When a part of light emitted by a laser is back-reflected or back-scattered from an external target and re-enters the laser cavity, both the laser intensity and its wavelength can be modulated. This is so-called self-mixing effect (SME), the optical feedback interferometry (OFI) utilizes such effect in an LD developed various applications. In this paper, we use a dualcavity OFI system that operating in period one state, the laser intensity from this system exhibits an oscillation with its amplitude modulated by a traditional single cavity OFI signal. The dual-cavity OFI system has the same measurement resolution as the single cavity which is half laser wavelength. This paper developed a method to improve the resolution by using fringe subdivision. Our simulation result shows that this method can achieve subnanometer resolution.