Integrated Optical Time Lenses for Passive Optical Networks: For Generation Of On-Chip Optical Fourier Transforms

Passive optical networks are a widely employed point to multi-point method of transmitting data to consumers in last mile networks. These networks are typically implemented with either time division or wavelength division multiplexed signal, but either implementation is inherently energy inefficient, with the inefficiency lying respectively on the receiver or transmission end. Using optical time lenses based on nonlinear optical processes, optical Fourier transforms can be carried out, which allows for the creation of a new type of passive optical network where time division multiplexed signals are transformed into wavelength division multiplexed signals using all optical signal processing. This type of network has been successfully demonstrated in fiber based systems. Due to the size of these and the low nonlinear efficiency and instability resulting from thermal effects of optical fiber, it remains in the experimental stage and has not yet been integrated in optical networks. Photonic integrated circuits offer an alternative road to successful implementation, since these are both compact and can be very efficient platforms for nonlinear optics. The subject of this PhD thesis is to investigate how a time lens based generator of an optical Fourier transform can be photonically integrated. Several important parts of this goal are achieved, including the design of photonic integrated circuits for optical Fourier transforms, demonstration of a four-wave mixing circuit with 50 dB extinction of the pump on-chip, the design of spiral Bragg gratings with a continuously varying radius of curvature, and the demonstration of circuits that allow access to light reflected from Bragg gratings with losses as low as 1 dB. These are important steps on the way and the lessons learned in this project lay the foundations for investigating heterogeneous integration in order to realize a system for fully integrated optical Fourier transforms.