Fiber laser sensing technology is an important part of fiber sensing technology. Firstly, the principle of fiber laser sensing technology is introduced, then the principle and characteristics of ten kinds of fiber laser sensors based on single structure and double structure are analyzed, and the application and temperature sensitivity of two kinds of sensor structures are compared. Finally, the fiber laser sensing technology is summarized and prospected from three aspects, such as demodulation mode, multi-parameter measurement and improved detection range.

Aiming at the problem that the existing vibration displacement monitoring methods are easy to be affected by the environment and the accuracy is not high, a monitoring method of structural vibration displacement based on the inversion of fiber Bragg grating （FBG） sensor array is proposed. This method uses FBG sensor array to obtain multi-point strain and single point acceleration data in the process of structural vibration. Firstly, the curve reconstruction algorithm based on orthogonal curvature and the obtained strain data are used to reconstruct the dynamic displacement of each point of the structure. Then, the displacement data derived from the curve reconstruction algorithm is fused with the single point acceleration data at the same position by Kalman filtering algorithm to obtain more accurate displacement data. The experimental results show that the method can reconstruct the vibration shape of the monitoring structure at any time successfully, and the relative root-mean-square error of the vibration displacement reconstruction of the cantilever aluminum plate and the simple supported pipeline is less than 5.5% and 7% respectively.

In order to improve the sensitivity of Mach-Zender（MZ） optical fiber strain sensor, a MZ optical fiber strain sensor sensitization demodulation system based on parallel cursor effect is designed. The system consists of a sensing interferometer and a reference interferometer in parallel, both of which are Mach-Zehnder interferometer（MZI） with a single mode fiber-no-core fiber-few-mode fiber-single mode fiber（SNFS） structure. By extracting the difference frequency components of two SNFS-MZI signals and tracking the movement of their troughs, the strain sensitivity of the system is improved. In addition, the temperature crosstalk during strain measurement is reduced by extracting the interference spectrum of the reference interferometer separately. The experimental results show that the strain sensitivity of the system is 7.39 pm/με, which is about 5 times that of a single sensor interferometer. By adjusting the sensing arm length of the reference interferometer and the sensing interferometer, the sensitivity performance of the MZ optical fiber strain sensor sensitization demodulation system can be flexibly adjusted.

In order to reduce the complexity of the traditional distributed acoustic sensor（DAS） system and improve the signal-to-noise ratio（SNR）, a DAS system based on a fiber ring laser（SOA-FRL） based on a semiconductor optical amplifier is proposed. This system uses SOA-FRL to replace the narrow linewidth laser and pulse modulator in the traditional DAS system, and realizes the highly stable optical pulse output. The double pulse heterodyne detection method is used to achieve accurate sound signal detection and sound source location. The experimental results show that the demodulation SNR of the proposed system is as high as 38.25 dB and the spatial resolution is 12 m under the action of the acoustic signal with frequency of 1 kHz and amplitude of 1.14 rad.

To solve the problem of noise in signal, an event detection method of optical time domain reflectometer（OTDR） based on improved wavelet transform is proposed. Firstly, by improving the wavelet de-noising algorithm, a new threshold selection method and threshold judgment function are obtained. Then, the event location and the beginning end location of the fiber are measured by combining the wavelet mode maximum method and the slope legal bit, and the event attenuation loss is calculated while the event is separated and the misjudgment is eliminated. The simulation and experimental results show that the proposed method has high positioning accuracy, and the calculated position deviation of reflected event and non-reflected event is less than 5 m and 15 m, respectively. The results of event detection and analysis of the measured fiber are consistent with the connection position and the total length of the fiber.

In order to improve the temperature sensitivity of the system, a fiber Bragg grating（FBG） temperature sensor based on tilted fiber Bragg grating（TFBG） edge filter is designed. In this system, a fiber ring mirror is introduced into the conventional TFBG edge filter demodulation system to reflect the transmitted light signal from TFBG back, so that it can pass through TFBG again, increase the depth of TFBG transmission spectrum, and encapsulate the sensor grating. The experimental results show that the drift of the center wavelength of the sensor grating before and after packaging is 0.55 nm and 7 nm respectively, and the drift of the sensor grating after packaging is expanded by more than ten times. At the same time, because the slope of the demodulation transfer function of TFBG edge filter is improved, the temperature sensitivity of the sensor after wavelength demodulation is also improved, which is 1.6~2.4 times that of the uncascaded optical fiber ring mirror sensor.

In order to improve the sensitivity of optical index sensor, a metal-medium-metal（MIM） waveguide coupled elliptic eight shape cavity is designed. Firstly, the principle and key performance index of the sensor structure are analyzed theoretically. Then, the simulation structure is constructed by using finite element analysis simulation software to study its sensing performance. The simulation results show that when a=540 nm, b=340 nm, g=10 nm, l=70 nm, the sensitivity of the designed sensor can reach 1 323 nm/RIU, and the corresponding quality factor can reach 16.

In order to further improve the sensing performance of biosensors, a dual-core symmetric D-type photonic crystal fiber （PCF） sensor based on the surface plasmon resonance（SPR） effect is designed. The sensor is prepared by stacking, stretching and chemical vapor deposition （CVD） technology, and has two different diameter pores, and the two kinds of pores are symmetrical. The principle of glucose concentration detection system based on the sensor is introduced. The effects of metal materials, stomatal parameters and polishing parameters on the performance of the sensor are simulated and analyzed. The simulation results show that when the refractive index detection range is 1.26~1.41, the maximum wavelength sensitivity, resolution and glucose concentration detection sensitivity of the sensor can reach 24 600 nm/RIU, 4.06×10-6 RIU and 2.73 nm/（g·L-1） respectively.

In order to compare the accuracy of two spectrum fitting algorithms based on the Lorentzian model and the pseudo-Voigt model, a distributed optical fiber sensing principle based on Brillouin scattering is used. Firstly, the calculation results of the measured Brillouin spectra using the Lorentzian model and the pseudo-Voigt model are compared. Then, The Brillouin spectrum with different shapes and signal-to-noise ratios is generated numerically through the pseudo-Voigt model, and the Brillouin frequency shift is calculated using spectral fitting methods based on the Lorentzian model and the pseudo-Voigt model, respectively. Finally, the accuracy of these two algorithms is compared. The simulation results show that underdifferent Brillouin spectrum shapes and signal-to-noise ratio conditions, the computational accuracy of the spectrum fitting algorithm based on the Lorentzian model and the pseudo-Voigt model is similar, but the former requires less computation than the latter.

The first large-scale application of optical fiber communication technology on the international space station （ISS） isan important milestone in the application of optical communication technology from the ground to space. The technological developmentof space optical cable and optical fiber connector used for optical fiber communication in ISS is reviewed, and the specialrequirements of ISS for optical fiber communication technology are expounded. The space adaptability test of optical fiberdevices carried out by national aeronautics and space administration （NASA）, NASA and european space agency （ESA） are responsiblefor building the optical fiber communication system of the module, and the quality investigation and rectification processof the defects of ISS optical fiber communication devices by NASA are introduced. Based on the case analysis of ISS opticalfiber communication device quality problems, the problems and lessons in manufacturing, process, materials, environment, inspectionand management of aerospace optical cable and optical fiber connector are summarized. Finally, the development directionof aerospace optical fiber communication devices is prospected.

In order to study the reliability lifetime model and failure mode of oxidized vertical cavity surface-emitting lasers （VCSELs）, aging experiments are performed on oxidized VCSELs containing AlGaAs/GaAs quantum wells under different stress conditions. The failure lifetime of VCSELs under different stress conditions is obtained using extrinsic function, and then the median lifetime under different stress conditions is obtained. Combined with the junction temperature of VCSELs, an accurate lifetime model is obtained. Finally, the main failure characteristics and causes of oxidized VCSELs are analyzed by transmission electron microscopy（TEM）. The test results show that the lifetime model parameter activation energy of oxidized VCSELs containing AlGaAs/GaAs quantum wells is 0.55 eV and the current acceleration factor is 2.01. The failure reason of oxidized VCSELs is mainly related to the oxide layer with internal stress.

To solve the problem of imprecise upper bound expression of three-branch signal detection（TBSD） scheme, a TBSD scheme of spectrum-amplitude coded optical code division multiple access（SAC-OCDMA） system is proposed, a rigorous mathematical model is established, and the scheme is numerically evaluated and simulated. The simulation results show that the scheme can completely eliminate multi-user interference（MUI） at the transmission rate of 500 Mb/s and 1 Gb/s, and most MUI can be eliminated at the transmission rate of 5 Gb/s, which proves the accuracy of the mathematical model.

In order to implement high speed error correction coding in 400 Gb/s Ethernet physical coding sublayer（PCS）, a recursive Reed-Solomon（RS） coding circuit is designed. By combining recurrence factor, input data and register data, the result of recursive RS coding circuit can be obtained. VCS+Verdi software is used to simulate the traditional RS coding circuit and the recursive RS coding circuit, and the Nangate 45 nm open source process is used for comprehensive testing. The simulation and test results show that compared with the parallel RS（544，514） coding circuit, the recursive RS coding circuit can greatly reduce the time cost. The area of the 32-channel recurrent RS（544，514） coding circuit is reduced by 68% and the power consumption is reduced by 60%.

In intent-driven optical networks, due to the sudden increase in the number of intents sent at the same time or the limitation of underlying physical resources, some users' intent requests cannot be successfully connected, resulting in intent conflicts. In this paper, an intent-driven optical network conflict resolution method based on reinforcement learning is proposed. According to the user intention rollback policy output by reinforcement learning, the network demand index corresponding to the user intention is updated, and the average quality of service（QoS） value in the current network is maximized on the premise of ensuring that the user intention can be successfully connected. The experimental results show that the proposed method can effectively improve the average QoS value of users in the current network environment and reduce the network blocking rate.

In order to take into account both optical fiber data communication and environment perception in a narrow space, a flexural three-core optical fiber is designed and prepared for the integrated system. The fiber has a triangular core arrangement and a deeply fluorine-doped refractive index channel structure with a standard outer diameter of 125 μm. The transmission characteristics of the O-band (1 260~1 360 nm) are optimized, and the Brillouin gain spectrum（BGS） distribution is similar to that of the G.657.A1 optical fiber. The test results show that the average loss of the core layer is 0.58 dB/km at 1 310 nm wavelength, and the average intercore crosstalk is lower than -50 dB/km. When the minimum bending radius R=10 mm and winding 50 times, the bending loss of the optical fiber is less than 0.1 dB.

When using the variational mode decomposition and wavelet threshold adjustment function（VMD-WTFD） algorithm to deal with noise, the signal waveform recovery often deviates from the standard harmonic signal, resulting in deviations of the inversion results. An improved VMD-WTFD algorithm is proposed, which uses a new threshold function to improve the VMD-WTFD algorithm, and then uses this improved algorithm to perform inversion analysis on the second harmonic spectral signal. The simulation and experimental results show that compared with several other denoising algorithms, the improved VMD-WTFD algorithm can invert the peak, peak position, and peak valley values of the original signal under different modulation degrees more closely to the original standard second harmonic spectral signal, with a signal-to-noise ratio of 17.545 dB and a correlation coefficient of 0.992 9 after denoising. It can clearly invert the second harmonic amplitude of CO2 in human exhaled gas.

Aiming at the problem of interference noise in the sampled ultra-weak fiber grating reflection spectrum, a hybrid network denoising algorithm for large-capacity ultra-weak sensor networks is proposed. The algorithm combines the complete ensemble empirical mode decomposition with adaptive noise(CEEMDAN) and the wavelet packet noise reduction algorithm. After the measurement signal is processed by the wavelet packet threshold denoising, the preliminarily processed signal is subjected to CEEMDAN. The eigenmode function(IMF) component and the residual component obtained by the decomposition are superimposed and reconstructed according to the order of the correlation coefficient, so as to obtain the denoised signal. Under the conditions of four different signal-to-noise ratios and 20 consecutive repeatability tests, the experimental results show that the signal-to-noise ratio of the optimization algorithm combined with CEEMDAN and wavelet packet noise reduction can be increased by 3 dB to the greatest extent, the root mean square error can be reduced by 0.245 dB and the correlation coefficient can be increased by 0.0353 at most. The three indexes have been significantly improved.

In order to effectively solve the problem that is difficult to detect for laser spot in underwater laser communication system, a simple and practical underwater laser spot detection algorithm is proposed for the low visibility and complex underwater environment where the water attenuation coefficient is about 5.5 dB/m and the emitter is 5-10 m away from the acquisition end. Firstly, the algorithm enhances the contrast between the target spot and the background through the image defogging operation, after Gaussian filtering, the image noise is eliminated. Then the appropriate threshold is selected for binarization to extract the target laser spot. Finally, the spot center is calculated by the improved gray center of gravity algorithm. The experimental results show that the algorithm is not only simple in calculation, but also can accurately identify the target laser spot and obtain its central coordinates in the case of water quality with low visibility and high attenuation, so that the underwater laser communication system can adjust according to the spot position and realize normal communication.

Distributed optical fiber sensing technology is widely used. In order to use the variation law of birefringence in single mode fiber for vibration signal monitoring, considering the factors such as waveguide shape birefringence, stress birefringence and dynamic strain birefringence caused by vibration in single mode fiber, a single mode fiber vibration monitoring model based on Jones matrix and Stokes vector analysis method is established, the response of the model to 10 Hz sinusoidal and square wave vibration signals is analyzed by simulation and experiment. The simulation results show that the model can identify the type and frequency of vibration signal received by optical fiber.

Compared with the traditional single-mode fiber Bragg Grating(FBG) sensor, the few-mode FBG sensor is less susceptible to the influence of external independent parameters, and has better precision. However, there is no corresponding theoretical basis for the design of grating parameters. For this problem, based on FBG coupled mode theory, the reflection spectrum of the few-mode FBG with LP01 mode and LP11 mode in the fiber core is simulated and analyzed by using OptiGrating and Matlab software. The simulation results show that the reflection spectrum of the few-mode FBG has a three peaks structure which is different from the single peak structure of the traditional single-mode FBG. The changes of grating period, grating length and refractive index modulation depth will have a regular effect on the reflectivity and central wavelength of each peak.

In order to make full use of the advantages of microwave photon frequency doubling and simplify the system complexity, a scheme of broadband terahertz vector signal generation and fiber transmission based on dual-parallel Mach-Zehnder modulator (DPMZM) and uni-traveling-carrier photodiode (UTC-PD) is proposed in this paper. A vector signal is modulated in the positive third-order sideband of the light wave, and the local oscillator signal is modulated in the negative third-order sideband of the light wave. The scheme is simulated and verified by VPI software. The simulation results show that when the system adopts six times the frequency of 36.7 GHz local oscillator signal, a terahertz vector signal with orthogonal phase shift keying with carrier frequency of 220 GHz and code rate of 20 GSym/s is generated. After 1-4 km optical fiber transmission, the power loss of the receiver is less than 3 dBm.

Aiming at the defects of passive compensation optical fiber loop radio frequency transfer scheme using discrete devices to realize double-sideband with carrier suppression(DSBCS) modulation, the stability optimization design and test verification of optical fiber loop radio frequency transmission system based on DSBCS modulation are carried out. An integrated access node circuit based on radio chip is designed to shield crosstalk and reduce the influence of external temperature with cavity separated metal and high-precision temperature control module. The system circuit bottom noise and 60 km optical fiber loop system performance are tested. The test results show that the integrated access node circuit significantly reduces the system circuit bottom noise and 1 m optical fiber transmission bottom noise. The relative stability of the output frequency at 20 km/40 km and 40 km/20 km of 60 km optical fiber loop is better than 4×10-14/s and 2×10-17/day. The long-term stability is about one order of magnitude better than that when the node circuit is realized by separate devices.

Aiming at the problem that the current optical transmitter of digital temperature control introduces the stray interference signal that can not be eliminated, an analog temperature controled microwave optical transmitter with the characteristics of simple circuit, small structure and low power consumption is designed, and the composition of the optical transmitter and the detailed design circuit of each module are given. According to the principle of direct modulation, a microwave link simulation test system is built, and the important index parameters such as S scattering parameters, spurious suppression ratio, harmonic suppression ratio and system noise coefficient of the simulated temperature controlled optical transmitter are tested. The test results show that the link gain of S scattering parameters is greater than or equal to -25 dB, and the gain flatness is ±2 dB. When the spurious suppression ratio is greater than 90 dB, the spurious signals are basically submerged in the background noise of the system. The harmonic suppression ratio exceeds 50 dB and reaches about 67 dB. The noise coefficient is controlled at the level of 2 GHz@35 dB–18 GHz@56 dB, which fully meets the practical requirements.

The signal phase change caused by dispersion is transformed into nonlinear damage after square law detection, which limits the performance of C-band intensity modulated direct detection(IMDD) optical system. Traditional Volterra nonlinear equalizer (VNLE) can compensate such nonlinear damage, but its implementation complexity is very high, so it is not suitable for low-cost and short-distance transmission systems. Neighbor grouped Volterra nonlinear equalizer(NG-VNLE) greatly reduces the implementation complexity by degenerating Volterra terms with the same coefficients, but the degeneracy operation also ignores the differences between Volterra nonlinear terms and reduces the equalization performance. A low complexity nonlinear equalizer for IMDD optical system is proposed. By introducing the nonlinear term based on absolute value, the difference between the neglected Volterra term is compensated. A 107 Gb/s four-level pulse amplitude modulation (PAM4) C-band transmission of IMDD optical system based on directly modulated laser (DML) was carried out to test the performance of the proposed nonlinear equalizer. The experimental results show that it can achieve the performance similar to that of traditional VNLE, and the implementation complexity is reduced by 28%.

In order to analyze the slow light effect in semiconductor optical amplifier (SOA), a theoretical model based on the slow light phenomenon induced by the coherent population oscillation effect in SOA is constructed. The effects of current modulation frequency, modulation current, direct current, linewidth enhancement factor, phase shift and relative phase of modulation current on phase delay in SOA are analyzed. The analysis results indicate that the slow light effect can be controlled by the magnitude of the modulating current and the modulating frequency. When the input direct current is less than 200 mA, the effect on controlling slow light in SOA is not obvious. Compared with the transparent current, the input direct current is larger or smaller to obtain fast light and slow light respectively. When the linewidth enhancement factor is not zero, the sideband signal light changes from fast light to slow light. It is always slow light when phase shift ψ = 0° or 90° and it is always fast light when phase shift ψ = 180°. Changing the relative phase of the modulating current enables the signal to be shifted between slow and fast light.

Due to the strong spatial directivity of the traditional Lambertian beam, the design of visible light communication transmitter based on isomorphic Lambertian beam is difficult to provide satisfactory spatial coverage. Considering the charac-teristics of various non-Lambertian light beams of commercial light-emitting diode(LED) light sources, a transmission diversity technology scheme based on non-Lambertian light beams is proposed. This scheme can make full use of the respective spatial radiation characteristics of the non-Lambertian optical beam to project more transmitted optical power to the coverage edge area far away from the optical transmitter. When the overall transmitted optical power is kept constant and the diversity angle is 60 °, the proposed non-Lambertian diversity scheme can introduce a minimum signal-to-noise ratio gain of 3.4 dB, at the same time, the fluctuation amplitude of signal-to-noise ratio is reduced from 19.4 dB in traditional design to 13.5 dB in non-Lambert design.

In order to improve the performance of free space quantum communication system, based on the principles of phase sensitive amplifier(PSA) and phase insensitive amplifier(PIA), Gaussian modulated continuous variable quantum key distribution (CVQKD) with PSA and PIA at the receiver of quantum communication system is studied, deduces the corresponding security-key rate formula. When the signal wavelength is 810 nm, 1550 nm and 3800 nm respectively, the simulation analyzes the relationship between the security-key rate and the distance when the receiver adopts homodyne detection and heterodyne detection under the collective attack and individual attack, and compares the improvement effects of PSA and PIA on the system performance under the same conditions. The simulation results show that when the receiver adopts homodyne detection and heterodyne detection respectively in detection and heterodyne detection, the system has better performance when PSA and PIA are selected accordingly.

In order to study the light intensity and phase characteristics of the composite vortex beam, two zero-order radial Laguerre-Gauss(LG) vortex beams with different topological charges are coaxially superimposed to produce a new type of composite vortex beam. The influence of the topological charge on the light intensity and phase distribution characteristics of the composite vortex beam is theoretically studied, and the linear relationship between the topological charge and the diameter of the central dark spot and the number of bifurcations of the inner and outer rings is analyzed, and numerical simulation is carried out. The simulation results show that when two zero-order LG vortex beams with different topological charge are superimposed, the light intensity distribution shows a pattern of alternating bright spots and dark spots, the number of bright spots is equal to the difference between the topological charges of the two vortex beams, the phase distribution shows a double ring mode, and the bifurcation numbers of the outer and inner rings are determined by the larger and smaller values of the topological charges respectively, which do not affect each other. When vortex beams with the same topological charge number are superimposed, the number of bright spots in the light intensity diagram is four times that of the topological charge number, and the bifurcation number in the phase distribution diagram is the same as that of the topological charge number.

Aiming at the problem that fiber loss and nonlinear effect will degrade the bending performance of optical fiber, a refractive index profile structure G.654.E optical fiber with ditch layer, transition layer and appropriate cladding ratio is designed, and the effects of waveguide structure of G.654.E optical fiber on attenuation and optical performance are studied. The test results show that at 1550 nm and 1625 nm wavelength, the typical attenuation values of optical fiber are 0.162 dB/km and 0.178 dB/km respectively. When the bending radius is 10 mm and one turn is wound, the macro bending loss is lower than 0.04 dB and 0.06 dB respectively. When the bending radius is 30 mm and 100 turns, the typical values of macro bending loss are 0.008 dB and 0.015 dB respectively. The typical effective area of optical fiber at 1550 nm wavelength can reach 130 μm2.

The existing 4G and 5G devices can generally support the dual-stack IP address networking carried by 5G base stations, but there are still difficulties in how to span a variety of professional networks and accurately complete the end-to-end networking configuration in the current network. To solve this problem, aiming at large-scale engineering deployment, an end-to-end dual-stack networking scheme for 5G base station is proposed, and the sliced packet network(SPN) system and the existing network end-to-end are tested and verified in the real network environment. The test results are given to verify the feasibility of the dual stack networking scheme. Finally, an example is given to introduce the troubleshooting method.

In view of the small number of core aggregation nodes in the local network of operators, the coverage area of a single aggregation node is too large, the service access aggregation cannot be realized quickly, and the multi-service access platform (MSAP) equipment is difficult to meet the demand of private line service with the rapid growth of bandwidth. This paper summarizes the capability and cost advantages of access optical transport network(OTN) equipment, and a feasible application proposal for networking deployment of access OTN equipment is put forward.

In order to increase the transmission capacity of communication system exponentially, a 3×3 mode division multiplexing experiment platform is constructed using 10 km few-mode optical fiber, the mode conversion and multiplexing are realized by the mode-selective photon lantern, and the modulation and detection process is carried out in the phase modulation-coherent receiving mode, and the effective transmission of the 3×34 Gb/s polarization division multiplexed-quadrature phase shift keying (PDM-QPSK) signal is finally completed. The results show that if the received power of LP01, LP11 and LP21 is not less than -25.32 dBm, the bit error rate can be certainly reduced to less than 10-3.

Most of the existing methods to enhance the security of optical transmission network are based on the network level and cannot guarantee the security of optical transmission equipment, this paper proposes to introduce the pseudo defense technology into the management and control system of optical transmission equipment, and designs a redundant heterogeneous multi-core architecture. Based on the system similarity, the attack probability model is constructed and verified by simulation. The results show that the proposed method significantly reduces the probability of successful attack and greatly improves the security performance of pseudo software defined optical network transmission system.

In order to match the link working mode in practical application, based on the in-depth understanding of JESD204B protocol theory, a general transmission layer circuit is designed, and the three-level mapping structure is used to realize the framing and deframing functions of the transmission layer at the sender and receiver. This paper establishes Verilog compilation simulator (VCS) verification platform for function verification. The simulation show that the circuit can complete the conversion between sampling data and frame format data according to the set link working mode, and realize the framing and deframing functions, and based on the comprehensive evaluation of 65 nm standard process library, the maximum frequency of single channel clock of the circuit is 1.25 GHz, which can reach the maximum transmission speed supported by the protocol of 12.5 Gb/s.