allow using the usual poling scheme for chromophores. So, a microwave filter solution is proposed to enable both DC and microwave operation of electrodes. The leaky optical field, distributed along the waveguide, must be collected and focused in the detection plane. The second challenge is then to design an appropriate superstrate over the leaky waveguide as well as micro-optical elements to collect and focus the leaky lightwave.
A task is specifically dedicated to the integrated design of the whole structure, optical and microwave parts, of the deflector, as well as the micro-optical components aiming collecting the leakage beam. The fabrication task is divided into several stages. At first, passive waveguides will be made, then phase modulators with the driving electrodes at the same level as the optical waveguide. The characterization of these intermediate components allows to determine the parameters requested for the optimization of the leak waveguide design for the deflector.