Ion-Gel-Gated Graphene Optical Modulator with Hysteretic Behavior

We propose a graphene-based optical modulator and comprehensively investigate its photonic characteristics by electrically controlling the device with an ion-gel top-gate dielectric. The density of the electrically driven charge carriers in the ion-gel gate dielectric plays a key role in tuning the optical output power of the device. The charge density at the ion-gel–graphene interface is tuned electrically, and the chemical potential of graphene is then changed to control its light absorption strength. The optical behavior of the ion-gel gate dielectric exhibits a large hysteresis which originates from the inherent nature of the ionic gel and the graphene–ion-gel interface and a slow polarization response time of ions. The photonic device is applicable to both TE- and TM-polarized light waves, covering two entire optical communication bands, the O-band (1.26–1.36 μm) and the C-band (1.52–1.565 μm). The experimental results are in good agreement with theoretically simulated predictions. The temporal behavior of the ion-gel–graphene-integrated optical modulator reveals a long-term modulation state because of the relatively low mobility of the ions in the ion-gel solution and formation of the electric double layer in the graphene–ion-gel interface. Fast dynamic recovery is observed by applying an opposite voltage gate pulse. This study paves the way to the understanding of the operational principles and future applications of ion-gel-gated graphene optical devices in photonics

Printed Nanolaser on Silicon

We propose and demonstrate a direct integration of a wavelength-scale III–V nanolaser onto a silicon-on-insulator (SOI) waveguide. By employing high-precision microtransfer printing techniques, with an optimally designed photonic crystal nanolaser structure, we experimentally achieved a coupling efficiency of 83% between the InGaAsP nanobeam laser and the SOI waveguide. Our III–V nanobeam laser is designed as an asymmetric one-dimensional photonic crystal cavity, which allows unidirectional coupling to the combined III–V nanobeam waveguide with high efficiency. Through the compact vertical coupler in the region where the III–V and SOI waveguides overlap at the optimal length of 3.2 μm, 88% of the light from the printed III–V nanolaser can theoretically be coupled to a vertically integrated SOI waveguide

Palladium-Decorated Hydrogen-Gas Sensors Using Periodically Aligned Graphene Nanoribbons

Polymer residue-free graphene nanoribbons (GNRs) of 200 nm width at 1 μm pitch were periodically generated in an area of 1 cm² via laser interference lithography using a chromium interlayer prior to photoresist coating. High-quality GNRs were evidenced by atomic force microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy measurements. Palladium nanoparticles were then deposited on the GNRs as catalysts for sensing hydrogen gases, and the GNR array was utilized as an electrically conductive path with less electrical noise. The palladium-decorated GNR array exhibited a rectangular sensing curve with unprecedented rapid response and recovery properties: 90% response within 60 s at 1000 ppm and 80% recovery within 90 s in nitrogen ambient. In addition, reliable and repeatable sensing behaviors were revealed when the array was exposed to various gas concentrations even at 30 ppm