Jin-Kyu Yang

Curved-microfiber photon coupling for photonic crystal light emitter

Highly-efficient evanescent coupling between a photonic crystal resonator and a curved fiber taper is demonstrated. The coupling is utilized to pump the photonic crystal laser and funnel its output photons through a single optical fiber, making it an all-fiber photon source. Photon collection efficiency of ∼70% into the fiber and output power of 27nW are achieved. Highly local pumping results in the record-low threshold of ∼35μW. This scheme provides an ideal platform for an on-demand single photon source based on two-dimensional photonic crystal.

Low threshold current single-cell hexapole mode photonic crystal laser

The authors report an electrically driven, hexapole mode, single-cell photonic crystal laser operating at 1537.8nm. Electrical current is supplied through a submicrometer-sized current post beneath the cavity center. This wavelength-scale single-cell photonic crystal laser operates in a single mode with threshold current of ∼100μA at room temperature. Operation in the hexapole mode is confirmed by the near-field profile, far-field polarization, and the finite-difference time-domain computation based on the fabricated cavity structure.

Slab-edge modes in two-dimensional photonic crystals

We demonstrate the existence of surface waves in two-dimensional photonic crystal slab edges. In finite-sized air-terminated photonic crystal boundaries, the slab-edge mode turns into a lasing mode under pulsed optical pumping conditions. Analyses of the modal behaviors of the slab-edge modes by means of calculations based on the plane wave expansion method and the finite-difference time-domain method show that resonant frequencies and quality factors are strongly dependent on the termination parameter and the shape of the slab corner.

Localized surface plasmon enhanced quantum efficiency of InGaN/GaN quantum wells by Ag/SiO 2 nanoparticles

Optical properties of InGaN/GaN multi-quantum-well (MQW) structures with a nanolayer of Ag/SiO2 nanoparticle (NP) on top were studied. Modeling and optical absorption (OA) measurements prove that the NPs form localized surface plasmons (LSP) structure with a broad OA band peaked near 440-460 nm and the fringe electric field extending down to about 10 nm into the GaN layer. The presence of this NP LSP electrical field increases the photoluminescence (PL) intensity of the MQW structure by about 70% and markedly decreases the time-resolved PL (TRPL) relaxation time due to the strong coupling of MQW emission to the LSP mode.

Lasing in localized modes of a slow light photonic crystal waveguide

We demonstrate lasing in GaAs photonic crystal waveguides with InAs quantum dots as gain medium. Structural disorder is present due to fabrication imperfection and causes multiple scat- tering of light and localization of light. Lasing modes with varying spatial extend are observed at random locations along the guide. Lasing frequencies are determined by the local structure and occur within a narrow frequency band which coincides with the slow light regime of the waveguide mode. The three-dimensional numerical simulation reveals that the main loss channel for lasing modes located away from the waveguide end is out-of-plane scattering by structural disorder.

Modal Characteristics in a Single-Nanowire Cavity with a Triangular Cross Section

In this study, the modal characteristics of a single-GaN nanowire cavity with a triangular cross section surrounded by air or located on a silicon dioxide substrate have been analyzed. Two transverse resonant modes, transverse electric-like and transverse magnetic-like modes, are dominantly excited for nanowire cavities that have a small cross-sectional size of <300 nm and length of 10 microm. Using the three-dimensional finite-difference time-domain simulation method, quality factors, confinement factors, single-mode conditions, and far-field emission patterns are investigated for a nanowire cavity as a function of one length of the triangular cross section. The results of these simulations provide information that will be vital for the design and development of efficient nanowire lasers and light sources in ultracompact nanophotonic integrated circuits.

Demonstration of laser action in a pseudorandom medium

We demonstrated lasing in localized optical resonances of deterministic aperiodic structures with pseudorandom morphologies. The localized lasing modes in two-dimensional arrays of air nanoholes in GaAs membranes occur at reproducible spatial locations, and their frequencies are only slightly affected by the structural fluctuations in different samples. A numerical study on the resonances of the passive systems and optical imaging of lasing modes enabled us to interpret the observed lasing behavior in terms of distinctive localized resonances in the two-dimensional pseudorandom structures.

Morphological and SERS Properties of Silver Nanorod Array Films Fabricated by Oblique Thermal Evaporation at Various Substrate Temperatures

Aligned silver nanorod (AgNR) array films were fabricated by oblique thermal evaporation. The substrate temperature during evaporation was varied from 10 to 100 °C using a home-built water cooling system. Deposition angle and substrate temperature were found to be the most important parameters for the morphology of fabricated films. Especially, it was found that there exists a critical temperature at ~90 °C for the formation of the AgNR array. The highest enhancement factor of the surface-enhanced Raman scattering (SERS), observed in the Ag films coated with benzenethiol monolayer, was ~6 × 107. Hot spots, excited in narrow gaps between nanorods, were attributed to the huge enhancement factor by our finite-difference time-domain (FDTD) simulation reflecting the real morphology.

Lasing in Thue–Morse structures with optimized aperiodicity

We demonstrate lasing in two-dimensional Thue–Morse structures fabricated in a semiconductor membrane. By changing the relative size of two scatterers that correspond to the building blocks A and B, we gradually vary structural aperiodicity and find an optimal degree of aperiodicity where light confinement is maximal and lasing is the strongest. At various degrees of aperiodicity, different types of modes acquire the highest quality factors and may be selected for lasing. This work opens a way of controlling lasing characteristic via structural aperiodicity.

Polarization-selective resonant photonic crystal photodetector

Resonance-assisted photonic crystal (PhC) slab photodetectors are demonstrated by utilizing six 7-nm-thick InGaAsP quantum wells. In order to encourage efficient photon coupling into the slab from the vertical direction, a coupled-dipole-cavity-array PhC structure is employed. Inheriting the characteristics of the dipole mode, this resonant detector is highly polarization selective and shows a 22-nm-wide spectral width. The maximum responsivity of 0.28A∕W, which is >20 times larger than that of the identical detector without the pattern, is observed near 1.56μm.