Top Bragg Reflector Research Articles

Optical characterization of a InGaN/GaN microcavity with epitaxial AlInN/GaN bottom DBR

ABSTRACTResonant coupling of an optical mode confined within a microcavity and an emitter is the basic prerequisite for the observation of Bose-Einstein condensation phenomena and the development of novel optical devices based on cavity polaritons.We demonstrate highly spatially resolved 2” wafer characterization of the reflectivity and emission properties of a nitride based multi quantum well semi microcavity (i.e. structure without top Bragg reflector) to verify resonant regions. Photoluminescence and reflectivity spectra recorded at the same positions on the wafer exhibit a strong spatial dependence of the multi quantum well emission and the center wavelength of the stop band of the bottom Bragg reflector across the sample. Resonance, i.e., matching of the emission and the center wavelength of the stop band, is found in a region 8 mm off the center of the wafer.The thickness profile across the AlInN/GaN Bragg reflector and multi quantum well layers was obtained by x-ray mappings over the full wafer. A perfect correlation between the local optical properties and the x-ray thickness distribution is found. Additional transmission electron microscopy investigations indicate a complete crack free structure and smooth interfaces between the layers within the Bragg reflector making the structure appropriate for strong coupling applications.

High reflectivity monolithic sub-wavelength diffraction grating withGaAs/AlOx stack

This paper presents the fabrication of high reflective sub-wavelength gratings in GaAs on wet oxidizedAlxOy low index layers. This structure can efficiently replace a top Bragg reflector in GaAs-basedvertical cavity lasers (VCSELs), while keeping all the advantages of a monolithic stack.Low refractive index and low loss can be achieved with the oxide sublayer, thus providing ahigh reflectivity over a large wavelength range. Reflectivities above 90% have beenmeasured with stopbands exceeding 130 nm. Further adjustments of the geometricalparameters will enable the reflectivity requirements to be fulfilled for implementation inmicrocavity devices.

Large vacuum Rabi splitting in a multiple quantum well GaN-based microcavity in the strong-coupling regime

An $\mathrm{Al}\mathrm{In}\mathrm{N}∕\mathrm{Al}\mathrm{Ga}\mathrm{N}$ microcavity (MC) containing a $\mathrm{Ga}\mathrm{N}∕{\mathrm{Al}}_{0.2}{\mathrm{Ga}}_{0.8}\mathrm{N}$ multiple quantum well (MQW) structure is investigated through room temperature (RT) photoluminescence and reflectivity experiments. A vacuum Rabi splitting as large as $50\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ at RT is reported for this MC structure, the highest value reported so far for a semiconductor MC containing QWs. This is shown to result from a geometry combining a state of the art nitride-based MC with a MQW system where the built-in electric field has a reduced impact on the oscillator strength of optical transitions. The contribution of Bragg modes seen in optical spectra is well accounted for by transfer matrix simulations. In addition, the sensitivity of the present system to the tuning between the various optical components of the microcavity (bottom and top Bragg reflectors and active cavity region) to maximize the strong-coupling regime is also shown through simulations. Prospects regarding the nonlinear polariton emission from such a structure indicate that this type of MCs could potentially sustain ultrafast polariton parametric amplification up to $440\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, thanks to an increased exciton binding energy. More generally, it is predicted that, owing to a large exciton saturation density in excess of $1\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ per QW, such a MC structure would be suitable for the observation of nonlinear effects associated with cavity polaritons (polariton lasing and polariton Bose-Einstein condensates) at RT and above.

Design of a top spatial filter Bragg waveguide vertical-cavity surface-emitting laser

We propose a new method for transverse-mode control in vertical-cavity surface-emitting lasers based on the idea of a Bragg waveguide. This method involves patterning concentric annuli into the top Bragg reflector of a vertical-cavity surface-emitting laser, inducing a cylindrical Bragg waveguide across the laser cavity. We use the effective-index approximation to evaluate the waveguiding effect of patterning the top Bragg reflector. A waveguide model has been developed to design the ideal Bragg waveguide for a specified HE11 mode. The model also calculates the field and power distributions and the optical confinement for the given mode.

2 µm resonant cavity enhanced InP/InGaAssingle quantum well photo-detector

Experimental results are presented for a resonant cavity enhanced photodetector operating at 2 µm based on absorption in a single, strain-compensated, In0.83Ga0.17As quantum well. The device exhibits a selectivity of 9 nm, and 18% quantum efficiency. InP/InGaAs and Si/SiO2 material systems are used for the bottom and top Bragg reflectors of the resonant cavity, respectively. The dark current densities are lower than 10-6 A/cm2 at 2 V reverse bias.

Performance of semiconductor planar microcavities for Raman-scattering enhancement

We report single and double optical resonant Raman scattering in both complete (high-$Q$) and without top Bragg reflector (low-$Q$) semiconductor planar microcavities. A calculation of the Raman efficiency relative amplifying capabilities of these photonic structures is presented, and compared with the experiments. These results indicate that a competition between better light confinement and reduced angular acceptance as the cavity finesse is increased determines the performance of a cavity for enhanced Raman signals.

Low threshold distributed Bragg reflector surface emitting laser diode with semiconductor air-bridge-supported top mirror

A surface emitting laser diode (SELD) with two distributed Bragg reflectors (DBR) and semiconductor multilayer air-bridge-supported top mirror is fabricated. A low threshold current of 1.5 mA is achieved under room temperature CW operation. The spectrum shows a strong peak at 891 nm with a FWHM of 10 AA. With light emission from the top Bragg reflector instead of from the back side of the substrate, laser arrays are easily formed with this novel structure.