Philip M. Watts

Electronic dispersion compensation by signal predistortion using digital Processing and a dual-drive Mach-Zehnder Modulator

We propose and investigate a novel electronic dispersion compensation technique, in which signal precompensation is achieved using a dual-drive Mach-Zehnder modulator, driven by adaptive nonlinear digital filters. The results demonstrate effective compensation of over 13600 ps/nm, equivalent to 800 km of standard single-mode fiber, at 10 Gb/s.

Performance of single-mode fiber links using electronic feed-forward and decision feedback equalizers

The performance limits of optically amplified links using electronic feed-forward equalizers and decision feedback equalizers are experimentally and numerically investigated. A 10-Gb/s transmission over 140 km of standard single-mode fiber with 22.7-dB optical signal-to-noise ratio sensitivity at 10/sup -9/ bit-error rate is demonstrated, allowing single-span operation with 4-dB margin.

Generation of optical OFDM signals using 21.4 GS/s real time digital signal processing

We demonstrate a field programmable gate array (FPGA) based optical orthogonal frequency division multiplexing (OFDM) transmitter implementing real time digital signal processing at a sample rate of 21.4 GS/s. The QPSK-OFDM signal is generated using an 8 bit, 128 point inverse fast Fourier transform (IFFT) core, performing one transform per clock cycle at a clock speed of 167.2 MHz and can be deployed with either a direct-detection or a coherent receiver. The hardware design and the main digital signal processing functions are described, and we show that the main performance limitation is due to the low (4-bit) resolution of the digital-to-analog converter (DAC) and the 8-bit resolution of the IFFT core used. We analyze the back-to-back performance of the transmitter generating an 8.36 Gb/s optical single sideband (SSB) OFDM signal using digital up-conversion, suitable for direct-detection. Additionally, we use the device to transmit 8.36 Gb/s SSB OFDM signals over 200 km of uncompensated standard single mode fiber achieving an overall BER<10(-3).

Motivating future interconnects: a differential measurement analysis of PCI latency

Local interconnect architectures are at a cusp in which advances in throughput have come at the expense of power and latency. Moreover, physical limits imposed on dissipation and packaging mean that further advances will require a new approach to interconnect design. Although latency in networks has been the focus of the High-Performance Computing architect and of concern across the computer community, we illustrate how an evolution in the common PCI interconnect architecture has worsened latency by a factor of between 3 and 25 over earlier incarnations.

Electronic dispersion compensation by signal predistortion

We review recent work on electronic dispersion precompensation, and present the results of simulations investigating the compensation of chromatic dispersion and intra-channel fibre nonlinearity in 10 Gb/s systems using a programmable look-up table and linear finite impulse response filters

An FPGA-Based Optical Transmitter Design Using Real-Time DSP for Advanced Signal Formats and Electronic Predistortion

Advances in the performance and flexibility of future optical networks will be brought about through the use of high-speed digital signal processing (DSP) for the generation of advanced optical signal formats and the compensation of transmission impairments. The use of field-programmable gate arrays (FPGAs) to implement experimental transceivers employing novel DSP techniques is attractive, as they are of low cost and are reprogrammable. In this paper, the design of a reprogrammable FPGA-based 10-Gb/s optical transmitter using real-time DSP is described and assessed through simulation. Using a single Xilinx Virtex-4 FPGA, digital filtering based on lookup tables with up to 12-bit addressing could be implemented. We also present, for the first time, a simulation technique using industry-standard digital design simulation tools (mentor graphics modelsim) in combination with a simulation of analog microwave components, optical transmission, and bit-error-rate estimation to assess the performance of the full transmission system. This simulation technique is used to demonstrate 10-Gb/s transmission over 550 km of standard single-mode fiber (SSMF) using electronic predistortion (EPD) and the generation of optical single sideband signals. A proof-of-principle experiment is described in which a single 10.7-Gb/s Mach-Zehnder modulator drive signal with 4-bit amplitude resolution and 1-sample/bit temporal resolution was generated. This was used as the input to Monte Carlo simulations to assess EPD transmission performance over SSMF links of up to 640 km.

10.7 Gb/s electronic predistortion transmitter using commercial FPGAs and D/A converters implementing real-time DSP for chromatic dispersion and SPM compensation

We present an experimental demonstration of simultaneous chromatic dispersion and self-phase modulation compensation at 10.7 Gb/s using real-time electronic digital signal processing. This was achieved using a pre-distorting transmitter based on commercially available field programmable gate arrays and 21.4 GS/s, 6-bit resolution digital-to-analog converters. The digital signal processing employed look-up tables stored in RAM. This resulted in the achievement of a BER of 10(-6) at an OSNR of 16 dB after transmission over a 450 km link of uncompensated standard single mode fiber with + 4 dBm launch power.

Reconfigurable Network Systems and Software-Defined Networking

Modern high-speed networks have evolved from relatively static networks to highly adaptive networks facilitating dynamic reconfiguration. This evolution has influenced all levels of network design and management, introducing increased programmability and configuration flexibility. This influence has extended from the lowest level of physical hardware interfaces to the highest level of network management by software. A key representative of this evolution is the emergence of software-defined networking (SDN). In this paper, we review the current state of the art in reconfigurable network systems, covering hardware reconfiguration, SDN, and the interplay between them. We take a top-down approach, starting with a tutorial on software-defined networks. We then continue to discuss programming languages as the linking element between different levels of software and hardware in the network. We review electronic switching systems, highlighting programmability and reconfiguration aspects, and describe the trends in reconfigurable network elements. Finally, we describe the state of the art in the integration of photonic transceiver and switching elements with electronic technologies, and consider the implications for SDN and reconfigurable network systems.

Real-Time Digital Signal Processing for the Generation of Optical Orthogonal Frequency-Division-Multiplexed Signals

In this paper, we investigate the design of a field-programmable-gate-array (FPGA) based optical orthogonal frequency-division multiplexing (OFDM) transmitter implementing real-time digital signal processing at 21.4 GSample/s. The transmitter was utilized to generate 8.34 Gb/s QPSK-OFDM signals for direct detection. We study the impact of the finite resolutions of the inverse fast Fourier transform cores and the digital-to-analog converters on the system performance. Furthermore, we describe a transmission experiment over 800 and 1600 km of uncompensated standard fiber with negligible optical SNR penalties and bit error rate <; 10-3.

10.7 Gb/s transmission over 1200 km of standard single-mode fiber by electronic predistortion using FPGA-based real-time digital signal processing

A 10.7 Gb/s electronic predistortion transmitter using FPGA-based real time 2 Samples/bit digital signal processing based on 55-tap finite impulse response filters is described. Transmission over 1200 km of standard single-mode fiber without optical dispersion compensation is demonstrated with an OSNR penalty of only 2.5 dB, compared with back-to- back operation.