Abstract
We reveal a triangular-lattice planar photonic crystal supports Bloch modes with radially and azimuthally symmetric electric field distributions at the top band-edge of the first photonic band. Bifurcated from the corresponding Bloch modes, two cylindrical vector resonant modes are achieved by simply enlarging the central air-hole of the planar photonic crystal, which have high quality factors around 3,000 and small mode volume of (λ/n)3. The far-field radiations of the two resonant modes present high-quality cylindrical vector beam profiles. The resonant modes could be optimized by modifying the six nearest neighboring air-holes around the central defect. The cylindrically symmetric characteristics of the resonant mode's near- and far-fields might provide a new view to investigate light-matter interactions and device developments in planar photonic crystal cavities.
Highlights
Planar photonic crystals (PPCs), characterized with periodic air-holes in a sub-wavelength thick slab, have great potentials for constructing chip-integrated functional devices and circuits because of the compact structure and engineerable photonic band structure [1]
Determined by the high-efficiency Bragg reflection and sub-wavelength period of air-holes, resonant modes in PPC cavities exhibit ultrahigh quality (Q) factor and ultra-small mode volume (Vmode), which have been widely employed in a variety of applications [4,5,6]
In a quantum dot embedded PPC cavity, a single-hole missing defect was designed to optimize the alignment between cavity field and emitter dipole for achieving strong modulation of the spontaneous emission [15]
Summary
Planar photonic crystals (PPCs), characterized with periodic air-holes in a sub-wavelength thick slab, have great potentials for constructing chip-integrated functional devices and circuits because of the compact structure and engineerable photonic band structure [1]. While the Q factors of these resonant modes are not high (~3,000) compared to those in other reported PPC cavities [4,5,6], their cylindrically symmetric characteristics may provide new aspects in enhanced light-matter interactions in PPC cavity to develop vector-mode based micro-lasers, nonlinear processes, and optical manipulations [22]. This could be considered as a unique feature of the proposed PPC cavity from other PPC cavities formed by missing or shifting air-holes. This work may open an alternative way to generate cylindrical vector beams on a photonic chip, which has benefits in compact footprint and stability [23,24]
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