M. Dreschmann

Error Vector Magnitude as a Performance Measure for Advanced Modulation Formats

We examine the relation between optical signal-to-noise ratio (OSNR), error vector magnitude (EVM), and bit-error ratio (BER). Theoretical results and numerical simulations are compared to measured values of OSNR, EVM, and BER. We conclude that the EVM is an appropriate metric for optical channels limited by additive white Gaussian noise. Results are supported by experiments with six modulation formats at symbol rates of 20 and 25 GBd generated by a software-defined transmitter.

Real-time Nyquist pulse generation beyond 100 Gbit/s and its relation to OFDM.

Nyquist sinc-pulse shaping provides spectral efficiencies close to the theoretical limit. In this paper we discuss the analogy to optical orthogonal frequency division multiplexing and compare both techniques with respect to spectral efficiency and peak to average power ratio. We then show that using appropriate algorithms, Nyquist pulse shaped modulation formats can be encoded on a single wavelength at speeds beyond 100 Gbit/s in real-time. Finally we discuss the proper reception of Nyquist pulses.

Real-Time Software-Defined Multiformat Transmitter Generating 64QAM at 28 GBd

We demonstrate a software-defined real-time optical multiformat transmitter. Here, eight different modulation formats are shown. Data rate and modulation formats are defined through software accessible look-up tables enabling format switching in the nanosecond regime without changing the transmitter hardware. No data are lost during the switching process. SP-64 quadrature amplitude modulation at 28 Gbd has been generated and tested. This allows us to generate a 336-Gb/s real-time pseudorandom bit sequence in a dual polarization setup.

Single-laser 32.5 Tbit/s Nyquist WDM transmission

Single-laser 32.5 Tbit/s 16QAM Nyquist-WDM transmission with 325 carriers over 227 km at a net spectral efficiency of 6.4 bit/s/Hz is reported.

Single source optical OFDM transmitter and optical FFT receiver demonstrated at line rates of 5.4 and 10.8 Tbit/s

OFDM data with line rates of 5.4 Tbit/s or 10.8 Tbit/s are generated and decoded with a new real-time all-optical FFT receiver. Each of 75 carriers of a comb source is encoded with 18 GBd QPSK or 16-QAM.

Real-time OFDM transmitter beyond 100 Gbit/s

Real-time OFDM transmitters breaking the 100 Gbit/s barrier require high-performance, usually FPGA-based digital signal processing. Especially the Fourier transform as a key operation of any OFDM system must be optimized with respect to performance and chip area utilization. Here, we demonstrate an alternative to the widely adopted fast Fourier transform algorithm. Based on an extensive yet optimized use of pre-set look-up tables, our FPGA implementation supports fast reconfigurable channel equalization and switching times in the nanosecond range without re-loading any code. We demonstrate the potential of the concept by realizing the first real-time single polarization OFDM transmitter generating a 101.5 Gbit/s data stream by modulating 58 subcarriers with 16QAM.

Implementation of a Virtual Internal Configuration Access Port (JCAP) for Enabling Partial Self-Reconfiguration on Xilinx Spartan III FPGAs

The exploitation of dynamic and partial hardware reconfiguration on FPGAs is currently being investigated in various research projects, dealing with systems for space applications to automotive and masurement applications. Despite challenges such as a complicated design flow, dynamic reconfigurable systems offer advantages in terms of flexibility and performance. Unfortunately only few kinds of commercial architectures support dynamic and partial reconfiuration, which has lead to Virtex II / IV being main target architectures for this kind of systems. Additionally, the Xilinx Spartan III architecture is dynamically and partially reconfigurable with some limitations, one of them being the lack of an internal configuration port. The Virtex II / IV and V architectures all include the ICAP port, which allows a system to reconfigure itself during run-time without additional external components. Until now, this was not possible on the Spartan III architecture. This paper presents the implementation of a virtual internal configuration port for the Spartan III family of FPGAs. The configuration port was implemented for a hardware reconfigurable measurement system, which is implemented on a Spartan III FPGA due to its cost-and power optimized characteristics.

Optically powered fiber networks

Optically powered networks are demonstrated. Heterogeneous subscribers having widely varying needs with respect to power and band-width can be effectively controlled and optically supplied by a central of-fice. The success of the scheme relies both on power-efficient innovative hardware and on a novel low-energy medium access control protocol. We demonstrate a sensor network with subscribers consuming less than 1 microW average power, and an optically powered high-speed video link transmitting data at a bitrate of 100 Mbit/s.

Quality metrics for optical signals: Eye diagram, Q-factor, OSNR, EVM and BER

Measuring the quality of optical signals is one of the most important tasks in optical communications. A variety of metrics are available, namely the general shape of the eye diagram, the optical signal-to-noise power ratio (OSNR), the Q-factor as a measure of the eye opening, the error vector magnitude (EVM) that is especially suited for quadrature amplitude modulation (QAM) formats, and the bit error ratio (BER). While the BER is the most conclusive quality determinant, it is sometimes difficult to quantify, especially for simulations and off-line processing. We compare various metrics analytically, by simulation, and through experiments. We further discuss BER estimates derived from OSNR, Q-factor and EVM data and compare them to measurements employing six modulation formats at symbol rates of 20 GBd and 25 GBd, which were generated by a software-defined transmitter. We conclude that for optical channels with additive Gaussian noise the EVM metric is a reliable quality measure. For nondata-aided reception, BER below 0.01 can be estimated from measured EVM.

An Optically Powered Video Camera Link

An optically powered camera sensor link is demonstrated. Power and data are transmitted over a 62.5-?m multimode glass fiber. Uncompressed video with 640 × 480 pixels resolution is streamed continuously at 100 Mb/s as soon as the fiber is illuminated with sufficient optical power. No energy has to be stored at the sensor location in batteries with limited capacities and lifetimes. Inexpensive fiber optics and low-power state-of-the-art electronics are used to make >100 mW available at sites which have no direct access to an electrical network. There is a complete electrical isolation between the remote camera unit and a base station.