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Increase of Q-factor in photonic crystal H1-defect nanocavities after closing of photonic bandgap with optimal slab thickness

A. Tandaechanurat, S. Iwamoto, M. Nomura, N. Kumagai, and Y. Arakawa

Open Access Open Access

Abstract

We investigate the dependence of quality factor Q of dipole modes in photonic crystal H1-defect nanocavity on the slab thickness and observe an increase of Q even after closing of the photonic bandgap both in numerical simulation and experimentation. This counter intuitive behavior results from the weak coupling between the cavity mode and the 2nd-guided mode in the photonic crystal slab. This is confirmed by computing the overlap between them in the momentum space.

©2008 Optical Society of America

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Figures (7)
Fig. 1.
Fig. 1. Field distributions at the center of the slab of (a) Ey component of x-dipole mode and (b) Ex component of y-dipole mode. The circular lines show boundaries of air holes.

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Fig. 2.
Fig. 2. Dependence of Q-factor on slab thickness for the x-dipole mode in H1-defect cavity with r=0.40a. The total Q-factor (square), the vertical Q-factor (circle) and the in-plane Q-factor (triangle) are plotted separately.

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Fig. 3.
Fig. 3. Band diagram for the structure with d=1.35a and r=0.40a. The x-dipole mode with normalized frequency of 0.292 overlaps with the 2nd-guided mode.

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Fig. 4.
Fig. 4. Ey -field distributions in momentum space for the cavity mode in the cavities with (a) d=1.35a and (b) d=1.75a including light lines (solid circles) and EFC of 2nd-guided modes at the cavity mode frequencies (dotted circles). (c) Q∥ and amounts of overlap between the cavity mode and the EFC of the 2nd-guided mode of each structure with the slab thickness from 1.20 to 1.75a.

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Fig. 5.
Fig. 5. (a) Scanning electron micrograph of the fabricated H1-defect nanocavity with the slab thickness of 390 nm viewed in (a) Cross sectional view and (b) Top view.

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Fig. 6.
Fig. 6. PL spectra from the PCS nanocavities with d=1.345a and the polarization dependence of the dipole modes.

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Fig. 7.
Fig. 7. Dependence of measured-Q (square) on slab thickness compared with calculated-Q (triangle) for (a) x-dipole mode and (b) y-dipole mode.

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Equations (4)

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U ( t ) = U ( 0 ) exp [ − ( ω t ) Q ] ,
1 Q total = 1 Q ⁄ ⁄ + 1 Q ⊥ = P ⁄ ⁄ ω U + P ⊥ ω U = P ω U ,
V eff = ∫ ∫ ∫ ε ( r ) → ∣ E → ( r ) → ∣ 2 dV max [ ε ( r ) → ∣ E → ( r ) → ∣ 2 ] ,
n eff = ∫ ∫ ∫ ε ( r ) → ∣ E → ( r ) → ∣ 2 dV ∫ ∫ ∫ ∣ E → ( r ) → ∣ 2 dV ,
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