Distributed Bragg Mirrors Research Articles

Fabrication of dual sensitive titania (TiO2)/graphene oxide (GO) one-dimensional photonic crystals (1DPCs)

1DPCs, such as Bragg stack and distributed Bragg mirrors, are the simplest photonic crystal. TiO2/GO 1DPCs were fabricated by spin-coating technique. The photonic stopbands of the 1DPCs were measured by fiber optic spectrometer. The results demonstrated that the 1DPCs with different stopbands could be obtained from controlling spin-coating and incident angles. The prepared 1DPCs have double response to both dimethyl sulfoxide (DMSO) and alkali solution.

A terahertz photonic crystal cavity with high Q-factors

A terahertz 1D photonic crystal cavity with very high Q-factor is demonstrated. The cavity consists of two parallel distributed Bragg mirrors and one air layer between them as defect layer. By increasing the length of the defect layer, the cavity has a very narrow transmission bandwidth of 30 MHz at resonant frequency of 336 GHz, i.e., a high Q over 1.1 × 104 is achieved. Furthermore, an optically controllable THz switch is demonstrated by light irradiating on one of the middle silicon wafer in the cavity. And the power of optical beam needed for the switch is remarkably reduced to 0.16 W/cm2, which is nearly 50 times smaller than that for a THz switch using a single silicon wafer.

3-D Vectorial Optical Model for High-Contrast Grating Vertical-Cavity Surface-Emitting Lasers

High-Contrast Gratings (HCG) are modeled in a rigorous way by a new mode-matching approach. They are highly attractive because they have recently proved suitable to replace distributed Bragg mirrors in Vertical-Cavity Surface-Emitting Lasers (VCSELs). Through a change of basis from plane to cylindrical waves, the generalized transmission matrix of the grating layer is obtained in a form that can be directly used within VCSEL ELectroMagnetic (VELM) code. This is the fully 3-D vectorial code developed at IEIIT-CNR (Turin, Italy) for a decade, which has proven to have the capability to reproduce the experimental details of the various structures investigated so far. The inclusion of HCG in VELM is performed on the same footing as all other geometrical details and in a way that preserves the code accuracy and numerical efficiency. A full set of modes of a large-size HCG VCSEL can be computed in a few minutes on an ordinary laptop.

Distributed Bragg reflector based on porous anodic alumina fabricated by pulse anodization

In this paper, we demonstrate a distributed Bragg reflector (DBR) based on nanoporous anodic aluminum oxide (AAO) formed by pulse anodization. The AAO structure with alternating mild anodized (MA) and hard anodized (HA) layers having different porosities and thereby different refractive indices was fabricated in 0.3 M H2SO4 using potential pulses of 25 and 35 V. The effective refractive index of the HA layers can be tailored by changing the porosity of the HA layers. The porosity of the HA layers can be significantly increased by selective chemical etching of HA segments in 0.52 M H3PO4. Before etching, the porous AAO structure was supported by a polymer nanorod frame. On the selected surface area pores were infiltrated with polymers (polystyrene and PMMA). The designed AAO structure consists of alternating high and low refractive index layers and behaves as a distributed Bragg mirror reflecting light in two different ranges of wavelength. This behavior is extremely important in optical communication lines where two separate spectral bands of high reflectivity in the infrared region are desired.

Design and simulation of a high power single mode 1550nm InGaAsP VCSELs

In the present work, a new structure of vertical cavity surface emitting laser (VCSEL) is designed and simulated. In this structure, InGaAsP is used as the active region which is sandwiched between GaAs/AlGaAs distributed bragg mirror at the top of structure and GaAs/AlAs distributed bragg mirror at the bottom. In this work, the hole etching depth was continued down to the top of lower spacer layer while in the previous work the hole etching depth was only down to top of the upper spacer. In this way, the threshold current decrement of 76.52% and increment the power by 28% from 5mW to 6.4mW at bias current of 9mA was achieved. In this paper, device characteristics such as light power versus electrical current and voltage versus current are simulated and compared with the previous work.

10-GHz Mode-Locked Extended Cavity Laser Integrated With Surface-Etched DBR Fabricated by Quantum-Well Intermixing

The 10-GHz passively mode-locked AlGaInAs/InP 1.55- μm extended cavity lasers integrated with optimized surface-etched distributed Bragg mirrors have been fabricated. A quantum-well intermixing process was used to provide low-absorption loss gratings with accurate wavelength control. The lasers produce 2.99-ps sech2-pulses with a time-bandwidth product (TBP) of 0.51.

Monolithic 40-GHz Passively Mode-Locked AlGaInAs–InP 1.55-$\mu$m MQW Laser With Surface-Etched Distributed Bragg Reflector

We have fabricated 40-GHz passively mode-locked AlGaInAs-InP 1.55- lasers integrated with surface-etched distributed Bragg mirrors. Numerically optimized gratings provide low-scattering losses and accurate wavelength control. The lasers produce 4.46-ps Gaussian pulses with time-bandwidth product of 0.47.

Monolithic 45-GHz Mode-Locked Surface-Etched DBR Laser Using Quantum-Well Intermixing Technology

The 45-GHz passively mode-locked AlGaInAs-InP 1.55- m lasers integrated with surface-etched distributed Bragg mirrors have been fabricated. Quantum-well intermixing was used to provide low absorption loss gratings with accurate wavelength control. The lasers produce 3.6-ps Gaussian pulses with time-bandwidth product of 0.57.

Optical investigation of a hybrid GaN based microcavity with AlInN/GaN bottom and dielectric top distributed Bragg mirror

A hybrid GaN based microcavity was fabricated to investigate light matter coupling. The sample consists of a lattice matched AnInN/GaN bottom and a dielectric upper Bragg mirror. To increase the coupling strength an InGaN/GaN multi quantum well was embedded inside a 3 λ / 2 ( λ = 435 nm ) GaN cavity. The emission characteristics of the structure without top Bragg mirror were analyzed using photoluminescence spectroscopy. Two emission peaks at nearly fixed energy but changing intensity ratio with respect to the position on the sample arise. A detuning of the cavity mode and the excitonic emission into resonant condition is demonstrated by scanning across the wafer and temperature dependent measurements at about 50 K. Angle resolved photoluminescence investigations at the full hybrid structure exhibit two emission peaks. Predominantly excitonic behavior was found for the high and photonic-like behavior for the low energy peak. No clear anticrossing behavior was observed.

1.2-$\mu$m Semiconductor Disk Laser Frequency Doubled With Periodically Poled Lithium Tantalate Crystal

In this letter, we demonstrate an optically pumped semiconductor disk laser frequency doubled with a periodically poled lithium tantalate crystal. Crystals with various lengths were tested for intracavity frequency conversion. The semiconductor disk laser exploited GaInNAs-based active region with GaAs-AlAs distributed Bragg mirror to produce emission at 1.2-μm wavelength. The frequency doubled power up to 760 mW at the wavelength of 610 nm was achieved with a 2-mm-long crystal.

Photonic crystal vertical-cavity surface-emitting lasers with true photonic bandgap

By calculating the band diagrams for the distributed Bragg mirrors of vertical-cavity surface-emitting lasers (VCSELs) with triangular two-dimensional lattice of etched holes we show that true photonic bandgap (PBG) confinement is possible for TE-like polarized light. We confirm this true PBG confinement for a low-index line defect as well as for a low-index cavity mode. Such PBG-VCSELs are compatible with the VCSEL technology and do not require a complicated assembly of three-dimensional photonic crystals.

Surface electromagnetic waves at the interface between a homogeneous medium and a system of coupled waveguides

An analysis is made of the experimental investigations of the surface waves existing at the interface between a homogeneous medium and a periodically stratified medium that represents a bounded system of coupled waveguides. It is shown that, in all cases of the observation of surface waves, the bounded system of coupled waveguides has its own spectrum of guided modes and a spectrum of leaky modes that become surface waves of the system. It is also demonstrated that a biosensor can successfully operate when two surface waves serve as leaky modes of a Bragg waveguide in which the periodic system of waveguides is used as a distributed Bragg mirror of this waveguide. A structure supporting surface waves is designed on the basis of ten pairs of Nb2O5-SiO2 layers and implemented experimentally. The surface waves are detected with a K8 glass prism according to the Kretschmann scheme.

Closed-loop modeling of silicon nanophotonics from design to fabrication and back again

We present a method for component-centric modeling of silicon nanophotonics, where a closed optimization loop allows to take the effects of the fabrication process into account during the design of nanophotonic components. This enables black-box component descriptions with functional parameters. Underlying mask layouts of the components can then automatically be optimized for their actual performance, and not just for their geometric layout. To simulate the effect of fabrication, we developed a projection lithography simulator which was included inside the optimization loop. This method was applied to the design of a 1-dimensional distributed Bragg mirror.

Design and Characterization of Fabry–Pérot MEMS-Based Short-Wave Infrared Microspectrometers

Microspectrometers based on the monolithic integration of a microelectromechanical system (MEMS) Fabry–Perot filter and a HgxCd1–xTe-based infrared detector are discussed and measured results presented. The microspectrometers are designed to operate in the 1.5 μm to 2.6 μm wavelength range. Design equations are presented which account for the mechanical and optical characteristics of the device. Measurements indicate linewidths as narrow as 55 nm, switching times of 40 μs, and a tuning range of 380 nm, which is limited by snap-down. Optical characterization of the distributed Bragg mirrors and the Fabry–Perot filter are presented, and these are shown to be in good agreement with simple first-order analytical models. Bowing of the movable Fabry–Perot mirror due to stress gradients is identified as the dominant source of linewidth broadening.

Characterization of (Al)GaAs/AlAs distributed Bragg mirrors grown by MBE and LP MOVPE techniques

Optical reflectance (R) and high-resolution X-ray diffraction (HR XRD) have been used for characterization and verification of the distributed Bragg reflectors (DBR) grown by two competing and complementary techniques: molecular beam epitaxy (MBE) and low-pressure metalorganic vapor phase epitaxy (LP MOVPE). The DBRs under study consisted of the stack of (Al)GaAs and AlAs quarter wavelength layers deposited on (1 0 0) oriented GaAs substrates. We demonstrate experimentally that employment of the above-mentioned methods allows for comprehensive characterization of the Bragg mirror properties and optimization of their fabrication procedure for application in highly demanding optical devices.

Broadband optical absorption enhancement through coherent light trapping in thin-film photovoltaic cells

We show that optical absorption in thin-film photovoltaic cells can be enhanced by inserting a tuned two-component aperiodic dielectric stack into the device structure. These coatings are a generalization and unification of the concepts of an anti-reflection coating used in solar cells and high-reflectivity distributed Bragg mirror used in resonant cavity-enhanced narrowband photodetectors. Optimized two-component coatings approach the physically realizable limit and optimally redistribute the spectral photon density-of-states to enhance the absorption of the active layer across its absorption spectrum. Specific designs for thin-film organic solar cells increase the photocurrent under AM1.5 illumination, averaged over all incident angles and polarizations, by up to 40%.

Surface waves at the boundary of a system of coupled waveguides

Experimental investigations of surface waves at the interface between a homogeneous medium and a periodically stratified medium representing a restricted system of coupled waveguides are analysed. It is found that in all cases of the observation of surface waves a restricted system of waveguides has its own spectrum of guided modes and the spectrum of leaky modes, which become the surface waves of the system. It is shown that when two surface waves are used in a biosensor scheme, they should be realised as leaky modes of a Bragg waveguide in which a periodic system of waveguides was used as a distributed Bragg mirror of this waveguide. It is pointed out that the prism method of excitation of surface waves can be used in sensors, where these waves are employed as a detecting tool.

Hybrid nitride microcavity using crack-free highly reflective AlN/GaN and Ta2O5/SiO2distributed Bragg mirrors

We report the growth over 2 inch sapphire substrates of hybrid nitride-based microcavities using one crack-free highly reflective AlN/GaN distributed Bragg reflectors (DBRs) incorporated with AlN/GaN superlattice (SL) insertion layers and Ta2O5/SiO2 DBRs. The optical cavity is formed by a 5λ cavity consisting of n-type GaN, 10 pairs multiple quantum wells and p-type GaN sandwiched by AlN/GaN and Ta2O5/SiO2 DBRs. Reflectivity and photoluminescence measurements were carried out on these structures. A 29 periods AlN/GaN DBR incorporated with six AlN/GaN superlattice insertion layers showed no observable cracks and achieved a peak reflectivity of 99.4% and a stopband of 21 nm. Based on these high quality DBRs, the cavity mode is clearly resolved with a linewidth of 2.6 nm. These results demonstrate that the AlN/GaN system is very promising for the achievement of strong light–matter interaction and the fabrication of nitride-based vertical cavity surface emitting lasers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical study of acoustic band‐gap structures made of porous silicon

AbstractIn this paper, we discuss the acoustic properties of porous silicon and outline the differences and similarities of the behaviour of elastic and light waves in mesoporous porous silicon etched in p+‐type silicon wafers. We then investigate the expected acoustic characteristics of distributed Bragg mirrors and rugate filters obtained by a modulation of porosity with depth. In particular, we emphasize some features these mirrors exhibit when compared to the optical equivalents in pSi. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Narrow spectral band monolithic lead chalcogenide on Si mid-IR photodetectors

Resonant cavity-enhanced detectors (RCEDs) with a narrow linewidth and high peak quantum efficiency have been realized for the first time in the mid-IR range. The detectors are fabricated with epitaxial narrow gap lead chalcogenide layers grown epitaxially on Si-substrates. They consist of an epitaxial bottom distributed Bragg mirror, a spacer layer, and the thin absorber layer followed by a metal top layer which forms the photovoltaic detector and in addition acts as top mirror. Devices with peak wavelengths varying from 4 to 8 μm, spectral widths below 1% and quantum efficiencies above 30% have been realised.