Toward non-reciprocal chip-scale silicon photonics
Date
2015
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
A critical problem in modern photonics is the optical isolation. An optical isolator allows light to pass through in one direction but blocks it in the other, thereby acting as the optical analogue of an electronic diode. Because such a device induces a preferred direction for light, it must break the symmetry of Maxwell's equations known as Lorentz reciprocity. This dissertation focuses on the reciprocity breaking photonic architecture that is comprised of optical modulators under prescribed driving conditions, optical delay lines and directional couplers in the silicon photonic platform. Unlike isolators based on magneto-optical Kerr effects or nonlinear effects, the author's non-reciprocal system is built by silicon photonic devices in the linear and reciprocal material platform. The system that works as the optical isolator and circulator at the same time is demonstrated by a fiber-based proof-of-concept experiment. The system architecture provides a practical answer to the challenge of non-reciprocal light routing in photonic integrated circuits (PICs). A silicon optical modulator that can satisfy the non-reciprocal system's demands is studied. The application of the PN junction's nonlinearity in the modulator can improve the robustness of the non-reciprocal system by removing the signal distortion's influence. The high-linear Mach-Zehnder modulator in silicon is also presented. The phase coherence length of the silicon photonic platform is studied to fulfill a reliable non-reciprocal system. The coherence length can quantitate the semiconductor fabrication uniformity that is critical in the design of complex PICs. A new method is proposed to analyze the random phase fluctuations from more than 800 on-chip silicon Mach-Zehnder interferometers across the wafer. For the first time, the waveguide coherence length of silicon photonic platform is extracted with statistical significance. Finally, a fabrication error model is proposed in order to effectively design the low loss compact directional coupler. High consistent performance of device is verified by experiments.