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Lithium niobate on insulator (LNOI) has emerged as a promising platform for photonic integrated circuits, with a fast‐growing toolbox of components. This paper proposes, designs, and experimentally demonstrates compact subwavelength grating (SWG) waveguides on an LNOI platform for on‐chip mode and polarization manipulation. To overcome the limitation of waveguide fabrication, the SWGs are designed and formed on a silicon nitride thin film deposited onto the surface of LNOI chip. As proof‐of‐concept devices, the SWG‐based spatial mode filters (including a TE1‐mode‐pass filter and a TE2‐mode‐pass filter) and a TM‐pass polarizer are fabricated successfully on the same chip, with the device lengths of only ≈50 μm. The measured insertion losses for the devices are lower than 3.1 dB, with high extinction ratio larger than 30 dB, at a wavelength of 1550 nm. The proposed and demonstrated SWGs can serve as important building blocks in a series of mode and polarization handling devices for LNOI integrated photonics. [ABSTRACT FROM AUTHOR]

The theoretical analysis and experimental demonstration of a waveguide resonator are presented based on bound states in the continuum in an integrated photonic chip platform. The continuum has the form of a collimated beam of light which is confined vertically in a transverse electric (TE) mode of a silicon slab. The bound state is a discrete transverse‐magnetic (TM)‐like mode of a ridge on the silicon slab. The coupling between the slab and ridge modes results in a single sharp resonance at the wavelength where they phase match. This phenomenon is experimentally demonstrated on a silicon photonic chip using foundry‐compatible parameters and it is interfaced on‐chip to standard single‐mode silicon nanowire waveguides. The fabricated chip exhibits a single sharp resonance near 1550 nm with a line width of a few nanometers, an extinction ratio of 25 dB, and a thermal stability of 19.5 pm °C−1. It is believed that the demonstration of a resonance operating near a bound state in the continuum realized using guided wave components will form the basis of a new approach to on‐chip wavelength filtering and sensing applications. [ABSTRACT FROM AUTHOR]