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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 46509 (05)
- University: Sharif University of Technology
- Department: Electrical Engineering
- Advisor(s): Banai, Ali
- Abstract:
- Ultralow phase noise microwave oscillators with high stability are one of the key components required for many applications. With recent advances in ultrapure microwave oscillators, optoelectronic oscillators (OEOs) culminated in the state-of-the-art ultralow phase noise microwave oscillators. In this thesis, a nonlinear analytical approach is used to predict the main oscillation mode power and spurious levels in ultrapure microwave OEOs. Our analytical predictions are verified by numerical simulations and experimental data. Performance of an intensity-modulation direct-detection (IMDD) microwave photonic link (MWPL) operating under nonlinear conditions when its input consists of a sum of several unequal-power sinusoidal signals is investigated theoretically. We introduce two concepts in this link, i.e. the capture effect and large-signal noise figure (LSNF) for the first time. The capture effect or the small-signal suppression is the change in the amplitude ratio of the two signals between input and output of the link. General analytical expression for the small-signal suppression is derived. It is also shown that the output SNR can severely be affected by the interaction of signal and noise due to the nonlinearity of the MWPL. It is shown that the NF of a nonlinear MWPL is dependent on its input power. The influences of these effects of the nonlinear MWPL on the OEO operation is shown that is verified by experimental data in the literature has already been published on the OEOs. We also propose and theoretically and experimentally demonstrate two novel OEO structures. In the first structure, a novel low-drift low-phase noise OEO is presented. It is based on a Sagnac-loop comprising a traveling-wave optical phase modulator (PM) and a nonreciprocal bias unit that function jointly as a bias-free intensity modulator. In the second structure, a novel tunable, spurious-free OEO with, low drift and low phase noise is presented. In the proposed transposed-frequency OEO (TF-OEO), a PM and a nonreciprocal bias unit in a fiber Sagnac interferometer function jointly as an intrinsically drift-free intensity modulator which improves the long-term drift. Besides, a transposed-frequency low-noise filtered amplifier (TF-LNFA) is used which replaces the conventional radio frequency (RF) filter and RF amplifier with an intermediate frequency (IF) filter, an ultralow phase noise IF amplifier and a tunable local oscillator (LO), to achieve simultaneously frequency tuning and single-frequency selection with ultralow phase noise. Performances of the generated microwave signals in both structures are theoretically investigated, which are verified by experiments. Preliminary phase noise, frequency stability, spurious levels and frequency tunability performances of the photonically generated microwave signals is also investigated. In this thesis, we also analyze the phase noise of the extracted microwave signal from femtosecond mode-locked lasers (MLL) using standard direct detection of the MLL repetition rate and using balanced optical-microwave phase detector (BOM-PD)-based delay-locked loop (DLL) for excess noise suppression. Phase noise of low phase noise VCO locked to MLL using BOM-PD-based phase-locked loop (PLL) is also analyzed. An analytical formulation based on the conversion matrix approach for characterizing the oscillator noise spectra as well as the phase and amplitude noise spectra for an OEO is also presented
- Keywords:
- Phase Noise ; Capture Effect ; Optoelectronic Oscillator ; Spurious Level ; Large-Signal Noise Figure (LSNF) ; Optical Frequency Division ; Transposed Frequency ; Stochastic Delay Differential Equations
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