X.Y. Wang, Y. Yin, H.Y. Dong, C.N. Saggau, M. Tang, L.X. Liu, H.M. Tang, S.K. Duan, L. Ma, O.G. Schmidt

ACS Nano 15, 18411 (2021)

We report the generation of multiple sets of 3D confined resonant modes in a single microtube cavity owing to nanogap induced resonant trajectory splits. The optical field largely overlaps in the split resonant trajectories, enabling strong optical coupling of 3D confined resonant light. The anticrossing feature and modes changing-over were demonstrated as direct evidence of strong coupling. In such an optical coupling system, the spatial optical field distribution of 3D coupling modes was experimentally mapped under the strong coupling regime, which allows direct observation of the energy transfer process between two hybrid states. Numerical calculations based on a quasi-potential model and the mode detuning process are in excellent agreement with the experimental results. The generation of multiple sets of 3D confined resonant modes and their efficient coupling in a single microcavity are of high interest for directional coupling with a higher degree of freedom to realize on-chip integration with elevated functionalities such as multiplexing, 3D lasing, and signal processing.

C.N. Saggau, F. Gabler, D.D. Karnaushenko, D. Karnaushenko, L. Ma, O.G. Schmidt

Adv. Mater. 32, 2003252 (2020)

Mechanical strain formed at the interfaces of thin films has been widely applied to self-assemble 3D microarchitectures. Among them, rolled-up microtubes possess a unique 3D geometry beneficial for working as photonic, electromagnetic, energy storage, and sensing devices. However, the yield and quality of microtubular architectures are often limited by the wet-release of lithographically patterned stacks of thin-film structures. To address the drawbacks of conventionally used wet-etching methods in self-assembly techniques, here a dry-release approach is developed to roll-up both metallic and dielectric, as well as metallic/dielectric hybrid thin films for the fabrication of electronic and optical devices. A silicon thin film sacrificial layer on insulator is etched by dry fluorine chemistry, triggering self-assembly of prestrained nanomembranes in a well-controlled wafer scale fashion. More than 6000 integrated microcapacitors as well as hundreds of active microtubular optical cavities are obtained in a simultaneous self-assembly process. The fabrication of wafer-scale self-assembled microdevices results in high yield, reproducibility, uniformity, and performance, which promise broad applications in microelectronics, photonics, and opto-electronics.

J. Wang, M. Tang, Y. Yang, Y. Yin, Y. Chen, C.N. Saggau, M. Zhu, X. Yuan, D. Karnaushenko, Y. Huang, L. Ma, O.G. Schmidt

Laser & Photon. Rev. 14, 200118 (2020)

Dielectric optical microcavities have been explored as an excellent platform to manipulate the light flow and investigate non-Hermitian physics in open optical systems. For whispering gallery mode optical microcavities, modifying the rotational symmetry is highly desirable for intriguing phenomena such as degenerated chiral modes and directional light emission. However, for the state-of-the-art approaches, namely deforming the cavity geometry by precision lithography or introducing local scatterers near the cavity boundary via micromanipulation, there is a lack of flexibility in fine-adjusting of chiral symmetry and far-field emission direction. Here, precise engineering of cavity boundary using electron-beam-induced deposition is reported based on rolled-up nanomembrane-enabled spiral-shaped microcavities. The deformation of outer boundary results in delicate tailoring of asymmetric backscattering between the outer and inner rolling edges, and hence deterministically strong mode chirality. Besides, the crescent-shaped high-index nanocap leads to modified light tunneling channels and inflected far-field emission angle. It is envisioned that such a localized deposition-assisted technique for adjusting the structural deformation of 3D optical microcavities will be highly useful for understanding rich insights in non-Hermitian photonics and unfolding exotic properties on lasing, sensing, and cavity quantum electrodynamics.

S. Valligatla, J. Wang, A. Madani, E.S.G. Naz, Q. Hao, C.N. Saggau, Y. Yin, L. Ma, O.G. Schmidt,

Adv. Opt. Mater. 8, 2000782 (2020)

3D photonic integrated circuits are expected to play a key role in future optoelectronics with efficient signal transfer between photonic layers. Here, the optical coupling of tubular microcavities, supporting resonances in a vertical plane, with planar microrings, accommodating in-plane resonances, is explored. In such a 3D coupled composite system with largely mismatched cavity sizes, periodic mode splitting and resonant mode shifts are observed due to mode-selective interactions. The axial direction of the microtube cavity provides additional design freedom for selective mode coupling, which is achieved by carefully adjusting the axial displacement between the microtube and the microring. The spectral anticrossing behavior is caused by strong coupling in this composite optical system and is excellently reproduced by numerical modeling. Interfacing tubular microcavities with planar microrings is a promising approach toward interlayer light transfer with added optical functionality in 3D photonic systems.

Y. Yin, J. Wang, X. Wang, S. Li, M.R. Jorgensen, J. Ren, S. Meng, L. Ma, O.G. Schmidt

Sci. Adv. 5, eaax6973 (2019)

The dynamic characterization of water multilayers on oxide surfaces is hard to achieve by currently available techniques. Despite this, there is an increasing interest in the evolution of water nanostructures on oxides to fully understand the complex dynamics of ice nucleation and growth in natural and artificial environments. Here, we report the in situ detection of the dynamic evolution of nanoscale water layers on an amorphous oxide surface probed by optical resonances. In the water nanolayer growth process, we find an initial nanocluster morphology that turns into a planar layer beyond a critical thickness. In the reverse process, the planar water film converts to nanoclusters, accompanied by a transition from a planar amorphous layer to crystalline nanoclusters. Our results are explained by a simple thermodynamic model as well as kinetic considerations. Our work represents an approach to reveal the nanostructure and dynamics at the water-oxide interface using resonant light probing.

Y. Yin, S.L. Li, V. Engemaier, E. Saei Ghareh Naz, S. Giudicatti, L. Ma, O.G. Schmidt

Laser Photon. Rev. 11, 1600219 (2017)

We report on the theoretical investigation of plasmonic resonances in metallic Möbius nanorings. Half-integer numbers of resonant modes are observed due to the presence of an extra phase π provided by the topology of the Möbius nanostrip. Anomalous plasmon modes located at the non-orientable surface of the Möbius nanoring break the symmetry that exist in conventional ring cavities, thus enable far-field excitation and emission as bright modes. The far-field resonant wavelength as well as the feature of half-integer mode numbers is constant to the change of charge distribution on the Möbius nanoring due to the topology of Möbius ring. Owing to the ultra-small mode volume induced by the remaining dark feature, an extremely high sensitivity as well as a remarkable figure of merit is obtained in our numerical calculations for sensing performance. The topological metallic nanostructure provides a novel platform for the investigation of localized surface plasmon modes exhibiting unique phenomena for potential plasmonic applications.

Y. Yin, S. L. Li, S. Böttner, F. Yuan, S. Giudicatti, E.S.G. Naz, L. Ma, O.G. Schmidt

Phys. Rev. Lett. 116, 253904 (2016)

Vertical gold nanogaps are created on microtubular cavities to explore the coupling between resonant light supported by the microcavities and surface plasmons localized at the nanogaps. Selective coupling of optical axial modes and localized surface plasmons critically depends on the exact location of the gold nanogap on the microcavities, which is conveniently achieved by rolling up specially designed thin dielectric films into three-dimensional microtube cavities. The coupling phenomenon is explained by a modified quasipotential model based on perturbation theory. Our work reveals the coupling of surface plasmon resonances localized at the nanoscale to optical resonances confined in microtubular cavities at the microscale, implying a promising strategy for the investigation of light-matter interactions.

L. Ma, S.L. Li, V.M. Fomin, M. Hentschel, J.B. Götte, Y. Yin, M.R. Jorgensen, O.G. Schmidt

Nat. Commun. 7, 10983 (2016)

When spinning particles, such as electrons and photons, undergo spin–orbit coupling, they can acquire an extra phase in addition to the well-known dynamical phase. This extra phase is called the geometric phase (also known as the Berry phase), which plays an important role in a startling variety of physical contexts such as in photonics, condensed matter, high-energy and space physics. The geometric phase was originally discussed for a cyclically evolving physical system with an Abelian evolution, and was later generalized to non-cyclic and non-Abelian cases, which are the most interesting fundamental subjects in this area and indicate promising applications in various fields. Here, we enable optical spin–orbit coupling in asymmetric microcavities and experimentally observe a non-cyclic optical geometric phase acquired in a non-Abelian evolution. Our work is relevant to fundamental studies and implies promising applications by manipulating photons in on-chip quantum devices.