Incoherent Optical Frequency Domain Reflectometry Using Balanced Frequency-Shifted Interferometry in a Downconverted Phase-Modulated Link

An incoherent optical frequency domain reflectometer (I-OFDR) has been implemented using frequency-shifted interferometry in a 9-GHz bandwidth. The system is based on low-bandwidth direct detection and balanced bidirectional phase modulation, which provides negligible amplitude and phase imbalance in frequency up and down-conversion. The setup is fed with dithered laser light to reduce coherent effects, and the intensity detected after the slope of a fiber Bragg grating. The reflectometer shows a dynamic range of 25 dB, a sensitivity <;-55 dB, and a resolution of 2.3 cm in fiber. These results show the feasibility of this type of I-OFDR systems for the interrogation of quasi-distributed, high-density optical fiber sensor networks.