We present an Nb₂O₅-based grating coupler that employs multiple Nb₂O₅ / SiO₂ layers to improve the optical input/output power efficiency of a scanning differential laser-Doppler integrated probe for two-dimensional cross-sectional velocity distribution measurements. The multiple Nb₂O₅ / SiO₂ layers are designed for both the transmitting grating coupler and the receiving grating coupler. To demonstrate the effect of the designed multiple layers, the field distribution around the grating coupler is simulated as a feasibility study of the concept. The results indicated that the input/output power at the grating coupler can be improved using multiple Nb₂O₅ / SiO₂ layers over the input/output angle of 0 to 20 deg and the wavelength of 1530 to 1570 nm. The increase of the input/output power and the focusing from the transmitting grating coupler were confirmed by the simulation using the finite-difference time-domain method and beam propagation method.