Seung-Woo Jeon

Second-harmonic generation in a silicon-carbide-based photonic crystal nanocavity

We demonstrate second-harmonic generation (SHG) in a silicon-carbide (SiC)-based heterostructure photonic crystal nanocavity by using a pulsed laser. We observe SHG light radiated from the SiC nanocavity and estimate the conversion efficiency in the cavity to be 2.59×10(-5) (=0.15  W(-1)) at an average input power of 0.17 mW. The near-field patterns and polarization characteristics of the SHG light are investigated experimentally and theoretically, and the results are in qualitatively good agreement.

Symmetrically glass-clad photonic crystal nanocavities with ultrahigh quality factors

We design and fabricate ultra-high-quality (Q) photonic nanocavities in a symmetrically glass-clad silicon (Si) two-dimensional (2D) photonic crystal (PhC) structure. We theoretically investigate the dependence of the refractive index of the glass on the Q factors for asymmetric and symmetric structures. We show that the index-symmetric distribution of the glass is a critical factor to realize ultrahigh Q factors for glass-clad 2D PhC structures. We fabricate symmetrically glass-clad Si PhC nanocavities and achieve a record Q factor of 1×10(6), comparable with the highest Q factors of nanocavities in air-bridge structures.

Glass-embedded two-dimensional silicon photonic crystal devices with a broad bandwidth waveguide and a high quality nanocavity

To enhance the mechanical stability of a two-dimensional photonic crystal slab structure and maintain its excellent performance, we designed a glass-embedded silicon photonic crystal device consisting of a broad bandwidth waveguide and a nanocavity with a high quality (Q) factor, and then fabricated the structure using spin-on glass (SOG). Furthermore, we showed that the refractive index of the SOG could be tuned from 1.37 to 1.57 by varying the curing temperature of the SOG. Finally, we demonstrated a glass-embedded heterostructured cavity with an ultrahigh Q factor of 160,000 by adjusting the refractive index of the SOG.

Multiple-channel wavelength conversions in a photonic crystal cavity.

We demonstrate multiple-channel wavelength conversions of second harmonic and sum frequency generations in a silicon carbide photonic crystal cavity. The cavity is designed to have multiple modes including a nanocavity mode and Fabry-Pérot modes. Multiple-channel wavelength conversions in the nanocavity and Fabry-Pérot modes are shown experimentally. Furthermore, we investigate the polarization characteristics of wavelength-converted light. The experimental results of the polarization are in good agreement with calculation.

Analysis of Q-factors of structural imperfections in triangular cross-section nanobeam photonic crystal cavities

We present comprehensive and quantitative analysis of the effect of structural imperfections on quality (Q)-factors in triangular cross-section nanobeam photonic crystal cavities. We investigated statistically the optical losses due to the various imperfections in the air holes’ positions, radii, alignments, and surface roughness, among other factors. It is revealed that the Q-factor decreases significantly from an ideally designed value due to such imperfections, with the main influence being the asymmetric alignment of the air hole line relative to the center of the nanobeam in the currently used fabrication process. Our analysis provides important information for achieving higher Q-factors in the cavities.

Investigation of second-harmonic generation efficiency in a waveguide-side-coupled photonic nanocavity

We theoretically investigate second-harmonic generation (SHG) efficiency in a waveguide-side-coupled photonic nanocavity using coupled-mode-theory-based equations. Using an additional condition for the critical input power, we investigated SHG efficiencies at a very low input power and the critical power. At a very low input power, the SHG efficiency is enhanced by the increase in various Q factors for fundamental and SHG light. Conversely, the maximum SHG efficiency at the critical input power is determined by the Q factors for fundamental light and increases up to 50% in a waveguide-side-coupled photonic nanocavity. Our results provide a design rule for waveguide-side-coupled photonic nanocavities for developing highly efficient SHG devices.

Measurement of optical loss in nanophotonic waveguides using integrated cavities

Measurement of optical loss in nanophotonic waveguides is necessary for monitoring the properties of integrated photonic devices. We propose a simple method of measuring the optical loss using integrated nanocavities. It is shown theoretically that weak coupling between the waveguide and cavities leads to a direct estimation of the optical loss by measuring light radiated from the cavities. In addition, we experimentally demonstrate the optical loss in a fabricated photonic crystal waveguide. Our method gives not only a degree of freedom in real-time monitoring of the optical properties of nanophotonic structures, but it also can be used for various waveguide-based applications.

Robust thin-film photonic crystals with complete photonic bandgaps

We investigate robust characteristics of thin-film photonic crystals with complete photonic bandgaps against fabrication errors. We show the characteristics of wide complete bandgaps and high Q factors can be maintained within reasonable errors.

Design of thin-film photonic crystal devices with complete bandgap

We design a broadband waveguide and a nanocavity in a thin-film photonic crystal with a complete bandgap. The waveguide has wide transmission wavelength range of 150nm, and the Q factor of the cavity is as high as 2,000.