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

We report on the experimental realization of a single comb generator based on phase modulation in an amplified fiber loop, which offers exact referencing to an arbitrary supplied reference frequency and a tunable comb-line spacing

Terahertz, zero frequency error, tunable optical comb generator for DWDM applications

Experiments are described in which laser illumination of the active device has reduced the FM noise output by up to 5 dB for a GaAs impatt oscillator and 2 dB for a Si impatt oscillator. A qualitative explanation of the observed results is given, and the effect of laser amplitude noise on the maximum noise reduction obtainable is shown.

Reduction of FM noise in impatt oscillators by optical illumination

Phase locking to an orthogonal-polarisation pilot by an optical injection phase lock loop is demonstrated for the first time, enabling homodyne demodulation of 10Gb/s BPSK with performance close to the LO-ASE limit (OSNR=6dB/0.1nm; BER=10−3).

Homodyne coherent receiver with phase locking to orthogonal-polarisation pilot carrier by optical injection phase lock loop

This paper presents a review of the recent development and research work on InP devices and their associated systems to generate and detect signal beyond 1 THz. The potential of the technology and the remaining challenges are also discussed. The paper will present recent results on laser sources that could be used as the basis of the THz sources as well as a set of potential THz emitters such as the UTC photodiode which has already permitted up to 25 muW to be emitted at 1 THz.

/pdf/photonically-enabled-communication-systems-beyond-1000-ghz-17w4rhypbs.pdf

Photonically enabled communication systems beyond 1000 GHz

In this paper we present a review of our work on photonic synthesis of high spectral purity THz signals. This work includes novel developments on optical frequency comb generation (integrated, 2THz span, 25 GHz spacing), frequency locking of semiconductor lasers (1kHz channel stability, 10 ns switching time) and high speed photodetectors integrated with antennas (3dB bandwidth > 108 GHz, 0.2 A/W responsivity , 148 muW output power at 457 GHz)

Alwyn J. Seeds

Papers

Terahertz, zero frequency error, tunable optical comb generator for DWDM applications

Reduction of FM noise in impatt oscillators by optical illumination

Homodyne coherent receiver with phase locking to orthogonal-polarisation pilot carrier by optical injection phase lock loop

Photonically enabled communication systems beyond 1000 GHz

Photonic synthesis of THz signals