A phase-stable transmission system is proposed based on high accuracy and fast measurement of optical transfer delay(OTD). Only 4 frequency points are required to solve the optical transfer delay, which can greatly reduce the time spent on continuous multi-frequency sweeping during the phase-derived process to enhance the robustness of an active phase stabilization system. The system achieved an OTD measurement accuracy of ±0.08 ps in the proof-of-concept experiment. We also measured the link delay stability of the two 2 km optical fiber links with and without phase stabilization for 2 hours. During the measurement, the fluctuation between the phase-stable link delay and the set delay was within ±0.18 ps, while the delay difference without phase stabilization was over 200 ps.
High-accuracy optical fiber transfer delay (OFTD) measurement is critical in the application of distributed optical sensing, optically controlled phased array, distributed coherent aperture radar, etc. There is always a need to measure multi-path OFTD in these scenarios. This paper proposes a fast multi-path OFTD measurement method based on compressed sensing (CS) technology with high spatial resolution. A sweep microwave signal with sparse frequency modulates an incoherent light microwave to generate the probe light. The signal from the fiber under test (FUT) with multiple delays is received by a photodetector and further reconstructed based on the compressed sensing technology to calculate the delays of the FUT. In the proof-of-concept experiment, the required amount of data to be collected and processed is only about 20%-30% of that needed in traditional approaches. The experimental results show that the time domain response of two optical links with a difference of 49 ps has been successfully obtained
A high-precision multinode GNSS-over-fiber three-dimensional (3D) baseline measurement system has been proposed for extensive structure health monitoring, distributed coherent radar, etc. In the proposed system, satellite signals received on different antennas are transmitted to the GNSS receiver based on wavelength-division multiplexing, while a phase-derived ranging technique based on time-division multiplexing is also applied to measure multi-path delay from different nodes in the same transmission optical fiber. The delay errors are compensated to eliminate hardware latency errors, achieving a 3D baseline with higher precision. The proposed method features high accuracy and long distance and satisfies the need for real-time monitoring of the transmission status of multiple GNSS signals. A proof-of-concept experiment is set up and shows that this system can measure the 3D baseline vectors of more than three nodes within a range of 10 km while improving the accuracy of the vertical components to below 4 mm.
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