Graphene-coupled silica microtoroid for optical polarization controlling and electro-optic modulation

Whispering gallery (WG) microcavities have been applied for a variety of optoelectronic devices due to their extraordinary characteristics of high quality factor (Q) and small mode volume, crucial to accurately tune the quality factor for realizing the high-speed optical modulation and short pulse laser. In this paper, we propose and theoretically analyze a hybrid, graphene-coupled silica microtoroid device and realize optical polarization control and electro-optic modulation due to the polarization-dependent absorption of graphene on the different cavity WG modes. By changing the gap distance between graphene and the microtoroid, the influence of graphene absorption on the different polarization modes is diverse due to the different electric field distributions of modes in the microtoroid, therefore demonstrating the different resonant wavelength shifts and quality factor variations. The transmission depth variation of the second-order transverse electric mode upon changing the gap distance between graphene and microtoroid is 4.5 dB more than that of the second-order transverse magnetic mode, verifying that the polarization control is because of the polarization-dependent absorption of graphene. Furthermore, by applying the voltage on the graphene flakes, electro-optic modulation with a high contrast of 21.7 dB is demonstrated based on this hybrid graphene-coupled silica microtoroid. (C) 2021 Optical Society of America

Automated summary

In this paper, a hybrid graphene-coupled silica microtoroid device is proposed and analyzed, demonstrating optical polarization control and electro-optic modulation. The influence of graphene absorption on different polarization modes is diverse due to the different electric field distributions of modes in the microtoroid, leading to different resonant wavelength shifts and quality factor variations. By applying voltage on the graphene flakes, electro-optic modulation with high contrast is achieved based on this hybrid graphene-coupled silica microtoroid.