Silicon photonic chips can achieve low-loss coupling with optical fibers through the on-chip silicon-based edge couplers (here in after referred to as edge couplers) integrated on the chips. In the packaging process of commercial silicon photonic chips, the demand for large-scale alignment of optical fibers and silicon photonic chips has raised higher requirements for the alignment efficiency of optical fibers and edge couplers. The research purpose of this paper is to optimize the alignment process between optical fibers and edge couplers based on the Fabry-Perot (FP) cavity formed between the optical fiber facet and the edge coupler facet. After measuring the distance between the optical fiber and the edge coupler in the axial direction of the fiber (represented as the x- axis in this article), high-precision alignment of the optical fiber and the edge coupler can be achieved by a single adjustment of the fiber position in this direction.

This paper studied the FP cavity structure formed between the optical fiber facet and the edge coupler facet. It also established the physical model between the reflection / transmission spectrum of the FP cavity and the distance between the facets. The optical fiber alignment platform is constructed to experimentally measure the distance between the facets through the FP cavity. Based on the distance measurement results, a single position adjustment of the optical fiber is realized along the axial direction of the optical fiber to achieve the alignment with the edge coupler.

The deviation between the FP cavity length obtained in the experiment and the FP cavity length simulated by the ideal FP cavity model is less than 1 μm. The measured displacement of the optical fiber is within the error range (± 1 μm) of the actual displacement. After adjusting the position of the optical fiber based on the distance measurement results, the optical coupling loss is 3.52 dB between the optical fiber and the edge coupler at the output port, and the error with the reference value (3.30 dB) is only 0.22 dB.

The work verifies the feasibility of achieving efficient alignment between optical fibers and edge couplers based on FP cavity. Through the FP cavity, the measurement accuracy of the distance between the optical fiber and the edge coupler is at the sub-micrometer level and the measurement accuracy of the optical fiber displacement is also at the sub-micrometer level. The experiments demonstrate that the high-precision alignment between the optical fiber and the edge coupler could be realized with only a single adjustment of fiber position according the measurement results obtained by the FP cavity.

To solve the problem of capacity limitation in optical communication system, this article designed and developed a new four-core Wavelength Division Multiplexing (WDM) original sample.

Firstly, the technology of WDM, air division multiplexing, MCF and multicore fiber coupling is analyzed. The four core fan-in fan-out device made with capillary, lens and etch fiber is selected as the medium. Then, by combining MCF technology and WDM technology, starting from the selection of four-core fiber, the debugging principle and debugging method of four-core WDM, a new four-core WDM original sample is designed and developed by using four-core fan-in fan-out device. The index of the device is tested by using the difference method of four-core fan-in fan-out device.

According to the test results of the experimental samples, the insertion loss of each reflection end and transmission end of the original four-core WDM 1 can be controlled within 0.8 dB, the isolation degree of each reflection end is >15 dB, and the isolation degree of each transmission end is ≥ 40 dB.

According to the test results, the following conclusions can be drawn: compared with the traditional single-core WDM scheme, the new four-core WDM can realize four-channel communication under the same device volume, and greatly improve the optical communication capacity. At the same time, it fills the gap in the research of air division multiplexing optical devices based on MCF technology and expands the application range of air division multiplexing, demonstrating the potential of multi-core fiber based long-distance transmission. WDM device based on space division multiplexing system has a wide application prospect in optical fiber communication system.

In order to achieve a highly sensitive refractive index sensor in a nanoscale spatial dimension, a square composite resonant cavity containing a stub resonator has been proposed as a resonant element adjacent to Metal-Dielectric-Metal (MDM) Surface Plasmon Polaritons (SPPs) waveguide in this paper.

The paper employs the finite element method to comparatively analyze the characteristics of the transmission peak spectrum and the mode field distribution at the peak position of the square resonant cavity coupled MDM waveguide structure before and after the introduction of the stub cavity. The analysis results reveal that the degeneracy separation phenomenon of the first and second order quasi resonant modes in the composite cavity can be observed clearly when the stub resonator is added in the square-shaped cavity. Consequently, four transmission peaks with sharp edges have emerged in the transmission spectra, which are generated by the quadruple Fano resonance. By changing the structural parameters such as the side length of the square cavity and stub length, as well as the refractive index of the medium filled in the cavity, the dependence of the transmission spectra on the structural and material parameters of the resonant cavity was calculated in detail.

By analyzing the quantitative impact of structural parameters on the peak wavelength, the resonance conditions responsible for the transmission peaks have been derived and the increments of the effective cavity length contributed by the stub resonator have been analyzed in turn for the four resonant modes. By calculating the transmission spectra associated with the varied medium filled in the composite cavity, the peak wavelength shows an approximate linear relationship with the refractive indexes of the filled medium. The sensing sensitivity of the quadruple transmission peaks has been obtained based on the linear fitting results.

The calculation results in the article indicate that the sensitivity of refractive index sensing is directly proportional to the effective cavity length of the composite cavity, and inversely proportional to the resonance order. When selecting a square composite cavity structure with a side length of 360 nm and a stub length of 210 nm, the sensing sensitivity of the transmission peak produced by the first-order Fano resonance can reach 2 000 nm/RIU. The research conclusion of this paper can provide a valuable reference for the design of nanoscale high sensitivity refractive index sensors.

Direct Sequence Spread Spectrum (DSSS) has been widely used in military and civilian communications due to its strong resistance to various common interferences, high security, and ease of implementation. It has been widely used in Code Division Multiple Access (CDMA) system. However, in non-cooperative communication scenarios, detecting DSSS signals, estimating DSSS signal parameters, and even intercepting information are all issues that need to be considered. In DSSS, correctly identifying the spread spectrum sequence used is an important prerequisite for correcting despreading. To address the problem of low success rate of spread code identification for low signal-to-noise ratio DSSS signals, this paper combines the Third-order Correlation Function (TCF) of m-sequences and its peak characteristics to identify the pseudo-code period of DSSS signals as prior information through power spectrum secondary processing on the premise of denoising preprocessing. The problem of spread code identification is transferred into a peak detection classification problem. The peak identification and classification is then studied.

This paper proposes a method of using Sparrow Search Algorithm (SSA) to optimize Extreme Gradient Boosting (XGBOOST) for third-order correlation peak classification of direct spread signals to improve the accuracy of m-sequence classification and identification.

By comparing conventional peak detection and decision tree classification methods at different signal-to-noise ratios and comparing the classification accuracy of different sequence periods, the simulation results show that the spread code identification and classification method optimized by SSA with XGBOOST after preprocessing has a higher classification and identification success rate than conventional machine learning and peak detection methods. Its performance gradually improves at high sequence periods.

This method can more accurately identify and classify m-sequence spread codes under low signal-to-noise ratio conditions.

In Reconfigurable Optical Add Drop Multiplexer (ROADM) downstream transmission, Tunable Optical Filters (TOF) are used to dynamically select wavelengths within a certain optical bandwidth range. By performing wavelength selection filtering and optical intensity attenuation equalization at the output ports of Wavelength Selective Switches (WSS) or Multicast Switches (MCS), the optical intensity at each output port of the ROADM is made consistent. MCS operates based on the Optical Switch (OSW) principle, enabling fast, accurate, and reliable transmission of multicast data by simultaneously switching multiple input channels to one or more output ports. Currently, most MCSs need to work in conjunction with TOF arrays to avoid accidental channels and ensure that the power entering the receiver after the MCS does not saturate or experience severe crosstalk. Most current TOF arrays are large, making integration with MCS difficult, thus affecting the realization of Colorless, Directionless and Contentionless (CDC)-ROADM. To reduce the implementation complexity of the ROADM downstream transmission system, it is necessary to address the issue of bulky module sizes. Therefore, this article designs an OSW device integrated with TOF functionality to reduce the size of the MCS module and optimize its structure.

The article integrates TOF functionality into the MCS module and designs a device that can achieve both optical channel selection and optical wavelength selection functions simultaneously. It is noted that Micro Electro Mechanical Systems (MEMS) can respectively realize the functions of OSW and TOF, and MEMS devices are relatively easy to implement with advantages such as fast tuning speed, wide tunable range, and small size. The article designs a new device combining both functions based on existing MEMS OSW and TOF solutions. This device is based on MEMS technology and is equipped with a multi-fiber collimator, enabling the X and Y axes of the device to respectively realize OSW and TOF functions with minimal mutual interference. The article introduces the basic principles and optical structure of this device and conducts optical design and simulation verification.

Simulation results show that the device has good optical performance and can meet the usage requirements of MCS devices.

The MCS module using the TOF-OSW device proposed in the article integrates the TOF function, thereby saving the cost and space of the original TOF, reducing costs, space occupation, and system complexity. Therefore, the TOF-OSW device has broad application prospects and practical demand, better meeting the ROADM system's need for implementing CDC functionality.

To avoid the operational risk of high-voltage transmission lines caused by thermal faults of composite insulators, a method for identifying abnormal hot spots on the surface of composite insulators is studied.

Three types of abnormal surface heating forms of composite insulators, current heating type, voltage heating type, and comprehensive heating type, are analyzed. Based on the analysis results, the fiber Bragg grating centralized temperature measurement technology is used to deploy the fiber Bragg grating sensor near the composite insulator. The fiber optic dispersion centralized temperature measurement unit is used to calculate the corresponding wavelength offset and temperature change value. After being analyzed by the digital signal processing unit, the thermal image of the composite insulator is generated. Using the maximum inter class variance method to segment the thermal image of composite insulators, the average gray level of the thermal image of composite insulators is calculated, and the optimal threshold to partition the pixels in the thermal image of composite insulators is obtained. Based on the thermal image segmentation results of composite insulators, pixel statistical methods are used to calculate the horizontal row pixel points of the composite insulator segmentation image and divide the structural area of the composite insulator. According to the application specification of thermal image diagnosis for live equipment and the principle of fiber grating centralized temperature measurement, the thermal image of composite insulator collected by the fiber grating sensor is displayed in pseudo color to show the surface temperature distribution of composite insulator. The abnormal hot spots on the surface of composite insulators are identified through the temperature relationship among various structural regions of the target image.

The experimental results show that this method can accurately measure the temperature of any point on the surface of composite insulators, and the maximum Root-mean-square deviation is only 1.39%. It is shown that the proposed method can effectively divide the structural regions of composite insulator segmentation images, with clear boundaries between each structure and no overlap phenomenon.

The recognition performance of abnormal hot spots on the surface of composite insulators in different areas of high-voltage transmission lines is relatively ideal, and the division effect of composite insulator structure areas is relatively good.

Visible Light Positioning (VLP) technology has gained increasing attention due to its potential for providing low-cost, high-precision indoor location services. However, traditional VLP systems rely on Line-of-Sight (LOS) paths and cannot function properly when obstructed by obstacles.

To address this issue, we propose a novel Non-Line-of-Sight (NLOS) VLP system based on deep learning. This system utilizes reflected light for VLP, overcoming the challenge of LOS obstruction and enhancing the robustness of the VLP system. Considering the low signal-to-noise ratio of the reflected light, the accuracy and adaptability of conventional image detection methods for extracting Light Emitting Diode (LED) spots are limited, resulting in reduced positioning accuracy for NLOS VLP. Therefore, the proposed system employs the deep learning model U-shaped Network (U-Net) to detect LED spots, which demonstrates high accuracy and adaptability after being trained on datasets collected from various environments, thereby improving the system performance. In the simulation, the system estimates the Three-Dimensional (3D) position of the receiver using the Perspective-Three-Point (P3P) algorithm.

This paper constructed a 1.84 m×1.84 m ×1.96 m 3D space simulating an indoor environment for indoor positioning experiments. The experimental results show that under NLOS paths, the system's 3D mean error and Root Mean Square Error (RMSE) are 16.09 and 17.18 cm, respectively. The Two-Dimensional (2D) positioning error has a 90% confidence level at less than 21 cm, and the 3D positioning error has a 90% confidence level at less than 24 cm.

The proposed system has high positioning accuracy and robustness, which can meet the positioning requirements of most indoor applications.

In order to solve the technical problems of large volume, low integration and small bandwidth of electro-optic modulator, a design method of parallel multi-channel thin film Lithium niobate electro-optic modulator is proposed. The design principle of thin film Lithium niobate electro-optic modulator is presented, and the gain and noise figure of microwave optical transmission link are analyzed.

A simulation model of microwave optical transmission links is established using Lumerical Interconnect optical simulation software. The effects of modulator half wave voltage on link gain and noise figure are then compared and analyzed. Finally, the key parameters of the 40 GHz four channel integrated thin film Lithium niobate electro-optic modulator are tested.

The test results show that the insertion loss, half wave voltage, 3 dB bandwidth and size of the designed four-channel integrated film Lithium niobate electro-optic modulator are 4.5 dB, 3.5 V, 40 GHz and 30 mm×20 mm×10 mm, respectively. The noise figure of microwave optical transmission link using thin-film Lithium niobate modulator is about 30 dB.

The designed four channel integrated film Lithium niobate electro-optic modulator in this paper is superior to the traditional Lithium niobate electro-optic modulator.

In the modern field of communications, optical fibers have become an important transmission medium in optical network systems due to their ultra-high transmission bandwidth and excellent optical properties. Multi-core optical fibers integrate multiple cores within a single fiber cladding to significantly enhance the data transmission capacity of a single fiber. However, an increase in the number of cores can also lead to additional channel impairment effects, which in turn affect the transmission performance and communication quality of the fiber link. Therefore, studying the theoretical model of the channel effects in coupled-core optical fibers, especially clarifying the relationship between the optical time-domain reflectometry process and channel response, can provide important references for the practical deployment and application of multi-core fibers.

To refine the model of optical time-domain reflection effects in coupled-core optical fibers, the article begins with basic principles, outlining the theories of forward transmission and backward Rayleigh scattering in coupled-core optical fibers. It details the derivation of coupled mode equations and the general expression for Rayleigh scattering power, including definitions and calculation methods for various coefficients such as the total capture factor. Based on the theoretical research, the article also proposes a modeling scheme for Rayleigh scattering effects in coupled-core optical fibers, taking into account the impact of fiber end-face reflection on the transmission process and providing a technical route to verify the Rayleigh scattering effects. Finally, the article processes the transmission data simulated by the model and conducts a comparative analysis based on the set parameters.

The article constructs a simulation model for Rayleigh scattering effects, calculating the scattering power curve received after optical time-domain reflection. The simulation results show that the received scattering power is consistent with the set parameters, with an error within 5%.

The high precision of the results indicates that the model proposed in the article effectively reflects the Rayleigh scattering effects in coupled-core optical fibers, laying a theoretical foundation for accurately testing parameters of coupled-core optical fibers using optical time-domain reflectometry technology.

Common optical switches are usually polarization sensitive or have complex structures, the article proposes a 2×2 microfluidic optical switch.

The optical switch proposed in this article employs a waveguide structure. It utilizes microfluidic driving technology based on magnetic fluids, along with trace amounts of liquid and air, to achieve optical path selection and switching functions for the optical switch. The transmission characteristics of optical switch are studied and discussed, and the structure of optical switch is optimized.

The results show that the insertion losses at two output ports of optical switch are 0.42 and 0.20 dB, and the crosstalk are -24.13 and -42.63 dB, respectively.

The proposed 2×2 microfluidic optical switch has simple structure and is not sensitive to polarization. It also has lower insertion loss and crosstalk than common optical switches. It can be used as the switching core for building Optical Cross Connect (OXC) equipment to realize the fault protection function of the optical network.

Affected by factors such as atmospheric attenuation and atmospheric turbulence, wireless laser communication will produce a certain degree of bit error, and it is often necessary to add error correction codes to improve the signal transmission quality. Low Density Parity Check codes (LDPC) have performance close to the Shannon's limit, and their error-correcting ability will increase significantly with the increase of codeword length. For codes with a large length of information segment, when each code corresponds to an Ethernet frame, its encoding efficiency will be seriously affected. Designing the transmission method for Ethernet frames in a way that allows both different speeds and lengths of Ethernet frames to fully leverage the encoding and decoding efficiency is crucial for enhancing the transmission rate of Ethernet data sources.

Based on the LDPC (4 050, 2 700) encoding with a data bit width of 16 bit, this paper designs a gigabit network service transmission method. The functions of each module are clearly divided, and the state machine is used in the design of the module. Therefore, the problems in the design process can be quickly located, and the development efficiency is very high. Setting an appropriate operational cycle at the transmitting end to process Ethernet frames, through operations such as framing, packet assembly, and filling with random sequences, enables Ethernet traffic of different frame lengths and rates to adaptively match the information segment length of the LDPC encoding module, thereby fully utilizing the efficiency of LDPC encoding. Each Ethernet frame can be finally recovered by deframing at the receiving end.

Finally, this article verified the design scheme on the Field Programmable Gate Array (FPGA) board of XILINX, and tested the transmission rate of Ethernet data with different frame lengths by using a gigabit network tester. The results show that the data rate can reach the limit rate of 1 Gbit/s. Afterwards, different services such as video and files are successfully tested.

The article proposes an Ethernet service transmission method specifically designed for scenarios where the information segment length exceeds the Ethernet frame length, enabling it to accommodate Ethernet data transmission with varying lengths, rates, and types of services. The efficiency of the encoding module can be fully utilized to meet the demand for high-speed Gigabit Ethernet service transmission in wireless laser communication.

With the continuous advancement of Integrated Circuit (IC) design and manufacturing process, the design scale of System on Chip (SoC) has become increasingly larger, and the corresponding Software Development Kit (SDK) has also become more complex. Shortening the development time and rapid application of SDK is the key to the success of chip development.

In this paper, a chip SDK simulation platform is designed, which supports automatic extraction of chip logic design information. The software local image of extracted logic information based on the designed chip data structure is realized. The multi-threading of configuration, alarm and performance is developed to simulate the multi-task polling and network management reporting in the actual single-disk application. By connecting the SDK project to the serial port tool through the virtual serial port, the Shell command set provides interaction among developers and the SDK projects under the SDK simulation platform.

The test results based on optical communication chip show that the SDK simulation platform can realize the functions of chip software level simulation, multi-thread debugging simulation and multi-function interaction under Shell command set.

The SDK simulation platform implemented in this paper can be applied to the early development and late application maintenance of chips. It has the functions of avoiding the development obstruction caused by the shortage of hardware resources, converging the difference of chip conversion, and providing a convenient SDK debugging method, which is of great significance to shorten the development time and accelerate the rapid application of chips.

To meet the requirements of timeliness, accuracy, and completeness of delay data in delay-sensitive application scenarios, it is necessary to implement end-to-end service delay estimation in Optical Transport Networks (OTN).

This paper first analyzes the transmission characteristics of OTN services, and collects service routing information according to the sub-net connections. Next, it discretizes the basic data such as Network Elements (NE), links, and cross-connection in service route. Then the characteristic variables for delay estimation are obtained. Finally, the paper proposes a delay estimation model based on engineering live network, and compares the simulation results of various machine learning algorithms.

The Mean Absolute Percentage Errors (MAPE) of the delay estimation results based on Support Vector Regression (SVR) and decision tree regression were 3.362 8% and 1.284 9%, respectively.

The OTN service delay estimation method based on machine learning and the characteristic of OTN transmission in this paper has high accuracy and wide application scenarios.

The world has entered the era of 5th Generation Mobile Communication Technology (5G) and satellite Internet, and the demand for communication speed and capacity in various fields has surged, while the application of traditional parabolic and narrowband planar phased array antenna systems is limited by factors such as bandwidth and beamforming. Based on the current trend of related industries and the application requirements of broadband multi-target, this paper studies the Ka-band wideband multi-beam solid-state phased array technology.

This paper theoretically establishes and derives a general vector mathematical simulation model of phased array antenna pattern, studies the subarray division, aperture effect, and crossing time of phased array antenna, and designs a broadband multibeam phased array system based on the combination of element-level electro-shift phase shift and sub-array stage optical-delay. The front-end single integrated subarray adopts the three-dimensional high-density heterogeneous tile integration scheme of different material substrates, which greatly improves the integration degree of the subarray. The sub-array post-stage adopts the Optical True Time Delay (OTTD) method based on optical switching, high-precision optical fiber delay line and wavelength division multiplexing to realize multi-channel delay and multi-beam synthesis of the sub-array stage.

By integrating and testing the principle prototype of the Ka-band wideband multi-beam receiving phased array system, it is verified that the principle prototype overcomes the bandwidth limitation problems such as aperture crossing time and beam skew. The prototype can realize the wide-angle scanning of eight independent receiving beams in the Ka-band, and the maximum transmission data rate of each receiving beam can reach 1 500 Mbit/s.

The test results show that the system has the advantages of high integration, large bandwidth, and multiple independent beams. The research results will help promote the further development of wideband multi-beam solid-state phased array, and lay a theoretical and practical foundation for the subsequent engineering and productization of Ka-band wideband multi-target phased array.

To address the device size and loss of the Bragg phase shift grating, this paper proposes a Bragg phase shift grating based on Silicon-on-Insulator (SOI) nanowires.

By leveraging photolithography technology, periodic grooves are created on silicon nanowires to construct the grating structure, effectively reducing the transmission loss of optical signals. In order to verify the performance of the Bragg phase-shifted grating, the transmission modes and characteristics of the device are analyzed and studied using the finite element method and the finite-difference time-domain method under conditions with an incident wavelength range of 1 400 to 1 600 nm. Additionally, to obtain the best structural parameters of the Bragg phase-shift grating, the Q factor is introduced as the optimization target parameter.

The results show that the Bragg phase shift grating has excellent wavelength selection performance in the wavelength range of 1 400～1 600 nm, and has a ultra-low transmission loss. Notably, when the maximum Q factor is 159, the Bragg phase shift grating achieves the best performance, with the grating period N of 60.

This grating offers significant advantages over surface plasmon-based Bragg phase shift gratings in terms of manufacturing cost and transmission loss of optical signal. As a result, it has wide applications in dense wavelength division multiplexing, biological sensing, filtering, and other related fields.

In order to obtain a higher sensitivity fiber optic humidity sensor,this paper proposes a humidity sensor of D-shaped silver (Ag)-coated optical fiber based on Surface Plasmon Resonance (SPR) effect.

Graphene Oxide (GO) is coated on the surface of D-shaped Ag-coated optical fiber. Since GO has water absorption characteristics and the effective Refractive Index (RI) will change after absorbing water, SPR will be excited when certain conditions are met. Therefore, it can be used as a humidity sensor. In order to obtain the maximum SPR sensitivity of the sensor, the structure of D-type Ag-coated optical fiber is firstly modeled by COMSOL Multiphysics software, and the influence of polishing depth and Ag film thickness on the sensing characteristics is explored by finite element analysis. Then the structure is verified by experiments Validity and rationality of parameters. Finally, a layer of GO film is coated on the surface of the D-shaped Ag-coated optical fiber to explore its performance of humidity detection.

The simulation results show that the optimal sensor structure is the polishing depth of 58.4 μm, the thickness of the Ag film is 50 nm, and the maximum wavelength sensitivity of 5 500 nm/RIU is obtained between the ambient RI of 1.34 and 1.40. On the basis of this parameter, the RI sensing characteristics are verified through experiments. The sensor has a maximum wavelength sensitivity of 3 668 nm/RIU, and the R square value is 0.98, which has good linearity. After coating the GO film on the surface, the humidity sensitivity of 0.545 nm/%RH is obtained when the relative humidity changes from 30% to 90%, and the linear R-squared values under the two conditions of increasing and decreasing relative humidity are 0.961 1 and 0.971 1, respectively.

The simulation results and the actual experiment have the same resonance peak change range, which shows the effectiveness and rationality of the sensor.GO isolates the Ag film from contact with air, preventing oxidation. The optical fiber humidity sensor obtained by combining its water-absorbing properties with the SPR properties of the metal film demonstrates high sensitivity, providing a novel approach for the development of highly sensitive humidity sensors.

Optical Signal-to-Noise Ratio (OSNR) is an important criterion for evaluating the performance of communication systems. For optical fiber communication systems, stable operation can only be ensured if the OSNR at the receiver end exceeds the receiver's OSNR receiving tolerance. The larger the value, the better the system stability. Therefore, monitoring the OSNR value of the transmission system is very important, and real-time and accurate monitoring of OSNR has always been a challenge in optical fiber communication systems.

To achieve a simple, efficient, and high-precision OSNR monitoring, based on the mean and variance of the signal amplitude histogram, combined with a Deep Neural Network (DNN), the article proposes a highly accurate OSNR monitoring method. This method utilizes the mean and variance of different regions of the received signal amplitude histogram to extract correlation features of the signal amplitude histogram as it changes with OSNR using the DNN, thereby enabling the monitoring of the system's OSNR.

This monitoring scheme is used to experimentally monitor the receiver OSNR of Quadrature Phase Shift Keying (QPSK) /16 Quadrature Amplitude Modulation (QAM) /32QAM transmission systems with three different modulation formats. The results show that the maximum standard errors of the estimated and actual OSNR values of the three different modulation formats in the back-to-back transmission system are 0.048, 0.140, and 0.180 dB without fiber transmission. After passing through 2 000, 800 and 800 km optical fiber transmission, the maximum standard errors of the estimated and actual OSNR values of the receiving end of the three different modulation formats transmission systems are 0.082, 0.250 and 0.630 dB, respectively. Compared with the non fiber transmission system, the maximum error of the estimated OSNR values of the system after optical fiber transmission does not exceed 0.5 dB. This indicates that the OSNR monitoring scheme can achieve precise monitoring of transmission system performance and is not affected by fiber optic lines.

The DNN OSNR monitoring method based on the mean and variance of the signal amplitude histogram proposed in this paper has been experimentally verified. The maximum error between this scheme and the actual system receiver OSNR does not exceed 1dB, indicating that this scheme can accurately predict the system receiver OSNR value.