Distributed reflection-spectrum analysis of photonic links using optical frequency domain reflectometry

The reflection spectrum of a photonic device or photonic link is intrinsically linked to its transmission characteristics, including bandwidth, coupling efficiency, and noise performance. Accurate measurement and analysis of this spectrum therefore constitute an essential foundation for evaluating photonic-link performance and for supporting the design and optimization of complex optical systems. However, conventional reflection-spectrum measurement methods provide only the overall spectral response of an entire photonic link and cannot resolve the local spectral characteristics of individual components embedded within complex architectures. To address this limitation, we propose a scheme of distributed reflection-spectrum analysis (DRSA) based on optical frequency-domain reflectometry (OFDR), enabling spatially resolved measurement and characterization of the reflection spectra of photonic devices and photonic links. The method integrates tunable-laser-based spectral analysis with OFDR-based distributed sensing technology. By extracting frequency components associated with a selected spatial region through digital filtering and reconstructing its spectral response using an amplitude-detection algorithm, the technique retrieves the local reflection spectrum with high fidelity. In addition, an auxiliary interferometer is employed to suppress the influence of laser frequency-sweeping nonlinearity and output-power fluctuations, ensuring high wavelength resolution and measurement accuracy. Using the proposed OFDR approach, we accurately characterize the DRSA of planar waveguide Bragg gratings and fiber Bragg gratings, experimentally verifying the feasibility and effectiveness of the method. The results show that with a wavelength-scanning range of 130nm, the FDR-based DRSA achieves a wavelength resolution of 0.1pm, an absolute wavelength accuracy of ±3pm, while maintaining a distributed reflectivity-measurement range exceeding 30m with a spatial resolution better than 10μm. These capabilities highlight the significant potential of OFDR-based DRSA for applications in fiber-link diagnostics, integrated-photonic-circuit design, fiber-optic sensing, and free-space optical detection.