Noritsugu Yamamoto

New realization method of three-dimensional photonic crystal in optical wavelength region

Summary form only given. An important issue for photonic crystals is how to realize 3D photonic crystals in the optical wavelength region. In this paper, we propose a new method by utilizing a wafer-bonding technique combined with a microfabrication technique.

Optical properties of three-dimensional photonic crystals based on III-V semiconductors at infrared to near-infrared wavelengths

The optical properties of three-dimensional photonic crystals based on III–V semiconductors are investigated. The crystals are constructed by stacking GaAs (or InP) stripes with a wafer-fusion technique to form an asymmetric face-centered-cubic structure. It is shown that a crystal with eight-stacked layers (two units), whose period is 4 μm, has a considerable band-gap effect (∼30 dB attenuation) in the transmission spectrum at infrared wavelengths (5–10 μm), and the band gap is observed independently of the incident angles. Then, a crystal with four-stacked layers with a submicron period is constructed, and a clear band gap (attenuation up to 10 dB) is successfully observed at near-infrared wavelengths (1–1.5 μm).

Alignment and stacking of semiconductor photonic bandgaps by wafer-fusion

Semiconductor-based three-dimensional (3D) photonic crystals are developed by utilizing a wafer fusion and alignment technique. A clear and considerable bandgap effect is successfully demonstrated in infrared to near-infrared wavelengths. It is pointed out that the introduction of arbitrary defect states and/or efficient light emitters can be possible in this method. For the example of the introduction of a light-emitting element, a surface-emitting laser with a two-dimensional (2D) photonic crystal structure is fabricated, and very unique lasing characteristics are demonstrated. These results encourage us very much for the development of various quantum optical devices and circuits including not only passive, but also active devices.

Photonic crystal directional coupler switch with small switching length and wide bandwidth

A directional coupler switch structure capable of short switching length and wide bandwidth is proposed. The switching length and bandwidth have a trade-off relationship in conventional directional coupler switches. Dispersion curves that avoid this trade-off are derived, and a two-dimensional photonic crystal structure that achieves these dispersion curves is presented. Numerical calculations show that the switching length of the proposed structure is 7.1% of that for the conventional structure, while the bandwidth is 2.17 times larger.

Development of One Period of a Three-Dimensional Photonic Crystal in the 5–10 µm Wavelength Region by Wafer Fusion and Laser Beam Diffraction Pattern Observation Techniques

One period of a three-dimensional photonic crystal operating in the 5~10-µm-wavelength region is developed, where four layers having a striped pattern are stacked using a wafer fusion and the alignment method based on a laser beam diffraction pattern observation technique. By measuring the transmission spectrum, considerable attenuation (of about 16 dB) is successfully achieved and is in good agreement with the theoretical calculation.

100-nm-Scale Alignment using Laser Beam Diffraction Pattern Observation Techniques and Wafer Fusion for Realizing Three-Dimensional Photonic Crystal Structure

We previously proposed a new method for realizing three-dimensional photonic crystals in the optical wavelength region, where two-dimensional basic structures are aligned using a laser beam diffraction pattern observation technique and stacked by means of a wafer fusion. In this method, it is essential to align the two-dimensional basic structures with an accuracy of optical wavelength order at wafer fusion. In this work, we develop an alignment system based on a laser beam diffraction pattern observation technique and achieve alignment and wafer fusion with accuracy of less than 100 nm, for the first time.

New realization method for three-dimensional photonic crystal in the optical wavelength region : Experimental consideration

We experimentally investigate the feasibility of a realization method for the three-dimensional photonic crystal in the optical wavelength region. Micromachining techniques of dry-etching, wafer-bonding and laser beam diffraction pattern observation techniques are utilized. Each process is investigated using an AlGaAs/GaAs semiconductor system, and the feasibility of this method is successfully demonstrated for a structure having a photonic bandgap in the 10 µm wavelength region.

GaAs-based two-dimensional photonic crystal slab ring resonator consisting of a directional coupler and bent waveguides

We experimentally demonstrated a GaAs-based air-bridge-type photonic crystal ring resonator that has a triangular lattice pattern of air holes. The fabricated photonic crystal ring resonator is composed of bent waveguides and an asymmetric directional coupler that has three rows of air holes between neighboring line-defect waveguides. We successfully demonstrated ring resonant spectral response in the fabricated devices and experimentally made clear the dependence of the oscillation period on the optical path length of the ring resonator and the dependence of ring resonant spectral response on the coupling properties of the directional coupler. In addition, we theoretically and experimentally discuss the group-velocity dispersion in the photonic crystal slab waveguide.

Design of Photonic Crystal Directional Coupler with High Extinction Ratio and Small Coupling Length

As one of the key component of photonic crystal optical circuit devices, the directional coupler is investigated. We explain the reason the directional coupler consisting of an ordinary symmetric parallel waveguide cannot have a high extinction ratio and a small coupling length simultaneously. To realize both characteristics simultaneously, we propose a novel directional coupler structure. By numerical calculation, we show the possibility of a directional coupler with a high extinction ratio (-24 dB) and a small coupling length (18a).

Semiconductor Photonic Crystals

Much interest has been drawn to photonic crystals, optical materials in which the refractive index changes periodically.1,2 A photonic band gap is formed in the crystals, and the propagation of electromagnetic waves is prohibited for all wave vectors. Various important scientific and engineering applications such as a control of spontaneous emission, a zero-threshold laser, a very sharp bending of light, and so on, are expected by utilizing the photonic band gap and the artificially introduced defect states and/or light-emitters.1–4