This work proves the feasibility of a novel concept of differential absorption lidar based on the Scheimpflug principle. The range‐resolved atmospheric backscattering signal of a laser beam is retrieved by employing a tilted linear sensor with a Newtonian telescope, satisfying the Scheimpflug condition. Infinite focus depth is achieved despite employing a large optical aperture. The concept is demonstrated by measuring the range‐resolved atmospheric oxygen concentration with a tunable continuous‐wave narrow‐band laser diode emitting around 761 nm over a path of one kilometer during night time. Laser power requirements for daytime operation are also investigated and validated with single‐band atmospheric aerosol measurements by employing a broad‐band 3.2‐W laser diode. The results presented in this work show the potential of employing the continuous‐wave differential absorption lidar (CW‐DIAL) technique for remote profiling of atmospheric gases in daytime if high‐power narrow‐band continuous‐wave light sources were to be employed.
Narrow‐linewidth lasers are key elements in optical metrology and spectroscopy. Spectral purity of these lasers determines accuracy of the measurements and quality of collected data. Solid state and fiber lasers are stabilized to relatively large and complex external optical cavities or narrow atomic and molecular transitions to improve their spectral purity. While this stabilization technique is rather generic, its complexity increases tremendously moving to longer wavelenghts, to the infrared (IR) range. Inherent increase of losses of optical materials at longer wavelengths hinders realization of compact, room temperature, high finesse IR cavities suitable for laser stabilization. In this paper, we report on demonstration of quantum cascade lasers stabilized to high‐Q crystalline mid‐IR microcavities. The lasers operating at room temperature in the 4.3‐4.6 μm region have a linewidth approaching 10 kHz and are promising for on‐chip mid‐IR and IR spectrometers.
The recent progress in integrated quantum optics has set the stage for the development of an integrated platform for quantum information processing with photons, with potential applications in quantum simulation. Among the different material platforms being investigated, direct‐bandgap semiconductors and particularly gallium arsenide (GaAs) offer the widest range of functionalities, including single‐ and entangled‐photon generation by radiative recombination, low‐loss routing, electro‐optic modulation and single‐photon detection. This paper reviews the recent progress in the development of the key building blocks for GaAs quantum photonics and the perspectives for their full integration in a fully‐functional and densely integrated quantum photonic circuit.
The generation of sub‐optical‐cycle, carrier–envelope phase‐stable light pulses is one of the frontiers of ultrafast optics. The two key ingredients for sub‐cycle pulse generation are bandwidths substantially exceeding one octave and accurate control of the spectral phase. These requirements are very challenging to satisfy with a single laser beam, and thus intense research activity is currently devoted to the coherent synthesis of pulses generated by separate sources. In this review we discuss the conceptual schemes and experimental tools that can be employed for the generation, amplification, control, and combination of separate light pulses. The main techniques for the spectrotemporal characterization of the synthesized fields are also described. We discuss recent implementations of coherent waveform synthesis: from the first demonstration of a single‐cycle optical pulse by the addition of two pulse trains derived from a fiber laser, to the coherent combination of the outputs from optical parametric chirped‐pulse amplifiers.
In recent years laser light has been used to control the motion of electron waves. Electrons can now be diffracted by standing waves of light. Laser light in the vicinity of nanostructures is used to affect free electrons, for example, femto‐second and atto‐second laser‐induced electrons are emitted from nanotips delivering coherent fast electron sources. Optical control of dispersion of the emitted electron waves, and optically controlled femto‐second switches for ultrafast electron detection are proposed. The first steps towards electron accelerators and matter optics on‐a‐chip are now being taken. New research fields are driven by these new technologies. One example is the optical generation of electron pulses on‐demand and quantum degenerate pulses. Another is the emerging development of interaction free electron microscopy. This review will focus on the field of free electron quantum optics with technologies at the interplay of lasers, electron matter waves, and nanostructures. Questions that motivate their development will also be addressed.
The terahertz (THz) radiation from InGaN/GaN dot‐in‐a‐wire nanostructures has been investigated. A submicrowatt THz signal is generated with just ten vertically stacked InGaN quantum dots (QDs) in each GaN nanowire. Based on the experimental results and analysis, a single quantum wire is expected to generate an output power as high as 10 pW, corresponding to 1 pW per dot. These structures are among the most efficient three‐dimensional quantum‐confined nanostructures for the THz emission. By applying a reverse bias along the wires in a light‐emitting device (LED) consisting of such nanostructures, the THz output power is increased more than fourfold. Based on THz and photoluminescence (PL) experiments, the mechanism for the THz emission is attributed to dipole radiation induced by internal electric fields and enhanced by external fields.
Recently, the coexistence of a parity‐time (PT) symmetric laser and absorber has gained tremendous research attention. While PT‐symmetric lasers have been observed in microring resonators, the experimental demonstration of a PT‐symmetric stripe laser is still absent. Here, we experimentally study a PT‐symmetric laser absorber in a stripe waveguide. Using the concept of PT‐symmetry to exploit the light amplification and absorption, PT‐symmetric laser absorbers have been successfully obtained. In contrast to the single‐mode PT‐symmetric lasers, the PT‐symmetric stripe lasers have been experimentally confirmed by comparing the relative wavelength positions and mode spacing under different pumping conditions. When the waveguide is half‐pumped, the mode spacing is doubled and the lasing wavelengths shift to the center of every two initial lasing modes. All these observations are consistent with the theoretical predictions and well confirm the PT‐symmetry breaking.
A scheme for active temporal‐to‐spatial demultiplexing of single photons generated by a solid‐state source is introduced. The scheme scales quasi‐polynomially with photon number, providing a viable technological path for routing n photons in the one temporal stream from a single emitter to n different spatial modes. Active demultiplexing is demonstrated using a state‐of‐the‐art photon source—a quantum‐dot deterministically coupled to a micropillar cavity—and a custom‐built demultiplexer—a network of electro‐optically reconfigurable waveguides monolithically integrated in a lithium niobate chip. The measured demultiplexer performance can enable a six‐photon rate three orders of magnitude higher than the equivalent heralded SPDC source, providing a platform for intermediate quantum computation protocols.
The progress on multi‐wavelength quantum cascade laser arrays in the mid‐infrared is reviewed, which are a powerful, robust and versatile source for next‐generation spectroscopy and stand‐off detection systems. Various approaches for the array elements are discussed, from conventional distributed‐feedback lasers over master‐oscillator power‐amplifier devices to tapered oscillators, and the performances of the different array types are compared. The challenges associated with reliably achieving single‐mode operation at deterministic wavelengths for each laser element in combination with a uniform distribution of high output power across the array are discussed. An overview of the range of applications benefiting from the quantum cascade laser approach is given. The distinct and crucial advantages of arrays over external cavity quantum cascade lasers as tunable single‐mode sources in the mid‐infrared are discussed. Spectroscopy and hyperspectral imaging demonstrations by quantum cascade laser arrays are reviewed.
Dewetting of thin metal films is one of the most widespread method for functional plasmonic nanostructures fabrication. However, simple thermal‐induced dewetting does not allow to control degree of nanostructures order without additional lithographic process steps. Here we propose a novel method for lithography‐free and large‐scale fabrication of plasmonic nanostructures via controllable femtosecond laser‐induced dewetting. The method is based on femtosecond laser surface pattering of a thin film followed by a nanoscale hydrodynamical instability, which is found to be very controllable under specific irradiation conditions. We achieve control over degree of nanostructures order by changing laser irradiation parametrs and film thickness. This allowed us to exploit the method for the broad range of applications: resonant light absorbtion and scattering, sensing, and potential improving of thin‐film solar cells.
We report complete spatial shaping (both phase and amplitude) of the second‐harmonic beam generated in a nonlinear photonic crystal. Using a collinear second‐order process in a nonlinear computer generated hologram imprinted on the crystal, the desired beam is generated on‐axis and in the near field. This enables compact and efficient one‐dimensional beam shaping in comparison to previously demonstrated off‐axis Fourier holograms. We experimentally demonstrate the second‐harmonic generation of high‐order Hermite–Gauss, top hats and arbitrary skyline‐shaped beams.
This article presents a novel III‐V on silicon laser. This work exploits the phenomenon that a passive silicon cavity, side‐coupled to a III‐V waveguide, will provide high and narrow‐band reflectivity into the III‐V waveguide: the resonant mirror. This results in an electrically pumped laser with a threshold current of 4 mA and a side‐mode suppression ratio up to 48 dB.
The design of micro‐optical resonator arrays are introduced and tailored towards refractive index sensing applications, building on the previously unexplored benefits of open dielectric stacks. The resonant coupling of identical hollow cavities present strong and narrow spectral resonance bands beyond that available with a single Fabry Perot interferometer. Femtosecond laser irradiation with selective chemical etching is applied to precisely fabricate stacked and waveguide‐coupled open resonators into fused silica, taking advantage of small 12 nm rms surface roughness made available by the self‐alignment of nanograting planes. Refractive index sensing of methanol‐water solutions confirm a very attractive sensing resolution of 6.5 × 10−5 RIU. Such high finesse optical elements open a new realm of optofluidic sensing and integrated optical circuit concepts for detecting minute changes in sample properties against a control solution that may find importance in chemical and biological sensors, telecom sensing networks, biomedical probes, and low‐cost health care products.
Monocrystalline titanium dioxide (TiO2) micro‐spheres support two orthogonal magnetic dipole modes at terahertz (THz) frequencies due to strong dielectric anisotropy. For the first time, we experimentally detected the splitting of the first Mie mode in spheres of radii m through near‐field time‐domain THz spectroscopy. By fitting the Fano lineshape model to the experimentally obtained spectra of the electric field detected by the sub‐wavelength aperture probe, we found that the magnetic dipole resonances in TiO2 spheres have narrow linewidths of only tens of gigahertz. Anisotropic TiO2 micro‐resonators can be used to enhance the interplay of magnetic and electric dipole resonances in the emerging THz all‐dielectric metamaterial technology.
High performance semiconductor lasers on silicon are critical elements of next generation photonic integrated circuits. Transfer printing methods provide promising paths to achieve hybrid integration of III‐V devices on Si platforms. This paper presents materials and procedures for epitaxially releasing thin‐film microscale GaAs based lasers after their full fabrication on GaAs native substrates, and for subsequently transfer printing arrays of them onto Si wafers. An indium‐silver based alloy serves as a thermally conductive bonding interface between the lasers and the Si, for enhanced performance. Numerical calculations provide comparative insights into thermal properties for devices with metallic, organic and semiconductor interfaces. Under current injection, the first of these three interfaces provides, by far, the lowest operating temperatures. Such devices exhibit continuous‐wave lasing in the near‐infrared range under electrical pumping, with performance comparable to unreleased devices on their native substrates.
We experimentally demonstrate an optically‐pumped III‐V/Si vertical‐cavity laser with lateral emission into a silicon waveguide. This on‐chip hybrid laser comprises a distributed Bragg reflector, a III‐V active layer, and a high‐contrast grating reflector, which simultaneously funnels light into the waveguide integrated with the laser. This laser has the advantages of long‐wavelength vertical‐cavity surface‐emitting lasers, such as low threshold and high side‐mode suppression ratio, while allowing integration with silicon photonic circuits, and is fabricated using CMOS compatible processes. It has the potential for ultrahigh‐speed operation beyond 100 Gbit/s and features a novel mechanism for transverse mode control.
We report on the theoretical investigation of plasmonic resonances in metallic Möbius nanorings. Half‐integer numbers of resonant modes are observed due to the presence of an extra phase π provided by the topology of the Möbius nanostrip. Anomalous plasmon modes located at the non‐orientable surface of the Möbius nanoring break the symmetry that exist in conventional ring cavities, thus enable far‐field excitation and emission as bright modes. The far‐field resonant wavelength as well as the feature of half‐integer mode numbers is constant to the change of charge distribution on the Möbius nanoring due to the topology of Möbius ring. Owing to the ultra‐small mode volume induced by the remaining dark feature, an extremely high sensitivity as well as a remarkable figure of merit is obtained in our numerical calculations for sensing performance. The topological metallic nanostructure provides a novel platform for the investigation of localized surface plasmon modes exhibiting unique phenomena for potential plasmonic applications.
In this work, we report optomechanical coupling, resolved sidebands and phonon lasing in a solid‐core microbottle resonator fabricated on a single mode optical fiber. Mechanical modes with quality factors (Qm) as high as 1.57 × 104 and 1.45 × 104 were observed, respectively, at the mechanical frequencies and . The maximum Hz is close to the theoretical lower bound of 6 × 1012 Hz needed to overcome thermal decoherence for resolved‐sideband cooling of mechanical motion at room temperature, suggesting microbottle resonators as a possible platform for this endeavor. In addition to optomechanical effects, scatter‐induced mode splitting and ringing phenomena, which are typical for high‐quality optical resonances, were also observed in a microbottle resonator.
A mid‐infrared (MIR) supercontinuum (SC) has been demonstrated in a low‐loss telluride glass fiber. The double‐cladding fiber, fabricated using a novel extrusion method, exhibits excellent transmission at 8–14 μm: < 10 dB/m in the range of 8–13.5 μm and 6 dB/m at 11 μm. Launched intense ultrashort pulsed with a central wavelength of 7 μm, the step‐index fiber generates a MIR SC spanning from ∼2.0 μm to 16 μm, for a 40‐dB spectral flatness. This is a fresh experimental demonstration to reveal that telluride glass fiber can emit across the all MIR molecular fingerprint region, which is of key importance for applications such as diagnostics, gas sensing, and greenhouse CO2 detection.
