The invention provides a heterogeneous integrated sub-
wavelength structure end face coupler adaptive to a single-mode
optical fiber and a preparation method of the heterogeneous integrated sub-
wavelength structure end face coupler, and relates to the technical field of
integrated optics. The coupler comprises a substrate, an insulating layer, a
waveguide layer and a cladding from bottom to top. The
waveguide layer comprises an upper
lithium niobate
ridge waveguide and a lower
lithium niobate
ridge waveguide, the lower waveguide is wider than the upper waveguide, and the upper waveguide is used for connecting an external waveguide; the heterogeneous integrated
coupling region comprises a
silicon nitride strip conical waveguide which forms
directional coupling with the lower-layer
lithium niobate waveguide, so that adiabatic transfer of a
light field is realized; the sub-
wavelength grating regulation and control region sequentially comprises a
silicon nitride tapered waveguide and sub-wavelength
grating combination section, a width gradually-changing
grating section and an equal-width buffer grating section. The whole structure is symmetrical about the central axis. Through the multi-section adiabatic transformation and heterogeneous integration design, efficient expansion of a mode field is achieved, the
coupling efficiency with a single-mode
fiber is improved, and the advantages of being insensitive to polarization, good in process compatibility and suitable for high-density integration are achieved.