講演情報
[22a-A308-7]Design of photonic crystals with a topological photonic bandgap below light line using a semiconductor-magnetooptical material layered structure
〇(M2)Xinyi Wang1,2, Guangtai Lu1,2, Siyuan Gao1,2, Nobukiyo Kobayashi3, Kenji Ikeda3, Yasutomo Ota4, Tianji Liu5, Satoshi Iwamoto1,2 (1.RCAST, Tokyo Univ., 2.IIS,Tokyo Univ., 3.Denjiken, 4.Keio Univ., 5.CIOMP)
キーワード：
Topological band gap、magnto-optical effect
Photonic chiral edge states hosted in topological photonic crystals (PhCs) with broken time-reversal symmetry can transport light unidirectionally even with structural disorders. So far, in the optical regime, a topological bandgap capable of supporting chiral edge states was realized only above the light line. A topological bandgap and chiral edge states below the light line would be more useful for their waveguide applications. Topological PhCs with a topological bandgap below the light line were theoretically examined. However, the proposed structures requiring the in-plane hybrid structure between dielectric and magneto-optical (MO) materials are difficult to fabricate. In this study, we designed air-suspended topological PhCs with a topological bandgap below the light line using a layered structure of dielectric and MO materials.
A triangular-lattice silicon PhC with two triangular air holes in a unit cell (Period a, side length of holes L = 0.9a) is bonded on a thin uniform MO layer. The thicknesses of Si and MO layers, d1 and d2 are 0.67a and 0.33a, respectively. A topological gap below the light line is observed. The gap-mid gap ratio is 0.004%, which corresponds to 62 pm at 1550 nm when bismuth substituted yttrium iron garnet (Bi-YIG) (exx = 5, exy =0.002i) is used as the MO layer. The gap-mid gap ratio increases up to 0.035% (540 pm at 1550 nm) when a FeCo-BaF nanogranular film (exx = 4.4, exy =0.01i)is used as the MO layer.
A triangular-lattice silicon PhC with two triangular air holes in a unit cell (Period a, side length of holes L = 0.9a) is bonded on a thin uniform MO layer. The thicknesses of Si and MO layers, d1 and d2 are 0.67a and 0.33a, respectively. A topological gap below the light line is observed. The gap-mid gap ratio is 0.004%, which corresponds to 62 pm at 1550 nm when bismuth substituted yttrium iron garnet (Bi-YIG) (exx = 5, exy =0.002i) is used as the MO layer. The gap-mid gap ratio increases up to 0.035% (540 pm at 1550 nm) when a FeCo-BaF nanogranular film (exx = 4.4, exy =0.01i)is used as the MO layer.