Research
以下の研究は、北海道大学電子科学研究所、および、京都大学大学院工学研究科（竹内研究室）で行なったものです。
Tapered optical fiber
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A tapered optical fiber is an optical fiber with a tapered part (diameter less than 1 μm). We fabricate the tapered optical fibers by heating at 1350 degrees with a ceramic heater and pulling the end of the fiber. The typical transmittance is much over 90 % even when the diameter of the tapered region is about 300 nm.
Microsphere laser
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The spontaneous emission coupling factor β
is essential for realization of quantum information devices. Fiber-coupled
microspheres have been attracting attention as ideal cavity systems with
ultra-high Q-factors and single spatial mode input-outputs. In order to apply
the fiber-coupled microspheres to the quantum information devices, it is
necessary to precisely estimate the β factor. For this purpose, we realized
fiber-coupled microsphere lasers with an Er3+-doped P2O5-Al2O3-SiO2thin film using a sol-gel method.
Applied Physics Letters, Vol. 90, pp. 101103/1-3 (2007).
Applied Physics Letters, Vol. 92, pp. 071115/1-3 (2008).
Highly efficient coupling to single metal nanostructure
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Localized surface plasmons (LSPs) of metal
nanostructures have attracted considerable attention because of the strong
enhancement of the exciton-photon coupling. Although the strong-coupling regime
can be obtained within the LSP field, the coupling efficiency between a single
LSP antenna and propagating light is extremely low. Therefore, we proposed
and realized nearly complete optical coupling method into a single metal
nanostructure using a tapered-fiber-coupled microspherical cavity system.
Physical Review A,Vol. 89, pp. 021801(R)/1-5 (2014).
Nanofiber Bragg grating cavity
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A Nanofiber Bragg grating cavity (NFBC) is a novel microcavity. The
NFBCs are fabricated on an optical tapered fiber using a focused ion beam
milling system. This cavity has small mode volume (less than 1 μm3),
ultra-wide tuning range (over 20 nm), and loss-less coupling to single mode fiber.
By coupling light emitters like quantum dots to the NFBCs, we observed enhanced
spontaneous emission.
Sci. Rep. 5, 9619 (2015).
Fabrication of NFBCs using Helium ion microscope
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In order to improve Q factors of NFBCs, we used a Helium ion microscope with ultra high resoluton (< 1 nm) instead of Ga FIB machine. As the result, we improved Q factors from about 300 to over 4000.
Optics Express, 27, 6792-6800 (2019).
Nanolight emitters
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Diamond, fascinating people from ancient times, is the most excellent materials with outstanding physical properties. It has the highest hardness and thermal conductivity in any materials. Besides, it has the largest optical band-gap, high refractive index, and robust fluorescence in broad optical band from various color centers and impurities as represented by nitrogen vacancies (NVs). The diamond, therefore, has been paid attention as an ideal and novel platform for photonic and quantum information applications. We study about effieict single photon sources and laser devices using the diamond nanocrystals.
Applied Physics Letters, Vol. 105, pp. 011112/1-3 (2014).