Cylindrical Microcavity Research Articles

Method for Preparation of Semiconductor Quantum‐Rod Lasers in a Cylindrical Microcavity

AbstractAn efficient method for preparation of semiconductor quantum rod films for robust lasing in a cylindrical microcavity is reported. A capillary tube, serving as the laser cavity, is filled with a solution of nanocrystals and irradiated with a series of intense nanosecond laser pulses to produce a nanocrystal film on the capillary surface. The films exhibit intense room‐temperature lasing in whispering‐gallery modes that develop at the film–capillary interface as corroborated from the spacing detected for the lasing modes. Good lasing stability is observed at moderate pump powers. The method was applied successfully to several quantum‐rod samples of various sizes.

Optical properties and microring laser of conducting polymers with Sn atoms in main chains

Optical properties of conducting polymers with Sn atoms in main chains, such as optical absorption, photoluminescence (PL), and electroluminescence, have been studied. The electronic energy structures have been determined by optical and electrochemical measurements. Strong PL with high quantum efficiency has been clarified in the films, and photopumped multimode laser emission was demonstrated from cylindrical microcavities formed by these polymers coated around optical fibers.

Laser oscillations of resonance modes in a thin gain-doped ring-type cylindrical microcavity

We studied the lasing characteristics of resonance modes in a thin dye-doped dielectric ring cavity made on the inner wall of a cylindrical capillary. Lasing spectra corresponding to the whispering gallery modes (WGMs) and waveguide modes were addressed by investigating the spectral changes before and after a liquid was inserted into the capillary. The cavity quality factors of waveguide modes increased while those of WGMs did not alter as the refractive index of inner region increased. By observing a red shift of lasing envelope when a liquid was inserted, we could address the lasing peaks were waveguide modes coming from the total internal reflections at the both boundaries of the ring cavity.

Integration of carbon nanotubes with microplasma device cathodes: reduction in operating and ignition voltages

Situating carbon nanotubes (CNTs) near the cathode of a microplasma device, or integrating CNTs directly into the device cathode, reduces significantly the operating and ignition voltages for the device. Radiant output is also improved and the greatest benefit to device operation is realised when the CNTs are deposited onto the interior wall of the cylindrical cathode microcavity.

Observation of Relatively High-Q Coupled Modes in a Layered Cylindrical Microcavity Laser

Relatively high-Q coupled modes were observed from a layered cylindrical microcavity laser. The layered microcavity was realized by flowing dye-doped ethanol through a thin-wall fused silica capillary tube whose refractive index was larger than that of the liquid. Lasing spectrum showed strong mode selection, and even nearly single constructive interference peaks, due to the interferential coupling of whispering-gallery modes (WGMs) at the inner boundary. Various mode orders, which are not allowed in the ray optics picture, were made to oscillate due to the evanescent propagation of WGMs at the outer boundary. The estimated cavity quality factors were higher than 1×106.

Lasing from CdSe/ZnS Quantum Rods in a Cylindrical Microcavity

ABSTRACTLasing from CdSe/ZnS quantum rods and quantum dots both in solution and in a film is studied by utilizing a high Q cylindrical microcavity, showing Whispering Gallery Mode (WGM) lasing. CdSe/ZnS quantum rods, in comparison to quantum dots, exhibited remarkably reduced lasing thresholds. In addition, polarization measurements revealed that quantum rods have a linear polarized lasing, in contrast to quantum dots that show no preferable lasing polarization. Furthermore, an efficient and reproducible method is employed for preparation of nanocrystal films inside capillaries by laser irradiation for achieving robust lasing. Further irradiation of the film resulted in a room temperature stable lasing over hundreds of pump pulses, lasing thresholds as low as 0.02mJ and lasing intensities that are three orders of magnitude larger than the saturated fluorescence intensity. This was successfully applied to CdSe/ZnS quantum rod samples of varied dimensions and was also demonstrated for quantum dot samples.

Interferential coupling effect on the whispering-gallery mode lasing in a double-layered microcylinder

Enhanced mode selection through a strong interferential coupling effect was observed in a double-layered cylindrical microcavity laser. The coupling was induced by partial reflection and recombination with refracted light on the internal circular boundary of the fused silica capillary tube, filled with a dye-doped liquid having lower reflective index than that of fused silica. The observed interference period agreed well with the prediction by a ray-optic model.

Sensor based on an integrated optical microcavity

A novel integrated optical sensor based on a cylindrical microcavity (MC) is proposed. A MC sustains so-called whispering-gallery modes (WGMs), in which the energy of the optical field can be efficiently stored. By monitoring the scattering intensity from the MC, one can detect minute changes in the refractive index of the WGM, for instance, as a result of analyte adsorption. Measurement of a change in refractive index of as little as 10(-4) is demonstrated experimentally. The MC-based integrated optical sensor may have a size of approximately 8mum , and it is rugged and inexpensive.

Lasing from Semiconductor Quantum Rods in a Cylindrical Microcavity

Lasers based on colloidal semiconductor nanostructures can benefit from the remarkable spectral coverage afforded through the quantum confinement effect. The first observation of lasing for colloidal CdSe/ZnS quantum rods in solution using a cylindrical microcavity is reported here (see also inside front cover). Lasing in the same configuration was also observed for spherical nanocrystal quantum dots. For the quantum dots lasing is not polarized, but in quantum rods the laser emission is highly linearly polarized, a desirable feature for laser and photonic applications.

Lasing from Semiconductor Quantum Rods in a Cylindrical Microcavity

Lasing from Semiconductor Quantum Rods in a Cylindrical Microcavity

Longitudinal pumping of polymer microring lasers

Pulsed, longitudinal photopumped multi-mode laser emission is demonstrated in the visible spectral range from cylindrical microcavities formed by luminescent polymer thin films coated around optical fibers. Thresholds for laser oscillation for picosecond excitation are 80 pJ/mm for longitudinal pumping as compared to 4 nJ/mm (5 μJ/cm 2 or 0.05 MW/cm 2) for transversal pumping. An important advantage of the longitudinal pumping configuration lies in a significantly lower excitation density at threshold in comparison with the transverse pumping configuration. This improvement is ascribed to a larger overlap factor between the optical pump and the gain medium in the longitudinal geometry. The emission spectra of plastic microrings under these different excitation configurations are reported and analyzed. We note that lowering the lasing threshold is an important prerequisite criterion towards the development of electrically pumped plastic lasers.

Cylindrical and Spherical Microcavity Lasers Based on Evanes Cent‐Wave‐Coupled Gain

AbstractWe report operation of microcavity lasers based on the gain only in the evanes cent field region of whispering gallery modes. Two types of microcavities, microsphere and microcylinder, were used. First a cylindrical microcavity of 125 micron in diameter was surrounded by Rhodamine 6G dye molecules in ethanol solution of lower refractive index such that WGM's of the microcavity undergo laser oscillation when the dye molecules in the evanescent field region out side the cavity are excited by a second harmonic of a Nd: YAG laser. In the second experiment an ultrahigh Q microsphere was used for a cavity. The dye molecules out side the sphere, near the equator, of 102 μm diameter were excited, resulting in WGM lasing in the lowest radial mode order. The loaded quality factors of the cavity in this case were found to exceed 2 × 109, which would be high enough to support lasing with only a single quantum radiator coupled to the WGM.

Experimental analysis of the whispering-gallery modes in a cylindrical optical microcavity

A real-space study of a cylindrical integrated optical microcavity by means of a photon scanning-tunneling microscope with a resolution of 50 nm reveals optical intensity distributions in great detail. Moreover, novel phenomena such as polarization conversion and conversion from copropagation to counterpropagation are observed. We present detailed maps of the optical field distribution of the whispering-gallery modes inside the microcavity as a function of both wavelength and position. We have made a quantitative comparison between measured and calculated field distributions. As a result, the buildup of the various whispering-gallery modes is better understood.

InP-based cylindrical microcavity light-emitting diodes

We have investigated the properties of InP-based microcavity light-emitting diodes (/spl lambda/=1.6 /spl mu/m). Our objective was mainly to study the effects of lateral confinement of optical modes, which was achieved by the wet oxidation of double In/sub 0.52/Al/sub 0.48/As layers. The smallest devices had a cavity radius of 0.5 /spl mu/m, which becomes comparable to /spl lambda//n, where n is the effective refractive index of the photon emitting heterostructure. Two types of devices were tested: the first without any mirrors in the vertical direction, and the second with a combination of MgF/ZnSe DBR (top) and silver (bottom) to produce a low Q/spl sim/35-45. The latter type of devices exhibited higher output power and narrower spectral linewidth; otherwise, the characteristics were very similar The output slope efficiency monotonically decreases with reduction of lateral cavity size up to /spl sim/2-/spl mu/m in diameter and then is enhanced again for smaller cavity sizes. The slope efficiency of the smallest device (aperture diameter 1 /spl mu/m) is almost equal to that measured for the largest devices. The maximum output power measured from the devices is 30 /spl mu/W. The far-field pattern of devices with aperture radii ranging from 1.5 to 20 /spl mu/m shows an angular width (FWHM) of 50/spl deg/. On the other hand, devices with smaller aperture (radius /spl sim/0.5 /spl mu/m) exhibit an angular width of 20/spl deg/. The measured small-signal modulation bandwidth increases from /spl sim/0.45 GHz for the larger devices to 0.8 GHz for the smallest devices. Our results indicate that microcavity effects can be observed with only lateral photon confinement, making device fabrication requirements less stringent compared to surface-emitting lasers.

Cylindrical microcavity laser based on the evanescent-wave-coupled gain.

A microcavity laser based on the gain only in the evanescent field region of whispering gallery modes has been demonstrated. A cylindrical microcavity of 125 microm diam was surrounded by rhodamine 6G dye molecules in an ethanol solution of lower refractive index such that whispering gallery modes of the microcavity underwent laser oscillation when the dye molecules in the evanescent field region outside the cavity were excited by a second harmonic of a Nd:YAG laser. For particular pumping spots, single-mode laser oscillation of a transverse magnetic mode was observed at about 600 nm with associated cavity Q of 3x10(7).

Cavity-Q-driven spectral shift in a cylindrical whispering-gallery-mode microcavity laser

Cavity-Q-driven spectral shift of lasing was observed in a cylindrical microcavity formed by rhodamine6G-doped quinoline in a capillary. The envelope of lasing spectrum showed a blueshift induced by the decreasing cavity Q of whispering gallery modes as the pump fluence increases. The thermally induced refractive index changes were measured from the shifts of individual lasing modes. The observed cavity-Q-driven spectral shift was well described by a simple dye laser model, which accounts for the dependence of cavity Q on the thermally induced refractive index change.

Exciton polaritons in a cylindrical microcavity with an embedded quantum wire

Exciton-light coupling in cylindrical microcavities containing quantum wires has been treated by means of classical electrodynamics within the nonlocal dielectric response model. A typical anticrossing behavior of quasi-one-dimensional exciton-polariton modes has been obtained, as well as the weak-coupling--strong-coupling threshold. Effects of the nonradiative damping of the exciton resonance in the quantum wire on the optical response of the microcavity structure have been analyzed.

Intersubband and interminiband GaAs/AlGaAs quantum cascade lasers

Electrically pumped injection lasers based on the GaAs/AlGaAs material system are investigated. Intersubband transitions in coupled quantum wells and intraband transitions in a finite superlattice are used to demonstrate lasing. The laser emission wavelength is 10 μm for the intersubband lasers and 12.9 μm for the laser structure having a finite superlattice as an active cell. Utilizing ridge waveguide laser bars at a heat-sink temperature of 10 K, peak optical powers of the intersubband quantum cascade lasers exceed 300 mW (interminiband: 100 mW). The maximum operating temperature is 160 K (interminiband: 50 K). Cylindrical micro-cavities show single-mode behavior with a side mode suppression ratio better than 25 dB for both kinds of lasers.

Optical eigenmodes of a cylindrical microcavity

Abstract The optical mode structure of a cylindrical microcavity has been investigated using a transfer matrix approach. We derive exact algebraic equations from which the frequencies of the optical eigenmodes of the two polarizations can be obtained, as well as approximate explicit algebraic expressions for those frequencies.

Exciton—Light Coupling in Cylindrical Microcavities

A quantum treatment of exciton–polaritons which are formed when a quantum well is embedded in a cylindrical microcavity is developed. Leakage of the photon modes in air reduces the Rabi splitting with respect to the planar cavity case. The two oscillator model does not describe anymore the exciton–cavity mode interaction, since lack of in-plane translational invariance is responsible for the coupling of the exciton with a great number of photon modes. Only at very large radii the two-oscillator model is recovered; moreover, in this limit the Rabi splitting tends to the same value as that attained in a planar microcavity.