Highly Reliable Silica-LiNbO3 Hybrid Modulator Using Heterogeneous Material Integration Technology

Silica-LiNbO3 (LN) hybrid modulators have a hybrid configuration of versatile passive silica-based planar lightwave circuits (PLCs) and simple LN phase modulators arrays. By combining the advantages the two components, these hybrid modulators offer large-scale, highly-functionality modulators with low losses for advanced modulation formats. However, the reliability evaluation necessary to implement them in real transmissions has not been reported yet. In terms of reliability characteristics, there are issues originating from the difference in thermal expansion coefficients between silica PLC and LN. To resolve these issues, we propose design guidelines for hybrid modulators to mitigate the degradation induced by the thermal expansion difference. We fabricated several tens of silica-LN dual polarization quadrature phase shift keying (DP-QPSK) modulators based on the design guidelines and evaluated their reliability. The experiment results show that the modules have no degradation after a reliability test based on GR-468, which confirms the validity of the design guidelines for highly reliable silica-LN hybrid modulators. We can apply the guidelines for hybrid modules that realize heterogeneous device integration using materials with different coefficients of thermal expansion.