[6a-A405-1~9] 3.11 Photonic structures and phenomena

[6a-A405-1] Slot effect in ultrahigh Q/V H1 photonic crystal nanocavities with a subwavelength slot

〇Eiichi Kuramochi^1,2, Shota Kita², Akihiko Shinya^1,2, Masaya Notomi^1,2 (1.NTT-NPC, 2.NTT-BRL)

Keywords:photonic crystal, Cavity-QED, silicon photonics

We report improved multi-hole-tuning of high-Q H1 slotted nanocavity that can focus the electric field to one electric field antinode filling out the sub-wavelength slot. The experimental Q factor and corresponding Q/V value (V: mode volume) were enhanced up to 3.4×10⁵ and 1.7×10⁷, respectively. We measured thermo-optic (TO) nonlinearity of two H1 slotted nanocavities with Q²/V 83 times and 2,705 times higher than that of the L4 nanocavity reported in Ref. 3. In these nanocavities we revealed that TO-based red-shift appeared above 100 μW and 25 μW, respectively, which were significantly higher than 10 μW reported in Ref. 3. The small TO effect in the H1 slotted nanocavities is considered to be suppression of light-matter interaction as a result of the focusing of electronic field inside the air-slot. Furthermore, we evaluate performances of the H1 slotted nanocavity as index sensor and nano-bio sensor by FEM-simulations (COMSOL). When we changed the background index (n_B) from 1.0 to 1.5, the slot cavity mode changed the wavelength (λ) linearly with slope of 267 nm/RIU. A high index resolution can be expected since we can expect a high Q factor for this cavity. Next, we evaluated the wavelength shift (δλ) induced by protein nano-particle (diameter: 15 nm, n: 1.45) placed just at the center of the slot. δλ in air (n_B =1) and D₂O (n_B =1.32) were 23 pm and 5 pm respectively, which was fairly high sensitivity as a nano-bio sensor. We numerically demonstrated that this bio-sensor had sub-wavelength spatial resolution correcponding to the size of the slot. This study was partly supported by JST, CREST (JPMJCR15N4).