An optical cavity based biosensor using a differential detection method has been proposed to provide a novel approach to point-of-care diagnostics. A two-laser based optical cavity based sensor system is designed and experimentally demonstrated. While the calculated differential value of the two-laser system shows larger responsivity compared to individual wavelengths, the dynamic range of the system is rather small. Because of that, it turned out its fabrication tolerance is also small based on the simulation. We employed a three-laser system and redesigned the optical cavity to increase the dynamic range and improve the fabrication tolerance. In this presentation, we report the measurement results of the three-laser system for the first time. This system increases the dynamic range threefold by a chaining action. Because of this large dynamic range, this three-laser system is anticipated to have a larger fabrication tolerance.