High Photonic Density Of States Research Articles

Progress in Germanium Tin (GeSn) Photonic Crystal Lasers

We report on lasing in two types of Germanium-Tin (GeSn) photonic crystal lasers, with band-edge and H4 hexagonal cavities. A GeSn 16% step-graded structure was used as the optical gain material. The strong out-of-plane emission observed in the band-edge cavity was attributed to the thick optical gain layer, in addition with the presence of leaky band-edge modes above the light cones and a high photonic density of states. The maximum lasing temperature in both types of photonic crystal lasers, 180 K, was lower than in a micro-disk laser fabricated from the same stack, i.e., 230 K. Meanwhile, the lasing thresholds at low temperature (15 K) were very similar (120 kW/cm² for a band-edge cavity and 140 kW/cm² for a H4 cavity, to be compared with 134 kW/cm² for a micro-disk cavity). Since the injected carrier density is governed by the pump power, we suggest the strong variation of optical gain at low temperature, for a small variation of injected carrier density, as a possible cause of such a phenomenon.

Enhanced laser action from smart fabrics made with rollable hyperbolic metamaterials

Rollable photonic devices that can adapt to freeform surfaces with reduced dimensions while maintaining their original functionalities are highly desirable. Among photonic devices, metamaterials with hyperbolic dispersion in momentum space, defined as hyperbolic metamaterial (HMM), possess a large photonic density of states that has been proven to boost light-matter interaction. However, these devices are mainly developed on rigid substrates, restricting their functionalities. Here, we present the attempt to integrate flexible and rollable HMMs consisting of polymer and metal multilayers on paper substrate. Quite interestingly, this design enables to exhibit high photonic density of states and scattering efficiency to enhance stimulated emission and induce pronounced laser action. The flexible and rollable HMM structure remains well its functionalities on freeform surfaces with curvature radius of 1 mm, and can withstand repeated bending without performance degradation. The intensity of laser action is enhanced by 3.5 times as compared to the flat surface. We anticipate that this flexible and rollable HMM structure can serve as a diverse platform for flexible photonic technologies, such as light-emitting devices, wearable optoelectronics, and optical communication.

Spectroscopic Analysis of Fluorescent Proteins Infiltrated into Photonic Crystals

Spectral properties of enhanced-green fluorescent protein and monomeric red fluorescent protein in porous photonic structures have been studied. The fluorescent proteins were successfully infiltrated into porous silicon photonic structures with different positions of the photonic band gap in visible spectral range. The intensity of fluorescence is enhanced in the spectral regions of high photonic density of states. The possibility to control the fluorescence spectra by the structure with the photonic band gap is demonstrated.

High-performance circular-polarization-sensitive organic photodetectors based on a chiral plasmonic nanocavity.

Chiral photodetectors, optoelectronic devices that can detect circularly polarized light (CPL), have attracted much attention as building blocks of next-generation information technology. However, their performance has been severely limited by the tradeoff between the external quantum efficiency (ηE) and the dissymmetry factor of photocurrent, the latter typically being limited by the small dissymmetry factor of absorption (gA). This work numerically demonstrates that a circular polarization-sensitive organic photodetector (CP-OPD) based on a chiral plasmonic nanocavity can achieve both high ηE and gA. The design of the chiral nanocavity, featuring a circular dichroic plasmonic mode with a high photonic density of states in the subwavelength thick photoactive layer, is decoupled with that of the photoactive layer, which enables the independent control of the circular dichroic and photon-to-charge conversion properties. By investigating the interaction between CPL and the molecules constituting the photoactive layer, a design principle of the plasmonic CP-OPD is established, resulting in superior performance with ηE = 23.8 % and gA = 1.6.

Spectroscopic Analysis of Fluorescent Proteins Infiltrated into Photonic Crystals-=SUP=-*-=/SUP=-

Spectral properties of enhanced-green uorescent protein and monomeric red uorescent protein in porous photonic structures have been studied. The uorescent proteins were successfully inЛtrated into porous silicon photonic structures with dirent positions of the photonic band gap in visible spectral range. The intensity of uorescence is enhanced in the spectral regions of high photonic density of states. The possibility to control the uorescence spectra by the structure with the photonic band gap is demonstrated. Keywords: photonic crystals, porous silicon, uorescent proteins, photonic band gap.

A Highly-Efficient Single Segment White Random Laser.

Production of multicolor or multiple wavelength lasers over the full visible-color spectrum from a single chip device has widespread applications, such as superbright solid-state lighting, color laser displays, light-based version of Wi-Fi (Li-Fi), and bioimaging, etc. However, designing such lasing devices remains a challenging issue owing to the material requirements for producing multicolor emissions and sophisticated design for producing laser action. Here we demonstrate a simple design and highly efficient single segment white random laser based on solution-processed NaYF4:Yb/Er/Tm@NaYF4:Eu core-shell nanoparticles assisted by Au/MoO3 multilayer hyperbolic meta-materials. The multicolor lasing emitted from core-shell nanoparticles covering the red, green, and blue, simultaneously, can be greatly enhanced by the high photonic density of states with a suitable design of hyperbolic meta-materials, which enables decreasing the energy consumption of photon propagation. As a result, the energy upconversion emission is enhanced by ∼50 times with a drastic reduction of the lasing threshold. The multiple scatterings arising from the inherent nature of the disordered nanoparticle matrix provide a convenient way for the formation of closed feedback loops, which is beneficial for the coherent laser action. The experimental results were supported by the electromagnetic simulations derived from the finite-difference time-domain (FDTD) method. The approach shown here can greatly simplify the design of laser structures with color-tunable emissions, which can be extended to many other material systems. Together with the characteristics of angle free laser action, our device provides a promising solution toward the realization of many laser-based practical applications.

Fast spontaneous emission and high Förster resonance energy transfer rate in hybrid organic/inorganic plasmonic nanostructures

We report an experimental study of the plasmon-assisted spontaneous emission and the Förster resonance energy transfer between organic molecules and semiconductor colloidal quantum dots. The localized plasmonic field in the nanogap between a gold nano-popcorn's tips and a 5-nm separated gold film supports high photonic density of states and provides pathways for the light-matter interaction mechanisms. We demonstrate that, besides the total enhanced decay rate up to 66 times for quantum dots and molecules, the Förster resonance energy transfer efficiency and rate constant are simultaneously modified. While the energy transfer efficiency is reduced from 84% to 35% due to the non-radiative quenching effect and fast donor decay rate, the energy transfer rate constant is significantly increased from 4 to 20 ns−1. Our results have quantitatively elucidated decay mechanisms that are important toward understanding and controlling of the light-matter interaction at the nanoscale.

Transient and Flexible Hyperbolic Metamaterials on Freeform Surfaces

Transient technology is deemed as a paramount breakthrough for its particular functionality that can be implemented at a specific time and then totally dissolved. Hyperbolic metamaterials (HMMs) with high wave-vector modes for negative refraction or with high photonic density of states to robustly enhance the quantum transformation efficiency represent one of the emerging key elements for generating not-yet realized optoelectronics devices. However, HMMs has not been explored for implementing in transient technology. Here we show the first attempt to integrate transient technology with HMMs, i.e., transient HMMs, composed of multilayers of water-soluble and bio-compatible polymer and metal. We demonstrate that our newly designed transient HMMs can also possess high-k modes and high photonic density of states, which enables to dramatically enhance the light emitter covered on top of HMMs. We show that these transient HMMs devices loss their functionalities after immersing into deionized water within 5 min. Moreover, when the transient HMMs are integrated with a flexible substrate, the device exhibits an excellent mechanical stability for more than 3000 bending cycles. We anticipate that the transient HMMs developed here can serve as a versatile platform to advance transient technology for a wide range of application, including solid state lighting, optical communication, and wearable optoelectronic devices, etc.

Metamaterial Perfect Absorber Analyzed by a Meta-cavity Model Consisting of Multilayer Metasurfaces

We demonstrate that the metamaterial perfect absorber behaves as a meta-cavity bounded between a resonant metasurface and a metallic thin-film reflector. The perfect absorption is achieved by the Fabry-Perot cavity resonance via multiple reflections between the “quasi-open” boundary of resonator and the “close” boundary of reflector. The characteristic features including angle independence, ultra-thin thickness and strong field localization can be well explained by this meta-cavity model. With this model, metamaterial perfect absorber can be redefined as a meta-cavity exhibiting high Q-factor, strong field enhancement and extremely high photonic density of states, thereby promising novel applications for high performance sensor, infrared photodetector and cavity quantum electrodynamics devices.

Epitaxial superlattices with titanium nitride as a plasmonic component for optical hyperbolic metamaterials

Titanium nitride (TiN) is a plasmonic material having optical properties resembling gold. Unlike gold, however, TiN is complementary metal oxide semiconductor-compatible, mechanically strong, and thermally stable at higher temperatures. Additionally, TiN exhibits low-index surfaces with surface energies that are lower than those of the noble metals which facilitates the growth of smooth, ultrathin crystalline films. Such films are crucial in constructing low-loss, high-performance plasmonic and metamaterial devices including hyperbolic metamaterials (HMMs). HMMs have been shown to exhibit exotic optical properties, including extremely high broadband photonic densities of states (PDOS), which are useful in quantum plasmonic applications. However, the extent to which the exotic properties of HMMs can be realized has been seriously limited by fabrication constraints and material properties. Here, we address these issues by realizing an epitaxial superlattice as an HMM. The superlattice consists of ultrasmooth layers as thin as 5 nm and exhibits sharp interfaces which are essential for high-quality HMM devices. Our study reveals that such a TiN-based superlattice HMM provides a higher PDOS enhancement than gold- or silver-based HMMs.

One Dimensional Polymeric Organic Photonic Crystals for DFB Lasers

We present a very simple method to realize a one-dimensional photonic crystal (1D PC), consisting of a dye-doped polymeric multilayer. Due to the high photonic density of states at the edges of the photonic band-gap (PBG), a surface emitting distributed feedback (DFB) laser is obtained with this structure. Furthermore, the incidence angle dependence of the PBG of the polymeric multilayer is reported.