Optical Resonance Modes Research Articles

Side-mode suppression in ultraviolet quasi-semicircle microlaser cavity

We report a quasi-semicircle GaN ultraviolet microcavity laser. Poincaré map of the quasi-semicircle cavity shows periodic, quasi-periodic and chaotic optical trajectories. Finite-element-method optical near-field distribution patterns of the periodic optical modes agree with the optical loops in the quasi-semicircle cavity. Based on the numerical results, optically pumped lasing experiment shows that ultraviolet multimode lasing action from different optical resonance modes can be effectively stimulated at low pumping intensity in the quasi-semicircle GaN cavity, and the side-mode suppression phenomenon can be obtained at high pumping intensity. Because the possible period optical loops are quasi-periodic and unstable, the quasi-whispering-gallery mode lasing with higher quality factor prefer to dominate the lasing action under high pumping. The experimental and simulated lasing modes suggest that side-mode suppression phenomenon can be caused by the mode competition between quasi-whispering-gallery modes and other quasi-periodic modes.

Highly regular rosette-shaped cathodoluminescence in GaN self-assembled nanodisks and nanorods

Self-assembled GaN nanorods were grown by metal-organic chemical vapor deposition. A highly regular rosette-shaped cathodoluminescence pattern in the GaN nanorods is observed, where its origin is helpful to deepen the understanding of GaN nanorod growth. The pattern forms at the very early stages of nanorod growth, which consists of yellow luminescence at the edges and the non-luminous region at six vertices of the hexagon. To clarify its origin, we carried out detailed cathodoluminescence studies, electron microscopy studies and nanoscale secondary ion mass spectrometry at both the nanorod surface and cross-section. We found the pattern is not related to optical resonance modes or polarity inversion, which are commonly reported in GaN nanostructures. After chemical composition and strain analysis, we found higher carbon and nitrogen cluster concentration and large compressive strain at the pattern area. The pattern formation may relate to facet preferential distribution of non-radiative recombination centers related to excess carbon/nitrogen. This work provides an insight into strain distribution and defect-related emission in GaN nanorod, which is critical for future optoelectronic applications.

Devices with Whispering Gallery Mode Optical Resonators: Current State of Research and Prospects for their Application in Time and Frequency Metrology

The development of highly stable, narrow-band laser sources and oscillators producing sets of equidistant narrow optical spectral lines (so-called optical frequency combs) constitutes one of the most urgent tasks in the metrological support of time and frequency measurements. These devices are necessary for the transmission of frequency reference signals, as well as for use in mobile sources of time and frequency reference signals in optical and microwave spectral ranges. Such devices are also used in precision, ultra-high resolution spectroscopy. A promising direction for the development of highly stable, narrow-band lasers and generation of optical frequency combs (OFCs) is the use of miniature whispering gallery mode (WGM) optical resonators. Recently, the properties of such resonators have been actively studied along with technologies for their production. This article presents a review of the current state of research into the use of WGM optical resonators in time and frequency metrology. The types, advantages, and disadvantages of WGM resonators, as well as methods for generating various signals, specifically microwave signals, are described. Examples of existing laboratory setups used by Russian and foreign scientific groups are given. The authors examine prospects for the further use of WGM resonators.

Stimulated Raman Scattering in Ge Nanowires.

Investigating group-IV-based photonic components is a very active area of research with extensive interest in developing complementary metal-oxide-semiconductor (CMOS) compatible light sources. However, due to the indirect band gap of these materials, effective light-emitting diodes and lasers based on pure Ge or Si cannot be realized. In this context, there is considerable interest in developing group-IV based Raman lasers. Nevertheless, the low quantum yield of stimulated Raman scattering in Si and Ge requires large device footprints and high lasing thresholds. Consequently, the fabrication of integrated, energy-efficient Raman lasers is challenging. Here, we report the systematic investigation of stimulated Raman scattering (SRS) in Ge nanowires (NWs) and axial Al-Ge-Al NW heterostructures with Ge segments that come into contact with self-aligned Al leads with abrupt metal–semiconductor interfaces. Depending on their geometry, these quasi-one-dimensional (1D) heterostructures can reassemble into Ge nanowires, Ge nanodots, or Ge nanodiscs, which are monolithically integrated within monocrystalline Al (c-Al) mirrors that promote both optical confinement and effective heat dissipation. Optical mode resonances in these nanocavities support in SRS thresholds as low as 60 kW/cm2. Most notably, our findings provide a platform for elucidating the high potential of future monolithically integrated, nanoscale low-power group-IV-based Raman lasers.

Permanent tuning of optical resonant modes of chalcogenide-coated microresonators.

Chalcogenide materials are promising for optical resonant mode tuning of whispering gallery mode (WGM) microresonators due to their high nonlinearity. In this study, this phenomenon was demonstrated for Ge2Sb2Te5-coated toroidal microresonators using an optical postprocess, which utilizes the intrinsically photosensitive property of the Ge2Sb2Te5 coating. A signal laser was used to illuminate the resonator for permanent tuning of the WGMs in a sensitive manner. 0.01 nm and 0.02 nm permanent tuning of the WGMs was recorded for 5 nm and 10 nm coated resonators, respectively. This technique enables resonance matching of coupled optical resonators, which could pave the way for optoelectronic circuitries employing multiple optical microresonators.

Double-triangular whispering-gallery mode lasing from a hexagonal GaN microdisk grown on graphene

The III-nitride semiconductor microdisk laser exhibits high quality factor and low excitation threshold with broad development potential in the field of nanophotonics such as nanoscale light-emitting devices and on-chip optical integration. So far, many works have been focused on process synthesis and nanostructural design of microdisk lasers. Nevertheless, there are still some limitations in the existing optical resonance mode which is an important internal influence factor for lasing characteristics. In this work, a new double-triangular whispering-gallery mode (D3-WGM) lasing from a hexagonal GaN microdisk with a high quality (Q) factor of 3049 and an excitation threshold of around 11.5 μW has been experimentally demonstrated. In addition, the optical properties of hexagonal-WGM (6-WGM), triangular-WGM (3-WGM) and D3-WGM lasing from microdisk are explored by numerical calculation and Comsol simulation. These results confirm that the D3-WGM lasing has its own significant performance advantages, namely high Q factor and easy light emission. Based on this novel laser mode characteristic, microcavity lasers are expected to be further developed and applied in the field of nanophotonics.

Effects of roughness and resonant-mode engineering in all-dielectric metasurfaces

Abstract The development of all-dielectric metasurfaces vigorously prompts the applications of optical metasurfaces for the visible and near-IR light range. Compared to IR or longer wavelength light, visible and near-IR light have shorter wavelengths. As a result, surface roughness and imperfections of all-dielectric metasurfaces have larger scattering or absorption of visible and near-IR light, thereby directly affecting the performance of an all-dielectric metasurface. In this article, a volume-current method is adopted to study the effect of metasurface roughness. Numerical calculations based on the finite difference time domain (FDTD) method are also used to study the relationship between the effects of metasurface roughness and the optical resonant modes. Numerical predictions based on our theoretical studies fit the experimental data well. Further, the effect of different roughness levels on the all-dielectric metasurface performance is predicted. More importantly, a method utilizing resonant-mode engineering to enhance the metasurface performance (e.g. incident angle insensitivity) is also proposed and demonstrated. This work deepens our understanding of the working mechanism of all-dielectric metasurfaces and paves the way for their use in a broad spectrum of applications.

High power edge-cum-surface emitting terahertz laser arrays phased locked by vacuum guided plasmon waves

Terahertz semiconductor quantum-cascade lasers (QCLs) are widely implemented with metallic cavities that support low-loss plasmonic optical modes at long wavelengths. However, resonant optical modes in such cavities suffer from poor radiative characteristics due to their subwavelength transverse dimensions. Consequently, single-mode terahertz QCLs with metallic cavities and large (>100 mW) output power have only been realized in the surface-emitting configuration that affords a large radiating surface. Here, we demonstrate a method to enhance radiative outcoupling from such plasmonic lasers for high-power emission in the edge-emitting (end-fire or longitudinal) direction. Single-sided plasmon waves propagating in vacuum are resonantly excited in surrounding medium of metallic cavities with the QCL semiconductor medium. The vacuum guided plasmon waves with a large wavefront phase-lock multiple metallic cavities longitudinally, which leads to intense radiation in multiple directions, including that in the longitudinal direction in a narrow single-lobed beam. The multicavity array radiates predominantly in a single spectral mode. A peak-power output of 260 mW and a slope efficiency of 303 mW/A are measured for the end-fire beam from a 3.3 THz QCL operating at 54 K in a Stirling cooler. Single-mode operation and lithographic tuning across a bandwidth of ∼150 GHz are demonstrated.

Stable Fano-like plasmonic resonance: its impact on the reversal of far- and near-field optical binding force

Even for a 100 nm interparticle distance or a small change in particle shape, optical Fano-like plasmonic resonance mode usually vanishes completely. It would be remarkable if stable Fano-like resonance could somehow be achieved in distinctly shaped nanoparticles for more than 1 μm interparticle distance, which corresponds to the far electromagnetic field region. If such far-field Fano-like plasmonic resonance can be achieved, controlling the reversal of the far-field binding force can be attained, like the currently reported reversals for near-field cases. In this work, we have proposed an optical set-up to achieve such a robust and stable Fano-like plasmonic resonance, and comparatively studied its remarkable impact on controlling the reversal of near- and far-field optical binding forces. In our proposed set-up, the distinctly shaped plasmonic tetramers are half immersed (i.e. air–benzene) in an inhomogeneous dielectric interface and illuminated by circular polarized light. We have demonstrated significant differences between near- and far-field optical binding forces along with the Lorentz force field, which partially depends on the object’s shape. A clear connection is shown between the far-field binding force and the resonant modes, along with a generic mechanism to achieve controllable Fano-like plasmonic resonance and the reversal of the optical binding force in both far- and near-field configurations.

Length dependent optical characteristics analysis for semiconductor nanowires

Resonant optical mode excitations in semiconductor nanowires result in enhanced absorptions. Nominally, only the diameter dependent radial mode excitations have been considered for the increased absorption. In this paper, we try to understand how the length of the nanowires affects the resonant wavelength and peak absorption wavelengths. We answer two questions viz (1) at what minimum length are radial optical modes stabilized and dominate the absorption characteristics and (2) do longitudinal modes play a role in absorption characteristics especially in determining the resonant wavelength. Two different semiconductors are studied viz silicon and gallium arsenide. We find that even nanowires as short as 200 nm exhibit absorption characteristics dominated by the radial mode excitation. However, for lengths smaller than 200 nm, the optical characteristics are dominated by scattering. Further, we observe that longitudinal modes are excited in low absorption semiconductor materials like silicon for lengths up to 700 nm and the absorption peak depends both on the diameter and the wavelength. Further, shorter length nanowires may have higher absorption than the longer ones in this regime. We also observed that scattering from the nanowires is less than 2% of the incident light. For higher absorption semiconductor like GaAs, absorption characteristics are mainly determined by the radial mode excitations even for shorter lengths. The results provide further insight into the radial mode excitations in semiconductor nanowires.

GaN microdisk with direct coupled waveguide for unidirectional whispering-gallery mode emission.

Microdisks are excellent whispering-gallery mode (WGM) optical resonators, but their emissions are invariably in-plane isotropic due to their circularities and thus difficult to be extracted efficiently. In this work, a waveguide with a width of 0.16 µm directly coupled to a microdisk with a diameter of 10 µm is fabricated on a 0.77 µm thick GaN thin film containing InGaN/GaN multi-quantum wells. This eliminates the need for precision patterning required by evanescent coupling schemes in which coupling gaps of the order of tens of nanometers must be maintained. The fabrication was carried out using nanosphere and nanowire lithography. Non-evanescent coupling of WGMs to the waveguide from the microdisk is successfully demonstrated.

Evolutions of acoustic and optical mode resonances in the spin reorientation Permalloy film

We investigate the static and dynamic magnetic properties of a wedge Permalloy film. The spin distribution of the wedge film depends on the film thickness, ranging from the homogeneous in-plane to the out-of-plane component. The spin reorientation region of the wedge film is determined by using a magnetic force microscopy and magneto-optical Kerr effect measurements as well as the micromagnetic simulation. The dynamic properties of the spin distribution depending on the thickness are investigated by the microwave method. The acoustic and optical mode resonances of the wedge film are controlled by changing the direction of the microwave magnetic field and the stripe domains. The resonance frequency could be influenced by its domain structure and reveals the different anisotropies of the film. The results show that the spin distribution of the stripe domain depending on the thickness can be used to control the spin dispersion and precession frequency of the film for high-frequency applications.

Properties of GaN optomechanical nanobeam cavity

Gallium nitride based nanobeam cavity system was theoretically analysed by using finite element method-based model. Optical and mechanical resonant localized modes structure of the nanobeam cavity was calculated. Depend on the geometrical properties there were found modes with high quality factor for the both cases. The maximum optical quality factor reaches value 5.104 in cavity with value d = 90nm.

A study of relative humidity sensor on micro-ball resonator

We investigate the use of a class of whispering gallery mode optical resonators, namely, optical micro-ball resonator (MBR) as a relative humidity (RH) sensor. The MBR is fabricated using fusion splicer at the tip of standard optical fibers; single-mode fibers (SMF-28). The MBR is then optically excited by using an 8?? optical microfiber and was found to have a Q-factor of >105. The MBR was then employed as a humidity sensor with an RH range of between 40% to 100%. The MBR RH sensor was found to have a sensitivity 0.284 dB/%, linearity >90% and is superior to the bare microfiber in all measured parameters. The MBR RH sensor was also found to have good repeatability and stability compared to bare microfiber.

Test of spin pumping into proximity-polarized Pt by in-phase and out-of-phase pumping in Py/Pt/Py

Spin pumping into proximity-polarized Pt was investigated by magnetic damping studies of Permalloy(Py)/Pt and Py/Pt/Py structures for a Pt thickness range of $0l{d}_{\mathrm{Pt}}l3$ nm. The observed exponential increase in damping with increasing ${d}_{\mathrm{Pt}}$ in Py/Pt is consistent with previous studies of single crystal Fe/Pt. However, at present there are no studies of magnetic double layer structures, ferromagnet/Pt/ferromagnet. The main reason is that the presence of an induced magnetic moment in Pt, by proximity effect, leads to a strong interlayer exchange coupling. Proximity effect has so far not been addressed in the framework of spin pumping. Due to the ferromagnetic interlayer exchange coupling mediated by Pt, the magnetic response of the Py/Pt/Py structure results in optical (out-of-phase) and acoustic (in-phase) resonance modes. The magnetic damping of both modes has a different dependence on ${d}_{\mathrm{Pt}}$ than that of the Py/Pt structure. The study of Py/Pt/Py is sensitive to both the magnitude and phase of spin pumping and thus provides a stringent test of validity for spin-pumping theory for systems with proximity magnetism. We found that the results in Py/Pt and Py/Pt/Py can be self-consistently interpreted by a standard spin pumping theory with ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}_{\ensuremath{\uparrow}\ensuremath{\downarrow}}=4.3\ifmmode\times\else\texttimes\fi{}{10}^{15}\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ and ${\ensuremath{\lambda}}_{\mathrm{sd}}=1.1\ifmmode\pm\else\textpm\fi{}0.1$ nm. We found no evidence of any additional contributions to the interface damping.

Multiplet independent resonance modes in multiplexed gratings.

Resonance modes in usual optical resonators are orthogonal, but correlated and their resonance properties cannot be independently controlled. Multiplexed gratings, consisting of multiple harmonic grating features, show multiplet resonance modes that can be independently adjusted. This offers flexibility in designing resonance characteristics for various potential applications in nonlinear optics and controlling/enhancement of light-matter interactions, e.g., to resonantly enhance the local densities of photonic modes of both the excitation and emission light in photoluminescence, which cannot be intentionally achieved with conventional resonators. Here we report the design, characteristics and experimental implementation of the multiplexed metal gratings that have doublet or triplet resonance modes. Based on numerical simulations, we investigated dependences of the resonance modes, field distributions and local field enhancements on structure features of the gratings. In implementation, we elaborated the experimental considerations, and demonstrated the consistency in structure features and their resonance characteristics for designed and as-fabricated multiplexed grating resonators.

The performance of CROW structures on detection of virus nanoparticles

Coupled resonator optical waveguide (CROW) structures were investigated as a whispering gallery mode optical resonator for biosensing applications. A single mode optical fiber taper was used to evanescently couple light into the microspheres. We have simulated the theoretical model of the crow structure with two and three microspheres. The coupled-resonator-induced transparency (CRIT) phenomenon was observed in the crow structures. In this paper, two crow structures and a single microsphere resonator are compared with each other. We have reported the high sensitivity of the crow structures compared to a single microsphere. We have demonstrated apparent shifts of CRIT transparent peak when the virus nanoparticles are placed on the surface of the microsphere. As a result, these crow structures can be used as a biosensing sensor with high sensitivity. The theoretical simulation was carried out at the operating wavelength of 1550 nm.

Measurement of hydrostatic pressure using a hollow bottle microresonator

In this paper, we report the experimental results of the design and manufacture of a device in the form of a hollow bottle manufactured from a polymer for the measurement of hydrostatic pressure of microfluids in microcavities. The fabricated device bases its operation on the optical resonances of a capillary optical microresonator that couples the light coming from the evanescent field of an optical fiber taper with a central diameter in the range of 3-5 μm, exciting the resonant optical modes WGMs inside the cavity. The microcavity was manufactured using a heating-pressurization technique by a system built to measure which allowed reaching a minimum wall thickness in the central region of the order of 19.78 μm with a sensitivity of the order of 0.5567 nm/bar.

Quantization of Quasinormal Modes for Open Cavities and Plasmonic Cavity Quantum Electrodynamics

We introduce a second quantization scheme based on quasinormal modes, which are the dissipative modes of leaky optical cavities and plasmonic resonators with complex eigenfrequencies. The theory enables the construction of multiplasmon or multiphoton Fock states for arbitrary three-dimensional dissipative resonators and gives a solid understanding to the limits of phenomenological dissipative Jaynes-Cummings models. In the general case, we show how different quasinormal modes interfere through an off-diagonal mode coupling and demonstrate how these results affect cavity-modified spontaneous emission. To illustrate the practical application of the theory, we show examples using a gold nanorod dimer and a hybrid dielectric-metal cavity structure.

Camera detection and modal fingerprinting of photonic crystal nanobeam resonances.

We demonstrate in simulation and experiment that the out-of-plane, far-field scattering profile of resonance modes in photonic crystal nanobeam (PCN) cavities can be used to identify resonance mode order. Through detection of resonantly scattered light with an infrared camera, the overlap between optical resonance modes and the leaky region of k-space can be measured experimentally. Mode order dependent overlap with the leaky region enables usage of resonance scattering as a "fingerprint" by which resonant modes in nanophotonic structures can be identified via detection in the far-field. By selectively observing emission near the PCN cavity region, the resonant scattering profile of the device can be spatially isolated and the signal noise introduced by other elements in the transmission line can be significantly reduced, consequently improving the signal to noise ratio (SNR) of resonance detection. This work demonstrates an increase in SNR of ∼ 19 dB in out-of-plane scattering measurements over in-plane transmission measurements. The capabilities demonstrated here may be applied to improve characterization across nanophotonic devices with mode-dependent spatial field profiles and enhance the utility of these devices across a variety of applications.