Single-fiber spectroscopy system using unmodified clinical laser fibers for tissue optical property recovery

Accurate extraction of tissue optical properties is essential for many light-based diagnostic and therapeutic applications, yet clinical translation remains limited by cost, complexity, and probe-specific models. Single-fiber reflectance (SFR) spectroscopy offers a simple and low-cost alternative, but previous implementations relied on customized angle-polished fibers. We present an SFR spectroscopy system that employs an unmodified, FDA-approved clinical optical fiber for quantitative optical property extraction. A semi-empirical photon path-length model was used to recover the absorption coefficient μ_a (λ) and reduced scattering coefficient μ_s' (λ) from tissue-mimicking phantoms containing methylene blue (MB) as the absorber and Intralipid-20% as the scatterer. Measurements acquired using three independent fibers demonstrated accurate optical property recovery and strong model generalizability. Across all fibers, MB concentration was recovered with an RMSE of 0.6-0.8 μM (MAPE = 30-37%, p = 0.94 between fibers), while μ_s' (665) was recovered with an RMSE of 1.1-1.7 1/cm (MAPE = 4.5-9.6%, p = 0.69 between fibers). These results demonstrate the potential of SFR spectroscopy using a standard clinical optical fiber as a scalable and clinically deployable tool for tissue optical property estimation.