Andreas Leven

Coherent Receivers for Practical Optical Communication Systems

Coherent receivers that utilize electrical signal processing techniques have attracted increased attention over the last couple of years. In this paper, we will discuss some practical aspects of these receivers and present some recent results.

Impact of Nonideal Phase Reference on Soft Decoding of Differentially Encoded Modulation

The performance of coded modulation schemes based on the concatenation of a forward-error correction (FEC) code and differentially encoded quadrature amplitude modulations (QAMs) in the presence of Wiener phase noise is considered. Log-likelihood ratios, required to perform soft decoding, are first derived for the case in which the phase of the received carrier is assumed to be perfectly known, and then used to obtain the performance for nonideal reference of phase. Simulation results of the post-FEC bit-error rate are presented for a near-Shannon limit low-density parity check code with an overhead of 20%. The performance loss, compared to ideal coherent demodulation, is evaluated for two different linewidths of the phase noise in case of quadrature-phase shift keying and 16-QAM transmission.

A 24GS/s 5-b ADC with closed-loop THA in 0.18μm SiGe BiCMOS

A 5-b flash ADC with a closed-loop THA is implemented in 0.18-mum SiGe BiCMOS. A global shunt feedback THA and a current-weighted comparator allow the ADC to achieve wide resolution bandwidth of 6.5 GHz and high sampling rate up to 24 GS/s. The ADC shows an SNDR of 28 dB and an SFDR of 36 dB with a 1 GHz input sampled at 16 GS/s. It consumes 3.3 W from 3.6/3-V supplies and occupies 8.68 mm2 silicon area.

Compact high-gain lumped differential 40 Gb/s driver amplifiers in production 0.15 /spl mu/m PHEMT technology

High-performance and very compact 40 Gb/s driver amplifiers were realized in mature 0.15 /spl mu/m depletion PHEMT technology. The 3-stage lumped differential drivers feature a large differential 40 Gb/s output swing of up to 7.5 V/sub pp/, RMS jitter of less than 800 fs, rise and fall times of less than 10 ps and more than 27 dB gain. The small size (1.4/spl times/1.7 mm) and ability to have DC coupled in- and output, enable compact and cost-effective optical 40 Gb/s long-haul transmitters with system grade NRZ and RZ eye diagrams.

High Gain-Bandwidth InP waveguide Phototransistor

We present a high speed phototransistor with integrated waveguide based on our InP double hetrojunction bipolar transistor (DHBT) process technology. We measured an optical-gain cutoff frequency F,* of 447 GHz with an internal optical gain of over gePt=30 at a base current of It.=650 pA using devices with emitter dimensions of A=0.7 x 4 pm2.

An Interferometer-based Optoelectronic Arbitrary Waveform Generator

A novel optoelectronic arbitrary waveform generator using high-speed optical phase modulators in an interferometric configuration is proposed. In our approach, optical and electrical techniques are combined to achieve the best overall performance. This technique has the potential to generate high resolution (8 bits and higher) waveforms with bandwidth up to 10 GHz and beyond. Using commercially available components we demonstrate a 12.5 GSample/s digital-to-analog converter with 5.5 effective bits up to Nyquist.