High efficiency coupling from fiber to slot and strip waveguides using a double-tip coupler is presented. The double tips
are inverse tapered, while their distance is decreased. The coupling efficiency reaches 90.9% with a taper length of only
30μm for coupling fiber to slot waveguides. With a mode transformer, the slot waveguide mode can be converted to strip
waveguide mode with an efficiency of 99.3% in a length of 15μm. The impact of several parameters, such as distance
between tips, taper length, and tip-end width, are simulated and optimized to improve the coupling efficiency.
Optical filters with box-like response were designed and realized based on parallel-coupled double microrings in
silicon-on-insulator. The properties of this design are simulated, considering the impact of the center-to-center distance
of two rings, and coupling efficiency. Flat-top passband in the drop channel of the fabricated device was demonstrated
with a 1dB bandwidth of 0.82nm, a 1dB/10dB bandwidth ratio of 0.51, an out of band rejection ratio of 14.6dB, as well
as a free spectrum range of 13.6nm.
A high quality (Q) factor microring resonator in silicon-on-insulator rib waveguides was fabricated by electron beam
lithography, followed by inductively coupled plasma etching. The waveguide dimensions were scaled down to
submicron, for a low bending loss and compactness. Experimentally, the resonator has been realized with a quality factor
as high as 21,200, as well as a large extinction ratio 12.5dB at telecommunication wavelength near 1550nm. From the
measured results, propagation loss in the rib waveguide is determined as low as 6.90dB/cm. This high Q microring
resonator is expected to lead to high speed optical modulators and bio-sensing devices.