Kyung-Sik Yu

We report on near infrared semiconductor nanopatch lasers with subwavelength-scale physical dimensions (0.019 cubic wavelengths) and effective mode volumes (0.0017 cubic wavelengths). We observe lasing in the two most fundamental optical modes which resemble oscillating electrical and magnetic dipoles. The ultra-small laser volume is achieved with the presence of nanoscale metal patches which suppress electromagnetic radiation into free-space and convert a leaky cavity into a highly-confined sub

Abstract Efficient light energy transfer between optical waveguides has been a critical issue in various areas of photonics and optoelectronics. Especially, the light coupling between optical fibers and integrated waveguide structures provides essential input‐output interfaces for photonic integrated circuits (PICs) and plays a crucial role in reliable optical signal transport for a number of applications, such as optical interconnects, optical switching, and integrated quantum optics. Significa

Abstract Passive multilayer coatings for windows have potential to improve energy consumption for indoor temperature regulation. The coatings should block the solar IR energy (800–2500 nm) while maintaining visible light transparency (400–700 nm) to prevent unwanted heating of the interior of a building or a vehicle. It should also efficiently radiate thermal energy to prevent excessive heating. Although solar energy management and radiative cooling techniques have been investigated individually

Two-dimensional materials such as hexagonal boron nitride (h-BN), graphene, and transition metal dichalcogenides have drawn great attention in various fields of photonics and electronics. Among them, h-BN has recently emerged as a promising material platform to study integrated quantum photonics due to its ultrabright quantum light emission capabilities. However, the fundamental optical properties of h-BN have not yet been investigated in the visible and near-infrared (NIR) spectrum thoroughly.

In this study, we propose the fabrication of a photodetector based on the heterostructure of p-type Si and n-type MoS₂. Mechanically exfoliated MoS₂ flakes are transferred onto a Si layer; the resulting Si-MoS₂ p-n photodiode shows excellent performance with a responsivity ( R) and detectivity ( D*) of 76.1 A/W and 10¹² Jones, respectively. In addition, the effect of the thickness of the depletion layer of the Si-MoS₂ heterojunction on perfo

We demonstrate longitudinal beam-steering with a 1×16 silicon optical phased array (OPA) using a monochromatic light source and thermo-optic control of the refractive index in the grating radiator region. The refractive index is controlled by forming a series of n-i-n heaters, placing i-regions in each radiator of the OPA. When the biased voltage in the heaters is increased, the refractive index of the radiator region is increased by the thermo-optic effect, and the longitudinal radiation angle

We propose a two-dimensional (2-D) code family and transmitter/receiver structures for incoherent multi-wavelength-time spread optical CDMA networks. The combination of metal-coated reflection delay lines and arrayed waveguide gratings (AWG) gives the proposed optical coder/decoder much enhanced flexibility in accommodating different code sets. Successful encoding/decoding has been demonstrated on signals up to 3-GHz time-chip rate with 4/spl times/15 code words.

Negative photoconductivity (NPC), a reduction in photoconductivity under light illumination, could provide low power consumption and high-speed frequency response. The NPC has been generally observed in low-dimensional materials, which can be easily affected by the trapping of photocarriers. However, a gradual transition between NPC and positive photoconductivity (PPC) by controlling the light intensity has not been reported. In this study, a gradual and reversible switching between NPC and PPC

A new two-dimensional code family is proposed for OCDMA networks having orthogonal properties in both the ‘wavelength’ and ‘time’ domains. This code family can be easily constructed from the Hamming correlation concept and dimension expansion, and can also be physically implemented by using an array of Bragg gratings. Numerical simulations and a theoretical analysis demonstrate an improved bit error rate performance with much smaller number of wavelength sets when compared to previous approaches

We present tunable optical filters based on a modified Gires-Tournois interferometer. The back reflection plane of the interferometer is replaced with a one-dimensional micromirror array for phase modulation. Using Gaussian beam optics, we show that the transfer function of the device has the form of the transversal filter in digital signal processing. The design and analysis techniques of conventional digital filters can, therefore, be adapted to tunable optical filters. Both the amplitude and

Internal photoemission (IPE) is a promising phenomenon for sub-bandgap photodetection at near-infrared wavelengths using large bandgap semiconductor materials. To improve the photon-to-electron conversion efficiency in silicon-based sub-bandgap Schottky barrier photodetectors (SBPDs), previous studies have mainly focused on subwavelength-scale nanostructures to enhance the electric fields and optical absorption. Here, in a different way from the previous approaches, we theoretically and experime

We demonstrate the on-chip monitoring of far-field patterns in a silicon-based optical phased array (OPA) using a planar diffractor and traveling-wave photodetectors (PDs) integrated at the end of the radiator array. To reproduce the diffraction patterns within a silicon slab, the planar diffractor is designed with a diffraction region surrounded by an absorptive boundary and seven discrete outlet waveguides. Each outlet waveguide is linked to the photon-assisted tunneling PD which has a silicon

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 phototh