A fiber-optic acoustic pressure sensor based on a large-area nanolayer silver diaphragm is demonstrated with a high dynamic pressure sensitivity of $160\mathrm{nm}/\mathrm{Pa}$ at 4 kHz frequency. The sensor exhibits a noise limited detectable pressure level of $14.5\mathrm{\mu Pa}/{\mathrm{Hz}}^{1/2}$. Its high dynamic pressure sensitivity and simple fabrication process make it an attractive tool for acoustic sensing and photo-acoustic spectroscopy.

A phase-shifted demodulation technique with a 3 × 3 coupler and ellipse fitting algorithm (EFA) for the interrogation of interferometric sensors is proposed. To reduce the error of the EFA as to measure small phase signals, additional phase modulation is introduced. The additional modulation provides a walk of the operating point along the Lissajous ellipse large enough to permit calculation of the ellipse parameters at every moment. Experimental result shows that this technique demonstrates high accuracy and stability for measuring small phase signals. The setting of this technology expands the application of the EFA in fiber-optic phase demodulation technology.

Orbital angular momentum (OAM) is an important property of vortex light, which provides a valuable tool to manipulate the light-matter interaction in the study of classical and quantum optics. Here we propose a scheme to generate vortex light fields via four-wave mixing (FWM) in asymmetric semiconductor quantum wells. By tailoring the probe-field and control-field detunings, we can effectively manipulate the helical phase and intensity of the FWM field. Particularly, when probe field and control field have identical detuning, we find that both the absorption and phase twist of the generated FWM field are significantly suppressed. Consequently, the highly efficient vortex FWM is realized, where the maximum conversion efficiency reaches around 50%. Our study provides a tool to transfer vortex wavefronts from input to output fields in an efficient way, which may find potential applications in solid-state quantum optics and quantum information processing.

An ameliorated phase generated carrier demodulation algorithm based on a reference interferometer is proposed. It is theoretically analyzed, numerically simulated, and experimentally verified in this paper. The method of matching the amplitude of the quadrature signal in the reference interferometer algorithm eliminates the harmonic distortion caused by modulation depth fluctuations, suppresses system noise, and improves system stability. In experiments, where the sensed signal amplitude is 0.68 rad, the frequency is 1 kHz, and the modulation depth ranges from 1.5 to 3.5 rad, the ameliorated algorithm has SINAD that reaches 24.5 dB, which is an average improvement of 7.9 dB over the PGC-DCM algorithm based on a reference interferometer and an average improvement of 3 dB over the PGC-Arctan algorithm based on a reference interferometer. The ameliorated algorithm achieves a THD of 0.451%, which consistently maintains the best level of the traditional PGC algorithm based on a reference interferometer. The method provides an effective reference for signal processing in practical applications of fiber-optic sensors.

A dual-optimized adaptive Kalman filtering (DO-AKF) algorithm based on back propagation (BP) neural network and variance compensation was developed for high-sensitivity trace gas detection in laser spectroscopy. The BP neural network was used to optimize the Kalman filter (KF) parameters. Variance compensation was introduced to track the state of the system and to eliminate the variations in the parameters of dynamic systems. The proposed DO-AKF algorithm showed the best performance compared with the traditional multi-signal average, extended KF, unscented KF, KF optimized by BP neural network (BP-KF) and KF optimized by variance compensation (VC-KF). The optimized DO-AKF algorithm was applied to a QCL-based gas sensor system for an exhaled CO analysis. The experimental results revealed a sensitivity enhancement factor of 23. The proposed algorithm can be widely used in the fields of environmental pollutant monitoring, industrial process control, and breath gas diagnosis.