Xiong Wu

Stokes space modulation format classification based on non-iterative clustering algorithm for coherent optical receivers

A Stokes-space modulation format classification (MFC) technique is proposed for coherent optical receivers by using a non-iterative clustering algorithm. In the clustering algorithm, two simple parameters are calculated to help find the density peaks of the data points in Stokes space and no iteration is required. Correct MFC can be realized in numerical simulations among PM-QPSK, PM-8QAM, PM-16QAM, PM-32QAM and PM-64QAM signals within practical optical signal-to-noise ratio (OSNR) ranges. The performance of the proposed MFC algorithm is also compared with those of other schemes based on clustering algorithms. The simulation results show that good classification performance can be achieved using the proposed MFC scheme with moderate time complexity. Proof-of-concept experiments are finally implemented to demonstrate MFC among PM-QPSK/16QAM/64QAM signals, which confirm the feasibility of our proposed MFC scheme.

Scalable mode division multiplexed transmission over a 10-km ring-core fiber using high-order orbital angular momentum modes

We propose and demonstrate a scalable mode division multiplexing scheme based on orbital angular momentum modes in ring core fibers. In this scheme, the high-order mode groups of a ring core fiber are sufficiently de-coupled by the large differential effective refractive index so that multiple-input multiple-output (MIMO) equalization is only used for crosstalk equalization within each mode group. We design and fabricate a graded-index ring core fiber that supports 5 mode groups with low inter-mode-group coupling, small intra-mode-group differential group delay, and small group velocity dispersion slope over the C-band for the high-order mode groups. We implement a two-dimensional wavelength- and mode-division multiplexed transmission experiment involving 10 wavelengths and 2 mode groups each with 4 OAM modes, transmitting 32 GBaud Nyquist QPSK signals over all 80 channels. An aggregate capacity of 5.12 Tb/s and an overall spectral efficiency of 9 bit/s/Hz over 10 km are realized, only using modular 4x4 MIMO processing with 15 taps to recover signals from the intra-mode-group mode coupling. Given the fixed number of modes in each mode group and the low inter-mode-group coupling in ring core fibres, our scheme strikes a balance in the trade-off between system capacity and digital signal processing complexity, and therefore has good potential for capacity upscaling at an expense of only modularly increasing the number of mode-groups with fixed-size (4x4) MIMO blocks.

Stokes-space modulation format identification for coherent optical receivers utilizing improved hierarchical clustering algorithm

A modulation format identification (MFI) technique is proposed for coherent optical receivers, by using improved hierarchical clustering algorithm. Good performance of the proposed MFI technique can be achieved among five modulation formats in the simulation. Proof-of-concept experiments with polarization multiplexed QPSK/16QAM signals confirm the feasibility of the proposed MFI scheme after long-distance fiber transmission.

Inter-mode crosstalk compensation for radio orbital angular momentum multiplexing systems under misaligned condition using multiple-input multiple-output techniques

Inter-mode crosstalk compensation in radio orbital angular momentum (OAM) multiplexing systems with misalignment between transmitters and receivers are investigated by utilizing the multiple-input multiple-output (MIMO) analytical model. Both the zero-forcing (ZF) and minimum-mean-square-error (MMSE) compensation schemes are analysed under the misaligned conditions including off-axis and non-parallel cases. The simulation results show that system performance is significantly improved after compensation than that without compensation in both of the off-axis and non-parallel cases.

Optical Modulation Format Identification Based on Gaussian Mixture Model of Signal Amplitude Distribution

A modulation format identification technique is proposed for coherent optical communications, based on Gaussian mixture model of signal amplitude distribution. The simulation and experimental results show successful recognition can be realized among five modulation formats.