There is an urgent need for high-speed atomic force microscopy (AFM) systems, and chip-AFM on an integrated optical waveguide provides a perfect solution. A differential splitter of double waveguides is introduced as a readout method of an integrated optical waveguide AFM to overcome the non-linear response of a conventional optical waveguide AFM. Results show that an optical waveguide AFM with a 190 nm width and 1  μm height nano-tip shows a good monotonic dependence on the cantilever deflection within a range of   ±  0.4  μm using a differential splitter readout method.