Title: Exploration of Novel Applications for Optical Communications using Silicon Nanophotonics
Description: Silicon photonics is considered to have the potential to enable future communication systems with optical input-outputs to circumvent the shortcomings of electronics. Today silicon is the material of choice for photonic and optoelectronic circuits, mainly due to its excellent material properties, established processing technology, low-cost, compact device footprint, and high-density integration. From sensing and detection to computing and communications, silicon photonics has advanced remarkably in the last couple of decades and found numerous applications. This thesis work focusses on three novel applications of silicon photonics for optical communications. The first application is the design and demonstration of a differential phase shift keying (DPSK) demodulator circuit using a ring resonator. DPSK-based transceivers are being actively considered for short-haul optical communication systems due to their advantages in terms of high extinction ratio, dispersion tolerance, and improved sensitivity.

The ring resonator utilizes the concept of coherent perfect absorption and results into a compact demodulator circuit that can be easily integrated into an all-optical system. The next application involves a nonlinear optical process, namely, four wave mixing (FWM) inside a silicon nanowire. For FWM to occur efficiently, phase matching between the real propagation constants of all the frequency components is a key requirement. However, this condition cannot be easily satisfied in integrated optics semiconductor platforms. We propose an altogether new approach to achieve signal gain within the context of non-Hermitian photonics and parity-time (PT) symmetry and show that the phase matching criterion is not necessary to achieve efficient nonlinear interactions. Instead by introducing losses only to the idler components while leaving the pump and signal waves intact, we analyze a coupled-wave system of silicon nanowires using finite difference time domain technique and find that signal gain is indeed possible in such a system, irrespective of the fulfillment of the phase-matching condition.

The final application of silicon photonics in this thesis is the engineering of zero group velocity dispersion (GVD) point in the C-band of communication channel. The problem of pulse broadening due to chromatic dispersion is becoming an increasingly important factor for signal degradation. We propose a hybrid silicon/plasmonic waveguide that can change the zero-GVD point by altering the geometry and material of the waveguide components. In addition, such hybrid system also has the potential to transmit both optical and electronic signals along the same circuitry.