Available at: https://digitalcommons.calpoly.edu/theses/1314
Date of Award
MS in Electrical Engineering
The mode-locked laser diode (MLLD) finds a lot of use in applications such as ultra high-speed data processing and sampling, large-capacity optical fiber communications based on optical time-division multiplexing (OTDM) systems. Integrating mode-locked lasers on silicon makes way for highly integrated silicon based photonic communication devices. The mode-locked laser being used in this thesis was built with Hybrid Silicon technology. This technology, developed by UC Santa Barbara in 2006, introduced the idea of wafer bonding a crystalline III- V layer to a Silicon-on-insulator (SOI) substrate, making integrated lasers in silicon chips possible.
Furthermore, all mode-locked lasers produce phase noise, which can be a limiting factor in the performance of optical communication systems, specifically at higher bit rates. In this thesis, we design and discuss an impedance matching solution for a hybrid silicon mode-locked laser diode to lower phase noise and reduce the drive power requirements of the device. In order to develop an impedance matching solution, a thorough measurement and analysis of the impedance of the MLLD is necessary and was carried out. Then, a narrowband solution of two 0.1 pF chip capacitors in parallel is considered and examined as an impedance matching network for an operating frequency of 20 GHz. The hybrid silicon laser was packaged together in a module including the impedance- matching circuit for efficient RF injection.
In conclusion, a 6 dB reduction of power required to drive the laser diode, as well as approximately a 10 dB phase noise improvement, was measured with the narrow-band solution. Also, looking ahead to possible future work, we discuss a step recovery diode (SRD) driven impulse generator, which wave-shapes the RF drive to achieve efficient injection. This novel technique takes into account the time varying impedance of the absorber as the optical pulse passes through it, to provide optimum pulse shaping.
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