SILPLL based forced opto-electronic oscillator using a phase modulator in a Sagnac loop

Abstract

Highly stable oscillators are an important component in heterodyne receivers used in telecommunications, remote sensing, and instrumentation. Opto-electronic oscillators (OEO) using very long low-loss fiber optic (FO) delay lines are considered as stable local oscillators and clock signals for a variety of RF applications. The standard OEO takes advantage of amplitude modulation of optical carrier using Mach-Zehnder modulators (MZM) and a long delay optical fibers (i.e. above kilometers). This paper proposes and employs photonic band-gap (PBG) phase modulation (PM) using optical modulation of E-O polymers in place of LiNbO3 (LN) for long fiber optic delay line. To use the phase modulator (PM) in the OEO, a Sagnac loop topology is proposed to perform the required phase modulation to intensity modulation (PM-IM) conversion. The phase sensitivity of the phase modulator and its losses influence the behavior of the PM which is a critical component to the overall performance of the OEO, and particularly for the forced oscillation OEOs using self-injection locking (SIL) and self-phase locking (SPLL). To improve on sensitivity of the optical modulators, photonic bandgap (PBG) based PM structures are considered with electro-optic (EO) polymers to enhance the modulation efficiency and increase modulation bandwidth using integrated Si-photonics structures. The previously developed and experimentally demonstrated self-injection locked phase locked loop (SILPLL) OEO is used as baseline comparison against the performance of PBG based PM with a Vn of 2.17 V is used. The predicted phase noise performance for the PBG based PM is estimated to be −149.6dBc/Hz at 10kHz offset.