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Physically unclonable functions (PUFs) have emerged as the most effective method against counterfeiting, leveraging the intrinsic randomness of objects to avoid data replication. However, despite their efficacy, the complexity and high cost of most PUF‐based counterfeiting labels hinder their practical application. Here, a high‐capacity PUF label based on vertically aligned perovskite nanowire (NW) arrays is demonstrated. The NW arrays are conveniently constructed using a low‐cost solution process using an anodized aluminum oxide template. Each pixel within the label is composed of closely packed CsPbBr3 NW arrays of different lengths, resulting in varied lasing signals. The collected signal of each pixel emerged from the lasing output of the NW arrays, generating high‐density and nonuniform multiple‐mode lasing to facilitate information encoding. A quaternary encoding mechanism is used to encode the number of laser modes per pixel. Impressively, it exhibits a mapping resolution of 1600 pixels within 400 µm2, achieving an impressive encoding capacity (1.97 × 10963) and a pixel density (4 bits µm−2) in this compact area. This work shows a promising approach for anticounterfeiting applications because of its simplicity, low cost, and high encoding capacity. [ABSTRACT FROM AUTHOR]

Semiconductor nano-lasers have been a topic of interest from the perspective of advancing the capabilities of photonic integration. Nano-lasers are perceived as the means to achieve improved functionality in photonic integrated circuits. The properties and performance of nano-lasers have been examined by means of simulations and laboratory measurements. Nano-lasers lend themselves to integration to form dense arrays in both one and two dimensions. In a recent work, a theoretical treatment was presented for the dynamic behaviour of stand-alone electrically pumped nano-laser arrays. In this work, the response of nano-laser arrays to direct current modulation is examined. As in previous works, attention is given to two prototype array geometries: a linear three-element linear array and an equilateral triangular array. Large one-dimensional arrays can be built by repeating this elementary linear array. Two-dimensional photonic integrated circuits can incorporate the triangular arrays studied here. Such prototypical configurations offer opportunities to tailor the modulation response of the nano-laser arrays. The principal factors which provide that capability are the coupling strengths between lasers in the arrays and the direct modulation parameters. The former are fixed at the design and manufacture stage of the array whilst the latter can be chosen. In addition, the enhancement of the spontaneous emission rate via the so-called Purcell effect in nano-lasers offers a device-specific means for accessing a range of modulation responses. Two-dimensional portraits of the regimes of differing modulation responses offer a convenient means for determining the dynamics that may be accessed by varying the laser drive current. It is shown by these means that a rich variety of modulation responses can be accessed in both linear and triangular arrays. [ABSTRACT FROM AUTHOR]

Semiconductor nano-lasers have been actively investigated both theoretically and experimentally with to the aim of providing a highly compact laser amenable to photonic integration. Such devices are naturally suited for assembly in close-packed one- and two-dimensional arrays. In such arrangements, optical coupling between elements of the array opens opportunities to generate a range of dynamical behaviours. In this paper, we present the first theoretical treatment of the dynamics of electrically pumped nano-laser arrays. Two specific forms of such arrays are analysed in detail: a three-element linear array, and triangular arrays. The former is the basis for extensive one-dimensional arrays, whilst the latter is a building block of many possible geometric configurations of two-dimensional nanolaser arrays. Using these prototypical configurations enables the identification of novel dynamical behaviours, which may be accessed using nano-laser arrays. A distinguishing physical feature of nano-lasers is the enhancement of the spontaneous emission rate via the so-called Purcell effect. Allowing for a range of Purcell enhancement factors, the analysis focusses on the effects of experimentally controllable parameters such as the laser drive current. It is shown that the Purcell enhancement factor is critical to the availability of a range of dynamical behaviours which arise simply due to inter-element optical coupling. Two-dimensional portraits of the regimes of differing dynamics offer a convenient means for determining the dynamics which may be accessed by varying the laser drive current. [ABSTRACT FROM AUTHOR]

Supersymmetry (SUSY) laser array with superpartner structure can suppress excess modes to achieve high‐intensity and high‐coherent radiation. Compared with complex superpartner, using parity time (PT) symmetry broken to manipulate SUSY laser arrays is a more flexible approach. Herein, based on ultrathin perovskite single crystal, a SUSY laser array is constructed without superpartner, but with auxiliary gain–loss structure. PT symmetry broken with high‐order exceptional point (EP) is realized in the visible spectral range. It intrinsically avoids superpartner field mismatch and improves side mode suppression ratio 8.8–12 dB for single‐mode lasing. Furthermore, variations in EP‐order enable the transition from single‐mode to dual‐mode or tri‐mode radiation and retain amplified radiation characteristics. In addition, these SUSY laser arrays with the high‐order EP have the potential to be small‐volume optical sensor devices. The new design combining SUSY and PT symmetry broken presents its potential in micro‐nanophotonic devices with the benefit of small size, flexibility in spectral control, expandability, simplicity, and multifunctionality feature. [ABSTRACT FROM AUTHOR]

Supersymmetry (SUSY) laser array with superpartner structure can suppress excess modes to achieve high‐intensity and high‐coherent radiation. Compared with complex superpartner, using parity time (PT) symmetry broken to manipulate SUSY laser arrays is a more flexible approach. Herein, based on ultrathin perovskite single crystal, a SUSY laser array is constructed without superpartner, but with auxiliary gain–loss structure. PT symmetry broken with high‐order exceptional point (EP) is realized in the visible spectral range. It intrinsically avoids superpartner field mismatch and improves side mode suppression ratio 8.8–12 dB for single‐mode lasing. Furthermore, variations in EP‐order enable the transition from single‐mode to dual‐mode or tri‐mode radiation and retain amplified radiation characteristics. In addition, these SUSY laser arrays with the high‐order EP have the potential to be small‐volume optical sensor devices. The new design combining SUSY and PT symmetry broken presents its potential in micro‐nanophotonic devices with the benefit of small size, flexibility in spectral control, expandability, simplicity, and multifunctionality feature.

Semiconductor nano-lasers have been a topic of interest from the perspective of advancing the capabilities of photonic integration. Nano-lasers are perceived as the means to achieve improved functionality in photonic integrated circuits. The properties and performance of nano-lasers have been examined by means of simulations and laboratory measurements. Nano-lasers lend themselves to integration to form dense arrays in both one and two dimensions. In a recent work, a theoretical treatment was presented for the dynamic behaviour of stand-alone electrically pumped nano-laser arrays. In this work, the response of nano-laser arrays to direct current modulation is examined. As in previous works, attention is given to two prototype array geometries: a linear three-element linear array and an equilateral triangular array. Large one-dimensional arrays can be built by repeating this elementary linear array. Two-dimensional photonic integrated circuits can incorporate the triangular arrays studied here. Such prototypical configurations offer opportunities to tailor the modulation response of the nano-laser arrays. The principal factors which provide that capability are the coupling strengths between lasers in the arrays and the direct modulation parameters. The former are fixed at the design and manufacture stage of the array whilst the latter can be chosen. In addition, the enhancement of the spontaneous emission rate via the so-called Purcell effect in nano-lasers offers a device-specific means for accessing a range of modulation responses. Two-dimensional portraits of the regimes of differing modulation responses offer a convenient means for determining the dynamics that may be accessed by varying the laser drive current. It is shown by these means that a rich variety of modulation responses can be accessed in both linear and triangular arrays.

Semiconductor nano-lasers have been actively investigated both theoretically and experimentally with to the aim of providing a highly compact laser amenable to photonic integration. Such devices are naturally suited for assembly in close-packed one- and two-dimensional arrays. In such arrangements, optical coupling between elements of the array opens opportunities to generate a range of dynamical behaviours. In this paper, we present the first theoretical treatment of the dynamics of electrically pumped nano-laser arrays. Two specific forms of such arrays are analysed in detail: a three-element linear array, and triangular arrays. The former is the basis for extensive one-dimensional arrays, whilst the latter is a building block of many possible geometric configurations of two-dimensional nanolaser arrays. Using these prototypical configurations enables the identification of novel dynamical behaviours, which may be accessed using nano-laser arrays. A distinguishing physical feature of nano-lasers is the enhancement of the spontaneous emission rate via the so-called Purcell effect. Allowing for a range of Purcell enhancement factors, the analysis focusses on the effects of experimentally controllable parameters such as the laser drive current. It is shown that the Purcell enhancement factor is critical to the availability of a range of dynamical behaviours which arise simply due to inter-element optical coupling. Two-dimensional portraits of the regimes of differing dynamics offer a convenient means for determining the dynamics which may be accessed by varying the laser drive current.

This paper presents the results of a thermal computational analysis of a two-dimensional laser array emitting from a surface. The array consisted of eight equispaced ridge-waveguide edge-emitting nitride diode lasers. Surface emission of light was obtained using mirrors inclined at 45°. The authors investigate how the geometrical dimensions of the array emitters and their pitch in the array affect the increase and distribution of temperature in the device. They also examine the influence on the temperature increase and distribution of the thickness of the insulating SiO2, the thickness of the gold layer forming the top contact of the laser, and the thickness of the GaN substrate, as well as the influence of the ridge-waveguide width. [ABSTRACT FROM AUTHOR]

The exhaust from engines close to the fuselage can cause extreme turbulence and have a significant impact on the performance of airborne laser systems. In this paper, the combined effect of the jet engine and atmospheric turbulence on propagation of a Gaussian Schell‐model (GSM) array beam over long distances is studied in detail. Based on the two‐step propagation method, the analytical expressions of the cross‐spectral density (CSD) function, mean‐squared beam width and spectral degree of spatial coherence (DOC) of GSM array beams are derived. It is shown that the jet engine turbulence has a significant effect on the beam broadening even at a very short distance. As the propagation distance in the jet engine turbulence increases, the beam width is less effected by the spatial coherence. Meanwhile, the resistance of lower spatially coherent beam to the turbulence increases as the distance of the jet engine turbulence or the strength of the atmospheric turbulence increases. It is demonstrated that the effect of jet engine turbulence on the beam spreading can be equivalent to moderate or even severe atmospheric turbulence. Moreover, the DOC is a function with oscillatory phenomenon when the propagation distance is short or the strength of turbulence is low. [ABSTRACT FROM AUTHOR]

Recent increased interest in spin-polarised vertical-cavity surface-emitting lasers (spin-VCSELs) as potential high-speed sources has spurred research into the analysis of their dynamics. This has often been explored by combining the spin-flip model (SFM) with numerical methods. However, numerical simulation does not readily expose key dependencies and to date there is a lack of accessible closed-form analytical results for the steady-state solutions and dynamic stability boundaries. Thus in the present contribution we address this and show that, for zero dichroism, the five rate equations of the SFM can be reduced to a set of three. These can be solved in the steady-state in terms of the intensity and polarisation of the pump (optical or electrical), and the ellipticity of the output. Additionally, a small-signal analysis leads to analytic results for the boundaries between stable and unstable operation in the plane of pump ellipticity versus pump intensity. Comparison of the results from these expressions with those from numerical bifurcation and continuation methods shows very good agreement. The accuracy of the reduced set of equations is confirmed by comparing the results with those from the full set of SFM equations. In the limiting case of very high birefringence, as would be required for a potential THz source, a simple algebraic relation is derived for the spin relaxation rate in terms of other parameters. Hence we find that the range of spin relaxation rates to achieve THz oscillations is very limited. The relative simplicity of the present approach thus offers a rapid, intuitive and convenient route to study the dynamics of spin-VCSELs. [ABSTRACT FROM AUTHOR]

Metal halide perovskites are promising materials for optoelectronic and photonic applications ranging from photovoltaics to laser devices. However, current perovskite devices are constrained to simple low‐dimensional structures suffering from limited design freedom and holding up performance improvement and functionality upgrades. Here, a micro‐origami technique is developed to program 3D perovskite microarchitectures toward a new type of microcavity laser. The design flexibility in 3D supports not only outstanding laser performance such as low threshold, tunable output, and high stability but also yields new functionalities like 3D confined mode lasing and directional emission in, for example, laser "array‐in‐array" systems. The results represent a significant step forward toward programmable microarchitectures that take perovskite optoelectronics and photonics into the 3D era. [ABSTRACT FROM AUTHOR]

Topological insulator lasers are arrays of semiconductor lasers that exploit fundamental features of topology to force all emitters to act as a single coherent laser. In this study, we demonstrate a topological insulator vertical-cavity surface-emitting laser (VCSEL) array. Each VCSEL emits vertically, but the in-plane coupling between emitters in the topological-crystalline platform facilitates coherent emission of the whole array. Our topological VCSEL array emits at a single frequency and displays interference, highlighting that the emitters are mutually coherent. Our experiments exemplify the power of topological transport of light: The light spends most of its time oscillating vertically, but the small in-plane coupling is sufficient to force the array of individual emitters to act as a single laser. [ABSTRACT FROM AUTHOR]

Selecting and tuning modes are useful in ultrasonic guided wave non-destructive testing (NDT) since certain modes at various center frequencies are sensitive to specific types of defects. Ideally one should be able to select both the mode and the center frequency of the launched waves. We demonstrated that an affordable laser diode array can selectively launch either the S0 or A0 ultrasonic wave mode at a chosen center frequency into a polymer plate. A fiber-coupled diode array (4 elements) illuminated a 2 mm thick acrylic plate. A predetermined time delay matching the selected mode and frequency was employed between the output of the elements. The generated ultrasound was detected by a 215 kHz piezo receiver. Our results imply that this array permits non-contacting guided wave ultrasonic NDT. The solution is small, affordable, and robust in comparison to conventional pulsed lasers. In addition, it does not require experienced operators. [ABSTRACT FROM AUTHOR]

A universal approach is demonstrated for realizing dual‐wavelength lasing in organic core–shell structured microlaser arrays, which show great promise in serving as all‐color laser display panels. By alternately printing hydrophilic and hydrophobic laser dye solutions on preprocessed substrates, precisely patterned core–shell heterostructure arrays were obtained. The spatially separated core and shell independently function as optical resonators to support dual‐wavelength tunable lasing in each heterostructure. Such a general method enables to flexibly control the lasing wavelength of the core–shell microlasers across a wide spectral range by systematically designing the gain media. Using as‐prepared microlaser arrays as display panels, full‐color laser displays were achieved with a color gamut much larger than that of standard RGB space. These results provide insights for design concepts and device construction for novel optoelectronic applications. [ABSTRACT FROM AUTHOR]

A newly-developed normal mode model of laser dynamics in a generalised array of waveguides is applied to extend the spin-flip model (SFM) to pairs of evanescently-coupled spin-VCSELS. The effect of high birefringence is explored, revealing new dynamics and regions of bistability. It is shown that optical switching of the polarisation states of the lasers may be controlled through the optical pump and that, under certain conditions, the polarisation of one laser may be switched by controlling the intensity and polarisation in the other. [ABSTRACT FROM AUTHOR]

The quest to explore new techniques for the manipulation of topological states simultaneously promotes a deeper understanding of topological physics and is essential in identifying new ways to harness their unique features. Here, we examine the potential of supersymmetric transformations to systematically address, alter and reconfigure the topological properties of a system. To this end, we theoretically and experimentally study the changes that topologically protected states in photonic lattices undergo as supersymmetric transformations are applied to their host system. In particular, we show how supersymmetry-induced phase transitions can selectively suspend and re-establish the topological protection of specific states. Furthermore, we reveal how understanding the interplay between internal symmetries and the symmetry constraints of supersymmetric transformations provides a roadmap to directly access the desirable topological properties of a system. Our findings pave the way for establishing supersymmetry-inspired techniques as a powerful and versatile tool for topological state engineering. Established to explain high-energy particle physics, supersymmetry has since been invoked to describe the interplay between symmetry and topology in numerous fields. Here, supersymmetric transformations are shown theoretically and experimentally to destroy and restore topology in a photonic crystal. [ABSTRACT FROM AUTHOR]

Neuromorphic computing has received considerable attention as promising alternatives to classical von Neumann computing architectures. An attractive concept in this field is reservoir computing which is based on coupled non-linear elements to enable for instance ultra-fast pattern recognition. We focus on the development of microlasers in a dense regular array for the implementation of photonic reservoir computing based on the diffractive coupling. The coupling relies on injection locking of microlasers and sets stringent requirements on the spectral homogeneity of the array, which needs to be on the order of the achievable locking range. We realize GaAs/AlGaAs micropillar arrays with InGaAs quantum dots as active medium. To achieve the high spectral homogeneity on the order of 100 μeV, as determined by injection locking experiments, the emission energy of each individual micropillar is adjusted to compensate for local inhomogeneities of order ∼1.3 meV in the underlying microcavity structure. The realized micropillar arrays have a spectral inhomogeneity as low as 190 μeV for an 8 × 8 array and down to 118 μeV for a 5 × 5 sub-array. The arrays have high potential to enable the implementation of powerful photonic reservoir computing, which can be extended to a reservoir of hundreds of microlasers in the future. [ABSTRACT FROM AUTHOR]

Lasers emitting mid-infrared (MIR) beams have become indispensable for spectroscopy, free space communication or remote security measures. To the one of the most promising families of the lasers suitable for these applications certainly belongs a group of the Quantum Cascade Lasers (QCL). However, among the conditions they must satisfy there is a high enough radiance of the beam they emit. Radiance depends in a complicated way on the laser output power and optical quality of the laser beam. This paper has been devoted to a description and a short analysis of the factors that decide about radiance of so far developed QCLs. Literature concerning both single devices and QCL arrays operating in beam combining systems have been examined and results described. The survey may be useful for estimation of how far the QCLs have come of age. [ABSTRACT FROM AUTHOR]

Abstract Axicons are widely used in many applications because of their unique optical characteristics. In this paper, a new method for measuring the base angle of an axicon lens based on auto-collimation optical path is presented. When a laser beam is vertically incident on the flat surface of an axicon lens, it deflects after transmission. Auto-collimation is achieved when the transmitted light is reflected by a parallel plate. By recording the deflection angle of the parallel plate before and after the axicon lens is placed in the experimental configuration, the base angle of the axicon lens can be computed. A preliminary experimental validation is presented with a 20°axicon lens. The measurement accuracy of the presented method can be better than 10 arcseconds. [ABSTRACT FROM AUTHOR]

Coherently coupled laser arrays can be described by the temporal coupled mode theory in which the array modal behavior can be classified according to the coupling matrix, M ¯ ¯ . Accounting for a nonuniform gain/loss distribution in a laser array makes M ¯ ¯ a non-Hermitian matrix, and experimentally we find phase-front tuning (beam steering) of the coherent supermode as a result of the non-Hermiticity. We report the experimental characterization of the supermodes in coherently coupled vertical cavity surface emitting laser diode arrays and demonstrate control of non-Hermiticity by spatially varying injection currents. Exceptional points are identified in these electrically injected microcavity diode arrays. [ABSTRACT FROM AUTHOR]

Scaling up the radiance of coupled laser arrays has been a long-standing challenge in photonics. In this study, we demonstrate that notions from supersymmetry—a theoretical framework developed in high-energy physics—can be strategically used in optics to address this problem. In this regard, a supersymmetric laser array is realized that is capable of emitting exclusively in its fundamental transverse mode in a stable manner. Our results not only pave the way toward devising new schemes for scaling up radiance in integrated lasers, but also, on a more fundamental level, could shed light on the intriguing synergy between non-Hermiticity and supersymmetry. [ABSTRACT FROM AUTHOR]

A general model for the dynamics of arrays of coupled spin-polarised lasers is derived. The general model is able to deal with waveguides of any geometry with any number of supported normal modes. A unique feature of the model is that it allows for independent polarisation of the pumping in each laser. The particular geometry is shown to be introduced via ’overlap factors’, which are a generalisation of the optical confinement factor. These factors play an important role in determining the laser dynamics. The model is specialised to the case of a general double-guided structure, which is shown to reduce to both the spin flip model in a single cavity and the coupled mode model for a pair of guides in the appropriate limit. This is applied to the particular case of a circular-guide laser pair, which is analysed and simulated numerically. It is found that increasing the ellipticity of the pumping tends to reduce the region of instability in the plane of pumping strength versus guide separation.

We present the fabrication of a low-cost multiwavelength laser array monolithically integrated with a passive optical combiner for optical line terminals (OLTs) in wavelength-division multiplexing (WDM) passive optical networks (PONs). By combining the upper separate confinement heterostructure layer selective area growth technique and the bundle integrated guide technique, both multiwavelength emission with highly uniform spacing and low-loss passive-waveguide material can be obtained in a single metal-organic chemical vapor deposition (MOCVD) growth step, which greatly simplifies the fabrication of the device. A prototype laser array, which has four distributed feedback (DFB) laser elements and a multimode interference coupler as combiner, is successfully fabricated. The shallow ridge structure of the DFB lasers and the deep ridge structure of the passive waveguides are obtained by a single dry etching step, which further eases the device fabrication. The properties of the device are measured and discussed. The results indicate that our method is promising for fabricating cost-effective OLT light sources for WDM-PONs.

This paper numerically investigates the relative intensity noise of quantum dot lasers through a rate equation model taking into account both the spontaneous emission and carrier contributions. In particular, results show that the carrier noise originating from the ground and excited states significantly enhances the relative intensity noise of the laser, while that from the carrier reservoir does not. Simulations also point out that a large energy interval between the quantum confined levels is more suitable for low-intensity noise operation due to the reduced contribution from the carrier noise in the excited state. Finally, the carrier noise is found to have little impact on the frequency noise, thus being negligible for the investigation of the spectral linewidth. Overall, this paper is useful for designing low-noise quantum dot oscillators for high-speed communications, optical frequency combs, and radar applications. [ABSTRACT FROM AUTHOR]

We demonstrate electrically controlled supermode switching and beam steering in separate-contact phased vertical cavity surface emitting laser arrays based on proton implantation. The mode switching between out-of-phase and in-phase mode was successfully achieved via controlling the injected currents. The beam steering in two directions is continuous and controllable by proper adjustment of driving currents. The properties of near-field, far-field, optical power and spectra under different currents are analyzed detailedly. [ABSTRACT FROM AUTHOR]

We investigate the influences of ridge-waveguide shape and width on performances of InP-based coupled ridge waveguide laser arrays emitting at $2.1~\mu \text{m}$. Four devices with different shapes and widths of ridge elements are fabricated. The trapezoid ridges reduce the optical losses at regions between ridge elements in the trapezoid devices, thus enhances the optical coupling between ridge elements and lead to larger coherent output powers compared with the rectangular ones. Meanwhile, narrower ridges with the same shape give a stronger optical confinement to the lateral modes in every single ridge and improve the overall modal and far-field characteristics of the device. The results show that the trapezoid and narrower ridges can lead to a comprehensive improvement in the performances of the coupled ridge waveguide laser arrays emitting at $2.1~\mu \text{m}$. [ABSTRACT FROM AUTHOR]

We study the laser arrays which are constructed by partially coherent beams with multi-Gaussian correlation function, i.e., circular, rectangular and elliptical multi-Gaussian Schell-model (MGSM) beam arrays. Analytical propagation formulas for circular, rectangular and elliptical MGSM beam arrays through a stigmatic ABCD optical system and in turbulent atmosphere are derived, with which the propagation properties of such laser arrays may be easily determined. It is found that in the near field, the irradiance distributions of circular, rectangular and elliptical MGSM beam arrays are mainly controlled by the distribution of beam arrays in the source plane. In the far field, the irradiance distributions of circular, rectangular and elliptical MGSM beam arrays in free space are determined by their correlation functions respectively; while in turbulent atmosphere, the correlation functions and turbulent atmosphere all influence the irradiance distributions, especially after enough long distance propagation, the turbulent atmosphere may change the irradiance distributions from non-circular symmetry to circular symmetry. [ABSTRACT FROM AUTHOR]

The thermal stress due to the thermal expansion mismatch could induce crystallographic defects such as buckling and cracking and degrade device performance. In this paper, the thermal stress distribution in a laser array structure selectively grown on V-groove-patterned Si substrates was investigated by two-dimension finite-element method. Surprisingly, unexpected results are observed that the top of the InGaAs active layer and the most region of the InP cap layer are in compression, which is far different from the thermal stress distribution in planar structures. Two mechanisms have been proposed and modeled to explain the difference—(i) the width of uncoalesced layers is smaller than that of the Si substrate, which causes thermal stress to change in epitaxial layers, and (ii) thermal stress in the InGaAs and InP layers is affected by the V-groove structure. The results show that whether or not the epitaxial layers are coalesced has significant effect on the thermal stress distribution. The effect of the height of the V-groove, the height and the width of the SiO2 mask on the thermal stress distribution was also studied. It is found that the height of V-groove and the height of SiO2 mask play a critical role in the stress distribution. These findings are useful for the optimal designs for the laser array and provide an important step towards the realization of photonic integration circuits on silicon. [ABSTRACT FROM AUTHOR]

A nonlinear optical approach to generate a localized hollow laser beam and its array using crossed nonlinear ZnSe crystals is proposed. We calculate the intensity distributions of the hollow beam and its propagating properties in free space, and study the dependences of the dark spot size of the hollow beam on the incident beam waist radius and the crystal length. Our studies show that the longitudinal size of the hollow beam can be reduced by ∼ 660 times than that generated by a single nonlinear crystal. Such laser beam with a dark hollow region and a large intensity gradient can be used to trap cold neutral atoms, molecules and microscopic particles. [ABSTRACT FROM AUTHOR]

Abstract: Stable and phase‐locked emission in an extended topological supermode of coupled laser arrays, based on concepts of non‐Hermitian and topological photonics, is theoretically suggested. A non‐Hermitian Su–Schrieffer–Heeger chain of coupled microring resonators is considered, and it is shown that application of a synthetic imaginary gauge field via auxiliary passive microrings leads to all supermodes of the chain, except one, to become edge states. The only extended supermode, that retains some topological protection, can stably oscillate suppressing all other non‐topological edge supermodes. Numerical simulations based on a rate equation model of the semiconductor laser arrays confirm stable anti‐phase laser emission in the extended topological supermode and the role of the synthetic gauge field to enhance laser stability. [ABSTRACT FROM AUTHOR]

High power diode lasers are applied in many different areas, including surface modification, welding and cutting. It is an important technical trend in laser processing of metals in the future. This paper aims to analyze the impact of the shape and homogeneity of the focal spot of the diode laser on surface modification. A focusing system using the triplet lenses for a direct output diode laser which can be used to eliminate coma aberrations is studied. A rectangular stripe with an aspect ratio from 8:1 to 25:1 is obtained, in which the power is homogeneously distributed along the fast axis, the power is 1117.6 W and the peak power intensity is 1.1587 × 10 6  W/cm 2 . This paper also presents a homogeneous focusing system by use of a Fresnel lens, in which the incident beam size is 40 × 40 mm 2 , the focal length is 380 mm, and the dimension of the obtained focal spot is 2 × 10 mm 2 . When the divergence angle of the incident light is in the range of 12.5–20 mrad and the pitch is 1 mm, the obtained homogeneity in the focal spot is the optimum (about 95.22%). Experimental results show that the measured focal spot size is 2.04 × 10.39 mm 2 . This research presents a novel design of homogeneous focusing systems for high power diode lasers. [ABSTRACT FROM AUTHOR]

Arrays of coupled semiconductor lasers are systems possessing complex dynamical behavior and are of major interest in photonics and laser science. Dynamical instabilities, arising from supermode competition and slow carrier dynamics, are known to prevent stable phase locking in a wide range of parameter space, requiring special methods to realize stable laser operation. Inspired by recent concepts of parity-time ( P T ) and non-Hermitian photonics, in this work, we consider non-Hermitian coupling engineering in laser arrays in a ring geometry and show, both analytically and numerically, that non-Hermitian coupling can help to mitigate the onset of dynamical laser instabilities. In particular, we consider in detail two kinds of nearest-neighbor non-Hermitian couplings: symmetric but complex mode coupling (type-I non-Hermitian coupling) and asymmetric mode coupling (type-II non-Hermitian coupling). Suppression of dynamical instabilities can be realized in both coupling schemes, resulting in stable phase-locking laser emission with the lasers emitting in phase (for type-I coupling) or with π/2 phase gradient (for type-II coupling), resulting in a vortex far-field beam. In type-II non-Hermitian coupling, chirality induced by asymmetric mode coupling enables laser phase locking even in the presence of moderate disorder in the resonance frequencies of the lasers. [ABSTRACT FROM AUTHOR]

Based on the spatial power spectrum of the refractive index of ocean water, we derive analytical expressions for the effective radius of curvature and Rayleigh length of partially-coherent Hermite-Gaussian linear array (PCHGA) beams propagating through oceanic turbulence. In addition, we discuss theoretically and analyze numerically the influence of oceanic turbulence and array parameters. The effective radius of curvature and Rayleigh length of PCHGA beams increase with the relative strength of temperature and salinity fluctuations, the rate of dissipation of turbulent kinetic energy per unit mass of fluid, the array beam number, beam order, and relative separation distance, but decrease with the increase in the rate of dissipation of the mean-square temperature. The analysis provided here will help to understand the propagation of array beams through ocean turbulence. [ABSTRACT FROM AUTHOR]

Concentrating light at the deep subwavelength scale by utilizing plasmonic effects has been reported in various optoelectronic devices with intriguing phenomena and functionality. Plasmonic waveguides with a planar structure exhibit a two-dimensional degree of freedom for the surface plasmon; the degree of freedom can be further reduced by utilizing metallic nanostructures or nanoparticles for surface plasmon resonance. Reduction leads to different lightwave confinement capabilities, which can be utilized to construct plasmonic nanolaser cavities. However, most theoretical and experimental research efforts have focused on planar surface plasmon polariton (SPP) nanolasers. In this study, we combined nanometallic structures intersecting with ZnO nanowires and realized the first laser emission based on pseudowedge SPP waveguides. Relative to current plasmonic nanolasers, the pseudowedge plasmonic lasers reported in our study exhibit extremely small mode volumes, high group indices, high spontaneous emission factors, and high Purell factors beneficial for the strong interaction between light and matter. Furthermore, we demonstrated that compact plasmonic laser arrays can be constructed, which could benefit integrated plasmonic circuits. [ABSTRACT FROM AUTHOR]

We present an improved scheme for coherent beam combination using a type of non-separable phase-controlled Dammann grating (NPDG), which is capable of generating multiple equal-intensity diffraction orders with good uniformity and high efficiency in the far field. Compared with conventional separable two-dimensional (2D) Dammann gratings, the efficiency of such gratings is significantly improved around 10% due to the non-separable structure. Such improvement in the diffraction efficiency is of high significance for coherent laser combination. Furthermore, the phases of those diffraction orders for this type of gratings are only two-valued in the far field, which leads to a great simplification of phase matching during the procedure of coherent beam combination. As an example, a 5 × 5 NPDG with efficiency of 73.6% is theoretically designed and a NPDG sample with efficiency as high as 66.8% is experimentally fabricated by lithography and wet-etching techniques. Also, we implemented further a proof-of-principle experiment for coherent beam combination based on the 5 × 5 NPDG sample, and the results show that the combining efficiency is as high as 65.7%. [ABSTRACT FROM AUTHOR]

We present a novel array of electroabsorption modulated lasers as compact and low-cost single-chip solution for future 200 Gb/s transmitters. The array is designed for high optical output power with semiconductor optical amplifiers at the front side of the chip. A common InGaAlAs-MQW active layer structure allows for simple and cost-effective monolithic integration. On chip RF transmission lines are implemented to bring all electrical contacts to the rear side of the array-chip which supports packaging with short wire bonds. The array operates at four different wavelengths spanning over 7.5nm in the L-band. Uniformity of each wavelength channel is experimentally proven regarding modulation bandwidth >30 GHz, extinction ratio >7 dB, and output power up to 8 dBm. The influence of the semiconducting optical amplifiers on signal quality is investigated by back to back bit error ratio measurements. In transmission experiments over standard single mode fiber links, the array's performance at 4 X 56 GBd NRZ and 4 X 28 GBd PAM4 is demonstrated and the arrays capability for up to 7 km transmission in case of PAM4 signaling is shown. [ABSTRACT FROM AUTHOR]

We present recent progress on the development of monolithic, broadband, widely tunable midinfrared quantum cascade lasers. First, we show a broadband midinfrared laser gain realized by a heterogeneous quantum cascade laser based on a strain balanced composite well design of Al0.63In0.37As/Ga0.35In0.65As/ Ga0.47In0.53As. Single mode emission between 5.9 and 10.9 µm under pulsed mode operation was realized from a distributed feedback laser array, which exhibited a flat current threshold across the spectral range. Using the broadband wafer, a monolithic tuning between 6.2 and 9.1 µm was demonstrated from a beam combined sampled grating distributed feedback laser array. The tunable laser was utilized for a fast sensing of methane under pulsed operation. Transmission spectra were obtained without any moving parts, which showed excellent agreement to a standard measurement made by a Fourier transform infrared spectrometer. [ABSTRACT FROM AUTHOR]

The high accuracy of lasing wavelength spacing is one of the key requirements of a distributed feedback (DFB) semiconductor laser array. However, the nonuniformity of the wavelength spacing is increasingly deteriorating with the increase in the channel number in the laser array. In this paper, theoretical study was made to investigate the effects of sampling pattern deviation and seed grating, as well as waveguide dispersion on the wavelength-spacing uniformity for multiwavelength DFB semiconductor laser arrays (MLAs) fabricated using the reconstruction equivalent chirp (REC) technique. A simple measurement method of dispersion for DFB semiconductor lasers based on the REC technique is also proposed. With the dispersion compensation being included in the sampling period design and small deviation in the seed grating period being guaranteed, a high-channel-count (16-channel) DFB laser array with precise channel spacing of 0.7944 nm/channel (design value of 0.80 nm/channel) was achieved in our experiment. It shows excellent channel-spacing uniformity, and most wavelength residuals are within ±0.10 nm.

Laser Desorption Ionization Mass Spectrometry (LDI MS), has grown in popularity solving the matrix interference problem that Matrix assisted Laser Desorption Ionization Mass Spectrometry (MALDI MS) faced. The silicon based nanostructure LDI platforms have manifested with hypes and spikes, yet have already started showing signs of premature decay or stagnation. Nanopost Array Laser Desorption Ionization Mass Spectrometry (NAPA LDI), the latest generation of the LDI variants has surfaced with an ability to overcome other LDI MS limitations. But, it is still confined within not more than tens of researchers. When MALDI MS has flourished inspite of the varied limitations; the slowing down of this technique inspite of no disclosed limitation, is what prompted this review. The current loss of enthusiasm with respect to this technique and the reasons behind the obvious lack of popularity inspite of this technique's versatility are speculated. [ABSTRACT FROM AUTHOR]

An interrogation system for large-capacity fiber-distributed sensing was proposed and implemented. The system is based on the time- and wavelength-division multiplexed method and ultraweak fiber Bragg grating (FBG) sensor arrays. A narrow-linewidth tunable light source consisting of a distributed feedback laser array is used, which can be directly modulated into nanosecond pulses with a wide tuning range. Theoretically, the system can achieve a demodulation of >10;000 gratings and the FBG can be placed closely. An experimental system was implemented and the performance of the established system was tested, including its wavelength demodulation, time-division multiplexing, and temperature-sensing characteristics. The prototype achieved 27-nm wavelength demodulation and successfully demodulated 10 ultraweak grating strings of the same wavelength. By rationally planning the grating network, we can evaluate from the experimental results that the prototype can achieve at least 220 grating demodulation. [ABSTRACT FROM AUTHOR]

Using an extended Huygens-Fresnel diffraction integral, we have derived analytical formulae that describe a partially coherent array of Gaussian beams passing through an optical target and going back along the entrance way in a turbulent atmosphere. These formulae include the light intensity distribution at the return place, as well as the light intensity distribution and the spatial correlation at the target place. Using numerical calculations, we have studied the effects of laser coherence length and turbulence strength on the interference fringe contrast and the spatial coherence degree at the target place, together with the light intensity distribution at the return place and the system operating range. We have found that the fringe contrast and the spatial coherence degree at the target place decrease with increasing turbulence strength and decreasing laser coherence length. Then the contrast of light intensity distribution at the return place decreases and the difficulties of identification of optical targets grow. The operating range can be as large as hundred kilometres under a weak-turbulence condition, decreasing rapidly to a kilometre level at strong turbulence. [ABSTRACT FROM AUTHOR]

To solve the problems with spraying over the inner wall of air-intake pipe, this paper introduces an algorithm of measurement path planning based on the spraying robot system and the laser displacement sensor technology. Scanning measurement path planning is the premise and basis of model construction and spray. Traditional methods, such as arc length extrapolation and polynomial are applicable only for the measurement of a plane curve with finite maximum curvature. Drawing references from existing method, this paper focuses on the pre-scanning measurement method for different types of cross-section curves. Algorithm simulation and model reconstruction show that this study solves the problem of collision avoidance for scanning measurement of the inner wall of air-intake pipe. [ABSTRACT FROM AUTHOR]

We show a phase-locked array of quantum cascade lasers with an intracavity spatial filter based on the Talbot effect. All the laser arrays show in-phase operation from the threshold current to full power current with a near-diffraction-limited divergence angle. The maximum power is just about 5 times that of a single-ridge laser for an eleven-laser array device and 3 times for a seven-laser array device. The structure was analyzed by using the multi-slit Fraunhofer diffraction theory, showing very good agreement with the experimental results. Considering the great modal selection ability, simple fabricating process, and potential for achieving continuous wave operation, this phase-locked array may be a hopeful solution to obtain higher coherent power. [ABSTRACT FROM AUTHOR]

Laser-based additive manufacturing has attracted much attention as a promising 3D printing method for metallic components in recent years. However, surface roughness of additive manufactured components has been considered as a challenge to achieve high performance. In this work, we demonstrate the capability of fiber laser in polishing rough surface of additive manufactured Ti-based alloys as Ti-6Al-4V and TC11. Both as-received surface and laser-polished surfaces as well as cross-section subsurfaces were analyzed carefully by White-Light Interference, Confocal Microscope, Focus Ion Beam, Scanning Electron Microscopy, Energy Dispersive Spectrometer, and X-ray Diffraction. Results revealed that as-received Ti-based alloys with surface roughness more than 5 µm could be reduce to less than 1 µm through laser polishing process. Moreover, microstructure, microhardness and wear resistance of laser-polished zone was investigated in order to examine the thermal effect of laser polishing processing on the substrate of additive manufactured Ti alloys. This proof-of-concept process has the potential to effectively improve the surface roughness of additive manufactured metallic alloy by local polishing method without damage to the substrate. [ABSTRACT FROM AUTHOR]

In this paper, we developed a 3-D thermal model of a modulator- and amplifier-integrated distributed feedback laser array with detailed heat sources based on finite element method. Thermoelectric cooler (TEC) power consumption in the laser array package was analyzed and we found that it was severe in high temperature environment. To reduce the TEC power consumption, circumstances of using different submount materials and using different stages of TECs were simulated. In hot environment, the laser array using an AlN-SiC two-stage submount has a decrease of 48% in the TEC power consumption comparing with an AlN-kovar submount. And the TEC power consumption can be reduced up to 39.7% by using a two-stage TEC instead of a single one. The thermal performance of the laser array can be improved by selecting proper submount materials and using suitable TECs. These results might be useful for optoelectronic device packaging with a similar thermal system. [ABSTRACT FROM AUTHOR]

In this paper the eigenmodes of finite length microring resonator arrays have been systematically studied, both analytically using temporal coupled mode theory (CMT), and numerically using two-dimensional finite element method (FEM). The method for obtaining the values of parameters appearing in simplified CMT model using results of FEM calculations is presented. Calculations were carried out by COMSOL FEM packages for a wide range of distances between the rings. The obtained results reveal that the rotational degeneracy is preserved for a wide range of interrings distances. It is shown how the eigenvalue spectrum depends on the number of cavities in the system. The differences for the cases of odd and even numbers of rings, and its implications on actual applications, are discussed in details. The central branch appearing in odd-number arrays plays significant role for the delay-lines and optical buffering applications. Based on the first order perturbation theory, an analytical expressions for the eigenfrequencies of arbitrary (finite) length linear array of microring resonators are derived. The analytical expressions describing eigenfrequencies are useful for determining positions of the maxima in transfer characteristics in microring arrays with external buses. [ABSTRACT FROM AUTHOR]

Based on the extended Huygens-Fresnel principle, the analytical expression for the cross-spectral density (CSD) function of the radial Gaussian-Schell-model array (RGSMA) beams propagating in oceanic turbulence is derived. Then, combined with the spatial power spectrum of oceanic turbulence, analytical formulas for the average intensity and the root-mean-square (rms) beam width of the RGSMA beams propagating in oceanic turbulence are obtained. The changes of the average intensity and the rms beam width with propagation distance z and three oceanic turbulence parameters, including temperature-salinity balance parameter w, mean square temperature dissipation rate $${\chi _{\text{T}}}$$ , and energy dissipation rate per unit mass $$\varepsilon$$ , are investigated in detail. The results have certain reference value for the propagation properties of the RGSMA beams in oceanic turbulence. [ABSTRACT FROM AUTHOR]