Advances on all-optical ADCs based on a polymer leaky waveguide deflector
Résumé
Design challenges and performance optimization of an all-optical analog-to-digital converter (AOADC) as well as the first realization results will be presented. The presentation addresses both microwave and optical design of a leaky waveguide optical deflector using electro-optic (E-O) polymer, the central element of the AOADC. The E-O polymer deflector converts magnitude variation of the applied RF voltage into variation of deflection angle of the leaky optical pulses from a mode-locked laser. This variation of deflection angle as result of the applied RF signal to digitize is then quantized using optical windows followed by an array of high-speed photodetectors.
We optimized the leakage coefficient of the optical waveguide and its physical length to achieve the best trade-off between bandwidth and the deflected optical beam resolution, by improving the phase velocity matching between lightwave and microwave on the one hand and using pre-emphasis technique to compensate for the RF signal attenuation on the other hand. In addition, for ease of access from both optical and RF perspective, a via-hole less broad bandwidth transition is designed between coplanar pads and coupled microstrip (CPW-CMS) driving electrodes. Very recently, DC contacts were proposed to be added to driving electrodes, allowing electrical polarization and regenerating chromophores orientations (poling).
With the best reported E-O coefficient of 350 pm/V, the designed E-O deflector should allow an AOADC operating over 44 GS/s with an estimated resolution of 6.5 bits on RF signals with Nyquist bandwidth of 22 GHz. The overall DC power consumption of all components used in this AOADC is of order of 4 W and is dominated by power consumption in the power amplifier to generate a 20 V RF voltage in 50 system. A higher sampling rate can be achieved at similar bits of resolution by interleaving a number of this elementary AOADC at the expense of a higher power consumption.