Jong-Bum You

Free-carrier electro-refraction modulation based on a silicon slot waveguide with ITO.

Recently, silicon-waveguide-based hybrid modulators with high-performance electro-optic materials have been proposed to overcome the intrinsic limitations of silicon materials. Indium-tin-oxide (ITO) is one of the important candidates for such applications due to its unique features including the ENZ effect and electrically tunable permittivity. In this paper, we propose an ultra-compact integrated phase modulator which consists of a silicon slot waveguide with a thin ITO film in the slot region. In the near-infrared regime, bias-voltage-dependent free-carrier accumulation at the dielectric-ITO interface induces an epsilon-near-zero (ENZ) effect, and contributes to the strong phase modulation of the guided electromagnetic wave. With a voltage swing of 2 V, the device experiences a large variation of the effective modal index, resulting in a π radian phase shift within the device length of <5 μm at 210 THz according to our computer simulations. A high modulation efficiency of V(π)L(π)~0.0071 V·cm and a large device bandwidth of ~70 GHz suggest a potential for an ultra-compact optoelectronic component in the integrated silicon photonics platform.

RF Frequency Doubling Using a Silicon p-i-n Diode-Based Mach–Zehnder Modulator

We demonstrate frequency doubling at 1 GHz using a new silicon Mach-Zehnder modulator (MZM). Modulation of the refractive index of silicon for an MZM action is achieved via the injection/depletion of electrons and holes in a p-i-n diode. The silicon MZM used in the experiment shows high phase-shift efficiency and a VpiLpi of 1.88times10-2Vldrcm which is nearly 350 times smaller than those of previously reported LiNbO3-based MZM. Also, a theoretical analysis of frequency doubling in the time domain shows good agreement with the experimental results.

Hybrid integration of III-V semiconductor lasers on silicon waveguides using optofluidic microbubble manipulation.

Optofluidic manipulation mechanisms have been successfully applied to micro/nano-scale assembly and handling applications in biophysics, electronics, and photonics. Here, we extend the laser-based optofluidic microbubble manipulation technique to achieve hybrid integration of compound semiconductor microdisk lasers on the silicon photonic circuit platform. The microscale compound semiconductor block trapped on the microbubble surface can be precisely assembled on a desired position using photothermocapillary convective flows induced by focused laser beam illumination. Strong light absorption within the micro-scale compound semiconductor object allows real-time and on-demand microbubble generation. After the assembly process, we verify that electromagnetic radiation from the optically-pumped InGaAsP microdisk laser can be efficiently coupled to the single-mode silicon waveguide through vertical evanescent coupling. Our simple and accurate microbubble-based manipulation technique may provide a new pathway for realizing high precision fluidic assembly schemes for heterogeneously integrated photonic/electronic platforms as well as microelectromechanical systems.

Near-infrared silicon sub-bandgap photo-detectors for on-chip integrated optical links

We report near-infrared and high-speed silicon photo-detectors capable of sub-bandgap light absorption based on the optically-assisted tunneling induced by a large electric field.

Electrically driven surface plasmon polaritons circuits

We report on the semiconductor-based integrated metal-dielectric-metal (MDM) photonic device platform for active generation and detection of confined surface plasmon polaritons in the MDM waveguides. By integrating integrated light emitting diodes and photodiodes between two metal layers, we can excite, transmit, and detect highly-confined plasmonic modes.

Wavelength-Selective Optical Filters Based on Metal-Patch Cavities With Slot Waveguide Interfaces

We theoretically propose and investigate the resonant wavelength-selective optical filters based on the subwavelength metallo-dielectric nanopatch cavities and the metal slot waveguides. Using the temporal coupled-mode theory and three-dimensional finite-difference time-domain simulations, we analyze the optical coupling efficiencies and filtering characteristics, which are optimized by adjusting the waveguide-cavity distance to modify the decay rates from the cavity. The proposed optical filters can be extended to multiport channel-dropping filters while maintaining subwavelength-scale dimensions including the coupling regions.

Lasing in hybrid metal-Bragg nanocavities

We report room-temperature lasing from an optically pumped subwavelength-scale cylindrical InGaAsP pillar surrounded by circular Bragg reflectors on a metal substrate with a dielectric spacer layer. By taking advantage of wide in-plane photonic bandgaps and proper vertical antiresonances, three dielectric Bragg pairs produce a sufficient optical feedback capable of low threshold lasing from the fundamental TE011 mode. A large spontaneous emission coupling into the lasing mode is obtained from the cavity-enhanced Purcell effects and effective suppression of nonlasing modes.

Nano pillar array laser with a bottom metal plane

We report a photonic bandedge laser using subwavelength-scale pillars with a metal reflector plane bonded on the silicon substrate. Surface-emitting operation near the gamma point of the photonic band diagram is observed at 77 K.

Two-dimensional beam-steering using 1x16 silicon optical phased array with thermo-optic tunable grating radiators (Conference Presentation)

Optical phased array (OPA) is considered as promising device in LiDAR application. We implemented a 1x16 silicon OPA consisting of an array of p-i-n electro-optic phase shifters and thermo-optic tunable grating radiators capable of two-dimensional beam-steering. The OPA was fabricated with CMOS-compatible process using SOI wafer. The p-i-n electro-optic phase shifters were formed in OPA channels for transversal beam-steering. With an array pitch of 2 μm, we attained transversal steering up to 45.6° at 1550 nm wavelength. For longitudinal beam-steering, we employed thermo-optic tunable grating radiators with p-i-n junction. The i-region covers whole radiator array and the p- and n-doped regions are placed on the both sides of the radiator array. This structure can provide fairly uniform heating of the radiator region, shifting the overall radiation field in longitudinal direction by the thermo-optic effect. As a result, a longitudinal beam-steering up to 10.3° was achieved by forward-biasing with a power consumption of 178 mW. This result proves a possibility of wide two-dimensional beam-steering with one-dimensional OPA without using tunable light source. We confirmed that the longitudinal tuning range obtained above is corresponding to near 100 nm wavelength tuning. Our device scheme can be a cost-effective solution of the OPA and also be a solution of self-adjustment for fluctuation of the wavelength-dependent performances.

Ultracompact bottom-up photonic crystal lasers on silicon-on-insulator

Compact on-chip light sources lie at the heart of practical nanophotonic devices since chip-scale photonic circuits have been regarded as the next generation computing tools. In this work, we demonstrate room-temperature lasing in 7 × 7 InGaAs/InGaP core-shell nanopillar array photonic crystals with an ultracompact footprint of 2300 × 2300 nm2, which are monolithically grown on silicon-on-insulator substrates. A strong lateral confinement is achieved by a photonic band-edge mode, which is leading to a strong light-matter interaction in the 7 × 7 nanopillar array, and by choosing an appropriate thickness of a silicon-on-insulator layer the band-edge mode can be trapped vertically in the nanopillars. The nanopillar array band-edge lasers exhibit single-mode operation, where the mode frequency is sensitive to the diameter of the nanopillars. Our demonstration represents an important first step towards developing practical and monolithic III-V photonic components on a silicon platform.