We propose a dispersion flattened fiber (DFF) front-haul transmission system with high bitrate, polarization multi-plexing (PM) and quadrature amplitude modulation (QAM) signal at low input optical power. The modulation format of the system is PM-16QAM, and the bitrate is 256 Gbit/s. The transmission characteristics over DFF link system are experimentally studied, which are compared with those over non-zero dispersion shifted fiber (NZDSF) link and stan-dard single mode fiber (SSMF) link. The experimental results show that the error vector magnitude (EVM) of 256 Gbit/s and PM-16QAM signal over 25 km DFF link is 0.75% better than that over 25 km NZDSF link at least, and the bit error rate (BER) and Q-factor are much better than those of NZDSF. Their EVM and BER are both decreased with the increase of input optical power, and the Q-factor is increased. Those characteristics over 25 km SSMF are the worst at the same case. The larger the dispersion is, the more the constellation points are deviated from their respective centers and the worse the constellation characteristics are. The greater the attenuation of the DFF is, the smaller the input power of the DFF is, the more the constellation points are deviated from their centers and the worse the constel-lation characteristics are. This study provides a new idea and experimental support for long span front-haul propaga-tion in mobile communication.

A graded-index mode division multiplexer with low loss and low crosstalk is proposed. The transmission channel adopts a pure silica core with large effective area to achieve low attenuation, which effectively reduces the splicing loss with pure silica core few-mode transmission fiber. Low differential mode group delay is realized by using grad-ed-index distribution. Also the effective index difference of the modes is greater than 0.5×10-3 to ensure low crosstalk between modes. The performance of the mode division multiplexer is investigated using the beam propagation method and full-vector finite element method. The result shows that the coupling efficiency of multiplexer is better than .0.479 dB, and the extinction ratio is higher than 31.2 dB in the wavelength of 1 400—1 700 nm. In C band, the aver-age coupling efficiency of all mode channels of multiplexer is better than that of .0.140 dB, which shows flatness. The proposed scheme is an effective way to implement a multiplexer with low crosstalk, low loss, low fusion loss, high coupling efficiency, high extinction ratio and wide operating band.

Erratum to: Optoelectronics Letters May 2018, Volume 14, Issue 3, pp 204–208 https://doi.org/10.1007/s11801-018-7251-6

围绕下一代光纤通信系统中轨道角动量(OAM)复用技术的关键问题，基于环状光纤中携带OAM的模式基础理论，仿真分析了环状光纤的不圆度对矢量合成OAM模式的本征奇模和偶模的有效折射率、走离长度以及模场强度分布的影响。结果表明，环状光纤不圆度会使得本征模式奇偶模之间的有效折射率差增大，走离长度减小，导致相应OAM模式在环状光纤中传输时稳定性下降。同时，不圆度的存在还会使矢量合成OAM模式的各本征模式的模场强度分布发生畸变，模场泄漏加剧。

?Tianjin University of Technology and Springer-Verlag Berlin Heidelberg 2016 In order to further improve the carrier synchronization estimation range and accuracy at low signal-to-noise ratio (SNR), this paper proposes a code-aided carrier synchronization algorithm based on improved nonbinary low-density parity-check (NB-LDPC) codes to study the polarization-division-multiplexing coherent optical orthogonal frequency division multiplexing (PDM-CO-OFDM) system performance in the cases of quadrature phase shift keying (QPSK) and 16 quadrature amplitude modulation (16-QAM) modes. The simulation results indicate that this algorithm can enlarge frequency and phase offset estimation ranges and enhance accuracy of the system greatly, and the bit error rate (BER) performance of the system is improved effectively compared with that of the system employing traditional NB-LDPC code-aided carrier synchronization algorithm.

An offset quadrature amplitude modulation orthogonal frequency-division multiplexing (OQAM-OFDM) passive optical network (PON) architecture with direct detection is brought up to increase the transmission range and improve the system performance. In optical line terminal (OLT), OQAM-OFDM signals at 40 Gbit/s are transmitted as downstream. At each optical network unit (ONU), the optical OQAM-OFDM signal is demodulated with direct detection. The results show that the transmission distance can exceed 20 km with negligible penalty under the experimental conditions.

We present an extra processing added to conventional least square (LS) channel estimation to further improve its performance in coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. The influence of noise, chromatic dispersion and polarization mode dispersion on the performance of the proposed algorithm is analyzed. The simulation results show that the improved algorithm has better performance and lower complexity.

A novel architecture for the colorless optical network unit (ONU) is proposed and experimentally demonstrated with direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM). In this architecture, polarization- division multiplexing is used to reduce the cost at ONU. In optical line terminal (OLT), quadrature amplitude modulation (QAM) intensity-modulated OFDM signal with x-polarization at 10 Gbit/s is transmitted as downstream. At each ONU, the optical OFDM signal is demodulated with direct detection, and y-polarization signal is modulated for upstream on-off keying (OOK) data at 5 Gbit/s. Simulation results show that the power penalty is negligible for both optical OFDM downstream and the on-off keying upstream signals after over 50 km single-mode fiber (SMF) transmission.

In this paper，a wavelength division multiplexing (WDM) transmission system derived from the coherent optical orthogonal frequency division multiplexing (CO-OFDM) with polarization division multiplexing (PDM) and 16-order quadrature amplitude modulation (QAM) is studied. A simulation of 80-channel WDM transmission system with data rate of 200 Gbit/s is built, and the transmission performance of the system is analyzed. The simulation results show that the system Q value of the WDM channels at 16 Tbit/s with a spectral efficiency of 7.14 bit/s/Hz is potentially over 10.0 dB for a long haul transmission up to 1800 km in a standard single-mode fiber.

相干光正交频分复用(CO-OFDM)由于其良好的传输性能成为近年来光传输领域的研究热点，波分复用技术可以在光纤中通过增加并行波长的数量来提高系统的容量， 将CO-OFDM和WDM技术结合，可以 构造出高速率、大 容量、低成本的光传输网络。首先对基于CO-OFDM的WDM传输系统的理论模型和基本 原理进行了研究， 对基于CO-OFDM的100Gb/s×32-信道WDM传输系统进行了仿真分析。 并研究了该系统的传输性能。结果 表明:在没有任何光纤的色散及非线性 补偿的情况下，当信号速率为3.2 Tb/s时，系统Q因子高于16.0 dB，在标准单模光纤中的传输距离可达1500 km。