Dielectric Bragg Mirrors Research Articles

Spin-vertical-cavity surface-emitting lasers with by-design-defined birefringence for high-speed modulation.

We propose a new, to the best of our knowledge, type of spin-vertical-cavity surface-emitting laser (VCSEL) with controlled by design birefringence. To this aim, we utilize the so-called columnar thin films (CTFs) in the VCSEL dielectric distributed Bragg mirror and/or in a second dielectric cavity. We design such CTF-VCSELs with pre-defined birefringence and calculate their polarization-resolved resonant longitudinal modes and the corresponding quantum-well confinement factors and threshold gains. Using the spin-flip VCSEL model, we show that such spin CTF-VCSELs can achieve small-signal modulation response with a 3 dB cutoff frequency of several hundreds of GHz.

Study of eigen frequency In1-xGaxAsyP1-y 1.55 µm VCSEL with SiO2 /TiO2 dielectric Bragg reflector

In this work, we focused on investigating the eigen frequency and internal standing wave characteristics of a vertical surface cavity emitting laser operating at a wavelength of 1.55 µm. The design of the cavity involved determining the cavity length, selecting the material for the cavity spacer, and carefully placing the quantum wells within the cavity to achieve maximum overlap with the electric field. In our case, the choice of the dielectric Bragg mirror with SiO2/TiO2 layers helps in achieving high reflectivity and low optical losses. The quantum wells are strategically placed within the cavity to ensure maximum overlap with the electric field. This allows for efficient carrier injection and recombination, leading to laser emission. The specific composition of the quantum wells, In0.54Ga0.46As0.99P0.01 / In0.75Ga0.25As0.55P0.45, indicates the proportions of indium (In), gallium (Ga), arsenic (As), and phosphorus (P) in the material. These compositions are chosen to achieve the desired electronic band structure and emission wavelength. By studying the eigen frequency and internal standing waves in our designed laser cavity, our aim is to understand the resonant modes and behavior of light within the device. This knowledge is crucial for optimizing the laser's performance and improving its efficiency for various applications.

High Quality Factor in Solution-Processed Inorganic Microcavities Embedding CsPbBr3 Perovskite Nanocrystals.

Optical microcavities grant manipulation over light-matter interactions and light propagation, enabling the fabrication of foundational optical and optoelectronic components. However, the materials used for high-performing systems, mostly bulk inorganics, are typically costly, and their processing is hardly scalable. In this work, we present an alternative way to fabricate planar optical resonators via solely solution processing while approaching the performances of conventional systems. Here, we couple fully solution-processed high dielectric contrast inorganic Bragg mirrors obtained by sol-gel deposition with the remarkable photoluminescence properties of CsPbBr3 perovskite nanocrystals. The approach yields microcavities with a quality factor of ∼220, which is a record value for solution-processed inorganic structures, and a strong emission redistribution resulting in a 3-fold directional intensity enhancement.

Transmission and Reflection Spectra of a Bragg Microcavity Filled with a Periodic Graphene-Containing Structure

The transmission and reflection spectra of a one-dimensional microresonator structure with dielectric Bragg mirrors, the working cavity of which is filled with several “dielectric-graphene” or “semiconductor-graphene” periods with controlled material parameters, were obtained using transfer matrices and numerical methods. Carrier drift in graphene monolayers is created to achieve amplification, which makes it possible to use the hydrodynamic approximation to represent graphene conductivity in the terahertz range. The transformation of spectra is achieved both by changing the energy state of the graphene monolayers and by changing the external magnetic field. It is shown that amplification is observed in the region where the real part of the conductivity is negative as the chemical potential (Fermi energy) increases, and the coefficients T and R become substantially greater than unity. The results of the work may be of interest to developers of graphene-based controlled photonic devices.

Spectra of a Bragg Microresonator Filled with a Graphene-Containing Medium

Transmission spectra of a symmetric microresonator structure, with dielectric Bragg mirrors, are obtained. The working cavity of the structure is partially filled by a layer of a quarter-wave thickness of finely layered “graphene–semiconductor” medium, with material parameters controlled by external electric and magnetic fields. It is shown, that the transformation of the spectra is achieved both by changing the energy state of the graphene layers and by changing the external magnetic field. The spectral characteristics for the inverted and doped states of graphene layers are established.

Electrostatic tapering for efficient generation of radiation.

We demonstrate the feasibility of electrostatic (dc) tapering such that the net average force of the electromagnetic (ac) field is compensated by a dc field, which at resonance may be interpreted as "direct" energy transfer from the dc to the ac field. This combination persists in all three components of the setup-e-gun, resonant zone, and collector, in each one playing a different role. In equilibrium, the two field components field-emit at the cathode a density modulated cylindrical beam which is accelerated along the e-gun by the dc field; the latter also focuses the e-beam. Radiation confinement perpendicular to the e-beam is ensured by an array of dielectric Bragg-mirrors and an array of metallic hollow electrodes impose synchronous bunches and wave. This double periodic structure ensures the coexistence of dc and ac fields in the same volume. Numerical simulations demonstrate the feasibility of generation of order of 1[W] power at 1 THz from a volume on a scale of few mm^{3} with efficiency of the order of 25%.

Design and simulation of the optical amplitude-shift keying modulator using Fabry–Perot resonator coupled with graphene at near-infrared frequencies

An optical amplitude modulator operating at near-infrared frequencies is presented. The proposed modulator structure consists of a Fabry–Perot (FP) cavity coupled with graphene located in the middle of two dielectric Bragg mirrors. Graphene’s presence as an active material with adjustable optical conductivity, as well as its effective interaction with powerful standing waves confined in the cavity, enables spectral tuning of the transmission spectrum. Since the resonator has a high quality factor, a small resonance frequency shift due to graphene Fermi energy change results in a huge change of the input light transmission value of the resonator, which makes it possible to achieve high modulation depth (MD). The results demonstrate that the proposed optical modulator has insertion loss lower than 0.1 and MD larger than 90%. It is believed that our study may be useful for optical wireless communication acting at near-infrared region.

One-dimensional optomagnonic microcavities for selective excitation of perpendicular standing spin waves

Here we propose a method of the excitation of perpendicular standing spin waves (PSSWs) of different orders in an optomagnonic microcavity by ultrashort laser pulses. The microcavity is formed by a magnetic dielectric film surrounded by dielectric non-magnetic Bragg mirrors. Optical cavity modes in the magnetic layer provide concentration and strongly non-uniform distribution of the optical power over the layer thickness and therefore induce the effective field of the inverse Faraday effect also spatially non-uniform. It results in excitation of PSSWs. PSSWs whose wavevector is closest to the wavevector characterizing distribution of the inverse Faraday effect field are excited most efficiently. Consequently, a key advantage of this approach is a selectivity of the PSSW excitation which allows to launch PSSWs of required orders only. All-optical operation of the optomagnonic cavities opens new possibilities for their applications for quantum technologies.

Refractive index sensor based on a Tamm Fabry-Perot hybrid resonance.

A highly sensitive refractive index sensor is proposed by using the resonant coupling of a Tamm state to a Fabry-Perot resonance in slits periodically pierced in a metal film. This new hybrid resonance exists at the interface between a dielectric Bragg mirror and a subwavelength metal grating. Contrary to a classic Tamm plasmon, it is sensitive to the ambient media refractive index due to its confinement inside the grating slits. The proposed sensor output can be either the reflected intensity or preferably the wavelength, and its sensitivity and figure of merit are numerically investigated with the help of rigorous coupled wave analysis. The sensitivity of the studied sensor is 87 nm/RIU for a refractive index range from 1.25 to 1.38, and, at the expense of the resolution, it can reach up to 160 nm/RIU for a grating duty cycle of 50%. The figure of merit is around ${{7.5}}\;{{\rm{RIU}}^{- 1}}$ with a large measuring range. The index sensor performances and operating resonance wavelength can be modified by adjusting the grating geometric parameters (height and duty cycle). The possibility to achieve wavelength modulation in any spectral range makes the proposed grating Tamm structure an attractive candidate to design refractive index sensors and photonic components in the infrared and terahertz domains.

Fano-resonant ultrathin film optical coatings.

Optical coatings are integral components of virtually every optical instrument. However, despite being a century-old technology, there are only a handful of optical coating types. Here, we introduce a type of optical coatings that exhibit photonic Fano resonance, or a Fano-resonant optical coating (FROC). We expand the coupled mechanical oscillator description of Fano resonance to thin-film nanocavities. Using FROCs with thicknesses in the order of 300 nm, we experimentally obtained narrowband reflection akin to low-index-contrast dielectric Bragg mirrors and achieved control over the reflection iridescence. We observed that semi-transparent FROCs can transmit and reflect the same colour as a beam splitter filter, a property that cannot be realized through conventional optical coatings. Finally, FROCs can spectrally and spatially separate the thermal and photovoltaic bands of the solar spectrum, presenting a possible solution to the dispatchability problem in photovoltaics, that is, the inability to dispatch solar energy on demand. Our solar thermal device exhibited power generation of up to 50% and low photovoltaic cell temperatures (~30 °C), which could lead to a six-fold increase in the photovoltaic cell lifetime.

Graphene-tuned EIT-like effect in photonic multilayers for actively controlled light absorption of topological insulators.

As newly emerging nanomaterials, topological insulators with unique conducting surface states that are protected by time-reversal symmetry present excellent prospects in electronics and photonics. The active control of light absorption in topological insulators are essential for the achievement of novel optoelectronic devices. Herein, we investigate the controllable light absorption of topological insulators in Tamm plasmon multilayer systems composed of a Bi1.5Sb0.5Te1.8Se1.2 (BSTS) film and a dielectric Bragg mirror with a graphene-involved defect layer. The results show that an ultranarrow electromagnetically induced transparency (EIT)-like window can be generated in the broad absorption spectrum. Based on the EIT-like effect, the Tamm plasmon enhanced light absorption of topological insulators can be dynamically tuned by adjusting the gate voltage on graphene in the defect layer. These results will pave a new avenue for the realization of topological insulator-based active optoelectronic functionalities, for instance light modulation and switching.

Planar optomagnonic cavities driven by surface spin waves

A generalized rigorous Floquet scattering-matrix method for stratified anisotropic optical media, subject to a periodic spatiotemporal modulation, is formulated and implemented. The method is applied for studying an optomagnonic cavity formed by an in-plane magnetized ferrite film, in which a magnetostatic surface spin wave propagates, sandwiched between two nonmagnetic dielectric Bragg mirrors. Our results provide unambiguous evidence that externally incident light, when trapped in a cavity mode, experiences a strongly enhanced interaction with the spin wave due to the increased coupling time, which can give rise to pronounced effects if the appropriate selection rules are fulfilled. By means of systematic calculations we reveal and explain some remarkable features of this interaction, such as formation of spectral gaps, controllable transmission, and the emergence of inelastic diffracted beams, and show that efficient conversion of the optical wave can be achieved by triply resonant inelastic scattering through (multi)magnon absorption and emission processes.

Layered optomagnonic structures: Time Floquet scattering-matrix approach

A fully dynamic theoretical approach to layered optomagnonic structures, based on a time Floquet scattering-matrix method, is developed. Its applicability is demonstrated on a simple design of a dual photonic-magnonic cavity, formed by sandwiching a magnetic garnet thin film between two dielectric Bragg mirrors, subject to continuous excitation of a perpendicular standing spin wave. Some remarkable phenomena, including nonlinear photon-magnon interaction effects and enhanced inelastic light scattering in the strong-coupling regime, fulfilling a triple-resonance condition, are analyzed and the limitations of the quasistatic adiabatic approximation are established.

Improvement of the polar magneto-optical Kerr effect in the spatial tunable one-dimensional magnetophotonic crystals

We have studied the magnetophotonic crystals (MPCs) with excellent capabilities to enhance reflection and Kerr rotation simultaneously. In order to simultaneously investigate the symmetric and nonsymmetric spatial structures, we have considered the different repetition numbers for dielectric photonic crystals around the magnetic defect layer. To construction of dielectric Bragg mirrors, we have used of Al2O3 due to low refractive index and its unique optical features. The Ce:YIG with high magneto-optical features is utilized as magnetic material to increasing the magneto-optical responses of structures. By adjusting spatial features such as repetition numbers of PCs and thickness of magnetic defect layers, we have achieved the magneto-optical Kerr rotation more than 70 degrees and reflection close to 1. We have introduced the structures with single and several cavities. For investigation of light localization at defect layer, the electric field distribution along the MPCs is simulated using finite element method (FEM). With light localization inside the cavity and multiple reflections in it, the magneto-optical (MO) responses of these MPCs are significantly increased. Our proposed structures having high MO responses, are suitable cases to design MO elements incorporated in integrated photonic devices and optical telecommunication tools.

Spatial confinement of the optical Tamm states under patterned metal films

Optical Tamm states are defect electromagnetic modes which appear at the discontinuity of the optical crystal. Being trapped at the interface of a dielectric Bragg mirror and a metal they demonstrate a tight localization in the direction perpendicular to the interface. Here we study the trapping of the Tamm states in the interface plane by patterning of the metal layer. In particular, we propose a method of metal film deposition based on a electro-induced lithography which possesses a nanometer lateral resolution.

Manipulating optical Tamm state in the terahertz frequency range with graphene

The optical Tamm state (OTS), which exists generally at the interface between metal and a dielectric Bragg mirror, has been studied extensively in the visible and near infrared spectra. Nevertheless, OTS in the terahertz (THz) region normally receives far less attention. In this Letter, we demonstrate the physical mechanism of OTS at the interface between graphene and a dielectric Bragg mirror in the THz frequency band by applying the transfer matrix method and dispersion characteristics. Based on such mechanisms, we propose an efficient method that can precisely generate and control OTS at a desired angle and frequency. Moreover, we show that the OTS is dependent on the optical conductivity of graphene, making the graphene–dielectric-Bragg-mirror a good candidate for dynamic tunable OTS device in the THz frequency range.

Purcell effect investigation in organic Tamm plasmon structures

We provide a theoretical and experimental investigation of a Purcell enhancement in a Tamm-plasmon based microcavity structure with an organic (4,4′-Bis(N-carbazolyl)−l,l′- biphenyl (CBP)) active layer. The microcavity structure was fabricated using several techniques as a magnetron deposition (Ta2O5/SiO2 dielectric Bragg mirror) and a thermal evaporation (CBP organic layer and silver layer on the top). Dependency of the modal Purcell factor on emission angle and frequency was calculated using S-quantization formalism. The emission spectra and the rate of fluorescence intensity decay of the Tamm structure was experimentally measured in ultraviolet region. We show, that at the frequencies corresponded to the Tamm plasmon resonance, the rate of the CBP molecule fluorescence decay increasing. Maximum registered value of the Purcell factor is close to 3.

Tunable Terahertz Absorption with Optical Tamm State in the Graphene-Bragg Reflector Configuration

Tunable terahertz absorption in the interface between graphene and dielectric Bragg reflector (DBR) has been numerically demonstrated. The near perfect absorption mainly originates from the enhancement of the electric field owing to the excitation of the optical Tamm state (OTS) at the interface between graphene and dielectric Bragg mirror. It has been found that the absorption peak occurs at specific incident angles, which can be employed for realizing the frequency and angular absorbers. Further, we demonstrate that the position of the absorption peak can be tuned by changing the Fermi energy of graphene. Moreover, the behaviors of the near perfect absorption are strongly related to the dielectric constants and thicknesses of the surrounding dielectrics. The tunability of graphene-DBR structure absorption may help to find favorable applications for the realization of high-performance graphene optoelectronic devices.

Optimization of one-dimensional photonic crystals with double layer magneto-active defect

Success of practical implementation of one-dimensional photonic crystals with magneto-active layers is evaluated in high values of magneto-optical (MO) quality factor Q and figure of merit F. The article relates to optimization of one-dimensional photonic crystals with double layer magneto-active (MA) defect of composition Bi1.0Y0.5Gd1.5Fe4.2Al0.8O12/Bi2.8Y0.2Fe5O12 located between the nongarnet dielectric Bragg mirrors. The structure design was performed by changing the number of layer pairs in Bragg mirrors m and the optical thickness of MA defect lM to achieve high values of MO characteristics. Theoretical predictions were confirmed by experimental investigation of eight synthesized configurations with m = 4 and m = 7. We have demonstrated the maximum Q = 15.1 deg and F = 7.5% at 624 nm for structure with m = 4 and lM = (2.5·λ0/2), where λ0 = 690 nm is the photonic band gap center. Configurations with m = 3 can also provide their effectiveness in realization. Maximum MO activity was achieved for configurations with m = 7. The structures with lM = (0.8·λ0/2) and lM = (2.5·λ0/2) showed respectively the specific Faraday rotation −113 deg/μm (that exceeds in 62 times the Faraday rotation of MA double layer film) at 654 nm and absolute Faraday rotation −20.6 deg at 626 nm.

One-dimensional Tamm plasmons: Spatial confinement, propagation, and polarization properties

Tamm plasmons are confined optical states at the interface of a metal and a dielectric Bragg mirror. Unlike conventional surface plasmons, Tamm plasmons may be directly excited by an external light source in both TE and TM polarizations. Here we consider the one-dimensional propagation of Tamm plasmons under long and narrow metallic stripes deposited on top of a semiconductor Bragg mirror. The spatial confinement of the field imposed by the stripe and its impact on the structure and energy of Tamm modes are investigated. We show that the Tamm modes are coupled to surface plasmons arising at the stripe edges. These plasmons form an interference pattern close to the bottom surface of the stripe that involves modification of both the energy and loss rate for the Tamm mode. This phenomenon is pronounced only in the case of TE polarization of the Tamm mode. These findings pave the way to application of laterally confined Tamm plasmons in optical integrated circuits as well as to engineering potential traps for both Tamm modes and hybrid modes of Tamm plasmons and exciton polaritons with meV depth.