Two-axis MEMS positioner for waveguide alignment in silicon nitride photonic integrated circuits

Abstract

Alignment is critical for efficient integration of photonic integrated circuits (PICs), and microelectromechanical systems (MEMS) actuators have shown potential to tackle this issue. In this work, we report MEMS positioning actuators designed with the ultimate goal of aligning silicon nitride (SiN) waveguides either to different outputs within a SiN chip or to active chips, such as lasers and semiconductor optical amplifiers. For the proof-of-concept, suspended SiN waveguides implemented on a silicon-on-insulator wafer were displaced horizontally in the direction of light propagation to close an initial gap of 6.92 µm and couple the light to fixed output waveguides located on a static section of the chip. With the gap closed, the suspended waveguides showed ∼ 345 nm out-of-plane misalignment with respect to the fixed waveguides. The suspended waveguides can be displaced laterally by more than ±2 µm. When the waveguides are aligned and the gap closed, an average loss of −1.6 ± 0.06 dB was achieved, whereas when the gap is closed with a ± 2 µm lateral displacement, a maximum average loss of ∼ −19.00 ± 0.62 dB was obtained. The performance of this positioner does not only pave the way for active chip alignment, but it could also be considered for optical switching applications.