Paikun Zhu

Experimental demonstration of 400 Gb/s optical PDM-OFDM superchannel multicasting by multiple-pump FWM in HNLF

OFDM superchannel that consists of multiple low speed individually-modulated subbands has been proposed for high speed optical transmission and flexible optical networks with multiple data rate accommodation. In this work, we investigate the feasibility of superchannel multicasting and verify it utilizing multiple-pump FWM in highly nonlinear fiber. 400 Gb/s PDM-OFDM superchannel that consists of ten subbands is successfully delivered from one superchannel to up to seven different superchannels with error free operation. Pump power and signal power are also optimized to achieve the optimal multicasting performance.

Novel MDM-PON scheme utilizing self-homodyne detection for high-speed/capacity access networks

In this paper, we propose a cost-effective, energy-saving mode-division-multiplexing passive optical network (MDM-PON) scheme utilizing self-homodyne detection for high-speed/capacity access network based on low modal-crosstalk few-mode fiber (FMF) and all-fiber mode multiplexer/demultiplexer (MUX/DEMUX). In the proposed scheme, one of the spatial modes is used to transmit a portion of signal carrier (namely pilot-tone) as the local oscillator (LO), while the others are used for signal-bearing channels. At the receiver, the pilot-tone and the signal can be separated without strong crosstalk and sent to the receiver for coherent detection. The spectral efficiency (SE) is significantly enhanced when multiple spatial channels are used. Meanwhile, the self-homodyne detection scheme can effectively suppress laser phase noise, which relaxes the requirement for the lasers line-width at the optical line terminal or optical network units (OLT/ONUs). The digital signal processing (DSP) at the receiver is also simplified since it removes the need for frequency offset compensation and complex phase correction, which reduces the computational complexity and energy consumption. Polarization division multiplexing (PDM) that offers doubled SE is also supported by the scheme. The proposed scheme is scalable to multi-wavelength application when wavelength MUX/DEMUX is utilized. Utilizing the proposed scheme, we demonstrate a proof of concept 4 × 40-Gb/s orthogonal frequency division multiplexing (OFDM) transmission over 55-km FMF using low modal-crosstalk two-mode FMF and MUX/DEMUX with error free operation. Compared with back to back case, less than 1-dB Q-factor penalty is observed after 55-km FMF of the four channels. Signal power and pilot-tone power are also optimized to achieve the optimal transmission performance.

Multicasting based optical inverse multiplexing in elastic optical network

Optical multicasting based inverse multiplexing (IM) is introduced in spectrum allocation of elastic optical network to resolve the spectrum fragmentation problem, where superchannels could be split and fit into several discrete spectrum blocks in the intermediate node. We experimentally demonstrate it with a 1-to-7 optical superchannel multicasting module and selecting/coupling components. Also, simulation results show that, comparing with several emerging spectrum defragmentation solutions (e.g., spectrum conversion, split spectrum), IM could reduce blocking performance significantly but without adding too much system complexity as split spectrum. On the other hand, service fairness for traffic with different granularity of these schemes is investigated for the first time and it shows that IM performs better than spectrum conversion and almost as well as split spectrum, especially for smaller size traffic under light traffic intensity.

Novel Pump-Switching FWM Scheme for Optical Superchannel Conversion in EON

Elastic optical networks (EONs) have caused great interest for their flexible allocation and efficient utilization of the spectral resource. In this letter, we investigate superchannel conversion in EON. Similar with conventional wavelength conversion in wavelength division multiplexing, superchannel conversion is transparent to the signal bit rate and modulation format. What is more, superchannel conversion should also support multi-band polarization division multiplexing (PDM) signal with wide tuning range to realize flexible bandwidth assignment. We propose a pump-switching four-wave-mixing scheme in highly nonlinear fiber to realize superchannel conversion and experimentally demonstrate it on a multi-band PDM orthogonal frequency division multiplexing (OFDM) superchannel. A flexible conversion region that covers from 1530 to 1565 nm is achieved by the proposed scheme.

Experimental demonstration of EON node supporting reconfigurable optical superchannel multicasting

Elastic optical networks (EON) based on optical superchannel enables higher spectral flexibility, in which the network nodes should provide multiple all-optical functionalities to manipulate bandwidth-variable data traffic. In this paper, we propose and demonstrate an EON node structure supporting reconfigurable optical superchannel multicasting. The node structure incorporates a shared multicasting module, which performs reconfigurable selection of target incoming/outgoing superchannels/replicas and leverages a group of nonlinear devices to satisfy multiple multicast requests. Moreover, an optical comb is utilized to efficiently provide and manage all pump resources for multicasting with potential cost reduction and phase noise inhibition. Based on the node structure, we experimentally demonstrate polarization division multiplexing (PDM) superchannel multicasting scenarios with different replica amount, input/output locations, and modulation formats. Less than 0.7 dB optical signal-to-noise ratio (OSNR) penalties are demonstrated in multiple multicasting scenarios.

Weighted Inter-frame Averaging-Based Channel Estimation for CO-OFDM System

We propose an efficient channel estimation method for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) based on weighted inter-frame averaging (WIFA), in which the channel estimation results of the adjacent frames are averaged to increase the estimation accuracy. The principle of the proposed WIFA method is theoretically analyzed, and the benefit is demonstrated by a polarization-division-multiplexed CO-OFDM transmission experiment. The channel magnitude and phase differences among adjacent frames are investigated. The effectiveness of WIFA method, combined with conventional least square method, time-domain averaging method, and intra-symbol frequency-domain averaging method, respectively, is demonstrated through 240-km standard single-mode fiber transmission with different launched power values. The experimental results show that the WIFA method can significantly enhance transmission performance.

Demonstration of all-optical MDM/WDM switching for short-reach networks

Mode division multiplexing (MDM) has been widely investigated in optical transmission systems and networks to improve network capacity. However, the MDM receiver is always expensive and complex because coherent detection and multiplex-input-and-multiplex-output (MIMO) digital signal processing (DSP) are required to demultiplex each spatial mode. In this paper, we investigate the application of MDM in short-reach scenarios such as datacenter networking. Two-dimensional MDM and wavelength division multiplexing node structure based on low modal-crosstalk few-mode fiber (FMF) and components is proposed, in which signal in each mode or wavelength can be independently switched. We experimentally demonstrate independent adding, dropping and switching functionalities with two linearly polarized modes and four wavelength channels over a total 11.8-km 2-mode low modal-crosstalk FMFs. The structure is simple without coherent detection or MIMO DSP. Only slight penalties of receiver sensitivity are observed for all switching operations. The influence of modal-crosstalk accumulation for cascaded switching nodes is also investigated.

Experimental Demonstration of Mode-Division-Multiplexing and Time-Division-Multiplexing Passive Optical Network

We propose and experimentally demonstrate for the first time mode-division-multiplexing and time-division-multiplexing passive optical network (MDM-TDM-PON). Both upstream and downstream transmissions with two individual linearly polarized (LP) spatial modes are investigated.

Experimental Demonstration of 1.2-Tb/s Optical PDM SCFDM Superchannel Multicasting by HNLF

Threefold 1.2-Tb/s optical polarization-division-multiplexing (PDM) single-carrier frequency-division-multiplexing (SCFDM) and orthogonal-frequency-division-multiplexing (OFDM) superchannel multicasting, utilizing multiple-pump four-wave mixing (FWM) by highly nonlinear fiber (HNLF), is proposed and experimentally demonstrated in this paper. The optical signal noise ratio (OSNR) penalties of the newly generated SCFDM and OFDM superchannels, at the bit error rate (BER) of 10-3, are 2.6 dB and 3.1 dB, respectively. Optimal pump power and signal power are also investigated for the two superchannels. The two superchannels have similar optimal pump power, whereas the SCFDM superchannel has higher optimal signal power due to the lower peak-to-average power ratio (PAPR).

Software-Defined Elastic Optical Network Node Supporting Spectrum Defragmentation

The elastic optical network (EON) benefits from improved spectrum utilization, but also faces new challenges in resource allocation. The spectrum continuity and contiguity constraints in routing and spectrum allocation can cause spectrum fragmentation, which would increase traffic blocking. In this paper, we present an EON node structure supporting spectrum defragmentation and a novel software-defined networking (SDN)-based control scheme to resolve the fragmentation problem. In the proposed node, bulk traffic can be spectrally separated and fit into multiple fragments. This way, fragmentationinduced traffic blocking can be mitigated intelligently. Moreover, the SDN control scheme features effective physical-layer abstraction, which is compatible with different defragmentation implementations. We experimentally demonstrate the software-defined EON node on a laboratorial test-bed. Four-wave-mixing-based spectrum multicasting is applied to implement defragmentation, and the corresponding operation procedure of the node Agent is presented. The captured controlling messages and measured signal performance confirm the effectiveness of the solution.