3D-Printed Möbius Microring Lasers: Topology Engineering in Photonic Microstructures.

Manipulating photons in artificially structured materials is highly desired in modern photonic technology. Nontrivial topological structures are rapidly emerging as a state-of-art platform for achieving unprecedented fascinating phenomena of photon manipulation. However, the current studies mainly focus on planar structures, and the fabrication of photonic microstructures with specific topological geometric features still remains a great challenge. Extending the topological photonics to 3D microarchitectures is expected to enrich the photon manipulation capabilities and further advance the topological photonic devices. Here, a femtosecond laser direct writing technique is employed to fabricate 3D topological Möbius microring resonators from dye-doped polymer. The high-quality-factor Möbius microring resonator supports a unique spin-orbit coupled lasing at very low threshold. Due to the spin-orbit coupling induced geometric/Berry phase, the Möbius microrings, in striking contrast with ordinary microrings, output laser signals with all polarization states. The manipulation of miniaturized coherent light sources in the fabricated Möbius microrings represents a significant step forward toward 3D topological photonics that offers a novel design philosophy for functional photonic and optoelectronic devices.

Nonlinearity-mediated collimation of optical beams.

We investigated the evolutions of optical beams in an optical system composed of free spaces and nonlocal nonlinear media layers in a cascaded manner. From an application point of view, two kinds of evolution processes for Gaussian beams, nonlinearity-mediated collimation and switching from breathers to solitons, were discussed in details. By adjusting the input optical power, the collimating, the compressing and the expanding of optical beams are convenient to be controlled.

Perpendicular coupler for standing wave excitation and wavelength selection in high-Q silicon microresonators.

High quality factor (Q) whispering gallery mode (WGM) resonators have been widely applied in photonics, while the excitation and collection of WGMs are mostly restricted to traveling wave coupler. Here, we experimentally demonstrate a novel on-chip perpendicular coupler (PC) for high-Q (∼1.1 × 105) silicon whispering gallery microresonators. The PC is compact and allows efficiently tunneling coupling between the waveguide and the microresonator, hence it holds great potential for fan-out photonic devices. Drastically different from the traveling wave couplers, standing wave mode can be excited through the PC. In addition, a PC working as an output coupler can also selectively collect the resonance of different wavelengths by locating on different azimuth angles. Our results show the feasibility of such novel coupler for WGM resonators and its potential use in future applications of integrated high Q microresonators.

Integrated optical circulator by stimulated Brillouin scattering induced non-reciprocal phase shift.

We propose a new approach to realize all-optical circulator based on stimulated Brillouin scattering in an integrated microresonator. Stimulated Brillouin scattering is a basic interaction between photon and traveling acoustic wave resulted from electrostriction and photoelastic effects. Due to the phase-matching requirement, the circulating acoustic wave can only couple to probe light which propagating along or opposite to the pump laser direction, thus exhibits a non-reciprocal phase shift. Combined with Mach-Zehnder interferometer, the optical circulator can be realized. Though the bandwidth is relatively small because of the narrow-band nature of microresonator, this magnetic-free all-optical integrated circulator may be applied for future on-chip photonic information processing.

Transient microcavity sensor.

A transient and high sensitivity sensor based on high-Q microcavity is proposed and studied theoretically. There are two ways to realize the transient sensor: monitor the spectrum by fast scanning of probe laser frequency or monitor the transmitted light with fixed laser frequency. For both methods, the non-equilibrium response not only tells the ultrafast environment variance, but also enable higher sensitivity. As examples of application, the transient sensor for nanoparticles adhering and passing by the microcavity is studied. It's demonstrated that the transient sensor can sense coupling region, external linear variation together with the speed and the size of a nanoparticle. We believe that our researches will open a door to the fast dynamic sensing by microcavity.

Theory of free space coupling to high-Q whispering gallery modes.

Theoretical study of free space coupling to high-Q whispering gallery modes (WGMs) are presented in circular and deformed microcavities. Both analytical solutions and asymptotic formulas are derived for a circular cavity. The coupling efficiencies at different coupling regimes for cylindrical incoming wave are discussed, and the maximum efficiency is estimated for the practical Gaussian beam excitation. In the case of a deformed cavity, the coupling efficiency can be higher than the circular cavity if the excitation beam can match the intrinsic emission which can be tuned by adjusting the degree of deformation. Employing an abstract model of slightly deformed cavity, we find that the asymmetric and peak like line shapes instead of the Lorentz-shape dip are universal in transmission spectra due to multi-wave interference, and the coupling efficiency cannot be estimated from the absolute depth of the dip. Our results provide guidelines for free space coupling in experiments, suggesting that the high-Q asymmetric resonator cavities (ARCs) can be efficiently excited through free space which will stimulate further experiments and applications of WGMs based on free space coupling.

Dielectric bow-tie nanocavity.

We propose a novel dielectric bow-tie (DBT) nanocavity consisting of two opposing tip-to-tip triangle semiconductor nanowires, whose end faces are coated by silver nanofilms. Based on the advantages of the dielectric slot and tip structures, and the high reflectivity of the silver mirror, light can be confined in this nanocavity with low loss. We demonstrate that at 4.5 K (300 K) around the resonance wavelength of 1550 nm, the mode excited in this nanocavity has a deep subwavelength mode volume of 2.8×10(-4) µm³ and a high quality factor of 4.9×10(4) (401.3), corresponding to an ultrahigh Purcell factor of 1.6×10(7) (1.36×10(5)). This DBT nanocavity may find applications for integrated nanophotonic circuits, such as high-efficiency single photon sources, thresholdless nanolasers, and strong coupling in cavity quantum electrodynamics experiments.

Organic Synthetic Photonic Systems with Reconfigurable Parity-Time Symmetry Breaking for Tunable Single-Mode Microlasers.

Synthetic photonic materials exploiting the quantum concept of parity-time (PT) symmetry lead to an emerging photonic paradigm-non-Hermitian photonics, which is revolutionizing the photonic sciences. The non-Hermitian photonics dealing with the interplay between gain and loss in PT synthetic photonic material systems offers a versatile platform for advancing microlaser technology. However, current PT-symmetric microcavity laser systems only manipulate imaginary parts of the refractive indices, suffering from limited laser spectral bandwidth. Here, an organic composite material system is proposed to synthesize reconfigurable PT-symmetric microcavities with controllable complex refractive indices for realizing tunable single-mode laser outputs. A grayscale electron-beam direct-writing technique is elaborately designed to process laser dye-doped polymer films in one single step into microdisk cavities with periodic gain and loss distribution, which enables thresholdless PT-symmetry breaking and single-mode laser operation. Furthermore, organic photoisomerizable compounds are introduced to reconfigure the PT-symmetric systems in real-time by tailoring the real refractive index of the polymer microresonators, allowing for a dynamically and continuously tunable single-mode laser output. This work fundamentally enhances the PT-symmetric photonic systems for innovative design of synthetic photonic materials and architectures.

Perpendicular coupler for whispering-gallery resonators.

In this Letter, we report on a perpendicular coupler (PC) for whispering-gallery resonators; it is a near field waveguide optimized for high coupling efficiency. The PC provides highly efficient tunneling coupling between the waveguide and microresonator without the need of a phase matching condition, and saves space for integration components. Compared to the Lorentz-shape in the transmission spectrum of the parallel coupler, the reflection spectrum of the PC shows an asymmetric Fano-shape near resonance. Furthermore, we demonstrate that the collection efficiency can be enhanced by near field scatterers, with a maximal efficiency of about 75%. Our simulations show that the PC is not sensitive to most parameters (including the refractive index of the waveguide), which makes the PC optimal for the application of whispering-gallery modes.

Synthesis and luminescence properties of ZnO:Eu3+ nano crystalline via a facile solution method.

Different ZnO:Eu3+ nanocrystalline were obtained from a facile solution method with two different precipitators. The comparison of photoluminescence property of two different ZnO:Eu3+ nanocrystalline was performed. The XRD patterns and the PL spectra indirectly indicate that the dopant Eu3+ ions had entered into the crystal lattices of ZnO. The study on the PL spectra of the as-prepared ZnO:Eu3+ nanocrystalline shows that with the change of dopant concentration, the ratio of relative emission intensity of electric dipole transition to magnetic dipole transition changes, which fully expresses that the presence of the inversion centers is associated with the dopant concentration of Eu3+.

Focusing of electromagnetic fields in high-Q hybrid wedge plasmon polariton microresonator.

We theoretically propose a hybrid microresonator consisting of a metallic wedge ring and a silica ring and investigate the existing whispering-gallery-like hybrid wedge plasmon polariton modes. These tightly confined hybrid plasmon modes are found to possess ultrasmall mode volumes while maintaining relatively high quality factors simultaneously at room temperature; that is, high values of Q/V are obtained. For example, a Purcell factor of 70 is achieved at the telecommunication wavelength of 1550 nm. This plasmon microresonator shows great potential in low-threshold plasmonic microlasers and cavity quantum electrodynamics.

Nonconfinement growth of edge-curved molecular crystals for self-focused microlasers.

Synthesis of single-crystalline micro/nanostructures with curved shapes is essential for developing extraordinary types of optoelectronic devices. Here, we use the strategy of liquid-phase nonconfinement growth to controllably synthesize edge-curved molecular microcrystals on a large scale. By varying the molecular substituents on linear organic conjugated molecules, it is found that the steric hindrance effect could minimize the intrinsic anisotropy of molecular stacking, allowing for the exposure of high-index crystal planes. The growth rate of high-index crystal planes can be further regulated by increasing the molecular supersaturation, which is conducive to the cogrowth of these crystal planes to form continuously curved-shape microcrystals. Assisted by nonrotationally symmetric geometry and optically smooth curvature, edge-curved microcrystals can support low-threshold lasing, and self-focusing directional emission. These results contribute to gaining an insightful understanding of the design and growth of functional molecular crystals and promoting the applications of organic active materials in integrated photonic devices and circuits.

Superkinetic Growth of Oval Organic Semiconductor Microcrystals for Chaotic Lasing.

Synthesis of novel mesoscopic semiconductor architectures continually generates new photonic knowledge and applications. However, it remains a great challenge to synthesize semiconductor microcrystals with smoothly curved surfaces owing to the crystal growth anisotropy. Here, a superkinetic crystal growth method is developed to synthesize 2D oval organic semiconductor microcrystals. The solid source dispersion induces an exceptionally large molecular supersaturation for vapor deposition, which breaks the crystal growth anisotropy. The synthesized stadium-shaped organic semiconductor microcrystals naturally constitute fully chaotic optical microresonators. They support low-threshold lasing on high-quality-factor scar modes localized near the stadium boundary and directional laser emission assisted by the chaotic modes. These results will reshape the understanding of the crystal growth theory and provide valuable guidance for crystalline photonic materials design.

Extended algorithm for the design of diffractive optical elements around the focal plane.

We present a multiplane algorithm for three-dimensional uniform illumination. The large-diameter diffractive optical element simulated by this algorithm homogeneously concentrates more than 86.5% of the incident energy into a 200 microm length of columnar space around the focal plane. The intensity profile in the whole space is nearly flattop, and the beam's quality measured by the root mean square is less than 20.6%. The algorithm is very useful if a great deal of tolerance is required for the installation error of the optical system or if it is used for some particular application, such as uniform illumination on an incline plane.