PhD defence of Deng Mao - Design and Characterization of Silicon Photonic Devices for Data-Center Optical Interconnects
Abstract
In this thesis, we explore Silicon Photonics (SiP) devices for optical data center interconnects (DCIs). This thesis can be divided into three parts. In the first part, we demonstrate the design and characterization of optical adiabatic couplers (OACs). The analytical relationship between splitting ratios (SRs) and waveguide properties is developed. Through experiment, OACs with SRs from 7%/93% to 50%/50% are demonstrated from 1260 to 1360 nm for the fundamental transverse electric (TE) mode. The variances of SRs for different wavelengths across the Original band (O-band) are within 1.3% when the chip temperature increases from 20°C to 50°C. To further decrease the footprint of OACs and the SR variance from 1500 nm to 1600 nm, we propose a time-efficient method to analyze and design the OACs. The measured SRs of the targeted 3-dB OACs are between 47%/53% from 1500 nm – 1600 nm with a mode-evolution region of 110 µm. The same mode-evolution method presents imbalanced OACs with SRs from 8%/92% to 42%/58%.
The second part of the thesis presents a CMOS-compatible and temperature insensitive 1×4 Conventional band (C-band) wavelength (de-) multiplexer. The (de-) multiplexer design is based on cascaded Mach-Zehnder interferometers (MZIs). The waveguide widths of the MZI delay lines are matched to decrease the overall thermo-optic coefficient (TOC). The proposed device is measured from 20°C to 50°C and the measured TOC is 4.8 pm/°C.
The last part of the thesis demonstrates the design, analysis, and characterization of a compact Mach-Zehnder modulator (MMZM) with meandered phase shifters on the SiP platform. With a footprint of 432 x 260 µm², the MMZM has an insertion loss of 2.1 dB. Using 0.5 V bias, the measured half-wave voltage and 3-dB EO BW are 6.4 V and 7.7 GHz, respectively. Using the fabricated MMZM, we experimentally demonstrate 53 Gbaud PAM-4 transmission over 2 km of standard single-mode optical fiber at a bit error rate (BER) below the hard-decision (HD) forward error correction BER threshold of 3.8 x 10¯³ having 6.7% overhead.