Numerical investigation on the effect of extra-feedback target position on the fringe visibility in a dual optical...

Optical feedback interferometry (OFI) exhibits good potential in laboratory and engineering applications as an interferometric measurement technology with unique structure. One challenge of this technology is that the OFI signals may be feeble, and the OFI fringe visibility is low when the optical feedback strength is weak. It has been demonstrated that the OFI fringe amplitude can be enhanced by introducing an extra-feedback into an OFI system. At the same time, it has been confirmed that the position of the extra-feedback target must be strictly controlled as it will directly affect the fringe amplitude. However, the details of how the extra-feedback positions affect the OFI fringe amplitude, and its underpinning mechanism still needs to be unveiled. In this paper, we aim to theoretically investigate the influence of the extra-feedback target position on the OFI fringe amplitude and explore the underpinning mechanism. Firstly, a simplified analytical model for characterizing a dual-channel optical feedback interferometry (DOFI) system in steady state was derived from the Lang-Kobayashi equations. A method of solving the analytical model was developed to further explore the nature of a DOFI system. On top of that, the influence of the extra-feedback target position on the OFI fringe amplitude and its underpinning mechanism was explored, based on which the criteria for how to achieve large fringe amplitudes were summarized. The obtained results provide helpful guidance in constructing a DOFI system with enhanced fringe visibility, and further promote the practical applications of OFI technology.