Bragg Reflector Mirrors Research Articles

SiO2/TiO2 distributed Bragg reflector near 1.5 μm fabricated by e-beam evaporation

The authors report on the fabrication and characterization of SiO2/TiO2 distributed Bragg reflector (DBR) mirrors operating at the eye safe and optical communication wavelength window, λ = 1.5 μm. Our experimental results demonstrated that SiO2/TiO2 DBR mirrors with reflectivity exceeding 95% at λ = 1.5 μm can be achieved using e-beam evaporation in conjunction with postdeposition thermal annealing process in ambient air. It was found that the postdeposition annealing process transformed the crystal structure of the as-deposited TixOy to TiO2, leading to a significant reduction in optical absorption. Erbium doped III-nitride semiconductors incorporating DBR mirrors at 1.5 μm emission may open up many novel applications, including infrared emitters, optical amplifiers, and high power infrared lasers.

High-performance GaN-based light-emitting diodes on patterned sapphire substrate with a novel hybrid Ag mirror and atomic layer deposition-TiO2/Al2O3 distributed Bragg reflector backside reflector

GaN-based light-emitting diodes (LED) on a patterned sapphire substrate with a novel hybrid atomic layer deposition (ALD)-TiO 2 Al 2 O 3 distributed Bragg reflector (DBR) and Ag mirror have been proposed and fabricated. Due to the excellent thickness uniformity of ALD for the proposed reflector, high reflectivity over 99.3% at an incident angle of 5 deg has been achieved. It was also found that the reflectivity of a backside reflector with an Ag mirror slightly depends on incident light wavelength and incident angle. Moreover, because of the good adhesion between TiO 2 /Al 2 O 3 DBR and the Ag mirror, the fabrication process was simplified and reliable. With a 60 mA current injection, an enhancement of 5.2%, 8.9%, and 47.1% in light output power (LOP) at the 460 nm wavelength was realized for the proposed LED with Ag mirror and 3-pair ALD-TiO 2 Al 2 O 3 DBR as compared with a LED with a traditional Ag mirror and 3-pair TiO 2 /SiO 2 DBR, with Al mirror and 3-pair ALD-TiO 2 Al 2 O 3 DBR, and without backside reflector, respectively. This result shows that the ALD-TiO 2 /Al 2 O 3 DBR can be used to enhance the LOP greatly and improve adhesion between the sapphire substrate and the metallic mirror, and thus is very promising for fabricating high performance GaN-based LEDs.

Monitoring the formation of oxide apertures in micropillar cavities

An imaging technique is presented that enables monitoring of the wet thermal oxidation of a thin AlAs layer embedded between two distributed Bragg reflector (DBR) mirrors in a micropillar. After oxidation we confirm by white light reflection spectroscopy that high quality optical modes confined to a small volume have been formed. The combination of these two optical techniques provides a reliable and efficient way of producing oxide apertured micropillar cavities for which the wet thermal oxidation is a critical fabrication step.

Contribution of Au nanoparticles to the longitudinal magneto-optical Kerr effect of Bragg reflector based magneto-plasmonicmultilayers

In this paper, we investigate a significant enhancement of the longitudinal magneto-optical Kerr effect when a magneto-optical thin film is covered by the Bragg reflector mirror and Au nanoparticles on its right and left side respectively. Our results indicate the sufficient longitudinal magneto-optical Kerr effect enhancement in this new structure by the aid of combination of surface plasmon resonance and light localization in magneto-optical garnet layer at one practical communication wavelength in the middle of the visible spectrum. These results confirmed by the aid of Finite difference frequency domain simulation method.

Longitudinal Magneto-Optical Kerr Effect in Magneto-Plasmonic Heterostructures

In this paper, the effect of Au nanoparticles and a Bragg reflector mirror on the optical and longitudinal magneto-optical Kerr effect of a new magneto-plasmonic structure has been investigated. The new magneto-plasmonic heterostructure consists of a Bragg reflector mirror beside a crystalline Ce:YIG thin film incorporating gold nanoparticles. Our results indicate sufficient broad band longitudinal magneto-optical Kerr effect enhancement in this new structure using the combination of surface plasmon resonance and Bragg reflector mirror.

Transforming Fabry-Pérot resonances into a Tamm mode

We propose an optical structure composed of two metal nanolayers enclosing a distributed Bragg reflector (DBR) mirror. The structure is an open photonic system whose bound modes are coupled to external radiation. We apply the special theoretical treatment based on inversion symmetry of the structure to classify its resonances. We show that the structure supports resonances transitional between Fabry-P\'erot modes and Tamm plasmons. When the dielectric contrast of the DBR is removed these modes are a pair of conventional Fabry-P\'erot resonances. They spectrally merge into a Tamm mode at high contrast. The optical properties of the structure in the frequency range of the DBR stop band, including highly beneficial $50%$ transmittivity through thick structures with sub-skin-depth metal films, are determined by the hybrid quasinormal modes of the open nonconservative structure under consideration. The results can find a broad range of applications in photonics and optoelectronics, including the possibility of coherent control over optical fields in the class of structures similar to the one proposed here.

Top-Hat HELLISH-VCSOA for optical amplification and wavelength conversion for 0.85 to 1.3μm operation

The Top-Hat hot electron light emission and lasing in semiconductor heterostructure (HELLISH)-vertical cavity semiconductor optical amplifier (VCSOA) is a modified version of a HELLISH-VCSOA device. It has a shorter p-channel and longer n-channel. The device studied in this work consists of a simple GaAs p-i-n junction, containing 11 Ga0.35In0.65 N0.02As0.08/GaAs multiple quantum wells in its intrinsic region; the active region is enclosed between six pairs of GaAs/AlAs top distributed Bragg reflector (DBR) mirrors and 20.5 pairs of AlAs/GaAs bottom DBR mirrors. The operation of the device is based on longitudinal current transport parallel to the layers of the GaAs p-n junction. The device is characterised through I-V-L and by spectral photoluminescence, electroluminescence and electro-photoluminescence measurements. An amplification of about 25 dB is observed at applied voltages of around V = 88 V.

Athermal and tunable operations of 850 nm vertical cavity surface emitting lasers with thermally actuated T-shape membrane structure

We demonstrate the athermal operation and the wavelength tuning of 850 nm GaAs-based vertical cavity surface emitting lasers with a thermally actuated cantilever structure. The thermal actuation of a top distributed Bragg reflector mirror enables us to compensate the temperature drift of lasing wavelengths. The temperature dependence of lasing wavelengths could be controlled from −0.011 nm/K to −0.18 nm/K by changing the cantilever length. In addition, a T-shape membrane structure was introduced for efficient electro-thermal tuning. A small temperature dependence of −0.011 nm/K and wavelength tuning of 4 nm were obtained.

Cavity Enhanced Longitudinal Magneto-Optical Kerr Effect in Magneto-Plasmonic Multilayers Consisting of Ce: YIG Thin Films Incorporating Gold Nanoparticles

Enhanced magneto-optical rotation has been the subject of intense interest for communication technology. In this paper, we report an experimental study on the effect of Bragg reflector mirror and Au nanoparticles on the magneto-optical rotation in a new magneto-optical structure named magneto-plasmonic construction. Our results indicate sufficient longitudinal magneto-optical Kerr effect enhancement in this new structure by the aid of combination of surface plasmon resonance and light localization in magneto-optical garnet layer. The presence of Au nanoparticles leads to screening of the surface plasmon resonance, while Bragg reflector mirror reduces the group velocity in magneto-optical medium as a defect layer and thus we have sufficient enhancement in magneto-optical rotation. These structures can be addressed as a new concept in the development of magneto-plasmonic devices.

Silicon-nanocrystal resonant-cavity light emitting devices for color tailoring

A silicon-nanocrsytal resonant-cavity light-emitting device (RCLED) is presented. The microcavity, made by a silicon nanocrystal layer inserted between a semitransparent Au reflector and a distributed Bragg reflector mirror, shows enhanced emission intensity by four times at resonance wavelength and 1/8 narrow emission spectrum compared to nonresonant devices. The external quantum efficiency and power conversion efficiency also increase by 3.5 times. Multiple colors, green, green-yellow, orange, and red are displayed by adjusting the cavity length of RCLED.

High conversion efficiency of second harmonic generation in a short nonlinear photonic crystal with distributed Bragg reflector mirrors

Second harmonic generation (SHG) in a short nonlinear photonic bandgap (PBG) structure coated with distributed Bragg reflector (DBR) mirrors is theoretically investigated by means of an iteration approach that fully considers pump depletion. A total conversion efficiency of about 96% can be obtained in an optimized structure with a size scale of about 0.2 mm and at the modest pump intensity of about 0.133 MW/cm2, which is four orders of magnitude more than that in a quasi-phase-matching (QPM) structure with the same sample length. Such a high conversion efficiency of SHG will greatly facilitate the success of short frequency conversion devices and all-optical integration in nanostructures.

Modeling of vertical external cavity semiconductor laser with MQW resonant structure

Numerical model is developed for modeling pulsed operation of a vertical external cavity semiconductor laser (VECSEL) with a resonant gain structure. Properties of optical modes for compound resonator formed by Bragg reflector, chip boundary and external spherical mirror were studied. For above threshold operation carrier density in each of quantum wells (QW) obeys non-linear diffusion equation with a source supplied by electron-hole pairs generated in barrier layers by pump radiation or fast electron beam. A new iteration procedure for round-trip operator evaluation was developed, which provides linear growth of computation time with the number of QWs. Results of numerical simulations are reported for a VECSEL comprising 25 QW in resonant configuration and the output spherical mirror with curvature radius 3 cm. Variation of distance to the external mirror is found to result in notable changes in power and optical quality of the output beam. The decisive role of gain and index non-linearity in these changes is identified. A range of values of distance to external mirror is found where iterative procedure does not converge. In another range, the resulting solution depends on the initial conditions for the iteration procedure.

Discretely Tunable Laser Based on Filtered Feedback for Telecommunication Applications

A novel discretely tunable laser based on filtered feedback is presented. The semiconductor device consists of a Fabry-Perot laser with deeply etched broadband distributed Bragg reflector mirrors. Single-mode operation is achieved by using feedback from an integrated filter. This filter contains an arrayed waveguide grating wavelength router and a semiconductor optical amplifier gate array. Design, simulation, and the first characterization results of this new integrated filtered-feedback tunable laser device are presented. It shows a combination of a simple and robust switching algorithm with good wavelength stability. A rate equation model predicts that a properly designed device can switch within 1 ns. The fast switching and reduced control complexity makes the device very promising for various advanced applications in optical telecommunication networks.

Surface-emitting dye-doped polymer laser coupled with stimulated resonant Raman scattering

Surface-emitting polymer laser was fabricated with 1,4-bis[2-[4-[N,N-di(p-totyl)amino]phenyl]vinyl]benzene-doped poly(vinyl-pyrrolidone) thin films sandwiched between two distributed Bragg reflector (DBR) mirrors. Under pulsed optical pumping, Fabry–Perot (FP) type resonation resulted in multi-mode laser oscillations depending upon the active film thickness. With increasing excitation wavelengths, an emission peak based on stimulated resonant Raman scattering (SRRS) was superimposed on the multimode band region. When the SRRS peak just overlapped with one of the FP modes, the emission intensity was enhanced and the line width was considerably narrowed. Such SRRS-coupled FP oscillations can be applied to realize a tunable single-mode surface-emitting polymer laser.

Giant enhancement of second harmonic generation in nonlinear photonic crystals with distributed Bragg reflector mirrors

We theoretically investigate second harmonic generation (SHG) in one-dimensional multilayer nonlinear photonic crystal (NPC) structures with distributed Bragg reflector (DBR) as mirrors. The NPC structures have periodic modulation on both the linear and second-order susceptibility. Three major physical mechanisms, quasi-phase matching (QPM) effect, slow light effect at photonic band gap edges, and cavity effect induced by DBR mirrors can be harnessed to enhance SHG. Selection of appropriate structural parameters can facilitate coexistence of these mechanisms to act collectively and constructively to create very high SHG conversion efficiency with an enhancement by up to seven orders of magnitude compared with the ordinary NPC where only QPM works.

Mode Control in Photonic Crystal Vertical-Cavity Surface-Emitting Lasers and Coherent Arrays

We demonstrate transverse mode control in vertical-cavity surface-emitting lasers (VCSELs) and 2-D VCSEL arrays. By etching a periodic arrangement of circular holes into the top distributed Bragg reflector mirror, we are able to control the lasing modes through index and loss confinement. Theoretical modeling of these confinement effects are shown to be consistent with experimental measurements. Photonic crystal etched patterns and ion-implanted photonic lattices have been employed to fabricate coherently-coupled 2-D arrays. Control of the array supermodes from the out-of-phase and in-phase conditions is discussed. Designs of photonic crystal coherent VCSEL arrays for high-power emission and beam steering applications are described.

Low thermal resistance, high-speed 980 nm asymmetric intracavity-contacted oxide-aperture VCSELs

We demonstrated high-speed characteristics of an oxide-aperture vertical-cavity surface-emitting laser (VCSEL) with intracavity structures for both p- and n-contacts, based on InGaAs/GaAs multiple quantum wells operating at λ ∼ 980 nm, indicating a low thermal resistance (Rth). The asymmetric current injection scheme is employed for reducing current crowding around the rim of the oxide aperture. A high aluminium content undoped Al0.88Ga0.12As and GaAs distributed Bragg reflector (DBR) mirror is used for efficient heat dissipation. The VCSEL with a 7 μm oxide aperture exhibited an output power of 2.5 mW and a threshold current of 0.8 mA with a slope efficiency of 0.39 mW/mA at 20 °C under continuous-wave operation and it still worked with 1.3 mW at 90 °C. The temperature tuning coefficient of 0.081 nm/°C and dissipated electrical power tuning coefficient of 0.104 nm/mW were observed, leading to a low Rth of 1.28 °C/mW. A high modulation bandwidth up to 13 GHz with a modulation current efficiency factor of 6.1 GHz/mA1/2 was achieved. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural analysis of distributed Bragg reflector mirrors

Quantum cascade (QC) lasers and vertical-cavity surface-emitting lasers (VCSELs) are of great interest due to their potential importance for a variety of device applications. Both kinds of lasers call for very highly reflective mirrors. Usually distributed Bragg reflector (DBR) mirrors, which consist of periodic quarter wavelength stacks of high and low refractive index compound semiconductors are used. These stacks are superlattices containing more than 40 individual layers. To obtain very high reflectivity DBRs alternating GaAs and AlAs layers are used for both the high and low index mirrors. GaAs/AlAs DBR structures containing 15 periods were characterized by the complementary use of RBS/channeling, TEM and HRXRD. Since the total thickness of a DBR exceeds 2 μm the RBS analysis was performed at two He-ion energies: 1.7 MeV and 3.82 MeV. After some stopping power corrections TEM and RBS provided similar results. Discrepancies with HRXRD data were attributed to the lateral inhomogeneity of produced superlattice. Virtues and pitfalls of complementary use of these techniques were discussed.

Polarization Switching in Vertical-Cavity Surface-Emitting Lasers by Asymmetrical Current Injection

Polarization switching between two orthogonal linear polarizations was experimentally demonstrated in newly designed 980-nm vertical-cavity surface-emitting lasers ( VCSELs ). A square-shaped mesa structure was prepared in a p-type distributed Bragg reflector mirror. Four p-side electrodes were placed in contact with the four sides of the square mesa. When the same current was injected into the four electrodes, the VCSEL oscillated with 0 or 90 linear polarizations. When the current was asymmetrically injected (the same current for two electrodes on the opposite sides of the square, but different for neighboring electrodes), the direction of the linear polarization became perpendicular to the direction of the line connecting the two electrodes injected with the larger current. It was confirmed that the VCSELs oscillated with a single frequency and the lowest order transverse mode in all cases.

Upstream vertical cavity surface-emitting lasers for fault monitoring and localization in WDM passive optical networks

As wavelength division multiplexed passive optical networks (WDM-PONs) are expected to be first deployed to transport high capacity services to business customers, real-time knowledge of fiber/device faults and the location of such faults will be a necessity to guarantee reliability. Nonetheless, the added benefit of implementing fault monitoring capability should only incur minimal cost associated with upgrades to the network. In this work, we propose and experimentally demonstrate a fault monitoring and localization scheme based on a highly-sensitive and potentially low-cost monitor in conjunction with vertical cavity surface-emitting lasers (VCSELs). The VCSELs are used as upstream transmitters in the WDM-PON. The proposed scheme benefits from the high reflectivity of the top distributed Bragg reflector (DBR) mirror of optical injection-locked (OIL) VCSELs to reflect monitoring channels back to the central office for monitoring. Characterization of the fault monitor demonstrates high sensitivity, low bandwidth requirements, and potentially low output power. The added advantage of the proposed fault monitoring scheme incurs only a 0.5dB penalty on the upstream transmissions on the existing infrastructure.