Abstract: An integrated biplane optical sensing core chip has a non-linear optical substrate, a first waveguide structure, a second waveguide structure and a waveguide coupled fiber. The non-linear optical substrate, the first waveguide structure and the second waveguide structure are made of the same nonlinear optical material. The first waveguide structure is connected to the second waveguide structure via a waveguide coupled fiber is outside and independent to the non-linear optical substrate. Therefore, the first waveguide structure and the second waveguide structure can overlap in the vertical direction, and can be set close to each other in the horizontal and vertical directions, so the integrated biplane optical sensing core chip can be miniaturized and can meet reciprocity. The integrated biplane optical sensing core chip is suitable for an optical fiber sensor, and the optical fiber sensor can be a fiber-optic gyroscope or a fiber-optic current sensor.