Bragg Mirror Structure Research Articles

Assessment of Bloch surface wave-based one-dimensional photonic crystal sensor using ultraviolet range

To generate resonance in the ultraviolet (UV) wavelength region, we have developed a Bragg mirror structure with a SiO2 top layer. This paper shows the wavelength at which sensitivity occurs by modifying the architecture of the one-dimensional photonic crystal (1D-PhC) structure appropriately. The structural parameters are adjusted to excite a Bloch surface wave with a wavelength of 256 and 281 nm at the top interface, which are the operational wavelengths. The spectrum’s distribution of electric fields and mode confinement confirmed the suggested structure with an 8-nm thick defect layer. The proposed design is empathetic at UV wavelength with varying analyte’s refractive index value. The investigation shows that the sensitivity is about 107.42 and 101.85 deg/RIU, and the quality factor is 1426.17 and 1708.14 nm at UV wavelengths of 281 and 256 nm, respectively.

Spectral-Free Double Light Detection of DNA Based on a Porous Silicon Bragg Mirror.

To improve the detection sensitivity of a porous silicon optical biosensor in the real-time detection of biomolecules, a non-spectral porous silicon optical biosensor technology, based on dual-signal light detection, is proposed. Double-light detection is a combination of refractive index change detection and fluorescence change detection. It uses quantum dots to label probe molecules to detect target molecules. In the double-signal-light detection method, the first detection-signal light is the detection light that is reflected from the surface of the porous silicon Bragg mirror. The wavelength of the detection light is the same as the wavelength of the photonic band gap edge of the porous silicon Bragg mirror. CdSe/ZnS quantum dots are used to label the probe DNA and hybridize it with the target DNA molecules in the pores of porous silicon to improve its effective refractive index and enhance the detection-reflection light. The second detection-signal light is fluorescence, which is generated by the quantum dots in the reactant that are excited by light of a certain wavelength. The Bragg mirror structure further enhances the fluorescence signal. A digital microscope is used to simultaneously receive the digital image of two kinds of signal light superimposed on the surface of porous silicon, and the corresponding algorithm is used to calculate the change in the average grey value before and after the hybridization reaction to calculate the concentration of the DNA molecules. The detection limit of the DNA molecules was 0.42 pM. This method can not only detect target DNA by hybridization, but also detect antigen by immune reaction or parallel biochip detection for a porous silicon biosensor.

Bloch surface waves biosensing in the ultraviolet wavelength range – Bragg structure design for investigating protein adsorption by in situ Kretschmann-Raether ellipsometry

We designed a Bragg mirror structure with an SiO2 top layer to create a resonance in the ultraviolet wavelength range, near the absorption peak position of various proteins. We demonstrate that the wavelength of enhanced sensitivity can be adjusted by proper design of the 1D photonic structure. The possibility to design the wavelength of enhanced sensitivity supports measurements of better selectivity, optimized for the absorption of the target material. Since the width of the resonant peak in the reflectance spectra can be sharper than those of plasmonics, and they can be positioned at more favourable regions of the instrument and material (e.g., in terms of intensity or selectivity), the sensitivity can exceed those of plasmon-enhanced measurements. In this study we demonstrate the main features of the concept at the example of in situ spectroscopic ellipsometry of fibrinogen adsorption in the Kretschmann-Raether configuration. We realized a resonant peak with a full width at half maximum of 3 nm near the wavelength of 280 nm, which coincides with the absorption maximum of fibrinogen. The influence of depolarization and surface roughness on the measurements, and the potential for improving the current experimental detection limit of 45 pg/mm2 is also discussed.

Detection of Ammonia-Oxidizing Bacteria (AOB) Using a Porous Silicon Optical Biosensor Based on a Multilayered Double Bragg Mirror Structure.

We successfully demonstrate a porous silicon (PS) double Bragg mirror by electrochemical etching at room temperature as a deoxyribonucleic acid (DNA) label-free biosensor for detecting ammonia-oxidizing bacteria (AOB). Compared to various other one-dimension photonic crystal configurations of PS, the double Bragg mirror structure is quite easy to prepare and exhibits interesting optical properties. The width of high reflectivity stop band of the PS double Bragg mirror is about 761 nm with a sharp and deep resonance peak at 1328 nm in the reflectance spectrum, which gives a high sensitivity and distinguishability for sensing performance. The detection sensitivity of such a double Bragg mirror structure is illustrated through the investigation of AOB DNA hybridization in the PS pores. The redshifts of the reflectance spectra show a good linear relationship with both complete complementary and partial complementary DNA. The lowest detection limit for complete complementary DNA is 27.1 nM and the detection limit of the biosensor for partial complementary DNA is 35.0 nM, which provides the feasibility and effectiveness for the detection of AOB in a real environment. The PS double Bragg mirror structure is attractive for widespread biosensing applications and provides great potential for the development of optical applications.

Dynamical calculation of third-harmonic generation in a semiconductor quantum well

Non-linear phenomena in optically excited semiconductor structures are of high interest. We here develop a model capable of studying the dynamics of the photoexcited carriers, including Coulomb interaction on a Hartree-Fock level, on the same footing as the dynamics of the light field impinging on an arbitrary photonic structure. Applying this method to calculate the third harmonic generation in a semiconductor quantum well embedded in a Bragg mirror structure, we find that the power-law exponent of the intensity dependence of the third harmonic generation depends on the frequency of the exciting pulse. Off-resonant pulses follow the expected cubic dependence, while the exponent is smaller for resonant pulses due to saturation effects in the induced carrier density. Our study provides a detailed understanding of the carrier and light field dynamics during non-linear processes.

Synchronization of semiconductor laser arrays with 2D Bragg structures

A model of a planar semiconductor multi-channel laser is developed. In this model two-dimensional (2D) Bragg mirror structures are used for synchronizing radiation of multiple laser channels. Coupling of longitudinal and transverse waves can be mentioned as the distinguishing feature of these structures. Synchronization of 20 laser channels is demonstrated with a semi-classical approach based on Maxwell-Bloch equations.

Hyperbolic metamaterials based on Bragg polariton structures

A new hyperbolic metamaterial based on a modified semiconductor Bragg mirror structure with embedded periodically arranged quantum wells is proposed. It is shown that exciton polaritons in this material feature hyperbolic dispersion in the vicinity of the second photonic band gap. Exciton–photon interaction brings about resonant nonlinearity leading to the emergence of nontrivial topological polaritonic states. The formation of spatially localized breather-type structures (oscillons) representing kink-shaped solutions of the effective Ginzburg–Landau–Higgs equation slightly oscillating along one spatial direction is predicted.

Enhancement of QDs' fluorescence based on porous silicon Bragg mirror

We fabricated a new porous silicon photonic device which is a special multi-layer porous silicon including two different single layer porous silicon and a porous silicon Bragg mirror, and investigated the influence of porous silicon Bragg mirror's structure on the fluorescence intensity of quantum dots (QDs) which infiltrated into porous silicon device, and CdSe/ZnS QDs we used emit at 605nm and 625nm respectively. By immersing porous silicon samples in QDs solution, QDs were successfully infiltrated into porous silicon devices which have high reflection band at or beyond fluorescence peak. Experimental results show that the fluorescence intensity of QDs which infiltrated into the first layer of porous silicon device can be enhanced when fluorescence peak falls into the high reflection band of porous silicon device.

Smelling in Chemically Complex Environments: An Optofluidic Bragg Fiber Array for Differentiation of Methanol Adulterated Beverages

A novel optoelectronic nose for analysis of alcohols (ethanol and methanol) in chemically complex environments is reported. The cross-responsive sensing unit of the optoelectronic nose is an array of three distinct hollow-core infrared transmitting photonic band gap fibers, which transmit a specific band of IR light depending on their Bragg mirror structures. The presence of alcohol molecules in the optofluidic core quenches the fiber transmissions if there is an absorption band of the analyte overlapping with the transmission band of the fiber; otherwise they remain unchanged. The cumulative response data of the fiber array enables rapid, reversible, and accurate discrimination of alcohols in chemically complex backgrounds such as beer and fruit juice. In addition, we observed that humidity of the environment has no effect on the response matrix of the optoelectronic nose, which is rarely achieved in gas-sensing applications. Consequently, it can be reliably used in virtually any environment without precalibration for humidity or drying the analytes. Besides the discussed application in counterfeit alcoholic beverages, with its superior sensor parameters, this novel concept proves to be a promising contender for many other applications including food quality control, environmental monitoring, and breath analysis for disease diagnostics.

Strain evaluation in AlInN/GaN Bragg mirrors by in situ curvature measurements and ex situ x-ray grazing incidence and transmission scattering

Strain in lattice matched and mismatched AlInN/GaN Bragg mirror structures were studied by in situ curvature and various ex situ x-ray measurements. In the case of lattice mismatched structures considerable deviations of the in-plane lattice parameters were evidenced near the surface region as well as in depth using x-ray grazing incidence and x-ray transmission scattering in Laue geometry. The experimental findings are explained in terms of partial stress relaxation of the AlInN/GaN Bragg layer stack with respect to the underlying GaN buffer and a mutual tensioning of the GaN and AlInN layers with respect to each other.

Strain profiling of AlInN/GaN distributed Bragg reflectors using in situ curvature measurements and ex situ X-ray diffraction

In this work, we show the use of in situ curvature and X-ray measurements to evaluate the metal organic vapor phase growth process of distributed Bragg reflectors consisting of an AlInN/GaN system. At first, it is investigated how the initial wafer bow and the heating of the bare substrates influences the curvature measurements. The strain induced by thermal mismatch and lattice mismatch is discussed at the example of multilayer AlInN/GaN Bragg mirror structures on sapphire substrate. We will demonstrate that thereby an estimation of the composition in the AlInN layers is possible. Additionally the samples were examined with multiple X-ray diffraction techniques, as symmetrical and asymmetrical reciprocal space maps, grazing-incidence in-plane diffraction and X-ray reflectivity. These results are compared with the in situ measurements.

Periodic modulation of extraordinary optical transmission through subwavelength hole arrays using surrounding Bragg mirrors

The enhanced light transmission through an array of subwavelength holes surrounded by Bragg mirrors is studied, showing that the mirrors act to confine the surface plasmons associated with the extraordinary optical transmission effect, forming a surface resonant cavity. The overall effect is increased light transmission intensity by more than a factor of 3 beyond the already enhanced transmission, independent of whether the Bragg mirrors are on the input or the output side of the incident light. The geometry of the Bragg mirror structures controls the enhancement and can even reduce the transmission by half. By varying these geometric parameters, we were able to periodically modulate the transmission of light for specific wavelengths, consistent with the propagation and interference of surface plasmon waves in a resonant cavity. Finite difference time domain simulations and a wave propagation model verify this effect.

Semiconductor quantum-well saturable absorbers for efficient passive Q switching of a diode-pumped 946 nm Nd:YAG laser

InGaAs quantum wells and a Bragg mirror structure are grown on a GaAs substrate to simultaneously serve as a low-loss saturable absorber and an output coupler for highly efficient Q switching of a diode-pumped Nd:YAG laser operating at 946 nm. With an incident pump power of 9.2 W, the laser produces pulses of 38 ns duration with average pulse energy of as much as 20 microJ at a pulse repetition rate of 55 kHz.

Passively Q-switched Yb^3+:YCa_4O(BO_3)_3 laser with InGaAs quantum wells as saturable absorbers

A diode-pumped Yb:YCOB laser at 1086 nm is passively Q switched by using InGaAs quantum wells as saturable absorbers and utilizing the Bragg mirror structure as an output coupler. With an absorbed pump power of 9.2 W the laser produces pulses of 100 ms duration with average pulse energy of as much as 165 microJ at a pulse repetition rate of 7 kHz.

Linewidth and Chirp of MEMS-VCSELs

This letter analyzes the influence of micromachined Bragg mirrors within active Fabry-Perot cavities on basic laser characteristics, like linewidth and chirp. The impact of thermal noise of the micromechanic structure is discussed and its influence on the linewidth of a microelectromechanical system (MEMS)-tunable vertical-cavity surface-emitting laser (VCSEL) is verified in an experiment. For the first time, we demonstrate for a MEMS-VCSEL a record low average linewidth of 210 MHz and extract an intrinsic linewidth of below 30 MHz. The second issue deals with the influence of microforces like radiation pressure, radiometric pressure, and length extension of the Bragg-mirror structure due to absorption on the chirp behavior of a MEMS-laser. For the first time, these effects and their influence on the VCSEL dynamics are modelled and discussed in detail. Further, the measured chirp characteristics are analyzed and compared with our modelling to quantify the influence of above effects on the device characteristics

Deepin situdry-etch monitoring of III-V multilayer structures using laser reflectometry and reflectivity modeling

Deep reactive ion etching of III-V multilayer structures is an important issue for long wavelength vertical cavity surface emitting laser (VCSELs) where full laser structures are usually very thick. Test etchings were performed on GaAs/AlxGa1−xAs Bragg mirror structures and monitored using laser reflectometry at 651.4 nm. In order to perform very deep etching, up to 9 μm, we designed and fabricated a special two-level mask made up of a thick nitride layer and a thin nickel layer. The etching rate is a complex function of many parameters and may change from run to run for similar structures. Therefore, it is important to have a method to control accurately the process in situ by continuously matching, experimental curves with the results of the reflectivity modeling. Here, we present a model, based on the Abelès matrix method, of the normal incidence reflectivity of a multilayer stack as a function of etch depth. Comparison between the model and the observed reflectivity variation during etching makes it possible to distinguish individual layers with very high precision.

Passively mode-locked diode-pumped surface-emitting semiconductor laser

A surface-emitting semiconductor laser has been passively mode locked in an external cavity incorporating a semiconductor saturable absorber mirror. The gain medium consists of a stack of 12 InGaAs-GaAs strained quantum wells, grown above a Bragg mirror structure, and pumped optically by a high-brightness diode laser. The mode-locked laser emits pulses of 22-ps full-width at half maximum duration at 1030 nm, with a repetition rate variable around 4.4 GHz.

Molecular-beam epitaxy growth of multiple-wavelength mirrors and applications for a dual-wavelength resonant-cavity photodetector

The growth of Bragg mirror structures by molecular-beam epitaxy (MBE) results in a variety of photonic devices employing microcavities. We have grown multiple-wavelength mirrors in the AlGaAs system which were designed to reflect dual and quadruple wavelengths. The dual-wavelength mirror structure has been applied in the design of a high efficiency resonant cavity photodiode. This dual-wavelength resonant cavity photodiode has external quantum efficiencies greater than 50% with very high selectivity of the two wavelengths.