Research on high-precision optical fiber length calibration system for optical frequency domain reflectometer

Optical Frequency Domain Reflectometers (OFDR) has been widely used in various fields due to their high spatial resolution and precision. However, the accuracy and traceability of their length measurement results highly depend on effective calibration methods. Temperature interference is a key factor that causes significant measurement deviations in OFDR-based fiber length calibration. To address this issue, this study developed a high-precision temperature-controlled fiber length calibration system based on Thermoelectric Coolers (TEC). A heating/cooling device was designed, where the standard fiber was uniformly and loosely wound. The fiber was then connected to the OFDR under calibration to obtain real-time length data. A PID control algorithm was adopted for temperature regulation, enabling precise temperature control and data recording at multiple temperature points. Experiments were conducted using a 10 m singlemode fiber, with temperature test points set at 5℃ intervals within the range of 20℃~50℃. After maintaining a constant temperature for 30 minutes, the average value of 10 length measurements by the OFDR was recorded. The results show that the system achieves a temperature control accuracy of ±0.001℃, and the fiber length changes linearly with temperature—an increase of 4.2×10⁻⁵ m per 1℃ rise. This research provides a reliable method and experimental basis for establishing metrological standards for OFDR length measurement, and lays a theoretical and technical foundation for precise fiber length calibration in complex temperature environments.