Performance Enhancement of Opto-electronic Oscillators using Photonic Bandgap Phase and Mach-Zehnder Modulators
Authors:   , Pantano Francis T. , Daryoush Afshin S. 
Published: July 2021

Highly stable oscillators are an important component in heterodyne receivers used in telecommunications, remote sensing, and instrumentation. Stable oscillators require high quality factor (Q) resonators that are challenging at radio frequencies of above 1GHz. The opto-electronic oscillators (OEO) using long low-loss fiber optic (FO) delay lines are developed for stable local oscillators for a variety of radio frequency (RF) applications at frequencies of 10 GHz and above. The OEO takes advantage of optical modulation by stable RF signal before transmission over kilometer long fiber spools. The optical modulation is being done using phase modulation, or interferometric modulation using the Mach-Zehnder modulator (MZM). The phase sensitivity of the phase modulator (PM) and its losses influence the behavior of the PM or MZM, which is a critical component to the overall performance of FO delay line in the OEO, and particularly for the forced oscillation neucleation noise of the OEOs using self-injection locking (SIL) and self-phase locking (SPLL). To improve on sensitivity of the optical modulators, photonic bandgap (PBG) based PM and MZM structures are considered with electro-optic (EO) polymers to increase the modulation efficiency and modulation bandwidth using integrated Si-photonics structures. This thesis covers the modeling and performance of the OEO with both PBG based and the conventional realization of PMs and MZMs each with various insertion loss and half-wave voltage performance characteristics. The half-wave voltage, V[pi], of the modulators is the voltage necessary to achieve a [pi] radian (180o) phase shift. The phase noise and frequency stability at close-in and far away from carrier is analyzed with MZMs operating at the quadrature point (V[pi]/2) and their impact is demonstrated on the overall SILPLL OEO performance. The previously developed and experimentally demonstrated self-injection locked phase locked loop (SILPLL) OEO is used and the performance is predicted when a PBG based modulator with a V[pi] of 2.17V and optical insertion loss of 1.6dB is used. The forced oscillation techniques of SIL and SPLL are also modeled to reduce the close-in to carrier phase noise of a 10GHz OEO. A Sagnac loop topology is analyzed and modeled as a method of performing the PM-IM conversion for the PM based OEO. The simulated phase noise performance for the PBG based PM is -149.6dBc/Hz as compared to -142.8dBc/Hz at 10kHz offset frequency for a conventional Lithium Niobate (LN) PM. At 10MHz offset frequency, the simulated phase noise is dominated by the amplitude noise of the FO delay line and for the PBG based PM is -166.5dBc/Hz compared to -158.3dBc/Hz for the conventional LN based PM. For the PBG based MZM, the simulated phase noise is -146.9dBc/Hz compared to -144.0dBc/Hz for the conventional MZM and -163.8dBc/Hz compared to -160.9dBc/Hz at offset frequency of 10kHz and 10MHz respectively. Time domain analyses of the Allan deviation and timing jitter are performed for each modulator and OEO topology. The Allan deviation at a sampling time of 10ms for the PBG based PM in the Sagnac loop SILPLL OEO was estimated to be 1.80x10-12, with an improvement from 2.80x10-12 for the conventional PM. Using the same topology, a jitter of 11.2fs was estimated, improving on calculated jitters of the conventional PM by 17.3fs. For the PBG based MZM in the SILPLL forced OEO, the Allan deviation at a sampling time of 10ms was calculated to be 2.47x10-12, improving by 2.40x10-12 from the conventional PM. A jitter of 15.3fs is expected, reducing by 14.9fs from the conventional PM's jitters. An analytical modeling and performance enhancement of both the standard and SILPLL OEO were presented in this thesis. Recommendation for experimental validations is also made in this thesis.