Aiming at the application research of polar code in optical communication system, this paper proposes the combination of polar coding modulation and optical fiber Module Division Multiplexing (MDM) system. We construct an MDM system based on bit interleaved polar coding modulation, and study the performance of Maximum Likelihood (ML) detection algorithm. The simulation results show that the addition of polar code greatly improves the system performance. Compared with the MDM system without coding, the MDM system with bit interleaved polar coding modulation improves the system performance by about 8 dB under the same Mode Dependent Loss (MDL). The paper also shows the performance of ML detection algorithm and Minimum Mean Square Error (MMSE) detection algorithm in MDM system. The impact of different mode loss on system performance is also studied. Compared with MMSE detection algorithm, ML detection algorithm improves the bit error performance by about 3 dB.

This paper defines the connotation of Digital China. Based on the concept of"Five-in-one"put forward by the Party Central Committee, this paper summarizes the construction logic of Digital China Index System from the three levels of macro objectives, strategy quantification and measurement, and puts forward five core indicators, nine main indicators and four sub item index systems of Digital China. At the same time, various types of efficacy functions, weighted factor analysis and cluster analysis are used to carry out dimensionless processing, weighted calculation and data statistical analysis of the basic data of Digital China index system. Finally, we propose some policy suggestions for the construction of Digital China in the future.

In view of insufficient security in the next generation passive optical network, an electro-optic hybrid encryption scheme based on MD5 message digest algorithm check is proposed in this paper. In the scheme, Baker scrambling algorithm and 256 bit Advanced Encryption Standard (AES) encryption algorithm are used to encrypt the picture data. The Low Density Parity Check Code (LDPC) error correction and MD5 check are combined to perform the error correcting coding and check the consistency of the encrypted picture data. In order to strengthen the security of key and MD5 digest distribution, Super Structure Fiber Bragg Grating (SSFBG) is also used to encode them so that they are hidden under the system noise. The simulation results show that after SSFBG coding, the power of the coded signal is as low as-50 dBm, which can achieve the effect of data hidden transmission over the optical fiber channel. Due to the fact that the MD5 check of the received data is added in the scheme, the information changes caused by malicious access attacks cannot be decoded by AES, which improves the security and saves Central Processing Unit (CPU) resources at the same time. Finally, Error rate curve analysis results show that the receiver sensitivity can be effectively reduced by adding LDPC error correction.

Aiming at the application research of polar code in optical communication system, this paper proposes the combination of polar coding modulation and optical fiber Module Division Multiplexing (MDM) system. We construct an MDM system based on bit interleaved polar coding modulation, and study the performance of Maximum Likelihood (ML) detection algorithm. The simulation results show that the addition of polar code greatly improves the system performance. Compared with the MDM system without coding, the MDM system with bit interleaved polar coding modulation improves the system performance by about 8 dB under the same Mode Dependent Loss (MDL) . The paper also shows the performance of ML detection algorithm and Minimum Mean Square Error (MMSE) detection algorithm in MDM system. The impact of different mode loss on system performance is also studied. Compared with MMSE detection algorithm, ML detection algorithm improves the bit error performance by about 3 dB.

In recent years, the emerging Deep Learning (DL) technology has made progress in the field of decoding. Current polar code neural network decoder has faster convergence speed and better Bit Error Rate (BER) performance than Belief Propagation (BP) decoding. However, it still has the problem of high computational complexity. Therefore, in order to improve this problem, this paper adopts the idea of improving information update in the iterative process, and proposes a Recurrent Neural Network (RNN) Offset Min-Sum (OMS) BP decoding algorithm that improves Left information update (RNN-OMSBP-L) . The simulation results show that, compared with the Deep Neural Network (DNN) BP(DNN-BP) decoding algorithm, this algorithm replaces all multiplications with a cost of 6.25% addition. Compared with the current optimized RNN OMS and approximate BP(RNN-OMS-BP) decoding algorithm, the decoding algorithm in this paper uses improved information to reduce 25% of the addition operations with almost no loss in BER performance, while saving part of the storage space overhead. Under the same BER performance, it reduces the number of iterations by 37.5%.

In the Pulse Position Modulation (PPM) space optical communication channel estimation based on photon detection, two schemes for the estimation of signal photon average and background photon average are proposed. Scheme 1 is based on the characteristic of M-order PPM, where only one of the M slots has a signal optical slot. The signal photon average and the background photon average are roughly estimated by comparing the number of photons in each slot in each symbol counted by the photon detector and by counting the total number of photons in each slot in the error correction frame. The proposed method in scheme 2 is based on that in scheme 1. The signal optical slot position is re-determined by decision feedback in the Serially Concatenated Pulse Position Modulation (SCPPM) system. Since the existence of SCPPM accumulator leads to error propagation, the soft information output by decoding is first interleaved, and then mapped from bit to PPM symbols after hard decision and accumulation. Finally, the position of signal optical slot is re-determined to obtain more accurate signal photon average and background photon average.

As the optical network structure becomes larger and more complex, optical network faults are more likely to occur. After a network fault occurs, due to the derivative characteristics of network alarms, the root cause alarms will generate multiple derivative alarms. Therefore, after network faults occur, the network management system will receive alarm storms. Due to the complex relationship between faults and alarms, the difficulty of locating network faults, especially multiple faults, has also risen sharply. In response to this problem, the knowledge graph technology that is good at managing massive amounts of information and revealing the characteristics of data is introduced into optical networks. The alarm knowledge graph contains rich relationships between alarms, which can be completed by combining Graph Neural Network (GNN) technology. The knowledge-guided automatic reasoning of the root cause of network faults is in line with the fault location ideas of the operation and maintenance personnel in the operation and maintenance process. Further, the network topology information is added in the fault location process, and the knowledge dimension of the knowledge graph is improved. The limitation of the single-fault scenario is lifted, and a high accuracy rate is obtained in the multi-fault location scenario.

Aiming at the problem of the interference of camouflage information to the carrier, this paper proposes an information hiding method based on audio technology, and forms a scheme of jointly shaping the camouflage information in the frequency domain and the time domain by the side information. In terms of limiting the interference of the carrier to the camouflaged information, this paper expands the embedding method of the improved spread spectrum modulation when the receiving and sending sequences do not match. The experimental results show that the proposed scheme has a good information hiding effect.

In order to realize tunable multichannel high sensitivity refractive index sensing, a square resonator connected with a Rectangular Groove (RG) is proposed to couple with the highly compact Metal-Dielectric-Metal (MDM) waveguide containing double metal baffles. The transmission spectrums of the proposed waveguide structure have been calculated by the finite element method, which exhibits four sharp, asymmetric transmittance peaks and the magnetic field patterns. Based on the coupling interference between the broadband reflection mode generated by the double baffles and the narrow resonance modes occurred in the composite cavity, the generation mechanism of quadruple Fano resonance is explained. Moreover, the structural parameters of the square cavity and the rectangular groove are changed to study the tunability of the wavelengths of the quadruple transmittance peaks. When the composite cavity is filled with different dielectric media, the calculated sensitivity corresponding to four transmittance peaks are 960, 1 120, 1 320 and 1 560 nm/RIU, respectively. It provides an effective theoretical reference for the design of multi-channel and high sensitivity refractive index sensor.

In recent years, 200/400 Gbit/s transceiver in the form of Quad Small Form Factor Pluggable-Double Density (QSFP-DD) is favored by the market due to their relatively low power consumption and small size for high-density deployment. However, the deterioration of heat dissipation caused by high speed and small size limits the application of QSFP-DD optical modules. In this paper, the finite element method is used to conduct thermal modeling and simulation of QSFP-DD module, and the internal temperature field of 200 Gbit/s QSFP-DD Long Range 4(LR4) optical module in high temperature environment is studied. The effect of thermal pad on improving the internal heat dissipation of the module is verified. The performance of the module in high temperature environment is measured. It provides a reference for the design and application of QSFP-DD transceiver module.

Distributed Raman Fiber Amplifier (DRFA) is widely used in modern communication systems because it has a series of excellent features. Considering the existing problems of DRFA gain control, this paper studies and improves a method of Automatic Gain Control (AGC) of DRFA by Amplifying Spontaneous Emission (ASE) out of band. In view of the fact that DRFA gain is greatly affected by the performance of optical fiber link, this paper firstly theoretically analyzes the influence of the joint loss at the position 0 away from the pump source in the optical fiber link on the Raman gain control. Then the splice loss at different positions from the pump source is set to be equivalent to the splice loss at position 0. The relationship between Raman gain and out-of-band ASE power is modified so that the AGC of DRFA can be realized more accurately. The Optical Time Domain Reflectometer (OTDR) function is integrated in the DRFA module to detect the distance between the joint loss and the pump source and the loss value in the engineering optical fiber link. Experimental results show that the proposed AGC method can control the influence of joint loss on DRFA gain within 0.2 dB.

A hybrid integrated 89 GHz sub-harmonic mixer based on Schottky diode was proposed for meteorological monitoring radiometer. In this paper, based on the theory of millimeter wave mixing technology, a three-dimensional electromagnetic model of diode is established in the field simulation software, and a W-band 89 GHz sub-harmonic mixer is designed based on the three-dimensional electromagnetic model. The simulation and test results show that when the Local Oscillator (LO) is fixed at 45 GHz, the conversion loss is better than 14 dB from 84 to 94 GHz, and the minimum conversion loss is 9 dB. The measured results are consistent with the simulation results.

Aiming at the problem that the two-dimensional uniformity of the frequency hopping pattern in differential frequency hopping communication is poor, and the frequency hopping frequency is easy to be eavesdropped, this paper designs an encryption scheme based on the pseudo-random sequence of logistic chaotic map to randomly scramble the frequency hopping pattern. After verification, the differential frequency hopping pattern after encryption and scramble is compared with the original frequency hopping pattern. Although the performance of the system is reduced, the correlation between frequencies is reduced, and the two-dimensional uniformity is improved, which has strong anti-deciphering ability.

Wavelength Division Multiplexing (WDM) devices, as one of the core components of 5G fronthaul network, have developed rapidly in recent years. The fronthaul network has proposed new requirements for WDM devices, components and products. However, the technical requirements and test method standards of WDM devices for 5G fronthaul network are not clear. Through in-depth analysis of the problems encountered in the test of WDM devices, we propose a test method of 5G fronthaul WDM devices, and build the corresponding test system, which is compared with the manual test method. The results show that the proposed test method has 10 times more efficient than manual test method with good consistency.