VCSEL photonics for communications and 3D sensing
The 40 years' research and developments of vertical cavity surface emitting lasers (VCSELs) opened up a new world of VCSEL photonics, including, sensors, optical interconnects in data center networks, laser printers, LiDAR and high power sources. The market of VCSELs has been growing up rapidly and they are now key devices in data center networks based on multi-mode optical fibers. High speed VCSELs beyond 50 Gbps are expected for future data center networks. Also, 3D sensing has been attracting much attention for a wide range of applications such as face ID in mobile phones, LiDAR for automatic driving cars, distance sensor of robot, security camera, and motion sensors in virtual reality. A big market is prospected for 3D depth camera, which was installed in iPhone X. A non-mechanical optical beam scanner is a key element for use in various applications such as laser displays, laser sensors and free-space optical communications. A mechanical beam scanner has been widely used, but non-mechanical scanner is attracting much attention for compact solid state LiDAR applications in recent days. We proposed and demonstrated a beam steering device based on a VCSEL structure, showing the record high-resolution beam steering. In this talk, the advances on VCSEL photonics will be reviewed. We address a lateral integration platform and new functions of VCSELs, including high speed coupled cavity VCSELs with low power consumption, high power VCSEL amplifiers of over 5W in a single-mode operation, high-resolution beam scanners, dot projectors and their integrations.
Fundamentals of plasmonic nanocavity and circuits
Plasmonics is a rapidly emerging branch of photonics, which offers variable means to manipulate light using plasmon excitations on metal nanostructures. Most prominently, the huge electromagnetic enhancement of plasmonic nanocavity offers the physical basis of single-molecule SERS and many other plasmon related research fields, such as tip-enhanced spectroscopy, plasmonic antennas, plasmon hybridization, quantum plasmonics, nonlinear plasmonics, plasmonic optical forces, and plasmochemistry. In this talk, the discovery, mechanism and applications of plasmonic nanocavity are briefly introduced firstly. Then we will talk about our recent studies using plasmonic nanocavity for sub-picometer sensitivity of spatial changes, extremely high optical nonlinearity and strong coupling. Another fundamental issue about plasmon propagation at the nanometer scale will be talked: The highly tunable beating of surface plasmon modes drives plasmon propagation in nanowaveguides and nanocircuits, which can realize plasmon routing, gain, logic functions etc. for nanophotonic chips.
Higher speed PON: evolution, technology, and applications
This talk considers the future evolution of PON technology through 2025, considering both the available technologies to implement them, and the apparent applications to use them. In a distinct shift from the previous linear speed-based evolution of PON, it is expected that several distinct PON systems will be developed. The first is the continuation of single-channel TDMA PONs, this time to 50 Gb/s. This is meant to be the successor to XG(S)-PON, and aims to be a lower cost solution. Since it is an evolutionary system, its coexistence with previous generations is very important. The second is an evolution of the TWDM-PON family of systems, also extending the per-channel line rate to 50 Gb/s. The TWDM-PON currently sees some application in business services where its special features are needed, and this extension allows the provision of multiple 10 Gb/s UNIs on each channel. The third is a system using wavelength routing devices to increase capacity and optical efficiency beyond that possible with splitters. The near term applications of this type of system include 5G wireless fronthaul, and the “SuperPON” concept (where several TWDM PONs are combined with a wavelength router to achieve greater fiber sharing). Beyond the physical layer technology, the talk also considers the application of SDN and NFV techniques. Counter to the popular opinion, we find very little to be gained by employing these methods. In contrast, it is the business model that requires innovation. Unbridled plug-and-play interoperability requires the equitable reallocation of development costs.
Spin-orbit coupling in nanophotonics
Photonic spin-orbit coupling describes how spin angular momentum of light, associated with circular polarisation of an electromagnetic wave, is coupled to orbital angular momentum of light (associated with the energy flow and propagation direction). Being strongly enhanced in a nanostructured environment, this effect provides interesting applications in polarisation-enabled control of optical signals, or in reverse, controlling light polarisation, sensing applications and quantum optical processes. The spin-orbit coupling involving waveguided modes results in the so-called photonic spin-Hall effect, in analogy to spin-Hall effect for electrons. In this talk we will overview the effects associated with the photon spin when circularly polarised light interacts with plasmonic nanostructures and metamaterials. Spin-dependent directional excitation of guided modes, spin-orbit coupling in surface plasmon scattering associated with the unusual, transverse spin of surface polaritons, and spin-dependent optical forces will be discussed. Nonlinear optical effects controlled by spin of interacting photons will be reviewed. Photonic spin-orbit interactions provide an important tool for harvesting new functionalities and applications of circularly polarised light in numerous photonic and quantum technologies, and metrology.
High spatiotemporal resolution fluorescence imaging of biological samples in vivo
Here we will present two pieces of high-resolution fluorescence microscopy methods we invented for live sample imaging. The first one is for in vivo imaging, which is a fast, high-resolution, miniaturized two-photon microscope (FHIRM-TPM). With a headpiece weighing 2.15 g and a new type of hollow-core photonic crystal fiber to deliver 920-nm femtosecond laser pulses, the FHIRM-TPM is capable of imaging commonly used biosensors at high spatiotemporal resolution (0.64 μm laterally and 3.35 μm axially, 40 Hz at 256 × 256 pixels). It compares favorably with benchtop two-photon microscopy and miniature wide-field fluorescence microscopy in the structural and functional imaging of Thy1-GFP- or GCaMP6f-labeled neurons. Further, we demonstrate its unique application and robustness with hour-long recording of neuronal activities down to the level of spines in mice engaging in social interaction. The second method is for live cell long-term super-resolution (SR) imaging. We have developed a deconvolution algorithm for structured illumination microscopy based on Hessian matrixes (Hessian-SIM). It uses the continuity of biological structures in multiple dimensions as a priori knowledge to guide image reconstruction and attains artifact-minimized SR images with less than 10% of the photon dose used by conventional SIM while substantially outperforming current algorithms at low signal intensities. Hessian-SIM enables rapid imaging of moving vesicles or loops in the endoplasmic reticulum without motion artifacts and with a spatiotemporal resolution of 88 nm and 188 Hz. Its high sensitivity allows the use of sub-millisecond excitation pulses followed by dark recovery times to reduce photobleaching of fluorescent proteins, enabling…
Nanophotonic designs for energy conversion and storage
Transformation of traditional energy system to a sustainable one requires developments of chemical and physical processes that can take advantage of renewable energy sources. Nanophotonics, with the ultimate spatial and temporal control over light, offers tremendous opportunities, to manipulate, enhance and/or monitor these physical or chemical processes. In this talk, I will summarize some of recent progress on this front.
PerovLight: perovskite materials for emergent nanophotonics and polaritonics
Halide perovskites have recently attracted tremendous attention due to their remarkable properties as an optical gain material, which have shown high performance in solar cells, light-emitting diodes, photodetectors and many other optoelectronic applications. In this talk, I will first review our recent progress in the investigation of halide perovskite materials as excellent optical gain materials, which can be synthesized by either physical or chemical ways. Steady-state and transient spectroscopy approaches can elaborate the large exciton binding energy higher than room temperature thermal excitation energy, and exciton dynamics. High crystalline quality supports the optically pumped photonic lasing based on the intrinsic whispering gallery mode cavity, while the lasing quality factor can be as high as 5000 in all-inorganic perovskite crystals. Next, I will present our experimental realization of room-temperature polariton lasing in all-inorganic cesium lead chloride perovskite crystals embedded in two distributed Bragg reflectors. The perovskite crystals possess efficient polariton-polariton scattering due to the Wannier-Mott exciton nature with large binding energy. The polariton lasing is evidenced by a superlinear power dependence, macroscopic ground state occupation, and increase of the temporal coherence. Finally, we will present our recent results using perovskite materials towards highly efficient light-emitting diode (LED) applications, with a recent record high 20% conversion efficiency in green emission region. This progress also suggests the possibility towards electrically pumped lasing devices.
Geometric phase and nonlinear photonic metasurfaces
By designing an ultrathin metasurface, which consists of spatially variant plasmonic structures with engineered geometric Berry phase, it is shown that spin-orbit coupling of light can be utilized to manipulate both the spin and orbital angular momentum of light. It was demonstrated that the spin dependent metasurface can be applied to design highly efficient optical holograms, which have important applications in the areas including holographic displays, beam shaping, data storage, optical trapping, optical tweezers and so on. In nonlinear optical regime, we applied the concept of nonlinear geometrical Berry phase for designing nonlinear photonic metasurfaces. For example, in a second- and third- harmonic generation processes, the plasmonic meta-atoms, with certain rotational symmetries, can acquire a nonlinear geometric Berry phase of 3θ, 4θ, where θ is the in-plane orientation angle of the meta-atoms. This nonlinear phase can be continuously tuned by from zero to 2π by simply varying theta. Several interesting applications such as nonlinear image encryption, nonlinear spin-orbit interaction and so on will be discussed.
Toward active dielectric metasurface devices
High refractive-index nano-antennas capture the best of both worlds – the strong interaction with light comparable to that of plasmonics and the low absorption loss of dielectrics. In the past few years, increasing interest has been seen toward discovering new properties and new applications of these nano-antennas, enabled by the advancement of nano-fabrication techniques. Many useful devices, static or dynamic, have been demonstrated. In this talk, I will start with a review of the development of technologies based on dielectric nano-antennas in our group. Then, I will elaborate on our recent push on large scale metalens fabrications and the latest development of spatial light modulators based on tunable dielectric metasurfaces.
Eigenmode engineering of nanolasers
Nanolasers generate coherent light at the nanoscale. In the past decade, they have attracted intense interest, because they are more compact, faster and more power-efficient than conventional lasers. The eigenmode of a nanolaser can be engineered in a controllable manner for novel inner laser cavity field and/or emission beam synthesis. Furthermore, ensembles of nanolasers operating in unison can provide a macroscopic response that would not be possible in conventional lasers.

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