Three-dimensional circular resonators connected with an output waveguide were simulated by the three-dimensional finite-difference time-domain (FDTD) technique. For the microcircular resonator with vertical waveguiding consisted of active layer confined by upper and lower cladding layers with the refractive indices of 3.4 and 3.17, the mode Q factors are greatly influenced by the thickness of the upper cladding layer. The numerical results of the near field and the farfield patterns indicate that the vertical waveguide with semiconductor materials does not provide enough optical confinement for the confined modes in the resonator. Furthermore, the lasing spectra and far-field patterns are measured for a circular microlaser with a radius of 15 μm and a 2-μm-width output waveguide. Single mode operation with the side mode suppression ratio up to 33 dB is realized at room temperature, and multiple peaks are observed in the vertical far-field pattern due to the vertical radiation of the mode field.
Unidirectional-emission microlasers are greatly demanded for photonic integrated circuits and optical interconnection. In
this paper, the mode characteristics of circular and coupled-circular microresonators with a bus waveguide are
numerically simulated by finite-difference time-domain technique. For a circular microresonator connected with a bus
waveguide, coupled-mode between two whispering-gallery modes can have high mode Q factor for realizing
unidirectional-emission lasing. In addition, symmetry and antisymmetry coupled modes are analyzed for the coupledcircular
microresonator with a middle bus waveguide. Furthermore, the output characteristics of a coupled-circular
microlaser, which is fabricated by standard photolithography and inductively-coupled-plasma (ICP) etching techniques,
are reported. Single mode operation is realized for the coupled-circular microlaser with a radius of 20 μm and a 2-μmwidth
bus waveguide.
Wavelength-scale defected circular microresonators with laterally confined metal layer are designed for directional
emission from high Q confined modes by boundary element method (BEM), which is firstly applied to the multilayer
structures. The influence of metal layer thickness on the mode filed patterns and Q factors are simulated. The results
indicate that the thickness of the metal layer has a great effect on far-field emission patterns and the mode Q factors.
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