Multimode processes for integrated photonics

Abstract

Multimode processes of integrated photonics are slowly emerging as extensions to our current single-mode architecture whilst also ushering in new possibilities that are impossible with the constraints of single-mode operations. Faster data processing and communication speeds are amongst many improvements that have been demonstrated yet are still to replace the existing infrastructure with work still required. This thesis focuses on three similar, yet distinct, topics in the realm of multimode photonics. I begin by comparing two platforms that show promise of nonlinear frequency generation via second order nonlinearities, namely LiNbO3 on insulator and AlGaAs on insulator. Mode combinations that lead to high conversion efficiency are found and simulated to compare the efficiency of both platforms over different regimes of power and pulse width. The effects of roughness on the nonlinear performance are also studied as I believe this is generally overlooked in this type of simulation. I then further simulate the possibility of generating light in the mid-infrared using the conditions found. Next, we propose, design, fabricate and test devices for compact, arbitrary multimode power splitting. Our choice of platform is SiN on insulator due to its low losses and precise, rapid fabrication here at the University of Southampton. We highlight low device losses with a small footprint whilst demonstrating arbitrary splitting in up to 5 output ports from a single input. Considering all parameters, I believe it sets a new benchmark in the field. I then move to my final chapter where I design and test a mode-splitting (or multiplexing) device with a sub-wavelength footprint. Temporal and spatial synchronisation of the modes is guaranteed due to the simple step junction approach we take. I highlight the significantly large bandwidth (above 200nm) with accurate duplexing of TE00 and TE01 modes. A mode decomposition method is developed alongside traditional techniques that perform the decomposition on chip that relaxes the experimental conditions required.

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