Electronic dispersion precompensation of direct-detected NRZ using analog filtering

We demonstrate (in real-time) electrical dispersion compensation in direct detection links using analog transmit side filtering techniques. By this means, we extend the fiber reach using a low complexity solution while avoiding digital preprocessing and digital-to-analog converters (DACs) which are commonly used nowadays. Modulation is done using an IQ MachZehnder modulator (MZM) which allows straightforward compensation of the complex impulse response caused by chromatic dispersion in the fiber. A SiGe BiCMOS 5-tap analog complex finite impulse response (FIR) filter chip and/or a delay between both driving signals of the MZMs is proposed for the filter implementation. Several link experiments are conducted in C-band where transmission up to 60 km of standard single-mode fiber (SSMF) of direct detected 28Gb/s NRZ/OOK is demonstrated. The presented technique can be used in applications where low power consumption is critical

Polygyny and strong genetic structuring within an isolated population of the wood ant Formica rufa

Social structuring of populations within some Formica species exhibits considerable variation going from monodomous and monogynous populations to polydomous, polygynous populations. The wood ant species Formica rufa appears to be mainly monodomous and monogynous throughout most of its distribution area in central and northern Europe. Only occasionally it was mentioned that F. rufa can have both polygynous and monogynous colonies in the same geographical region. We studied an isolated polydomous F. rufa population in a deciduous mixed forest in the north-west of Belgium. The level of poly-domy within the colonies varied from monodomous to 11 nests per colony. Our genetic analysis of eight variable microsatellites suggest an oligo- to polygynous structure for at least the major part of the sampled nests. Relatedness amongst nest mate workers varies considerable within the population and colonies but confirms in general a polygynous structure. Additionally high genetic diversity (e.g. up to 8 out of 11 alleles per nest for the most variable locus) and high within nest genetic variance (93%) indicate that multiple queens contribute to the gene pool of workers of the same nest. Moreover significant genetic structuring among colonies indicates that gene flow between colonies is restricted and that exchange of workers between colonies is very limited. Finally we explain how possible factors as budding and the absence of Serviformica can explain the differences in genetic structure within this polygynous F. rufa population

DSP-free and real-time NRZ transmission of 50Gb/s over 15km SSMF and 64Gb/s back-to-back with a 1.3um VCSEL

We demonstrate and analyze 50 Gb/s non-return-to-zero (NRZ) transmission over 15 km of standard single-mode fiber (SSMF), 60-Gb/s NRZ transmission over 5 km of SSMF and up to 64-Gb/s NRZ back-to-back using a directly modulated short-cavity long-wavelength single-mode vertical-cavity surface-emitting laser (VCSEL) emitting at 1326 nm. Owing to an analog 6-tap transmit feedforward equalizer, the link can operate without digital signal processing. In all three cases, real-time bit error ratio measurements below the 7% overhead hard-decision forward error correction threshold are demonstrated when transmitting a pseudorandom bit sequence with a period of 2(7) - 1 bits. In addition, we analyze the interplay between the residual fiber chromatic dispersion at the operating wavelength of the VCSEL and the chirp due to direct modulation. These results demonstrate how O-band, short-cavity long-wavelength single-mode VCSELs can be used in intradata center networks, as well as in interdata center networks at reaches below 15 km

Real-time 28 Gb/s NRZ over 80 km SSMF in C-band using analog electronic precompensation

We demonstrate real-time C-band transmission of direct detected 28Gb/s NRZ/OOK over 80km SSMF using a Dual-Drive MZM and custom-designed SiGe BiCMOS 5-tap analog FIR filters to compensate chromatic dispersion without digital signal processing

Electro-optic frequency response shaping using embedded FIR filters in slow-wave modulators

A novel method is presented to embed finite-impulse-response filters in slow-wave Mach-Zehnder modulators. This allows to adjust the electro-optic frequency response to the designer's needs. The filter is embedded by adding optical delay lines and optical crossings between phase shifter segments. The position of the delay lines and crossing in the modulator and the delay line length determine the final response. In this work, we provide a full analysis and modeling approach of the proposed technique and apply it to a silicon photonic modulator. However, the technique is generally applicable to slow-wave modulators and thus not limited to a silicon photonics platform. The modeling is verified using measurements on the manufactured devices. A shaped modulator is used in C-band transmission experiments with 56 Gb/s NRZ data over 3 km fiber to counteract chromatic dispersion and show the advantage over a standard modulator

Demonstration of 80 Gbps NRZ-OOK electro-absorption modulation of InP-on-Si DFB laser diodes

High-speed electro-absorption modulation of a heterogeneously integrated InP-on-Si DFB laser diode is used for the transmission of an 80 Gbps NRZ-OOK signal over 2 km of NZ-DSF link below the hard-decision forward-error-correction threshold. (C) 2019 The Author(s

Demonstration of 80 Gbps NRZ-OOK electro-absorption modulation of InP-on-Si DFB laser diodes

High-speed electro-absorption modulation of a heterogeneously integrated InP-on-Si DFB laser diode is used for the transmission of an 80 Gbps NRZ-OOK signal over 2 km of NZ-DSF link below the hard-decision forward-error-correction threshold. (C) 2019 The Author(s

Electro-optic frequency response shaping in high speed Mach-Zehnder modulators

We demonstrate a simple technique to shape the electro-optic frequency response of high-speed TW-MZMs. C-band transmission of 56Gb/s NRZ over 3km SSMF shows 5dB power-penalty improvement at KP4-FEC between a standard and shaped MZM design