This PDF file contains the front matter associated with SPIE Proceedings Volume 11191, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

H₂S and moisture content are important indicators to evaluate the potential faults and insulation performance of H₂S electrical appliances. Currently, there is no report on the simultaneous detection of H₂S gas and moisture content. In order to realize the accurate detection of H₂S gas and H₂O at the same time, Lorentz simulation analysis was performed on the absorption spectra of H₂S gas and H₂O molecules. The absorption was strongest near 2684nm, and there was no cross interference of SF₆ other decomposition products. H₂S and moisture content at different concentrations were measured by TDLAS technology in a customized CW-DFB laser with a central wavelength of 2.68μm combined with a small-volume Herriott long-range cell with multiple reflections. In order to verify the detection ability of selected spectral lines to H₂S gas and H₂O molecules at low concentration, trace H₂S and H₂O vapor with SF₆ as background were detected by direct absorption technology and wavelength modulation technology respectively. In the second harmonic absorption, the minimum detection lower limit of H₂S and H₂O is 9.01×10^-6 and 4.54×10^-6, respectively. The maximum harmonic signal amplitude has a good linear correlation with concentration, and the linear fitting degree R² is 0.978 and 0.997, respectively. SF₆ gas displacement experiments with different flow rates showed that the equilibrium time of H₂S and moisture content at 708mL/min was 90s and 100s, respectively. The response time of H₂S and H₂O at the same concentration and injection velocity is 30s and 45s, respectively. Wavelength modulation technology can provide a reliable experimental basis for the simultaneous detection of trace H₂S and H₂O in high voltage combination electrical appliances.

The Scheimpflug lidar technique has been widely developed for atmospheric remote sensing during recent years. However, the correlations or discrepancies of the lidar signals measured by the Scheimpflug lidar (SLidar) technique and the conventional pulsed lidar technique, which is crucial for understanding the measurement results of the SLidar technique, has yet been investigated. In this work, a 520-nm Scheimpflug lidar system and a conventional 532-nm pulsed lidar system have been developed for comparison studies on a near-horizontal measurement path.

We experimentally report a proof-of-concept demonstration of a few-mode fiber (FMF) based distributed acoustic sensor (DAS) design, aiming at upgrading the capabilities of the typical DAS that employs the standard single mode fiber (SMF). We only excite the fundamental mode at the input port of the FMF, and further, we minimize the impact of intermodal coupling within it such that the FMF operates in a quasi-single mode (QSM) state. The QSM operated FMF keeps the basic operation principle of the DAS valid and, in comparison with the standard SMF, it allows injection of higher pump peak-power before reaching the threshold power of nonlinearity. We validate our design by sensing vibration events produced by a piezoelectric transducer (PZT) cylinder. The FMF based DAS successfully figures out the locations and frequencies of these events. This reported design would enable the realization of a DAS design with longer sensing range and higher spatial resolution, in comparison to the standard SMF based DAS.

Optical Backscattering Reflectometry (OBR) can be used for one-dimensional distributed strain sensing of medical needles. To achieve 3D shape sensing the needle should be equipped with multiple optical fibers. A feasible configuration can be done using two pairs of parallel optical fibers, which will measure the strain in two directions perpendicular to a needle axis. However, OBR is limited to a single fiber sensing because of its inability to discriminate scattering patterns of different fibers. To achieve multiplexing, it is proposed to use nanoparticle doped fibers (NP-doped) with high scattering power and splice them to standard single-mode (SMF) pigtails with different lengths. As a result of such configuration, the NP-doped fibers, which are used as sensing fibers, are spatially separated by standard fibers.

We propose a miniaturized fiber optic fabry-perot pressure measuring system, which consists of two parts: ultra-high pressure sensor with embedded MEMS Fabry-Perot cavity and miniaturized phase demodulation system, for marine pressure measurement. The ultra-high pressure sensor have been analyzed and proved to meet the requirements of the full ocean pressure measurement by analyzing mechanical and optical characteristics. In order to meet the application demands of marine pressure measurement, the pressure fatigue test and hydrostatic pressure test have been carried out. The test results show that the pressure measuring system has a stable response relationship between the absolute phase and pressure in the range of 2–120 MPa, and no significant changes was found neither in four consecutive months of ultra-high pressure tests. The repeated error of system is less than 0.012MPa at 60MPa. The miniaturized measuring system can be applied to the ocean profiling measurement plan named the Argo plan.

The temperature dependence of a refractive index (RI) sensor based on a core-offset in-line fiber Mach-Zehnder interferometer was investigated in order to eliminate the temperature and RI cross sensitivity caused by the thermo-optic effect. The RI sensitivity of the sensor was around -20.00 nm/RIU, and the RI correction was given for the sensor in the temperature range of 25-60℃. The experimental results showed that the temperature variation might lead to deviation in the measurement of RI, but hardly affected the RI sensitivity.

A D-type fiber optic refractive index sensor based on surface plasmon resonance (SPR) principle is proposed in this paper. The sensor is composed of a double core structure and a grid-coated photonic crystal fiber (PCF) on the polishing surface. The resonant wavelength can be adjusted and the refractive index sensitivity can be improved by introducing a gold grating film. Under the anisotropic perfect matching layer boundary condition, the simulation was preformed through the full-vector finite element method (FEM). The results show that the refractive index measurement range of the sensor is 1.30~1.33, the sensitivity can reach 12000 nm• RIU^-1, and the resolution can reach 1.01×10^-5 RIU.

In recent decades a noticeable surge in research on nanostructured materials and their interactions with light has been observed. This is explained not only by basic interest, but also by the potential of miniaturization of devices and the expansion of their functional capabilities through the use of metasurfaces. On the other hand, in the last decade a pronounced tendency towards miniaturization of position control and navigation systems can be observed either. A need of positioning and navigation of small-sized mobile objects arises frequently. At the same time, the size of controlled objects is constantly decreasing, and the development of sensors for micro- and nanoscale objects is already required nowadays. Therefore, the use of nanostructured metasurfaces in position control and navigation systems seems to be extremely promising. We focus on the use of nanostructured metasurfaces for rotation angle determination. We discuss a new rotation angle measurement method where metasurface amplitude response is used, its main advantages and disadvantages are demonstrated, a variant of its improvement is proposed.

Arrayed waveguide grating (AWG) has been widely used as a multiplexer in FBG demodulation system because of its high stability, low loss and fast read-write ability. They substitute expensive and vibration fragile spectrometers. In this paper, we compare two kinds of AWG demodulation systems experimentally. One is a multi-channel ultrasonic sensor system using fiber ring laser based on erbium-doped fiber amplifier (EDFA) and arrayed waveguide grating (AWG) as the intensity demodulator. And another is a one-way amplified system based on EDFA. When the external dynamic strains are applied on the FBG sensor, the central wavelength of the FBG will move between two adjacent channels of the AWG. Therefore, the modulation of the central wavelength of the FBG is converted to the amplitude modulation of the output of the two adjacent channels. Experimental results show that the multi-channel ultrasonic sensor system of one-way amplified configuration based on EDFA is more stable and can test high-frequency dynamic strain stably. The ultrasonic signal in water is successfully detected through one-way amplifier configuration.

The present paper considers a ring confocal resonator in which the fulfillment of the confocal condition and the spectrum degeneracy are achieved through the use of a concave toroidal reflective surface with specified values of curvature radii in two main meridional sections. Such resonators can be used, in particular, as sensors in resonator micro-optic gyroscopes resonant optical gyroscope. This work is devoted to a review of technologies suitable for manufacturing of ring confocal resonators, and to an estimation of the deviations of the geometric parameters of confocal resonators acceptable during this manufacturing. To achieve this, the Fox and Li method is used, which was earlier modernized to calculate ring resonators with astigmatic reflecting elements.

Measuring equipment is very important in smart grid, for example, the real-time accurate current measurement is necessary for over-current protection, leakage detection. Faraday Effect causes light polarization to rotate when the fiber is exposed to a magnetic field in the direction of light propagation. Thus, the magnetic field strength can be determined from the light polarization change. By applying Ampere’s law, we can get the current by measuring the light rotation. In this paper, optical current sensor (OCS) based on magneto-optic crystal has been developed. The sensing principles, optical and electronic design, as well as its characterization have been described. The weak current signal detection technique is further discussed by means of spectral analysis and lock-in amplifier methods. The performance of the prototype was tested experimentally, the sensor has a high sensitivity for currents and is capable of achieving weak electric current detection with accuracy of 1mArms (50 Hz). A linear response is obtained for current amplitude as low as several mArms at an AC frequency of 50 Hz. For the direct current (DC) current measurement, a lock-in amplifier is used in our scheme; the detection limit of the magneto-optic crystal current sensor is less than 1 mA. There is a wide range of applications for the magneto-optic crystal current sensor, which will be mainly used to monitor currents both on photovoltaic grid-connected system and insulator operating state.

We have proposed and demonstrated the fabrication of fiber-optic Fabry-Perot interferometer (FPI)-based fiber-optic sensor by 3D printing technology with digital optical processing (DLP) for water pressure sensing application. The mirrors of FPI are provided by the end face of the fiber and the inner surface of the printed resin sensor head. By analyzing the characteristics of the sensor head prepared by 3D printer, the interference contrast is enhanced through the optical fiber end face with an eight degrees angle. The obtained pressure sensitivity is 536.9 nm/MPa. This method of fiber optic pressure sensor has the characteristics of simple manufacturing process, mass production and high sensitivity. Keywords: fiber-optic sensor, 3D printing technique, pressure sensor, Fabry-Perot cavity.

Hypersonic wind tunnel experiment technologies are involved to many subjects such as aerodynamic forces, aerothermodynamics, thermal protection of aircraft structures, heat-fluid-solid coupling, hypersonic boundary layer, airbreathing propulsion system and light-weighted and high-strength material. In comparison with traditional electromechanical or electronic sensors, the fiber optic sensors have relatively high potential to work in hypersonic wind tunnel. This article has classified and summarized the research status and the representative achievement on the fiber optic sensing technologies, giving special attention to the summary of research status on the popular Fabry-Perot interferometric, fiber Bragg gratings and (quasi) distributed fiber optic sensors working in hypersonic wind tunnel environment, and discussed the current problems in special optical fiber sensing technologies.

An intensity-modulated optical fiber sensor is presented for static strain and vibration monitoring, which is fabricated by splicing a small section thin-core fiber between two standard single-mode fibers. Static strain measurement is performed using a simple cantilever system and a referenced fiber Bragg grating for sensing strain. The results show that optical loss increases with the rising strain for TCF sensor and the maximum optical loss is 0.133 dB. The dynamic response measurement of the cantilever vibration is demonstrated. The experimentally measured vibration frequency range is from 1 Hz to 200 Hz. The developed thin-core fiber sensor has the advantage of no complex demodulation, cost efficient and simple in structure, which is a potential monitoring method for large-scale construction, mechanical equipment, aerospace, and even earth activities.

A compact tunable quintuple Fano-like plasmonics structure, composed of a metal-insulator-metal, a baffle, a quarter ring and a rectangular cavity, was proposed and applied to refractive index sensor in this paper. According to the numerical simulations, quintuple Fano resonances, which derived from the coupling and interference between the narrow discrete state supported by the quarter ring and the rectangular cavity and the broad continuum state excited by the baffle, were obtained in its transmission spectrum. Additionally, the quintuple Fano resonances obtained can be easily tuned by changing the geometric parameters of the resonators. Because of the sharp asymmetry of Fano resonance, the proposed system can be served as a high efficient refractive index sensor with a sensitivity of 1600 nm/RIU and figure of merit (FOM) of 6743. Considering the development of high integrated photonic circuits, it is believed that the proposed structure can find significant applications in optical sensing and optical communication areas.

For the first time, we experimentally study the transversal-stress (T-stress) induced polarization crosstalk behaviors in polarization maintaining fibers (PMFs) including the linearity, sensitivity, response time and recovery time, using a distributed polarization crosstalk analysis (DPXA) system. Using two Panda PMFs with or without polyacrylate buffer coating and one Bow-tie PMF with golden polyimide coating as experimental samples, we find that: I) the polarization crosstalk can be highly linear with the T-stress for PMFs no matter with or without coating; II) the polyacrylate coating can reduce the crosstalk sensitivity of naked PMFs by more than hundreds of times, while replacing the polyacrylate coating with polyimide coating can increase the sensitivity by tens or even hundreds of times; III) the polyacrylate coating can induce a significant recovery time of crosstalk when a T-stress is removed after a long loading time compared with that in naked PMFs or golden PMF with polyimide coating, however the crosstalk response speed is too fast to be measured by the DPXA system. Additionally, we also find that the current polyimide coating technique still needs to be improved further to reduce the crosstalk base level. This work will be very useful for PMF-based distributed sensing applications and sensing PMF manufacturing.

In this paper, a helical structure is fabricated on a commercial plastic optical fiber (POF) by heat pressing and twisting method. The helical POF is proposed as a RI sensor. A POF is firstly heated and pressed to form a flat-shape with a thickness of 60% of the diameter of the POF. After that, the flat-shape is twisted into a helical structure. The helical structures fabricated on POFs (with diameters of 0.25, 0.50, and 1.00 mm) and with lengths (of 10, 15, and 20mm) are experimentally evaluated for liquid RI measurement, and the results show that when the helical structure is fabricated on the POF with a diameter of 1.00 mm, a helical pitch of 2mm, and a length of 15mm, the RI sensitivities of 2292%/RIU, 4128%/RIU, and 1750%/RIU are obtained in the RI ranges of 1.33-1.37, 1.37-1.40, and 1.41-1.45, respectively. The experiment results have demonstrated that the proposed sensor is a low-cost solution for RI measurement, and with the features of high sensitivity, simple structure, easy fabrication, compact size and intensity modulation at visible wavelengths.

A novel quasi-distributed fiber temperature sensor based on the cascaded quantum dot fibers (QDFs) is proposed in this paper. The cascaded QDFs are fabricated by the 3D printing technology and can be divided into two parts QDF1 and QDF2. When the excitation light is coupled into the fiber, the QDF1 emits the 630nm fluorescence and the QDF2 emits the 530nm fluorescence. Because the fluorescence peaks will change with the temperature linearly, it can be used as the fiber temperature sensor. In the experiment, by controlling the temperature at each QDF, the sensor realizes the temperature measurement at different position. The sensitivity of the sensor at different position is 0.15nm/°C and 0.153nm/°C, respectively. The results verify the feasibility of the structure for distributed temperature sensing. The spatial resolution is 1.8mm, which is limited by the length of the printed QDF.

The small amount of hydrogen sulfide gas generated during the oil exploitation process is enough to cause great harm to the human body and mining equipment. It is necessary to detect hydrogen sulfide gas timely and accurately. Based on the principle of spectral absorption, a new method for detecting the concentration of hydrogen sulfide gas with high sensitivity is studied. According to Lambert Beer's law, increasing the optical path can enhance the intensity of the absorbed signal, thereby proposing a method using a long path gas absorption cell and increasing the sensitivity of the system detection. The improved Herriot absorption cell is used to make multiple round trips of light in the air chamber, which can obtain a longer absorption path and improve detection accuracy. The chamber is designed and simulated to test the practicality and accuracy. The light source part uses a Bragg fiber grating to modulate the LED broadband light source into a narrow-band light source, thereby reducing cost and enhancing practicability. The obtained light source is modulated and filtered, and the reference optical path is set, and then the dual optical path difference method is combined to eliminate the systematic error caused by noise interference and source fluctuation. The second harmonic in output signal is extracted by the lock-in amplifier, and then the gas concentration is inverted. At the same time, an adaptive algorithm is used to maintain the stability of the light source temperature, which can avoid the effects of temperature changes. The simulation experiments show that the long-range high-sensitivity measurement method of hydrogen sulfide greatly improves the measurement accuracy, and can be effectively applied to the on-line accurate detection of low-concentration hydrogen sulfide gas.

An ultra-low emission Cl₂ monitoring optical system based on differential optical absorption spectroscopy has been set up. We have found through comparison experiments that UV reflection enhanced aluminum is damaged and the dielectric film mirror is intact under high concentration of Cl₂. Then verify the performance characteristics of ultralow Cl₂ emission online monitoring device. The maximum absorbance of 50ppm Cl₂ exceeds 0.1, while the 30ppm Cl₂ reaches 0.063, so the measurement range can be 0-95 mg/m³, which meets the maximum allowable emission concentration of Cl₂ required by the new regulations for detection of 65mg/m³.

As a Class 2B carcinogen, C₈H₈ has great hidden danger to human health. Domestic research on the detection of styrene in the atmosphere is relatively lacking. Therefore, this article determined proper retrieval range of wavelength and a method to eliminate interference based on the absorption feature in the UV region. An open optical path detection system was set up based on the principle of ultraviolet differential absorption spectroscopy. The detection limit of C₈H₈ is 9.0μg/m³ when the optical path reaches 100m. The outdoor field measurement of C₈H₈ was carried out in Binjiang District of Hangzhou, indicating the daily average variation of styrene gas. The results showed that the maximum concentration of C₈H₈ is 60.6μg/m³, the minimum concentration is 38.2μg/m³ and the average concentration is 53.5μg/m³.

Base on computational imaging, a new imaging system is proposed by making full use of global optimization, system reconstruction and control mechanism in practical operation. The theory and engineering method of space-time adaptive imaging are established, which overcome the shortcomings of complex traditional system structure and control factors, and large amount of computation and so on. In the design and implementation of the core optical system, the scientific nature of the standard group, the running speed and the maneuverability of the technology are effectively considered. It promotes a new type of large field of view, super resolution imaging technology, especially wide area applications. The physical and mathematical models are used, as well as the reconstruction algorithm is improved. The experimental system is established, and the simulation results support our theoretical prediction. This technology has potential value in brand fields.

In engineering practice, especially in the structural health monitoring (SHM) of civil engineering, the deformation of concrete is usually small, so a strain sensor don’t need a large measuring range but a high sensitivity. This work presents the structural design, measuring and sensitization principle, and full test of an embedded FBG strain sensor for SHM of reinforced concrete. Two capillary steel tubes protected by a stainless steel tube and embedded with each end fiber of a FBG have been proposed, which possesses the capacity of strain sensitization and adjustment. Experimental results show that sensor provides a sensitivity of 4.2 pm/με in measurement range of ±300με, which is 3.5 times than the bare FBG with center wavelength of 1550 nm. Test results also demonstrate that the sensor possesses good repeatability and creep resistance, which is promising for applications in civil engineering.

A miniaturized underwater polarized radiation measuring instrument (MUPRMI) LiDAR system applied in detecting the polarization optical parameter profiles for shallow water has been designed. This system will be used for detecting the depolarization of laser propagating underwater. For that purpose, a 532 nm linearly polarized laser with the repetition rate of 100 Hz and per pulse of energy of 50 μJ will be used in the system. When propagating underwater, the polarization state of laser will be changed in case of collision with the particles suspended in water. The linearly polarized laser will gradually become non-polarized due to depolarization, and the depolarization degree is related to the suspended particles. In order to detect the depolarization effect of waters, two orthogonal polarization receiving channels have been assembled in the MUPRMI system. For signal receiving, a photomultiplier tube has been assembled in each of the channels. By detecting the change of polarization state, parameters of scattering particles suspended in water in the detecting area can be inverted using inversion algorithm. The MUPRMI system can be controlled by a host computer, which communicate with the MUPRMI system using ethernet communication protocol. An adjustable aperture driven by a stepping motor has been assembled in the receiving optical path. Using this adjustable diaphragm, we can control the change of receiving field of view by transmitting instructions from the host computer, and change the reception of signals from different kind waters. A ship-borne experiments have been conducted in South China Sea, results show that the deepest bathymetry of the MUPRMI system is about 9 meters with the pulse energy of 50 μJ, in South China Sea.

In order to achieve rapid detection of chemical oxygen demand (COD) in seawater, in-situ monitoring technology and instrument for seawater COD based on spectrum analysis were studied. The influence of chloride ion (Cl-), bromine ion (Br-) and turbidity on COD measurement was studied using quantitative method. The results show that the absorption peak of Cl- and Br- is mainly between 190nm and 225nm. The absorption spectral intensity almost unchanged adding Cl- and Br- with different concentrations. The influence of Cl- and Br- on ecological parameters measurement was fixed. The absorbance at 300-720nm is caused by turbidity. Turbidity compensation can be carried out by the absorbance at 300-720nm, the effect of turbidity is eliminated on COD calculation. An absorption spectrum model based on least square method was established using artificial seawater in the laboratory. The model was validated using blind samples, and comparison was done between model calculation and actual value.

We propose an optical gyrocompass using a three-axis Fiber Optic Gyroscope (FOG) that is the technological heart of the optical gyrocompass. The core of the optical gyrocompass is a compact strap-down Inertial Measurement Unit (IMU), which contains a three-axis FOG, three accelerometers, and a real-time computer that is responsible for computing all the necessary data for demanding navigation. Thermal design is performed to manage heat conduction and quickly balance inner temperature of the optical gyrocompass for suppressing the thermally induced error, and then the uniform temperature environment is obtained for three-axis FOG. The long-endurance sea trial experiment result proves that the dynamic accuracy of the optical gyrocompass is lower than ±0.25° secant latitude, and it is capable of navigating in high latitude region. The optical gyrocompass is also certified to meet the requirements of the International Maritime Organization (IMO) for gyrocompasses.

Visibility is one of the important parameters of meteorological observation. Based on the principle of infrared forward scattering and phase-locked amplification, a self-stable visibility meter is designed. The transmitter unit of visibility meter generates 875 nm light pulse at 2.3 kHz. Narrow pulse modulation technology is used to solve the problem of total power and instantaneous power of infrared LED when working, as well as the problem of natural heat dissipation, so as to reduce the aging speed of LED. The photodiode of the backscattering receiver monitors the transmitted light intensity, and adjusts the automatic feedback and the amplitude of the light pulse to keep the light intensity of the LED as the preset value. The visibility meter is compared with Visala PWD20 in the visibility measurement and verification laboratory. The experimental results show that the measurement deviations of one minute and ten minutes are within ±10% and ±4% in the range of 10~20000m. The forward scattering visibility meter is stable and has small measurement error, which can meet the requirements of visibility detection of meteorological stations.