Black-Hole Solutions with Scalar Hair in Einstein-Scalar-Gauss-Bonnet Theories

In the context of the Einstein-scalar-Gauss-Bonnet theory, with a general coupling function between the scalar field and the quadratic Gauss-Bonnet term, we investigate the existence of regular black-hole solutions with scalar hair. Based on a previous theoretical analysis, that studied the evasion of the old and novel no-hair theorems, we consider a variety of forms for the coupling function (exponential, even and odd polynomial, inverse polynomial, and logarithmic) that, in conjunction with the profile of the scalar field, satisfy a basic constraint. Our numerical analysis then always leads to families of regular, asymptotically-flat black-hole solutions with non-trivial scalar hair. The solution for the scalar field and the profile of the corresponding energy-momentum tensor, depending on the value of the coupling constant, may exhibit a non-monotonic behaviour, an unusual feature that highlights the limitations of the existing no-hair theorems. We also determine and study in detail the scalar charge, horizon area and entropy of our solutions.Comment: PdfLatex file, 29 Pages, 18 figures, the analysis was extended to study the scalar charge, horizon area and entropy of our solutions, comments added, typos corrected, version to appear in Physical Review

Semiconductor Optical Amplifier (SOA)–Based Amplification of Intensity-Modulated Optical Pulses — Deterministic Timing Jitter and Pulse Peak Power Equalization Analysis

During the last few years, large-scale efforts towards realizing high-photonic integration densities have put SOAs in the spotlight once again. Hence, the need to develop a complete framework for SOA-induced signal distortion to accurately evaluate a system’s performance has now become evident. To cope with this demand, we present a detailed theoretical and experimental investigation of the deterministic timing jitter and the pulse peak power equalization of SOA-amplified intensity-modulated optical pulses. The deterministic timing jitter model relies on the pulse mean arrival time estimation and its analytic formula reveals an approximate linear relationship between the deterministic timing jitter and the logarithmic values of intensity modulation when the SOA gain recovery time is faster than the pulse period. The theoretical analysis also arrives at an analytic expression for the intensity modulation reduction (IMR), which clearly elucidates the pulse peak power equalization mechanism of SOA. The IMR analysis shows that the output intensity modulation depth is linearly related to the respective input modulation depth of the optical pulses when the gain recovery time is faster than the pulse period. This novel theoretical platform provides a qualitative and quantitative insight into the SOA performance in case of intensity-modulated optical pulses

Quaternary TDM-PAM as upgrade path of access PON beyond 10Gb/s

A 20 Gb/s quaternary TDM-PAM passive optical network with chirped and non-linear optical transmitters is experimentally demonstrated. The migration from legacy TDM-PONs and the implications of using available 10 Gb/s components are analyzed. We show that a loss budget of 27.3 dB is compatible together with a packet power ratio of 10 dB between loud and soft optical network units. (c) 2012 Optical Society of Americ

PAM-4 VCSEL driver with selective falling-edge pre-emphasis

Data centre optical links are migrating to four-level pulse amplitude modulation (PAM-4) as a method to extend the data rate while covering longer distances. Vertical-cavity surface-emitting lasers (VCSELs) enable the integration of low-power transmitters, but their non-linear and bias-dependent behaviour makes conventional feed-forward equalisation less effective. This Letter presents a 0.13 mu m SiGe BiCMOS PAM-4 driver that boosts the falling-edge to the bottom level through a selective pre-emphasis technique. Experiments at 25 GBd (50 Gb/s) reveal that adding selective pre-emphasis to a 4-tap equalised current driving a 20.6 GHz 1.5 mu m VCSEL, relaxes the critical PAM-4 link budget requirements by >1 dB at the KP4 forward error correction threshold of 2.2 x 10(-4). The potential of PAM-4 VCSEL transmitters can be significantly enhanced by including selective pre-emphasis to the equalisation topology while requiring minimal overhead

Towards Brain Imaging using THz Technology

Abstract- We demonstrate recent advances towards the development of a novel 2-D THz imaging system for brain imaging applications both at macroscopic and at biomolecule level. A frequency synthesized THz source based on Difference Frequency Generation between optical wavelengths is presented, utilizing supercontinuum generation in a highly-nonlinear optical fiber with subsequent spectral carving by means of a fiber FabryPerot filter. Experimental results confirm the successful generation of THz radiation in the range of 0.2-2 THz, verifying the enhanced frequency tunability properties of the proposed system. Finally, the roadmap towards capturing functional brain information by exploiting THz imaging technologies is discussed, outlining the unique advantages offered by THz frequencies and their complementarity with existing brain imaging techniques

High-speed electronics for short-link communication

High-speed electronic integrated circuits are essential to the development of new fiber-optic communication systems. Close integration and co-design of photonic and electronic devices are becoming more and more a necessity to realize the best performance trade-offs. This paper presents our most recent results and a brief introduction to our research in recently started EU projects