Ghost-peak-based estimation of modulation amplitude in optical correlation-domain reflectometry

Reliable and efficient evaluation of the modulation amplitude is essential for achieving accurate spatial resolution in optical correlation-domain reflectometry (OCDR). Conventional measurement methods, such as those using optical or electrical spectrum analyzers, require additional equipment or independent setups, which increase system complexity and cost. In this study, we propose a simple and accurate method to estimate the modulation amplitude directly within the OCDR configuration by exploiting ghost peaks that appear when a small frequency shift is introduced in the optical path. The ghost-peak positions are analytically related to the modulation amplitude through a derived expression, enabling quantitative estimation without auxiliary instruments or analyzer setting changes. Experiments confirm that the estimated modulation amplitudes agree well with the reference values obtained by heterodyne detection, with errors below 1.4% across all tested modulation frequencies. Moreover, the approximate analytical formula achieves a deviation of less than 0.015%. These results demonstrate that the proposed method provides a compact and self-contained approach for evaluating the modulation amplitude in OCDR and may serve as a foundation for more stable and easily calibrated implementations in future correlation-domain reflectometry.