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.

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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 review our recent developments, through several approaches, in the direct epitaxial growth of III-V quantum dot lasers on silicon substrates.

III-IV quantum dot lasers epitaxially grown on Si

A wireless data communications link operating at a carrier frequency of 200 GHz and a data rate of 1 Gb/s is demonstrated. Photonic carrier generation and modulation was employed at the transmitter, with the optical signal converted to millimeter waves using a uni-traveling carrier photodiode. Heterodyne detection was used to demodulate the signal, the first time, to our knowledge, that this approach has been used for Gb/s data on a carrier above 100 GHz. Baseband data was recovered by offline processing of a sampled version of the intermediate frequency signal captured by a real-time oscilloscope. A bit error ratio of 10−3, sufficient for reliable transmission with forward error correction, was obtained for a received power of approximately −52 dBm.

1 Gb/s wireless link at 200 GHz using heterodyne detection

The first theoretical analysis and experimental realisation of an optical frequency modulation link working at microwave frequencies is reported. Advantages over conventional optical intensity modulation links in terms of reduced effects of fibre non-linearity, facilitation of multi-channel operation and bandwidth/signal to noise ratio trade-offs are identified theoretically. Results from an experimental demonstrator are presented. >

https://ieeexplore.ieee.org/iel5/1100/7886/00335258.pdf

Optical frequency modulation link for microwave signal transmission

We report the first demontration of an indoor realtime location system, based on an optical fibre backbone, using an active RFID tag emitting 83.5 MHz wide linear FM chirp in the 2.4 GHz ISM band.

Demonstration of an indoor real-time location system with optical fibre backbone

The accuracy of high-resolution spectroscopy depends critically on the stability, frequency control, and traceability available from laser sources. In this work, we report exact tunable frequency synthesis and phase control of a terahertz laser. The terahertz laser is locked by a terahertz injection phase lock loop for the first time, with the terahertz signal generated by heterodyning selected lines from an all-fiber infrared frequency comb generator in an ultrafast photodetector. The comb line frequency separation is exactly determined by a Global Positioning System-locked microwave frequency synthesizer, providing traceability of the terahertz laser frequency to primary standards. The locking technique reduced the heterodyne linewidth of the terahertz laser to a measurement instrument-limited linewidth of <1Hz, robust against short- and long-term environmental fluctuations. The terahertz laser frequency can be tuned in increments determined only by the microwave synthesizer resolution, and the phase of the laser, relative to the reference, is independently and precisely controlled within a range ±0.3π. These findings are expected to enable applications in phase-resolved high-precision terahertz gas spectroscopy and radiometry.

Alwyn J. Seeds

Papers

III-IV quantum dot lasers epitaxially grown on Si

1 Gb/s wireless link at 200 GHz using heterodyne detection

Optical frequency modulation link for microwave signal transmission

Demonstration of an indoor real-time location system with optical fibre backbone

Exact frequency and phase control of a terahertz laser