We have recently discovered a novel phenomenon for the fabrication of nanostructures. A self-organization phenomenon of a strained InGaAs/AlGaAs system on a GaAs (311)B substrate during metal-organic vapor phase epitaxial growth is described, and nano-scale confinement lasers with self-organized InGaAs quantum disks are mentioned. Low-threshold operation of strained InGaAs quantum disk lasers is achieved under a continuous-wave condition at room temperature. The threshold current is around 20 mA, which is consider-ably lower than that of a reference double-quantum-well laser on a GaAs (100) substrate grown side-by-side. However, the light output versus the driving current exhibits a pronounced tendency towards a saturation compared to that of the (100) quantum well laser. We also discuss new methods using self-organization for nanofabrication to produce high-quality low-dimensional optical devices, considering requirements and the current status for next-generation optical devices.

We studied various types of 2D and 3D Si-based photonic crystal structures that are promising for future photonic integrated circuit application. With regard to 2D SOI photonic crystal slabs, we confirmed the formation of a wide photonic bandgap at optical communication wavelengths, and used structural tuning to realize efficient single-mode line-defect waveguides operating within the bandgap. As regards 3D photonic crystals, we used a combination of lithography and the autocloning deposition method to realize complicated 3D structures. We used this strategy to fabricate 3D full-gap photonic crystals and 3D/2D hybrid photonic crystals.

The design, fabrication, and measurement of photonic-band-gap (PBG) waveguides and resonators in two-dimensional photonic crystal slabs have been investigated. Although photonic crystal slabs have only partial gaps, efficient waveguides and resonators can be realized by appropriate design. As regards PBG waveguides, we show various designs for efficient single-mode waveguides in PhC slabs with SiO2 cladding, we report group dispersion measurements of PBG waveguides in PhC slabs, and describe the successful fabrication of PBG waveguides with adiabatic connectors that enable us to couple the light from single-mode fibers efficiently to PBG waveguides. As regards PBG resonators, we show how to realize very high-Q and small volume resonators in hexagonal PhC slabs, and report the fabrication of resonant tunneling filters that consist of PBG resonators coupled with PBG waveguides. We also describe the successful fabrication of resonant tunneling mode-gap filters with adiabatic mode connectors.

Photonic crystals have optical properties characterized by photonic bandgap, large anisotropy and high dispersion, which can be applied to various optical devices. We have proposed an autocloning method for fabricating 2D or 3D photonic crystals and are developing novel structures and functions in photonic crystals. The autocloning is an easy process based on the combination of sputter deposition and sputter etching and is suitable for industry. We have already demonstrated devices or functions such as polarization splitters and surface-normal waveguides. In this paper, we describe our latest work on photonic crystals utilizing the autocloning technology. Phase plates and polarization selective gratings for optical pick-ups are demonstrated utilizing TiO2/SiO2 photonic crystals. The technology to introduce CdS into 3D photonic crystals is also developed and photoluminescence from the introduced CdS is observed, which is the first step to realize luminescent devices with 3D confinement or high polarization controllability.

An ultra-compact InGaAs photodetector (PD) is demonstrated based on a photonic crystal (PhC) waveguide to meet the demand for a photoreceiver for future dense photonic integration. Although the PhC-PD has a length of only 1.7µm and a capacitance of less than 1fF, a high responsivity of 1A/W was observed both theoretically and experimentally. This low capacitance PD allows us to expect a resistor-loaded receiver to be realized that requires no electrical amplifiers. We fabricated a resistor-loaded PhC-PD for light-to-voltage conversion, and demonstrated a kV/W efficiency with a GHz bandwidth without using amplifiers. This will lead to a photoreceiver with an ultralow energy consumption of less than 1fJ/bit, which is a step along the road to achieving a dense photonic network and processor on a chip.