Abstract

The large normal dispersion of the fundamental mode (${\mathrm{TE}}_{n=1}$ mode) in the whispering gallery modes (WGM) microsphere is detrimental to the visible comb generation. Herein, we demonstrate that this fundamental limitation can be removed by considering the high-order radial modes (${\mathrm{TE}}_{n=2}$ mode) of the hybrid microsphere cavity (HMC). The studied HMC consists of a high-refractive-index coating (${\mathrm{TiO}}_2$ or ${\mathrm{HfO}}_2$) and silica microsphere. The simulated electric field energy distribution and measured $Q$ value in our experiment show that optical confinement of the coating effectively excites the ${\mathrm{TE}}_{n=2}$ mode and reduces the free spectral range (FSR) and modal dispersion. In addition, the observed redshift of WGM and decreased trend of FSR are in accordance with simulations. The zero-dispersion wavelength can be linearly shifted to a shorter wavelength or even into the visible region with the reduction of coating thickness or refractive index and larger microcavity, which advances the visible comb generation.

© 2019 Optical Society of America

Dispersion engineering of a microsphere via multi-layer coating

Xueying Jin, Jing Wang, Mengyu Wang, Yongchao Dong, Fei Li, and Keyi Wang
Appl. Opt. 56(28) 8023-8028 (2017)

Thermostable refractive index sensors based on whispering gallery modes in a microsphere coated with poly(methyl methacrylate)

Nai Lin, Lan Jiang, Sumei Wang, Hai Xiao, Yongfeng Lu, and Hailung Tsai
Appl. Opt. 50(7) 992-998 (2011)

Tailoring of the free spectral range and geometrical cavity dispersion of a microsphere by a coating layer

Davor Ristić, Maurizio Mazzola, Andrea Chiappini, Alphonse Rasoloniaina, Patrice Féron, Roberta Ramponi, Giancarlo C. Righini, Gilles Cibiel, Mile Ivanda, and Maurizio Ferrari
Opt. Lett. 39(17) 5173-5176 (2014)

Material candidates for optical frequency comb generation in microspheres

Nicolas Riesen, Shahraam Afshar V., Alexandre François, and Tanya M. Monro
Opt. Express 23(11) 14784-14795 (2015)

Whispering gallery modes in hybrid Au-ZnO microsphere resonators: experimental and theoretical investigations

Trong Huynh-Buu Ngo and Yia-Chung Chang
Opt. Mater. Express 7(8) 2962-2967 (2017)