The remarkable performance of lead halide perovskites in solar cells can be attributed to the long carrier lifetimes and low non-radiative recombination rates, the same physical properties that are ideal for semiconductor lasers. Here, we show room-temperature and wavelength-tunable lasing from single-crystal lead halide perovskite nanowires with very low lasing thresholds (220 nJ cm(-2)) and high quality factors (Q ∼ 3,600). The lasing threshold corresponds to a charge carrier density as low as 1.5 × 10(16) cm(-3). Kinetic analysis based on time-resolved fluorescence reveals little charge carrier trapping in these single-crystal nanowires and gives estimated lasing quantum yields approaching 100%. Such lasing performance, coupled with the facile solution growth of single-crystal nanowires and the broad stoichiometry-dependent tunability of emission colour, makes lead halide perovskites ideal materials for the development of nanophotonics, in parallel with the rapid development in photovoltaics from the same materials.

Lead halide perovskite nanowire lasers with low lasing thresholds and high quality factors

The arbitrary control of electromagnetic waves is a key aim of photonic research. Although, for example, the control of freely propagating waves (PWs) and surface waves (SWs) has separately become possible using transformation optics and metamaterials, a bridge linking both propagation types has not yet been found. Such a device has particular relevance given the many schemes of controlling electromagnetic waves at surfaces and interfaces, leading to trapped rainbows, lensing, beam bending, deflection, and even anomalous reflection/refraction. Here, we demonstrate theoretically and experimentally that a specific gradient-index meta-surface can convert a PW to a SW with nearly 100% efficiency. Distinct from conventional devices such as prism or grating couplers, the momentum mismatch between PW and SW is compensated by the reflection-phase gradient of the meta-surface, and a nearly perfect PW-SW conversion can happen for any incidence angle larger than a critical value. Experiments in the microwave region, including both far-field and near-field characterizations, are in excellent agreement with full-wave simulations. Our findings may pave the way for many applications, including high-efficiency surface plasmon couplers, anti-reflection surfaces, light absorbers, and so on.

http://www.physics.fudan.edu.cn/tps/people/lzhou/papers/84-NM%2011,426.pdf

Gradient-index meta-surfaces as a bridge linking propagating waves and surface waves

Reliable, efficient electrically pumped silicon-based lasers would enable full integration of photonic and electronic circuits, but have previously only been realized by wafer bonding. Here, we demonstrate continuous-wave InAs/GaAs quantum dot lasers directly grown on silicon substrates with a low threshold current density of 62.5 A cm–2, a room-temperature output power exceeding 105 mW and operation up to 120 °C. Over 3,100 h of continuous-wave operating data have been collected, giving an extrapolated mean time to failure of over 100,158 h. The realization of high-performance quantum dot lasers on silicon is due to the achievement of a low density of threading dislocations on the order of 105 cm−2 in the III–V epilayers by combining a nucleation layer and dislocation filter layers with in situ thermal annealing. These results are a major advance towards reliable and cost-effective silicon-based photonic–electronic integration.

/pdf/electrically-pumped-continuous-wave-iii-v-quantum-dot-lasers-rmg1qnqnyt.pdf

Electrically pumped continuous-wave III–V quantum dot lasers on silicon

A laser frequency comb is a broad spectrum composed of equidistant narrow lines. Initially invented for frequency metrology, such combs enable new approaches to spectroscopy over broad spectral bandwidths, of particular relevance to molecules. The performance of existing spectrometers — such as crossed dispersers employing, for example, virtual imaging phase array etalons, or Michelson-based Fourier transform interferometers — can be dramatically enhanced with optical frequency combs. A new class of instruments, such as dual-comb spectrometers without moving parts, enables fast and accurate measurements over broad spectral ranges. The direct self-calibration of the frequency scale of the spectra within the accuracy of an atomic clock and the negligible contribution of the instrumental line-shape will enable determinations of all spectral parameters with high accuracy for stringent comparisons with theories in atomic and molecular physics. Chip-scale frequency comb spectrometers promise integrated devices for real-time sensing in analytical chemistry and biomedicine. This Review gives a summary of the developments in the emerging and rapidly advancing field of atomic and molecular broadband spectroscopy with frequency combs. Frequency comb spectroscopy is a recent field of research that has blossomed in the past five years. This Review discusses developments in the emerging and rapidly advancing field of atomic and molecular broadband spectroscopy with frequency combs.

Frequency comb spectroscopy

The conversion from spatial propagating waves to surface plasmon polaritons (SPPs) has been well studied, and shown to be very efficient by using gradient-index metasurfaces. However, feeding energies into and extracting signals from functional plasmonic devices or circuits through transmission lines require the efficient conversion between SPPs and guided waves, which has not been reported, to the best of our knowledge. In this paper, a smooth bridge between the conventional coplanar waveguide (CPW) with 50 Ω impedance and plasmonic waveguide (e.g., an ultrathin corrugated metallic strip) has been proposed in the microwave frequency, which converts the guided waves to spoof SPPs with high efficiency in broadband. A matching transition has been proposed and designed, which is constructed by gradient corrugations and flaring ground, to match both the momentum and impedance of CPW and the plasmonic waveguide. Simulated and measured results on the transmission coefficients and near-filed distributions show excellent transmission efficiency from CPW to a plasmonic waveguide to CPW in a wide frequency band. The high-efficiency and broadband conversion between SPPs and guided waves opens up a new avenue for advanced conventional plasmonic integrated functional devices and circuits.

Broadband and high-efficiency conversion from guided waves to spoof surface plasmon polaritons

Fundamental and technical noise sources in III-V-on-silicon mode-locked lasers are investigated and minimized. Their frequency stability is optimized to make them suited to applications such as dual-comb spectroscopy or dual-comb LIDAR.

III-V-on-Silicon 1-GHz Mode-Locked Lasers Towards Frequency-Comb Applications

Deeply-etched SiO2 waveguide is fabricated and characterized. The fabrication process is easier than the conventional buried SiO2 waveguide. The fabricated waveguide exhibits good performances, such as low propagation loss, broad band.

Fabrication and characterization of deeply-etched SiO2 waveguides

Silicon Photonics more and more is considered as a competitive platform for building complex photonic ICs, applicable in various fields, but the lack of a practical on-chip integrated compact, high-yield and electricallydriven laser source remains a major bottleneck. Due to its indirect bandgap, silicon itself is a poor light emitter. Therefore, new materials such as Germanium, III-V compounds and rare earth doped nanocrystals are being investigated and laser operation from hybrid III-V lasers 1, monolithic Germanium lasers 2 and monolithic IIIV nanowire lasers 3 has been demonstrated. While III-V provides generally better performance, realizing monolithically integrated in-plane lasers that can be integrated with other waveguide circuits remains extremely challenging. In this paper, using a selective area growth technique originally developed for realizing nextgeneration ultrafast electronic transistors, we demonstrate a room temperature operating monolithic integrated inplain InP DBR laser grown on a standard 300mm (001)-silicon substrate. Conventional approaches for growing III-V compounds on silicon require a micrometers-thick buffer to cope with the large lattice mismatch and thermal expansion coefficient difference between silicon and III-Vs. In our work, InP waveguides were selectively grown inside narrow trenches defined by a Shallow-Trench-Isolation (STI) method 4 and V-groove etching. The transmission electron microscope (TEM) image shown in Fig. 1a shows that the InP-material is of high crystalline quality except for the 20nm buffer layer located at the InP-Si interface. Following the epitaxy, we defined first order Bragg gratings (165 nm period, 60 nm etching depth, and 50% Duty Cycle) on top of the diamond-shape InP-waveguides using electron beam lithography (EBL) and plasma etching. Next, the silicon substrate beneath the InP was removed using a selective dry etch process to prevent leakage of the optical field (Fig. 1b). For characterization, 7 ns pump pulses from a 532 nm Nd:YAG nanosecond pulsed laser are delivered to the sample in a uniform rectangular area covering a single cavity. After being scattered by the second order grating located at one end of the DBR laser, the laser emissions is collected by a 50x, 0.65 numerical aperture (NA) objective and measured through a 1⁄4 m monochromator. The single mode spectrum in Fig. 1c and the S-shaped light-light curve convincingly show the devices exhibit indeed laser operation. Efficiencies of more than 5% and high reproducibility of these results over multiple devices and multiple wafers has been demonstrated. The top-down integration process, high yield and high controllability together with the in-plane laser configuration, thin buffer layer and selective area process make this device highly promising as a source for future photonic ICs.

https://biblio.ugent.be/publication/7196707/file/7196726.pdf

Monolithic integrated InP distributed bragg reflector (DBR) lasers on (001) silicon

Silicon photonics holds the promise of converging electronics and photonics. The key component, a low-cost high-performance laser, is still missing however within this platform. Although novel solutions have been proposed to increase the light emission directly from silicon (or Ge), compared with their III-V counterparts, these solutions are still in their infancy. Recently, the epitaxial growth of III-Vs on silicon regained a wide interest. III-V nanowire growth has been widely investigated. However, most of the III-V nanowire lasers on silicon require a complex cleaving and transfer process, which make these devices not suitable for dense integration. In addition, the large cavity dimensions along the nanowire axis (several microns) hinder dense integration. Here, we present the first room-temperature operation of an ultra-short InP nanowire laser that is epitaxially grown on an exactly [001] oriented silicon substrate. The sub-micron sized laser cavity largely enhances the interaction of the lasing mode with the gain medium, and a large spontaneous emission factor has been obtained.

/pdf/an-ultra-short-inp-nanowire-laser-monolithic-integrated-on-2pskfg7j5q.pdf

An ultra-short InP nanowire laser monolithic integrated on (001) silicon substrate

RF frequency down-conversion is of key importance in communication satellites. While the available high-end microwave electronic mixers and circuitry are bulky, heavy, expensive and sensitive to electromagnetic interference (EMI), microwave photonics emerges to be a promising and low-cost alternative.

/pdf/ka-to-l-band-frequency-down-conversion-using-a-micro-3kbpdikq84.pdf

Zhechao Wang

Papers

III-V-on-Silicon 1-GHz Mode-Locked Lasers Towards Frequency-Comb Applications

Fabrication and characterization of deeply-etched SiO2 waveguides

Monolithic integrated InP distributed bragg reflector (DBR) lasers on (001) silicon

An ultra-short InP nanowire laser monolithic integrated on (001) silicon substrate

Ka-to-l-band frequency down-conversion using a micro-photonic III-V-on-silicon mode-locked laser and Mach-Zehnder modulator