Wenzhao Sun

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.

Highly Reproducible Organometallic Halide Perovskite Microdevices based on Top-Down Lithography

Herein we fabricate highly reproducible-organometallic-halide-perovskite based devices, various device shapes that are hard to directly synthesize, unique properties and an improved photodetector have been successfully achieved. The advances will shed light on the practical applications.

Integrated photonic power divider with arbitrary power ratios.

Integrated optical power splitters are one of the fundamental building blocks in photonic integrated circuits. Conventional multimode interferometer-based power splitters are widely used as they have reasonable footprints and are easy to fabricate. However, it is challenging to realize arbitrary split ratios, especially for multi-outputs. In this Letter, an ultra-compact power splitter with a QR code-like nanostructure is designed by a nonlinear fast search method. The highly functional structure is composed of a number of freely designed square pixels with the size of 120×120  nm which could be either dielectric or air. The light waves are scattered by a number of etched squares with optimized locations, and the scattered waves superimpose at the outputs with the desired power ratio. We demonstrate 1×2 splitters with 1:1, 1:2, and 1:3 split ratios, and a 1×3 splitter with the ratio of 1:2:1. The footprint for all the devices is only 3.6×3.6  μm. Well-controlled split ratios are measured for all the cases. The measured transmission efficiencies of all the splitters are close to 80% over 30 nm wavelength range.

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.

Hybridizing CH3NH3PbBr3 microwires and tapered fibers for efficient light collection

Lead halide perovskite micro-devices such as microplates and microwires have shown great potential in microlasers, especially in the “green gap” wavelength region of conventional semiconductors. However, the synthesized perovskite lasers are usually randomly distributed on the substrate, making their laser emissions hard to be collected and utilized. Here we demonstrate a simple way to efficiently couple perovskite microlasers into conventional single mode fibers. By attaching a perovskite microwire onto a tapered fiber via micromanipulation, we found that the emissions along the single mode fiber are more than an order of magnitude larger than the collected emission with a 40× objective lens (NA = 0.6). The detailed estimation shows that the experimentally measured collection efficiency at one end of the tapered fiber can be around 13–20%, which is good enough for practical applications. Our numerical calculations show that the collection is mainly induced by the diffraction at the end of the microwire instead of the evanescent coupling and the total coefficient at the two ends can be further improved by optimizing the tapered fiber and microwire. As the tapered fiber is drawn from a commercial single-mode fiber, this research clearly shows the potential of perovskite devices to be integrated with conventional fiber systems.

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.

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.

Three-dimensional light confinement in a PT-symmetric nanocavity

Light confinement and manipulation in nanoscale have gained intense research attention due to their potential applications ranging from cavity quantum electrodynamics to nano-networks. Within all this research, the effective mode volume (Veff) is the key parameter that determines light–matter interaction. While various nano-cavities have been developed in past decades, very few have successfully confined light within the nanoscale in all three dimensions. Here we demonstrate a robust mechanism that can improve light confinement in nanostructures. By breaking the parity–time (PT) symmetry in nanowire based nanocavities, we find that the resonant modes are mostly localized at the interfaces between gain and loss regions, providing an additional way to confine light along a third direction. Taking a hybrid plasmonic Fabry–Perot cavity as an example, we show that the Veff has been dramatically improved from ∼0.0092 μm3 to ∼0.00169 μm3 after the breaking of PT symmetry. In addition to the perfect PT symmetric cavities with (n(r) = n(−r)*), we have also observed similar three-dimensional light confinements and an ultrasmall Veff in quasi-PT symmetric systems with fixed losses. We believe that our finding will significantly improve light–matter interaction in nanostructures and help the advance of their applications.

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.