This PDF file contains the front matter associated with SPIE Proceedings Volume 12279, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Micro-cavity sustaining whispering gallery mode (WGM) has been widely used in physical parameter sensing and biosensing applications. We explored three type micro-cavity enhancement methods to realize highly sensitive optical fiber sensors. Firstly, optofluidic-enhanced micro-cavity optical fiber sensors are discussed. Secondly, optomechanical oscillation micro-cavity optical fiber sensor is introduced using a hollow silica microbubble cavity. Finally, fiber laser enhancement mechanism is proposed to avoid the difficulty in direct fabrication of active micro-cavity.

Magnetic field as a kind of objective substance contains abundant physical information, so high sensitivity and resolution measurement for the magnetic field has great significance in scientific and industrial fields. In this work, we verify a highly sensitive cascaded Mach-Zehnder interferometer (C-MZI) sensor based on optical Vernier effect for the magnetic field measurement, which is composed of a reference MZI (R-MZI) without magnetic fluids (MFs) connected in series with a sensing MZI (S-MZI) with MFs. An evident envelope and shift induced by the external magnetic field is observed in the transmission spectra of the C-MZI, resulting in the sensitivity being elevated by an amplification factor. The experimental results reveal a wavelength sensitivity of -5.148 nm/mT in the range of 10.15~30.44 mT, being ~4.77 of that in the single S-MZI. In order to further improve the detection resolution of the magnetic field, a magnetic field measurement system based on the combination of the above S-MZI and an optoelectronic oscillator (OEO) is proposed, and the spectral response is tested in a small magnetic field range of 1.45~1.90 mT, obtaining a spectral sensitivity of 3.18 kHz/mT, which proves the detection of less than 1 Oe. The designed sensor and system possess the merits of high sensitivity, high resolution, simple fabrication, fast response and low phase noise, having broad prospects in the fields of magnetic field measurement.

We proposed and analyzed a fiber-laser ultrasonic sensor based on remote coupling. Utilizing the unique anti-environmental disturbance ability of the remote coupling, together with the transient response characteristics of the fiber laser, a good detection of the ultrasonic signal can be achieved under configurations with different coupling parameters. The detection effect of continuous and pulsed ultrasonic signals under different distances among the ultrasonic signal source, the fiber sticking position and the ultrasonic receiving unit was experimentally demonstrated. The ultrasonic sensor has high value in practical engineering applications.

In this paper, a whisker array sensor for object surface shape measurement is designed and experimentally demonstrated. The developed sensor is based on a 4×4 whisker array with fiber Bragg grating, which imitates the structure of the facial whiskers of animals like mice and dogs. The surface shape reconstruction is based on the curvature information of each sensing point by measuring the wavelength shift of each fiber Bragg grating fixed on the whisker. The conversion coefficient between wavelength shift and bending curvature is obtained then the change of fiber Bragg grating is converted into corresponding bending curvature. The measurement error on the altitude of the whisker of each sensing point is about 1.2%. By curve fitting the curvature information of the whole fiber Bragg grating whisker array, the surface shape of the target surface is reconstructed. In this experiment, the spatial resolution of the sensor is 10 mm, which can theoretically meet the need of any spatial resolution by adjusting the measurement algorithm. The design successfully realizes surface shape sensing, which has important practical value in the field of robot tactile, in aviation and disaster relief.

The key technology for expanding the scope of application fields for the phase-sensitive optical time domain based reflectometer (Φ-OTDR) is to accurately demodulate the vibration position with a wide frequency range. Unfortunately, due to the restriction of the traveling time of the modulated pulse, it is very difficult to obtain the low frequency response with a high signal to noise ratio (SNR) and to achieve a higher detectable frequency response in the Φ-OTDR. In this paper, a scheme based on dual-wavelength probes is proposed and demonstrated to enhance the dynamic frequency range with a high SNR in the Φ-OTDR based distributed optical fiber vibration sensing system. Utilizing the small difference between the central wavelengths of the two laser sources, the location and the frequency information can be simultaneously obtained by the reflectometer and a symmetric based interferometer. In addition, to further improve the SNR of the demodulated vibration spectrum and to suppress the high-order harmonic effect induced by the piezoelectric transducer, an enhanced phase generated carrier demodulation algorithm is employed in the proposed scheme. In experiments, the proposed sensing scheme showed better performance compared to previous studies. Foreseeably, the proposed sensing scheme will greatly extend the sensing scope for the Φ-OTDR based system where a wide frequency response is required.

A distributed pH sensor was proposed by using the optical frequency domain reflectometry and a hydrogel coated single mode fiber (SMF). The swelling of the hydrogel will convert the pH value to the axial strain in the fiber. Taking capacity of distributed strain measurement with high spatial resolution, the pH value of the external medium surrounding the hydrogel-based optical fibers is distributed measured by the optical frequency shifts of the local back-reflection spectra in optical frequency domain reflectometry. In the experiment, the range of the pH value from 2 to 5 was measured with a spatial resolution of a 3.1 mm and a sensitivity of 60 pm/pH when the hydrogel coating diameter is 0.8 mm.

In this paper, a FMF sensor with double gourd structure is prepared. The transmission spectrum and mode changes of double gourd structure with different lengths are studied, the temperature sensitivity and linearity of the sensor are analyzed. Five sensors with different FMF lengths are prepared. The waist-enlarged spacing are 0.7cm, 1.0cm, 1.3cm, 1.6cm and 1.9cm, respectively. The FMF length are 4.1cm, 5cm, 5.9cm, 6.8cm and 7.7cm, respectively. The experimental results show that the highest temperature sensitivity of FMF sensor is 86.95pm/℃. There is no one-to-one correspondence between the temperature sensitivity and the length of the sensor.

Distributed acoustic sensing technology has a wide range of applications such as seismology, mineral exploration, and so on. For practical application needs, we contributed to increase demodulation rate of optical fiber distribution acoustic sensing system. Aiming at the problem of large volume of signal acquisition data and long demodulation time, we proposed to apply a hardware circuit as a part of data acquisition system. We also applied a GPU-based fast processing algorithm to realize simultaneous calculation of different units. Through the combination of hardware and software, the fast signal demodulation based on low sampling rate was successfully realized.

Aiming at the current demand for precise fault location and early warning of power OPGW optical cables, a method of OPGW optical cable fault location and early warning based on BOTDR/A technology is proposed. This paper proposes a method for locating the connection pole based on the DBSCAN algorithm. The connection point is located through the Brillouin frequency shift curve, and then the fault is accurately located. The Brillouin frequency shift is linearly affected by temperature and strain, which are linear relationships and cross-sensitive. The isolation of the OPGW cable strain and temperature is achieved by the identification result of the fiber optic splicing point. The abnormal region is positioned and warned by strain measurement. Field picture collections are performed for typical abnormal strain areas, and the positioning and cause of fault warning is confirmed. The OPGW fault positioning and early warning method proposed herein, significantly improves the efficiency of fault processing and improves the operational reliability of OPGW optical cables.

A multi-dimensional hybrid feature extraction scheme for optical fiber distributed vibration sensing system has been proposed in this work. Firstly, the hybrid features are extracted through using zero-crossing rate, wavelet packet energy entropy, empirical mode decomposition based kurtosis, skewness and multiscale permutation entropy. Secondly, an effective feature vector are built based on all the above-mentioned features. Finally, the established features are classified and recognized by a radial basis foundation neural network. A series of experiments have been implemented to validate the effectiveness of the proposed scheme. Results show that the proposed scheme can efficiently and accurately identify five common sensing patterns. Specifically, the average recognition accuracy of 99.2 % is achieved and the response time can be limited less than 1 s. Therefore, it is believed that the proposed pattern recognition scheme has a good potential in the application of the optical fiber distributed vibration sensing system.

This paper reports a compact, universal and all-digital lock-in amplifier design to complete the broadband optical spectrum signal measuring, which can be utilized in the optical spectrum analysis, coded Brillouin optical time-domain sensors, and ultra-low optical signal capturing. With the development of the integrated circuit these days, all the components, including the phase detector, reference signal generator, and complex calculators, required in such system are built digitally, leading to a compact and universal design that can be implemented in the various situations. Furthermore, benefited from the 24-bit analog-digit converter (ADC) employed in the design, this lock-in amplifier has achieved a real-time dynamic range over 100dB.

Fiber Bragg grating (FBG) sensor has been one of the main research objects in the field of optical sensing due to its advantages of compact size and capability of multiplexing and long-distance measurement. Since its central wavelength shift has a linear relationship with the measurand change, the typical demodulation method is to fit such relationship linearly or nonlinearly, and demodulate the measured parameter based on the change of Bragg wavelength. In this paper, particularly for an FBG temperature sensor, an effective sensing signal measurement method employing deep convolutional neural networks (DCNN) is proposed. This method can extract temperature automatically with a comparable and even more accurate precision. After training process of DCNN, the temperature information can be directly extracted from the experimentally obtained FBG spectra instead of tracking the peak. Since it makes full use of the spectral information rather than only the central wavelength, it overcomes the limit of traditional fitting method and can improve the measurement accuracy of FBG effectively, with an accuracy of 99.38% and mean error of 0.608. The proposed approach to demodulate the FBG sensors is experimentally verified by checking various spectra obtained at different temperatures, and superior accuracy could be achieved. It provides a cost-effective solution for multiplexing of FBG sensors, and is promising for establishing sensing networks to implement smart monitoring.

There are anti-electromagnetic interference and electrical insulation of distributed optical fiber sensing technology. It is widely applicable to industrial fields. However, the fully distributed optical fiber sensing system produces a huge amount of data in the monitoring process. The compression of distributed optical fiber sensing data has become the focus of scholars at home and abroad. The time dimension of vibration signal is considered in the compression of Phase-OTDR vibration data. However, the spatio-temporal structure characteristics of distributed optical fiber vibration signals have not been considered. Therefore, phase OTDR vibration data are analyzed from two dimensions of time and space. The improved Otsu signal-to-noise separation method is applied to complete the signal-to-noise separation of vibration data. Firstly, the distributed optical fiber data is randomly divided into different parts. Secondly, the processed data is initialized to the threshold. Then the inter class variance is calculated, and the optimal threshold is determined by simulated annealing algorithm. The optimal solution obtained is regarded as the optimal solution of signal-to-noise separation. Finally, three different signals adopt EMD algorithm and improved algorithm for comparative experiment. The SNR evaluation index and visualization are adopted to show the advantages of the improved algorithm. The experimental results show that the algorithm has good signal-to-noise separation effect than other algorithms.

Hollow waveguide (HWG) as an absorption cell for gas spectral sensing has the advantages of low transmission loss, fast response speed, and high path length to volume ratio. However, the transmission of laser beams in HWGs relies on the multiple reflections by the inner wall, and it makes the path length of laser beams emitted from HWGs unequal, thereby limiting the high-precision measurement of gas concentration. Two mathematical models were established based on geometric optics to characterize the effective path length ratio (EPLR) distribution of the laser beam emitted from a straight HWG and a bent HWG, respectively. The effects of HWG parameters and incident conditions on EPLR distribution was investigated, and quantitative analysis was carried out. Experimental verification was performed by basing heterodyne interferometry. A formula to calculate the equivalent path length ratio of a laser beam propagating in an HWG was given, which simplifies the complicated calculation caused by the path length not unique and demonstrates 1-6% reduction in measurement error. The proposed method has guiding significance for high-precision measurement of absorption spectroscopy, and can extend to both substrate-integrated HWG (iHWG) and liquid waveguide capillary cell (LWCC) based optical sensors.

It is small footprint, simplicity, and inexpensive that the direct modulation of a semiconductor laser to generate optical frequency combs (OFCs). However, their OFCs spectral characteristics are heavily dependent on the modulation signal waveform and the current parameters of the laser. It is essential that the research of more useful modulation signal and driving conditions to optimize the OFC performance. We evaluated the performance of the OFCs under gain-switched distributed feedback (DFB) lasers with several common modulation waveforms. It is showed that the relaxation oscillation frequency (ROF) was a restricted condition on the coherence of the OFC under the gain-switching (GS) mode when modulation frequency lower than ROF. We demonstrated that OFCs can be realized in a gain-switched DFB laser with a narrow pulse-width modulation signal under a lower modulation frequency than the ROF of the laser. The OFCs was realized with a comb spacing of 100 MHz, spectral width of 2 GHz, and carrier-to-noise ratio of 29.01 dB by a narrow pulse modulation signal with modulation frequency of 50 MHz at I_ON = 38.72 mA, I_OFF = 0.12 mA, pulse width of 1 ns. The performance of the OFCs under the narrow pulse and sinc modulation signals with different modulation frequency parameters and current driving conditions is further evaluated. This method of tuning the pulse modulation signals to achieve optimization of OFC performance has the advantages of simple operation, flexible settings, and inexpensive. This will have greater application value in high-resolution spectroscopy detection, especially a dual comb spectrum technology.

The random fiber laser (RFL) combining a 3×3 coupler phase interrogation technique is demonstrated and applied to acoustic emission (AE) detection for damage detection of buoyant materials. The random chirped grating array (RCGA) is used to provide random distributed feedback and act as an AE sensing head. The random distributed feedback inside RCGA significantly extends the effective cavity length of the RFL, thus reduces the thermal frequency noise of the RFL and improves the resolution of AE signal. A π-phase-shifted fiber Bragg grating (π-FBG) loop mirror is used as a wavelength locking to ensure a stable and narrow lasing. A high AE signal resolution of 2.6×10^-7 pm/√Hz@10 kHz is achieved.

In this paper, we build a noise model to investigate the number of sensors in fiber-optic interferometric sensing TDM system. The noise model incorporates many parameters which may have an effect on the number of sensors in the system, such as the various key noise and the optical power. Utilizing the noise model, we get the characteristics of system noise and major noise contributions under different numbers of sensors by simulation. The noise model we build can offer guidelines for the design of the interferometric fiber-optic sensing TDM system.

To realize the non-contact on-line measurement of the crucial dimension for the fuel assembly and assist the nuclear power plant to carry out regular maintenance works in the core, we design an underwater fuel assembly deformation measurement system (UFADMS). Based on the principle of dual-optical line laser triangulation, the deformation measurement system integrates two sets of optical units. During the measurement, each optical unit projects two beams of laser to the surface and captures the relevant image for further process, respectively. According to the point clouds obtained by underwater calibration, three-dimensional (3D) reconstruction, and global calibration, we can calculate the relative relationship between the two optical units, and normalize the corresponding measurement data to calculate the bow and twist deformation of the fuel assembly. Benefitting from the novel waterproof design, the dual-optical line laser triangulation principle, and the underwater single-layer refractive geometry, the measurement system has strong environmental adaptability, high measurement accuracy, and short measurement time. Through the underwater field measurement and validation of standard blocks and fuel assembly, the bow deformation measurement accuracy is within 0.4 mm, and the twist deformation measurement accuracy is within 0.15°. What’s more, the proposed system allows transient measurement at a certain depth of water, which provides a guarantee for on-line measurement of fuel assembly underwater.

A zero drift suppression method of arctangent demodulation algorithm for fiber optic acoustic sensors is studied in this paper. Firstly, the principle of the arctangent demodulation algorithm is introduced, with emphasis on the principle and implementation method of the phase unwrapping. Then, the design and implementation idea of the zero drift suppression method are described in detail. A PID method is used to get the compensation value, which will be fed back to the next phase unwrapping stage, so as to gradually eliminate the zero drift. By adding a decimation unit and combining the low-pass filter unit and the PID unit, the complexity of the algorithm and the design difficulty of the filter are greatly reduced. The designed zero drift suppression method is implemented in FPGA. An actual fiber optic microphone is demodulated under laboratory conditions. The experiment results prove that the zero drift suppression method designed in this paper can stabilize the static operating point of the fiber optic microphone effectively. As the zero drift problem is solved in algorithm, there are no any hardware modification and additional cost.

We propose and experimentally demonstrated a Tunable-Diode-Laser-Absorption-Spectroscopy (TDLAS) system using low-cost tunable DFB laser array. We implement Reconstruction-Equivalent-Chirp (REC) technology for a low-cost DFB laser array which is suitable for TDLAS system. Meanwhile, monolithic integration of multi-wavelength laser array is achieved, covering multiple absorption spectral lines. A gas sensing system for multi-peak detection is built. We chose methane as the interested gas in the experiment. The sensing data for absorption peaks of methane, including 1642.9nm, 1645.5nm, 1650.9nm and 1653.7nm are obtained. The methane concentration is measured as low as 500ppm.

The visible light communication system based on LED display has the functions of display and information transmission at the same time, and has a wide range of potential applications in information broadcasting and stealth advertising. This paper proposes a real-time visible light communication system based on LED display. The system uses the LED display screen as the light source, completes data processing through FPGA, and the detection system uses PIN diodes as the detector to receive the light radiation signal of the display panel. In this paper, the universal asynchronous receiving/transmitting and coding mark reversal scheme is adopted to solve the most critical problem of the display communication system, that is, the timing problem of display data and optical communication data. Experimental results show that the system can receive characters, files, and pictures. Combined with FPGA data processing, when the system transmits data at a rate of 9.6kbps, under the condition of full-screen LED display, the communication distance is 105cm and the bit error rate is 2.7 ×10^-4.

Spun fiber has been used for current-sensing applications for decades. However, in actual situation, disturbance like squeezing or bending of spun fibers often causes evolution of polarization and eventually causes Faraday phase shift error. In this paper, we try to find out how bending will influence the polarization state of propagating light in spun fiber. We use a big bending spun fiber coil (50 cm in diameter) with a small disturbance coil (2-3cm in diameter) to easily simulate and quantify the magnitude of fiber bending. We calculate the polarization states of the left-hand and right-hand circular polarizations by solving differential equation of a spun fiber coil placed in the magnetic field generated by a current. Our results show that fiber bending will weaken the polarization-maintaining ability of spun fiber, causing polarization state oscillates periodically.

In this paper, we propose a fast endpoint detection method for dual Mach-Zehnder interferometer-based vibration sensing system. Firstly, we analyze the varying trend of the signal by derivation to detect the approximate endpoint. Secondly, we split part of the signal before the estimated endpoint into frames. Finally, we estimate the signal to noise ratio of each frame to calibrate the endpoint. Experiments have been carried out to verify the effectiveness of the proposed algorithm. The results show that the accuracy is improved by using threshold judgement twice. And the mean processing time of the proposed method is 0.024s which is at least three times faster than the conventional zero-crossing ratio-based method which is the fastest algorithm as we know. Therefore, the proposed method has great potential in real-time monitoring based on distributed fiber interferometer vibration system.

According to the difficulty in selecting the parameter of SVM when modeling on the gas quantitative analysis, and existing methods need a long time, SVM optimized by improved grid search method is proposed to build an NH₃ gas quantitative analysis model of ring cavity system based on thulium doped fiber laser. Firstly, the initial spectral data of NH₃ are preprocessed and dimensionality reduced by principal component analysis (PCA). Then, the optimized cost factor C and RBF kernel function parameter g are obtained by the improved grid search method, which is substituted into a support vector machine for concentration regression analysis. Experiments show that the optimal SVM parameters obtained by the improved grid search method are C = 1.6245 and g = 2.2191. And it greatly reduces the optimization time compared with the traditional grid search method. The mean square error of the prediction results is within 10%, R² is 0.984, which basically meets the requirements of gas concentration prediction.

As a kind of non-contact displacement sensor modulated by wavelength, spectral confocal microscopy system has high measurement accuracy and is insensitive to object tilt and surface texture, and has strong anti-stray light ability, which makes it become a hotspot of current research. The traditional spectral confocal microscopy system uses a wide-spectrum light source to illuminate the pinhole and dispersion objective lens to generate dispersion on one side of the measured object. The dispersion objective lens focuses the light of different wavelengths at different positions of the optical axis, converts the displacement information into wavelength information, and detects the reflected spectral information by CCD industrial camera or spectrometer to determine the peak wavelength of the focused light on the object surface, Thus, the axial distance information of the object surface to be measured is obtained. In this paper, based on the analysis of the traditional confocal microscopic system, a linear dispersion objective lens of the confocal microscopic system was designed. The axial dispersion of 3.228mm was achieved in the wavelength range of 450nm to 650nm, and the linear determination coefficient between axial dispersion and wavelength was greater than R²=0.9859.On this basis, a dual-optical path detection structure based on edge light is designed. By adding three impurity filters to filter stray light except the target wavelength, the results show that the new spectral confocal light path has high sensitivity, small stray light and strong anti-interference ability.

A DNA modified long period fiber grating (LPFG) was proposed and fabricated for measurement of mercury ion (Hg²⁺) concentration. The T-T base pair of Hg²⁺ and DNA can specifically bind to form T-Hg²⁺-T complex, which leads to the transition of DNA from irregular free helix conformation to hairpin structure, thereby changing the refractive index of the fiber surface. Firstly, the DNA sequence and coating methods were analyzed and optimized, and the sensing mechanism and phase matching conditions of LPFG were analyzed by using Rsoft. The simulation results showed that reducing the cladding diameter and period could increase the refractive index sensitivity, and changing the length of the gate region would not affect the sensitivity. Besides, the LPFG at the phase matching turning point had higher sensitivity. Then, a CO₂ laser was used to prepare LPFG with a period of 250 μm, and the DNA was fixed on the surface of the grating by electrostatic adsorption with using Poly-L-lysine as the polycation molecule. The results of Hg²⁺ detection experiments showed that when the concentration of Hg²⁺ increased from 6 μM to 18 μM, the resonance wavelength at the trough shifted from 1623.8 nm to 1627.37 nm. There was a linear relationship in the range of 6~12 μM with sensitivity of 0.505 nm/μM. In conclusion, the proposed Hg²⁺ sensor based on DNA modified LPFG structure behaves the advantages of simple production, low cost, and high specificity, which has great potential in the actual environment.

In this paper, we propose an improved denoising and positioning method for fiber optic perimeter security system based on the φ-OTDR. We combine the lifting scheme of the discrete wavelet transform (LSDWT) and the total variation (TV) based image denoising algorithm to suppress the background noises and magnify the man-made intrusion signals, and the positions of man-made intrusion can be acquired with the denoised signals through the variance-based positioning method, which mainly determines the man-made intrusion signals by calculating the variance of the temporal signal. A series of experiments have been carried out to validate this method. In the scheme, three types of man-made intrusion behaviors such as knocking, waggling, and tapping were implemented at the end of the 40 km optical cable, while the background noises such as natural noise and sound of car driving were continuing. Compared with the original signals, the peak signal-to-noise ratio (PSNR) of the signals after the proposed scheme has been greatly enhanced, and a ±15m positioning error can be realized at the end of the 40 km fiber cable. Therefore, the proposed method can provide new thinking to address the high positioning error at the end of the long-distance optical fiber cable.

A modular 32-channel ultra weak fiber Bragg grating (uw-FBG) demodulation system is proposed. This system includes an optical pulse generating unit, an optical circuit unit, a signal processing and control unit. The signal processing and control unit is developed with Xilinx ZYNQ-7020 SOC as the core to collect the data from the 250 MSPS high-speed AD chip, and obtain the position information of all uw-FBGs after calibrating each channel with C# host computer firstly. In the test mode, the signal processing and control unit controls the wavelength scanning of the optical pulse unit, coordinates the switching of 32 optical channels in the optical line, and demodulates and stores the grating wavelength changes on each channel in real time based on the embedded wavelength demodulation algorithm. The system is less than 13 W of the power consumption, the volume is 230 mm × 170 mm × 40 mm, the single channel sensing distance is greater than 10 km, and the number of gratings is greater than 5000. It truly has realized the massive sensing of uw-FBGs.

The 16m spatial resolution of the Gaofen-1 satellite WFV camera (GF-1 WFV) has potential advantages in ground feature recognition. However, due to the lack of shortwave infrared channels, it is difficult to invert the ground surface reflectivity using the traditional dark pixel method. Taking GF-1 WFV apparent reflectance data and ground-based atmospheric data as input, an atmospheric correction algorithm based on the 6S radiation transmission model is constructed. In order to verify the accuracy of the algorithm, the inversion reflectance value of Dunhuang calibration site was compared and analyzed with the measured Gobi surface reflectance data. The results showed that the relative errors of the blue, green, red, and near-infrared bands were all within 6%; Comparing and analyzing the reflectance products of Sentinel-2 and GF-1 WFV, the results show that the relative errors of blue, green, red, and near-infrared bands are all within 4%.

This paper shares a conjecture that in a specific low temperature region, the fiber delay coefficient with temperature exists a transition process. In the specific low temperature region, the soft and hard state of the optical fiber coating changes with temperature, which affects the strain effect of the coating on fiber core. At normal temperature, the soft inner coating layer has no strain on fiber core, while at ultra-low temperature, the inner plastic coating becomes frozen and hard. The frozen coating exerts strain on fiber core, resulting in additional length change and the increase of fiber delay coefficient. According to the theoretical analysis and experimental data, this paper briefly introduces the sources and main influencing factors of optical fiber delay, emphatically analyzes the influence of optical fiber coating on fiber delay coefficient in a specific low temperature region, and gives the possible explanation of the action of coating on fiber delay coefficient.

For farmland, water bodies, villages and other areas in the Julu, Hebei, the inversion of GF-1 surface reflectance was carried out. Based on time-series remote sensing images, the Sentinel-2 satellite surface reflectance product was used to compare and verify the surface reflectance inversion results of the Gaofen-1 satellite. From February 2020 to January 2021, a total of 10 sets of valid images were acquired, with 5*5 pixels as a sample unit, and the test results of a total of 210 samples showed that the average absolute error of the reflectance is within 0.03 with the farmland, villages and other ground objects, and the average absolute error of the reflectance for the water body is within 0.055. In terms of correlation coefficients with Sentinel 2 data, the average correlation coefficient between farmland and villages was 0.999, and the correlation coefficient for water bodies was low, 0.158. This algorithm performs well in the target areas of farmland and villages, which is not suitable for water targets.