| PhD Viva

Name of the Speaker: Mr. Arnab Goswami (EE17D011)
Guide: Dr. Bijoy Krishna Das
Venue: Online
Online meeting link: https://meet.google.com/twa-krwr-kbk
Date/Time: 5th July(Friday) 2024, at 10AM
Title: Four Wave Mixing in Silicon Waveguide Devices for Quantum Photonic Applications

Abstract :

The commercial success of CMOS-compatible silicon photonics technology in data center applications has opened many promising application areas, including on-chip quantum photonics circuits for computing, communication, and sensing. Achieving high-quality photon sources and high-extinction pump rejection filters is crucial for advancing large-scale quantum photonic signal processing in silicon. However, current performance limitations of these photon sources and filters hinder the scalability of photonic circuits. This thesis focuses on enhancing the figure of merit for both devices, addressing challenges in correlated photon pair generation through spontaneous four-wave mixing in a microring resonator and demonstrating pump rejection filters with distributed Bragg gratings. Initially, stimulated four-wave mixing in a silicon photonic wire showed an idler-to-signal conversion efficiency of approximately -35 dB for a launched pump power of 15 dBm. Improved conversion efficiency was achieved using a microring resonator with a radius of 20 μm (Q > 50,000). A properly designed asymmetric bus-ring waveguide coupler improved the spectral purity of heralded single photons from 93% to ~99% at resonant wavelengths around 1550 nm. For pump rejection, a single-stage distributed Bragg grating in a multimode rib waveguide exhibited a stopband extinction of ~65 dB. On-chip stimulated four-wave mixing experiments validated the pump rejection efficiency, attenuating the pump laser to the idler power level. Integrating the filter with a microring resonator, we reported bistable generation of entangled photon pairs via spontaneous four-wave mixing in a silicon microring resonator integrated with a pump rejection filter (>45 dB). The observed photon generation rate exceeded 20 MHz in one bistable state for a launched input power of ~0.75 mW in the C-band. This integration reduces the need for external filters before single-photon detectors. Furthermore, the grating-based filter design for pump rejection was extended to the silicon nitride waveguide platform, demonstrating four-wave mixing and on-chip pump suppression capabilities up to 65 dB.