Quasi-guiding modes in microfibers on high refractive index substrate

Light confinement and amplification in micro- & nano-fiber have been intensively studied and a number of applications have been developed. However, the typical micro- & anno- fibers are usually free-standing or positioned on a substrate with lower refractive index to ensure the light confinement and guiding mode. Here we numerically and experimentally demonstrate the possibility of confining light within a microfiber on a high refractive index substrate. In contrast to the strong leaky to the substrate, we found that the radiation loss was dependent on the radius of microfiber and the refractive index contrast. Consequently, quasi-guiding modes could be formed and the light could propagate and be amplified in such systems. By fabricating tapered silica fiber and dye-doped polymer fiber and placing them on sapphire substrates, the light propagation, amplification, and laser behaviors have been experimentally studied to verify the quasi-guiding modes in microfer with higher index substrate. We believe that our research will be essential for the applications of micro- and nano-fibers.Comment: 17 pages, 6 figure

Experimental demonstration of PT-symmetric stripe lasers

Recently, the coexistence of parity-time (PT) symmetric laser and absorber has gained tremendous research attention. While the PT symmetric absorber has been observed in microwave metamaterials, the experimental demonstration of PT symmetric laser is still absent. Here we experimentally study PT-symmetric laser absorber in stripe waveguide. Using the concept of PT symmetry to exploit the light amplification and absorption, PT-symmetric laser absorbers have been successfully obtained. Different from the single-mode PT symmetric lasers, the PT-symmetric stripe lasers have been experimentally confirmed by comparing the relative wavelength positions and mode spacing under different pumping conditions. When the waveguide is half pumped, the mode spacing is doubled and the lasing wavelengths shift to the center of every two initial lasing modes. All these observations are consistent with the theoretical predictions and confirm the PT-symmetry breaking well.Comment: 17 pages, 4 figure

Formation of Single-mode Laser in Perovskite Nanowire via Nano-manipulation

Perovskite based micro- and nano- lasers have attracted considerable research attention in past two years. However, the properties of perovskite devices are mostly fixed once they are synthesized. Here we demonstrate the tailoring of lasing properties of perovskite nanowire lasers via nano-manipulation. By utilizing a tungsten probe, one nanowire has been lifted from the wafer and re-positioned its two ends on two nearby perovskite blocks. Consequently, the conventional Fabry-Perot lasers are completely suppressed and a single laser peak has been observed. The corresponding numerical model reveals that the single-mode lasing operation is formed by the whispering gallery mode in the transverse plane of perovskite nanowire. Our research provides a simple way to tailor the properties of nanowire and it will be essential for the applications of perovskite optoelectronics.Comment: 16 pages, 5 figure

Multimode Coupling by Boundary Wave Scattering

We show that coupling among multiple resonances can be conveniently introduced and controlled by boundary wave scattering. We demonstrate this principle in optical microcavities of quasi-circular shape, where the couplings of multiple modes are determined by the scattering from different harmonic boundary deformations. We analyze these couplings using a perturbation theory, which gives an intuitive understanding of the first-order and higher-order scattering processes. Different scattering paths between two boundary waves can either enhance or reduce their coupling strength. The effect of controlled multimode coupling is most pronounced in the direction of output from an open cavity, which can cause a dramatic change of the external cavity field distribution.Comment: 9 pages, 10 figure

Two-photon pumped lead halide perovskite nanowire lasers

Solution-processed lead halide perovskites have shown very bright future in both solar cells and microlasers. Very recently, the nonlinearity of perovskites started to attract considerable research attention. Second harmonic generation and two-photon absorption have been successfully demonstrated. However, the nonlinearity based perovskite devices such as micro- & nano- lasers are still absent. Here we demonstrate the two-photon pumped nanolasers from perovskite nanowires. The CH3NH3PbBr3 perovskite nanowires were synthesized with one-step solution self-assembly method and dispersed on glass substrate. Under the optical excitation at 800 nm, two-photon pumped lasing actions with periodic peaks have been successfully observed at around 546 nm. The obtained quality (Q) factors of two-photon pumped nanolasers are around 960, and the corresponding thresholds are about 674?J=cm2. Both the Q factors and thresholds are comparable to conventional whispering gallery modes in two-dimensional polygon microplates. Our researches are the first demonstrations of two-photon pumped nanolasers in perovskite nanowires. We believe our finding will significantly expand the application of perovskite in low-cost nonlinear optical devices such as optical limiting, optical switch, and biomedical imaging et al.Comment: 14 pages, 5 figure

End-fire injection of guided light into optical microcavity

Coupling light into microdisk plays a key role in a number of applications such as resonant filters and optical sensors. While several approaches have successfully coupled light into microdisk efficiently, most of them suffer from the ultrahigh sensitivity to the environmental vibration. Here we demonstrate a robust mechanism, which is termed as end-fire injection. By connecting an input waveguide to a circular microdisk directly, the mechanism shows that light can be efficiently coupled into optical microcavity. The coupling efficiency can be as high as 0.75 when the input signals are on resonances. Our numerical results reveal that the high coupling efficiency is attributed to the constructive interference between the whispering gallery modes and the input signals. We have also shown that the end-fire injection can be further extended to the long-lived resonances with low refractive index such as n = 1.45. We believe our results will shed light on the applications of optical microcavities.Comment: 5 pages, 5figure

Whispering-gallery-mode based CH3NH3PbBr3 perovskite microrod lasers with high quality factors

Lead halide perovskite based micro- and nano- lasers have been widely studied in past two years. Due to their long carrier diffusion length and high external quantum efficiency, lead halide perovskites have been considered to have bright future in optoelectronic devices, especially in the "green gap" wavelength region. However, the quality (Q) factors of perovskite lasers are unspectacular compared to conventional microdisk lasers. The record value of full width at half maximum (FWHM) at threshold is still around 0.22 nm. Herein we synthesized solution-processed, single-crystalline CH3NH3PbBr3 perovskite microrods and studied their lasing actions. In contrast to entirely pumping a microrod on substrate, we partially excited the microrods that were hanging in the air. Consequently, single-mode or few-mode laser emissions have been successfully obtained from the whispering-gallery like diamond modes, which are confined by total internal reflection within the transverse plane. Owning to the better light confinement and high crystal quality, the FWHM at threshold have been significantly improved. The smallest FWHM at threshold is around 0.1 nm, giving a Q factor over 5000.Comment: 7 pages, 4 figure

Random lasing actions in self-assembled perovskite nanoparticles

Solution-based perovskite nanoparticles have been intensively studied in past few years due to their applications in both photovoltaic and optoelectronic devices. Here, based on the common ground between the solution-based perovskite and random lasers, we have studied the mirrorless lasing actions in self-assembled perovskite nanoparticles. After the synthesis from solution, discrete lasing peaks have been observed from the optically pumped perovskites without any well-defined cavity boundaries. The obtained quality (Q) factors and thresholds of random lasers are around 500 and 60 uJ/cm2, respectively. Both values are comparable to the conventional perovskite microdisk lasers with polygon shaped cavity boundaries. From the corresponding studies on laser spectra and fluorescence microscope images, the lasing actions are considered as random lasers that are generated by strong multiple scattering in random gain media. In additional to conventional single-photon excitation, due to the strong nonlinear effects of perovskites, two-photon pumped random lasers have also been demonstrated for the first time. We believe this research will find its potential applications in low-cost coherent light sources and biomedical detection.Comment: 16 pages, 5 figure

Enhancing the Three-Photon Luminesce via the Resonance in Lead Halide Perovskite Metasurfaces

Lead halide perovskites (MAPbX3) have emerged as promising materials for photovoltaic and optoelectronic devices. However, their exceptional nonlinear properties have not been fully exploited in nanophotonics yet. Herein we fabricate MAPbX3 perovskite metasurfaces and explore their internal nonlinear processes. While both of third-order harmonic generation (THG) and three-photon luminescence are generated, the latter one is less affected by the material loss and has been significantly enhanced by a factor of 60. The corresponding simulation reveals that the improvement is caused by the resonant enhancement of incident laser in perovskite metasurface. Interestingly, such kind of resonance-enhanced three-photon luminescence holds true for metasurfaces with a small period number of 4, enabling new applications of perovskite metasurface in high-resolution nonlinear color nanoprinting and optical encoding. The encoded information "NANO" is visible only when the incident laser is on-resonance. The off-resonance pumping and the single-photon excitation just produce a uniform dark or photoluminescence background.Comment: 11 pages,5 figure

Lead Halide Perovskite based Dynamic Metasurfaces

Lead halide perovskites (MAPbX3) are known to have high refractive index and controllable bandgap, making them attractive for all-dielectric and tunable metasurfaces. Till now, perovskite metasurfaces have only been used in structural colors. More interesting meta-devices with 2{\pi} phase control are still absent. Here we experimentally demonstrate the MAPbX3 perovskite based metasurfaces with a complete control of phase shift in a reflection mode. By utilizing MAPbBr3 cut-wires as meta-atoms on a ground metal film, we find that the MAPbBr3 perovskite metasurface can produce full phase control from 0 to 2{\pi} and high reflection efficiency simultaneously. Consequently, high-efficiency polarization conversion, anomalous reflection and meta-hologram have been successfully produced. Most interestingly, the bandgap of MAPbX3 perovskite can be post-synthetically and reversibly tuned via anion exchange, providing a new approach to dynamically control of the all-dielectric meta-devices with novel function such as anomalous reflection and hologram et al