Planar Optical Cavity Research Articles

Broadband and Spectrally Selective Photothermal Conversion through Nanocluster Assembly of Disordered Plasmonic Metasurfaces.

Plasmonic metasurfaces have been realized for efficient light absorption, thereby leading to photothermal conversion through nonradiative decay of plasmonic modes. However, current plasmonic metasurfaces suffer from inaccessible spectral ranges, costly and time-consuming nanolithographic top-down techniques for fabrication, and difficulty of scale-up. Here, we demonstrate a new type of disordered metasurface created by densely packing plasmonic nanoclusters of ultrasmall size on a planar optical cavity. The system either operates as a broadband absorber or offers a reconfigurable absorption band right across the visible region, resulting in continuous wavelength-tunable photothermal conversion. We further present a method to measure the temperature of plasmonic metasurfaces via surface-enhanced Raman spectroscopy (SERS), by incorporating single-walled carbon nanotubes (SWCNTs) as an SERS probe within the metasurfaces. Our disordered plasmonic system, generated by a bottom-up process, offers excellent performance and compatibility with efficient photothermal conversion. Moreover, it also provides a novel platform for various hot-electron and energy-harvesting functionalities.

Derivation of the Transient and Steady Optical States from the Poles of the S‐Matrix

AbstractThe electromagnetic response of optical systems can be described by scattering operators, S, that link the incoming fields onto the system to the outgoing fields emerging from it. Considerable efforts have been devoted to retrieve the spectral response of the optical systems by expanding the S‐matrix in terms of its singularities. Here a planar optical cavity that allows to derive analytical expressions of poles (in the case of lossless materials) and residues, and reflection/transmission Fresnel coefficients in the harmonic domain is considered. This singularity expansion is used to derive the impulse response function (IRF) of the cavity with respect to the poles of the S‐matrix. The singular expression of the IRF consists of contributions oscillating at the excitation frequency and exponentially decaying contributions that impact signals only during the transient regimes. The convergence of this approach is thoroughly discussed in the case of a dispersive and metallic slab. The convergence is achieved by increasing the number of poles in the singularity expansion. It can also be achieved by considering only the poles within the spectral range of interest plus a fictive resonant term encapsulating the contribution of the singularities outside this spectral range.

Planar Optical Cavities Hybridized with Low-Dimensional Light-Emitting Materials.

Low-dimensional light-emitting materials have been actively investigated due to their unprecedented optical and optoelectronic properties that are not observed in their bulk forms. However, the emission from low-dimensional light-emitting materials is generally weak and difficult to use in nanophotonic devices without being amplified and engineered by optical cavities. Along with studies on various planar optical cavities over the last decade, the physics of cavity-emitter interactions as well as various integration methods are investigated deeply. These integrations not only enhance the light-matter interaction of the emitters, but also provide opportunities for realizing nanophotonic devices based on the new physics allowed by low-dimensional emitters. In this review, the fundamentals, strengths and weaknesses of various planar optical resonators are first provided. Then, commonly used low-dimensional light-emitting materials such as 0D emitters (quantum dots and upconversion nanoparticles) and 2D emitters (transition-metal dichalcogenide and hexagonal boron nitride) are discussed. The integration of these emitters and cavities and the expect interplay between them are explained in the following chapters. Finally, a comprehensive discussion and outlook of nanoscale cavity-emitter integrated systems is provided.

Nonvolatile Optically Reconfigurable Radiative Metasurface with Visible Tunability for Anticounterfeiting.

Control of thermal emission underpins fundamental science, as it is related to both heat and infrared electromagnetic wave transport. However, realizing nonvolatile reconfigurable thermal emission is challenging due to the inherent complexity or limitation in conventional radiative materials or structures. Here, we experimentally demonstrate a nonvolatile optically reconfigurable mid-infrared coding radiative metasurface. By applying laser pulses, infrared emissive patterns are directly encoded into an ultrathin (∼25 nm) Ge2Sb2Te5 layer integrated into a planar optical cavity with the optically crystallized Ge2Sb2Te5 spots, and the peak spectral emissivity is repeatedly switched between low (∼0.1) and high (∼0.7) values. In addition, the visible scattering patterns are independently modulated with submicron-sized bumps generated by high-power laser pulses. An anticounterfeiting label is demonstrated with spatially different infrared emission and visible light scattering information encoded. This approach constitutes a new route toward thermal emission control and has broad applications in encryption, camouflage, and so on.

(Invited) Experimental Quantum Transport in Strained Graphene and SWCNTs - Towards Noems

We measure ballistic charge conductivity in strained suspended graphene and observe the theoretically predicted [1] strain-induced scalar and vector potentials. To do so, we built an experimental platform for in-situ quantum transport strain engineering in 2D materials. This instrumentation also permits low temperature (0.3 K) transport in 0 to 9 Tesla magnetic fields. The tunable uniaxial strain (up to 3%) is completely decoupled from the gate-tunable charge density, permitting quantitative understanding of strain effects. We show slippage-free mechanical clamping of high aspect-ratio graphene crystals, where atomically ordered edges are unnecessary for quantitative straintronics. We study in detail transport in a ballistic graphene channel whose length is 90 nm and width is 600 nm. By applying strain up to 0.6 % in this device, we observe that the strain-induced scalar potential shifts its low energy band structure downward by up to 30 meV. We show precise control of the gauge vector potential which reversibly suppresses the conductance. We discuss our progress towards strain engineering in SWCNTs, and calculations showing its potential in valley filtering and tuning electron-hole asymmetric quantum transistors.We conclude with an overview of another project to integrate suspended bilayer graphene devices in planar optical cavities towards achieving fully tunable nano-opto-electro-mechanical (NOEMS) carbon systems. To do so, we discuss a nitrocellulose-based dry-stamping method to manipulate and suspend individual 2D materials [2]. Using this method we assembled optical cavities able to a widely tune Raman scattering and absorption in graphene. [1] A. C. McRae, G. Wei, and A. R. Champagne, Phys. Rev. Applied 11, 054019 (2019). [2] I. G. Rebollo, F. C. Rodrigues-Machado, W. Wright, G. J. Melin, A. R. Champagne, ArXiv:2011.14166 Figure 1

Negligible Effect of Vibrational Polaritons on Chemical Reaction Rates via the Density of States Pathway.

We show that the polariton density of states in planar optical cavities strongly coupled to vibrational excitations remains much lower than the density of vibrational states even at the frequency of the lower and upper polaritons under most practical circumstances. The polariton density of states is higher within a narrow window only when the inhomogeneous line width is at least an order of magnitude smaller than the Rabi splitting. Therefore, modification of reaction rates via the density-of-states pathway appears small or negligible for the scenarios reported in the literature. While the polariton density of states is bounded from above by the free-space optical density of states in dielectric cavities, it can be much higher for localized phonon polariton modes of nanoscale particles. We conclude that other potential explanations of the reported reactivity changes under vibrational strong coupling should be examined.

Free-fall of photons in a planar optical cavity

We consider a planar optical cavity with one of its in-plane axis aligned with the Earth’s local gravity field. We examine the motion of a wavepacket of light trapped within the cavity spacer under the action of gravity. Using a general relativity framework, we find that the wavepacket initially at rest in terms of its in-plane group velocity, is subject to a non-relativistic free-fall motion of acceleration in the Earth-bound reference frame.

Direct measurement of polariton–polariton interaction strength

Exciton-polaritons in a microcavity are composite two-dimensional bosonic quasiparticles, arising from the strong coupling between confined light modes in a resonant planar optical cavity and excitonic transitions, typically using excitons in semiconductor quantum wells (QWs) placed at the antinodes of the same cavity. Quantum phenomena such as Bose-Einstein condensation (BEC), quantized vortices, and macroscopic quantum states have been reported at temperatures from tens of Kelvin up to room temperatures, and polaritonic devices such as spin switches \cite{Amo2010} and optical transistors have also been reported. Many of these effects of exciton-polaritons depend crucially on the polariton-polariton interaction strength. Despite the importance of this parameter, it has been difficult to make an accurate experimental measurement, mostly because of the difficulty of determining the absolute densities of polaritons and bare excitons. Here we report the direct measurement of the polariton-polariton interaction strength in a very high-Q microcavity structure. By allowing polaritons to propagate over 40 $\mu$m to the center of a laser-generated annular trap, we are able to separate the polariton-polariton interactions from polariton-exciton interactions. The interaction strength is deduced from the energy renormalization of the polariton dispersion as the polariton density is increased, using the polariton condensation as a benchmark for the density. We find that the interaction strength is about two orders of magnitude larger than previous theoretical estimates, putting polaritons squarely into the strongly-interacting regime. When there is a condensate, we see a sharp transition to a different dependence of the renormalization on the density, which is evidence of many-body effects.

Microscopic theory of equilibrium polariton condensates

We present a microscopic theory of the equilibrium polariton condensate state of a semiconductor quantum well in a planar optical cavity. The theory accounts for the adjustment of matter excitations to the presence of a coherent photon field, predicts effective polariton-polariton interaction strengths that are weaker and condensate exciton fractions that are smaller than in the commonly employed exciton-photon model, and yields effective Rabi coupling strengths that depend on the detuning of the cavity photon energy relative to the bare exciton energy. The dressed quasiparticle bands that appear naturally in the theory provide a mechanism for electrical manipulation of polariton condensates.

High-quality-factor planar optical cavities with laterally stopped, slowed, or reversed light.

In a planar optical cavity, the resonance frequencies increase as a function of in-plane wavevector according to a standard textbook formula. This has well-known consequences in many different areas of optics, from the shifts of etalon peaks at non-normal angles, to the properties of transverse modes in laser diodes, to the effective mass of microcavity photons, and so on. However, this standard formula is valid only when the reflection phase of each cavity mirror is approximately independent of angle. There is a certain type of mirror-a subwavelength dielectric grating near a guided mode resonance-with not only a strongly angle-dependent reflection phase, but also very high reflectance and low losses. Simulations show that by using such mirrors, high-quality-factor planar cavities can be designed that break all these textbook rules, leading to resonant modes that are slow, stopped or even backward-propagating in the in-plane direction. In particular, we demonstrate experimentally high-Q planar cavities whose resonance frequency is independent of in-plane wavevector-i.e., the resonant modes have zero in-plane group velocity, for one polarization but both in-plane directions. We discuss potential applications in various fields including lasers, quantum optics, and exciton-polariton condensation.

Broadband Absorption Engineering to Enhance Light Absorption in Monolayer MoS2

Here we take a first step toward tackling the challenge of incomplete optical absorption in monolayers of transition metal dichalcogenides for conversion of photon energy, including solar, into other forms of energy. We present a monolayer MoS2-based photoelectrode architecture that exploits nanophotonic light management strategies to enhance absorption within the monolayer of MoS2, while simultaneously integrating an efficient charge carrier separation mechanism facilitated by a MoS2/NiOx heterojunction. Specifically, we demonstrate two extremely thin photoelectrode architectures for solar-fuel generation: (i) a planar optical cavity architecture, MoS2/NiOx/Al, that improves optical impedance matching and (ii) an architecture employing plasmonic silver nanoparticles (Ag NPs), MoS2/Ag NPs/NiOx/Al, that further improves light absorption within the monolayer. We used a combination of numerical simulations, analytical models, and experimental optical characterizations to gain insights into the contributions ...

Electrically Driven Quantum Light Sources

Typical applications of quantum light require optical sources which generate either individual photons or entangled (correlated) photons. For the sake of practicality and scalability, these quantum sources should be easily produced, operate at room temperature, and be electrically excited and controlled. Here, recent research on quantum sources obtained from electrically driven (ED) devices constructed from p–n junctions integrated in planar optical cavities, micropillars, nanowires, photonic crystals, and active plasmonic elements is reviewed. Single‐photon and entangled‐photon sources are distinguished by their different roles in the development of either quantum cryptography or quantum computing protocols, and the different types of devices used to produce them are highlighted, with a focus on their spectral emission, brightness, and conditions of operation. Achievements to date are summarized and compared with prerequisites for the practical use of these sources. Important recent results that could provide future novel quantum sources are also in focus, where more practical requirements could be addressed by the judicious engineering of materials and careful device design.

Integration of Gold Nanoparticles in Optical Resonators

The optical absorption of one-dimensional photonic crystal based resonators containing different types of gold nanoparticles is controllably modified by means of the interplay between planar optical cavity modes and localized surface plasmons. Spin-casting of metal oxide nanoparticle suspensions was used to build multilayered photonic structures that host (silica-coated) gold nanorods and spheres. Strong reinforcement and depletion of the absorptance was observed at designed wavelength ranges, thus proving that our method provides a reliable means to modify the optical absorption originated at plasmonic resonances of particles of arbitrary shape and within a wide range of sizes. These observations are discussed on the basis of calculations of the spatial and spectral dependence of the optical field intensity within the multilayers.

Near-field intensity correlations in parametric photoluminescence from a planar microcavity

We study the spatio-temporal pattern of the near-field intensity correlations generated by parametric scattering processes in a planar optical cavity. A generalized Bogolubov-de Gennes model is used to compute the second order field correlation function. Analytic approximations are developed to understand the numerical results in the different regimes. The correlation pattern is found to be robust against a realistic disorder for state-of-the-art semiconductor systems.

Hybrid silica-polymer ultra-high-Q microresonators

Ultra-high-quality (UHQ) factor optical cavities have numerous applications throughout engineering and science. Incorporating active elements into these UHQ cavities to create dynamic devices would extend their applicability; however, it is inherently difficult to develop an active UHQ device. Ultra-thin films formed from optically active polymers provide one route to overcome this limitation. In the present work, hybrid devices composed of UHQ planar optical cavities with ultra-thin films are fabricated on a silicon wafer. Using finite element method simulations, the optical field overlap between the cavity and the polymer film is modeled and experimentally verified using two polymers: poly(methyl methacrylate) and polystyrene. These hybrid devices have demonstrated material-limited Q factors above 10(7).

Light-mass Bragg cavity polaritons in planar quantum dot lattices

The exciton-polariton modes of a quantum dot lattice embedded in a planar optical cavity are theoretically investigated. Umklapp terms, in which an exciton interacts with many cavity modes differing by reciprocal lattice vectors, appear in the Hamiltonian due to the periodicity of the dot lattice. We focus on Bragg polariton modes obtained by tuning the exciton and the cavity modes into resonance at high symmetry points of the Brillouin Zone. Depending on the microcavity design these polaritons modes at finite in-plane momentum can be guided and can have long lifetimes. Moreover, their effective mass can be extremely small, of the order of $10^{-8} m_0$ ($m_0$ is the bare electron mass), and they constitute the lightest exciton-like quasi-particles in solids.

Embedded cavities and waveguides in three-dimensional silicon photonic crystals

To fulfil the promise that complete-photonic-bandgap materials hold for optoelectronics applications, the incorporation of three-dimensionally engineered defects must be realized. Previous attempts to create and characterize such defects were limited because of fabrication challenges. Here we report the optical and structural characterization of complex submicrometre features of unprecedented quality within silicon inverse opals. High-resolution three-dimensional features are first formed within a silica colloidal crystal by means of two-photon polymerization, followed by a high-index replication step and removal of the opal template to yield embedded defects in three-dimensional silicon photonic crystals. We demonstrate the coupling of bandgap frequencies to resonant modes in planar optical cavities and the first waveguiding of near-infrared light around sharp bends in a complete-photonic-bandgap material.

Two-dimensionally-patterned silicon nanocrystal arrays

Abstract Recent efforts to enhance and control the optical properties of silicon nanocrystal composites have led to the realization of planar optical cavities and optical waveguide structures. Here, we report on methods to pattern the in-plane location of the silicon nanocrystals. First, we applied conventional lithographic methods to fabricate masks sufficiently thick and durable to withstand high-dose (>1017 ions/cm2) ion implantation protocols without losing structural integrity or delaminating from the specimen surface. We used this method to create single and two-color micropixelated arrays of nanoparticles with feature sizes below one micron. Implantation of silica microspheres can also be used to create in-plane spatial control over the location of the nanocrystals, although in this case there was significant material deformation. Both methods, however, offer effective means of patterning silicon nanocrystals on a micron- to sub-micron scale, and suggest the possibility for the development of new types of patterned luminescent materials based on silicon nanocrystal composites.

Nonlinear Compton scattering and electron acceleration in interfering laser beams

The exact solution of the classical nonlinear equation of motion for a relativistic electron in the field of two electromagnetic (EM) waves is obtained. For the particular case of the linearly polarized standing EM wave in the planar optical cavity, intensity of the nonlinear Compton scattering, the time of flight, and the momentum variation after the relativistic electron passes along the cavity axis are calculated in weak and strong field limits. These effects depend on the initial phase of the EM wave at the electron entrance into the cavity and can be used for producing, diagnostics, and acceleration of relativistic electron (positron) microbunches.

Silicon thermooptical micromodulator with 700-kHz -3-dB bandwidth

A silicon Fabry-Perot waveguide modulator, operating at the fiber optic communication wavelengths of 1.3 and 1.55 /spl mu/m, has been entirely fabricated using microelectronic techniques. The planar optical cavity has been defined by plasma etching and has a length of 100 /spl mu/m. The device, based on the thermooptic effect, is electrically driven and exhibits a maximum modulation depths of 60%. The measured -3 dB bandwidth is 700 kHz, which is by far the best result ever reported, to our knowledge, for thermooptic effect based modulators. >