Structural health monitoring (SHM) is critical for aircraft safety and maintenance. This paper presents a DAS-inspired nondestructive crack inspection framework that identifies cracks by sensing perturbations in radiated acoustic-field patterns rather than relying on point-wise sensors. A coupled structural-acoustic model of an Al7075 aircraft-skin panel is established to generate distributed sound-pressure-level (SPL) fields, and virtual distributed sensing trajectories are used to emulate a dense readout within the simulated air domain. A region-of-interest (ROI)-guided sensing-path selection strategy is developed to highlight crack-induced field distortions. Statistical descriptors, specifically skewness and kurtosis, are employed to form a two-dimensional feature space for crack classification using a linear support vector machine (SVM). Trained exclusively on the 30 N dataset, the proposed method achieves accuracies of 93.33% and 96.00% on the 30 N and 100 N test sets, respectively. The proposed framework provides a promising technical pathway for real-time structural health monitoring and early warning of aircraft-skin risks.

Significance High-coherence and widely tunable laser sources are key enabling components in modern silicon photonic systems, playing a critical role in coherent optical communications, frequency-modulated continuous-wave (FMCW) LiDAR, precision metrology, and distributed fiber-optic sensing. With the rapid growth of data traffic, increasing demands on sensing accuracy, and the continuous evolution toward system-level integration, laser sources are no longer required to merely provide stable emission, but must instead support precise phase and frequency control with high stability, wide tuning range, and low noise. Different applications impose distinct and often competing performance requirements on laser sources. In coherent communication systems, narrow linewidth and low phase noise directly determine achievable modulation formats, transmission capacity, and bit error rate, while precise wavelength locking to standardized channels is essential for dense wavelength division multiplexing. In LiDAR and three-dimensional imaging, high output power and broadband linear frequency sweeping are required to enhance detection range and spatial resolution. In fiber-optic sensing and precision metrology, long-term frequency stability and low drift are critical for achieving high sensitivity and measurement accuracy. Conventional semiconductor lasers are fundamentally limited by short cavity length and intrinsic noise mechanisms, which restrict their linewidth and frequency stability. Although discrete external-cavity lasers can achieve excellent coherence and tunability, they are not compatible with large-scale integration. Silicon-based integrated external-cavity lasers, realized through integration of III-V gain media with low-loss silicon photonic circuits, have therefore emerged as a promising solution, offering both high performance and scalability. This review focuses on precise phase-frequency control technologies for silicon-based integrated external-cavity lasers and their applications. Progress This paper systematically reviews the working principles, key phase-frequency control techniques, recent research advances, and representative applications of silicon-based integrated external-cavity lasers. We first introduce the fundamental configurations and physical mechanisms of two mainstream device architectures (Figs. 1-3). Subsequently, three core phase-frequency control techniques are discussed in detail. For wavelength tuning and locking, implementations based on Fabry-P & eacute;rot (FP) etalons combined with servo feedback circuits are introduced (Fig. 4), enabling precise alignment with International Telecommunication Union (ITU) channels. For frequency stabilization, the widely adopted Pound-Drever-Hall (PDH) technique is described (Fig. 5), which locks the laser to a high-stability optical reference to enhance long-term stability. For linear frequency sweeping in FMCW applications, two representative linearization approaches, namely iterative pre-distortion and electro-optic phase-locked loops, are comparatively analyzed (Fig. 6), both of which effectively suppress chirp nonlinearity. Furthermore, recent representative research progress is comprehensively summarized. Advances in narrow-linewidth tunable lasers are reviewed, including linewidth reduction to the Hz level enabled by low-loss extended cavities and high-Q resonators (Fig. 7), wide-range mode-hop-free tuning and high-linearity frequency sweeping (Fig. 8), as well as power scaling strategies (Fig. 9). A comparative analysis of material platforms, including Si, Si3N4, and lithium niobate on insulator (LNOI), is also provided. In addition, wavelength-locking technologies based on discrete FP etalons (Fig. 10) and integrated wavelength-locked lasers (Fig. 11) are discussed. Progress in integrated frequency stabilization is reviewed, covering miniaturized optical frequency references (Fig. 12), on-chip reference cavities (Fig. 13), and dual-polarization self-referenced stabilization schemes (Fig. 14). Finally, the application potential of silicon-based external-cavity lasers is validated through system-level demonstrations in space coherent optical communication (Figs. 15-17), FMCW LiDAR (Fig. 18), and distributed fiber-optic sensing (Figs. 19-23). Conclusions and Prospects Silicon-based integrated external-cavity lasers have achieved significant progress in linewidth reduction, wavelength tuning, frequency stabilization, and power scaling, demonstrating strong potential for next-generation coherent photonic systems. By leveraging the integration of III-V gain media with low-loss photonic circuits, these devices effectively combine their respective advantages, enabling high-performance and scalable on-chip laser sources. Despite these advances, several challenges remain for practical deployment. A key limitation is the lack of high-stability on-chip optical frequency references, which constrains long-term absolute frequency stability. Future efforts should focus on complementary metal oxide semiconductor (CMOS) compatible materials with improved thermal stability and hybrid stabilization schemes combining self-injection locking with integrated absorption-based references. In parallel, advances in multi-material integration and optoelectronic co-design, enabled by wafer-scale bonding and advanced integration technologies, will be essential for achieving compact, low-power, and system-level solutions. Furthermore, intelligent control strategies such as machine-learning-assisted optimization are expected to enhance real-time phase and frequency stabilization in complex environments. Overall, these developments will drive highly integrated, high-performance laser sources for applications in communication, sensing, and precision metrology.

In this paper, a high signal-to-noise ratio (SNR) phase-sensitive optical time-domain reflectometer (Φ-OTDR) system based on the 1440-level diversity merging technique is proposed, aiming to solve the problem of SNR degradation in long-distance detection of the conventional Φ-OTDR. The 1440-level diversity merging scheme is realized by combining 4-level wavelength diversity, 3-level frequency diversity, 30-level space diversity, and 4-level time diversity techniques, which can significantly improve the detection capability and the system SNR without triggering the nonlinear effect of the fiber. The experimental results show that the system achieves the fading suppression over the whole-line 20 km fiber, the mean noise floor reaches -77.4 dB (re 1rad2/Hz)@500 Hz, and the SNR is improved by 28.5 dB compared with the conventional Φ-OTDR system, and the external disturbance signal is successfully reconstructed. Furthermore, the system is verified to achieve the long-distance detection up to 70 km, which noise performance rivals that of commercial long-distance system. This study provides effective technical support for the application of Φ-OTDR in long-distance and high-SNR detection scenarios such as geophysical prospecting and marine acoustics.

Frequency-modulated continuous-wave (FMCW) ranging is essential for LiDAR and fiber-optic sensing, and its photonic integration requires on-chip lasers with wide mode-hop-free tuning and highly linear frequency sweeps. However, existing integrated lasers fall short of these requirements, restricting ranging performance to the centimeter scale. Here, we demonstrate a hybrid integrated external-cavity laser based on III-V and Si3N4 platforms that overcomes these limitations. By optimizing the cavity length and thermal tuning electrodes, the laser achieves a 102.4 GHz mode-hop-free tuning range and an intrinsic linewidth below 1.2 kHz. We further develop an unambiguous frequency-recovery algorithm using a 3 & times; 3 interferometer, enabling real-time frequency estimation and substantially improving sweep linearity. With pre-distortion compensation, we obtain a frequency-sweep non-linearity of 2.36 & times; 10-9at a 50 Hz chirp rate. FMCW ranging experiments demonstrate a 3.2 mm resolution and a 0.37 mm precision over a 28 m fiber link, representing nearly an order-of-magnitude improvement over state-ofthe-art integrated systems. These results offer a promising pathway toward high-precision LiDAR, fiber sensing, and biomedical imaging applications. (c) 2026 Chinese Laser Press

Distributed acoustic sensing (DAS) exhibits great potential for underwater target detection. The line-spectrum component serves as a distinctive acoustic fingerprint for ship detection, and its accurate reconstruction relies on precise DAS phase demodulation. However, complex marine ambient noises severely deteriorate the signal-to-noise ratio (SNR) of the line-spectrum component, introducing additional phase jumps and even distortion during the unwrap process. To address these challenges, this work proposes a residual module nested long short-term memory (RMN-LSTM) neural network for high-SNR phase unwrap and line-spectrum target detection, combining the deep spatial feature extraction of residual module and long-range temporal dependency of the LSTM with symmetric left-right encoder-decoder network structure. The RMN-LSTM directly learns the mapping between distorted wrapped and true phase signals, enabling effective recovery of high-fidelity phase information. Experimental results demonstrate that this method accurately rebuilds line-spectrum signals and significantly outperforms conventional algorithms. The root mean square error (RMSE) of RMN-LSTM is reduced to 0.661, representing decreases of 95.5% and 96.3% against numerical optimization methods, 19.3% reduction against classical convolutional neural network (CNN)-based method, and 4.4% reduction against LSTM-based methods, achieving a comprehensive SNR improvement of about 27 dB. This work provides a robust technical approach for high-SNR underwater target detection without hardware upgrades.

Three-dimensional distributed shape sensing of marine optical cables is critical for marine information acquisition, given that the time-varying of marine optical cables influence affects the accuracy of multi-dimensional localization of marine objects, personnel underwater operations, etc. In this work, a novel distributed hydro-acoustic shape sensing (DHS) method is proposed with distributed acoustic sensing (DAS) and an adaptive constrained inversion method (ACIM). DAS is introduced to detect the acoustic field and time-delay distribution of signals along the sensing fiber, from two sources or two positions of a moving acoustic source. The arrival time difference equations are built and resolved with the proposed adaptive constrained inversion method, and then the cable shape is obtained. Sea trials verify the feasibility of the proposed method with a 93 m acoustic sensitive optical cable (ASOC), where the reconstructed root-mean-square error is 2.41 m, and the maximum error is less than 4.30 m. This method achieves distributed shape sensing with only a few asynchronous acoustic sources. which provides a practical and flexible solution both for ASOC and existing cables based on DAS, potentially improving the application of DAS in complex marine environments.

Fiber Bragg grating (FBG) shape sensors play a crucial role in three-dimensional (3D) shape sensing fields such as medical robotics and aerospace. However, existing methods suffer from a fundamental contradiction: the strain coefficient, temperature coefficient, and encapsulation angle must be calibrated in separate steps, making the process cumbersome and prone to error accumulation, while simultaneously compensating for temperature drift and encapsulation deviations remains challenging. To fill this gap, we propose a two-stage thermal-strain-based framework that simultaneously decouples the strain and temperature coefficients in a single thermal-variation experiment, fundamentally eliminating the error propagation of multi-step calibration. The method consists of two stages: (1) a thermal-variation experiment that decouples and determines the strain and temperature coefficients for all sensing units, and (2) a simplified bending test that identifies the actual encapsulation angles without requiring repeated maximum strain point identification. Experimental validation shows that this integrated approach greatly improves reconstruction accuracy, reducing the endpoint error (EPE) to a range of 1.70 mm to 4.48 mm, corresponding to 0.4-1.1% of the 0.4 m sensor length under room temperature conditions. More importantly, the method exhibits exceptional robustness in thermally varying environments (10-25°C), effectively compensating for thermal drift. This work establishes a robust, efficient, and high-precision calibration paradigm, paving the way for the reliable deployment of FBG shape sensors in complex real-world applications.

Distributed acoustic sensing (DAS) technology plays a significant role in marine biological monitoring, fisheries research, underwater scientific investigations, and underwater search and rescue. However, conventional full-scale DAS systems are restricted to shore-based infrastructure and cannot be deployed in remote open-sea areas or isolated islands and reefs. To address this limitation, this study proposes a miniaturized DAS technology with low power consumption based on a field programmable gate array (FPGA). Frequency diversity is adopted to suppress interference fading to ensure system reliability. A four-stage pipeline acceleration algorithm is designed to realize real-time demodulation of multi-channel diversity signals. By multi-domain clock homology, the low-frequency phase noise introduced by clock asynchrony is suppressed fundamentally. Through isolated integrated packaging, thermal and vibration isolation for the passive optical components is achieved, resolving phase variations caused by the connection of exposing passive and active components in the external environment. Experimental results demonstrate that the proposed DAS system exhibits a stable millihertz-level very low-frequency (VLF) response capability. The sea trial successfully captured the signals of the diver's movement (0.05-0.1 Hz). To the best of our knowledge, this is the first time that diver detection and 1 mHz frequency response are realized by such a miniaturized DAS, less than half the size of an A4 sheet, with a low power consumption of 30 W. This study provides a feasible technical pathway for remote open sea monitoring that was previously difficult to realize.

We propose a hybrid integrated narrow-linewidth silicon nitride (Si3N4) external cavity laser module with high power output, full C-band wavelength tuning, and precise wavelength locking. The external cavity laser (ECL) consists of a gain chip and a Si3N4 external cavity chip, achieving a wavelength tuning range of 43 nm, a side mode suppression ratio (SMSR) exceeding 50 dB, and a linewidth of less than 1.5 kHz. The laser module integrates a semiconductor optical amplifier (SOA) for optical power amplification, a maximum output power is amplified up to 270 mW after the SOA, and the fiber-coupled output power reaches 220 mW. High precision wavelength locking of 55 International Telecommunication Union (ITU)-grid at 100 GHz intervals are achieved using a wavelength locker based on the Fabry-P & eacute;rot (FP) etalon, with frequency deviations all less than +/- 0.3 GHz and frequency drift less than 30 MHz over 24 hours. The frequency-locked laser has demonstrated excellent temperature stability, exhibiting no mode-hopping and maintaining a frequency variation of less than 1.57 GHz throughout ambient temperature cycling tests ranging from 15 degrees C to 55 degrees C. Furthermore, this module, serving as the transmitter laser, has enabled 200 Gbps dual-polarization (DP) 16 QAM/QPSK coherent transmission, verifying its feasibility for inter-satellite coherent laser communication.

An isolation apparatus for far-infrared wavelengths was developed and integrated into a CO2 nanosecond laser system for performance evaluation. The apparatus uses a dual acousto-optic modulator (AOM) configuration combined with an image-relaying delay line to achieve high isolation of back-reflected light. This design is based on the Bragg diffraction mechanism of the AOMs to achieve a high isolation for back-reflected radiation along the primary optical path. The delay line's extended propagation distance and image-relaying properties effectively compensate for the slow switching speeds of the AOMs. Experimental investigation within the CO2 nanosecond laser system demonstrates an isolation of 31.82 dB for back-reflected light, with output beam quality factors of MX2 = 1.070 and MY2 = 1.017, an overall transmittance of 35.73%, and a power-handling capability exceeding 130.60 W.

Objectives In the short-wavelength light sources required for semiconductor manufacturing, high-power, short-pulse CO2 lasers serve as driving lasers. When the single-pulse energy of a 10.6 mu m driving laser exceeds 100 mJ, the metal target ablated by the CO2 laser reaches the plasma state required for efficient in-band soft X-ray emission, achieving a conversion efficiency (CE) above 4%. Gigaphoton demonstrates a CO2 master oscillator power amplifier (MOPA) configuration delivering an average output power of 27 kW at a repetition rate of 100 kHz, corresponding to 270 mJ per pulse. Cymer achieves a 30 kW CO2 driving laser output in the NXE:3400B lithography system, with pulse widths ranging from 10 ns to 100 ns at a 50 kHz repetition rate. In China, relevant research reports an average power of 3552 W, corresponding to 142 mJ per pulse at 25 kHz with a pulse width of 200 ns. However, domestic research on high-average-power, high-energy nanosecond CO2 laser systems remains immature and shows obvious gaps compared with international advanced levels. Two major challenges still exist: a low signal-to-noise ratio (SNR) and parasitic laser oscillation. Solving these challenges while realizing kilowatt-level, hundred-millijoule, short-pulse CO2 laser output constitutes the core objective of this study. Methods A nanosecond CO2 laser system is designed based on a MOPA architecture. A Q-switched seed source generates nanosecond CO2 laser pulses, which are amplified sequentially by waveguide preamplifiers and main amplifiers to realize kilowatt-level, high-energy output. Numerical simulations of energy extraction in the main amplifier are performed using the Frantz- Nodvik equation. Stepwise active pulse shaping and passive saturable absorption techniques are proposed to enhance the temporal signal-to-noise ratio of laser pulses. Active acousto-optic isolation is adopted to suppress back-reflected light, and gain-aperture matching is applied to prevent self-oscillation. Finally, a nanosecond CO2 laser system is constructed for experimental verification. Results and Discussions The seed laser generates pulses with a temporal SNR of 16.23 dB and features a pedestal on the leading edge; after passing through an electro-optic pulse-slicing unit, the SNR rises to 20.58 dB and the pedestal disappears. With two-stage isolators integrated with saturable gas absorption cells, the SNR further increases to 22.46 dB, and the temporal SNR remains as high as 21.42 dB at the kilowatt-level system output. By adopting active isolation and passive saturable gas absorption, the back-reflected power in the front-end optics decreases to only 30 mW when the laser system delivers 1.07 kW to a metal target. Gain-aperture matching mitigates beam profile distortion inside the main amplifier; when the main amplifier outputs a fundamental Gaussian beam distribution, parasitic envelopes on the pulse leading edge vanish and self-oscillation is fully suppressed. At a repetition rate of 10 kHz, the seed laser produces 0.16 mJ per pulse, which increases to 0.34 mJ after injection into the first main amplifier. High-power experiments conducted on the system achieve a single-pulse energy of 103 mJ with an energy stability of 4.27% [root mean square (RMS)], an average output power of 1.03 kW with a power stability of 3% (RMS), and a pulse duration of 13 ns, while the measured beam quality factors are M-X(2)=1.32 and M-Y(2)=1.23. Conclusions We present a kilowatt-level, high-energy nanosecond CO2 laser system based on a MOPA architecture. The system adopts a Q-switched CO2 laser to generate 10.6 mu m nanosecond seed pulses, which are sequentially amplified by two waveguide preamplifiers and six fast axial-flow main amplifiers in a cascaded configuration. At a repetition rate of 10 kHz, the system delivers a single-pulse energy of 103 mJ with an energy stability of 4.27% (RMS), an average output power of 1.03 kW with a power stability of 3% (RMS), a pulse duration of 13 ns, and beam quality factors of M-X(2)=1.32 and M-Y(2)=1.23. A combined scheme of active pulse shaping and stepwise passive saturable gas absorption is proposed to enhance the temporal signal-to-noise ratio, achieving a temporal SNR of 21.42 dB for output pulses. Active isolation and gain aperture matching effectively suppress self-oscillation, enabling the back-reflected power in front-end optics to remain as low as 30 mW during 1.07 kW irradiation on the target. Further optimization strategies, including increasing the number of amplification stages or the pumping power of individual stages, replacing transmission components with high thermal conductivity diamond materials, employing optical isolators with higher damage thresholds, and introducing a tunable seed source, are expected to support higher-power and higher-energy pulse output in future implementations.

A novel phase-sensitive optical time-domain reflectometry (Phi-OTDR) based on the temporally sequenced multi-frequency multi-wavelength chirped source is proposed, with 50kHz detection bandwidth and -52.5dB rad(2)/Hz mean noise floor. The scheme can simultaneously meet the requirements of high-bandwidth and high signal-to-noise ratio (SNR) in the fields of large-scale structural health inspection and oil and gas pipelines.

An integrated phase-sensitive optical time domain reflectometer (Phi-OTDR) based on injection locking laser and frequency diversity is reported with high signal to noise ratio (SNR). The integrated Phi-OTDR utilizes injection locking laser for frequency shift and semiconductor optical amplifier (SOA) for chopping. By employing 3-order frequency diversity, a high SNR of 57 dB and an excellent strain resolution as high as 0.835 p epsilon/root Hz at a 10 m gauge length can be obtained.

Real-time monitoring of natural gas pipeline network can ensure the life and health of human beings and property safety in the surrounding area of the pipeline. Therefore, how to realize the rapid identification of pipeline leakage signal when leakage occurs is extremely important. Distributed acoustic sensing (DAS) technology is widely used in the field of pipeline leakage monitoring because of its advantages of wide coverage and high sensitivity. In this paper, a pipeline leak identification method based on DAS and one dimensional DPR-net (DAS pipeline leakage recognition network) are proposed. Pipeline leakage signal samples are collected under different working conditions (leakage aperture, leakage pressure, leakage direction). In test, the recognition accuracy of this method reached over 99%. There are reasons to believe that this method will provide an important technical means for DAS to detect pipeline leakage.

Fiber interferometer based on low noise lasers are crucial to the micro-vibration sensing systems. Laser noise is a key factor impacting the detection resolution of such systems. To enhance the minimum measurable acceleration of the micro-vibration sensing system, a compact external cavity diode laser (ECDL) is designed and fabricated to reduce the frequency/phase noise and the relative intensity noise (RIN) of the laser source. The ECDL is composed of a gain chip and an external cavity based on two high-Q Fabry-Perot (FP) etalons with small FSR differences. The two FP etalons enable a narrowband filtering response that selects a single longitudinal mode in the laser cavity, resulting in a single-frequency laser output with low noise. In this way, the intrinsic linewidth of less than 400 Hz with the RIN of -153 dBc/Hz@10 MHz and the output power of 9.5 mW are realized. The ECDL is employed in the micro-vibration sensing system, the noise evaluation experiment results reveal that the overall noise floor is 21.47 ng/Hz1/2 with an average sensitivity of 43.5 dB re rad/g.

The un-pumped erbium-doped fiber (EDF) Sagnac loop (UESL) is an attractive com ponent for narrow line lasers due to the saturable absorption (SA). Its characteristics are analyzed in detail in this paper, including the power dependent attenuation (PDA) and the dynamic Bragg grating based on the optical standing wave in the loop. The former can be utilized to enhance the side mode suppression ratio (SMSR) of lasers, and the latter is useful to reduce the linewidth effectively. To describe their characteristics, two equations are deduced. One equation defines the averaged absorption of the loop as a function of the EDF length and input power. The other is the spectrum of dynamic grating in the medium with losses, illustrating how the peak reflectivity decreases with the loss. Both effects are related to the material properties, especially the absorption ${{{\bm{\alpha }}}_{\bm{0}}}$ at the low power limit, the saturating power ${{{\bm{I}}}_{{\bm{sat}}}}$, and the coefficient of index change over the loss K based on the universal Kramers-Kronig (K-K) relations. The two effects were measured experimentally; by fitting the experimental data with the theoretical calculations, the typical values were given as ${{\alpha }_0} = 1.6{\bf }\,{{\mathrm{m}}<^>{ - 1}}$, ${{I}_{sat}}{\rm{ = 0}}{\rm{.91}}{\bf }\text{ mW}$, and $K = 1.0\times{{10}<^>{ - 7}} \, {\rm{ m}}$ for the EDF used in this work. The UESL was connected in a fiber laser as a mode controller; the multiply modes was suppressed and a stable single longitudinal mode operation was obtained; the instantaneous linewidth was narrowed from 660 Hz to 190 Hz experimentally.

Objective Ship-information monitoring is vital to marine ecological protection, fishery resource management, and sea-area safety maintenance. The current mainstream ship-monitoring methods include automatic identification systems, optical cameras, infrared thermal imaging, radar monitoring, and remote-sensing technologies. However, these technical methods present the disadvantages of active monitoring, being affected by light, limited monitoring range, susceptibility to electromagnetic-wave interference, and high cost. By contrast, distributed acoustic sensing (DAS) offers unique advantages. It can use the existing submarine communication optical cables, offers passive monitoring, resists electromagnetic interference, supports large-scale networking and long-distance monitoring, and costs lower than remote-sensing technology. Diane et al. used a submarine communication cable to obtain the direction and speed of a ship. Liu et al. used a sensitized optical cable suspended in water to obtain ship voiceprint information and proposed an array-orientation method based on adaptive phase-difference correction. These studies achieved significant advancements in ship-speed estimation, trajectory tracking, and voiceprint recognition. However, DAS has not been used to analyze ship hydrodynamic pressure field (SHPF) in ship monitoring, and the inherent parameters of ships (such as length) have not been obtained. This study proposes DAS combined with a submarine photoelectric composite cable to synchronously monitor the hydrodynamic pressure field and acoustic field of an overtopped ship. Additionally, ship information is derived by combining the signal characteristics of SHPF, acoustic-field information, a signal-enhancement algorithm, and Doppler-frequency shifts. Methods In this study, a phase-sensitive optical time-domain reflectometer (Phi-OTDR) combined with a submarine photoelectric composite cable was used to synchronously monitor the SHPF and acoustic field of an overtopped ship to perceive ship information. First, based on potential flow theory and the spatial response characteristics of an optical fiber, a response model of the optical fiber to SHPF was established, and the ship-overtopping time and duration were obtained based on the characteristics of the hydrodynamic pressure field. Subsequently, a signal-enhancement algorithm was used to improve the signal-to-noise ratio of the ship's acoustic signal, and high-definition spectrum features were successfully extracted. Next, a Doppler-frequency-shift distribution model was established along the axial direction of the optical cable. Based on the least-squares fitting method, the ship speed was inverted using the experimental spectrum information, and the ship length was estimated by combining the ship-overtopping duration. This method successfully combines an existing submarine photoelectric composite cable and a Phi-OTDR to quantitatively acquire ship speed and length, thus providing a new approach for ensuring marine information security. Results and Discussions The proposed method realizes SHPF monitoring, acquires the high-definition spectrum characteristics of ship spectra, and quantitatively acquires ship speed and length. The SHPF curves obtained from theoretical simulation and experiment are consistent (Fig. 9). The center of the hydrodynamic pressure curve of the ship exhibits a symmetrical distribution with a prominent negative pressure peak. Based on the characteristics of the SHPF, the ship-overtopping time and duration can be estimated. Using the obtained high-definition ship-spectrum feature map (Fig. 8), a signal with a center frequency of 21.29 Hz was selected for further processing. The ship speed was obtained via inversion using the least-squares method. The absolute error is only 0.09 m/s, and the relative error is 2.22 degrees o. The absolute error of the ship length estimated using the ship-overtopping duration is 4 m, and the relative error is 3.88 degrees o. Conclusions In this study, DAS and existing submarine photoelectric composite cables were used to simultaneously monitor the hydrodynamic-pressure-field and acoustic-field signals of ships. This approach is an improvement over the previous method, where DAS detects only a single physical field (acoustic field) signal of ships. Thus, it allows more ship parameters to be obtained from SHPF and acoustic-field signals. A response model of an optical fiber to an SHPF was established, and the accuracy of the theory was verified experimentally. The ship-overtopping duration was estimated using the zero-crossing negative pressure peak of the hydrodynamic pressure field. A model depicting the Doppler-frequency shift along the optical cable was established, and high-definition ship spectrum characteristics were obtained using a signal-enhancement algorithm. The ship speed was inverted using the least-squares method, and the ship length was obtained by combining the ship-overtopping duration. In this study, DAS was successfully used to synchronously detect SHPF and acoustic-field signals as well as to quantitatively acquire ship speed and length, thus expanding the information-perception ability of DAS in ship monitoring.