Jan Conradi

Reduction of pulse-to-pulse interaction using alternative RZ formats in 40-Gb/s systems

We show that pulse-to-pulse interaction at 40 Gb/s can be reduced by alternating the optical phase of adjacent bits by using either a modified-duobinary return-to-zero (RZ) modulation format or RZ with alternating phase. Also, the generation of ghost pulses can be greatly suppressed using the modified-duobinary and duobinary RZ format.

Hybrid modulator structures for subcarrier and harmonic subcarrier optical single sideband

Optical single-sideband (OSSB) modulation is useful for mitigation of fiber chromatic dispersion effects on intensity modulated-direct detection (IMDD) optical links. We show that hybrid modulator structures based on compatible single-sideband (CSSB) theory serve as general purpose OSSB modulators. We further show that both harmonically upconverted optical double-sideband (ODSB) and harmonically upconverted OSSB signals, generated through the nonlinear characteristics of optical modulators, both provide significant dispersion improvements.

Effect of Mach-Zehnder modulator DC extinction ratio on residual chirp-induced dispersion in 10-Gb/s binary and AM-PSK duobinary lightwave systems

It is shown through numerical simulation that residual frequency chirping in lithium niobate external modulators, which accompanies devices with a finite-optical extinction ratio, always degrades the performance of lightwave systems that use optical AM-PSK duobinary signaling. This is unlike binary systems which will exhibit either an improvement or degradation, depending on the polarity of residual chirp.

Bandwidth reduced codes to overcome dispersion and electronic bottlenecks in high-speed systems

Summary form only given. This paper will review progress in the area of transmission formats as well as consider other approaches, some of which are well known for their application in radio-based transmission (e.g., M-ary signalling, poly-binary signalling, QAM) by which both the bandwidth of various electrical components and the transmission bandwidth of the signal can be reduced to provide optical fiber network dispersion and bandwidth relief.

Comments on "On the relationship between chromatic dispersion and transmitter filter response in duobinary optical communication systems" [and Reply]

For original paper see ibid., vol. 9, p 1005-7 (1997). A new interpretation has been recently proposed in the spectral domain to explain the good performance obtained by certain AM-PSK duobinary signals. However, we show in this comment that many counter-examples to this interpretation suggested by a previous time-domain theory can be found.

Advances in regenerative receiver design

Until recently the design of digital optical receivers revolved around the characteristics of the photodetector, structure of the preamplifier, and characteristics of the discrete components from which the preamplifier and regenerative sections of the receiver were made. The circuit designs for these sections had in many cases evolved from designs originally conceived for copper cable and digital radio systems. Today’s commercially available high-speed digital fiber-optic transmission systems operate up to the Gb/s range. This has required the development of improved electrooptical components and more highly integrated circuits that make up the functional blocks of a regenerative repeater. These functional blocks include automatic gain control (AGC) amplifiers, timing recovery circuits, and regenerator circuits.