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

Our understanding of the cellular implementation of systems-level neural processes like action, thought and emotion has been limited by the availability of tools to interrogate specific classes of neural cells within intact, living brain tissue. Here we identify and develop an archaeal light-driven chloride pump (NpHR) from Natronomonas pharaonis for temporally precise optical inhibition of neural activity. NpHR allows either knockout of single action potentials, or sustained blockade of spiking. NpHR is compatible with ChR2, the previous optical excitation technology we have described, in that the two opposing probes operate at similar light powers but with well-separated action spectra. NpHR, like ChR2, functions in mammals without exogenous cofactors, and the two probes can be integrated with calcium imaging in mammalian brain tissue for bidirectional optical modulation and readout of neural activity. Likewise, NpHR and ChR2 can be targeted together to Caenorhabditis elegans muscle and cholinergic motor neurons to control locomotion bidirectionally. NpHR and ChR2 form a complete system for multimodal, high-speed, genetically targeted, all-optical interrogation of living neural circuits.

Multimodal fast optical interrogation of neural circuitry

* The only book describing applications of nonlinear fiber optics * Two new chapters on the latest developments: highly nonlinear fibers and quantum applications* Coverage of biomedical applications* Problems provided at the end of each chapterThe development of new highly nonlinear fibers - referred to as microstructured fibers, holey fibers and photonic crystal fibers - is the next generation technology for all-optical signal processing and biomedical applications. This new edition has been thoroughly updated to incorporate these key technology developments.The book presents sound coverage of the fundamentals of lightwave technology, along with material on pulse compression techniques and rare-earth-doped fiber amplifiers and lasers. The extensively revised chapters include information on fiber-optic communication systems and the ultrafast signal processing techniques that make use of nonlinear phenomena in optical fibers.New material focuses on the applications of highly nonlinear fibers in areas ranging from wavelength laser tuning and nonlinear spectroscopy to biomedical imaging and frequency metrology. Technologies such as quantum cryptography, quantum computing, and quantum communications are also covered in a new chapter.This book will be an ideal reference for: RD scientists involved with research on fiber amplifiers and lasers; graduate students and researchers working in the fields of optical communications and quantum information. * The only book on how to develop nonlinear fiber optic applications* Two new chapters on the latest developments; Highly Nonlinear Fibers and Quantum Applications* Coverage of biomedical applications

Applications of nonlinear fiber optics

Under strong laser radiation, a Dirac material, the topological insulator (TI) Bi2Te3, exhibits an optical transmittance increase as a result of saturable absorption. Based on an open-aperture Z-scan measurement at 1550 nm, we clearly show that the TI, Bi2Te3 under our investigation, is indeed a very-high-modulation-depth (up to 95%) saturable absorber. Furthermore, a TI based saturable absorber device was fabricated and used as a passive mode locker for ultrafast pulse formation at the telecommunication band. This contribution unambiguously shows that apart from its fantastic electronic property, a TI (Bi2Te3) may also possess attractive optoelectronic property for ultrafast photonics.

Ultra-short pulse generation by a topological insulator based saturable absorber

The emergence of novel two-dimensional (2D) monoelemental materials (Xenes) has shown remarkable potential for their applications in different fields of technology, as well as addressing new discoveries in fundamental science. Xenes (e.g., borophene, silicene, germanene, stanene, phosphorene, arsenene, antimonene, bismuthene, and tellurene) are of particular interest because they are the most chemically tractable materials for synthetic exploration. Owing to their excellent physical, chemical, electronic and optical properties, Xenes have been regarded as promising agents for biosensors, bioimaging, therapeutic delivery, and theranostics, as well as in several other new bio-applications. In this tutorial review, we summarize their general properties including the classification of Xenes according to their bulk properties. The synthetic and modification methods of Xenes are also presented. Furthermore, the representative Xene nanoplatforms for various biomedical applications are highlighted. Finally, research progress, challenges, and perspectives for the future development of Xenes in biomedicines are discussed.

Emerging two-dimensional monoelemental materials (Xenes) for biomedical applications

Countering the optical network ‘capacity crunch’ calls for a radical development in optical fibres that could simultaneously minimize nonlinearity penalties, chromatic dispersion and maximize signal launch power. Hollow-core fibres (HCF) can break the nonlinear Shannon limit of solid-core fibre and fulfil all above requirements, but its optical performance need to be significantly upgraded before they can be considered for high-capacity telecommunication systems. Here, we report a new HCF with conjoined-tubes in the cladding and a negative-curvature core shape. It exhibits a minimum transmission loss of 2 dB km−1 at 1512 nm and a <16 dB km−1 bandwidth spanning across the O, E, S, C, L telecom bands (1302–1637 nm). The debut of this conjoined-tube HCF, with combined merits of ultralow loss, broad bandwidth, low bending loss, high mode quality and simple structure heralds a new opportunity to fully unleash the potential of HCF in telecommunication applications. Countering the optical network ‘capacity crunch’ requires developments in optical fibres. Here, the authors report a hollow-core fibre with conjoined tubes in the cladding and a negative-curvature core shape. It exhibits a transmission loss of 2 dB/km at 1512 nm and less than 16 dB/km bandwidth in the 1302–1637 nm range.

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Hollow-core conjoined-tube negative-curvature fibre with ultralow loss.

We demonstrate stable 70 ns pulse generation from a Yb-doped fiber laser passively Q-switched by a graphene-based saturable absorber mirror in a short linear cavity. The maximum output power was 12 mW and the highest single pulse energy was 46 nJ. The repetition rate of the fiber laser can be widely tuned from 140 to 257 kHz along with the increase of the pump power. To the best of our knowledge, this is the first report for passively Q-switched sub-100-ns pulse operation of a graphene-based saturable absorber in a Yb-doped fiber laser.

Stable nanosecond pulse generation from a graphene-based passively Q-switched Yb-doped fiber laser.

We demonstrated the femtosecond erbium-doped all-fiber lasers mode-locked with graphene oxide, which can be conveniently obtained from natural graphite by simple oxidation and ultra-sonication process. With proper dispersion management in an all-fiber ring cavity, the laser directly generated 200 fs pulses at a repetition rate of 22.9 MHz and the average output power was 5.8 mW. With the variation of net cavity dispersion, output pulses with pulse width of 0.2~3 ps were obtained at a repetition rate of 22.9~0.93 MHz. These results are comparable with those of graphene saturable absorbers and the superiority of easy fabrication and hydrophilic property of graphene oxide will facilitate its potential applications for ultrafast photonics.

Graphene oxide mode-locked femtosecond erbium-doped fiber lasers

We report high power mid-infrared (mid-IR) supercontinuum (SC) generation in a single-mode ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fiber with up to 21.8 W average output power from 1.9 to beyond 3.8 μm pumped by amplified picosecond pulses from a single-mode thulium-doped fiber (TDF) master oscillator power amplifier (MOPA). The optical-optical conversion efficiency from the 793 nm pump laser of the last stage thulium-doped fiber amplifier (TDFA) to mid-IR SC output is 17%. It is, to the best of our knowledge, the highest average power mid-IR SC generation from a ZBLAN fiber to date.

High power mid-infrared supercontinuum generation in a single-mode ZBLAN fiber with up to 21.8 W average output power

we report three types of pulse generation in Yb-doped nonlinear polarization rotation mode-locked fiber lasers in all-normal-dispersion regime through simulation, including dissipative soliton, dissipative soliton resonance and noise-like pulse. We distinguish the different conditions of generating such different pulses by analyzing the transmission curve of saturable absorber, which plays a key role in pulse shaping.

Pu Wang

Papers

Hollow-core conjoined-tube negative-curvature fibre with ultralow loss.

Stable nanosecond pulse generation from a graphene-based passively Q-switched Yb-doped fiber laser.

Graphene oxide mode-locked femtosecond erbium-doped fiber lasers

High power mid-infrared supercontinuum generation in a single-mode ZBLAN fiber with up to 21.8 W average output power

Simulation of generation of dissipative soliton, dissipative soliton resonance and noise-like pulse in Yb-doped mode-locked fiber lasers