Whispering gallery modes in photoluminescence and Raman spectra of a spherical microcavity with CdTe quantum dots: anti-Stokes emission and interference effects

We have studied the photoluminescence and Raman spectra of a system consisting of a polystyrene latex microsphere coated by CdTe colloidal quantum dots. The cavity-induced enhancement of the Raman scattering allows the observation of Raman spectra from only a monolayer of CdTe quantum dots. Periodic structure with very narrow peaks in the photoluminescence spectra of a single microsphere was detected both in the Stokes and anti-Stokes spectral regions, arising from the coupling between the emission of quantum dots and spherical cavity modes.     

Pure color emission in transparent organic light-emitting diodes

The microcavity effect in transparent organic light-emitting diodes (TOLEDs) was investigated according to the structure of an anode and a cathode. Color purity of green TOLEDs could be improved from (0.29, 0.62) to (0.23, 0.68) and the light emission in TOLED could be well manipulated by controlling the microcavity effect in the device. In addition, the total light-emitting efficiency of TOLED in normal direction could be improved by 60% compared with that of conventional devices by using semitransparent metal electrodes both as an anode and a cathode.     

Sputtered hydrogenated amorphous silicon thin films for distributed Bragg reflectors and long wavelength vertical cavity surface emitting lasers applications

In this work, we report a study of hydrogenated amorphous silicon (a-SiH) films deposited by radio frequency magnetron sputtering for application in Vertical Cavity Surface Emitting Lasers (VCSEL) elaboration. The influence of the hydrogen dilution in the plasma during the deposition on the optical and surface properties is investigated. After selection of the deposition parameters, a-SiH films have been combined with amorphous silicon nitride (a-SiN_x) films to provide high reflectivity Bragg reflectors. Distributed Bragg reflector (DBR) based on these quarter wavelength thick dielectric layers have been realized and characterized by optical measurements and compared with theoretical calculations based on the transfer matrix method. A maximum reflectivity of 99.2% at 1.6 μm and a large spectral bandwidth of 700 nm have been reached with only four and a half periods of a-SiH/a-SiN_x deposited on a glass substrate. Residual absorption at 1.55 μm has been measured to be as low as 60 cm⁻¹ with a-SiH layers, compared with 400 cm⁻¹ loss with amorphous silicon without hydrogenation step. Finally, DBR comprising six a-SiH/a-SiN_x periods have been included in an InP-based VCSEL. Laser emission is demonstrated at room temperature in continuous wave operation with a photopumping experiment.     

Thermally induced whispering gallery mode laser in MEH-PPV solutions

We report on thermally activated whispering gallery laser modes of a solution of MEH-PPV conjugated polymer supported by a silica optical fiber. The viscosity of the polymer solution gives place to a thin shell of the gain solution around the fiber driven by capillary action. Whispering gallery modes (WGMs) are thermally induced by a decrease in the refractive index of the polymer solution under intense optical pumping. The laser emission is produced because the evanescent waves of the WGMs couple the surrounding gain medium. These results support the use of conjugated polymers in optofluidic laser systems and highlight the importance of physicochemical properties, such as viscosity and optically induced heating, on the performance of the devices.     

Advanced lanthanide doped upconversion nanomaterials for lasing emission

Microlasers are narrow-band and coherent light from small cavities, which have been widely applied in biomedicine, optical interconnection, integration devices, etc. Lanthanide doped upconversion materials are potential gain media for microlasers from near infrared (NIR) to visible and UV regimes due to their multi ladder-like metastable energy levels and superior optical frequency conversion capability. The optical feedback from photon scattering of the porous upconversion nanoparticles clusters has been reported to produce upconversion random lasers. The light bouncing back and forth between two reflective surfaces or internal surface has been utilized to achieve modulated upconversion lasing emission. In addition, photon lattices and plasmonic cavities with enhanced electromagnetic fields can amplify the upconversion process within the sub-diffraction volumes and produce highly efficient upconverting lasers. In this review, the recent advances on using lanthanide doped upconversion materials for random, whispering gallery mode (WGM)/Fabry-Perot (FP) cavity and photon lattice/plasmonic cavity modulated upconversion microlasers are overviewed. Current challenges and future directions of the upconverting lasers are also discussed.     

半导体微腔激光器瞬态特性的分析

建立了反映半导体微腔激光器特性的模型,借助计算机手段,运用Matlab软件直接给出了半导体微腔激光器瞬态响应的仿真结果及载流子密度和光子密度的相图,分析了自发辐射因子、注入电流和腔长对微腔器的激射阈值、延迟时间、驰豫振荡频率和光输出等参量的影响。该模型及有关结合为半导体微胶激光器的工艺制作,改善的高频调制特性和优化器件提供了理论依据。     

Lasing Behavior of BMPPV:PVK Mixture in Microcavity

The surface emitting microcavity is formed by sandwiching a polymer film containing poly (para-phenylene vinylene) (BMPPV) and poly (N-vinylcarbazole)(PVK) between a DBR with a reflectivity of 99.5% and a silver film.The sample is optically pumped by a 337.1 nm line of nitrogen laser with 10 ns pulses at 20 Hz repetition rate.The lasing phenomenon is observed in BMPPV and PVK mixture microcavity .The full width at half maximum( FWHM) is 6 nm at the peak wavelength of 460 nm.The lasing threshold energy is estimated to be about 5μJ.     

Performance enhancement of top‐ and bottom‐emitting organic light‐emitting devices using microcavity structures

Abstract— In order to improve the efficiency of top‐ and bottom‐emitting devices, metallic electrodes have been used to create microcavity effects within the OLED structure. Semi‐transparent Ag is used as the anode in bottom‐emitting microcavity structures, whereas various reflective opaque metallic anodes are used for the top emitters. The cathode used in both configurations is MgAg — thick and opaque in the case of the bottom emitter and thin and semi‐transparent in the case of the top emitter. Modeling and experiments show that for the top‐emitting structures, the device efficiency is roughly proportional to the reflectivity of the anode in the low reflectivity range and increases significantly more than predicted by reflectivity alone in the high‐reflectivity range. An ultrathin CF_x or MoO_x hole‐injecting layer allows for the use of many metals as anodes and is an important feature of the device structure. With an Ag anode, both the top‐ and bottom‐emitting microcavity devices are about twice as efficient (on axis) as the analogous nonmicrocavity bottom‐emitting device. Microcavity devices employing a C545T‐doped Alq emitter exhibit efficiencies of 21 cd/A at 6.4 V and 20 mA/cm², with operational stability equivalent to conventional bottom‐emitting structures.     

Functionalization control of porous silicon optical structures using reflectance spectra modeling for biosensing applications

Modeling and experimental reflectance spectra of porous silicon single layers at different steps of functionalization and protein grafting process are adjusted in order to determine the volume fraction of the biomolecules attached to the internal pore surface. This method is applied in order to control the efficiency of the chemical functionalization process of porous silicon single layers. Using results from single porous silicon layer study, theoretical microcavity is simulated at each step of the functionalization process. The calculated reflectance spectrum is in good agreement to the experimental one. Therefore the single layers study can be applied to multilayer structures and can be adapted for other optical structures such as waveguides, interferometers for biosensing applications.     

Development of Microreplication Process—Micromolding

A microreplication process, micromolding, was developed to replicate three-dimensional microcomponents. It included modifying a conventional molding machine, developing a thermal control unit to control the mold temperature, and developing a vacuum unit to evacuate the microcavity before filling it with plastic melt. Focused ion beam sputtering, a maskless patterning of material, was used to fabricate a microcavity that was then used as a mold insert. Feasibility of the micromolding process was investigated by simulation, and results were verified with the replication of polymer microcomponents (e.g., microgear, gear-train). Commercial simulation software was used to reveal possible issues in micromolding by integrating the microcomponent with a larger base. The simulations predict the filling time, pressure distribution, volumetric shrinkage, stress distribution, etc., of the microcomponent.