Kyoungsik 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 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 report on a tunable optical wavelength deinterleaver based on a microelectromechanical system micromirror array in a modified Gires-Tournois interferometer. Continuous wavelength tuning and switching of the deinterleaver outputs are achieved by vertical micromirror motion of less than 1 μm. Control of the channel spacing, or free spectral range of the device, is also experimentally demonstrated.

Organic photodetectors (OPDs) show their advantages in flexibility, lightweight, and ultrathin form factors, large area compatibility, and low-cost manufacturability, but their absorption wavelengths are typically limited to the visible range. Although internal photoemission is a promising platform to achieve sub-bandgap photodetection in the near-infrared (NIR) or mid-IR wavelengths, very few studies have been reported for organic-based Schottky barrier photodetectors (SBPDs) operable in the NI

Abstract Two-dimensional (2D) materials have attracted great attention because of their unique physical properties and versatile applications in electronics and photonics. Following the trends of large-area 2D materials-based devices and systems implementation, large-area, high-throughput thickness and surface characterization techniques are required. Optics-based thin film characterization techniques have promising advantages in fast characterization speed, contactless large-area probing, and h