Semiconductor Nanowire Lasers Research Articles

Single-mode nanolasers based on FP-WGM hybrid cavity coupling

As an idealized light source, semiconductor nanowire (NW) lasers have been extensively studied due to its potential applications in many fields such as optoelectronics, nanophononics, optical communication, signal processing, and displays. In this letter, we proposed a novel approach to realize a single-mode nanolaser by forming an Fabry–Perot whispering gallery mode (FP-WGM) hybrid nanocavity between two cross-contact CdS NWs, i.e. x and y-NW. In our method, x-NW supports the regular FP oscillation in the axis direction while the cross section of y-NW provides a ultrasmall WGM nanocavity with a higher Q-factor and mode election which confirms the specific single mode can be excited. Experimentally, single-mode lasing emission centered at 517 nm was obtained with full width at half maximum of 0.08 nm and lasing threshold of ∼50 kW cm−2. The suggested designing skills projected a general strategy for lasing mode regulation and single-mode realization. The single-mode low-threshold lasing strategy in coupled NWs may open a new avenue for practical applications of NW lasers and further trigger other photonic devices at a visible range.

Damage protection from focused ion beam process toward nanocavity-implemented compound semiconductor nanowire lasers

A focused ion beam (FIB) can precisely mill samples and freely form any nanostructure even on surfaces with curvature, like a nanowire surface, which are difficult to implement by using conventional fabrication techniques, e.g. electron beam lithography. Thus, this tool is promising for nanofabrication; however, fabrication damage and contamination are critical issues, which deteriorate optical properties. In this work, we investigated the protective performance of Al2O3 against the FIB process (especially by a gallium ion). Nanowires were coated with Al2O3 as a hard mask to protect them from damage during FIB nanofabrication. To estimate the protective performance, their emission properties by photoluminescence measurement and time-resolved spectroscopy were compared with and without Al2O3 coating conditions. From the results, we confirmed that the Al2O3 coating protects the nanowires. In addition, the nanowires also showed lasing behavior even after FIB processing had been carried out to implement nanostructures. This indicates that their optical properties are well maintained. Thus, our study proves the usefulness of FIBs for future nanofabrication.

Lasing modes in ZnO nanowires coupled to planar metals.

Semiconductor nanowire lasers can be subject to modifications of their lasing threshold resulting from a variation of their environment. A promising choice is to use metallic substrates to gain access to low-volume Surface-Plasmon-Polariton (SPP) modes. We introduce a simple, yet quantitatively precise model that can serve to describe mode competition in nanowire lasers on metallic substrates. We show that an aluminum substrate can decrease the lasing threshold for ZnO nanowire lasers while for a silver substrate, the threshold increases compared with a dielectric substrate. Generalizing from these findings, we make predictions describing the interaction between planar metals and semiconductor nanowires, which allow to guide future improvements of highly-integrated laser sources.

Advanced transfer printing with in-situ optical monitoring for the integration of micron-scale devices

Transfer printing integration of planar membrane devices on photonic and electronic circuits is becoming a well established technology. Typical systems incorporate a single planar layer printed into full contact with the host substrate. In this work we present an advanced transfer print system that enables printing of optical devices in non-planar geometries and allows in-situ optical monitoring of devices. We show micro-resonators with air-clad whispering gallery modes coupled to on-chip waveguides, inverted device printing and three dimensionally assembled micro-cavities incorporating semiconductor micro-lenses and nanowire lasers. We demonstrate printing onto non-standard substrates including optical chip facets and single-mode fibre ends. The optical fibre printing was carried out with alignment assistance from in-situ optical coupling through the transfer printing system in real-time allowing active alignment of the system.

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.

Characterization, Selection, and Microassembly of Nanowire Laser Systems.

Semiconductor nanowire (NW) lasers are a promising technology for the realization of coherent optical sources with ultrasmall footprint. To fully realize their potential in on-chip photonic systems, scalable methods are required for dealing with large populations of inhomogeneous devices that are typically randomly distributed on host substrates. In this work two complementary, high-throughput techniques are combined: the characterization of nanowire laser populations using automated optical microscopy, and a high-accuracy transfer-printing process with automatic device spatial registration and transfer. Here, a population of NW lasers is characterized, binned by threshold energy density, and subsequently printed in arrays onto a secondary substrate. Statistical analysis of the transferred and control devices shows that the transfer process does not incur measurable laser damage, and the threshold binning can be maintained. Analysis on the threshold and mode spectra of the device populations proves the potential for using NW lasers for integrated systems fabrication.

Optimized waveguide coupling of an integrated III-V nanowire laser on silicon

The recent integration of III-V semiconductor nanowire (NW) lasers on silicon waveguides marked a key step toward their usage as coherent light sources for future silicon photonics applications. However, the low index contrast between III-V semiconductors and silicon results in a weak modal reflectivity, calling for improved design structures that enable both low-threshold lasing and good in-coupling efficiency into waveguides. Here, we perform numerical simulations to explore how the alternating refractive index of a silicon waveguide with a thin SiO2 interlayer can be used to significantly improve the reflectivity at the III-V–silicon interface to values of up to 83%. We further investigate the frequency dependencies of the end-facet reflectivity and in-coupling efficiency as a function of the nanowire and waveguide dimensions. Our results are kept general by the normalization to the nanowire radius R and show for a waveguide width of 2.75⋅R a maximum coupling efficiency of 50%. Variations in waveguide height or SiO2 interlayer thickness by ±0.1⋅R increase the coupling efficiency by a factor of 2, with little effect on the end-facet reflectivity. Ultimately, a prototypical NW-laser structure consisting of a 1.3-μm emitting InGaAs MQW active region in a core-multishell structure was simulated, showing an optimized low-threshold gain of <500 cm−1 for a TE01 mode with a coupling efficiency of ∼13%. By simplified approximations, we illustrate that these analyses can be adapted to a variety of material systems and serve as guidelines in the construction of optimized nanowire lasers on silicon-on-insulator waveguides for future on-chip optical interconnects.

Tailoring Spectral and Temporal Properties of Semiconductor Nanowire Lasers

AbstractSemiconductor optoelectronics have contributed tremendously to various aspects of the technological progress in the past. Recently, they also stimulate research in nanophotonics seeking to overcome the inherent limitations of electronic integrated circuits and satisfy the growing demand for faster on‐chip communications. In particular, nanowire (NW) lasers generate coherent light at the nanoscale and meanwhile work consistently at room temperature covering a huge spectral range from the ultraviolet down to the mid‐infrared depending on the NW material. The underlying physics of their electronic and photonic systems are also studied very recently, thus NW lasers become relevant as an emergent tool for a variety of practical applications. In this review, the origins determining the emission wavelength of the device are explained, and approaches toward efficient improvement of the NW laser devices in terms of emission energy tunability are summarized. The optical mode field distribution strongly influences the emission dynamics of the nanolaser device; it will be highlighted how increasing the light–matter interaction in plasmonic type nanolasers causes a significant acceleration of their temporal emission dynamics. Both spectral and temporal tuning will help to solve scientific and engineering challenges forging semiconductor nanowire lasers into powerful tools for nanosensing, nanospectroscopy, and nanotechnology.

Threshold reduction and yield improvement of semiconductor nanowire lasers via processing-related end-facet optimization.

Both gain medium design and cavity geometry are known to be important for low threshold operation of semiconductor nanowire lasers. For many applications nanowire lasers need to be transferred from the growth substrate to a low-index substrate; however, the impact of the transfer process on optoelectronic performance has not been studied. Ultrasound, PDMS-assisted and mechanical rubbing are the most commonly used methods for nanowire transfer; each method may cause changes in the fracture point of the nanowire which can potentially affect both length and end-face mirror quality. Here we report on four common approaches for nanowire transfer. Our results show that brief ultrasound and PDMS-assisted transfer lead to optimized optoelectronic performance, as confirmed by ensemble median lasing threshold values of 98 and 104 μJ cm−2 respectively, with nanowires transferred by ultrasound giving a high lasing yield of 72%. The mean threshold difference between samples is shown to be statistically significant: while a significant difference in mean length from different transfer methods is seen, it is shown by SEM that end-facet quality is also affected and plays an important role on threshold gain for this nanowire architecture.

Tuning Lasing Emission toward Long Wavelengths in GaAs-(In,Al)GaAs Core–Multishell Nanowires

Semiconductor nanowire (NW) lasers are attractive as integrated on-chip coherent light sources with strong potential for applications in optical communication and sensing. Realizing lasers from individual bulk-type NWs with emission tunable from the near-infrared to the telecommunications spectral region is, however, challenging and requires low-dimensional active gain regions with an adjustable band gap and quantum confinement. Here, we demonstrate lasing from GaAs-(InGaAs/AlGaAs) core-shell NWs with multiple InGaAs quantum wells (QW) and lasing wavelengths tunable from ∼0.8 to ∼1.1 μm. Our investigation emphasizes particularly the critical interplay between QW design, growth kinetics, and the control of InGaAs composition in the active region needed for effective tuning of the lasing wavelength. A low shell growth temperature and GaAs interlayers at the QW/barrier interfaces enable In molar fractions up to ∼25% without plastic strain relaxation or alloy intermixing in the QWs. Correlated scanning transmission electron microscopy, atom probe tomography, and confocal PL spectroscopy analyses illustrate the high sensitivity of the optically pumped lasing characteristics on microscopic properties, providing useful guidelines for other III-V-based NW laser systems.

Compound Semiconductor Nanowire Laser Integrated in Silicon Photonic Crystal

Compound Semiconductor Nanowire Laser Integrated in Silicon Photonic Crystal

Vertically Emitting Indium Phosphide Nanowire Lasers

Semiconductor nanowire (NW) lasers have attracted considerable research effort given their excellent promise for nanoscale photonic sources. However, NW lasers currently exhibit poor directionality and high threshold gain, issues critically limiting their prospects for on-chip light sources with extremely reduced footprint and efficient power consumption. Here, we propose a new design and experimentally demonstrate a vertically emitting indium phosphide (InP) NW laser structure showing high emission directionality and reduced energy requirements for operation. The structure of the laser combines an InP NW integrated in a cat's eye (CE) antenna. Thanks to the antenna guidance with broken asymmetry, strong focusing ability, and high Q-factor, the designed InP CE-NW lasers exhibit a higher degree of polarization, narrower emission angle, enhanced internal quantum efficiency, and reduced lasing threshold. Hence, this NW laser-antenna system provides a very promising approach toward the achievement of high-performance nanoscale lasers, with excellent prospects for use as highly localized light sources in present and future integrated nanophotonics systems for applications in advanced sensing, high-resolution imaging, and quantum communications.

Single-Mode Near-Infrared Lasing in a GaAsSb-Based Nanowire Superlattice at Room Temperature.

Semiconductor nanowire lasers can produce guided coherent light emission with miniaturized geometry, bringing about new possibilities for a variety of applications including nanophotonic circuits, optical sensing, and on-chip and chip-to-chip optical communications. Here, we report on the realization of single-mode and room-temperature lasing from 890 to 990 nm, utilizing a novel design of single nanowires with GaAsSb-based multiple axial superlattices as a gain medium under optical pumping. The control of lasing wavelength via compositional tuning with excellent room-temperature lasing performance is shown to result from the unique nanowire structure with efficient gain material, which delivers a low lasing threshold of ∼6 kW/cm2 (75 μJ/cm2 per pulse), a lasing quality factor as high as 1250, and a high characteristic temperature of ∼129 K. These results present a major advancement for the design and synthesis of nanowire laser structures, which can pave the way toward future nanoscale integrated optoelectronic systems with superior performance.

Transfer printing of semiconductor nanowire lasers

The authors review their work on the accurate positioning of semiconductor nanowire (NW) lasers by means of nanoscale Transfer Printing (nano-TP). Using this hybrid nanofabrication technique, indium phosphide NWs are successfully integrated at selected locations onto heterogeneous surfaces with high positioning accuracy. Moreover, they show that NW lasers can also be organised to form bespoke spatial patterns, including (one-dimensional) 1D or 2D arrays, or complex configurations with a defined number of NWs and controlled separation between them. Besides, their nano-TP technique also permits the integration of NWs with different dimensions in a single system. Notably, the nano-TP fabrication protocols do not affect the optical or structural properties of the NWs and they retain their room-temperature lasing emission after their positioning onto all investigated receiving surfaces. This developed nano-TP technique offers therefore new exciting prospects for the fabrication of hybrid bespoke nanophotonic systems using NW lasers as building blocks.

Enhanced absorption and cavity effects of three-photon pumped ZnO nanowires

Semiconductor nanowire (NW) lasers attract a lot of attention as potential elements of nanophotonic circuits and lab-on-a chip devices. Here, we report on the experimental investigation of stimulated near ultraviolet (NUV) emission, pumped by three-photon absorption from near infrared femtosecond laser pulses, from ZnO NW arrays of different morphologies and compare it to the bulk. The spectrally and temporally resolved measurements of the NUV emission show both strong enhancements in the absorption and emission properties of the nanowire arrays compared to bulk samples. Thus, we determine a many times higher three-photon absorption in the nanostructure morphology compared to the bulk material. Furthermore, the threshold pumping intensity for stimulated emission in a vertically oriented nanowire array is twice lower and the emission onset time is shorter than in randomly oriented arrays, revealing strong influence of the macroscopic nanowire arrangement.

Integration of Semiconductor Nanowire Lasers with Polymeric Waveguide Devices on a Mechanically Flexible Substrate.

Nanowire lasers are integrated with planar waveguide devices using a high positional accuracy microtransfer printing technique. Direct nanowire to waveguide coupling is demonstrated, with coupling losses as low as -17 dB, dominated by mode mismatch between the structures. Coupling is achieved using both end-fire coupling into a waveguide facet, and from nanowire lasers printed directly onto the top surface of the waveguide. In-waveguide peak powers up to 11.8 μW are demonstrated. Basic photonic integrated circuit functions such as power splitting and wavelength multiplexing are presented. Finally, devices are fabricated on a mechanically flexible substrate to demonstrate robust coupling between the on-chip laser source and waveguides under significant deformation of the system.

Direct Coupling of Coherent Emission from Site-Selectively Grown III–V Nanowire Lasers into Proximal Silicon Waveguides

Semiconductor nanowire (NW) lasers are nanoscale coherent light sources that exhibit a small footprint, low-threshold lasing characteristics, and properties suitable for monolithic and site-selective integration onto Si photonic circuits. An important milestone on the way toward novel on-chip photonic functionalities, such as injection locking of laser emission and all-optical switching mediated by coherent optical coupling and feedback, is the integration of individual, deterministically addressable NW lasers on Si waveguides with efficient coupling and mode propagation in the underlying photonic circuit. Here, we demonstrate the monolithic integration of single GaAs-based NW lasers directly onto lithographically defined Si ridge waveguides (WG) with low threshold power densities of 19.8 μJ/cm2 when optically excited. The lasing mode of individual NW lasers is shown to couple efficiently into propagating modes of the underlying orthogonal Si WG, preserving the lasing characteristics during mode propagati...

Telecom-Wavelength Bottom-up Nanobeam Lasers on Silicon-on-Insulator.

Semiconductor nanowire lasers are considered promising ultracompact and energy-efficient light sources in the field of nanophotonics. Although the integration of nanowire lasers onto silicon photonic platforms is an innovative path toward chip-scale optical communications and photonic integrated circuits, operating nanowire lasers at telecom-wavelengths remains challenging. Here, we report on InGaAs nanowire array lasers on a silicon-on-insulator platform operating up to 1440 nm at room temperature. Bottom-up photonic crystal nanobeam cavities are formed by growing nanowires as ordered arrays using selective-area epitaxy, and single-mode lasing by optical pumping is demonstrated. We also show that arrays of nanobeam lasers with individually tunable wavelengths can be integrated on a single chip by the simple adjustment of the lithographically defined growth pattern. These results exemplify a practical approach toward nanowire lasers for silicon photonics.

Refractive index sensing based on semiconductor nanowire lasers

We demonstrate a refractive index (RI) sensor based on semiconductor nanowire lasers. It is shown that the TE01 mode is responsible for lasing and sensing with the lasing threshold of 3 μJ/mm2 and the lasing peak width as narrow as 0.22 nm. A RI sensitivity of 21.2 nm/RIU (refractive index units), a figure of merit of approximately 100, and an RI detection limit of 1.4×10−3 RIU are achieved.

Long-term mutual phase locking of picosecond pulse pairs generated by a semiconductor nanowire laser

The ability to generate phase-stabilized trains of ultrafast laser pulses by mode-locking underpins photonics research in fields, such as precision metrology and spectroscopy. However, the complexity of conventional mode-locked laser systems has hindered their realization at the nanoscale. Here we demonstrate that GaAs-AlGaAs nanowire lasers are capable of emitting pairs of phase-locked picosecond laser pulses with a repetition frequency up to 200 GHz when subject to incoherent pulsed optical excitation. By probing the two-pulse interference spectra, we show that pulse pairs remain mutually coherent over timescales extending to 30 ps, much longer than the emitted laser pulse duration (≤3 ps). Simulations performed by solving the optical Bloch equations produce good quantitative agreement with experiments, revealing how the phase information is stored in the gain medium close to transparency. Our results open the way to phase locking of nanowires integrated onto photonic circuits, optical injection locking and applications, such as on-chip Ramsey comb spectroscopy.