The combination of metallic structure and graphene has become a promising platform for electrically controlled plasmonic devices. However, the current designs mainly utilize graphene as an active medium, which only modulate the devices performance slightly and the applications in tunable magnetic response have not been explored. Here, we explore the applications of graphene in the control of magnetic resonance in nanoantennas. By optimizing the design and parameter of the nanoantennas, gold–graphene hybrid diabolo antennas turn out to be the best candidate to achieve tunable magnetic response in mid-infrared wavelength range. The magnetic resonance of gold–graphene hybrid diabolo antennas has been significantly tuned from 32.3 μm to 19.8 μm, which is beyond one order of magnitude higher than conventional diabolo nanoantennas with graphene as active materials below the antenna structure. The corresponding absorption modulation and magnetic field enhancement can be as high as 12% and 1460%, respectively.

Solution‐processed lead halide perovskites have shown good applicability in both solar cells and microlasers. Very recently, the nonlinear properties of perovskites have attracted considerable research attention. Second harmonic generation and two‐photon absorption have been successfully demonstrated. However, perovskite devices based on these nonlinear properties, such as micro‐ and nanolasers have thus far not been fabricated. Here we demonstrate two‐photon pumped microlasers from CH3NH3PbBr3 perovskite microwires. These CH3NH3PbBr3 perovskite microwires are synthesized through a one‐step solution precipitation method and dispersed on a glass substrate. Under optical excitation at 800 nm, two‐photon pumped lasing action with periodic peaks is successfully observed at around 546 nm. The obtained quality (Q) factors of the two‐photon pumped microlasers are around 682, and the corresponding thresholds are about 674 µJ cm‐2. Both the Q factors and thresholds are comparable to conventional whispering‐gallery modes in two‐dimensional polygon microplates. This work is the first demonstration of two‐photon pumped microlasers in CH3NH3PbBr3 perovskite microwires. We believe our finding will significantly expand the application of perovskites in low‐cost nonlinear optical devices, such as optical limiters, optical switches, and biomedical imaging devices.

Perovskite microdisk lasers have been intensively studied recently. But their lasing properties are usually fixed once the devices are synthesized. Here, for the first time, we demonstrated the switchable and tunable perovskite microdisk lasers by surrounding them with 5CB liquid crystals. With the increase of the environmental temperature from 24 °C to 34 °C, the lasing wavelength slightly changed from 552.91 nm to 552.11 nm at the beginning and suddenly shifted to around 552.54 nm at T = 32 °C, where the phase transition of liquid crystals occurs. Our numerical calculation shows that the wavelength shift is caused by the changes of the refractive index of liquid crystals. More than tuning of the wavelength, a more dramatic wavelength transition from ∼554 nm to 550 nm has also been observed. This sudden transition is mainly induced by the reduction of scattering rather than the change in the refractive index when the liquid crystals are changed from the nematic phase to the isotropic phase. We believe that our research can shed light on the applications of perovskite optoelectronics.

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.

All-dielectric metamaterials offer a potential low-loss alternative to plasmonic metamaterials at optical frequencies. Here, we experimentally demonstrate a silicon based large-scale magnetic metamaterial, which is fabricated with standard photolithography and conventional reactive ion etching process. The periodically arrayed silicon sub-wavelength structures possess electric and magnetic responses with low loss in mid-infrared wavelength range. We investigate the electric and magnetic resonances dependencies on the structural parameters and demonstrate the possibility of obtaining strong dielectric-based magnetic resonance through a broad band range. The optical responses are quite uniform over a large area about 2 × 2 cm2. The scalability of this design and compatibility fabrication method with highly developed semiconductor devices process could lead to new avenues of manipulating light for low-loss, large-area and real integrated photonic applications.

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.

Transparent high refractive index materials are of the central importance for the development of metasurface in visible range. Titanium dioxide (TiO2) has been considered as a perfect candidate due to its wide band gap and high refractive index. However, till now, it is still quite challenging to fabricate high-quality TiO2 films with high refractive indices and low losses. Here we demonstrate the fabrication of high-quality TiO2 film using an electron-beam evaporation method. We show that the post-annealing conditions play key roles in the microstructure crystallographic and the optical refractive index of the TiO2 films. A predominately oriented TiO2 film has been achieved by annealing at 700 °C in oxygen ambient. The refractive index is as high as 2.4, and the corresponding loss is negligible at 632 nm. Further studies on dielectric antennas show that our TiO2 film can be an ideal platform to fabricate metasurface in visible frequency range. We believe that our research will be important for the advances of all-dielectric metasurfaces.

By dint of unique physical/chemical properties and bio-compatibility, graphene can work as a building block for a SERS substrate and open up a unique platform for tumor cells detection with high sensitivity. Herein we demonstrate a facile system with highly enhanced surface enhanced Raman spectroscopy of graphene (G-SERS). The system consists of a reduced graphene oxide (rGO) sandwiched by silver and gold nanostructures. Due to the ultrasmall thickness of rGO, the inter-coupling between Ag and Au nanoparticles is precisely controlled and the local field enhancement has been improved to more than 70 times. Associated with the unique chemical mechanism of rGO, the hybrid system has been utilized to identify tumor cells without using any biomarkers. We believe this research will be important for the applications of rGO in cancer screening.

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.

Single-crystalline, hexagon shaped lead halide perovskite microplates have been synthesized and their lasing actions have attracted intensive research attention. However, up to now, only the hexagonal whispering gallery modes (WGMs) have been experimentally observed. The dominant high Q modes, the triangular WGMs, are still surprisingly absent. Herein we study the mechanisms of forming different WGMs. We show that tiny nanoparticles can strongly affect the lasing modes in hexagonal cavities. In addition, we also explore a simple way to selectively excite the triangular WGMs in hexagon shaped microplates. By introducing either one-dimensional or rotational parity-time (PT) symmetry into the hexagonal microdisk, the hexagonal WGMs experience balanced gain and loss and cannot lase until their PT symmetries are broken. The triangular WGMs show quite different behaviors due to their unique field distributions. The modes along one triangular orbit are mostly confined within the gain region, whereas the modes along the other triangular orbit are mostly localized within the loss area. Then the PT symmetries of triangular WGMs are naturally broken and one set of triangular WGMs can lase very quickly. Consequently, only triangular WGMs can be excited in lasing experiments. We believe our research will be important for tailoring and understanding the lasing actions in hexagon shaped microcavities.