Study Of Driving Electrodes For Silicon Mach-zehnder Electro-optic Modulators

With the continuous improvement in central processing units(CPUs) speed, the electrical interconnects gradually become the bottleneck for the further improvement of computing performances due to its large delay, low bandwidth, and high power consumption. Optoelectronic integrated circuit based on silicon photonics have been regarded as a promising solution to this issue. As a key component in photoelectric conversion, modulators are very important. Due to compatibility with complementary metal-oxidesemiconductor(CMOS) processes, silicon modulators can achieve low-cost optoelectronic integration.In this thesis, design principles and experimental performance of the drive electrodes of Mach-Zehnder electro-optic modulator have been studied. By optimizing the design of traveling-wave electrodes, High-speed modulation has been verified by experimental results. The main content is listed as follow:(1) Optimal design of a single-drive push-pull traveling wave electrodesIn order to facilitate the design of higher-order modulators, single-drive push-pull traveling wave electrodes are designed. In this structure, the traveling wave electrodes locate on both sides of the modulation arms and the heavily doped silicon layer in middle of the two arms is connected to the external DC bias power supply through the metal via hole. Equivalent circuit model and simulation results are used to analyze the influence of electrode parameters on the transmission performance, which helps us to optimize the electrodes to achieve 32Gbit/s binary phase shift keying(BPSK) modulation.(2) Design of multiple DC bias power supplyIn order to provide multiple and stable DC bias voltage to modulator, 40 outputs sophisticated adjustable DC power supply has been designed based on chips named LM317. The experimental results show that we can achieve high adjustable precision and stable output voltage.(3) Design of on-chip 50Ω matching resistorIn order to match impendence of the traveling wave electrodes, heavily doped silicon layer is used to design a 50Ω matching resistor, which is located at the end of traveling wave electrodes. Based on the length, width, height, doping concentration and via hole position of silicon layer, dimensional simulation tool of SILVACO can simulate the specific resistance value of the silicon layer. A series of silicon resistors with different values are designed and compared with the experimental results to find out stable process tolerances. In subsequent design, we can compensate for process tolerances to design an accurate 50Ω silicon resistor.(4) Realization of optoelectronic interconnectionIn order to connect DC bias power supply with electro-optical modulator chip, we use wire bonding to achieve optoelectronic interconnection. It can overcome the limitations of the number and space of probes, which reduces the cost of experiments and makes it more possible and flexible to design largescale electronic device.