Electrically tunable dual polarization states of light using lithium niobate-based nanograting

Tuning polarization states of light electrically has unique advantages in the integration of optoelectronic devices. Here, a lithium niobate-based nanograting is proposed to dynamically tune the polarization state of both the reflected and transmitted lights simultaneously in the near-infrared range. By judiciously designing the nanograting, a quasi-bound state in the continuum (qBIC) is excited under the excitation of an obliquely incident plane wave. The excited mode with a high quality-factor and enhanced local electric field can respond to a refractive index change in nanograting structures as small as 10⁻⁴ level, which can be generated with a low external voltage via the electro-optic effect. As a result, both the polarization states of reflected and transmitted lights can be dynamically tuned from a right circular polarization to a linear polarization state. The proposed lithium niobate-based nanograting for tuning dual polarization states of light with a qBIC mode suggests a promising electrical scheme for achieving high speed optoelectronic devices.