A narrowband retroreflector consisting of a grating coupler and a waveguide cavity integrated on a highly reflective substrate is proposed. A theoretical model based on coupled-mode theories is discussed to provide analytical expression of the reflection and transmission coefficients under oblique incidence. The retroreflector was designed with a 20-µm aperture for 1540-nm-wavelength operation and 8-deg-angle incidence. Finite-difference time-domain simulation showed a retroreflection spectrum with a bandwidth of 2 nm and a maximum retroreflectance of 85% and a minimum specular reflectance of 5%.

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This research aimed to clarify the physical effects of plasma on microorganisms levitated in radio-frequency (RF) plasma and to develop a technology for classifying and confining microorganisms by controlling their behavior when levitated. In the experiment, multiple types of microorganisms were injected into the RF plasma one by one, and their behavior was analyzed. An external electric field was applied to the plasma. The experimental results revealed that the behavior of the levitated microorganisms differs depending on the species and the magnitude of RF discharge power.