The invention relates to the technical field of
optical fiber sensors, and discloses a low-
coupling-loss spot size converter based on a film
lithium niobate platform, which comprises a substrate, a lower cladding and a
lithium niobate film layer located on the lower cladding, the
lithium niobate film layer comprises a first
waveguide part, a second
waveguide part, a third
waveguide part and a lens body which are connected in sequence, the lens body is located on the lower cladding, the lens layer is connected with the lens body, the first waveguide part and the second waveguide part are coated with the lens layer, and the first end of the first waveguide part is connected with the lens body; light is sequentially transmitted in the lens body, the first waveguide part, the second waveguide part and the third waveguide part, and in the
light transmission direction, the transverse sizes of the first waveguide part, the second waveguide part and the third waveguide part are sequentially increased, and the transverse size of the lens layer is sequentially reduced, so that mode field conversion between the single-mode
optical fiber and the
ridge waveguide structure is realized; the structure size is smaller, the
coupling loss is lower, and the matching between the waveguide and an
optical fiber with a larger
mode field diameter can be efficiently realized.