| dc.description.abstract | In silicon photonics, integrated optical circuit replaces electrical circuit, and it provide a data transmission channel with high transmission speed, wide bandwidth, and low loss. Moreover, group velocity dispersion (GVD) is an important physical quantity in many photonic applications, such as optical communication, nonlinear optics, and ultrafast optics. In this thesis, we propose a flexible way to engineer waveguide dispersion with patterning different coverage ratios of polymer cladding layer on silicon nitride waveguides. First, the finite element method is used to simulate the waveguide dispersion of different waveguide cross-section designs and to observe the changes of the waveguide dispersion under different widths, heights, and cladding materials. The second part is the establishment of the dispersion measurement system. Fiber-based Mach-Zehnder interferometer is used as the reference spectrum to confirm the stability of the tunable laser during scanning and to build a calibrated frequency axis, which has a better resolution than that of the laser.
Experimentally, air, oxide and polymer cladding layers are coated on the microring resonaters and the waveguide dispersion is measured accordingly. The waveguide dispersion can be tuned from −143 ps/nm-km to −257 ps/nm-km by integrating the SU-8 polymer as the outer cladding layer. In order to realize the reconstructability of polymer cladding, we remove the polymer cladding layer. After stripping the polymer layer, the waveguide dispersion can be recovered to the original value, and there is no obvious impact on the quality factor. In addition, different coverage ratios of cladding layer are patterned on the microrings with traditional UV contact lithography. The measured dispersion shows linear dependence to the coverage ratio, showing good agreement with the simulated data. Thus, the waveguide dispersion can be engineered within a varied dispersion range by controlling the coverage ratio of the polymer cladding layer. Last, by increasing the waveguide height to 700 nm, the measured dispersion is tailored to be 66 ps/nm-km, which is in anomalous dispersion. After 100% coverage ratio of polymer cladding layer is patterned on microring, the measured dispersion is tuned to be -508 ps/nm-km, which is in normal dispersion. This provides a flexible way to engineer the dispersion. The dispersion can be tuned from anomalous to normal by superimposing different coverage ratios of polymer cladding layer on the waveguide.
The research presented in this thesis provides a flexible and novel approach to fabricate a multifunctional integrated optical circuit to meet the dispersion requirements of different applications. | en_US |