ABSTRACT
In this paper, we present a real-time measurement technology for the free spectral range (FSR) of an ultrahigh-aspect-ratio silicon nitride (Si3N4) waveguide ring resonator (WRR). Two different correlated resonant modes were tracked by two optical single-sideband frequency-shifted lights to eliminate interference noise in the Pound-Drever-Hall error signals. A relative precision of 0.1474â ppm was achieved for a 35 mm WRR with FSR = 1,844,944.5 kHz and finesse (F) = 13.2. Furthermore, a cross-correlation of 0.913 between FSR-calculated and thermistor-measured temperatures indicated a high correlation between the real-time FSR and room temperature. We believe this technology is currently the best way to realize low-finesse (F < 50) real-time FSR measurements in the GHz range.
ABSTRACT
A new technology for Brillouin optical correlation domain analysis (BOCDA) based on chaotic laser is proposed, analyzed and demonstrated. The numerical simulation shows that the stimulated acoustic field has the secondary spurious peaks, which are the result of a weak amplitude autocorrelation of the chaotic signal occurring at the delay time of the external cavity, i.e., time delay signature (TDS). These secondary spurious peaks deteriorate the Brillouin gain spectrum and decrease the performance of the chaotic BOCDA system. The effect of the injection current and feedback strength on the TDS suppression is theoretically analyzed. By optimizing the two free parameters, chaotic laser sources operate in a TDS suppression region. Ultimately, a 3.2 km long single-mode fiber with a spatial resolution of 7.4 cm is experimentally demonstrated. The uncertainty of the local Brillouin frequency shift is ± 1.2 MHz.
ABSTRACT
We propose and experimentally demonstrate a chaotic Brillouin optical correlation-domain analysis system for distributed fiber sensing. The utilization of a chaotic laser with a low coherence state ensures high spatial resolution. The experimental results demonstrate a 4 cm spatial resolution over a 906 m measurement range. The uncertainty in the measurement of the local Brillouin frequency shift is ±1.2 MHz. The analysis of the expected spatial resolution and signal-to-noise ratio is also given.