Tomofumi Oyama

A Novel Quasi-Passive, Software-Defined, and Energy Efficient Optical Access Network for Adaptive Intra-PON Flow Transmission

In this paper, we propose, design, and demonstrate a novel Intra-PON Flow transmission with optical reroute using a Quasi-PAssive Reconfigurable (QPAR) node. The network can be reconfigured adaptively according to the monitored traffic status in a software-defined manner. Simulations show that PON with reroute architecture can achieve ~20% higher network capacity comparing to PON without reroute case with the same traffic waiting time or blocking probability requirement. PON with reroute consistently outperforms PON without reroute configuration with 20% larger throughput and 24% less power consumption with the Intra-PON traffic ratio of 0.3. In addition, adaptive Intra-wavelength assignment with a QPAR node can adapt to the subscription rate growth with time, and provide cost and power savings compared to PON without reroute and fixed PON with reroute architectures by approximately 20% and 10%. Moreover, adaptive Intra-PON architecture with a QPAR node can facilitate efficient multicast transmission for video or file backup among multiple serves located in different access networks, which can provide lower traffic waiting time, 14% power saving, and support roughly 30% higher traffic comparing to the fixed PON with reroute design with a multicast ratio of 0.5.

Digital nonlinear compensation for spectrally efficient superchannel transmission at 400Gbit/s and beyond

In order to push the nonlinear Shannon limit further within practical implementation constraints, we discuss various nonlinear compensation techniques for intra- and inter-subcarrier nonlinear effects. Experimental and numerical results prove the benefit is not just pre-FEC BER improvement.

Experimental investigation on nonlinear tolerance of subcarrier multiplexed signals with spectrum optimization

We numerically and experimentally investigate spectrum optimization techniques including adjustment of subcarrier symbol rate and subcarrier frequency spacing for multi-subcarrier modulation. Improvement of nonlinear tolerance is experimentally evaluated in Nyquist-FDM-DP-QPSK through 2,400 km transmission.

Nonlinear compensation technologies for future optical communication systems

Digital nonlinear compensation techniques have been thought to be keys to realize further spectrally efficient optical fiber communication systems. The most critical issue of the digital nonlinear compensation algorithms has been their computational complexity, or gate count of digital signal processing circuit. Among several approaches, digital nonlinear compensation algorithms based on perturbation analysis are attractive in terms of the hardware efficiency because the algorithms can compensate the accumulated nonlinear noise over all transmission spans with only one stage. In this paper, we discuss three approaches to sophisticate the perturbation nonlinear compensation. First, we illustrate a perturbation-based post-equalization method to improve the robustness to transceiver device imperfections. We next propose and numerically evaluate a symbol degeneration method to extend the perturbation nonlinear compensation methods to higher-order QAM without increasing the computational complexity. Finally, we discuss a sub-band processing of perturbation nonlinear compensation for further computational complexity reduction. By combining the perturbation method with Nyquist frequency division multiplexing, the computational complexity of perturbation calculation is reduced by a factor of more than 10 for 3000-km single-channel transmission of 128 Gbit/s dualpolarization QPSK with only 0.1 dB performance degradation.

Launch power optimization co-operated with digital nonlinear compensator for elastic optical network

We propose an individual channel launch power control method co-operated with nonlinear compensation in digital signal processing. Its effectiveness is evaluated in a network case study with various distances and modulation formats by numerical simulation.

Transmission performance of 3-bit/symbol modulation formats in dispersion-unmanaged link

We numerically investigate the transmission performance of 3-bit/symbol modulation formats in dispersion-unmanaged transmission systems. We find that probabilistic-shaped 64QAM has higher achievable rate than the other formats in back-to-back condition as well as after transmission.

In-phase/quadrature skew measurement for optical Mach-Zehnder modulator

We propose an accurate and robust in-phase/quadrature (IQ) skew measurement method for optical Mach-Zehnder IQ modulator based on image spectrum analysis. Numerical simulation and experiment results demonstrate 0.7ps measurement accuracy. The robustness to bias deviations and finite extinction ratios were also investigated.

Impact of fiber nonlinearity on duobinary-QPSK in super-Nyquist WDM transmission

We numerically confirm that duobinary-pulse format suffers larger nonlinear impairment than NRZ and Nyquist-pulse formats. Nonlinearity-induced penalty, however, is found to be constant against the channel spacing in super-Nyquist WDM transmission. Also, we evaluate the benefit of digital nonlinear compensation.