Jaehyeon Son

Graphene–ferroelectric metadevices for nonvolatile memory and reconfigurable logic-gate operations

Memory metamaterials are artificial media that sustain transformed electromagnetic properties without persistent external stimuli. Previous memory metamaterials were realized with phase-change materials, such as vanadium dioxide or chalcogenide glasses, which exhibit memory behaviour with respect to electrically/optically induced thermal stimuli. However, they require a thermally isolated environment for longer retention or strong optical pump for phase-change. Here we demonstrate electrically programmable nonvolatile memory metadevices realised by the hybridization of graphene, a ferroelectric and meta-atoms/meta-molecules, and extend the concept further to establish reconfigurable logic-gate metadevices. For a memory metadevice having a single electrical input, amplitude, phase and even the polarization multi-states were clearly distinguishable with a retention time of over 10 years at room temperature. Furthermore, logic-gate functionalities were demonstrated with reconfigurable logic-gate metadevices having two electrical inputs, with each connected to separate ferroelectric layers that act as the multi-level controller for the doping level of the sandwiched graphene layer.

THz near-field spectral encoding imaging using a rainbow metasurface

We develop a spectral encoding image technique in the terahertz range using a space-frequency converting metasurface. From our developed technique, 2-dimensional images are successfully reconstructed using only 1-dimensional data acquisition processes.

A printed nanobeam laser on a SiO 2 /Si substrate for low-threshold continuous-wave operation

A small-footprint nanobeam photonic crystal laser made of InGaAsP material is directly integrated on a SiO₂/Si substrate without using adhesive material via transfer-printing processes (i.e., dry transfer-printing). The transferred nanobeam structure with a physical volume of ~6.6 × 0.58 × 0.28 µm(3) (~10.5 (λ/n)3) shows single mode lasing near 1550 nm with continuous-wave (CW) operation at room-temperature, where effective lasing threshold power was as low as 9 µW. This CW operation was achieved mainly due to efficient heat dissipation provided by direct contact between the nanobeam and the substrate. This transfer-printed nanobeam laser could be a promising candidate for the next-generation light source with a feature of low-power consumption in ultracompact photonic integrated circuits.

Control of terahertz nonlinear transmission with electrically gated graphene metadevices

Graphene, which is a two-dimensional crystal of carbon atoms arranged in a hexagonal lattice, has attracted a great amount of attention due to its outstanding mechanical, thermal and electronic properties. Moreover, graphene shows an exceptionally strong tunable light-matter interaction that depends on the Fermi level - a function of chemical doping and external gate voltage - and the electromagnetic resonance provided by intentionally engineered structures. In the optical regime, the nonlinearities of graphene originated from the Pauli blocking have already been exploited for mode-locking device applications in ultrafast laser technology, whereas nonlinearities in the terahertz regime, which arise from a reduction in conductivity due to carrier heating, have only recently been confirmed experimentally. Here, we investigated two key factors for controlling nonlinear interactions of graphene with an intense terahertz field. The induced transparencies of graphene can be controlled effectively by engineering meta-atoms and/or changing the number of charge carriers through electrical gating. Additionally, nonlinear phase changes of the transmitted terahertz field can be observed by introducing the resonances of the meta-atoms.

A printed nanobeam laser on a SiO2/Si substrate for low-threshold continuous-wave operation

A small-footprint nanobeam photonic crystal laser made of InGaAsP material is directly integrated on a SiO2/Si substrate via transfer-printing process. The transferred nanobeam structure shows single mode lasing near 1550 nm with continuous-wave (CW) operation at room-temperature,

Linear frequency conversion via sudden merging of meta-atoms in time-variant metasurfaces

The energy of an electromagnetic wave is converted as the wave passes through a temporal boundary. Thus, effective temporal control of the medium is critical for frequency conversion. Here, we propose rapidly time-variant metasurfaces as a frequency-converting platform and experimentally demonstrate their efficacy at terahertz frequencies. The proposed metasurface is designed for the sudden merging of two distinct metallic meta-atoms into a single one upon ultrafast optical excitation. This sudden merging creates a spectrally designed temporal boundary on the metasurface, by which the frequency conversion can be achieved and engineered. Interestingly, the time delay between the abrupt temporal boundary and the input terahertz pulse is found to be strongly related to the phase of the converted wave as well as its amplitude. As the proposed scheme does not rely on the nonlinearity, it may be particularly advantageous for the frequency conversion of waves with weak intensities.A linear frequency conversion based on the sudden merging of two distinct split-ring resonators into a single resonator on a rapidly time-variant THz metasurface is reported.

InGaAsP nanobeam light emitter integrated with Si waveguide via transfer printing

A nanobeam photonic crystal cavity made with InGaAsP quantum well and Si waveguide is integrated on SiO2/Si substrate via transfer printing. The light emitted from the nanobeam showed coupling to waveguide. We demonstrated novel way to integrate III-V devices on Si based photonic integrated circuits.

A printed nanobeam laser on silicon

A nanobeam laser made of InGaAsP material is printed on a SiO2/Si substrate via transfer-printing process. From this structure, single mode lasing near 1550 nm with continuous-wave (CW) operation at room-temperature is achieved.

Waveguide Coupled Nanobeam Photonic Crystal Cavity via Transfer Printing Method

We demonstrated waveguide coupling of InGaAsP nanobeam photonic crystal cavity integrated on SiO2/Si substrate via transfer printing. The coupled light from the cavity was imaged through grating vertical coupler at the end of the waveguide