Design and simulation of integrated photonic devices based on tilted Bragg gratings

Abstract

Integrated photonics is a versatile technology in which optical components are integrated in a single photonic chip. This has a wide range of applications including in telecommunications, optical information processing and quantum computing. A highly flexible integrated photonics platform has previously been developed at the ORC for inscribing waveguides and tilted Bragg gratings. It has previously been used to implement devices using tilted gratings such as polarizers, spectrometers and refractometers. The potential has been identified for using this platform to implement more complex devices employing tilted Bragg gratings. For this reason, it is interesting to explore the full capabilities of this platform and see if it could be used to implement optical information processing.

In this thesis, I theoretically investigate new devices employing tilted Bragg gratings and simulate their implementations in this platform. I begin by deriving an analytical expression relating the scattering efficiency of a tilted grating to its parameters and light wavelength and I have found good agreement with numerical simulations for a moderate grating width and tilt angle.

I present a new class of devices based on two parallel single-mode waveguides in a single ridge structure. The waveguides contain tilted gratings that couple the light between them using the modes of the ridge. These devices have potential application in optical information processing and are investigated analytically and numerically using coupled mode theory.

A version of this device employing single-mode waveguides and a backward propagating cladding mode is investigated with a theoretical maximum transfer efficiency of 100%. I find that this device exhibits grating induced transparency and has high robustness to temperature and to phase-error noise. I find that, with realistic fabrication tolerances and the use of a refractive index oil, the device is theoretically fabricable. I present the results of simulations with the parameters intended for fabrication in this thesis.

In order to increase the number of inputs and outputs and thus achieve more complex information processing, I present a version of this device involving two-mode waveguides, and show that I am able to achieve a mode division multiplexer and an arbitrary power splitter. By concatenating individual transformations, I am able to achieve any 4 × 4 arbitrary unitary matrix.

Finally, I present a novel device exploiting both directions of propagation of two singlemode waveguides in order to unlock more degrees of freedom in a compact device. By attaching circulators to the waveguide end facets, I can achieve a device with four input and four output ports. I identify four fundamental grating-based couplers on this device that can be concatenated to achieve any 4 × 4 symmetric unitary transfer matrix. I present the implementation of a compact Walsh-Hadamard gate based on superimposed gratings that can be achieved on this platform and show that an entire class of transformations can be similarly implemented.

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Identifiers

ORCID for Mathias John Weisen: orcid.org/0000-0003-0387-972X

ORCID for Peter Horak: orcid.org/0000-0002-8710-8764

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