Design of thin-film lithium niobate structure for integrated filtering and sensing applications

Lithium Niobate (LN) is a premium material with strong electro-optic coefficient and low-loss transparency window covering from visible to mid-infrared wavelength regions. Thin-film LN on Insulator (LNOI) is an emerging integrated photonic platform with excellent optical properties of LN and large refractive index contrast, which has attracted considerable research interests in the field of integrated optics. In this paper, we present an integrated structure on LNOI platform, which could serve as an electro-optic tuning filter with ultra-narrow bandwidth and large wavelength-tuning range. Moreover, the wavelength-tuning sensitivity reaches ~37.25 pm/V, which is about 8 times higher than that of the LN-based tunable filter proposed in our previous study. In addition, a method to expose this structure under external applied for sensing applications is proposed. Q-factor of our proposed sensor structure reaches 10⁶ or even higher. When the refractive index of sensing materials changes by an order of 10^-4, this sensor still exhibits observable transmission spectral responses. Structural flexibility and ease of integration make the proposed sensor a promising candidate for potential applications in the fields of optical communications, biological and chemical sensing.