Fabry-Perot Modes Research Articles

Single and Multiple Longitudinal Wavelength Generation in Green Diode Lasers

Single and multiple wavelength laser systems are presented that employ self-injection locked InGaN/GaN green laser diodes in an external cavity configuration with a partially reflective mirror. A stable and simultaneous locking of up to four longitudinal Fabry–Perot modes of the system cavity is demonstrated with appreciable signal-to-noise-ratio of ∼13 dB and average mode linewidth of ∼150 pm. The multi-wavelength spectrum exhibited a flat-top emission with nearly equal power distribution among the modes and an analogous mode spacing of ∼0.5 nm. This first demonstration of multi-wavelength generation source is highly attractive in a multitude of cross-disciplinary field applications besides asserting the prospects of narrow wavelength spaced multiplexed visible light communication. Moreover, an extended two-stage self-injection locked near single wavelength visible laser system is also presented. An ultra-narrow linewidth of ∼34 pm is realized at 525.05 nm locked wavelength from this innovative system, with ∼20 dB side-mode-suppression-ratio; thus signifying a paradigm shift toward semiconductor lasers for near single lasing wavelength generation, which is presently dominated by other kinds of laser technologies.

Temperature-Dependent Lasing of CsPbI3 Triangular Pyramid.

In this work, the lasing performance of a microsized single-crystal CsPbI3 triangular pyramid (MSCTP) is evaluated by measuring the lasing threshold at low temperature. The MSCTPs of well-defined facets are synthesized on a Si/SiO2 substrate with chemical vapor deposition. The MSCTP shows a spontaneous emission around 719 nm at room temperature and a stimulated emission resonant in a single Fabry-Perot mode within 148-223 K. The lasing threshold varies from 21.56 to 53.15 μJ/cm2 and presents a temperature dependence in an empirical exponential function with a characteristic temperature of 72.73 K. The temperature dependence of lasing behavior is ascribed to the competition between the exciton binding energy and thermal disturbance energy of CsPbI3. The results of this work provide us a perspective to engineer and optimize optoelectrical devices based on perovskite materials and a microsized optical cavity to investigate the light-matter interaction in quantum optics.

A plasmonic ellipse resonator possessing hybrid modes for ultracompact chipscale application

We propose a plasmonic ellipse resonator possessing hybrid modes based on a metal–insulator–metal waveguide system. Specially, this nanocavity has hybrid characteristic of rectangle and disk resonator, therefore supporting both Fabry–Perot modes (FPMs) and whispering-gallery modes (WGMs). Besides, by changing the length of major and minor radius of the ellipse, the resonant wavelengths of FPMs and WGMs can be independently tuned and close to each other, thus constructing a plasmon-induced transparency—like spectrum profile. Benefitting from this, a dual-band slow light is achieved with one single resonator. Furthermore, this component can also act as a multi-band color filter and refractive index sensor. We believe such a multi-mode resonator with an ultra-small footprint will play an important role in more compact on-chip optical circuits in the future.

Incoherent scattering from dielectric metasurfaces under the influence of electromagnetic eigenmodes.

Anomalous optical properties of microscopically inhomogeneous dielectric films placed on a thick metal sublayer are investigated. We study the reflection, scattering, and absorption of the coherent electromagnetic radiation as a function of the incidence angle. Computer simulations show the existence of the incidence angle of the laser beam when the scattering and absorption increase simultaneously for the s-polarization so that almost 60% of the incident light goes in the scattering channel. The critical angle corresponds to the excitation of Fabry-Perot mode. The effect makes it possible to manipulate the reflection from the metafilms.

Understanding the nano-photonics absorption limit in both front-side and front/rear-side textured slabs

Surface texturing is one of the main techniques to enhance light absorption in solar cells. In thin film devices, periodic texturing can be used to excite the guided resonances supported by the structure. Therefore, total absorption is enhanced largely due to the excitation of these resonances. Although the maximum absorption enhancement limit in both bulk and photonic structures is known already, the weight of each resonance type in this limit is not yet clear. In this contribution, we extend the temporal couple-mode theory, deriving a closed formula to distinguish the contribution of Fabry-Perot and wave-guided modes within the absorption limit for 1-D grating structures. Secondly, using this analytical approach, we can clearly address cases of bulk and thin absorber thicknesses. Our results, supported by rigorous electromagnetic calculation, show that absorption enhancement in a 1-D grating structure can be much higher than the nano-photonic limit (2πn) reported by Yu et al. Thirdly, beyond the framework put forward by Yu et al., we extended our theory to describe the absorption enhancement in double side textured slabs. We have found that when the periods of top and bottom gratings are aliquant, absorption is enhanced in a wider frequency range. We provide rigorous numerical calculations to support our theoretical approach.

Elongated hexagonal ZnO micro-fence optical resonator

A highly symmetric ZnO micro-fence is prepared to form an optical resonator, which a symmetric array consisting of six elongated hexagonal microcolumns. It is found that the luminescence emission could be enhanced at the edge of ZnO micro-fence and the wavelength dependent light intensity could be influenced by its geometry. The optical characterization along with theoretical calculations and computer simulation analysis suggest that the Fabry-Perot and Cross-whispering gallery modes are generated in ZnO micro-fence. The individual ZnO micro-fence can regarded as an optical resonator structure. Furthermore, it is proposed that the source concentration around the substrate during the growth is a crucial factor for forming such a micro-fence.

Tunable, polarized and deeply modulated photoluminescence based on gold nano-islands and liquid crystal

Tunable, polarized and strongly modulated photoluminescence from liquid crystal (LC)-based Fabry Perot (FP) cavity is reported. Reflectors of this cavity are a continuous metal thin film and a plasmonic gold nano-island (NI) layer. The NI layer is selectively reflective and transparent inside and outside of the plasmonic spectral region. The NI layer strongly enhances the quality of the cavity modes in a defined plasmonic spectral area, unlike what happens in thick metal layer. The defect free nature of LC layer in the cavity can excite the FP mode and work as a light emitter by doping a dye in LC layer. Photoluminescence (PL) of the cavity is anisotropic and polarized due to the alignment of molecular dipole moment of dye along the LC director. The role of the NI layer and the LC layer on the optical quality of the cavity is investigated theoretically and experimentally. This FP cavity could be applicable in tunable optoelectronics and lasing applications.

Optical Cavity Based on GaN Planar Nanowires Grown by Selective Area Metal‐Organic Vapor Phase Epitaxy

GaN planar nanowires (NWs) are fabricated by selective area metal‐organic vapor phase epitaxy using focused ion beam etching of trench pattern in the Si3N4 mask. Two crystallographic orientations of NWs along and directions are investigated. The coherent growth is confirmed for both directions; however, the best morphology, crystalline and optical properties are found in the GaN planar NWs fabricated along the axis. Cathodoluminescence (CL) at 5 K reveals a presence of Fabry–Perot modes in the region of 1.8–2.5 eV for the NWs fabricated in the direction. The position and intensity of the Fabry–Perot peaks vary depending on measured point within the NW, which is explained by the model based on the Purcell coefficient calculations. It is shown that small fluctuations in the NW thickness cause a noticeable shift of the Fabry–Perot modes energies, while the enhancement or reduction of the emission intensity for the Fabry–Perot peaks depend on the position of the emitter inside the planar NW.

Wavelength-Tunable Waveguide Emissions from Electrically Driven Single ZnO/ZnO:Ga Superlattice Microwires

Because of the superlattice structures comprising periodic and alternating crystalline layers, one-dimensional photon crystals can be employed to expand immense versatility and practicality of modulating the electronic and photonic propagation behaviors, as well as optical properties. In this work, individual superlattice microwires (MWs) comprising ZnO and Ga-doped ZnO (ZnO/ZnO:Ga) layers were successfully synthesized. Wavelength-tunable multipeak emissions can be realized from electrically driven single superlattice MW-based emission devices, with the dominant wavelengths tuned from ultraviolet to visible spectral regions. To illustrate the multipeak character, single superlattice MWs were selected to construct fluorescent emitters, and the emission wavelength could be tuned from 518 to 562 nm, which is dominated by Ga incorporation. Especially, by introducing Au quasiparticle film decoration, emission characteristics can further be modulated, such as the red shift of the emission wavelengths, and the multipeaks were strongly modified and split into more and narrower subbands. In particular, electrically pumped exciton-polariton emission was realized from heterojunction diodes composed of single ZnO/ZnO:Ga superlattice MWs and p-GaN layers in the blue-ultraviolet spectral regions. With the aid of localized surface plasmons from Au nanoparticles, which deposited on the superlattice MW, significant improvement of emission characteristics, such as enhancement of output efficiencies, blue shift of the dominant emission wavelengths, and narrowing of the spectral linewidth, can be achieved. The multipeak emission characteristics would be originated from the typical optical cavity modes, but not the Fabry-Perot mode optical cavity formed by the bilateral sides of the wire. The resonant modes are likely attributed to the coupled optical microcavities, which formed along the axial direction of the wire; thus, the emitted photons can be propagated and selected longitudinally. Therefore, the novel ZnO/ZnO:Ga superlattice MWs with a quadrilateral cross section can provide a potential platform to construct multicolor emitters and low-threshold exciton-polariton diodes and lasers.

Tamm plasmon in a structure with the nanocomposite containing spheroidal core–shell particles

Spectral peculiarities of the structure consisting of a photonic crystal coated with a nanocomposite (NC) have been investigated. The NC used contains spheroidal nanoparticles with a dielectric core and a metallic shell, which are uniformly dispersed in a transparent matrix. The spectral manifestation of the observed Tamm plasmon polariton (TPP) and Fabry–Perot mode has been examined. A significant polarization sensitivity of the spectra upon variation in the nanoparticle shape has been demonstrated. The dispersion curves presented for the TPP and Fabry–Perot mode are shown to be in good agreement with the spectra obtained by the transfer matrix method.

Polymer dispersed liquid crystal-mediated active plasmonic mode with microsecond response time

Active plasmonics combined with liquid crystal (LC) has found many applications in nanophotonics. In this Letter, we propose a fast response active plasmonic device based on the interplay of the plasmonic spectrum and Fabry-Perot (FP) modes. The plasmonic spectrum and FP modes are excited in a layer of gold nanoparticle (NP) islands and an LC microcavity, respectively. The FP mode splits the extinction spectrum of the NP to narrow bands, which are named hybrid modes (HMs). Due to multiple reflections of photons inside the cavity, the extinction coefficient is enhanced compared to a bare NP layer. An external electric field shifts the HM leading to a significant increase in the figure of merit (FoM) related to the activation ability by up to a factor of 45. Additionally, we could reduce the response time of active plasmonics. This decrease in response time is achieved through polymer-dispersed LC (PDLC) in the microcavity. Utilizing a mesogenic monomer in PDLC reduces the response time of the HM into the microsecond range, while the sample remains transparent.

Cost-Effective Realization of Multimode Exciton-Polaritons in Single-Crystalline Microplates of a Layered Metal-Organic Framework.

We report the observation of multimode exciton-polaritons in single-crystalline microplates of a two-dimensional (2D) layered metal-organic framework (MOF), which can be synthesized through a facile solvothermal approach, thereby eliminating all fabrication complexities usually involved in the construction of polariton cavities. With a combination of experiments and theoretical modeling, we have found that the exciton-polaritons are formed at room temperature as a result of a strong coupling between Fabry-Perot cavity modes formed inherently by two parallel surfaces of a microplate and Frenkel excitons provided by the 2D layers of dye molecular linkers in the MOF. Flexibility in rational selection of dye linkers for synthesizing such MOFs renders a large-scale, low-cost production of solid-state, micro-exciton-polaritonic devices operating in the visible and near-infrared range. Our work introduces MOFs as a new class of potential materials to explore polariton-related quantum phenomena in a cost-effective manner.

Flexible properties of THz graphene bowtie metamaterials structures

Tunable propagation properties of graphene asymmetrical bowtie metamaterials (MMs) structures have been investigated in the terahertz regime, including the effects of graphene Fermi levels, structural parameters and operation frequencies. Because of its thin film thickness, the strong resonant curves of the proposed graphene MMs structures are dominated by the plasmonic mode instead of the Fabry-Perot mode for the metal structures. Compared with existing tunable graphene devices, the sharp Fano resonant curve manifests a large Q-factor of more than 40. In addition, as the width of graphene bowtie aperture increases, the resonant frequency dip shifts low frequency, and the resonant amplitude and figure of merit increase. The results are very helpful in order to understand the tunable mechanisms of graphene components and design high sensitivity functional devices, sensors, modulators, and antenna.

Measurement of wavelength-dependent radiation pressure from photon reflection and absorption due to thin film interference

Opto-mechanical forces result from the momentum transfer that occurs during light-matter interactions. One of the most common examples of this phenomenon is the radiation pressure that is exerted on a reflective surface upon photon reflection. For an ideal mirror, the radiation pressure is independent of the wavelength of light and depends only on the incident power. Here we consider a different regime where, for a constant input optical power, wavelength-dependent radiation pressure is observed due to coherent thin film Fabry-Perot interference effects. We perform measurements using a Si microcantilever and utilize an in-situ optical transmission technique to determine the local thickness of the cantilever and the light beam’s angle of incidence. Although Si is absorptive in the visible part of the spectrum, by exploiting the Fabry-Perot modes of the cantilever, we can determine whether momentum is transferred via reflection or absorption by tuning the incident wavelength by only ~20 nm. Finally, we demonstrate that the tunable wavelength excitation measurement can be used to separate photothermal effects and radiation pressure.

Holmium doped fiber thermal sensing based on an optofluidic Fabry-Perot microresonator

An optical temperature sensor suitable for label free liquid sensing has been designed and characterized. The sensor combines the photochemical stability of rare earth doped glasses and the high sensitivity of interferometric resonators. It is formed by a planar Fabry-Perot (FP) microcavity filled with the liquid to be monitored. A Ho3+ doped tapered optical fiber has been placed inside the microcavity surrounded by the fluid medium. An external laser is focused on the optical fiber inside the cavity to induce the luminescence of the Ho3+ ions, which couples to the FP optical resonances. The spectral position of the FP resonances is highly sensitive to the refractive index of the cavity medium. A second laser is co-aligned with the first one to locally heat the liquid medium around the optical fiber. An average blue shift of the FP resonances around 32 pm/°C is measured. The limit of detection of the laser induced heating of the liquid medium is about 0.3 °C in the biological temperature range. Alternatively, a hot-plate is used to heat the system. Interestingly, a red shift of the FP modes is observed with 75 pm/°C dependence and 0.12 °C limit of detection features.

Enhanced plasmonic light absorption on silicon solar cells: The case of silver (Ag) grid-indium tin oxide (ITO) composite front electrode

A novel silver (Ag) crossing grid-ITO composite front electrode with plasmonic light absorption enhancement has been designed to resolve the problem of inadequate light absorption in ultrathin film crystal silicon (c-Si) solar cells (SCs). In this novel structure, the ultrathin ITO layer primarily collects charge and the Ag crossing grids work as a charge transportation path and an optical absorption enhancer. The defined absorption enhancement factor G and structural parameters, such as ITO film thickness and linewidth, height and period of the Ag grid, were systematically optimized using finite-difference time-domain (FDTD) stimulations, and absorption enhancements were analyzed. A 61% light absorption enhancement was observed for the c-Si solar cell with an Ag crossing grid in the composite front electrode compared to that without the Ag crossing grid. Four types of resonance modes such as Fabry–Perot (FP) modes, waveguide modes, localized surface plasmon resonances (LSPR) and surface plasmon polaritons (SPPs) are supported by the designed structure. FP modes may be excited in bare c-Si SCs, but the inclusion of the 2D Ag crossing grid introduces waveguide modes sandwiched by Ag grids and the Ag back electrode, and SPPs and LSPR modes that lead to enhanced light absorption.

Fabry-Perot type polariton modes and their dynamics revealed by Young’s interference experiment

We report experimental studies on the Fabry-Perot (F-P) type polariton modes and their dynamics using a modified Young's double-slit interference technique. The technique was based on the angle-resolved micro-photoluminescence spectroscopy and optimized for nanostructure measurements. Using this technique, we directly revealed the parity of the F-P type polariton modes from the angle-dependent interference spectra. Moreover, clear features of mode competition were observed from the power dependence of the interference patterns. The observed competition behaviors can be well simulated by a five-level rate equation model.

Enhanced light trapping in thin-film silicon solar cells with concave quadratic bottom gratings.

We present a theoretical crystalline silicon thin-film solar cell with concave quadratic bottom gratings using parametric design of the gratings and systematically perform optoelectronic simulations of the proposed grating structures. Numerical results reveal that the concave quadratic grating structure leads to a desirable enhancement of light absorption in the near-IR region (750-1100nm), and this enhancement is dominated by TE-polarized light. The mechanisms of light absorption enhancement under TE-polarized light are based on the hybrid effect of optical waveguide modes and Fabry-Perot modes. Moreover, research results indicate that the concave quadratic grating structure has excellent light-focusing effects, which is conducive to the excitation of optical waveguide modes. The study findings can be utilized to improve the efficiency of thin-film solar cells based on grating structures.

Detection of ultracold molecules using an optical cavity

We theoretically study non-destructive detection of ultracold molecules, using a Fabry-Perot cavity. Specifically, we consider vacuum Rabi splitting where we demonstrate the use of collective strong coupling for detection of molecules with many participating energy levels. We also consider electromagnetically induced transparency and transient response of light for the molecules interacting with a Fabry-Perot cavity mode, as a mean for non-destructive detection. We identify the parameters that are required for the detection of molecules in the cavity electromagnetically induced transparency configuration. The theoretical analysis for these processes is parametrized with realistic values of both, the molecule and the cavity. For each process, we quantify the state occupancy of the molecules interacting with the cavity and determine to what extent the population does not change during a detection cycle.

Approach to high quality GaN lateral nanowires and planar cavities fabricated by focused ion beam and metal-organic vapor phase epitaxy

We have developed a method to fabricate GaN planar nanowires and cavities by combination of Focused Ion Beam (FIB) patterning of the substrate followed by Metal Organic Vapor Phase Epitaxy (MOVPE). The method includes depositing a silicon nitride mask on a sapphire substrate, etching of the trenches in the mask by FIB with a diameter of 40 nm with subsequent MOVPE growth of GaN within trenches. It was observed that the growth rate of GaN is substantially increased due to enhanced bulk diffusion of the growth precursor therefore the model for analysis of the growth rate was developed. The GaN strips fabricated by this method demonstrate effective luminescence properties. The structures demonstrate enhancement of spontaneous emission via formation of Fabry-Perot modes.