Development of quasi-passive optical substrates for photonic packaging

While the silicon micro-bench with purely passive locational features was an attempt at PCB-like integration for photonic applications, it failed to provide the high tolerance alignment required for efficient light coupling between devices and/or fibers. To optimize the final alignment without the introduction of on-board active actuators or external high-precision manipulators, we have developed and demonstrated a low-cost, micro-machined optical bench with quasi-passive locational features capable of sub-micron alignment optimization. The concept capitalizes on inherent residual tensile stresses produced during the stoichiometric Si³N⁴ thin-film deposition process. By selectively trimming stress element on either side of a suspended platform, the equilibrium position can be biased to one side or another, enabling high resolution relative motion between the suspended platform and the base. We have demonstrated, as a first attempt, high-efficiency fiber-to-fiber alignment using this concept.