Extraction Efficiency Of Emission Research Articles

Modelling the enhancement of spectrally broadband extraction efficiency of emission from single InAs/InP quantum dots at telecommunication wavelengths

Hereby, we present results of finite-difference time-domain simulations of technologically undemanding photonic structures offering a significant improvement in the spectrally broad extraction efficiency of emission from a quantum emitter at the third telecommunication window. The modelling is performed for cylindrical and cuboidal mesa structures containing an exciton confined in a single InAs/InP quantum dot. We investigate the emission pattern from such mesas made of InP (which can be exchanged with AlGaInAs lattice-matched to InP) for two cases: monolithic InP material or InP/AlGaInAs distributed Bragg reflector (DBR) underneath the mesa. The calculations are performed as a function of geometrical parameters, i.e. mesa shape and dimensions, and the emitter position. For the case with DBR, we obtain extraction efficiencies above 25% (for a numerical aperture of 0.4 of a common optical detection system), which also exhibits weak spectral dependence – values above 20% can be obtained in the range of 60 nm around 1550 nm. When the numerical aperture is increased to 0.9, extraction efficiencies about 45% are reachable within the proposed solution. The extraction efficiency is rather weakly sensitive to the in-plane dipole alignment (in the range of 100–200 nm), however, it is more susceptible to even slight changes in its vertical position or to mesa sizes. Eventually, we also comment on the Purcell effect in such weak photonic confinement structures, influence of which on the source brightness is not negligible in some cases.

Enhanced emission extraction and selective excitation of NV centers with all–dielectric nanoantennas

A novel approach to facilitate excitation and readout processes of isolated negatively charged nitrogen‐vacancy (NV) centers is proposed. The approach is based on the concept of all‐dielectric nanoantennas. It is shown that the all‐dielectric nanoantenna can significantly enhance both the emission rate and emission extraction efficiency of a photoluminescence signal from a single NV center in a diamond nanoparticle on a dielectric substrate. The proposed approach provides high directivity, large Purcell factor, and efficient beam steering, thus allowing an efficient far‐field initialization and readout of several NV centers separated by subwavelength distances. image

Study of the emission extraction efficiency of mesa-LEDs with a narrow-gap InAsSb active region

A series of light-emitting diodes (LEDs) (emission peak wavelength λmax = 3.6 μm) with cone-shaped mesas, which have concave lateral surfaces and heights between 10 to 130 μm, has been developed. The dependence of the emission efficiency for these LEDs on mesa height has been studied at different injection currents at the temperatures 77 and 298 K. The form of the dependence observed is in agreement with the results of theoretical calculations. It is shown that the effective absorption coefficient, caused by emission extraction from the crystal, may be as large as 3 cm−1 for LEDs with the highest mesa (130 μm) among the diodes in this series. The emission extraction coefficient is close to 30% at the temperature 298 K and 94% at 77 K.

J221 微細構造によるLED光取り出し効率向上に関する電磁波解析(OS-4: ふく射輸送制御とエネルギー変換(2))

J221 微細構造によるLED光取り出し効率向上に関する電磁波解析(OS-4: ふく射輸送制御とエネルギー変換(2))

Optical enhancement in nanoparticle-decorated ZnO nanorods

Based on the concept of optical enhancement in nanoparticle-mediated coupling, a novel composite consisting of ZnO nanorods and ZnO nanoparticles has been synthesized and characterized. The ZnO nanoparticles can be regarded as light-coupling media to increase the absorption cross section of excitation light as well as the emission extraction efficiency due to the relaxation of momentum selection rule. With our devised ZnO nanostructures, the band gap emission of ZnO nanorods can be enhanced by up to 8.5 times. The strategy of optical enhancement provided here should be very useful in designing many other nanostructures for high efficiency optoelectronic devices.

Ultrahigh spontaneous emission extraction efficiency induced by evanescent wave coupling

A spontaneous emission extraction efficiency greater than 50% is observed in a GaAs/AlGaAs quantum well structure grown on the subwavelength-sized ridge top facet of a V-grooved substrate by means of photoluminescence study. This is an extraction efficiency about 20 times higher than that of a similar structure grown on a flat substrate. It is demonstrated both experimentally and theoretically that the high extraction efficiency is the result of the efficient conversion of evanescent waves into propagating waves in air through constructive coupling of evanescent waves generated on the two sidewall facets of the V-grooved substrate by total internal reflection.

Ferroelectric Thin Film Microcavities and their Optical Resonant Properties

AbstractTwo dimensional photonic crystal (PhC) microcavity structures were fabricated using epitaxial ferroelectric thin film as the optical media and their resonant optical properties were measured. The PhC structures are utilized in order to achieve strong light localization to enhance the interaction between the incident light and the nonlinear optical barium titanate (BTO). Fluorescence measurements were used to assess the resonant properties. Two types of resonant structures were investigated consisting of either dopant or vacancy PhC arrays. The nano patterning on BTO thin films was achieved using dual beam focused ion beam (FIB). For the dopant type PhC microcavity structure, a larger air hole is generated in every 5 x 5 unit cells forming a super cell. The spatial profiles of PhC microcavity structures are characterized by laser scanning confocal microscopy. Structures with a feature size approaching the optical diffraction limit are clearly resolved. Fluorescence measurements on PhCs coated with a fluorescent dye were carried out to determine the relationship between the degree of light localization and the photonic band structure. Enhanced fluorescence at wavelengths 550-600 nm is observed in the dye covered PhCs with lattice period a =200 nm and a =400 nm. The large fluorescence enhancement results from the presence of PhC stop bands that increase the emission extraction efficiency due to the strong light confinement. Since the only allowed propagation direction for the scattered fluorescence light is out-of-plane, this enhances the vertically fluorescent extraction efficiency. These BTO optical microcavity structures can potentially serve as active nano-photonic components in bio-sensors and integrated photonic circuits.

Enhancement of white luminescence fromSiNx films by surface roughening

White photoluminescence was obtained from multi-layered silicon nitride thin films preparedby plasma-enhanced chemical vapor deposition. The emission colors from single-layeredsilicon nitride films could be adjusted over the range of 440–660 nm by controlling theSiH4/NH3 flow ratio during deposition. Surface roughening by anisotropic KOH etching of the Si(100)substrate significantly improved the emission extraction efficiency and changed thecolor-rendering properties from the silicon nitride thin films. This was attributed tothe suppression of internal reflection and interference effects from the thin films.