Push-pull Polymer Integrated Mach-Zehnder Modulators

Nonlinear optical (NLO) polymers have been used to demonstrate broadband electro-optic (E-O) modulators in laboratories [1-3]. Because of the small and nondispersive dielectric constants of polymer materials, over 100 GHz modulation can be achieved with a simple integrated microstrip line circuit [3]. However, in order for these polymer modulators to be usable in commercial fiber-optic data links, several other device performance figures have to be improved. In addition to the often-discussed thermal stability issue, the halfwave voltage, optical insertion loss, optical power handling capability, and bias control stability are all of vital importance to the commercial application of polymer E-O modulators. Future polymer photonic devices must have a balanced overall performance, with a much lower cost, broader bandwidth, and competitive thermal, photochemical and bias control stability. We have reported our fabrication and testing of integrated Mach-Zehnder modulators using a double-end-crosslinked NLO polymer LD-3 [4-5]. The LD-3 based modulators have exhibited higher thermal stability, photochemical stability and low optical insertion loss compared to the E-O modulators based on the PUR-DR19 polymer [2]. However, because the LD-3 polymer has a lower E-O coefficient r33, and the corona poling schedule was not optimized, our LD-3 modulators exhibited a higher halfwave voltage which is not acceptable in most applications. In this paper, we report our new device fabrication technique that effectively reduced the halfwave voltage by one-half using an optical push-pull structure in M-Z modulators.