A waveguide core layer (100), a spot-size converter (400), a silicon photonic device and an optical communication device. The waveguide core layer (100) comprises a first waveguide region (110) and a second waveguide region (120) connected in sequence along a first direction, and the first waveguide region (110) and the second waveguide region (120) both extend along the first direction. One end of the first waveguide region (110) facing away from the second waveguide region (120) is used to be connected to a silicon photonic chip (200). One end of the second waveguide region (120) facing away from the first waveguide region (110) is used to be connected to an optical fiber (300). The size of the first waveguide region (110) along a second direction increases from the end facing away from the second waveguide region (120) to the end close to the second waveguide region (120). The refractive index of the second waveguide region (120) decreases from the end close to the first waveguide region (110) to the end facing away from the first waveguide region (110), so that light can be converted from a small spot size into a large spot size matching the optical fiber (300) after passing through the first waveguide region (110) and the second waveguide region (120), ensuring that the waveguide core layer (100) and the silicon photonic chip (200) are accurately docked, improving the channel uniformity of the silicon photonic device and the optical communication device, and having a low production cost as the waveguide core layer (100) can be directly machined and molded without the need of fusion.
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