Whispering Gallery Mode Microdisk Research Articles

Multimode Emission in GaN Microdisk Lasers

AbstractQuantum well nanolasers usually show single‐mode lasing, as gain saturation suppresses emissions in other modes. In contrast, for whispering gallery mode microdisk lasers with GaN quantum wells as active material, above threshold multimode laser emission is observed. This intriguing emission feature is manifested in the fact that several modes simultaneously show the characteristic kink in the input–output curve at the onset of lasing. A quantum theory for nanolasers is used to support the experimental finding and to analyze this behavior in the presence of gain saturation. Coupling effects between neighboring modes are identified as the origin of multimode lasing, which initiate photon exchange between modes via population pulsations similar to classical wave‐mixing effects. A reduction of this type of mode coupling with increasing mode spacing is demonstrated. The results can pave the way for multimode application of nanolasers in integrated photonic circuits.

Photolithographed Whispering Gallery Mode Microdisk Cavities Coupled to Semiconductor Quantum Dots

Photolithographed Whispering Gallery Mode Microdisk Cavities Coupled to Semiconductor Quantum Dots

Red-Shifted Excitation and Two-Photon Pumping of Biointegrated GaInP/AlGaInP Quantum Well Microlasers.

Biointegrated intracellular microlasers have emerged as an attractive and versatile tool in biophotonics. Different inorganic semiconductor materials have been used for the fabrication of such biocompatible microlasers but often operate at visible wavelengths ill-suited for imaging through tissue. Here, we report on whispering gallery mode microdisk lasers made from a range of GaInP/AlGaInP multi-quantum well structures with compositions tailored to red-shifted excitation and emission. The selected semiconductor alloys show minimal toxicity and allow the fabrication of lasers with stable single-mode emission in the NIR (675–720 nm) and sub-pJ thresholds. The microlasers operate in the first therapeutic window under direct excitation by a conventional diode laser and can also be pumped in the second therapeutic window using two-photon excitation at pulse energies compatible with standard multiphoton microscopy. Stable performance is observed under cell culturing conditions for 5 days without any device encapsulation. With their bio-optimized spectral characteristics, low lasing threshold, and compatibility with two-photon pumping, AlGaInP-based microlasers are ideally suited for novel cell tagging and in vivo sensing applications.

Refractive Index Sensor Based on Gold-Coated Whispering Gallery Mode Microdisk Resonator

Refractive index (RI) sensors based on whispering gallery mode microdisk resonator with creasent-shape and full gold layer coating are numerically investigated. Benefit from the surface plasmon polaritions (SPPs) induced by gold coating, the crescent-shaped and fully gold-coated microresonators reveal sensitivity increasement of up to 31.8% and 81.1% over the resonator without gold coating, respectively. The extinction ratio of crescent-shaped gold-coated microresonator is demonstrated to be adjusted by changing the coupling distance. Furthermore, a maximum surface energy enhancement of up to 83.3% is obtained for microresonator with a full gold coating.

Room-temperature optically pumped InAs/GaAs quantum dots microdisk lasers on SiO2/Si chip * * Project supported by the National Key Research and Development Program of China (No. 2016YFA0301202) and the National Natural Science Foundation of China (Nos. 11474275, 61674135, 91536101).

We report on room temperature continuous-wave optically pumped InAs/GaAs quantum dot whispering gallery mode microdisk lasers, heterogeneously integrated on silica/silicon chips. The microdisks are fabricated by photolithography and inductively coupled plasma etching. The lasing wavelength is approximately 1200 nm and the obtained lowest laser threshold is approximately 28 μW. The experimental results show an approach of possible integrated III–V optical active materials on silica/silicon chip for low threshold WGM microdisk lasers.

Single-mode unidirectional microcavity laser.

In this Letter, we report a suspended whispering gallery mode microdisk with a hole pierced through its surface. The novel disk is made up of Rhodamine B-doped resin, which is fabricated by femtosecond laser direct writing technology. The pierced microcavity achieves highly directional emission of single-mode lasing with a far field divergence angle of about 10 deg, and its high Q factor exceeds 2.6×103. The excellent properties are confirmed by numerical simulation based on the finite-difference time-domain method. The effect of the pierced hole on the microcavity performance is discussed in detail. The method is easy to implement and has a guiding significance for improving the characteristics of an existing microcavity by simple modification.

Improved emission outcoupling from microdisk laser by Si nanospheres

Far field emission of optically pumped QD microdisk lasers with spherical Si nanoantenna placed on the top surface of microdisk is studied theoretically and experimentally. The interaction of the whispering gallery mode microdisk resonator with properly designed and positioned Si nanospheres results in improvement of light outcoupling and directed emission.

Dark-field imaging as a noninvasive method for characterization of whispering gallery modes in microdisk cavities

Whispering gallery mode microdisk cavities fabricated by direct laser writing are studied using dark-field imaging and spectroscopy in the visible spectral range. Dark-field imaging allows us to directly visualize the spatial intensity distribution of whispering gallery modes. We extract their azimuthal and radial mode indices from dark-field images, and find the axial mode number from the dispersion relation. The scattering spectrum obtained in the confocal arrangement provides information on the density of optical states in the resonator. The proposed technique is a simple noninvasive way to characterize the optical properties of microdisk cavities.

Fabrication of High-Q Microresonators Using Femtosecond Laser Micromachining

We report a technique to fabricate whispering gallery mode microdisk resonators using femtosecond laser micromachining and a heat reflow process to improve the optical quality of the resonator. The fabricated resonators have suppressed higher order modes with a measured Q-factor as high as 7.2×106. The described fabrication process, which relies on material non-thermal laser ablation, offers the ability to fabricate microresonators using a wide variety of materials of nearly any dimensional size or shape.

Planar native-oxide-based AlGaAs-GaAs-InGaAs quantum well microdisk lasers

Data are presented on the 300 K photopumped (pulsed) laser operation of ultrathin (∼0.15 μm) planar microdisk lasers. The tiny lasers employ the wet oxidation of an AlGaAs layer beneath the disks to form semiconductor cavities that are in solid contact but optically isolated from the GaAs substrate. The resulting microcavity lasers operate at low pump intensities and exhibit spectra characteristic of whispering gallery mode microdisk lasers.

Electrically pumped, room-temperature microdisk semiconductor lasers with submilliampere threshold currents

Summary form only given. Electrically pumped whispering-gallery mode microdisk lasers with single-mode operation and submilliampere threshold current at room temperature have been demonstrated. Semiconductor microdisks 10 mu m in diameter and 340-nm thick including four 100-AA InGaAs quantum well layers separated by 150-AA InGaAsP barriers are fabricated with InP support pedestals above (p-type) and below (n-type) the disk. A 4.5- mu m-diameter metal disk atop the p-type pedestal provides electrical contact to the laser structure. The semiconductor disks form high-Q optical resonators for the whispering-gallery mode around the edge of the disk. Electrical pulses 0.3 mu s in length at levels near 1 V and 1 mA result in lasing at room temperature for wavelengths near 1.58 mu m with emission from the edge of the disk. At 1-mA current levels the peak laser emission is 9 dB above the spontaneous emission background and at 8 mA it is 26 dB above the background. >