Juhao Li

Survivable Virtual Network Design and Embedding to Survive a Facility Node Failure

As virtualization is becoming a promising way to support various emerging application, provisioning survivability to requested virtual networks (VN) in a resource efficient way is important. In this paper, we investigate the survivable VN embedding (SVNE) problem from a new perspective. First, we consider the failure dependent protection (FDP) in which each primary facility node would have a different backup facility node, as opposed to the Failure Independent Protection (FIP) which has been studied before, in order to provide the same degree of protection against a single node failure with less substrate resources. Secondly, we enhance the VN with additional computing and communication resources and design the Enhanced VN (or EVN) before embedding it to the substrate in order to further reduce the amount of substrate resources needed to survive a single facility node failure. The work is the first that combines the FDP with EVN design (FD-EVN) to explore a resource efficient solution to the SVNE problem. After presenting a binary quadratic programming (BQP) formulation of the FD-EVN design problem and a Mixed Integer Linear Programming (MILP) formulation of the EVN embedding (EVNE) problem, we propose two heuristic algorithms for FD-EVN design, as well as an EVNE algorithm that explores primary and backup substrate resources sharing. Simulations are conducted to evaluate the performance of the solutions to the BQP/MILP formulation when possible, and the heuristics. The proposed FD-EVN approach has shown to be resource efficient and in particular, outperform other approaches in terms of request acceptance ratio and embedding cost, although as a tradeoff, requiring more service migration after failures.

Comparison of DSB and SSB transmission for OFDM-PON [Invited]

We investigate the restriction of double-sideband (DSB) transmission for a next-generation orthogonal frequency division multiplexing passive optical network (OFDM-PON). First, the power fading induced by chromatic dispersion is well described for DSB OFDM signals. Then we show by simulation and experiment that the power fading effect can be made negligible for an access network by employment of high-order modulation and a low radio frequency carrier and allocating subcarriers dynamically according to the power penalty. 20-Gbit/s DSB OFDM transmission over 26.7-km and 100-km standard single-mode fiber is experimentally demonstrated. Compared with single-sideband transmission, the DSB transmitter has a simpler structure, which reduces the access cost or complexity.

Experimental demonstration of 1.08 Tb/s PDM CO-SCFDM transmission over 3170 km SSMF.

Coherent optical single-carrier frequency-division-multiplexing (CO-SCFDM) is a promising candidate for future high-speed long-haul optical fiber transmission system. Being a modified form of coherent optical orthogonal frequency division multiplexing (CO-OFDM), the CO-SCFDM can inherit the advantages such as low computation complexity and high flexibility, while suffers less nonlinear impairment due to much lower peak-to-average power ratio (PAPR). In this paper, we experimentally demonstrate 1.08 Tb/s polarization-division multiplexing (PDM) CO-SCFDM transmission over 3170 km standard single-mode fiber (SSMF) with Erbium-doped fiber amplifier (EDFA) only. The back-to-back and nonlinear transmission performances for CO-OFDM and CO-SCFDM are also compared.

Controllable shrinking and shaping of silicon nitride nanopores under electron irradiation

Modification of silicon nitride nanopores under electron beam (e-beam) irradiation was investigated using a scanning electron microscope (SEM). Under e-beam irradiation, all pores with diameters ranging from 40to200nm undergo shrinkage, and the shrinkage rate increases with the rate of energy deposition. By using the selected-area scanning tool in the SEM, the silicon nitride nanopores can be selectively reshaped based on localized e-beam irradiation, with a characteristic dimension smaller than 10nm. A selected-area shaping technique was proposed to controllably shrink and shape the nanopores to a special structure.

DSP-Based Evolution From Conventional TDM-PON to TDM-OFDM-PON

Recently, digital signal processing (DSP) methods have been extensively studied and various DSP-based schemes have been proposed for next-generation passive optical network (PON). In this paper, we combine the time-division-multiplexing (TDM) architecture with advanced DSP methods to achieve high spectrum-efficiency colorless transmission. Orthogonal frequency division multiplexing (OFDM), as the original form of various DSP methods with frequency-domain equalization (FDE), is chosen for both upstream and downstream transmissions. In the TDM-PON based on OFDM (TDM-OFDM-PON) architecture, OFDM symbols are transmitted in different time slots instead of on-off-key (OOK) bits in conventional TDM-PON. This architecture can be extended for single-carrier with FDE easily. Due to the same TDMA scheme, it can achieve maximum compatibility with current TDM-PON. A DSP-based evolution scheme from conventional TDM-PON to TDM-OFDM-PON is proposed and experimentally demonstrated by upgrading the optical line terminal (OLT) to support both OOK and OFDM signals, which can maintain the current optical distribution network (ODN) and minimize the impact for the existing service and equipment.

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.

Experimental Demonstration of 120-Gb/s PDM CO-SCFDE Transmission Over 317-km SSMF

Single-carrier transmission with frequency-domain equalization (SCFDE) is promising for a 100-Gb/s or even higher optical fiber transmission system by combining the advantages of lower peak-to-average power ratio and less computation complexity. In this letter, we present the first polarization-division-multiplexed coherent optical SCFDE transmission experiment. By utilizing three optical carriers, we demonstrate a 120-Gb/s coherent optical system over 317-km standard single-mode fiber without inline chromatic dispersion compensation.

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.

Demonstration of Bidirectional PON Based on Mode Division Multiplexing

Recently, mode division multiplexing (MDM) has been introduced into optical transmission systems and networks for capacity enhancement. In this letter, we propose a bidirectional passive optical network (PON) architecture based on MDM. The bidirectional optical distribution network (ODN) of the MDM-PON consists of few-mode fiber, passive mode multiplexer/demultiplexer and few-mode circulators (FMCs), all of which are characterized by low modal-crosstalk. Signals in different modes are able to be transmitted and received independently for both downstream and upstream transmission. We experimentally demonstrate the bidirectional MDM-PON transmission over 10-km 2-mode optical fiber. 10-Gb/s on-off-keying (OOK) signals can be independently transmitted and directly detected without coherent receiver and multi-input-multiple-output (MIMO) processing. Moreover, nonlinear transmission impairments are experimentally investigated.

Cascaded Mode-Division-Multiplexing and Time-Division-Multiplexing Passive Optical Network Based on Low Mode-Crosstalk FMF and Mode MUX/DEMUX

We propose cascaded mode-division-multiplexing and time-division-multiplexing passive optical network (MDM-TDM-PON) based on low mode-crosstalk few-mode fiber (FMF) and all-fiber mode multiplexer/demultiplexer (MUX/DEMUX), in which optical network units communicate with the optical line terminal utilizing different time slots and specific optical linearly polarized spatial modes. An MDM optical distribution network (ODN) is cascaded with multiple conventional TDM ODNs to effectively extend a larger scale of current commercial PON systems based on TDM. The upgrade from TDM-PON to the cascaded MDM-TDM-PON is simple and cost-effective. No multiple-input-multiple-output (MIMO) digital signal processing is required to eliminate the mode crosstalk. The all-fiber mode MUX/DEMUXs are composed of mode selective couplers, which simultaneously multiplex or demultiplex multiple modes. We experimentally demonstrate MDM-PON transmission over 10 and 55 km two-mode FMFs and cascaded MDM-TDM-PON transmission over a 10-km two-mode FMF and a 10-km standard single-mode fiber with 10-Gb/s optical on-off keying (OOK) signal and direct detection.