A Terabit Optical Link in Silicon
Streshinsky, Matthew Akio
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As data centers grow, there is a need to be able to densely pack low power, high bandwidth, kilometer-reach interconnects into the same available rack space as existing technologies. Silicon is particularly well suited for this task due to its ability to accommodate high-speed single-mode optical systems-on-chip. An outstanding question is whether silicon photonics can easily scale to these larger systems and, more importantly, if these types of systems can yield reliably. This dissertation first investigates the design, fabrication, and test of a bi-wavelength polarization splitting grating coupler and two high-speed Mach-Zehnder modulators for integration into the OpSIS process development kit library (PDK). Finally, this dissertation discusses the integration of these components from the OpSIS PDK to demonstrate a 48 × 50 Gb/s parallel single mode transceiver. A novel bi-wavelength polarization splitting grating coupler is designed and tested. It is experimentally shown that it is possible to couple C-band and O-band wavelengths and perform polarization splitting simultaneously in a single device. For C-band light, we measure a maximum transmission of 7.6 dB, polarization isolation of 24 dB, and -1.5 dB transmission window of 35 nm. For O-band light, we measure a maximum transmission of 8.2 dB, polarization isolation of 8.4 dB, and -1.5 dB transmission window of 18 nm. Two differentially driven Mach-Zehnder modulators are designed and characterized for digital and analog applications. The first is demonstrated to operate at 50 Gb/s with a differential 1.5 Vpp RF driving signal with 0 V DC bias, suggesting an RF power efficiency of 450 fJ/bit. The second device is placed into an analog optical link and spur-free dynamic range measurements are performed. A SFDRIMD of 97 dB.Hz2/3 and SFDRSHD of 82 dB.Hz1/2 are measured by differentially driving the modulator. Lastly, the parallel single mode transceiver we report here represents nearly an order of magnitude greater aggregate data rate and four to five times the channel count compared against other silicon transmitters. Our receiver also compares favorably against previous arrays of Ge-on-Si photodetectors and is monolithically integrated on the same wafer as the transmitter. We present bit-error-rate versus received optical power curves as well as DC performance for all 48 channels of the transmitter and open eyes at 50 Gb/s for the receiver.
- Electrical engineering