The wavelength-encoded optical fiber position sensor has the advantages of being insensitive to light intensity changes and high stability. In order to further simplify the structure and reduce the cost, a new type of wavelength-encoded optical fiber position sensor is proposed. Using 10-order binary pseudo-random m-sequence as the coding standard of the sensor, the coding scale is made with a grating pitch of 100 μm and the sensing system is built, and the absolute position information is demodulated by the output voltage of the working channel. At the same time, the arrayed waveguide grating(AWG) is used as the demultiplexer and multiple photodiodes form a multi-wavelength detection system, which simplifies the sensing system and improves the response speed. Using a stepping motor with a unidirectional positioning accuracy of 6 μm as the displacement standard, the feasibility of designing a sensor with a resolution of 100 μm is verified.

The structure, material, processing technology and driving power characteristics of semiconductor pulse laser are important factors affecting its performance. Combined with the technical indexes such as pulse width, output power and repetition frequency, the development and research status of semiconductor pulse laser are summarized. This paper focuses on five ways to improve the performance of driving power supply, including narrow pulse superposition direct-current(DC) bias method, application of energy storage elements, cascade or array of high-speed switches, application of programmable logic devices, device selection and layout innovation, and points out the shortcomings of current technology. Finally, the development trend of semiconductor pulse laser is prospected.

Nd: YAG ceramics have the characteristics of large size and low cost, but the mode-locked laser based on Nd:YAG ceramics has not been widely verified. Using Nd:YAG ceramic as gain medium and semiconductor saturable absorption mirror (SESAM) as mode-locked element, the W-type resonator is optimized. When the pump power is 11.49 W, 1.25 W stable mode-locked laser with laser wavelength of 1.06 μm and repetition frequency of 144 MHz is generated. The pulse width of the mode-locked laser is 33.6 ps, the single pulse energy is 8.7 nJ, and the peak power is 0.26 kW. The experimental results show that Nd:YAG ceramics can be used as gain medium in passively mode-locked ultrafast picosecond lasers.

The laser driving circuit is an important part of the transmitter in the optical communication system. In order to meet the needs of high-speed electric/optical conversion, an externally modulated laser(EML) driving circuit is designed based on the 28 nmcomplementary metal oxide semiconductor(CMOS) process. The whole driving circuit adopts a five-stage cascade architecture, including variable gain amplifier (VGA) and two-stage continuous time linear equalizer (CTLE), preamplifier and output stage. The driving circuit adopts a new complementary amplification and cascode structure, the input of the drive circuit is a 50 Gb/s fourth-order pulse amplitude modulation(PAM4) signal. The simulation results show that the small signal bandwidth of the driving circuit is 27 GHz. When the output swing is 1 VPP at 12.5 GHz and 0.22 VPP sinusoidal input, the total harmonic distortion(THD) is 2.21%. The voltage gain range is 13.98~20.24 dB, and the total power consumption is 340 mW.

The bidirectional erbium-doped fiber amplifier(Bi-EDFA) is a key component of the spatial domain active fiber cavity ring-down sensing system, and its gain characteristics and noise characteristics directly affect the stability of the sensing system. A low-gain and low-noise gain-clamped Bi-EDFA suitable for spatial active fiber cavity ring-down sensing systems is designed and optimized by Optisystem simulation software. The simulation results show that by optimizing the design, a Bi-EDFA with gain coefficient and noise coefficient of 15.35 dB and 3.52 dB respectively can be obtained, and the gain can be clamped.

In view of the test requirement of 400 Gb/s optical module in research and development and production, a low-cost 4-level pulse amplitude modulation(PAM4) signal bit error ratio tester(BERT) design scheme is proposed. Firstly, the overall scheme and implementation principle of BERT are introduced, and the requirement of 400 Gb/s optical module test for BERT and the characteristics of digital signal processing(DSP) chip inside the optical module are analyzed. Secondly, according to different application scenarios, two hardware implementation forms and software design points of BERT are detailed. Finally, the BERT is tested in practice, and the results of PAM4 electrical signal and optical signal are given, and the results show that the BERT can meet the needs of practical application.

The structure of tapered fiber is of great significance to optimize the optical performance of tapered fiber amplifier. The variation of evanescent wave transmission depth of tapered fiber with different structure forms is analyzed, and two optimization schemes of tapered fiber structure are proposed. Combined with rate equation, power equation and finite difference beam transmission method, the model of quantum dot tapered fiber amplifier is established, and the influence of tapered fiber structure form on the performance of the amplifier is studied. The simulation results show that changing the initial melting length and stretching length can make the incident angle closer to the critical angle under the condition of total reflection, so as to increase the evanescent wave depth on the surface of the cone. The optimized tapered fiber structure is conducive to the improvement of the performance of the fiber amplifier.

In order to achieve low-cost, long-distance high-precision distributed temperature measurement and improve the cost-effectiveness of the Raman distributed temperature sensor(RDTS) system, a novel Raman distributed temperature sensor based on chirp pulse compression technique using intensity-modulated is proposed. The system structure and corresponding signal modulation and demodulation methods are described, and the performance of the system is verified by experiments. The experimental results show that the new RDTS system achieves 1.6 m spatial resolution and 1.8 ℃ temperature resolution at 35 km sensing distance, which solves the problem of mutual restriction between spatial resolution and temperature resolution in traditional RDTS system.工作。

In order to identify and locate the degree and type of fault in hydraulic pipeline, a method of multivariate variational mode decomposition(MVMD) and weighted fusion of instantaneous phase characteristics and dominant frequency amplitude is proposed. The pipeline strain is monitored by distributed fiber Bragg grating(FBG), and the effective fault characteristics are extracted from the phase and amplitude of sensor signals, and the simulation experiments are carried out. The simulation results show that the pipeline fault features can be identified and located effectively according to the weighted fusion feature vector, and the accuracy of fault degree recognition is more than 98%.

As the optical fiber composite overhead ground wire(OPGW) in a complex environment will be affected by environmental changes for a long time, and the optical fiber, metal single wire, grease and optical unit tube in the optical cable structure will be affected to varying degrees, eventually leading to power communication failure. A risk assessment method for OPGW optical cable status based on environmental parameters and principal component analysis is proposed. According to the environmental parameters collected by fiber grating sensors in overhead lines, subjective and objective weighting method and principal component analysis are used to evaluate the OPGW optical cable status and data analysis. The data analysis results show that this method can effectively reflect the operating status of OPGW optical cable.

Aiming at the problem of high peak-to-average power ratio(PAPR) in asymmetrically limited optical orthogonal frequency division multiplexing(ACO-OFDM) systems, an uplink multiple access scheme that reduces PAPR is proposed, using selective mapping-sparse code division multiple access(SLM-SCMA) technology suppresses the PAPR of the ACO-OFDM system, and the performance of the ACO-OFDM system is simulated through Matlab software. The simulation results show that when the number of subcarriers N=512 and the CCDF value is 10-4, the PAPR of the ACO-OFDM system without and with SLM-SCMA technology is 11.82 dB and 7.02 dB respectively.

Aiming at the problem that the existing defragmentation methods in elastic optical networks can not make full use of the maximum free spectrum block and the number of service migrations is large, a defragmentation algorithm with maximum bandwidth service precise migration triggered by residual duration(BBSEM-DF) is proposed. Firstly, a fragment measurement model is constructed to measure the distribution of spectrum fragments in the link. Then, the threshold is set according to the amount of fragments and the remaining duration of business to trigger the defragmentation process. Finally, the maximum continuous service group is migrated to the free spectrum block in the link that matches the required number of frequency slots for accurate migration. The simulation results show that compared with the traditional defragmentation algorithm, this algorithm can reduce the spectrum fragments, reduce the blocking rate, and improve the network performance.

In order to improve the survivability of optical networks, this paper proposes a fault service recovery algorithm based on service delay sensitivity and alarm feedback measurement. The algorithm first applies the link multi-fault location model based on hybrid evolutionary neural network to accurately locate the fault location from a large number of alarm information. Then, the time delay tolerance of the faulty business is evaluated, and the recovery sequence of the faulty business is arranged based on this. In addition, the algorithm also evaluates the reliability of each link according to the type and quantity of alarm information on each link, and gives priority to the link with higher reliability when choosing the recovery path for the fault service. The simulation results show that the fault location accuracy of this algorithm is as high as 91%, the relative recovery delay of fault service decreased by 48.83% and the reliability of recovery path increased by 6.05% on average.