Shigeru Nakayama

Independence and choice: Western impacts on Japanese higher education

Japans universities were established in order to import Western knowledge and ideas to assist in the development of the nation beginning in the mid-19th century. Because it was never colonized and because it has sucessfully developed not only its academic system but also its economy, Japan is a particularly significant case study. Japans academic development can be seen in two phases. First there was a “window shopping” period in which many Western models were explored and some partially adopted. Second, there has been an “involvement” mode in which specific Western models are adopted. This essay follows the development of Japanese higher education through its various phases, including the post World War Two impact of the United States and the growth of a mass university system. The process of internationalization of various foreign influences is examined.

Effect of cavity mode volume on photoluminescence from silicon photonic crystal nanocavities

We experimentally investigated photoluminescence (PL) from silicon photonic crystal nanocavities with different mode volumes at room temperature. The integrated cavity mode intensity, which was estimated from the observed PL signal by considering extraction and collection efficiencies for each cavity mode, increased as the cavity mode volume decreased. This result suggests that smaller cavities have larger mode emission efficiency per volume than that for larger cavities at room temperature.

Silicon-based three-dimensional photonic crystal nanocavity laser with InAs quantum-dot gain

We report on the demonstration of lasing oscillation in a silicon-based three-dimensional photonic crystal nanocavity using InAs quantum dots as gain material by pulsed optical pumping at 11 K. An active layer embedding InAs quantum dots was inserted in the cavity using micromanipulation technique. The highest quality factor for silicon-based three-dimensional photonic crystal cavities (∼22 000) was achieved. We also evaluated the spontaneous emission coupling factor of the laser to be ∼0.78 by fitting the experimental light-in light-out curve with coupled rate equations. This result would pave the way to the realization of CMOS-compatible high-density three-dimensional photonic integrated circuits.

Fabrication of high-Q silicon-based three-dimensional photonic crystal nanocavity and its lasing oscillation with InAs quantum-dot gain

We fabricated a silicon-based three-dimensional photonic crystal nanocavity by micromanipulation technique, exhibiting a high quality factor of ∼14,500. Lasing oscillation with an InAs/GaAs quantum-dot layer inserted in the cavity was successfully demonstrated at 11K.

Outcoupling of Light Generated in a Monolithic Silicon Photonic Crystal Nanocavity through a Lateral Waveguide

We report the design, fabrication and optical investigation of silicon nanocavity light sources based on silicon on insulator photonic crystal nanocavities. The planar geometry of the two-dimensional photonic crystal allows light to be efficiently out-coupled into a planar photonic circuit and our results demonstrate enhanced light transmission from a defect nano-cavity into a W1 photonic crystal waveguide. When compared to the sample without the cavity, we observe an 11-fold enhancement of the luminescence emitted from the cleaved facets of the waveguide measured at the cavity wavelength. The emission exhibits a characteristically strong spatial dependence, confirming that it indeed arises from light generated in the cavity and out-coupled via the waveguide. The obtained cavity mode frequency and spatial dependence are in excellent agreement with finite-difference time-domain simulations and their dependence on the photonic crystal structural properties.

Enhanced photoluminescence from silicon photonic crystal nanocavities with different sizes of mode volume

We report on effects of cavity mode volume V on the enhancement of PL from crystalline silicon, demonstrating that nanocavities with smaller mode volume are useful to obtain a larger improvement of the internal quantum efficiency of crystalline silicon.

Delivery of photons generated in silicon photonic crystal nano-cavity through lateral waveguide

We demonstrate light transmission from a photonic crystal nano-cavity into a planer photonic crystal waveguide. Enhanced photo-luminescence at a cavity resonant wavelength is observed from the cleaved facet of a waveguide with strong position dependence.