Microcavity Device Research Articles

Packaged and robust microcavity device based on a microcylinder–taper coupling system

We propose and realize a packaged structure for the microcylinder–taper coupling system by only gluing a glass tube and two glass plates together. Our package method avoids embedding the coupling system into the polymer, thus leaving the whispering gallery mode evanescent fields available for environmental sensing. The excitation of localized high-order axial modes in the cylindrical resonator fabricated by using a fusion splicer is demonstrated and a quality factor (Q) up to 1.4×107 is obtained. The Q maintenance and stable spectrum are realized by sealing the packaged device in a clean box. Moreover, the robustness of the packaged structure is also tested, demonstrating its remarkable antivibration ability. The portability and robustness of the device make it attractive in practical applications such as sensors, lasers, and especially some applied areas in strong vibration environments.

Room temperature fabrication of dielectric Bragg reflectors composed of a CaF2/ZnS multilayered coating.

We describe the design, fabrication, and characterization of mechanically stable, reproducible, and highly reflecting distributed Bragg reflectors (DBR) composed of thermally evaporated thin films of calcium fluoride (CaF2) and zinc sulfide (ZnS). CaF2 and ZnS were chosen as the low and high refractive index components of the multilayer DBR structures, with n = 1.43 and n = 2.38 respectively, because neither material requires substrate heating during the deposition process in order to produce optical quality thin films. DBRs consisting of seven pairs of CaF2 and ZnS layers, were fabricated with thicknesses of 96 and 58 nm, respectively, as characterized by high-resolution scanning electron microscopy (HR-SEM), and exhibited a center wavelength of λc = 550 nm and peak reflectance exceeding 99%. The layers showed good adhesion to each other and to the glass substrate, resulting in mechanically stable DBR coatings. Complete optical microcavities consisting of two such DBR coatings and a CaF2 spacer layer between them could be fabricated in a single deposition run. Optically, these structures exhibited a resonator quality factor of Q > 160. When a CaF2/ZnS DBR was grown, without heating the substrate during deposition, on top of a thin film containing the fluorescent dye Rhodamine 6G, the fluorescence intensity showed no degradation compared to an uncoated film, in contrast to a MgF2/ZnS DBR coating grown with substrate heating which showed a 92% reduction in signal. The ability to fabricate optical quality CaF2/ZnS DBRs without substrate heating, as introduced here, can therefore enable formation of low-loss high-reflectivity coatings on top of more delicate heat-sensitive materials such as organics and other nanostructured emitters, and hence facilitate the development of nanoemitter-based microcavity device applications.

Highly efficient ITO-free polymer solar cells based on metal resonant microcavity using WO3/Au/WO3 as transparent electrodes

Indium tin oxide (ITO)-free polymer solar cells (PSCs) with the structure of Glass/tungsten trioxide (WO3)/Au/WO3/PCDTBT: PC70BM/LiF/Al was fabricated and studied. The multilayer structure of WO3/Au/WO3 is used as the potential transparent electrode to replace ITO. Metal resonant microcavity, which can enhance light harvesting of active layers, was constructed between Au and Al electrodes. According to the J–V and IPCE characterization with 70nm active layer, power conversion efficiency (PCE) of the ITO-free microcavity device is approaching 4.55%, which is higher than that of the ITO-based device. However, PCE of the ITO-free device is much lower than that of the ITO-based device when the thickness of active layer increases to 130nm. The opposite experimental tendency leads to theoretical research toward the simulation of light absorption and optical electric field and the calculation of maximum short circuit current density (Jsc max) as a function of active layer thickness based on ITO-free and ITO-based devices. The research results show that microcavity effect is closely linked to intrinsic absorption of active layers.

Spectrum and entanglement of phonons in quantum fluids of light

We study the quantum state of phonons propagating on top of a fluid of light coherently generated in a planar microcavity device by a quasiresonant incident laser beam. In the steady state under a monochromatic pump, because of the finite radiative lifetime of photons, a sizable incoherent population of low-frequency phonons is predicted to appear. Their mean occupation number differs from a Planck distribution and is independent of the photon lifetime. When the photon fluid is subjected to a sudden change of its parameters, additional phonon pairs are created in the fluid with remarkable two-mode squeezing and entanglement properties. Schemes to assess the nonseparability of the phonon state from measurements of the correlation functions of the emitted light are discussed.

红色磷光微腔有机电致发光器件的发光性能

Red phosphorescent microcavity organic light-emitting device( MOLED) with structure of Glass / DBR / ITO / Mo O3( 1 nm) /Tc Ta( 55 nm) /CBP∶ Ir( piq)2acac( 44 nm,6%) / TPBI( 55 nm) /Li F( 1 nm) / Al( 80 nm) was fabricated. For comparison,an OLED without cavity also was fabricated. The effect of microcavity structure on luminescent properties of phosphorescent devices was studied. The electroluminescence( EL) spectrum peak of OLED is at 626 nm,and the full width at half maximum( FWHM) is 92 nm. The electroluminescence( EL) spectrum peak of MOLED is at628 nm,and the FWHM is 42 nm which is narrowed half compared with the 92 nm value. The micro cavity structure can narrow the luminescence spectrum of OLED and improve the colour purity.For MOLED,the maximum brightness,the maximum current efficiency,the maximum external quantum efficiency( EQE) are 121 000 cd / m2,27. 8 cd /A and 28. 4%,respectively. For OLED,its maximum brightness,current efficiency and external quantum efficiency are 54 500 cd / m2,13. 1cd / A and 16. 6%,respectively. Comparing with the no cavity device,the luminescence properties of microcavity device have been improved greatly.

Electrically driven, narrow-linewidth blackbody emission from carbon nanotube microcavity devices

We report electrically driven narrow-linewidth blackbody emission from carbon-nanotube with Fabry-Perot microcavities. We fabricated two types of devices with microcavities consisting of either gold mirrors or distributed Bragg reflectors (DBR). Gold-mirror microcavity devices exhibit blackbody emission with narrowed full-width at half-maximum of ∼50 nm in contrast to the broad normal blackbody emission spectrum. The spectra from these devices can be explained by theoretical calculations accounting for the temperature-dependent intrinsic blackbody spectra and transmittance spectrum of the microcavity. Moreover, the DBR microcavity devices show a narrower resonant peak inside the photonic bandgap, compared with the gold-mirror microcavity device.

Microcavity tandem solar cells with a short circuit current higher than single cells

We demonstrate by numerical simulation that microcavity tandem organic photovoltaic cells (OPVs) with a capping layer can have a higher short circuit current (Jsc) than normal ITO based tandem OPVs without the microcavity structure and corresponding single cells. A microcavity tandem OPV consists of SubPc–C60 and PbPc–C60 donor–acceptor pairs of each subcell. Two reflecting electrodes, spacer layers, and a capping layer in the microcavity structure control the optical electric field of the device so that Jsc in the tandem OPV becomes higher than the normal cells even in its thinner active layers. The optimized microcavity device leads to a 25% increase in Jsc compared with the conventional ITO-based device employing the same donor–acceptor pair, and a 5% increase in Jsc compared with conventional ITO-based single cells.

Design of all-optical switching component based on pillar-array hybrid nonlinear photonic crystal cavity

A Kerr-effect sensitive microcavity device based on the two-dimensional pillar-array hybrid nonlinear photonic crystal slab has been designed for all-optical switching. The cavity is made from infiltrating the void space of the pillar-array semiconductor photonic crystal slab with polystyrene. The structure parameters have been optimized by numerical simulations based on the three-dimensioanl finite-difference time-domain method. It is found that the resonant wavelength can shift 15 nm under the pump light with an intensity of 80  GW/cm2, which is far larger than the shift magnitude of the holes-array nonlinear photonic crystal slab.

Simulation of electroluminescence of quantum dot-based microcavity light-emitting device

We present a detailed analysis and computations of the emitted radiation spectrum for quantum dots (QDs) microcavity light-emitting device, where the total physical thickness of the cavity spacer was kept at 254 nm which corresponds to the wavelength of the mode number (m) = 1 resonant mode of the cavity. Our calculation gives good results for QD diameter only from 1.2 to 6.4 nm. The computations are used to examine how the emitted radiation spectrum can be optimized by varying the position of the light-emitting layer, the type of cathode material, the choice of hole transport layer material, and the thickness of electron transport layer, QD layer, and hole transport layer. These studies showed that the variation of layers geometry and the position of the light-emitting layer will optimize the output intensity and the radiation spectrum and varying the ETL and QD layer thickness will have a more effect on the emitted spectrum than varying HTL thickness. In addition, we have examined the effect of using different quantum dots sizes in emission layer. On the other hand, we have investigated the difference between the electroluminescence (EL) emissions for microcavity device in comparison with the non-cavity device, and we have found that the full width at half maximum (FWHM) of the EL is reduced from 45 nm for the QD non-cavity LED to 30 nm for the output of a resonant microcavity device. Finally, we have investigated the compatibility between our calculation and the experimental results and found a fairly good agreement between them.

Simulation of microcavity organic light emitting device with two kinds of resonant cavity lengths

The resonant cavity length of microcavity influences the light emitting characteristics of microcavity organic light emitting device (MOLED) directly. According to the related calculation formula of microcavity device, when the lengths of microcavity are lambda/2 and lambda, the authors use transfer matrix method to simulate and compare with the functions of composite light emitting EL when exciton is in different positions of microcavity. The authors found that when the length of microcavity is lambda/2, the peaks of luminous spectrum are all at the 520 nm, and the width of half-peaks are all 17 nm. The peak intensity and integral intensity are biggest when exciton is in the central area of microcavity. When the length of microcavity is lambda and exciton is at different positions of microcavity, the peaks of luminous spectrum are all at the 520 nm of designed center wavelength, and the widths of half-peaks are all 12 nm. The peak intensity and integral intensity are smallest when exciton is in the central area of microcavity. After analyzing, The authors found that the light emitting characteristics is best when the exciton is at the maximum position of the electric field. This is because the electric field's intensities in the microcavity with two kinds of lengths are distributed differently. It illustrates that one should distinguish different resonant cavity length and exciton at the maximum position of the electric field within microcavity if one wants to create an efficient MOLED.

White‐emitting OLED devices in an RGBW format with microelement white subpixels

Abstract— OLED devices with an RGBW pixel format using an unpatterned white emitter have the potential to provide very good efficiency and color gamut while enabling lower‐cost and large‐format manufacturing. However, the white subpixel often has unacceptably large color shifts with viewing angle. Furthermore, for some architectures such as top‐emitting microcavity devices, it can even be difficult to produce a white subpixel with good on‐axis color. In this paper, we describe the use of a white subpixel made up of a combination of differently tuned microelements and demonstrate how such an approach can overcome these problems. By carefully tuning the color and areas of each of the microelements in the white subpixel, we can trade off between better on‐axis color, less color change with angle, and higher efficiency. Furthermore, it was demonstrated that an RGBW top‐emitter microcavity device with a microelement white subpixel can achieve an increase in both power efficiency and color gamut relative to a conventional RGBW bottom‐emitter non‐microcavity device.

Enhancement of the short circuit current in organic photovoltaic devices with microcavity structures

We demonstrate that the use of a microcavity structure can overcome the trade-off between exciton diffusion and optical absorption in planar heterojunction organic photovoltaic cells. Optical simulation based on the copper phthalocyanine (CuPc)-fullerene donor-acceptor system showed that the microcavity device with the spacer layer confines a large electric field inside the cavity so that high external quantum efficiency can be achieved even with a 10-nm-thick CuPc layer, which is comparable to the exciton diffusion length of the layer. The optimized microcavity device leads to an enhancement of the short circuit current of up to 51.6% compared with the conventional device.

Porous silicon optical microcavity for chemical sensing application using tris-(8-hydroxyquinoline) aluminum (Alq3)

The present paper reports the study of a porous silicon based microcavity for a potential chemical sensing application using tris-(8-hydroxyquinoline) aluminum (Alq 3 ) molecules. Porous silicon based planar microcavity was first designed and fabricated using the electrochemical etching technique. Photoluminescence emission of a single porous silicon layer after immersion in an Alq 3 solution was first carried out in order to verify that the Alq 3 molecules were bound to the porous surface. A wide green band centered at 519 nm, typical of a nano-structured Alq 3 film, was observed. Reflectivity measurements of the porous silicon microcavity were then performed for different aluminum concentrations of the Alq 3 solution. The microcavity device showed a good sensibility for the Alq 3 molecules and an important shift of the microcavity photonic resonance was observed. This device might be considered for a potential aluminiun sensing application.

High-efficiency red phosphorescent organic light-emitting diodes based on metal-microcavity structure

Multilayer electroluminescent (EL) diodes with red emission were fabricated using Bis(2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C3′) iridium (acetyl-acetonate) [(btp)2Ir(acac)] as dopant. Double metal-microcavity structure with a semitransparent Ag anode was introduced into the EL diodes. The cavity device structure was ITO/Ag/N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine [NPB]/4,4′-N,N′-dicarbazole-biphenyl [CBP]: 5wt% (btp)2Ir(acac)/2,2′,2″-(1,3,5-benzenetriyl)tris[1-phenyl-1H-benzimidazole] [TPBi]/LiF/Al. The sharp bright red emission of cavity device was observed. Compared with noncavity device the full width at half maximum (FWHM) of top normal emission spectrum was narrowed from 38nm to 23nm, and the maximum brightness of the cavity device was increased from 3500cd/m2 to 5800cd/m2, i.e., was improved by a factor of 1.7. The blue-shift of emission spectrum with increasing detection angle in traditional microcavity device was no longer observed, which attributed to a very steep rising of the EL-emission from (btp)2Ir(acac). Besides, it was importantly found that at higher current density EL efficiency was obviously higher for the cavity device than for noncavity device, i.e., at J=200mA/cm2 the former and later were 1.8cd/A and 1.0cd/A, respectively. And the increasing mechanism of the EL efficiency was ascribed to the shortened lifetime of triplet excited state (T1) and the weakened hole injection of Ag anode.

Circularly polarized emission from colloidal nanocrystal quantum dots confined in microcavities formed by chiral mirrors

Colloidal semiconductor nanocrystal quantum dots (NQDs) confined in a microcavity device emit resonance-enhanced, circularly polarized (CP) light, when the device consists of a pair of chiral sculptured-thin-film mirrors separated by layers of emissive nanocrystals and spacers that form a λ∕2-resonant cavity. The resonant emission from the NQDs within the microcavity is strongly directed normally to the mirror surfaces. It is speculated that the enhanced coupling between the NQD excitons and the confined electromagnetic field resulted in the observed CP emission from the embedded NQDs with significant improvements in the light output's directionality and color purity.

All-Optical Reshaping Based on a Passive Saturable Absorber Microcavity Device for Future 160-Gb/s Applications

A vertical-access passive all-optical switching gate has been used to regenerate the zero levels of a "...01010101..." 160-Gb/s bit pattern at 1561 nm. Autocorrelation function measurements show that an extinction up to 11.7 dB of the "ghost-pulses" can be achieved

Gallium nitride based micro-cavity light emitting diodes emitting at 498 nm

A gallium nitride based micro-cavity light emitting diode emitting at a peak wavelength of 498 nm has been fabricated. The epitaxial structure was grown by metalorganic chemical vapor deposition, and the device was fabricated using a laser lift-off process. Cavity thinning was carried out using reactive ion etching until a cavity length of roughly 830 nm (corresponding to a cavity order of ∼8 for λ = 498 nm in GaN) was achieved. Electroluminescence measurements of the micro-cavity device show a narrowed spectral width compared to the un-thinned device, and angularly resolved spectral measurements yielded a spectral shift, evincive of micro-cavity effects.

Investigation of dye-doped red emitting organic electroluminescent devices with metal-mirror microcavity structure

Organic electroluminescent (EL) devices with planar microcavity structure, indium-tin-oxide/Ag∕N,N′-diphenyl-N , N ′-bis(3-methylphenyl)-1,1′-biphenyl-4 , 4′-diamine/tris(8-hydroxyquinoline)-aluminum (AlQ):4-(dicyanomethylene)-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran/AlQ∕LiF∕Al, were fabricated. The Ag and Al layers acted as not only hole-injection layer and cathode, respectively, but reflective mirrors, resulting in strong microcavity effects, such as spectral narrowing and directional emission. The effects of device parameters on the EL performance were studied in detail and were discussed in terms of conventional microcavity theory. On-axis light magnification with a coefficient (EL enhancement ratio between cavity and noncavity devices) of ∼5 was observed, which was consistent with the theoretical calculation. At the same time, optimized microcavity device with bright pure red emission showed maximum luminance of 5140cd∕m2, peak at 624nm, Commission International de I’Eclairage coordinates of x=0.663 and y=0.336, and high EL efficiency of 1.71cd∕A were obtained.

Reduced angular dependence of the emission from tris(8-hydroxyquinoline) aluminum based microcavity

Organic microcavity light emitting diodes typically exhibit a significant blue shift of the emission wavelength with the viewing angle. In this work, we demonstrate significant reduction of the emission angular dependence of a microcavity device consisting of two organic layers, N,N′-di(naphthalene-1-yl)-N,N′-diphenylbenzidine (NPB) as a hole transport layer and tris(8-hydroxyquinoline) (Alq) as emitting layer, between two metal mirrors. The reduction of the angular dependence of the emission was achieved by optimizing the thickness of the layers within the device. The reasons for the reduced emission wavelength shift with the viewing angle are discussed.

High-Sensitivity Two-Photon Absorption Microcavity Autocorrelator

A GaAs-AlAs microcavity device has been used as a photodetector in an autocorrelator for measuring the temporal pulsewidth of 1.5-/spl mu/m optical pulses. Enhancement of the two-photon absorption photocurrent due to the microcavity structure results in an autocorrelation (average power times peak power) sensitivity of 9.3/spl times/10/sup -4/ (mW)/sup 2/, which represents two orders of magnitude improvement when compared with conventional autocorrelators.