Mode-division Multiplexing Optical Network Research Articles

Mode-selective power splitters for mode-division multiplexing optical networks

We propose an all-fiber mode-selective power splitter (MSPS) for non-circular-symmetric LP lm (l = 1, 2, …) modes, which is suitable for multicasting and optical performance monitoring in mode-division multiplexing optical fiber networks. The MSPSs are asymmetric two-core few-mode directional couplers composed of a few-mode fiber and a two-mode fiber. We theoretically studied the three conditions required by the MSPSs. By carefully choosing the core-to-core distance and coupling length, the MSPS can achieve arbitrary splitting ratio regardless of the modal field orientation of the input non-circular-symmetric LP mode. By using an asymmetric structure, the MSPS can ensure the power splitting only happens on the target non-circular-symmetric LP mode when the phase matching condition is satisfied. In addition, we designed and numerically simulated LP31 MSPSs with four kinds of splitting ratios, among which the one with 90/10 splitting ratio was fabricated based on tapering and polishing method. The fabricated LP31 MSPS is characterized and the results show that its splitting ratio is much more stable than regular LP31 mode-selective coupler.

Multi-Function Mode Processing Device for Mode Division Multiplexing Optical Networks

In this study, we propose a configurable multifunction device for the mode division multiplexing (MDM) optical networks. The device can simultaneously function as low- and high-order mode block filters and a mode exchanger by selectively tuning different working states. We fabricated the device using standard microfabrication technology and the experimental performance of the device adequately follows the simulated performance. Particularly, the device exhibits a measured mode extinction ratio of 22.20 dB and 19.46 dB as a low-order mode block filter at 1.550 μm wavelength. The proposed device has great potential for use in a fully flexible and advanced MDM optical system.

Scalable selective high order mode pass filter architecture with asymmetric directional couplers.

We propose a novel design architecture to realize scalable selective mode filter based on the asymmetric directional coupler structure. In this structure, any arbitrary high-order mode can pass, whereas other unwanted modes are blocked. Furthermore, multiple optical modes can be blocked by only adjusting the structural parameters. As a proof of concept, we experimentally demonstrated a three-mode device and the scalability of the proposed structure is demonstrated by another design of four-mode filter. The proposed architecture offers scalability and high-design flexibility, and it has excellent potential to be used in advanced mode division multiplexing optical networks.

Recent Advances in DSP Techniques for Mode Division Multiplexing Optical Networks with MIMO Equalization: A Review

This paper provides a technical review regarding the latest progress on multi-input multi-output (MIMO) digital signal processing (DSP) equalization techniques for high-capacity fiber-optic communication networks. Space division multiplexing (SDM) technology was initially developed to improve the demanding capacity of optic-interconnect links through mode-division multiplexing (MDM) using few-mode fibers (FMF), or core-multiplexing exploiting multicore fibers (MCF). Primarily, adaptive MIMO filtering techniques were proposed to de-multiplex the signals upon different modes or cores, and to dynamically compensate for the differential mode group delays (DMGD) plus mode-dependent loss (MDL) via DSP. Particularly, the frequency-domain equalization (FDE) techniques suggestively lessen the algorithmic complexity, compared with time-domain equalization (TDE), while holding comparable performance, amongst which the least mean squares (LMS) and recursive least squares (RLS) algorithms are most ubiquitous and, hence, extensively premeditated. In this paper, we not only enclose the state of the art of MIMO equalizers, predominantly focusing on the advantage of implementing the space–time block-coding (STBC)-assisted MIMO technique, but we also cover the performance evaluation for different MIMO-FDE schemes of DMGD and MDL for adaptive coherent receivers. Moreover, the hardware complexity optimization for MIMO-DSP is discussed, and a joint-compensation scheme is deliberated for chromatic dispersion (CD) and DMGD, along with a number of recent experimental demonstrations using MIMO-DSP.

Integrated tunable mode filter for a mode-division multiplexing system.

Mode-division multiplexing (MDM) using multiple spatial modes as independent signals has been a promising technique to increase the communication capacity in conjunction with wavelength-division multiplexing (WDM). In MDM systems, mode filters are key components to filter out the undesired signals on specific mode. Analogous to a wavelength tunable filter used in a WDM system, here we propose and experimentally demonstrate a fundamental- or high-order-mode-pass tunable filter for a flexible MDM optical network based on a silicon platform. It consists of two switchable mode exchangers (MEs) and a fundamental-mode pass filter. By controlling the working state of the MEs, dynamic filtering and a tunable output can be achieved. This tunable mode filter exhibits a high extinction ratio of 18dB and low insertion loss of 3dB over the C-band. For further demonstration, the proposed device is tested using a modulated signal at 20Gb/s. The eye diagrams and the bit error rates indicate a good filtering performance.

Crosstalk-aware virtual network embedding over inter-datacenter optical networks with few-mode fibers

Abstract Virtualization of datacenter (DC) infrastructures enables infrastructure providers (InPs) to provide novel services like virtual networks (VNs). Furthermore, optical networks have been employed to connect the metro-scale geographically distributed DCs. The synergistic virtualization of the DC infrastructures and optical networks enables the efficient VN service over inter-DC optical networks (inter-DCONs). While the capacity of the used standard single-mode fiber (SSMF) is limited by their nonlinear characteristics. Thus, mode-division multiplexing (MDM) technology based on few-mode fibers (FMFs) could be employed to increase the capacity of optical networks. Whereas, modal crosstalk (XT) introduced by optical fibers and components deployed in the MDM optical networks impacts the performance of VN embedding (VNE) over inter-DCONs with FMFs. In this paper, we propose a XT-aware VNE mechanism over inter-DCONs with FMFs. The impact of XT is considered throughout the VNE procedures. The simulation results show that the proposed XT-aware VNE can achieves better performances of blocking probability and spectrum utilization compared to conventional VNE mechanisms.

High-speed two-mode switch for mode-division multiplexing optical networks

Mode-division multiplexing technology using the high-order modes of multimode waveguides enables high-bandwidth data transmission. High-speed mode channel switching is a pivotal function for these optical networks. Here, we propose a modal switching scheme on a silicon-on-insulator platform and demonstrate a high-speed two-mode switch that exploits a Y-junction and multimode interference structure. The design allows for simultaneous switching of two optical modes. A PN-doped junction-based phase shifter in one branch of a Y-junction enables dynamic switching in 2.5 ns. The measured switching extinction ratio is 12.5 dB or better with an open eye diagram for a 10 Gb/s on–off key optical payload signal. The optical power penalty is within 0.5 dB for the two-mode switching at a bit error rate of 10−9. This two-mode switch could enable on-chip mode-based switching network topology for greater aggregated throughput capacity.

On-chip data exchange for mode division multiplexed signals.

Data exchange is an important function for flexible optical network, and it has been extensively investigated for the time and wavelength domains. The mode division multiplexing (MDM) has been proposed to further increase the transmission capacity by carrying information on different modes with only single wavelength carrier. We propose and experimentally demonstrate a novel on-chip data exchange circuit for the MDM signals by utilizing two micro-ring resonator (MRR) based mode converters. For demonstration, single and four wavelengths non-return-to-zero on-off-keying (NRZ-OOK) signals at 10 Gb/s carried on different modes are successfully processed, with open and clear eye diagrams. Measured bit error ratio (BER) results show reasonable power penalties. The proposed circuit can be potentially used in advanced and flexible MDM optical networks.

Optical Mode Interleaver Based on the Asymmetric Multimode Y Junction

An optical mode interleaver (OMIL) based on the asymmetric multimode Y junction is proposed for realizing flexible selection of group of modes in mode-division multiplexing optical network. The odd and even modes of the stem can be sorted by carefully controlling the widths of the narrow and wide arms according to the constraint conditions of the propagation constants. A four-mode OMIL is analyzed as an example using the beam propagation method. The device is able to realize a low excess loss of <;0.13 dB, a high mode extinction ratio that exceeded 28.4 dB, and a mode crosstalk lower than -25.5 dB over a common spectral bandwidth of 210 nm.