Shanshan Wang

An ultra-compact positioning system based on fiber optic extrinsic Fabry-Perot interferometer (EFPI) array is proposed and demonstrated. The sensitivity of EFPI fiber sensor is investigated theoretically, by which parameters of the EFPI fiber sensor are optimized and sensitivity (re 1 V/μPa) of -198 dB at 5 kHz is reached. In addition, to realize the accurate positioning within a relatively large dynamic range, a demodulation method based on F-P laser is proposed. Based on the design, fabrication and demodulation of five EFPI fiber sensors, a five-element cross array for underwater positioning is built and tested in both anechoic sink and lake environments. Results show that positioning errors of 0.0247 m and 0.0296 m are obtained, respectively, which demonstrates the good performance and environmental applicability of the positioning array. The positioning array demonstrated here shows advantages of compact structure, fast employment, easy fabrication, good applicability and large dynamic range, which shows potential applications in marine resource exploration, unmanned collaborative equipment underwater and marine environment monitoring.

Dependence of optical refractive index (RI) of seawater on temperature, salinity, and pressure is crucial for optical fiber sensors operated in seawater. Expressions of RI of seawater on temperature, salinity, pressure, and wavelength applicable to near-infrared waveband are developed based on a great deal of RI data measured by a semi-encapsulated microfiber Mach-Zehnder interferometer sensor. To verify the accuracy of these expressions, RI measured by infrared refractometer, theoretical calculated sensitivity and experimental measured sensitivity are used, by which the most accurate expression is determined. Based on this expression, a variable sensitivity matrix is established to demodulate temperature, salinity and pressure simultaneously with errors of 10.91 %, 6.09 % and 18.80 %, respectively. The expression proposed here will provide valuable references for theoretical and experimental study on optical fiber sensors operated in infrared waveband and push the applications of fiber optical sensors in ocean investigations.

Optical fiber sensors (OFSs) have attracted more and more attention in the field of in-situ ocean observation because of their advantages of the small size, light weight, low cost, and intrinsic immunity to electromagnetic interference. Here, we comprehensively reviewed the development of various advanced physical and chemical OFSs for in-situ measurement of ocean key parameters, including temperature, salinity, pressure, acoustics, flow velocity and turbulence, potential of hydrogen (pH), heavy metal ions, nitrates, and gases. Moreover, the performances of different kinds of OFSs and their practical sea trial reports for in-situ measurement in the marine environment are provided. As we discussed, the field of OFS is rapidly evolving and is poised to make essential breakthroughs in marine monitoring, leading to better utility of marine resources.

A robust strain sensor is demonstrated based on a microfiber Mach–Zehnder interferometer (MMZI) encapsulated by the polymer polydimethylsiloxane (PDMS). Benefiting from the low Young’s modulus of PDMS, both a robust structure and high sensitivity can be realized based on three different encapsulations. In the experiment, the proposed sensors are fabricated and tested with strain sensitivities ranging from −20.95 pm/με to 127.00 pm/με within the wavelength range of 1200–1650 nm. Compared with the bare MMZI sensor, at least one order of magnitude higher sensitivity is reached. To further evaluate the performance of the sensor, the dependences of sensitivity on probing wavelength and the different types and quantities of polymers used in encapsulation are discussed. Results show that the sensitivity of the sensor will increase with the probing wavelength. The type and quantity of polymer used are also very critical to sensitivity. Additionally, a response time of 24.72 ms can be reached. Good recoverability and repeatability of the sensor are also demonstrated by repeated experiments. The strain sensor demonstrated here shows the advantages of simple fabrication, robust structure, high and tunable sensitivity, fast response, good recoverability and repeatability.

Two-parameter demodulation based on variable sensitivity matrix (VSM) for temperature and salinity measurement in seawater is proposed based on the developed refractive index (RI) expression of seawater in infrared band of 1200nm - 1650nm. The RI expression of n ( S , T , λ) is obtained from a great deal of RI data measured by microfiber Mach-Zehnder interferometer and fitted by different methods. The accuracy of the developed n ( S , T , λ) is verified experimentally, and demodulation error of about 2.5% is reached by VSM method, which is at least twice lower than traditional sensitivity matrix used. The VSM and RI expression proposed here will be useful for theoretical or experimental research on optical fiber sensors operated in infrared band and they can also be expanded to other sensors based on RI change of seawater.

Detection of simultaneous measurement of temperature and pressure of seawater is very meaningful in oceanography research. To realize the goal, the reflecting polarization interferometer incorporated with the bow tie fiber is proposed. First, the formation of birefringence in the bow tie fiber and the working principle of the sensor are studied. Then, the temperature and pressure sensing experiments are performed, respectively. The least square method is adopted to eliminate the crosstalk influence. The best temperature and pressure sensitivities after adjustment are -1.2349nm/°C and 1.9209nm/MPa, respectively. The sensitivity matrix is built by extracting the information of two dips in the spectra. After comparison between the sensor demodulated results and the CTD measured data, the correlation coefficient (r), the mean absolute error (MAE), the mean absolute percentage error (MAPE), and the root mean square error (RMSE) of temperature are 0.9984, 0.3789°C, 1.18%, 0.4365°C, respectively, and r, MAE, MAPE, and RMSE of pressure are 0.9982, 0.0266MPa, 3.18%, and 0.0308MPa, respectively. So the method is verified to be accurate and feasible. This work could provide reference to who does oceanography research, and is very prospective in the field of ocean detection.

Doping of Mn²⁺ greatly enhances the non-pre-irradiated near-infrared mechanoluminescence (NIR ML) of CaZnOS:Nd³⁺ by energy transfer from the host to Mn²⁺ to Nd³⁺. This effect allows the acquisition of NIR ML images with high signal-to-background ratios in biomechanical imaging.

Temperature, salinity, and pressure (TSP) are essential parameters for the ocean. Optical fiber sensors (OFSs) have rapidly come into focus as an ocean detection technology in recent years due to their advantages of electromagnetic interference, light weight, low cost, and no waterproof requirement. In this paper, the most recently developed TSP sensors for single parameter and multi-parameter TSP sensing and measurement based on different OFSs are reviewed. In addition, from the practical point of view, encapsulation methods that protect fibers and maintain the normal operation of OFSs in seawater, and the response time of the OFS, are addressed. Finally, we discuss the prospects and challenges of OFSs used in marine environments and provide some clues for future work.