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

III–V semiconductors monolithically grown on Si substrates are expected to be an ideal solution to integrate highly efficient light-emitting devices on a Si platform. However, the lattice mismatch between III–V and Si generates a high density of threading dislocations (TDs) at the interface between III–V and Si. Some of these TD will propagate into the III–V active region and lead to device degradation. By introducing defect filter layers (DFLs), the density of TDs propagating into the III–V layers can be significantly reduced. In this paper, we present an investigation on the development of InGaAs/GaAs strained-layer superlattices as DFLs for 1.3-μm InAs/GaAs quantum-dot lasers monolithically grown on a Si substrate. We compare two broad-area InAs/GaAs quantum-dot lasers with non-optimized and optimized InGaAs/GaAs DFLs. The laser device with optimal DFLs has a lower room-temperature threshold current density of 99 A/cm2 and higher maximum operation temperature of 88 °C, compared with 174 A/cm2 and 68 °C for the reference laser.

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Optimizations of Defect Filter Layers for 1.3-μm InAs/GaAs Quantum-Dot Lasers Monolithically Grown on Si Substrates

An Optical Phase Lock Loop (OPLL) is a feedback control system that allows the phase stabilization of a laser to a reference laser with absolute but adjustable frequency offset Such phase and frequency locked optical oscillators are of great interest for sensing, spectroscopy, and optical communication applications, where coherent detection offers advantages of higher sensitivity and spectral efficiency than can be achieved with direct detection As explained in this paper, the fundamental difficulty in realising an OPLL is related to the limitations on loop bandwidth and propagation delay as a function of laser linewidth In particular, the relatively wide linewidth of semiconductor lasers requires short delay, which can only be achieved through shortening of the feedback path, which is greatly facilitated through photonic integration This paper reviews the advances in the development of semiconductor laser-based OPLLs and describes how improvements in performance have been enabled by improvements in photonic integration technology We also describe the first OPLL created using foundry fabricated photonic integrated circuits and off-the-shelf electronic components Stable locking has been achieved for offset frequencies between 4 and 12 GHz with a heterodyne phase noise below –100 dBc/Hz at 10 kHz offset This is the highest performance yet reported for a monolithically integrated OPLL and demonstrates the attractiveness of the foundry fabrication approach

/pdf/integrated-semiconductor-laser-optical-phase-lock-loops-dt1ye3d31j.pdf

Integrated Semiconductor Laser Optical Phase Lock Loops

A 02 A/W responsivity waveguide-uni-travelling carrier photodiode with a -3 dB electrical frequency 
response > 108 GHz is demonstrated Up to -5 dBm electrical power at 110 GHz, and 28 mA 
photocurrent (DC excitation) were detected The photodiode was also integrated with an antenna to 
permit a record breaking emission of up to 148 μW at 457 GHz and 25 μW at 914 GHz

/pdf/a-high-responsivity-broadband-waveguide-uni-travelling-1yac6r8bf9.pdf

A high responsivity, broadband waveguide uni-travelling carrier photodiode

In a coherent optical transmission system an input optical signal is amplified by being frequency down converted to an intermediate frequency, for example by means of a photodiode (1) and a reference optical local oscillator signal, and the photodiode output current is amplified in a GaAs FET wideband amplifier (6) and inserted on an optical carrier signal comprised by the reference signal by means, for example, of an integrated optical single sideband modulator (up converter) (7). By use of the same optical local oscillator to drive both the photodiode down converter and the integrated optic single sideband up converter, input/output coherence is ensured. The optical local oscillator may be comprised by a GaAlAs laser (3) stabilized to an "atomic" standard (4,5). Channel dropping/insertion may be carried out at the intermediate frequency, for example following the amplifier (6).

Optical transmission system

We present a review of recent developments in THz coherent systems based on photonic local oscillators. We show that such techniques can enable the creation of highly coherent, thus highly sensitive, systems for frequencies ranging from 100 GHz to 5 THz, within an energy efficient integrated platform. We suggest that such systems could enable the THz spectrum to realize its full applications potential. To demonstrate how photonics-enabled THz systems can be realized, we review the performance of key components, show recent demonstrations of integrated platforms, and give examples of applications.

Alwyn J. Seeds

Papers

Optimizations of Defect Filter Layers for 1.3-μm InAs/GaAs Quantum-Dot Lasers Monolithically Grown on Si Substrates

Integrated Semiconductor Laser Optical Phase Lock Loops

A high responsivity, broadband waveguide uni-travelling carrier photodiode

Optical transmission system

Coherent terahertz photonics.