EO Polymer-based Bias-Free Highly-Linear Domain Inverted Directional Coupler

Omega Optics and the University of Texas at Austin propose an innovative approach to build a high speed (40GHz), highly linear electro-optic (E-O) modulator (spurious free dynamic range (SFDR)>121dB/Hz) based on domain inverted Y-fed directional coupler using advanced E-O polymer materials developed by DARPA MORPH program. The proposed structure with inverted domains, which has an opposite poling direction with respect to each other, can potentially eliminate the nonlinear response of the modulator due to the fact that the higher order spurious signals are cancelled out in each adjacent domain. The bandwidth of the proposed linear modulator can be enhanced to 40GHz using a traveling wave electrode, which will surpass any state-of-the-art linearization technologies. Furthermore, the symmetric waveguide structure of the Y-fed directional coupler will be intrinsically bias-free providing the linear modulator at 3-dB point regardless of the ambient temperature. This feature ensures the linear modulator insensitive over a large temperature operation range with minimized harmonic distortion. In the Phase I program, we have laid a solid foundation by demonstrating necessary fabrication processes and prototype linear modulators with lumped electrodes. These progresses include high efficiency E-O poling (r33=56pm/V in active EO device) on AJLS102/APC, reactive ion etching (RIE) and high precision photolithography. A distortion suppression of 65dB on a two domain modulator is also demonstrated. The advanced E-O polymers developed through the sponsorship of the DARPA MORPH program, will be fine-tuned to provide remarkable features to our proposed modulator in terms of lower driving voltage, lower insertion loss and better noise figure. In the Phase II program, we will also conduct in-depth investigation of device physics such as the interaction between the traveling wave electrode and the optical waveguides. The outcome of such studies will assist us to enhance the performance of the device in microwave and millimeter wave frequencies. Device engineering and packaging issues will also be addressed to ensure the demonstration of a fully packaged polymer linear modulator. Application of such a linear modulator in RF photonic transmission system will be explored as well, with emphasis on power margin and noise figure of the entire system.