Interferometric fiber-optic hydrophones are an important means in the field of underwater acoustic detection. The design of the hydrophone sensor head is the key technology related to its detection sensitivity. In this paper, a high-sensitivity cuboid interferometric fiber-optic hydrophone based on planar rectangular film sensing is proposed, and the sensitivity of the sensor is compared with that of the widely used air-backed mandrel hydrophone under the same conditions. The acoustic characteristic models of the two types of sensors were established by theoretical calculation and simulation analysis to obtain the theoretical pressure sensitivity. Some experiments were performed to examine the theory and design. According to the experiment results, the mean phase sensitivity of the mandrel type was −112.85 dB re 1 rad/μPa in the operating frequency range of 10–300 Hz, and that of the cuboid type was −84.50 dB re 1 rad/μPa. The latter was 28.35 dB higher than the former was. These results are useful for improving hydrophone sensitivity.

In advanced sensor system designs, one of the common methods involves converting target physical quantities into phase/frequency-modulated signals. Then, the in-phase/quadrature-phase (I/Q)-based phase demodulation structure is mainly employed to enhance flexibility and efficiency in obtaining the phase information. However, the presence of I/Q imbalance and additive noise in analog I/Q channels greatly degrade the overall system detection performance. Specifically, we investigated the detailed degradation of signal detection, including the introduction of unwanted interference frequency components, elevated noise floor, and distortion of the target signal. To solve this problem, we proposed a novel controlled-carrier closed-loop structure to realize the phase demodulation. This structure, built upon the zero-error closed-loop structure, further mitigates the imbalance distortion and optimizes the noise performance by modifying the control method. The detailed structure and key issues are provided. Further, the effectiveness and enhanced performance of the proposed structure are verified by simulation and experiments. The experimental results align with the simulations and it shows that the proposed structure can achieve enhanced imbalance-distortion mitigation and noise suppression without the need for complex I/Q estimation and compensation.

Frequency-modulated (FM) signals are widely used in sensing, measurement, and signal detection due to their strong anti-interference and easy transmission characteristics. Although the high-precision measurement methods for static signals are quite complete, the high-precision measurement methods for dynamic FM signals still need to be studied, and the measurement accuracy in the high-sampling system still has room for improvement. Traditionally, the equal-precision measurement method is widely applied in most scenarios. However, its accuracy is limited by the quantization error of ±1 word and the sampling gate time, making it difficult to improve the frequency measurement accuracy while ensuring a high sampling rate at the same time. In this paper, a high-precision feedback frequency measurement system with the capability to eliminate the quantization error of ±1 word is proposed. The proposed system consists of two stages, the rough measurement stage based on the equal-precision measurement method and the precise measurement stage based on the negative feedback tracking architecture using the phase–frequency detector (PFD) and direct digital synthesizer (DDS). The effectiveness and feasibility of the system are verified by both simulation and experiment. At the sampling rate of 2 kHz, the frequency measurement accuracy is improved by more than 30 dB.

Noise floor is an important metric for fiber optic sensors. In particular, common-mode noise (CMN) suppression is critical to improving the system’s ability to detect weak signals. In this paper, an innovative method for reducing noise in white-light-driven sensors is proposed. This structure fully utilizes the broad spectrum of white light and the wavelength selectivity of fiber gratings. The proposed CMN suppression method is capable of suppressing the phase noise of the light source, as well as the noise due to environmental disturbances. The experiments demonstrate that the noise floor of this vibration sensor is about -88 dB/Hz above 30Hz with 10km disturbed transmission fiber. The max 1/f noise reduction can reach approximately 60 dB near 5 Hz, while the max transmission path noise suppression exceeds 103 dB at hundreds of Hz. The proposed structure has the potential to achieve higher resolution in wavelength division multiplexing (WDM) sensor arrays without excessive cost.

The white light interferometer is advantageous for wavelength division multiplexing (WDM), but the excessive noise floor limits its application in practicality. In this Letter, we propose a fiber-optic sensor driven by a broadband light source, which uses a fiber-optic Fabry-Perot cavity and a reference interferometer to enhance strain resolution. In the experiment, the strain resolution of a 5.86 m resonant sen root sor is 18.5 f epsilon/ Hz at 1.5 kHz, while the maximum detectable signal is over 230 rad at 1 kHz. With low cost, this method provides a new, to the best of our knowledge, solution for WDM sensing arrays with a large dynamic range. (c) 2024 Optica Publishing Group

Unlike aerial or terrestrial navigation, the global navigation satellite system (GNSS) is not available underwater. This is a big challenge for underwater navigation. The inertial navigation system (INS) aided by the single-beacon acoustic positioning system (APS) provides one solution, but the long-range case is limited by low-SNR conditions. Inspired by passive synthetic aperture detection, we proposed a new tightly coupled navigation algorithm based on spatial synthesis and one-way-travel-time (OWTT) range measurement. We design two estimators: the DOA/range estimator using the model-based method and the tightly coupled INS/APS navigation estimator. Based on the improved UKF, all information is combined. Simulation is carried out in MATLAB. Compared with range-only tightly coupled INS/APS navigation, synthetic long baseline (SLBL) algorithm and Doppler velocity logger (DVL) aided centralized extended Kalman filter (CEKF) based single beacon INS/OWTT navigation, the proposed method’s performance is proven. The main contributions of this work are: (1). Propose a new architecture of underwater integrated navigation; (2). Apply the passive acoustic detecting method in the navigation to improve accuracy. (3). Apply the tightly coupled method to improve availability.