Compact and high-performance vortex mode sorter for multi-dimensional multiplexed fiber communication systems

With the amplitude, time, wavelength/frequency, phase, and polarization/spin parameter dimensions of the light wave/photon almost fully utilized in both classical and quantum photonic information systems, orbital angular momentum (OAM) carried by optical vortex modes is regarded as a new modal parameter dimension for further boosting the capacity and performance of the systems. To exploit the OAM mode space for such systems, stringent performance requirements on a pair of OAM mode multiplexer and demultiplexer (also known as mode sorters) must be met. In this work, we implement a newly discovered optical spiral transformation to achieve a low-cross-Talk, wide-opticalbandwidth, polarization-insensitive, compact, and robust OAM mode sorter that realizes the desired bidirectional conversion between seven co-Axial OAM modes carried by a ring-core fiber and seven linearly displaced Gaussian-like modes in parallel single-mode fiber channels. We further apply the device to successfully demonstrate high-spectralefficiency and high-capacity data transmission in a 50-km OAM fiber communication link for the first time, in which a multi-dimensional multiplexing scheme multiplexes eight orbital-spin vortex mode channels with each mode channel simultaneously carrying 10 wavelength-division multiplexing channels, demonstrating the promising potential of both the OAM mode sorter and the multi-dimensional multiplexed OAM fiber systems enabled by the device. Our results pave the way for futureOAM-based multi-dimensional communication systems

Obstacle evasion in free-space optical communications utilizing Airy beams

A high speed free-space optical communication system capable of self-bending signal transmission around line-of-sight obstacles is proposed and demonstrated. Airy beams are generated and controlled to achieve different propagating trajectories, and the signal transmission characteristics of these beams around the obstacle are investigated. Our results confirm that, by optimising their ballistic trajectories, Airy beams are able to bypass obstacles with more signal energy and thus improve the communication performance compared with normal Gaussian beams.Comment: 8 pages, 4 figure

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

Orbital-angular-momentum mode-group multiplexed transmission over a graded-index ring-core fiber based on receive diversity and maximal ratio combining

An orbital-angular-momentum (OAM) mode-group multiplexing (MGM) scheme using high-order mode groups (MGs) in a graded-index ring-core fiber (GIRCF) is proposed, in which a receive-diversity architecture is designed for each MG to suppress the mode partition noise resulting from random intra-group mode crosstalk. The signal-to-noise ratio (SNR) of the received signals is further improved by a simple maximal ratio combining (MRC) technique on the receiver side to efficiently take advantage of the diversity gain of the receiver. Intensity-modulated direct-detection (IM-DD) systems transmitting three OAM mode groups with total 100-Gb/s discrete multi-tone (DMT) signals over a 1-km GIRCF and two OAM mode groups with total 40-Gb/s DMT signals over an 18.4-km GIRCF are experimentally demonstrated, respectively, to confirm the feasibility of our proposed OAM-MGM scheme

Mode division multiplexing based on ring core optical fibers

The unique modal characteristics of ring core fibers (RCFs) potentially enable the implementation of mode-division multiplexing (MDM) schemes that can increase optical data transmission capacity with either low-complexity modular multi-input multi-output (MIMO) equalization or no MIMO equalization. This paper attempts to present a comprehensive review of recent research on the key aspects of RCF-based MDM transmission. Starting from fundamental fiber modal structures, a theoretical comparison between RCFs and conventional step-index and graded-index multi-mode fibers in terms of their MDM capacity and the associated MIMO complexity is given first as the underlining rationale behind RCF-MDM. This is followed by a discussion of RCF design considerations for achieving high-mode channel count and low crosstalk performances in either MIMO-free or modular MIMO transmission schemes. The principles and implementations of RCF mode (de-)multiplexing devices are discussed in detail, followed by RCF-based optical amplifiers culminating in MIMO-free or modular-MIMO RCF-MDM data transmission schemes. A discussion on further research directions is also given

Significant effects of cross term of Poynting vector on an electromagnetic wave propagation through a slab with low real part of impedance

Energy conversion and conservation for an electromagnetic wave traveling through a slab are analyzed. It is demonstrated that a cross term of Poynting vector may occur due to interference between forward and backward waves in the slab, and may play the leading role if the slab owns low real part of impedance. Several novel electromagnetic phenomena are predicted. For example, both reflection and transmission can be enhanced significantly even if the slab is made of lossy material. This work indicates that materials with low real part of impedance, like left-handed materials and near-zero-refractive-index materials, may hold unique electromagnetic properties and merit further exploration

A Comprehensive Model for Estimating Stimulated Reservoir Volume Based on Flowback Data in Shale Gas Reservoirs

Stimulated reservoir volume (SRV) which is generated by horizontal drilling with multistage hydraulic fracturing governs the production in the shale gas reservoirs. Although microseismic data has been used to estimate the SRV, it is high-priced and sometimes overestimated. Additionally, the effect of stress sensitivity on SRV is not considered in abnormal overpressure areas. Thus, the objective of this work is to characterize subsurface fracture networks with stress sensitivity of permeability through the shale gas well production data of the early flowback stage. The flowback regions are first identified with the flowback data of two shale gas wells in South China. Then, we measured the permeability stress sensitivity of the core after fracturing, coupled to the dynamic relative permeability (DRP) calculation to obtain an accurate and simple DRP curve. After that, a comprehensive model is built considering dynamic two-phase relative permeability function and stress sensitivity. Finally, we compared the calculated results with the microseismic data. The results show that the proposed model could reasonably predict the SRV using the flowback data after fracturing. Additionally, compared with the microseismic data, the stress sensitivity should be included, especially in the abnormal overpressure block. It is believed that this mathematical model is accurate and useful. The work provides an efficient approach to estimate stimulated reservoir volume in the shale gas reservoirs