Peter Gysel

Statistical properties of Rayleigh backscattering in single-mode fibers

An analytical model that takes into account the influence of the laser linewidth on Rayleigh backscattering is given. For an unmodulated source the power spectral density is found to be identical to the delayed self-homodyne spectrum of the laser. The backscattered signal was measured for different laser linewidths, and the results are compared with the theory. The effects of Rayleigh backscattering noise on fiber gyroscopes and bidirectional optical systems are discussed. >

Crosstalk penalities due to coherent Rayleigh noise in bidirectional optical communication systems

The statistical properties, i.e. power spectral densities and probability density functions, of the noise due to Rayleigh backscattered light and due to interference of backscattered and reflected light are derived from the autocorrelation function of the optical source field. The crosstalk penalties due to Rayleigh backscattering in single- and double-source bidirectional systems are calculated. It is shown that it is possible to realize a bidirectional system with commercially available connectors in which Rayleigh backscattering is the dominant crosstalk contribution. The measured crosstalk penalties and bit-error probabilities in a double-source bidirectional system confirm the theoretical results. >

Spectral properties of Rayleigh backscattered light from single-mode fibers caused by a modulated probe signal

The statistical properties of Rayleigh backscattering from single-mode fibers are investigated, taking into account the modulation and the coherence of the source light. The autocorrelation function and the power spectral density of the backscattered field and intensity are derived. To describe the noise due to Rayleigh backscattering in bidirectional systems, the spectrum of the interference of backscattered light with reflected source light is also calculated. The measurements confirm the theoretical results. It is shown that, if no optical isolator is used and the laser diode is exposed to Rayleigh backscattering, the interaction between laser and fiber depends strongly on the modulation of the light. >

Statistical properties of single-mode fiber Rayleigh backscattered intensity and resulting detector current

An analytical model for Rayleigh backscattering from a single-mode fiber which takes into account the coherence properties of the optical source, the modulation of the source field and the polarization state changes during propagation along the fiber is presented. It allows a full description of the statistical properties of the backscattered signals. Expressions for the power spectral densities and for the probability density functions of Rayleigh backscattered intensity and of the corresponding detector current are derived from the autocorrelation function of the optical source field. The measurements are shown to correspond to the theoretical results. >

Timing recovery in high bit-rate transmission systems over copper pairs

This letter proposes a timing recovery scheme for transmission systems with baud-rate sampling allowing the use of an all digital phase-locked loop. The impact of the numerically controlled oscillator on the attainable signal-to-noise ratio and jitter under conditions of the European Telecommunications Standardization Institute (ETSI) HDSL standard is discussed.

Power penalties due to multiple Rayleigh backscattering in coherent transmission systems using in-line optical amplifiers

The power penalties due to double Rayleigh backscattering are calculated for coherent lightwave systems with optical in-line amplifiers. It is shown that coherent systems are less sensitive to Rayleigh noise than high-speed direct-detection systems. For PSK heterodyne systems, the maximum gain of in-line amplifiers that can be achieved without optical isolation is limited to about 25 dB.<<ETX>>

A new method for high-resolution measurement of semiconductor laser linewidth in coherent optical systems

A method for the observation of laser linewidth during operation in a coherent optical system is presented. The measurements agree well with the theoretical calculations and show that the power density spectrum of the backscattered intensity from a single-mode fiber corresponds to the laser spectrum with twice the source linewidth, shifted to baseband.<<ETX>>

Spectral behavior of directly modulated laser diodes exposed to Rayleigh backscatter from a single-mode fiber

The spectral behavior of a laser diode exposed to Rayleigh backscattering (RB) from a single-mode fiber is investigated for arbitrary laser-fiber coupling efficiency, fiber length, and coherence time of the light of the free-running source. It is found that resonance effects in the spectral behavior of laser diodes exposed to RB from a single-mode fiber occur only for coupling efficiencies above a critical value eta /sub c/. This threshold is very low for unmodulated light but it is substantially increased when the light is modulated. A simple mathematical relation is given showing the dependence of the threshold on the fiber length and on the coherence time of the light.<<ETX>>

EoD designer: a computation tool for energy optimization of data centers

Total energy consumption in a data center is the sum of various components. We consider six main subsystems: Voltage transformer, uninterruptable power supply, IT equipment, computer room air handler, chiller and cooling tower. In this project a mathematical model for all six components was derived. Based on this model, a software tool was developed. It allows to simulate different variants of a data center and to minimize the total energy consumption by optimizing equipment and operating parameters. Thus potential energy savings can be evaluated. Finally the resulting reduction of operation expenses can directly be derived from the energy savings.

Secure Communications for Ancillary Services

Networking of distributed energy resources for ancillary services like control pooling introduces new security challenges. For economic reasons public IP networks are often used for the transport, resulting in sophisticated security requirements. Legacy devices as well as compliance with corporate network security policies must be taken into account. In this paper, we compare different communication technologies and discuss the problems of integrating legacy devices. We describe an approach that uses standardized technologies to provide secure communications for ancillary services, while at the same time requiring minimal configuration by administrators of corporate networks.