UC Santa Barbara

Silicon photonics offer a low-cost platform for large-scale optical systems, and find applications in data-centers, long-haul optical networks, LiDAR, and RF/microwave photonics. RF photonic systems offer interference-tolerant, wideband radio systems in RF and millimeter-wave bands. This is feasible through analog optical links that take advantage of low loss and immune to electromagnetic interference fiber optical cables. Performance of such systems is characterized by spur-free dynamic range (SFDR). Most of current RF Photonic systems are based on LiNbO3 Mach-Zehnder modulators (MZM), which are expensive and difficult to fabricate in large volume. Silicon phonics, on the other hands, offer low cost low large scale integration, however the performance is below what LiNbO3 technology offers.

In this work, fundamental sources of nonlinearity in Silicon photonics MZMs are analyzed and characterized, and methods and techniques are proposed to overcome the limitations in order to design high SFDR silicon photonic based optical RF receivers. First, A SiGe low-noise distributed driver is co-designed for the SiP MZM to linearize and extend the bandwidth over which the SFDR remains high, by focusing on improving NF of the receiver. The RoF transmitter achieves 1-20 GHz bandwidth and an SFDR of 109 dB at 11 GHz. This is the highest SFDR demonstrated for a SiP technology without incorporating predistortion. Next, a distributed silicon-germanium (SiGe) HBT-based low-noise amplifier (LNA) is co-designed for linearization with a Silicon phonics MZM for a broadband RoF link. The SiGe LNA incorporates a distributed, tunable predistortion scheme that is inherently wideband and improves the third-order intercept point over an 18 GHz range. The assembled SiGe LNA and SiP MZM prototype demonstrates an SFDR as high as 120 dB at 9 GHz, a 14 dB improvement over previous SiP RF components or RoF links, and a record among Silicon photonic MZM based RoF systems.

In the next part of dissertation, integration strategies of Silicon photonics are compared for compact, efficient integrated optical transmitters with CMOS drivers, to be used in coherent intra-data center optical link. An integrated optical transmitter, based on a CMOS driver and a silicon photonic segmented MZM with travelling wave segments, that operates to 50 Gb/s, is designed. The MZM consists of 4 traveling wave segments along a 3.2 mm length in a 90-nm Silicon Photonic technology. The broadband distributed amplifier is a pseudo-differential design with 3-stack driver stages to deliver sufficient voltage swing in a 45nm CMOS SOI technology. The optical eye is open to 50 Gb/s and indicates error-free operation to 30 Gb/s. The total circuit consumes 480 mW. Next, A fully integrated optical transmitter with 90-nm CMOS driver is presented. The novel design, based on a distributed amplifier merged in a travelling wave Mach-Zehnder modulator, maximizes area and bandwidth efficiency. Open optical eyes are measured up to 30 Gb/s for the first run implementation.