Sub-wavelength grating structure end face coupler formed based on single etching of thin film lithium niobate

The invention is suitable for the technical field of optical communication, and discloses a sub-wavelength grating structure end face coupler formed based on single etching of thin film lithium niobate, which comprises a quartz substrate, chemical vapor deposition silicon dioxide, a thin film lithium niobate bottom plate, a thin film lithium niobate ridge waveguide formed by etching and a chemical vapor deposition silicon dioxide upper cladding, the thin-film lithium niobate ridge waveguide formed by etching comprises an equal-width same-period sub-wavelength grating area, a sub-wavelength grating area with the width gradually changing in an inverted-cone shape, a sub-wavelength grating filling buffer area and an inverted-cone-shaped waveguide in the buffer area. According to the invention, a sub-wavelength grating structure is introduced, and the mode field conversion is completed by changing the waveguide refractive index and matching a symmetrical guiding mode and a thin-film lithium niobate ridge waveguid