The antenna scan period is a core technical parameter of radar, and its robust, real-time, and high-precision measurement is of great engineering significance. Based on filed-measured full-pulse radar data, two measurement methods for the antenna scan period are proposed in this paper: the smoothing-fitting method and the smoothing-correlation method. Verified by filed-measured data, the measurement error fluctuation of the smoothing-fitting method is no more than 2 pulse repetition intervals (PRIs), and that of the smoothing-correlation method is no more than 1 PRI, both meeting the requirements of engineering applications. Adopting a point-by-point sliding processing flow without batch fitting, the smoothing-correlation method is more suitable for streaming and real-time data processing compared with the smoothing-fitting method and has a distinct engineering transformation value. Compared with batch processing methods such as the cepstrum method, which need to buffer data of at least one complete scanning period, the smoothing-correlation method avoids full-sequence FFT/IFFT operations. It can significantly reduce memory occupation and processing time and achieve superior real-time performance.

We experimentally demonstrate an elliptical-aperture multimode diversity receiver to resist beam wander under anisotropic turbulence. The proposed scheme reduces outage probability from 35% to 1.8% for detecting polarization-diversity 30-Gbaud QPSK signal.

To enhance the robustness of interdependent power grids and communication networks, the configuration of maximally disjoint dual paths in the communication network is proposed. The interdependency relationship between power grids and communication networks is established first; then, the primary and backup paths are calculated according to the k-shortest-path algorithm, and a maximally disjoint dual path is configured to reduce the number of failed nodes when cascading failures occur. In addition, the robustness of an electrical cyber-physical system under the dual path method is evaluated. Case simulations on IEEE 14-bus and IEEE 39-bus systems indicate that the proposed method can obtain better robustness of interdependent networks than other methods in the case of random and intentional attacks. The proposed method can provide guidance on current topics to improve the robustness of interdependent networks.

The antenna scanning period (ASP) of radar is a crucial parameter in electronic warfare (EW) which is used in many applications, such as radar work pattern recognition and emitter recognition. For antennas of radars and EW systems, which perform scanning circularly, the method based on threshold measurement is invalid. To overcome this shortcoming, this study proposes a method using the convolutional neural network (CNN) to recognize the ASP of radar under the condition that antennas of the radar and EW system both scan circularly. A system model is constructed, and factors affecting the received signal power are analyzed. A CNN model for rapid and accurate ASP radar classification is developed. A large number of received signal time–power images of three separate ASPs are used for the training and testing of the developed model under different experimental conditions. Numerical experiment results and performance comparison demonstrate high classification accuracy and effectiveness of the proposed method in the condition that antennas of radar and EW system are circular scan, where the average recognition accuracy for radar ASP is at least 90% when the signal to-noise ratio (SNR) is not less than 30 dB, which is significantly higher than the recognition accuracy of NAC and AFT methods based on adaptive threshold detection.

We experimentally demonstrate an elliptical-aperture multimode diversity receiver to mitigate the impairment from anisotropic turbulence, which is emulated by employing an electrically-controlled heater. The anisotropy gradually decreases as the flow-level of the introduced airflow from fans increases. In contrast to circular-aperture reception, the elliptical-aperture multimode diversity receiver can effectively resist beam wander under anisotropic turbulence, reducing outage probability from 14.63% to 0.38% for detecting a dual-polarization 30-Gbaud QPSK signal. Without the aid of an adaptive optics system, this work demonstrates the feasibility of realizing an anisotropic-turbulence-resistant FSO link using multimode and multi-aperture diversity reception employing digital coherent combining techniques.

In this paper, an improved end-to-end autoencoder based on reinforcement learning by using Decision Tree for optical transceivers is proposed and experimentally demonstrated. Transmitters and receivers are considered as an asymmetrical autoencoder combining a deep neural network and the Adaboost algorithm. Experimental results show that 48 Gb/s with 7% hard-decision forward error correction (HD-FEC) threshold under 65 km standard single mode fiber (SSMF) is achieved with proposed scheme. Moreover, we further experimentally study the Tree depth and the number of Decision Tree, which are the two main factors affecting the bit error rate performance. Experimental research afterwards showed that the effect from the number of Decision Tree as 30 on bit error rate (BER) flattens out under 48 Gb/s for the fiber range from 25 km and 75 km SSMF, and the influence of Tree depth on BER appears to be a gentle point when Tree Depth is 5, which is defined as the optimal depth point for aforementioned fiber range. Compared to the autoencoder based on a Fully-Connected Neural Network, our algorithm uses addition operations instead of multiplication operations, which can reduce computational complexity from 108 to 107 in multiplication and 106 to 108 in addition on the training phase.

In this paper, an improved Volterra nonlinear equalizer with low computational complexity and good performance is proposed to compensate the distortions caused by bandwidth limitation and optical devices. The performance of the equalizer is improved by introducing one-hot encoding, and the complexity is reduced by using absolute operations and weight sharing based on k-means clustering. We employ the k-means clustering algorithm to replace some weights that are close in value with another similar weight, which greatly reduces the multiplications of this equalizer. Finally, we experimentally demonstrate a 50 Gb/s PAM4 IM/DD transmission with 10G-class optics using this proposed equalization scheme. The results show that, compared with the conventional 3(rd)-order Volterra nonlinear equalizer, the sensitivity of the proposed scheme is improved by > 2 dB, and the number of multiplication operations is reduced by ~81.2%.

We experimentally transmit 10-Gbaud 64QAM signal over 300-m duplex fiber using an intensity-noise-suppressed ASE source in self-homodyne coherent detection (SHCD). ASE-based SHCD outperforms ECL-based system at medium-to-low OSNR region benefiting from spectral expansion.

In this study, the loss budget for adopting non-return-to-zero (NRZ) and four-level pulse amplitude modulation (PAM4) in next-generation passive optical networks (NG-PONs) was investigated by simulation and experiment. Through simulation, the signals are distorted by four-wave mixing (FWM) when the zero-dispersion wavelength locates in the middle of the channels. For 25-Gb/s NRZ, a maximal loss budget of approximately 32.5 dB is obtained. For 50-Gb/s PAM4, the bit error rate cannot reach 1 x 10(-3). While, the impact becomes negligible whens the zero-dispersion wavelength stays away from the middle of the channels, and the loss budget is 36 and 25.7 dB for NRZ and PAM4 systems. Therefore, at least a 32.5-dB loss budget ise obtained in a 4 x 25G NRZ system. While, the loss budget cannot reach the basic requirement of 29 dB in the 4x50G PAM4 system. The experimental resultso verify this conclusion.

We introduce recently developed space division multiplexing (SDM)-associated technologies into optical wireless communications (OWC) and propose to use incoherent and low-coherence spatial modes to realize optical broadcasting with reliable performance by mitigating coherent interference. We experimentally demonstrate reconfigurable optical beam steering using a programmable multi-plane light conversion (MPLC)-based mode multiplexer (MMUX) and realize point-to-multi-point optical wireless communications with low-loss up-link optical beam combining and reach extension using multimode fiber (MMF). Both incoherent and low-coherence spatial modes can be generated employing cost-efficient components such as a multimode vertical cavity surface emitting laser (MM-VCSEL) and broadband amplified spontaneous emission (ASE) noise source.

We experimentally demonstrate on-chip modal crosstalk mitigation over two mode-division multiplexing (MDM) integrated circuits supporting four and eleven waveguide modes employing low-coherence matched detection. 30-Gbaud 8-PSK mode-multiplexed signal is successfully transmitted over the circuits without using multiple-in-multiple-output (MIMO) processing under a maximum modal crosstalk of 10 dB. Ten-mode-multiplexed on-chip transmission achieves a total capacity of 900 Gbit/s. This work shows the feasibility of using high-order modes in on-chip MDM transmission for future high-capacity optical interconnects.

We experimentally compare the performance with and without employing three-mode diversity reception over a 8-m free-space link under a laboratory-simulated turbulence. Few-mode preamplification is applied to enhance the receiver’s sensitivity.

We experimentally demonstrate modal crosstalk mitigation over an on-chip mode-division multiplexing link employing low-coherence matched detection. 20-Gbaud QPSK and 8-PSK mode-multiplexed signals are successfully transmitted with a maximum modal crosstalk of-6.5 dB.

We demonstrate secure optical coherent communications employing low-coherence matched detection based on the randomness of amplified spontaneous emission (ASE) noise. Two-level physical-layer optical encryption is achieved through temporal and spectral coding over a broadband ASE source. An ASE-carried signal and unmodulated carrier are polarization multiplexed, transmitted over a same single-mode fiber (SMF), and separated with the aid of polarization tracking before having matched detection at the receiving side. The impact of chromatic dispersion on the low-coherence matched detection system is analyzed and experimentally investigated. We experimentally realize optically coded 20 Gbaud QPSK and 8-PSK signals transmission over a 43 km SMF span with a maximum line rate of 60 Gbits/s.

We experimentally demonstrate 160 Gbit/s on-chip mode-multiplexed transmission over a multimode silicon-on-insulator (SOI) waveguide using four spatial and polarization modes. 4x4 MIMO-based DSP is used to compensate mode coupling.

We experimentally demonstrate 112-Gb/s/λ PAM-4 transmission based on 25-Gb/s optics. Over 31-dB power budget is achieved by using OLT-side pre-equalization, amplification and only simple FFE in ONU.

In this paper, aiming at the problem of vibration event classification based on phase sensitive optical time domain reflectometer (Phi-OTDR), we propose an efficient multi class event recognition scheme based on Variational Mode Decomposition (VMD). The signals collected by optical fiber sensors are preprocessed by the VMD algorithm, and then the features of the signals are extracted by Mel Frequency Cepstral Coefficients (MFCC). Finally, the extracted features are classified and identified by using machine learning algorithm. In order to improve the reliability of identification, the VMD algorithm can be used to decompose the signal into different modes. We extract and identify the features of each mode signal. Finally, the result with the highest number of occurrences is taken as the identification result. Six different vehicle vibration signals are classified and identified, and the recognition accuracy is 97.7%.

Aiming at the problem of the safety monitoring of the surrounding environment of the glass window on the building, a scheme of distributed optical fiber acoustic sensors based on the phase sensitive time-domain reflection is proposed. Firstly, Wigner bispectrum is used to analyze the time-frequency energy distribution of vibration signal, then the axially integrated bispectrum algorithm is used to extract the time-frequency characteristic components, and the method of sub-band division is used to avoid information loss and decrease the cost of computing. The eigenvectors of different vibration events are recognized by extreme gradient boosting tree algorithm. Based on the diversity of acoustic signal types in the environment, there are eight kinds of events including wind blowing, knocking, window opening, watering, hammering, dog barking, aircraft sound and no disturbance to be selected for vibration experiments. The experimental results show that the scheme can get better recognition effect, and the average recognition rate of eight kinds of events reaches 93.3%.

In this paper, the influence factors of phase noise are first analyzed in detail and verified by experiments, and its principle is theoretically derived. Besides, we propose a novel, to the best of our knowledge, frame structure for m-quadrature amplitude modulation-orthogonal frequency division multiplexing (m-QAM-OFDM) in underwater wireless optical communication. The frame structure contains OFDM signals and their phase-conjugated signals. At the receiving end, by the simple superposition of phase-conjugated symbols, the noise suppression can be achieved. The feasibility is experimentally demonstrated by transmitting m-QAM-OFDM signal in different modulation formats and scenarios. The results show that bit error rate performance can be significantly improved, and there is also a significant increase in transmission capacity compared to the traditional phase-conjugated method. Moreover, the proposed frame structure can provide a robust and simple compromise between transmission capacity and distance.

We demonstrate 60 Gbit/s transmission over 43-km SMF using low-coherence matched detection combined with spectral phase coding as two-layer optical encryption. Encrypted signal and carrier are multiplexed through polarization diversity and demultiplexed using polarization tracking.