There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

/pdf/the-observation-of-gravitational-waves-from-a-binary-black-58srpupgg9.pdf

The Observation of Gravitational Waves from a Binary Black Hole Merger

Microwave photonics, which brings together the worlds of radiofrequency engineering and optoelectronics, has attracted great interest from both the research community and the commercial sector over the past 30 years and is set to have a bright future. The technology makes it possible to have functions in microwave systems that are complex or even not directly possible in the radiofrequency domain and also creates new opportunities for telecommunication networks. Here we introduce the technology to the photonics community and summarize recent research and important applications.

Microwave photonics combines two worlds

An overview of analog microwave photonics will be presented. The performance requirements for externally-modulated analog microwave photonic links will be reviewed with specific emphasis placed on modulator efficiency, laser noise, detected photocurrent, and link linearity.

http://ieeexplore.ieee.org/iel5/6387506/6403300/06403360.pdf

Microwave photonics

© 2002 IEEE. We have fabricated air-bridged modulators with bandwidths exceeding 10-GHz, the highest yet reported for InGaAsP/InGaAsP MQW AFPMs. Third-order intermodulation between the photodetected downlink signal and the modulated uplink signal is characterised for the first time.

Normal-incidence 1.56- mu m MQW asymmetric Fabry-Perot modulator (AFPM) for passive picocells

Using optical comb generation, SG-DBR laser comb line selection and uni-travelling-carrier photodiode, opto-electronic generation of 10 GHz to 110 GHz, -80 dBc/Hz SSB phase noise millimetre wave signals at powers up to 2 mW is demonstrated using no electrical amplification.

110 GHz opto-electronic frequency synthesiser using optical comb generator and uni-travelling-carrier photodiode

Radio over fibre systems can be used to provide coverage for cellular radio and other wireless services in areas where direct reception is ineffective, such as within large buildings or underground. This tutorial will present the technologies used for such systems.

Radio over fibre systems

Wireless bridges operating at THz frequencies have drawn a lot of attention in recent years. This application requires multiple optical local oscillators (LOs) throughout the link and, hence, the accumulated phase noise may impose a major challenge for its practical implementation. Of all the techniques to mitigate phase noise, single sideband (SSB) modulation is a very promising candidate due to its simple implementation. In this paper, we show, for the first time, the transmission of a 6 GBd SSB quadrature phase shift keying (QPSK) signal at 250 GHz and investigate the impact of laser phase noise on the quality of the THz signal. The performance of the system is investigated by digitally tuning the linewidth of the optical local oscillator up to 10 MHz. The results show no observable penalty associated with increasing linewidth, confirming the validity of SSB for applications where multiple domain conversions are required.

/pdf/experimental-investigation-of-phase-noise-tolerance-of-ssb-59j03r58rb.pdf

Experimental investigation of phase noise tolerance of SSB THz signals

Security and efficiency at airports has, in recent years, become a critical issue in the eyes of the general public, security services and politicians alike. This paper presents a high-resolution, indoor location technique, based on RF-over-fibre, that is ideally suited to the monitoring of a high density of people and/or objects in such a situation.

Alwyn J. Seeds

Papers

Normal-incidence 1.56- mu m MQW asymmetric Fabry-Perot modulator (AFPM) for passive picocells

110 GHz opto-electronic frequency synthesiser using optical comb generator and uni-travelling-carrier photodiode

Radio over fibre systems

Experimental investigation of phase noise tolerance of SSB THz signals

RF-ID tag location using RF-over-fibre techniques