Polarization-stable single-mode 795†nm grating-coupled surface-emitting laser for quantum sensing.

We demonstrate a polarization-stable and single-mode grating-coupled surface-emitting laser (GCSEL) with high side-mode suppression ratio (SMSR) of ∼40 dB and orthogonal polarization suppression ratio (OPSR) of ∼25 dB around 795 nm. The fabricated devices have low threshold current of ∼4.8 mA and low electrical resistance of 53 Ω at 25 °C. Meanwhile, a low thermal resistance of ∼1 K/mW is achieved, which is comparable with that of the record of ever reported for vertical-cavity surface-emitting lasers (VCSELs). The far-field divergence angle of surface-emitting beam is ∼14.5°x14.7° at an injection current of 12 mA indicating a relatively good beam quality. Our results open what we believe is a new way to produce polarization-stable single-mode surface-emitting lasers with simple fabrication process. While the GCSEL is specifically designed for quantum sensing applications such as atomic clocks, magnetometers, and gyroscope, its performance in terms of low-power consumption, low thermal resistance, good beam qualities, and wafer-level testing are of particular interest for a wide range of applications.

Exploring the conformational dynamics and thermodynamics of EGFR S768I and G719X + S768I mutations in non-small cell lung cancer: An in silico approaches.

Non-small cell lung cancer (NSCLC) is often driven by mutations in the epidermal growth factor receptor (EGFR) gene. However, rare mutations such as G719X and S768I lack standard anti-EGFR targeted therapies. Understanding the structural differences between wild-type EGFR and these rare mutants is crucial for developing EGFR-targeted drugs. We performed a systematic analysis using molecular dynamics simulations, essential dynamics (ED), molecular mechanics Poisson-Boltzmann surface area, and free energy calculation methods to compare the kinetic properties, molecular motion, and free energy distribution between wild-type EGFR and the rare mutants' structures G719X-EGFR, S768I-EGFR, and G719X + S768I-EGFR. Our results showed that S768I-EGFR and G719X + S768I-EGFR have higher global and local conformational flexibility and lower thermal and global structural stability than WT-EGFR. ED analysis revealed different molecular motion patterns between S768I-EGFR, G719X + S768I-EGFR, and WT-EGFR. The A-loop and αC-helix, crucial structural elements related to the active state, showed a tendency toward active state development, providing a molecular mechanism explanation for NSCLC caused by EGFR S768I and EGFR G719C + S768I mutations. The present study may be helpful in the development of new EGFR-targeted drugs based on the structure of rare mutations. Our findings may aid in developing new targeted treatments for patients with EGFR S768I and EGFR G719X + S768I mutations.

Metasurface Enabled On-Chip Generation and Manipulation of Vector Beams from Vertical Cavity Surface-Emitting Lasers.

Metasurface polarization optics that consist of 2D array of birefringent nano-antennas have proven remarkable capabilities to generate and manipulate vectorial fields with subwavelength resolution and high efficiency. Integrating this new type of metasurface with the standard vertical cavity surface-emitting laser (VCSEL) platform enables an ultracompact and powerful solution to control both phase and polarization properties of the laser on a chip, which allows to structure a VCSEL into vector beams with on-demand wavefronts. Here, this concept is demonstrated by directly generating versatile vector beams from commercially available VCSELs through on-chip integration of high-index dielectric metasurfaces. Experimentally, the versatility of the approach for the development of vectorial VCSELs are validated by implementing a variety of functionalities, including directional emission of multibeam with specified polarizations, vectorial holographic display, and vector vortex beams generations. Notably, the proposed vectorial VCSELs integrated with a single layer of beam shaping metasurface bypass the requirements of multiple cascaded optical components, and thus have the potential to promote the advancements of ultracompact, lightweight, and scalable vector beams sources, enriching and expanding the applications of VCSELs in optical communications, laser manipulation and processing, information encryption, and quantum optics.

Extraction of silver losses at cryogenic temperatures through the optical characterization of silver-coated plasmonic nanolasers.

We report on the extraction of silver losses in the range 10 K-180 K by performing temperature-dependent micro-photoluminescence measurements in conjunction with numerical simulations on silver-coated nanolasers around near-infrared telecommunication wavelengths. By mapping changes in the quality factor of nanolasers into silver-loss variations, the imaginary part of silver permittivity is extracted at cryogenic temperatures. The latter is estimated to reach values an order of magnitude lower than room-temperature values. Temperature-dependent values for the thermo-optic coefficient of III-V semiconductors occupying the cavity are estimated as well. This data is missing from the literature and is crucial for precise device modeling. Our results can be useful for device designing, the theoretical validation of experimental observations as well as the evaluation of thermal effects in silver-coated nanophotonic structures.

Group Velocity Modulation and Light Field Focusing of the Edge States in Chirped Valley Graphene Plasmonic Metamaterials.

The valley degree of freedom, like the spin degree of freedom in spintronics, is regarded as a new information carrier, promoting the emerging valley photonics. Although there exist topologically protected valley edge states which are immune to optical backscattering caused by defects and sharp edges at the inverse valley Hall phase interfaces composed of ordinary optical dielectric materials, the dispersion and the frequency range of the edge states cannot be tuned once the geometrical parameters of the materials are determined. In this paper, we propose a chirped valley graphene plasmonic metamaterial waveguide composed of the valley graphene plasmonic metamaterials (VGPMs) with regularly varying chemical potentials while keeping the geometrical parameters constant. Due to the excellent tunability of graphene, the proposed waveguide supports group velocity modulation and zero group velocity of the edge states, where the light field of different frequencies focuses at different specific locations. The proposed structures may find significant applications in the fields of slow light, micro-nano-optics, topological plasmonics, and on-chip light manipulation.

Chiral graphene plasmonic Archimedes' spiral nanostructure with tunable circular dichroism and enhanced sensing performance.

Circular dichroism spectroscopy is frequently used to characterize the chiral biomolecules by measuring the absorption spectra contrast between the left-handed circularly polarized light and the right-handed circularly polarized light. Compared with biomolecules, chiral metal plasmonic nanostructures also produce a strong circular dichroism response in the range of near-infrared. However, due to the large damping rate, the non-adjustable resonant frequency of the conventional metals, the applications of chiral metal plasmonic nanostructures in the fields of photoelectric detection and chemical and biochemical sensing are restricted. Here, we present a chiral graphene plasmonic Archimedes' spiral nanostructure that displays a significant circular dichroism response under the excitation of two polarizations of circularly polarized light. By manipulating the material and geometric parameters of the Archimedes' spiral, the stronger circular dichroism responses and modulation of the resonant wavelength are achieved. The optimized plasmonic nanostructure has outstanding refractive index sensing performance, where the sensitivity and figure of merit reach 7000nm/RIU and 68.75, respectively. Our proposed chiral graphene plasmonic Archimedes' spiral nanostructure might find potential applications in the fields of optical detection and high performance of index sensing.

"Fast" Plasmons Propagating in Graphene Plasmonic Waveguides with Negative Index Metamaterial Claddings.

We propose the monolayer graphene plasmonic waveguide (MGPW), which is composed of graphene core sandwiched by two graphene metamaterial (GMM) claddings and investigate the properties of plasmonic modes propagating in the waveguide. The effective refraction index of the GMMs claddings takes negative (or positive) at the vicinity of the Dirac-like point in the band structure. We show that when the effective refraction index of the GMMs is positive, the plasmons travel forward in the MGPW with a positive group velocity (vg > 0, vp > 0). In contrast-for the negative refraction index GMM claddings-a negative group velocity of the fundamental mode (vg < 0, vp > 0) appears in the proposed waveguide structure when the core is sufficiently narrow. A forbidden band appears between the negative and positive group velocity regions, which is enhanced gradually as the width of the core increases. On the other hand, one can overcome this limitation and even make the forbidden band disappear by increasing the chemical potential difference between the nanodisks and the ambient graphene of the GMM claddings. The proposed structure offers a novel scheme of on-chip electromagnetic field and may find significant applications in the future high density plasmonic integrated circuit technique.

Multiple Fano Resonances with Tunable Electromagnetic Properties in Graphene Plasmonic Metamolecules.

Multiple Fano resonances (FRs) can be produced by destroying the symmetry of structure or adding additional nanoparticles without changing the spatial symmetry, which has been proved in noble metal structures. However, due to the disadvantages of low modulation depth, large damping rate, and broadband spectral responses, many resonance applications are limited. In this research paper, we propose a graphene plasmonic metamolecule (PMM) by adding an additional 12 nanodiscs around a graphene heptamer, where two Fano resonance modes with different wavelengths are observed in the extinction spectrum. The competition between the two FRs as well as the modulation depth of each FR is investigated by varying the materials and the geometrical parameters of the nanostructure. A simple trimer model, which emulates the radical distribution of the PMM, is employed to understand the electromagnetic field behaviors during the variation of the parameters. Our proposed graphene nanostructures might find significant applications in the fields of single molecule detection, chemical or biochemical sensing, and nanoantenna.

Metasurface-integrated vertical cavity surface-emitting lasers for programmable directional lasing emissions.

Vertical cavity surface-emitting lasers (VCSELs) have made indispensable contributions to the development of modern optoelectronic technologies. However, arbitrary beam shaping of VCSELs within a compact system has remained inaccessible until now. The emerging ultra-thin flat optical structures, namely metasurfaces, offer a powerful technique to manipulate electromagnetic fields with subwavelength spatial resolution. Here, we show that the monolithic integration of dielectric metasurfaces with VCSELs enables remarkable arbitrary control of the laser beam profiles, including self-collimation, Bessel and Vortex lasers, with high efficiency. Such wafer-level integration of metasurface through VCSEL-compatible technology simplifies the assembling process and preserves the high performance of the VCSELs. We envision that our approach can be implemented in various wide-field applications, such as optical fibre communications, laser printing, smartphones, optical sensing, face recognition, directional displays and ultra-compact light detection and ranging (LiDAR).

Nineteen-element in-phase coherent vertical-cavity surface-emitting laser array with low side lobe intensity.

We apply the antenna coherence theory in order to evaluate characteristic behavior of phase-coherent VCSEL arrays. Large 19-element phase-locked VCSEL arrays with a near-diffraction-limited beam were firstly realized using proton implantation technology. The central lobe intensity is about four times that of side lobes in far-field patterns. The angular full width at half maximum (FWHM) of the far field lobes is only 1.42 degrees. A good matching between theory and experiment opens new perspectives for optimizing devices.

A flexible control on electromagnetic behaviors of graphene oligomer by tuning chemical potential.

In this work, we demonstrate that the electromagnetic properties of graphene oligomer can be drastically modified by locally modifications of the chemical potentials. The chemical potential variations of different positions in graphene oligomer have different impacts on both extinction spectra and electromagnetic fields. The flexible tailoring of the localizations of the electromagnetic fields can be achieved by precisely adjusting the chemical potentials of the graphene nanodisks at corresponding positions. The proposed nanostructures in this work lead to the practical applications of graphene-based plasmonic devices such as nanosensing, light trapping and photodetection.

Dynamic tailoring of electromagnetic behaviors of graphene plasmonic oligomers by local chemical potential.

In the mid-infrared and terahertz (THz) regime, graphene supports tunable surface plasmon resonance (SPR) by controlling the chemical potential, which promotes light-matter interaction at the selected wavelength, showing exceptional promise for optoelectronic applications. In this article, we show that the electromagnetic (EM) response of graphene oligomers can be substantially modified by the modification of the local chemical potential, strengthening or reducing the intrinsic plasmonic modes. The effect mechanism is corroborated by a graphene nanocluster composed of 13 nanodisks with D6h symmetry; by transforming to D3h symmetry, the effect mechanism was retained and more available plasmonic resonance modes appeared. The intriguing properties open a new way to design nanodevices made of graphene oligomers with highly efficient photoresponse enhancement and tunable spectral selectivity for highly accurate photodetection.

Pseudospin Dependent One-Way Transmission in Graphene-Based Topological Plasmonic Crystals.

Originating from the investigation of condensed matter states, the concept of quantum Hall effect and quantum spin Hall effect (QSHE) has recently been expanded to other field of physics and engineering, e.g., photonics and phononics, giving rise to strikingly unconventional edge modes immune to scattering. Here, we present the plasmonic analog of QSHE in graphene plasmonic crystal (GPC) in mid-infrared frequencies. The band inversion occurs when deforming the honeycomb lattice GPCs, which further leads to the topological band gaps and pseudospin features of the edge states. By overlapping the band gaps with different topologies, we numerically simulated the pseudospin-dependent one-way propagation of edge states. The designed GPC may find potential applications in the fields of topological plasmonics and trigger the exploration of the technique of the pseudospin multiplexing in high-density nanophotonic integrated circuits.

Tailoring axial intensity of laser beams with a heart-shaped hole.

We demonstrated a simple heart-shaped hole to tailor the axial intensity of a collimated laser beam. This hole is transformed from a soft-boundary one, which avoids the difficulty in fabricating the soft-boundary mask designed by the apodization method, as well as the interference problem caused by the pixel structure of the spatial light modulator. When a collimated light passes through this hole, its axial intensity oscillates less than 11% within a certain distance, while the fluctuation after the circular aperture is up to 200%. We compared the propagation of beams after this hole and a circular aperture experimentally and theoretically. The results show that this hole is a useful tool to get the laser beam with uniform axial intensity.

High-efficiency terahertz devices based on cross-polarization converter.

Metasurface-based devices have been investigated intensively because of their attractive properties but these devices generally suffer from low efficiency. Here we demonstrate several high-efficiency terahertz (THz) devices based on cross-polarization converters that is composed of bilayer metasurface-based structures. The converter can transfer the polarization states of transmitted THz waves from the x-direction into the y-direction with an experimental conversion efficiency of 85%. This high-efficiency transfer mechanism is investigated in detail. Furthermore, this kind of devices can be fabricated easily. A THz metalens is designed and fabricated and its focusing and imaging properties are investigated experimentally. A pure phase THz hologram that can generate different images on different propagation planes is also designed and the image reconstruction capabilities of the phase holograms are demonstrated experimentally. The performance levels of all designed devices show excellent agreement between the theoretical expectations and the corresponding experimental results. This technology may pave the way towards practical applications of such metasurface devices.

Topologically protected edge states in graphene plasmonic crystals.

A two-dimensional graphene plasmonic crystal composed of periodically arranged graphene nanodisks is proposed. We show that the band topology effect due to inversion symmetry broken in the proposed plasmonic crystals is obtained by tuning the chemical potential of graphene nanodisks. Utilizing this kind of plasmonic crystal, we constructed N-shaped channels and realized topologically edged transmission within the band gap. Furthermore, topologically protected exterior boundary propagation, which is immune to backscattering, was also achieved by modifying the chemical potential of graphene nanodisks. The proposed graphene plasmonic crystals with ultracompact size are subject only to intrinsic material loss, which may find potential applications in the fields of topological plasmonics and high density nanophotonic integrated systems.

Investigation of beam splitter in a zero-refractive-index photonic crystal at the frequency of Dirac-like point.

The Dirac-like cone dispersion of the photonic crystal induced by the three-fold accidental degeneracy at the Brillouin center is calculated in this paper. Such photonic crystals can be mapped to zero-refractive-index materials at the vicinity of the Dirac-like point frequency, and utilized to construct beam splitter of high transmission efficiency. The splitting ratio is studied as a function of the position of the input/output waveguides. Furthermore, variant beam splitters with asymmetric structures, bulk defects, and some certain bending angles are numerically simulated. Finally, we show that 1 × 2 to 1 × N beam splitting can be realized with high transmission efficiency in such a zero-refractive-index photonic crystal at the frequency of Dirac-like point. The proposed structure could be a fundamental component of the high density photonic integrated circuit technique.

Optimization of the Fano Resonance Lineshape Based on Graphene Plasmonic Hexamer in Mid-Infrared Frequencies.

In this article, the lineshape of Fano-like resonance of graphene plasmonic oligomers is investigated as a function of the parameters of the nanostructures, such as disk size, chemical potential and electron momentum relaxation time in mid-infrared frequencies. Also, the mechanism of the optimization is discussed. Furthermore, the environmental index sensing effect of the proposed structure is revealed, and a figure of merit of 25.58 is achieved with the optimized graphene oligomer. The proposed nanostructure could find applications in the fields of chemical or biochemical sensing.