Wakayama University · Faculty of Systems Engineering · 教授

Research keywordsoptical coherence tomography・InAs quantum dots・photonic crystal waveguides・terahertz generation・surface-emitting lasers・multi-wavelength light sources・near-infrared photonics

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• Multimodal spectral-domain optical coherence tomography with multiple light sources for water–ethanol mixture sensing toward industrial applications2026 · Abstract In this study, a spectral-domain optical coherence tomography (SD-OCT)-based method for sensing water–ethanol mixtures using multiple light sources with different peak wavelengths was developed. The differences in the optical absorption coefficients of water and ethanol at these wavelengths resulted in variations in the reflected light intensity. The dependence of OCT image contrast on ethanol concentration was clearly demonstrated using the developed SD-OCT system, enabling measurement of ethanol concentration during OCT imaging. This multimodal SD-OCT was realized by corresponding the sensitivity roll-off associated with each light source. The developed multimodal SD-OCT, which provides both structural and concentration-dependent information, is particularly suitable for industrial applications such as the nondestructive inspection of products containing ethanol–water mixtures.
• Spectral domain optical coherence tomography using multi-wavelength light sources for simultaneous water sensing applications2025 · Water sensing was verified using spectral-domain optical coherence tomography (OCT) with multiple light sources at different peak wavelengths. Variations in the optical absorption coefficient of water for the light sources resulted in differences in the reflected light intensities, which can be applied to analyze water content in OCT imaging.
• Monolithic vertical cavities via selective-area growth using a rotational metal mask and InAs quantum dots for near-infrared multiple-wavelength surface-emitting light source applications2025 · We herein report a method for fabricating near-infrared multiple-wavelength surface-emitting light sources. After growing a GaAs layer containing stacked InAs quantum dots (QDs) on a GaAs/AlAs distributed Bragg reflector by molecular beam epitaxy, additional GaAs layers were grown via selective-area growth using a rotational metal-mask. The GaAs thickness variation generated different vertical cavity (VC) modes that resonated with different emission wavelengths within the broadband emission from the InAs QDs. Photoluminescence measurements confirmed monolithic VCs formation in the selected areas. This method offers a simple fabrication process and extends the emission wavelength range of near-infrared multiple-wavelength surface-emitting light sources.
• Numerical validation of low-coherence interferometers using low-group-velocity and low-dispersion photonic crystal waveguides for ultra-compact OCT applications2025 · In this study, an ultra-compact optical coherence tomography (OCT) system based on integrated photonic crystal waveguides (PhC-WGs) was proposed and validated numerically. A low-velocity and low-dispersion (LVLD) PhC-WG is employed in the reference arm, enabling significant reduction in its length because of the high group index achieved with a broadband light source. Optical delays in the reference arm were found to increase with the designed group index of the LVLD-PhC-WG, confirming the low-coherence interference. Additionally, similar findings were observed in a PhC-WG-based OCT (PhC-OCT) model integrating a directional coupler and the LVLD-PhC-WG. The PhC-OCT with a considerably small footprint, e.g. 20 × 100 μm2, for the interferometer including the reference arm indicated interferometric signals with an axial resolution of approximately 40 μm. These results demonstrate the feasibility of an ultra-compact OCT system using PhC-WGs.

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