Monolithic Waveguide-Coupled InAs Quantum-Dot Microdisk Modulators
Date Issued
2014
Date
2014
Author(s)
Chu, Cheng-Hao
Abstract
In this thesis, we demonstrate the monolithic integration of an InAs quantum-dot microdisk modulator and its waveguide coupling structure. By designing the coupling structure with numerical simulation and fabrication technique, we verify the monolithic mode coupling between the microdisk and the waveguide. The device was fabricated by process mainly based on electron beam lithography and dry plasma etching in order to define the structure precisely.
Optical characterization was performed by a fiber-based transmission measurement setup. Mode coupling between the cavity and the waveguide was confirmed by measuring the transmission spectrum through the waveguide. Quality factors of the microdisk cavity were found to be about 300. Depth of dips up to 15dB is observed at the resonance wavelength of whispering-gallery modes of the microdisk cavity. The strength of mode coupling can be controlled by varying the disk size and the cavity-waveguide gap. Mode shift owing to the electric-field-induced refractive index change can be observed when a negative bias is applied to the microdisk cavity. By varying the voltage over the cavity, transmitted light with specific wavelength could be modulated through Kerr effect. The quadratic electro-optic coefficient was found to be 8.88×〖10〗^(-18) m^2/V^2, which is larger than that in bulk GaAs materials and in GaAs/AlGaAs quantum well structures. From the aspect of fundamental physical theory, the measured electro-optic effect is attributed to the quantum confined Stark effect and Kramers-Kronig relations.
The optical modulation is also demonstrated through time-resolved measurement, and the extinction ratio of 1.47 can be achieved. The quantum-dot microdisk cavities show the potential for optical modulation applications.
Subjects
量子點
微碟
調制器
Type
thesis
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