Daniel Fritzsche

Aperture averaging: theory and measurements

Atmospheric laser communications using direct-detection systems do suffer from severe degradation caused by scintillation. Because the atmospheric cut-off frequency can be as low as 100 Hz, temporal averaging is not applicable in high-speed communications. The simplest way of reducing fading is to increase the receiver size and to take advantage of aperture averaging. Spatial and temporal variations of the received intensity have to be investigated in order to predict the efficiency of aperture averaging. This paper reviews briefly the theory of spatial averaging that characterizes the direct-detected optical power. For comparison purposes, results of measurements are presented. These measurements consist of recorded pupil intensity patterns for a scenario with known turbulence profile. Statistics derived from measurement data are compared with theoretical second-order statistics.

37.5 km urban field trial of OFDMA-PON using colorless ONUs with dynamic bandwidth allocation and TCM [invited]

The orthogonal frequency division multiple access (OFDMA)-based passive optical network (PON) is a potential candidate to meet the flexibility requirements for next-generation optical access networks. We propose an OFDMA-based PON with a transmission employing intensity modulation/direct detection in the downstream and a remodulation of a remotely seeded carrier provided by the optical line terminal with coherent detection in the upstream, which enables cost-effective colorless optical network units (ONUs). Furthermore, an OFDMA-PON field trial using the proposed scheme over 37.5 km feeder fiber is demonstrated. A power budget supporting 32 ONUs with dynamic bandwidth allocation and trellis coded modulation (TCM) is reported.

Field trial investigation of 16-states MLSE equalizer for simultaneous compensation of CD, PMD and SPM

We investigate 16-states MLSE equalization over buried fibers having CD up to 4480 ps/nm, PMD up to 92 ps and launch powers up to 12 dBm. Results show a superior performance for joint compensation of all distortion effects.

Trials of a Coherent UDWDM PON Over Field-Deployed Fiber: Real-Time LTE Backhauling, Legacy and 100G Coexistence

Transmission capabilities of a coherent real-time UDWDM PON over deployed fibers in two testbeds (Berlin and Darmstadt, Germany) are demonstrated. Extensive coexistence tests including LTE backhauling and GPON, RF-Video, 100G and OTDR were performed. A silicon photonics-integrated CMOS laser was used for parts of the trial.

Measuring the Link Distribution of PMD: Field Trial Using an RS-POTDR

A new POTDR measurement technique is used to investigate the spatial distribution of PMD in deployed fibers. Results help to identify high-PMD fiber sections that need to be replaced to enable 40Gbit/s transmission and beyond.

Analysis of Crosstalk in Mixed 43 Gb/s RZ-DQPSK and 10.7 Gb/s DWDM Systems at 50 GHz Channel Spacing

In DWDM field experiments over 1047 km of standard fiber and in simulations we analyze the impact of crosstalk on a 43 Gb/s RZ-DQPSK channel both by 10.7 Gb/s OOK and 43 Gb/s RZ-DQPSK neighbors at 50 GHz channel spacing.

Quasi-Analytic Synthesis of Nonrecursive Optical Delay Line Filters for Reliable Compensation of Dispersion Effects

A quasi-analytic synthesis algorithm is presented to determine the coefficients of nonrecursive optical delay line filters with approximately constant or linear dispersion. These filters can be used to compensate the dispersion and dispersion slope effects in high-speed optical transmission systems. The synthesis of the coefficients is based on a rigorous analysis of the impact of transfer function on the filters dispersion behavior. The advantages of this algorithm are that filters of arbitrary order have similar dispersion shapes and that the dispersion values of the filters can be adjusted by controlling a single parameter instead of optimizing all the filter coefficients independently. The realized dispersion shapes are reproducible, and no iterative algorithms are needed for the calculation. The abilities of the synthesized filters are proven in system simulations at 40 Gb/s. Therefore, filters of different orders were investigated in the static case (i.e., with a fixed dispersion) and the dynamic case, where the dispersion of the filter is adapted to the requirements of the simulated optical transmission channel. In addition, the influences of the filters free spectral range and of the utilized bandwidth inside a filter period were investigated. To the best of our knowledge, both the analytical synthesis approach and the investigation of the optimal filter configuration are presented for the first time

Characterisation of the PMD Distribution along Optical Fibres and Improvement of the Backbone Fibre Infrastructure by a POTDR

Fibre links in optical networks generally comprise several relatively short fibre segments which have been spliced together in cables. These fibre segments or “sections” are assembled with optical connectors and have a typical length of some tens of km. The important characteristic parameters of the fibre sections are attenuation, chromatic dispersion (CD) and polarisation mode dispersion (PMD). However, the PMD of the optical fibres can hamper the upgrade of optical backbone networks towards higher data rates of 40 Gbit/s and beyond. The PMD distribution along a buried fibre link is not constant and can also significantly vary between the concatenated fibres of the same optical cable. In the absence of such spatial information, the whole cable with higher PMD-values may have to be replaced in order to transmit 40 Gbit/s transparently over long distances. But investigations have shown that frequently localized pieces within a section are the major contributors to the overall high PMD value of the whole fibre, rendering the link unsuitable for higher data rates. A new random-scrambling polarization optical time domain reflectometry (POTDR) measurement technique is used to investigate the spatial distribution of the cumulative PMD in deployed fibres. Results help to identify high-PMD fibre pieces or sections which need to be replaced to enable 40 Gbit/s transmission and beyond, rather than substitution of a whole fibre link. Techno-economical investigations show the high economic potential of this method leading to significant reduction of expenses for infrastructure improvements. These improvements will enable network operators to transmit high data rates without limitation given by PMD.

Field trials of a coherent UDWDM PON: Real-time LTE backhauling, legacy and 100G coexistence

Transmission capabilities of a coherent UDWDM PON over deployed fiber are demonstrated, including LTE backhauling and GPON, RF-Video, 100G and OTDR coexistence. A Silicon Photonics integrated CMOS laser was used for parts of the trial.

Field trial of a novel FTTH/PON monitoring technique based on unique wavelength-selective mirror combinations

Our novel PON monitoring concept succeeded in a field trial. Subscribers located at equal distances were individually identified across a PON with at least 30.7 dB one-way loss and utilization of low cost components.