The physics of phase-noise mitigation : signal and filtering using microwave-photonic generation links

Abstract

The spectral purity of every oscillator system is limited by noise. This thesis explores the physics and measurements of noise fundamental to oscillators operating in the electrical and optical domains. Our analysis leads to a unified theory of phase noise applicable to perturbations whose characteristics are both white and colored. To minimize phase noise, the oscillator delay length must be made long. This principle motivates us to study a recent class of hybrid optoelectronic oscillators (OEOs) that operate based on concepts of microwave-photonic (MWP) gain. The delay of an OEO is made long (1-15 km) by taking advantage of the low losses afforded by optical fiber. Furthermore, the additional sidemodes are suppressed by a process of superhomogeneous gain exhibited by the MWP link. In this work, we demonstrate an OEO comprising of high-power low-noise slab-coupled optical waveguide (SCOW) components. The use of SCOW technology enables low-noise oscillation without the need for additional external amplification. We also show results of a similar system based on a SCOW coupled optoelectronic oscillator (COEO) configuration whose operation resembles that of a regeneratively modelocked laser. Both oscillators achieve phase noise significantly lower than that of conventional free-running microwave oscillators. Our ultimate goal is the monolithic integration of the OEO onto a single chip of InP. Towards that end, we will show our development of a SCOW distributed feedback laser (DFB) as a replacement to the bulky pump laser currently employed in the OEO.