Trapping photons with optical black hole.

An optical black-hole cavity based on transformation optics enables Q-factor enhancement and strong field confinement, by eliminating the intrinsic radiation loss of the conventional whispering-gallery modes, holding potential for applications in energy harvesting and optoelectronics.

Vibrational Kerr Solitons in an Optomechanical Microresonator.

Kerr soliton microcombs in microresonators have been a prominent miniaturized coherent light source. Here, for the first time, we demonstrate the existence of Kerr solitons in an optomechanical microresonator, for which a nonlinear model is built by incorporating a single mechanical mode and multiple optical modes. Interestingly, an exotic vibrational Kerr soliton state is found, which is modulated by a self-sustained mechanical oscillation. Besides, the soliton provides extra mechanical gain through the optical spring effect, and results in phonon lasing with a red-detuned pump. Various nonlinear dynamics is also observed, including limit cycle, higher periodicity, and transient chaos. This work provides a guidance for not only exploring many-body nonlinear interactions, but also promoting precision measurements by featuring superiority of both frequency combs and optomechanics.

Operando monitoring transition dynamics of responsive polymer using optofluidic microcavities.

Optical microcavities have become an attractive platform for precision measurement with merits of ultrahigh sensitivity, miniature footprint and fast response. Despite the achievements of ultrasensitive detection, optical microcavities still face significant challenges in the measurement of biochemical and physical processes with complex dynamics, especially when multiple effects are present. Here we demonstrate operando monitoring of the transition dynamics of a phase-change material via a self-referencing optofluidic microcavity. We use a pair of cavity modes to precisely decouple the refractive index and temperature information of the analyte during the phase-transition process. Through real-time measurements, we reveal the detailed hysteresis behaviors of refractive index during the irreversible phase transitions between hydrophilic and hydrophobic states. We further extract the phase-transition threshold by analyzing the steady-state refractive index change at various power levels. Our technology could be further extended to other materials and provide great opportunities for exploring on-demand dynamic biochemical processes.

Single-mode characteristic of a supermode microcavity Raman laser.

Microlasers in near-degenerate supermodes lay the cornerstone for studies of non-Hermitian physics, novel light sources, and advanced sensors. Recent experiments of the stimulated scattering in supermode microcavities reported beating phenomena, interpreted as dual-mode lasing, which, however, contradicts their single-mode nature due to the clamped pump field. Here, we investigate the supermode Raman laser in a whispering-gallery microcavity and demonstrate experimentally its single-mode lasing behavior with a side-mode suppression ratio (SMSR) up to 37 dB, despite the emergence of near-degenerate supermodes by the backscattering between counterpropagating waves. Moreover, the beating signal is recognized as the transient interference during the switching process between the two supermode lasers. Self-injection is exploited to manipulate the lasing supermodes, where the SMSR is further improved by 15 dB and the laser linewidth is below 100 Hz.

Regulated Photon Transport in Chaotic Microcavities by Tailoring Phase Space.

Manipulating light dynamics in optical microcavities has been made mainly either in real or momentum space. Here we report a phase-space tailoring scheme, simultaneously incorporating spatial and momentum dimensions, to enable deterministic and in situ regulation of photon transport in a chaotic microcavity. In the time domain, the chaotic photon transport to the leaky region can be suppressed, and the cavity resonant modes show stronger temporal confinement with quality factors being improved by more than 1 order of magnitude. In the spatial domain, the emission direction of the cavity field is controlled on demand through rerouting chaotic photons to a desired channel, which is verified experimentally by the far-field pattern of a quantum-dot microlaser. This work paves a way to in situ study of chaotic physics and promoting advanced applications such as arbitrary light routing, ultrafast random bit generation, and multifunctional on-chip lasers.

Chaos-assisted two-octave-spanning microcombs.

Since its invention, optical frequency comb has revolutionized a broad range of subjects from metrology to spectroscopy. The recent development of microresonator-based frequency combs (microcombs) provides a unique pathway to create frequency comb systems on a chip. Indeed, microcomb-based spectroscopy, ranging, optical synthesizer, telecommunications and astronomical calibrations have been reported recently. Critical to many of the integrated comb systems is the broad coverage of comb spectra. Here, microcombs of more than two-octave span (450 nm to 2,008 nm) is demonstrated through χ(2) and χ(3) nonlinearities in a deformed silica microcavity. The deformation lifts the circular symmetry and creates chaotic tunneling channels that enable broadband collection of intracavity emission with a single waveguide. Our demonstration introduces a new degree of freedom, cavity deformation, to the microcomb studies, and our microcomb spectral range is useful for applications in optical clock, astronomical calibration and biological imaging.

Reconfigurable symmetry-broken laser in a symmetric microcavity.

The coherent light source is one of the most important foundations in both optical physics studies and applied photonic devices. However, the whispering gallery microcavity, as a prime platform for novel light sources, has the intrinsically chiral symmetry and severely rules out access to directional light output, all-optical flip-flops, efficient light extraction, etc. Here, we demonstrate a reconfigurable symmetry-broken microlaser in an ultrahigh-Q whispering gallery microcavity with the symmetric structure, in which a chirality of lasing field is empowered spontaneously by the optical nonlinear effect. Experimentally, the ratio of counter-propagating lasing intensities is found to exceed 160:1, and the chirality can be controlled dynamically and all-optically by the bias in the pump direction. This work not only presents a distinct recipe for coherent light sources with robust and reconfigurable performance, but also opens up an unexplored avenue to symmetry-broken physics in optical micro-structures.

Chiral emission and Purcell enhancement in a hybrid plasmonic-photonic microresonator.

A high-Q hybrid plasmonic-photonic microresonator, which consists of a dielectric microdisk hybridized with a plasmonic nanoantenna dimer, enables an enlarged local density of states of the optical field and chiral propagation of photons inside the cavity.

Layered localization in a chaotic optical cavity.

We propose and demonstrate the localization of resonant modes in a Limaçon optical microcavity with layered phase space involving both major and minor partial barriers. By regulating the openness of the cavity through the refractive index control, the minor partial barriers, which do not directly confine the long-lived resonant modes, are submerged successively into the leaky region. During the invalidation process of the minor partial barriers, it is found that the quality factor and the conjugate momentum of the resonant modes exhibit changes with the emergence of turning points. Such phenomena are attributed to the joint confinement effect by the minor partial barriers together with the major one in the layered phase space. This paper helps to improve the understanding of complex dynamics, and sheds light on the fine design of photonic devices with high performance.

Regular-Orbit-Engineered Chaotic Photon Transport in Mixed Phase Space.

The dynamical evolution of light in asymmetric microcavities is of primary interest for broadband optical coupling and enhanced light-matter interaction. Here, we propose and demonstrate that the chaos-assisted photon transport can be engineered by regular periodic orbits in the momentum-position phase space of an asymmetric microcavity. Remarkably, light at different initial states experiences different evolution pathways, following either regular-chaotic channels or pure chaotic channels. Experimentally, we develop a nanofiber technique to accurately control the excitation position of light in the phase space. We find that the coupling to high-Q whispering gallery modes depends strongly on excitation in islands or chaotic sea, showing a good agreement with the theoretical prediction. The engineered chaotic photon transport has potential in light manipulation, broadband photonic devices, and phase-space reconstruction.

Microcavity Nonlinear Optics with an Organically Functionalized Surface.

We report enhanced optical nonlinear effects at the surface of an ultrahigh-Q silica microcavity functionalized by a thin layer of organic molecules. The maximal conversion efficiency of third harmonic generation reaches ∼1680%/W^{2} and an absolute efficiency of 0.0144% at pump power of ∼2.90 mW, which is approximately 4 orders of magnitude higher than that in a reported silica microcavity. Further analysis clarifies the elusive dependence of the third harmonic signal on the pump power in previous literature. Molecule-functionalized microcavities may find promising applications in high-efficiency broadband optical frequency conversion and offer potential in sensitive surface analysis.

Publisher's Note: Enhancing Coherent Light-Matter Interactions through Microcavity-Engineered Plasmonic Resonances [Phys. Rev. Lett. 119, 233901 (2017)].

This corrects the article DOI: 10.1103/PhysRevLett.119.233901.

Spontaneous T-symmetry breaking and exceptional points in cavity quantum electrodynamics systems.

Spontaneous symmetry breaking has revolutionized the understanding in numerous fields of modern physics. Here, we theoretically demonstrate the spontaneous time-reversal symmetry breaking in a cavity quantum electrodynamics system in which an atomic ensemble interacts coherently with a single resonant cavity mode. The interacting system can be effectively described by two coupled oscillators with positive and negative mass, when the two-level atoms are prepared in their excited states. The occurrence of symmetry breaking is controlled by the atomic detuning and the coupling to the cavity mode, which naturally divides the parameter space into the symmetry broken and symmetry unbroken phases. The two phases are separated by a spectral singularity, a so-called exceptional point, where the eigenstates of the Hamiltonian coalesce. When encircling the singularity in the parameter space, the quasi-adiabatic dynamics shows chiral mode switching which enables topological manipulation of quantum states.

Enhancing Coherent Light-Matter Interactions through Microcavity-Engineered Plasmonic Resonances.

Quantum manipulation is challenging in localized-surface plasmon resonances (LSPRs) due to strong dissipations. To enhance quantum coherence, here we propose to engineer the electromagnetic environment of LSPRs by placing metallic nanoparticles (MNPs) in optical microcavities. An analytical quantum model is first built to describe the LSPR-microcavity interaction, revealing the significantly enhanced coherent radiation and the reduced incoherent dissipation. Furthermore, when a quantum emitter interacts with the LSPRs in the cavity-engineered environment, its quantum yield is enhanced over 40 times and the radiative power over one order of magnitude, compared to those in the vacuum environment. Importantly, the cavity-engineered MNP-emitter system can enter the strong coupling regime of cavity quantum electrodynamics, providing a promising platform for the study of quantum plasmonics, quantum information processing, precise sensing, and spectroscopy.

Experimental Demonstration of Spontaneous Chirality in a Nonlinear Microresonator.

Chirality is an asymmetric property widely found in nature. Here, we propose and demonstrate experimentally the spontaneous emergence of chirality in an on-chip ultrahigh-Q whispering-gallery microresonator, without broken parity or time-reversal symmetry. This counterintuitive effect arises due to the inherent Kerr-nonlinearity-modulated coupling between clockwise and counterclockwise propagating waves. Above an input threshold of a few hundred microwatts, the initial chiral symmetry is broken spontaneously, and the counterpropagating output ratio exceeds 20∶1 with bidirectional inputs. The spontaneous chirality in an on-chip microresonator holds great potential in studies of fundamental physics and applied photonic devices.