Total net-rate of 27.88 Tb/s full C-band transmission over 4,550†km using 150†km span length and high-gain EDFA amplification.

We experimentally demonstrate a total net-rate of 27.88 Tb/s for C-band wavelength-division multiplexing (WDM) transmission over an ultralong span-length of 150 km. It is the largest net capacity × span-length product of 4182 Tb/s·km for C-band, single-core, standard single-mode optical fiber transmission over a length of more than 3,000 km. A total of 99 channels, spaced at 50 GHz intervals, are employed for transmitting 32 GBaud probabilistically constellation-shaped (PCS) 64QAM signals with an information entropy of 5.5. High gain amplifiers can achieve wavelength-division multiplexing (WDM) transmission with a bandwidth of 6.25 THz, at a noise figure below 4.3 dB, without the assistance of distributed Raman amplification.

Power evolution prediction of bidirectional Raman amplified WDM system based on PINN.

We propose using physical-informed neural network (PINN) for power evolution prediction in bidirectional Raman amplified WDM systems with Rayleigh backscattering (RBS). Unlike models based on data-driven machine learning, PINN can be effectively trained without preparing a large amount of data in advance and can learn the potential rules of power evolution. Compared to previous applications of PINN in power prediction, our model considers bidirectional Raman pumping and RBS, which is more practical. We experimentally demonstrate power evolution prediction of 200 km bidirectional Raman amplified wavelength-division multiplexed (WDM) system with 47 channels and 8 pumps using PINN. The maximum prediction error of PINN compared to experimental results is only 0.38 dB, demonstrating great potential for application in power evolution prediction. The power evolution predicted by PINN shows good agreement with the results simulated by traditional numerical method, but its efficiency is more suitable for establishing models and calculating noise, providing convenience for subsequent power configuration optimization.

Two-stage equalization for ultra-fast RSOP and inter symbol interference compensation based on a simplified Kalman filter.

We propose a two-stage equalization based on a simplified Kalman filter, which is used to solve the rapid rotation of the state of polarization (RSOP) that is caused by lightning strikes on optical cables and the extra inter symbol interference (ISI) introduced in the system. By analyzing the special expression of matrix coefficient in the Kalman filter under polarization demultiplexing, the simplified idea of a Kalman filter is provided, and its updating process is transformed into a kind of multiple-input-multiple-output (MIMO) structure algorithm. At the same time, the second stage finite impulse response filter is used to solve the ISI that is difficult to be solved by a Kalman filter. The performance of the proposed algorithm was tested in a coherent system of 28Gbaud PDM-QPSK/16QAM. The results confirm that on the basis of lower complexity than a Kalman filter, the proposed algorithm reduces its complexity by more than 30% compared to traditional MIMO equalization algorithm under the premise of linear operation, and which also can handle RSOP of 20 Mrad/s. When the system suffers from the extra ISI due to the limited device bandwidth, the optical signal to noise ratio of the proposed algorithm is about 4 dB lower than the Kalman filter at the same bit error rate.

Compact MEMS external cavity tunable laser with ultra-narrow linewidth for coherent detection.

A compact and ultra-narrow linewidth tunable laser with an external cavity based on a simple single-axis-MEMS mirror is presented in this paper. We discuss the simulation of this tunable laser using a two-step hybrid analysis method to obtain an optimal design of the device. A wide wavelength tuning range about 40 nm in C-band with a narrow linewidth of less than 50 kHz and wavelength accuracy of ± 1 GHz over the entire tuning range can be achieved experimentally. We also conduct several experiments under different conditions to test the tunable laser. This device shows an excellent performance in both single-carrier polarization-multiplexed quadrature phase-shift keying (PM-QPSK) and multi-carrier orthogonal frequency division multiplexing (OFDM) coherent systems.