Nanowire Lasers Research Articles

Stable, multi-mode lasing in the strong localization regime from InP random nanowire arrays at low temperature

Disorder is generally considered an undesired element in lasing action. However, in random lasers whose feedback mechanism is based on random scattering events, disorder plays a very important and critical role. Even though some unique properties in random lasers such as large-angle emission, lasing from different surfaces, large-area manufacturability, and wavelength tunability can be advantageous in certain applications, the applicability of random lasers has been limited due to the chaotic fluctuations and instability of the lasing modes because of weak confinement. To solve this, mode localization could reduce the spatial overlap between lasing modes, thus preventing mode competition and improving stability, leading to laser sources with high quality factors and very low thresholds. Here, by using a random array of III-V nanowires, high-quality-factor localized modes are demonstrated. We present the experimental evidence of strong light localization in multi-mode random nanowire lasers which are temporally stable at low temperatures.

Halide-modulated self-assembly of metal-free perovskite single crystals for bio-friendly X-ray detection

Halide-modulated self-assembly of metal-free perovskite single crystals for bio-friendly X-ray detection

Thermal effect of InP/InAs nanowire lasers integrated on different optical platforms

III-V nanowire lasers for future photonic on-chip processors require continuous-wave operation at room temperature; however, this has not been achieved yet due to heating effects. In this work, the heating effects limiting laser performance is systematically investigated for nanowires placed on Au-coated substrates before and after Al2O3 deposition and on Si and SiN waveguides. Our findings indicate that nanowire heating is strongly related to the thermal resistance between the nanowires and substrates. Our results reveal the potential for continuous-wave nanowire laser operation, towards future photonic on-chip processors with nanowires integrated on photonic platforms.

Low-threshold strain-compensated InGaAs/(In,Al)GaAs multi-quantum well nanowire lasers emitting near 1.3 μm at room temperature

Realizing telecom-band lasing in GaAs-based nanowires (NW) with low bandgap gain media has proven to be notoriously difficult due to the high compressive strain built up in the active regions. Here, we demonstrate an advanced coaxial GaAs-InGaAs multi-quantum well (MQW) nanowire laser that solves previous limitations by the introduction of a strain compensating InAlGaAs buffer layer between the GaAs core and the MQW active region. Using a buffer layer thickness comparable to the core diameter applies a significant tensile strain to the GaAs core which efficiently minimizes the compressive strain in the InGaAs MQW and enables large In-content without plastic relaxation. Experimental verification is shown for NW-lasers with an In-content of up to 40% in the MQW, evidencing a clear strain-relieved redshift of the lasing emission and a strong reduction of the lasing threshold compared to highly strained MQWs in state-of-the-art GaAs NW-lasers. This way we achieve optically pumped room temperature lasing operation with a threshold below 50 μJ cm−2 in the telecom O-band close to 1.3 μm.

Ultralow Threshold, Single-Mode InGaAs/GaAs Multiquantum Disk Nanowire Lasers.

We present single-mode nanowire (NW) lasers with an ultralow threshold in the near-infrared spectral range. To ensure the single-mode operation, the NW diameter and length are reduced specifically to minimize the longitudinal and transverse modes of the NW cavity. Increased optical losses and reduced gain volume by the dimension reduction are compensated by an excellent NW morphology and InGaAs/GaAs multiquantum disks. At 5 K, a threshold low as 1.6 μJ/cm2 per pulse is achieved with a resulting quality factor exceeding 6400. By further passivating the NW with an AlGaAs shell to suppress surface nonradiative recombination, single-mode lasing operation is obtained with a threshold of only 48 μJ/cm2 per pulse at room temperature with a high characteristic temperature of 223 K and power output of ∼0.9 μW. These single-mode, ultralow threshold, high power output NW lasers are promising for the development of near-infrared nanoscale coherent light sources for integrated photonic circuits, sensing, and spectroscopy.

Two photon pumped nanowire laser based on all inorganic perovskite with high exciton binding energy grown by physical vapor deposition

Cesium lead halide (CsPbBr3) perovskite nanomaterials exhibit attractive optical properties, particularly in higher nonlinear optical effects and larger multiphoton absorption efficiency, compared with conventional semiconductors. The unique feature of stable lasing action under photon pumping conditions grants such materials great potential in photonics. Herein, through an in-depth study of the growing mechanism, all-inorganic perovskite nanomaterials with a high crystalline quality and tunable morphologies were synthesized, by a modified physical vapor deposition procedure. The prepared nanowire laser not only presents a high-performance laser output under single-photon pumping conditions, but also maintains decent behavior under two-photon pumping conditions. Importantly, the temperature-dependent fluorescence spectroscopy test of the nanowires reveals that the high exciton binding energy, twice as large as the thermal disturbance at room temperature, is the dominant reason for maintaining stable lasing under high energy density injection conditions.

The Electron–Hole Plasma Contributes to Both Plasmonic and Photonic Lasing from CH3NH3PbBr3 Nanowires at Room Temperature

AbstractLead halide perovskites have gained tremendous attentions in many fields, especially in nanolasers, owing to the excellent optoelectronic properties. However, the underlying lasing mechanism is not clear in both plasmonic and photonic nanolasers at room temperature. Here, the plasmonic lasers and the photonic counterparts based on organic–inorganic hybrid lead tri‐bromine perovskite nanowires are achieved at room temperature and are compared in terms of lasing evolution, lasing wavelengths, and lasing dynamics. The same spectra evolution and the same emission wavelength indicate that the plasmonic and the photonic CH3NH3PbBr3 nanowire lasers have the same gain origination. The calculated Mott density lower than the threshold density and lasing photon energy lower than exciton energy prove that an electron–hole plasma contributes to both the two types of lasing actions from perovskite nanowires at room temperature. The work deepens the understanding of underlying mechanism of perovskite nanowire lasers.

The effects of AlGaN quantum barriers on carrier flow in deep ultraviolet nanowire laser diode

Aluminium (Al) composition is a critical parameter of performance for deep ultraviolet (DUV) AlGaN devices. In multiple-quantum-wells (MQW) nanowire laser diode, quantum barriers play an important role in carriers’ flow (electrons, holes). In this work, the impact of composition, and the thickness of AlGaN-based quantum barriers is being studied. The study suggests that by properly increasing Al composition of quantum barriers, the height of the conduction band barrier decreases, which enhances electron leakage from MQW, while increasing the height of the valance band barrier, which, in turn, suppresses hole injection efficiency toward MQW. Such variations in band height greatly affect opto-electronic characteristics and performance of AlGaN nanowire. Furthermore, the study also suggests that quantum barrier thickness has much influence on DUV nanowire performance. The decrease in thickness of quantum barriers has little effect on confinement of the optical field, but significant effect on optical emitted power. It is found that by decreasing the thickness of quantum barriers, optical emitted power along with stimulated recombination rate is reduced. Contrastingly, as the thickness of quantum barriers increases, hole injection efficiency gets enhanced while electron leakage from MQW gets reduced. The above observations suggest that the higher the thickness of quantum barriers, the better the carriers’ flow toward MQW and hence, the performance is improved.

Single-Mode Semiconductor Nanowire Lasers With Coupled Cavities.

Semiconductor nanowires are one of the most fascinating topics over the past few decades. As miniaturized coherent light sources, semiconductor nanowires have been attracting tremendous attention in recent years for scientific and technological interest as potential ultra-compact, low cost, high efficiency, and low power consumption. Among different types of lasers, one-dimensional nanowires are of great interest as a promising material for next-generation nanophotonics and nanoelectronics applications due to their unique optical and electrical properties. Semiconductor nanowire lasers with single-mode output are vital in a variety of practical applications ranging from signal processing, spectroscopy, displays, optical sensing, on-chip communications, and biological studies. This article reviews the basic technology and research progress of single-mode semiconductor nanowire lasers. Afterward, the key methods and development of the different types of coupling to achieved single-mode laser output are elaborated. Finally, the challenges faced by each scheme are summarized.

Nanowire Waveguides and Lasers: Advances and Opportunities in Photonic Circuits.

Due to their single-crystalline structures, comparatively large aspect ratios, tight optical confinement and smooth surfaces, nanowires have increasingly attracted research interests for both fundamental studies and technological applications in on-chip photonic devices. This class of nanostructures typically have cross-sections of 2~200 nm and lengths upwards of several micrometers, allowing for the bridging of the nanoscopic and macroscopic world. In particular, the lasing behaviors can be established from a nanowire resonator with positive feedback via end-facet reflection, making the nanowire a promising candidate in the next generation of optoelectronics. Consequently, versatile nanowire-based devices ranging from nanoscale coherent lasers, optical sensors, waveguides, optical switching, and photonic networks have been proposed and experimentally demonstrated in the past decade. In this article, significant progresses in the nanowire fabrication, lasers, circuits, and devices are reviewed. First, we focus on the achievements of nanowire synthesis and introduce the basics of nanowire optics. Following the cavity configurations and mode categories, then the different light sources consisting of nanowires are presented. Next, we review the recent progress and current status of functional nanowire devices. Finally, we offer our perspective of nanowires regarding their challenges and future opportunities in photonic circuits.

Nanowire Oligomer Waveguide Modes towards Reduced Lasing Threshold.

Semiconductor nanowires offer a promising route of realizing nanolasers for the next generation of chip-scale optoelectronics and photonics applications. Established fabrication methods can produce vertical semiconductor nanowires which can themselves act both as a gain medium and as a Fabry–Pérot cavity for feedback. The lasing threshold in such nanowire lasers is affected by the modal confinement factor and end facet reflectivities, of which the substrate end reflectivity tends to be limited due to small refractive index contrast between the nanowire and substrate. These modal properties, however, also depend strongly on the modal field profiles. In this work, we use numerical simulations to investigate waveguide modes in vertical nanowire oligomers (that is, arrangements of few vertical nanowires close to each other) and their modal properties compared to single nanowire monomers. We solve for the oligomer waveguide eigenmodes which are understood as arising from interaction of monomer modes and further compute the reflectivity of these modes at the end facets of the nanowires. We consider either the nanowires or an additional coating layer as the gain medium. We show that both types of oligomers can exhibit modes with modal properties leading to reduced lasing threshold and also give directions for further research on the topic.

Design and Simulation of Low-Threshold Miniaturized Single-Mode Nanowire Lasers Combined with a Photonic Crystal Microcavity and Asymmetric Distributed-Bragg-Reflector Mirrors.

A low-threshold miniaturized single-mode nanowire laser operating at telecommunication wavelengths was proposed and simulated. The device was constructed by combining a single InGaAs nanowire with a photonic crystal microcavity and asymmetric distributed-Bragg-reflector mirrors. The mode characteristics and threshold properties were calculated using the three-dimensional finite-different time-domain method. Due to the effective subwavelength confinement and strong optical feedback, provided by the photonic crystal microcavity, and distributed-Bragg-reflector mirrors, respectively, the confinement factor, end-facet reflectivity, and quality factor significantly improved. A lowest threshold of ~80 cm−1 and ultra-small cut-off radius of ~40 nm are obtained, reduced by 67%, and 70%, respectively, compared with a traditional nanowire laser. In addition, due to the photonic band gap effect, single-mode lasing is achieved with a high side-mode suppression ratio of >12 dB. By placing several identical nanowires in the photonic crystal with different lattice constants, an on-chip laser array is realized, which is promising in wavelength division multiplexing applications. This work may pave the way for the development of low-threshold miniaturized nanolasers and low-consumption high-density photonic integrated circuits.

Current Modulation of Plasmonic Nanolasers by Breaking Reciprocity on Hybrid Graphene-Insulator-Metal Platforms.

A hybrid graphene–insulator–metal (GIM) platform is proposed with a supported surface plasmon polariton (SPP) wave that can be manipulated by breaking Lorentz reciprocity. The ZnO SPP nanowire lasers on the GIM platforms are demonstrated up to room temperature to be actively modulated by applying external current to graphene, which transforms the cavity mode from the standing to propagation wave pattern. With applying 100 mA external current, the laser threshold increases by ≈100% and a 1.2 nm Doppler shift is observed due to the nonreciprocal propagation characteristic. The nanolaser performance also depends on the orientation of the nanowire with respect to the current flow direction. The GIM platform can be a promising platform for integrated plasmonic system functioning laser generation, modulation, and detection.

NV center pumped and enhanced by nanowire ring resonator laser to integrate a 10 μm-scale spin-based sensor structure

In this work, we propose a 10 μm-scale spin-based sensor structure, which mainly consists of a nanowire (NW) ring resonator laser, nitrogen-vacancy (NV) defects in a nanodiamond (ND) and a microwave (MW) antenna. The NW laser was bent into a ring with a gap to pump the NV defects in the ND which was assembled in the gap with the diameter of ∼8 μm. And the fluorescent light of NV defects was enhanced by the NW ring resonator about 8 times. Furthermore, the NW laser pulse was produced by the optical switch and a simple plus-sequences was designed to get the Rabi oscillation signal. Based on the Rabi oscillation, a Ramsey-type sequence was used to detect the magnetic field with the sensitivity of 83 nT √Hz−1 for our 10 μm-scale spin-based sensor structure. It proves the spin state in our structure allows for coherent spin manipulation for more complex quantum control schemes. And our structure fulfills the fundamental requirements to develop chip-scale spin-based sensors.

A Low-Threshold Miniaturized Plasmonic Nanowire Laser with High-Reflectivity Metal Mirrors.

A reflectivity-enhanced hybrid plasmonic GaAs/AlGaAs core-shell nanowire laser is proposed and studied by 3D finite-difference time-domain simulations. The results demonstrate that by introducing thin metal mirrors at both ends, the end facet reflectivity of nanowire is increased by 30–140%, resulting in a much stronger optical feedback. Due to the enhanced interaction between the surface charge oscillation and light, the electric field intensity inside the dielectric gap layer increases, resulting in a much lower threshold gain. For a small diameter in the range of 100–150 nm, the threshold gain is significantly reduced to 60–80% that of nanowire without mirrors. Moreover, as the mode energy is mainly concentrated in the gap between the nanowire and metal substrate, the output power maintains >60% that of nanowire without mirrors in the diameter range of 100–150 nm. The low-threshold miniaturized plasmonic nanowire laser with simple processing technology is promising for low-consumption ultra-compact optoelectronic integrated circuits and on-chip communications.

Nanowire photonics toward wide wavelength range and subwavelength confinement [Invited

Semiconductor nanowires have attracted much attention for photonic applications, especially for lasers, because of their availability in a wide variety of materials and compositions, exceptionally small size, and rich functionality. So far, most nanowire laser studies have been done in rather short wavelength (λ) ranges of less than 1 µm. In addition, the diameter (d) of most nanowire lasers has been relatively large (d > λ/n, n is the refractive index) because of the requirement for sufficient optical confinement. Recently, however, we are seeing new trends in nanowire research towards much longer wavelengths and much thinner nanowires for photonic applications. This article reviews the latest research activities in these directions, which shows that it is possible to fabricate excellent nanowire lasers operating at telecom wavelengths or even in the mid-infrared region and extremely thin subwavelength nanowires can be applied to make nanophotonic devices in a wide range of wavelengths. We believe that these research trends will have an impact on applications for functional energy-saving devices in future photonic integrated circuits.

Efficient adjustable light couplers of integrated III-V nanowire emitters on silicon waveguides based on ring resonators.

The development of integrated vertical III-V nanowire (NW) stimulated emitters in silicon photonics while achieving an efficient light coupling through vertical III-V NW lasers into horizontal optical silicon waveguides is demanding. This is mainly due to the directionality and contradiction of the simultaneously satisfied low threshold stimulated emission conditions of the vertical NWs and efficient light coupling from the NW emitters into the horizontal silicon waveguide. However, we propose a new, to the best of our knowledge, design by taking advantage of resonating features of ring structures and theoretically demonstrate that an interfacial ring resonator between GaAs NW emitters and the silicon waveguide achieves a coupling efficiency up to about 70% at a given wavelength. We also show that the interfacial resonator enables us to adjust the coupling efficiency from about 10% to over 70%. The adjustable coupling efficiency might also be a solution to compromise between the low threshold stimulated emission of NWs and efficient light coupling for realizing efficient silicon couplers based on integrated III-V NW lasers in silicon photonics. Besides the simple fabrication process compared to counterparts, we believe that the novel structure is promising for future optical on-chip data communication in silicon photonics, and the results are expandable to varying wavelengths and materials.

Enhancement of the optoelectronic characteristics of deep ultraviolet nanowire laser diodes by induction of bulk polarization charge with graded AlN composition in AlxGa1-xN waveguide

AlGaN based Nanowire laser diodes (NW-LDs) grown on sapphire substrates have strong polarization induced electric field. Such electric field has the ability to degrade the optoelectronic characteristics of deep ultraviolet (DUV) NW-LD. In this work, a graded AlN composition AlxGa1-xN waveguide (WG) layer is used for the enhancement of DUV NW-LD performance. Grading of WG induces bulk polarization charges which compensates the effect of polarization induced electric field. According to the calculated optoelectronic characteristics of NW-LD, it is found that grading of n-type WG (n-WG) increases the optical confinement factor (OCF) by 82%. Fortunately, the proposed graded n-WG structure suppresses the leakage of optical field from active region and enhances carrier injection efficiency. Furthermore, if both n-WG and p-WG graded layers are used, the improvement is not obvious because of the current leakage from graded p-WG. Thus, graded n-WG based NW-LD gives highest 33.5% OCF with the lowest 7 mA and 4.59 V threshold current and voltage respectively.

Perovskite nanowire lasers on low-refractive-index conductive substrate for high-Q and low-threshold operation

Abstract Over the last five years, inorganic lead halide perovskite nanowires have emerged as prospective candidates to supersede standard semiconductor analogs in advanced photonic designs and optoelectronic devices. In particular, CsPbX3 (X = Cl, Br, I) perovskite materials have great advantages over conventional semiconductors such as defect tolerance, highly efficient luminescence, and the ability to form regularly shaped nano- and microcavities from solution via fast crystallization. However, on the way of electrically pumped lasing, the perovskite nanowires grown on transparent conductive substrates usually suffer from strong undesirable light leakage increasing their threshold of lasing. Here, we report on the integration of CsPbBr3 nanowires with nanostructured indium tin oxide substrates possessing near-unity effective refractive index and high conductivity by using a simple wet chemical approach. Surface passivation of the substrates is found out to govern the regularity of the perovskite resonators’ shape. The nanowires show room-temperature lasing with ultrahigh quality factors (up to 7860) which are up to four times higher than that of similar structures on a flat indium tin oxide layer, resulting in more than twofold reduction of the lasing threshold for the nanostructured substrate. Numerical modeling of eigenmodes of the nanowires confirms the key role of low-refractive-index substrate for improved light confinement in the Fabry–Pérot cavity which results in superior laser performance.

Optical coherence tomography and fluorescence microscopy dual-modality imaging for in vivo single-cell tracking with nanowire lasers.

Emerging cell-based therapies such as stem cell therapy and immunotherapy have attracted broad attention in both biological research and clinical practice. However, a long-standing technical gap of cell-based therapies is the difficulty of directly assessing treatment efficacy via tracking therapeutically administered cells. Therefore, imaging techniques to follow the in vivo distribution and migration of cells are greatly needed. Optical coherence tomography (OCT) is a clinically available imaging technology with ultrahigh-resolution and excellent imaging depth. It also shows great potential for in vivo cellular imaging. However, due to the homogeneity of current OCT cell labeling contrast agents (such as gold and polymer nanoparticles), only the distribution of entire cell populations can be observed. Precise tracking of the trajectory of individual single cells is not possible with such conventional contrast agents. Microlasers may provide a route to track unique cell identifiers given their small size, high emission intensities, rich emission spectra, and narrow linewidths. Here, we demonstrate that nanowire lasers internalized by cells provide both OCT and fluorescence signal. In addition, cells can be individually identified by the unique lasing emission spectra of the nanowires that they carry. Furthermore, single cell migration trajectories can be monitored both in vitro and in vivo with OCT and fluorescence microscopy dual-modality imaging system. Our study demonstrates the feasibility of nanowire lasers combined with the dual-modality imaging system for in vivo single cell tracking with a high spatial resolution and identity verification, an approach with great utility for stem cell and immunomodulatory therapies.