Hybrid Si-LiNbO3 micro-ring resonators for active microphotonic devices

A hybrid structure of Si-LiNbO3 micro-ring resonator was fabricated. Free standing single crystal LiNbO3 micro-platelets (mm long and 1 um thick) were obtained from a bulk LiNbO3 wafer by ion implantation and thermal shock. They were then transferred, positioned and bonded to Si micro-ring structure. In this hybrid structure, a large portion of the TM field is located above and below the Si waveguide. Then, the effective index of the Si waveguide can be changed by varying the refractive index of the LiNbO3 cladding layer. Theoretical calculation with finite difference method proved that the ratio between effective index change of the Si waveguide and index change of LiNbO3 cladding layer was 0.31 (Delta n(Si)/Delta n(LNO) = 0.31) for TM mode. Then, calculated Delta n(Si) was about 1x10(-4) with 3 V. The effective r coefficient of Si and tuning sensitivity were about 7.2 pm/V and 2.55 GHz/V, respectively. These values are comparable to current active Si photonics with plasma dispersion methods. In addition, high speed modulation (over 40 GHz) is possible in this hybrid structure. This demonstration of a single crystalline LiNbO3 acting as the upper cladding shows the possibility of integrating a very good EO and NLO material into the silicon-on-insulator photonics technology.