Shuai Liu

Formation of single-mode laser in transverse plane of perovskite microwire via micromanipulation

The synthesized perovskites are randomly distributed and their optical properties are fixed after synthesis. Here we demonstrate the tailoring of lasing properties of perovskite microwire via micromanipulation. One microwire has been lifted by a tungsten probe and repositioned on a nearby perovskite microplate with one end suspended in air. Consequently, the conventional Fabry-Perot lasers are completely suppressed and a single laser peak has been observed. The numerical calculations reveal that the single-mode laser is formed by the whispering-gallery mode in the transverse plane of microwire. Our research provides a simple way to tailor the properties of microwire postsynthesis.

High-Density and Uniform Lead Halide Perovskite Nanolaser Array on Silicon

The realization of high density and highly uniform nanolaser arrays in lead halide perovskite is quite challenging, especially on silicon. Herein, we demonstrate a simple way to form lead halide nanolaser array on silicon chip with high density and uniform lasing wavelengths. By positioning a perovskite microwire onto a silicon grating, only the suspended parts can hold high quality (Q) resonances and generate laser emissions. As the perovskite microwire is periodically segmented by the silicon grating, the transverse lasers are divided into a periodic nanolaser array and the lasing wavelengths from different subunits are almost the same. The transverse laser has been observed in an air gap as narrow as 420 nm, increasing the density of nanolasers to about 1250 per millimeter (800 nm period in experiment). We believe this research shall shed light on the development of perovskite microlaser and nanolaser arrays on silicon and their applications.

Far-field single nanoparticle detection and sizing

Whispering gallery mode based optical microcavities are important for highly sensitive optical sensing. However, the current experimental realizations are strongly dependent on high-resolution tunable lasers and evanescent coupling, which are too cumbersome and too expensive for portable devices. Herein we experimentally demonstrate a cost-effective and robust approach to detect and size a single nanoparticle with far-field laser emissions. By placing a limacon microdisk close to a spiral microdisk, chiral resonances have been successfully generated. In contrast to previous research, here the internal chirality is strongly correlated with the far-field patterns (FFPs) and thus can be transduced to far-field emissions. Once a nanoparticle is attached to the limacon microdisk, the asymmetrical backscattering at the notch of the spiral can be averaged by the symmetrical scattering of the nanoparticle. Consequently, the internal chirality and the corresponding FFPs are changed. By measuring a far-field directional laser emission, nanoparticles with a radius of ∼50  nm have been successfully detected and sized without employing any spectral information. As a narrow-linewidth tunable laser is not used in our experiment and microdisks lasers may be electrically driven, this research will provide a new path to cost-effective, portable, highly sensitive optical sensors.

Tailoring the lasing modes in CH3NH3PbBr3 perovskite microplates via micro-manipulation

Laser emissions from perovskite microplates have been intensively studied recently. However, due to their relatively large sizes, most of them produced multiple lasing modes simultaneously. In order to improve the monochromaticity of perovskite microlasers without significantly affecting the output energy, here we demonstrate a simple way to tailor the number of lasing modes in a microcavity. By pushing an additional microplate to contact the lasing microplate, the number of lasing modes has been effectively reduced and single-mode laser operation has been achieved even though the size of the microplate is orders of magnitude larger than the lasing wavelengths. The corresponding extinction ratio can be as high as 11.8 dB. Our experimental results show that introducing the second microplate and the extremely narrow gain region play essential roles in achieving single-mode laser operation. We believe that our findings will be interesting for the applications of perovskite microdisk lasers.

The combination of directional outputs and single-mode operation in circular microdisk with broken PT symmetry

Monochromaticity and directionality are two key characteristics of lasers. However, the combination of directional emission and single-mode operation is quite challenging, especially for the on-chip devices. Here we propose a microdisk laser with single-mode operation and directional emissions by exploiting the recent developments associated with parity-time (PT) symmetry. This is accomplished by introducing one-dimensional periodic gain and loss into a circular microdisk, which induces a coupling between whispering gallery modes with different radial numbers. The lowest threshold mode is selected at the positions with least initial wavelength difference. And the directional emissions are formed by the introduction of additional grating vectors by the periodic distribution of gain and loss regions. We believe this research will impact the practical applications of on-chip microdisk lasers.

Deformed microdisk coupled to a bus waveguide for applications in resonant filter

Here we explore the applications of a deformed microdisk as a passive photonic element by coupling it to a bus waveguide. We show that deformed microdisk-based resonant filters are able to have transmittance of more than 99%, and the dropped signals can be routed to two different ports for particular applications. Interestingly, our results show that the splitting ratio can be dynamically tuned by locally changing the refractive index of microdisk. Our research opens new opportunities for the applications of deformed microdisks.

Formation of Lead Halide Perovskite Based Plasmonic Nanolasers and Nanolaser Arrays by Tailoring the Substrate

Hybrid plasmonic nanolasers are intensively studied due to their nanoscale mode confinement and potentials in highly integrated photonic and quantum devices. Until now, the characteristics of plasmonic nanolasers are mostly determined by the crystal facets of top semiconductors, such as ZnO nanowires or nanoplates. As a result, the spasers are isolated, and their lasing wavelengths are random and difficult to tune. Herein, we experimentally demonstrate the formation of lead halide perovskite (MAPbX3) based hybrid plasmonic nanolasers and nanolaser arrays with arbitrary cavity shapes and controllable lasing wavelengths. These spasers are composed of MAPbX3 perovskite nanosheets, which are separated from Au patterns with a 10 nm SiO2 spacer. In contrast to previous reports, here, the spasers are determined by the boundary of Au patterns instead of the crystal facets of MAPbX3 nanosheets. As a result, whispering gallery mode based circular spasers and spaser arrays were successfully realized by patterning the Au substrate into circles and gratings, respectively. The standard wavelength deviation of spaser arrays is as small as 0.3 nm. Meanwhile, owing to the anion-exchangeable property of MAPbX3 perovskite, the emission wavelengths of spasers were tuned more than 100 nm back and forth by changing the stoichiometry of perovskite postsynthetically.

The Role of Excitons on Light Amplification in Lead Halide Perovskites

The role of excitons on the amplifications of lead halide perovskites has been explored. Unlike the photoluminescence, the intensity of amplified spontaneous emission is partially suppressed at low temperature. The detailed analysis and experiments show that the inhibition is attributed to the existence of exciton and a quantitative model has been built to explain the experimental observations.

End-fire injection of light into high-Q silicon microdisks

High-quality (Q)-factor silicon microdisks are promising platforms for revolutionizing bio-sensing, medical diagnoses, and frequency combs. Nevertheless, their practical applications are hindered by the regular waveguide–resonator coupling configuration, which relies on sophisticated and high-cost nanofabrication. Here, we demonstrate a simple, cost-effective, and counterintuitive mechanism to couple light into a high-Q silicon microdisk. In contrast to the evanescent coupling, the incident light is injected into silicon microdisks through the waveguides directly connected to them. The end-fire injection coefficients and Q factors of waveguide-connected microdisks are around 57% and 2×105–7×105, comparable to conventional microdisks. Importantly, the end-fire injection configuration is quite robust to fabrication deviations and can be simply realized without using electron-beam lithography. Meanwhile, their applications in monitoring nanoparticles and tiny ambient changes have also been explored. This research will route a new way to on-chip biosensors and integrated photonic circuits.

Dark-Field Sensors based on Organometallic Halide Perovskite Microlasers

The detection of nanoscale objects is essential for homeland security, environmental monitoring, and early-stage diagnostics. In the past few years, optical sensors have mostly been developed with passive devices such as microcavity and plasmonic nanostructures, which require external laser sources to operate and significantly increase the costs and bulks of sensing systems. To date, the potential of their active counterparts in optical sensors has not been well explored. Herein, a novel and robust mechanism to detect nanoscale objects with lead halide perovskite microlasers is demonstrated. Nanoparticles can be simply detected and sized by measuring the intensity of scattered laser light. In principle, the proposed concept is also applicable to electrically driven microlasers and it could find applications in portable point-of-care devices.