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A scheme of integrated sensing and communication in an optical fibre (ISAC-OF) using the same wavelength channel for simultaneous high-speed data transmission and distributed vibration sensing.

Short reach optical communications are desperate for cost-effective solutions to improve capacity and compatibility in dealing with massive access and applications. Single sideband-direct detection (SSB-DD) is highly recognized for improving capacity with single PD, but it is confronted with signal-signal beating interference (SSBI). Recently, a DC-Value method has been proposed for optical signal phase retrieval for single carrier signal transmission. To further explore the effectiveness and compatibility of DC-Value method, in this letter for the first time, the orthogonal frequency division multiplexing (OFDM)-based multi-carrier modulation formats are processed by the DC-Value method in the receiver. Simulation results demonstrate that, for both OFDM and Nyquist-shaped single carrier (SC), the DC-Value method is beneficial in applying lower sampling rate to achieve comparable transmission performance than that of Kramers-Kronig receiver. In addition, althrough OFDM holds 2 dB increment of the optimum carrier-signal power ratio (CSPR) than Nyquist-SC, it offers more robustness to fibre transmission.

A fast polarization tracking and demultiplexing algorithm in polarization-division-multiplexing (PDM) systems is proposed and demonstrated. The scheme utilizes two optimizing parameters in Stokes Space, including the polarization angle and the phase information. In addition to its transparency to modulation formats, the angle-plus-phase algorithm (APA) could provide fast convergence up to >100-Mrad/s polarization tracking speed. Compared to common polarization demultiplexing algorithms such as constant modulus algorithm (CMA) and linear Kalman filter (LKF), experimental results show that the polarization tracking capability of the proposed APA algorithm is significantly improved without sacrificing the transmission performance. Specifically, compared to CMA, the tracking speed can be improved from 9-Mrad/s to 160-Mrad/s for PDM quadrature phase shift keying (PDM-QPSK) signals. Furthermore, compared to CMA and LKF, APA has the best tracking performance, and the tracking speed can be reached to 34-Mrad/s for PDM 16 quadrature amplitude modulation (PDM-16QAM) signal.

Sparse code multiple access (SCMA) is a promising technology to provide high throughput and overall improved system performance at affordable cost for next-generation passive optical networks (NG-PONs). Message passing algorithm (MPA) based on a factor graph is usually used for low-complexity multi-user detection in SCMA. However, MPA requires accurate and effective channel estimation due to the interference between the user's signals on the same resource block and suffers uncertain convergence caused by the cycles in the factor graph. In this paper, a graph neural networks (GNN)-based detection method is proposed for SCMA-PON, which performs channel impairment compensation and signal detection in a joint manner. 25.5 Gb/s SCMA-OFDM system over 20/60 km single mode fiber link is simulated to demonstrate the feasibility with 8.5-G class optical devices. The simulation results show that GNN-based detection method outperforms MPA and is more robust to the nonlinear distortion for the same level of computational complexity.

Due to the interaction between chromatic dispersion (CD) and direct detection, the CD induced power-fading effect has been considered as the key point to limit transmission rate and distance in intensity modulation direct-detection (IM/DD) systems. Besides, the performance of the IM/DD systems will be further affected by the bandwidth limitation and nonlinearity effect. In this paper, we propose a low complexity nonlinear equalizer (NLE) based on temporal convolutional neural network (TCNN) regression model which combines dilated convolutions with residual connections. Then, the performance of our proposed equalizer is experimentally demonstrated in 56-Gbit/s 4-level pulse amplitude modulation (PAM4) intensity modulation direct-detection system. The results show that the receiver sensitivity with the help of our TCNN equalizer can be improved about 1.5 dB and 3.5 dB compared to 2D-CNN and 1D-CNN equalizer under 70-km single mode fiber (SMF) transmission. Furthermore, the proposed equalizer can extend maximum transmission distance to 100 km at bit error rate threshold of 3.8 × 10−3.

An OSNR monitoring method assisted by support vector ordinal regression (SVOR) is proposed for digital coherent receivers. According to Godard's error of equalized signals obtained after polarization demultiplexing, the optical signal-to-noise ratio (OSNR) value could be effectively estimated by using SVOR. The effectiveness of the proposed OSNR monitoring method is verified via numerical simulations with 28-Gbaud PDM-QPSK, PDM-8PSK, PDM-8QAM, PDM-16QAM and PDM-32QAM signals. The simulation results show that the 100% accuracies for the five modulation formats can be obtained over a wide OSNR range. The feasibility is further demonstrated by proof-of-concept experiments in 28-Gbaud PDM-QPSK, PDM-8PSK, PDM-8QAM and PDM-16QAM systems. The errors of averaged values of estimated OSNR for all the signals are less than or equal to 0.2 dB.

This paper considers Godard's error as signal quality metric to monitor chromatic dispersion (CD), nonlinear parameter and modulation format in the DSP module of the coherent receivers. We first review a CD monitoring based on Godard's error that can be able to accurately monitor arbitrarily large dispersion values in uncompensated transmission links in combination with frequency domain equalizer, then extend the previous nonlinear parameter monitoring method based on Godard's error by blindly obtaining the optimized value γξp to significantly improve the adaptive capability, and present a simple and effective modulation format monitoring based on Godard's error. Meanwhile, the effectiveness has been experimentally verified in 128-Gb/s PDM-QPSK, 192-Gb/s PDM-8QAM, and 256-Gb/s PDM-16QAM systems.

A Stokes space modulation format identification (MFI) method using probabilistic neural network (PNN) is proposed for coherent optical receivers. According to amplitude histograms obtained by the distribution of Stokes vectors on the s1 axis, the incoming signals are first classified into PDM-mPSK, PDM-16QAM, and PDM-64 QAM signals based on PNN. To further identify PDM-mPSK signals, the constellation feature of Stokes vectors on s2-s3 plane is extracted by image processing techniques and then processed by PNN. The high identification accuracy is demonstrated via numerical simulations with 28-Gbaud PDM-QPSK, PDM-8PSK, PDM-16QAM, and PDM-64QAM signals over a wide optical signal-to-noise ratio range. Owing to the characteristic of PNN, the proposed MFI method has simple training process, small training data size and a small number of required symbols. Proof-of-concept experiments have been implemented to verify the effectiveness of the proposed MFI method among 28-Gbaud PDM-QPSK, PDM-8PSK, and PDM-16QAM signals.

Nonlinear phase noise (known as Gordon-Mollenauer phase noise) results from power fluctuations arising from amplified spontaneous-emission noise of the inline amplifier which is converted into phase fluctuations due to the self-phase modulation effect. It may severely impair the phase of optical signal, and would further degrade the performance of the long-haul optical transmission systems. The case can be compensated partially by mid-span optical phase conjugation(OPC). In this paper, an effective k-nearest neighbor (KNN) detector have been introduced to further improve the performance of OPC system by mitigating non-Gaussian impairments caused by nonlinear phase noise. The effectiveness is investigated in a 112-Gb/s 16QAM optical phase conjugation system with 800-km dispersion-managed link and 1280-km dispersion-shifted-fiber link. The results show that the effective and optimal KNN detector can enhance the overall performance of OPC system, even the asymmetric system.

Polarization-beam-splitters with both broadband operation window and high extinction ratio are highly desirable in optical communication systems. In this paper, a compact noncascaded-directional-couplers PBS with an ultrahigh extinction ratio and low excess loss is proposed. The PBS utilizes an asymmetrical directional coupling structure consisted of a TE-pass-polarizer waveguide and a TE- and TM-pass waveguide. The simulation results show that the extinction ratio is up to 35.41 dB and the excess loss is only 0.11 dB around the central wavelength 1550 nm for both polarizations (TE and TM). Meanwhile, when the extinction ratio is 30, 25, and 20 dB, the corresponding bandwidth is 72, 145, and 188 nm, respectively. Also, the EL is 1 and 0.5 dB in a bandwidth of ∼73 and ∼48 nm, respectively. A fabrication tolerance of ±10 nm for the waveguide width is also achieved.

According to different transmission distances, application scenarios of a data center mainly include intra- and inter-data center optical interconnects. The intra-data center optical interconnect is considered as a few kilometers optical interconnect between servers and racks inside a data center, which accounts for nearly 80% of data traffic of a data center. The other one, inter-data center optical interconnect, is mainly applied in tens of kilometers data transmission among different data centers. Since data exchange in data centers generally occurs between many servers and racks, and a lot of transmitter and receiver components are required, optical interconnects become highly sensitive to component costs. In this paper, we firstly review the development and applications of mainstream transmitter components (e.g., VCSEL, DML, EML, MZM, and monolithic integrated transmitter) and receiver components (e.g., single-end photodetector, Kramers-Kronig receiver, Stokes vector receiver, and monolithic integrated receiver), which have been widely applied in short-reach transmission systems. Then, two types of integrated solutions including simplified detection scheme and transceiver integration scheme are presented in detail. Finally, we summarize and discuss the technological and component options for different transmission distances. We believe that monolithic integrated components, especially transceiver integration, will become a powerful solution for next-generation high-speed short-reach transmission systems.

The minimization of polarization multiplexing angle in a polarization-division-multiplexed (PDM) transmission system is explored. An effective polarization demultiplexing algorithm based on Stokes space is proposed to realize the demultiplexing of two nonorthogonal polarization states. Both simulation and experimental results verify the effectiveness of the proposed algorithm for the transmission of a 56-Gb/s PDM-dual phase-shift keying (DPSK) signal over different polarization multiplexing angles (i.e., θ 1/4 23°, 45°, 67°, 90°) and different lengths of transmission links (i.e., back-to-back, 320 km, 400 km).

A low-complexity and adaptive nonlinearity estimation module is proposed and experimentally demonstrated based on Godard's error and low-pass filter (LPF). The computational complexity of the proposed adaptive estimation module is significantly reduced by avoiding utilizing the polarization demultiplexing, frequency offset compensation, and carrier phase recovery in the process of finding the optimal value γξopt compared with the previous approach based on phase noise variance. The performance of the proposed module is experimentally verified in a 40-Gb/s polarization-division-multiplexing-quadrature-amplitude modulation (PDM-QPSK) coherent optical communication system over 720-km single-mode fiber (SMF). Experimental results show that the computational complexity of the proposed nonlinearity estimation module is only ~7.35% of the previous approach and ~27.8% of that with an LPF inserted.

We propose and experimentally demonstrate an effective and highly flexible polarization demultiplexing scheme based on a Stokes analyzer, which could be also applied to the nonorthogonal polarization division multiplexing (NPDM) schemes. Compared with the conventional direct detection, the proposed method has better tolerance to the polarization-dependent loss. Furthermore, such an approach can significantly enhance system flexibility without increasing cost and complexity since the transmitted signals are not required to maintain strict orthogonality, and no additional polarization-tracking feedback circuit is needed. Experimental results show that any polarization multiplexing degree that is larger than 23° can be adaptively demultiplexed after 10-km transmission using optical orthogonality monitoring and digital-signal-processing (DSP) algorithms.

All-optical format conversion plays an important role in future transparent optical networks in order to enhance reconfigurability. On the other hand, the polarization-division multiplexing (PDM) technique has been extensively studied for achieving high-speed and high-spectral-efficiency optical networks. Since the state of polarization of PDM signals are randomly changed along the transmission optical link, it is important to elaborately design a polarization-insensitive conversion scheme in such a network. In this paper, we proposed and experimentally demonstrated an all-optical nonreturn-to-zero-return-to-zero format conversion for PDM on-off keying (OOK), binary phase-shift keying (BPSK), and quadrature phase-shift keying (QPSK) signals. Polarization-insensitive operation is achieved by utilizing the merit of the dual-orthogonal-pump four-wave mixing (FWM) process in a highly nonlinear fiber, and receiver-sensitivity-gain operation is observed in the conversion process. The bit error ratio (BER) results show that receiver-sensitivity gains of ~1.5, ~0.8, and 0.3 dB for the OOK, BPSK, and QPSK PDM signals at BER values of 10-9, 10-9, and 10-3 are obtained, respectively.

Mild thermal stimulation plays an active role in bone tissue repair and regeneration. In this work, a bioactive polydopamine/Ti3C2/poly(vinylidene fluoride trifluoroethylene) (PDA/Ti3C2/P(VDF-TrFE)) nanocomposite coating with excellent near-infrared light (NIR)-triggered photothermal effect was designed to improve the osteogenic ability of implants. By incorporating dopamine (DA)-modified Ti3C2 nanosheets into the P(VDF-TrFE) matrix and combining them with alkali initiated in situ polymerization, the resulting PDA/Ti3C2/P(VDF-TrFE) nanocomposite coating gained high adhesion strength on Ti substrate, excellent tribological and corrosion resistance properties, which was quite important for clinical application of implant coatings. Cell biology experiments showed that NIR-triggered mild thermal stimulation on the coating surface promoted cell spreading and growth of BMSCs, and also greatly upregulated the osteogenic markers, including Runt-Related Transcription Factor 2 (RUNX2), alkaline phosphatase (ALP), osteopontin (OPN), osteocalcin (OCN). Simultaneously, the synthesis of heat shock protein 47 (HSP47) was significantly promoted by the mild thermal stimulation, which strengthened the specific interaction between HSP47 and collagen Ⅰ (COL-Ⅰ), thereby activating the integrin-mediated MEK/ERK osteogenic differentiation signaling pathway. In addition, the results also showed that the mild thermal stimulation induced the polarization of macrophages towards M2 phenotype, which can attenuate the inflammatory response of injured bone tissue. Antibacterial results indicated that the coating exhibited an outstanding antibacterial ability against S. aureus and E. coli. Conceivably, the versatile implant bioactive coatings developed in this work will show great application potential for implant osseointegration.