Kwang Hyo Chung

Flexible and Transparent Gas Molecule Sensor Integrated with Sensing and Heating Graphene Layers

Graphene leading to high surface-to-volume ratio and outstanding conductivity is applied for gas molecule sensing with fully utilizing its unique transparent and flexible functionalities which cannot be expected from solid-state gas sensors. In order to attain a fast response and rapid recovering time, the flexible sensors also require integrated flexible and transparent heaters. Here, large-scale flexible and transparent gas molecule sensor devices, integrated with a graphene sensing channel and a graphene transparent heater for fast recovering operation, are demonstrated. This combined all-graphene device structure enables an overall device optical transmittance that exceeds 90% and reliable sensing performance with a bending strain of less than 1.4%. In particular, it is possible to classify the fast (≈14 s) and slow (≈95 s) response due to sp(2) -carbon bonding and disorders on graphene and the self-integrated graphene heater leads to the rapid recovery (≈11 s) of a 2 cm × 2 cm sized sensor with reproducible sensing cycles, including full recovery steps without significant signal degradation under exposure to NO2 gas.

Thermo-optic mode extinction modulator based on graphene plasmonic waveguide

We developed a thermo-optic (TO) mode extinction modulator based on graphene plasmonic waveguide. For compact device design and fabrication, the graphene plasmonic waveguide and heating element are configured all-in-one. Thermally induced inhomogeneous refractive-index distribution of the polymer near the microribbon cut off the long-range surface plasmon polariton (LRSPP) stripe mode propagating along a graphene microribbon. Numerical modeling are conducted on the time-dependent temperature (and hence the refractive-index) distribution by resistive heating element inside the graphene TO modulator. Experimental results demonstrate 30 dB attenuation with 12 mW electrical power injection at a telecom wavelength and exhibit a good agreement with the thermal modeling.

Graphene-based photonic waveguide devices

In this paper, we demonstrate recent progress in graphene-based photonic waveguide devices such as polymer waveguide polarizer, thermo-optic mode extinction modulator and plasmonic photodetector for graphene-based photonic integrated circuits.

Graphene Plasmonic Photodetector for Planar-Type Photonic Integrated Circuits

Based on graphene plasmonic waveguides, we developed a graphene plasmonic photodetector to detect horizontally incident light signal. The photocurrent is the maximum at the graphene-metal interface and the time constant is less than 39.7 ms.