Scaling multimode fibre IM/DD transmission capacity through spatial-spectral multiplexing

Data centre connections can greatly benefit from parallel transmission channels on one multimode fibre (MMF). Shortwave wavelength division multiplexing (SWDM) achieves parallel transmission through spectral multiplexing. Furthermore, MMFs offer a spatial dimension that should be exploited to increase parallel transmission, albeit in a cost-effective way. In this paper, it is shown that SWDM and spatial multiplexing can be combined in intensity modulation and direct detection MMF transmission systems that use selective offset excitation and mode-selective spatial filtering

Mitigation of impairments in MGDM transmission with mode-selective spatial filtering

A model for a mode group diversity multiplexing (MGDM) transmission system is derived. The factors that may limit MGDM transmission are identified. An optical method to reduce the spatial overlap among the fields of the detected mode groups could mitigate impairments that may occur in MGDM transmission. Mode-selective spatial filtering (MSSF) is such an optical method. Experimental results support that a robust five-channel MGDM system could be realized with MSSF, as long as modal noise is limited. MSSF facilitates the combination of MGDM with wavelength-division multiplexing

Mode selective spatial filtering for increased robustness in a mode group diversity multiplexing link

We propose a very simple optical method to reduce the cross talk among the channels of a mode group diversity multiplexing (MGDM) link. MGDM is an intensity modulation, direct detection, multiple-input, multiple-output technique that creates independent communication channels over a multimode fiber (MMF). The cross talk among the channels is mitigated electronically. However, by properly employing a lens between the output of a graded-index MMF and the detectors, we achieve mode-selective spatial filtering (MSSF) and optically reduce the cross talk. The robustness of the link is then increased when compared with an implementation without MSSF. This allows for a larger number of channels

Symmetric few-mode fiber couplers as the key component for broadband mode multiplexing

All-fiber broadband mode multiplexers (MMUXs) for mode and wavelength division multiplexing transmission systems are designed and analyzed. The MMUXs are based on cascaded 2-D or 3-D symmetric few-mode fiber (FMF) couplers. The MMUXs are optimized for operation over the C band and multiplex modes LP 01 , LP11a, LP11b, LP21a, LP 21b, and LP02with a nearly flat response and an average insertion loss around 1.6 dB, depending on the design approach. The operation of the FMF couplers and the MMUXs is analyzed numerically by means of a full-vectorial beam propagation method. If the two polarization states of each LP mode are further considered, such all-fiber MMUXs can be used to combine 12 spatial channels, supporting an order of magnitude capacity increase-compared to a single spatial channel system-in optical fiber transmission systems through space (mode and polarization) division multiplexing. © 2014 IEEE

All-fiber broadband 02 mode converter for future wavelength and mode division multiplexing systems

A novel broadband all-fiber 02 mode converter is proposed and numerically analyzed. The converter is based on multimode interference in a multimode fiber (MMF) that interconnects a single-mode fiber (SMF) with a few-mode fiber, considered the transmission medium in future mode division multiplexing (MDM) systems. The proposed 02 converter is reciprocal and polarization independent, and supports a very broad optical bandwidth of 150 nm with an over 20 dB extinction ratio, as well as an efficient coupling and easy connectivity as an all-fiber device. In a reciprocal operation, it performs mode filtering as well, therefore supporting mode demultiplexing. The dependence of the performance of the converter on the MMF length and core diameter is further investigated. The very broad bandwidth of the device renders it suitable for future transmission systems that need to combine MDM with wavelength division multiplexing targeting to achieve record transmission rates that cannot be reached with SMF transmission systems. © 2012 IEEE

Quality of transmission estimation in WDM and elastic optical networks accounting for space-spectrum dependencies

We develop a framework for estimating the quality of transmission (QoT) of a new lightpath before it is established, as well as for calculating the expected degradation it will cause to existing lightpaths. The framework correlates the QoT metrics of established lightpaths, which are readily available from coherent optical receivers that can be extended to serve as optical performance monitors. Past similar studies used only space (routing) information and thus neglected spectrum, while they focused on oldgeneration noncoherent networks. The proposed framework accounts for correlation in both the space and spectrum domains and can be applied to both fixed-grid wavelength division multiplexing (WDM) and elastic optical networks. It is based on a graph transformation that exposes and models the interference between spectrum-neighboring channels. Our results indicate that our QoT estimates are very close to the actual performance data, that is, to having perfect knowledge of the physical layer. The proposed estimation framework is shown to provide up to 4 × 10-2 lower pre-forward error correction bit error ratio (BER) compared to theworst-case interference scenario,which overestimates the BER. The higher accuracy can be harvested when lightpaths are provisioned with low margins; our results showed up to 47% reduction in required regenerators, a substantial savings in equipment cost. © 2016 Optical Society of America