Narrow Divergence Research Articles

Directional emission with super narrow divergence from perforated elliptical microdisk

In this work, a perforated polymeric elliptical microcavity is investigated by using the finite difference time domain (FDTD) method, highly directional laser emission with a far-field divergence angle of 2.57°, which is achieved without spoiling Q much. Further simulation analyses reveal that the far-field profile is insensitive to the deformation parameter of the hole, demonstrating the device is robust. In addition, the position of the hole and deformation parameter of the elliptical microcavity is vital for optimizing the far-field profile. Our work has provided an effective way to achieve directional whispering gallery mode emission with super narrow divergence, which will be important in integrated optics, optical communication and biochemical sensing.

Reconfigurable plasma OAM vortex wave generated by reflective metasurfaces

In this paper, a planar OAM reconfigurable plasma reflective metasurface with size 30 × 30 cm2 is designed. It consists of the reconfigurable plasma metasurface reflector and a feed horn antenna. The phase distribution of the plasma reflective metasurface combines the OAM phase distribution and the beam focusing required phase distribution. The required phase shifting range is 360° which obtained by adjusting the plasma frequency with changing the applied DC biasing voltage for the argon gas. The advantages of the design are high gain 22.4 dBi, narrow divergence angle 5°, high purity, good stability, planar structure, and easy fabrication. Beam scanning using the reflective metasurface for l = 1 at (θ = φ = 0°), (θ = 10°, φ = 0°), (θ = 20°, φ = 0°) and (θ = 30°, φ = 0°) is demonstrated.

Switchable unidirectional emissions from hydrogel gratings with integrated carbon quantum dots

Directional emission of photoluminescence despite its incoherence is an attractive technique for light-emitting fields and nanophotonics. Optical metasurfaces provide a promising route for wavefront engineering at the subwavelength scale, enabling the feasibility of unidirectional emission. However, current directional emission strategies are mostly based on static metasurfaces, and it remains a challenge to achieve unidirectional emissions tuning with high performance. Here, we demonstrate quantum dots-hydrogel integrated gratings for actively switchable unidirectional emission with simultaneously a narrow divergence angle less than 1.5° and a large diffraction angle greater than 45°. We further demonstrate that the grating efficiency alteration leads to a more than 7-fold tuning of emission intensity at diffraction order due to the variation of hydrogel morphology subject to change in ambient humidity. Our proposed switchable emission strategy can promote technologies of active light-emitting devices for radiation control and optical imaging.

Mode selection and unidirectional emission in multiple-deformed microcavity through dynamic tunneling

Microcavity holds great promise in demonstrating coherent light sources and photonic circuits due to its superior properties such as high-quality factor, small mode volume, etc. Generally, the rotationally symmetric geometry of microcavity naturally makes its output beams isotropic, which is hard to efficiently collect the emissions. Though several solutions have been proposed to tackle this issue, for instance, boundary deformation, nanoparticle scattering, and mode coupling, at the cost of quality (Q)-factor degradation, large divergence angle of output beams, and complex designs, therefore, which more or less hinders the practical potential of microcavity. Herein, to examine the possibility of simultaneously achieving high-Q and unidirectional emission with narrow angular divergence, we employ a spirally deformed quadrupolar microcavity to manipulate the intracavity physics. Our numerical results show that the chaotic-to-regular tunneling and unstable manifolds synergistically dominate the chirality and the corresponding far-field patterns. The spiral implies sufficient backscattering onto the chaotic modes, which sequently breaks the balance of clockwise and counterclockwise waves and brings such non-equivalence into diamond modes without spoiling their Q-factors. Then strong chirality is formed in the chaotic microcavity that initially reduces the output beams. Meanwhile, the geometry deformation from pristine quadrupolar further alters the unstable manifolds, finally yielding highly unidirectional emission with narrower divergence angle (≤30°). As a result, mode selection and unidirectional emission are constructed simultaneously in the presented microcavity through a simple but robust method. This research is of great significance to the research of microcavity and the practical application of optical sensing and single-photon sources.

88×nm High-Efficiency Narrow Divergence Angle Laser Diodes With Coupled Waveguide Photonic Crystal

88x nm laser diodes with coupled waveguide photonic band crystal (CPBC) are designed and fabricated. By optimizing the optical confinement factor in the lightly doped coupled waveguide, the internal loss reduces to 0.52 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The CPBC lasers achieve maximum power conversion efficiency of 65.57% under a continuous wave (CW) mode condition at room temperature, which is the highest reported value to our knowledge at 88x nm. The corresponding vertical divergence angel is 19.8°.

Transverse Photonic Crystal Mode Engineering for Broad-Area Semiconductor Lasers With Narrow-Divergence Angles

Broad-area semiconductor lasers, coupled with asymmetric transverse photonic crystals (TPCs), are designed by the effective index method and the transfer matrix method. Due to the propagation constant of the fundamental mode lying in the forbidden band of the TPCs, but those of the high-order modes lying in the allowed band of the TPCs, the fundamental mode is mainly concentrated in the active ridge waveguide, while all the high-order modes extend into the lossy TPCs on both sides of the active ridge waveguide. Therefore, the fundamental mode possesses larger optical confinement factor than those of the high-order modes, and reaches the lasing threshold more easily, which is demonstrated by the single-lobe horizontal far-field pattern of the TPC broad-area laser under an injection current of 0.3 A near the threshold. The proposed TPC broad-area laser provides a new strategy of designing broad-area semiconductor lasers with narrow divergence angles.

Promotion of Specific Single-Transverse-Mode Beam Characteristics for GaSb-Based Narrow Ridge Waveguide Lasers via Customized Parameter Design

GaSb-based single-transverse-mode narrow ridge waveguide (RW) lasers with high power and simultaneous good beam quality have broad application prospects in the mid-infrared wavelength region. Yet its design and formation have not been investigated systematically, while the beam characteristics that affect their suitability for specific applications remain rarely analyzed and optimized. The present work addresses these issues by theoretically establishing a waveguide parameter domain that generalizes the overall possible combinations of ridge widths and etch depths that support single-transverse-mode operation for GaSb-based RW lasers. These results are applied to develop two distinct and representative waveguide designs derived from two proposed major optimization routes of model gain expansion and index-guiding enhancement. The designs were evaluated experimentally based on prototype 1-mm cavity-length RW lasers in the 1950 nm wavelength range, which were fabricated with waveguides having perpendicular ridge and smooth side-walls realized through optimized dry etching conditions. The model gain expanded RW laser design with a relatively shallow-etched (i.e., 1.55 upmum) and wide ridge (i.e., 7 upmum) yielded the highest single-transverse-mode power to date of 258 mW with a narrow lateral divergence angle of 11.1^circ full width at half maximum at 800 mA under room-temperature continuous-wave operation, which offers promising prospects in pumping and coupling applications. Meanwhile, the index-guiding enhanced RW laser design with a relatively deeply etched (i.e., 2.05 upmum) and narrow ridge (i.e., 4 upmum) provided a highly stable and nearly astigmatism-free fundamental mode emission with an excellent beam quality of M^2 factor around 1.5 over the entire operating current range, which is preferable for seeding external cavity applications and complex optical systems.

Towards optimization of photonic-crystal surface-emitting lasers via quantum annealing.

Photonic-crystal surface-emitting lasers (PCSELs), which utilize a two-dimensional (2D) optical resonance inside a photonic crystal for lasing, feature various outstanding functionalities such as single-mode high-power operation and arbitrary control of beam polarizations. Although most of the previous designs of PCSELs employ spatially uniform photonic crystals, it is expected that lasing performance can be further improved if it becomes possible to optimize the spatial distribution of photonic crystals. In this paper, we investigate the structural optimization of PCSELs via quantum annealing towards high-power, narrow-beam-divergence operation with linear polarization. The optimization of PCSELs is performed by the iteration of the following three steps: (1) time-dependent 3D coupled-wave analysis of lasing performance, (2) formulation of the lasing performance via a factorization machine, and (3) selection of optimal solution(s) via quantum annealing. By using this approach, we discover an advanced PCSEL with a non-uniform spatial distribution of the band-edge frequency and injection current, which simultaneously enables higher output power, a narrower divergence angle, and a higher linear polarization ratio than conventional uniform PCSELs. Our results potentially indicate the universal applicability of quantum annealing, which has been mainly applied to specific types of discrete optimization problems so far, for various physics and engineering problems in the field of smart manufacturing.

Wide-bandgap GaN-based watt-class photonic-crystal lasers

Short-wavelength (blue-violet-to-green) lasers with high power and high beam quality are required for various applications including the machining of difficult-to-process materials and high-brightness illuminations and displays. Promising light sources for such applications are wide-bandgap GaN-based photonic-crystal surface-emitting lasers (PCSELs), which are based on two-dimensional resonance in the photonic crystal. Developments of these devices have lagged behind those of longer-wavelength GaAs-based PCSELs, because device designs for achieving robust two-dimensional resonance and a nanofabrication process that avoids introducing disorders have remained elusive for wide-bandgap GaN-based materials. Here, we address these issues and successfully realize GaN-based PCSELs with high, watt-class (>1 W) output power and a circular, single-lobed beam with a very narrow (~0.2°) divergence angle at blue wavelengths. In addition, we demonstrate continuous-wave operation with a high output power (~320 mW) and a high beam quality (M2~1). Our results will enable the use of GaN-based PCSELs in the above-mentioned applications.

Efficient generation of a dual-polarized vortex wave with an ultrathin Huygens' metasurface.

In this paper, an ultrathin Huygens' metasurface is designed for generating an orbital angular momentum (OAM) beam. The Huygens' metasurface is a double-layered metallic structure on a single-layer PCB. Based on induced magnetism, the Huygens' metasurface achieves the abilities of available near-complete transmission phase shift around 28 GHz. According to the principle of vortex wave generation, a Huygens' metasurface is designed, implemented and measured. The simulated and measured results show that the dual-polarized OAM transmitted waves with the mode l = 1 can be efficiently generated on a double-layered Huygens' metasurface around 28 GHz. The measured peak gain is 23.4 dBi at 28 GHz, and the divergence angle is 3.5°. Compared with conventional configurations of OAM transmitted beam generation, this configuration has the advantages of high gain, narrow divergence angle, and low assembly cost. This investigation will provide a new perspective for engineering application of OAM beams.

High Power Conversion Efficiency Narrow Divergence Angle Photonic Crystal Laser Diodes

9xx nm laser diodes (LDs) with aluminum component continuous gradient photonic band crystal (CCG-PBC) waveguide structure are designed and fabricated. The simulation results indicate that the CCG-PBC structure can significantly reduce the heterojunction barrier and carrier accumulation at the interface of the conventional PBC structure. We demonstrate that the LD with CCG-PBC structure can achieve a narrow vertical divergence angle of 16.2° at full width at half maximum, and the divergence angle changes with current not more than 0.5°. Meanwhile, the power conversion efficiency (PCE) of the narrow divergence angle LD can reach 66.7%, and the PCE at 20 W is still over 60%. After optimizing the coating reflectivity and cavity length of the CCG-PBC structure LD, the peak PCE and power are 71.5% and 17.2 W at 25 °C and 77.7% and 23.3 W at 0 °C, respectively, which are optimal results for any edge-emitting LD. Our device provides valuable guidance for researching high power and high efficiency narrow vertical divergence angle LDs.

Narrow Emission of Blue GaN-Based Vertical-Cavity Surface-Emitting Lasers With a Curved Mirror

We report a narrow divergence angle in a blue gallium-nitride-based visible vertical-cavity surface-emitting laser (GaN-VCSEL) with a curved mirror. This device exhibited continuous-wave operation at a wavelength of 447.9 nm. The full-width at half-maximum divergence angle of the 8 μm-aperture VCSEL was 3.9° when the device was operated at a current of 1.2 × Ith, where Ith is the threshold current. In this type of cavity, the radius of curvature (ROC) of the curved mirror determines the near-field pattern (NPF) and far-field pattern (FFP). The authors fabricated devices having ROC up to 988 μm, which is more than 10 times greater than the ROC of the mirror used in the previously reported structures, allowing this narrow emission. The I–L characteristics showed that the Ith value increased with increasing ROC. The present study investigates the mechanism behind this tendency in detail.

Transverse photonic crystal semiconductor laser arrays

Transverse photonic crystal (TPC) laser arrays are designed by effective index method and transfer matrix method, and fabricated by the process of standard photolithography. The fundamental supermode of the TPC laser array possesses a larger optical confinement factor in the active region than those of high-order supermodes, because the propagation constant of the fundamental supermode lies in the forbidden band of the TPC while all the propagation constants of the high-order supermodes lie in the allowed band of the TPC. Therefore, the fundamental supermode can lase firstly near the threshold when the laser is injected with currents. The fabricated TPC laser achieves a single-lobe horizontal far-field pattern under an injection current of 0.3 A, and the corresponding near-field pattern is well confined to the center five waveguides injected with currents. The TPC semiconductor laser array may be a good candidate for optical sources with narrow horizontal divergence angles.

Separated electrodes for the enhancement of high-speed data transmission in vertical-cavity surface-emitting laser arrays.

In this work, a novel design for the electrodes in a near quasi-single-mode (QSM) vertical-cavity surface-emitting laser (VCSEL) array with Zn-diffusion apertures inside is demonstrated to produce an effective improvement in the high-speed data transmission performance. By separating the electrodes in a compact 2×2 coupled VCSEL array into two parts, one for pure dc current injection and the other for large ac signal modulation, a significant enhancement in the high-speed data transmission performance can be observed. Compared with the single electrode reference, which parallels 4 VCSEL units in the array, the demonstrated array with its separated electrode design exhibits greater dampening of electrical-optical (E-O) frequency response and a larger 3-dB E-O bandwidth (19 vs. 15 GHz) under the same amount of total bias current (20 mA). Moreover, this significant improvement in dynamic performance does not come at the cost of any degradation in the static performance in terms of the maximum near QSM optical output power (17 mW @ 20 mA) and the Gaussian-like optical far-field pattern which has a narrow divergence angle (full-width half maximum (FWHM): 10° at 20 mA). The advantages of the separated electrode design lead to a much better quality of 32 Gbit/sec eye-opening as compared to that of the reference device (jitter: 1.5 vs. 2.8 ps) and error-free 32 Gbit/sec transmissions over a 500 m multi-mode fiber has been achieved under a moderate total bias current of 20 mA.

Electrically injected supersymmetric semiconductor lasers with narrow vertical divergence angle.

Electrically injected supersymmetric (SUSY) semiconductor lasers are proposed and fabricated. Two successive SUSY transformations are applied to the main array arranged along the direction of epitaxial growth, which can remove the propagation constants of the fundamental mode and the leaky mode of the main array from the superpartner while keeping those of other high-order modes. The SUSY laser possesses an excellent mode discrimination and favors the lasing of the fundamental mode. The fabricated SUSY laser can emit light with a single-lobe vertical far-field pattern with the full width at half maximum of 16.87° under an injection current of 1.4 A.

‘Her own and her children's share’: luck, misogyny and imaginative resistance in twentieth-century Irish folklore

AbstractIn twentieth-century Irish folklore, luck had much to do with women. While women were rarely seen as legitimate possessors of good fortune, luck was frequently perceived as being communicated through women's bodies and lost as a result of their actions. A caul, an intact amniotic membrane over a newborn's head and by-product of a pregnant woman's body, was believed to convey luck and health to either the mother or the child but not to both. The emphasis in this tradition on women's corporeality cast women and their maternal by-products as appropriable familial and communal resources. This and additional lore reveal that women were constructed as dangerous, ‘object-like others’ whose mere presence could threaten men's safety. Twentieth-century Ireland's folk and political cultures each operated within frameworks of supporting ideological systems. Despite being easily distinguishable in articulation, these cultures were frequently in concert with one another, especially relating to prescriptive gender roles. In numerous instances, lore about luck bolstered legislative, social and religious policies of the Irish Free State and the early Irish Republic regarding women. However, narrow divergences allowed women limited space to contest gender hierarchy in folk communities. Some women found opportunities for subversion in the very cultural fabric that restricted them, resorting to imaginative resistance to reject and counter misogynist discourse and assert female subjectivity.

Ka‐band 1‐bit ultra‐thin reflective metasurface for generating vortex beams based on wideband polarization converter

A 1-bit ultra-thin (~λ/12) reflective metasurface is proposed to generate vortex beams, whose mechanism of realizing 1-bit phase quantization is based on wideband polarization converter (PC). A diamond-shaped patch is studied as the unit cell of PC, which has the properties of high polarization conversion transmission efficiency, simple structure, wideband, and ultra-thin. By employing the proposed PC and its mirror image, a stable 180° phase shift is realized over the bandwidth of 18–36 GHz. Phase distributions of vortex beams with different modes and the corresponding radiation patterns are calculated and simulated. Reflective metasurface employing the proposed unit cells are arranged according to the calculated phase distribution, and the microstrip quasi-Yagi antenna is used as the feed antenna to illuminate the metasurface to generate vortex electromagnetic waves. A prototype is fabricated and measured, verifying that vortex beams can be generated flexibly by the proposed design. The measured gain of the vortex beams reaches to 19.5 dBi with the narrow divergence angle of ±4°. The proposed 1-bit measurface is compact, ultra-thin and offers a new possibilities for vortex beams generation.

Study of High Polarized Nanostructure Light-Emitting Diode

In this study, we investigated the characteristic difference between the two different configurations of the three-dimensional shell–core nanorod LED. We achieve a degree of polarization of 0.545 for tip-free core–shell nanorod LED and 0.188 for tip core–shell nanorod LED by combining the three-dimensional (3D) structure LED with photonic crystal. The ability of low symmetric modes generated by photonic crystals to enhance degree of polarization has been demonstrated through simulations of photonic crystals. In addition, light confinement in GaN-based nanorod structures is induced by total internal reflection at the GaN/air interface. The combination of 3D core–shell nanorod LED and photonic crystals cannot only produce a light source with a high degree of polarization, but also a narrow divergence angle up to 56°. These 3D LEDs may pave the way for future novel optoelectronic components.

Narrow vertical divergence 780 nm lasers with modulated refractive index of photonic crystal structure

Narrow vertical divergence lasers for the 780 nm wavelength based on step index photonic crystal (STIN PC) and graded index photonic crystal (GRIN PC) structure are investigated. The effects of GaAsP and InGaAlAs as quantum well materials on device performance are studied. The STIN PC structure realizes a low threshold current of 0.52 A and high output power of 4.75 W at 5 A, while the GRIN PC structure has lower resistance and vertical divergence angle of only 21°. The device performance of GaAsP as a quantum well material is overall better than that of InGaAlAs.

Beam Parameter Product Optimization for High Power SWIR Laser Diode Stack Fiber Coupling

An optimized setup for fiber optic injection of a kilowatt peak power laser diode stack emitting in the SWIR spectral range is proposed. Starting from a fast axis collimated (FAC) and slow axis collimated (SAC) 15 bars, 19 emitters off the shelf laser diode stack, the beam is transformed using spatial beam combining and polarization coupling. Both techniques integrated in a compact design enable to couple the kilowatt level beam into a standard 600 μm core, 0.22 numerical aperture (NA) multimode optical fiber. An application in the field of long range SWIR laser illuminator for gated viewing is presented. A comparison between two illuminators is realized both based on the same laser diode stack but one using beam parameter product (BPP) reduction and one without. It could be demonstrated that BPP reduction is the best way for efficient, narrow divergence and compact semi-conductor based laser illuminators design and realization. The global laser illuminator efficiency could be improved by 75% for the narrowest divergences thanks to this approach.