Rabia Riaz | Technische Universität Dresden (original) (raw)

Papers by Rabia Riaz

IEEE Access, 2022

Coordinated and efficient operation in large, complex systems requires the synchronization of the... more Coordinated and efficient operation in large, complex systems requires the synchronization of the rhythms of spatially distributed components. Such systems are the basis for critical infrastructure such as satellite navigation, mobile communications, and services like the precision time protocol and Universal Coordinated Time. Different concepts for the synchronization of oscillator networks have been proposed, in particular mutual synchronization without and hierarchical synchronization from a reference clock. Established network synchronization models in electrical engineering address the role of inevitable cross-coupling time delays for network synchronization. Mutual synchronization has been studied using linear approximations of the coupling functions of these models. We review previous work and present a general model in which we study synchronization taking into account nonlinearities and finite time delays. As a result, dynamical phenomena in networks of coupled electronic oscillators induced by time delays, such as the multistability and stabilization of synchronized states can be predicted and observed. We study the linear stability of nonlinear states and predict for which system parameters synchronized states can be stable. We use these results to discuss the implementation of mutual synchronization for complex system architectures. A key finding is that mutual synchronization can result in stable in-and anti-phase synchronized states in the presence of large time delays. We provide the condition for which such synchronized states are guaranteed to be stable. INDEX TERMS Synchronization, delay effects, systems engineering and theory, control theory, phase locked loops, mutual coupling.

This work presents synchronization of two bidirectionally delay-coupled phase locked loop (PLL) s... more This work presents synchronization of two bidirectionally delay-coupled phase locked loop (PLL) systems with voltage controlled oscillator frequencies of 24 GHz to validate a non-hierarchical clock distribution approach. For this purpose, a PLL architecture that allows mutual coupling between two such nodes is introduced. An existing phase domain model is extended to include the nonlinear response of the oscillator to the tuning signal. With this extension the frequencies and phase-relations of self-organized synchronized states can be precisely predicted. This is verified by measurements obtained from two synchronized PLLs for different time delays and division factors. The predictions of the model are in good agreement with the measurements. For time delays up to 14 ns it is shown that self-organized synchronization is feasible at microwave frequencies.

2022 IEEE BiCMOS and Compound Semiconductor Integrated Circuits and Technology Symposium (BCICTS)

2022 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

We have numerically studied the formation of frequency comb in a silicon nitride microring resona... more We have numerically studied the formation of frequency comb in a silicon nitride microring resonator with a single-mode waveguide and normal group velocity dispersion (GVD). Various dark pulses such as soliton, breather, and complex soliton have been obtained. The waveform shape in the time domain and the optical spectrum of several dark frequency combs have been presented. Recently, optical microresonator have been studied to be used for wide range of applications. Frequency combs have been initially shown in a resonator with anomalous GVD where the formation of bright soliton(s) and Turing roll is occurred [1–3]. Compared to bright pulses, dark frequency combs in normal-dispersion microresonator have some advantages. First, precise laser detuning is not substantial to overcome the thermal instability issue, which has a vital role in the anomalous-dispersion regime. Furthermore, since the formation of dark pulses is dominantly the result of mode interaction and not the broadband chaotic states, they can be obtained repeatedly in experiment [4]. In order to reach stable dark frequency comb and high order of family-mode interaction, multimode waveguide microresonators have been considered before [4–6]. However, in this study, we have considered a single-mode thin silicon nitride waveguide for the microring resonator (Fig. 1a). The formation of various dark frequency pulses, have been numerically simulated using Lugiato-Lefever model.

2020 European Conference on Circuit Theory and Design (ECCTD), 2020

This paper presents a generalization of the classical phase-locked loop (PLL) theory. It includes... more This paper presents a generalization of the classical phase-locked loop (PLL) theory. It includes the effects of timedelays and mutual coupling between PLLs. Two methods for finding stable solutions to locked states and their transient dynamics are discussed. The theoretical predictions of these methods are verified by experimental measurements obtained of a classical PLL entrained by a clock. For entrainment the generalized and classical PLL theory overlap. The analysis correctly predicts the phase-relations of phase-locked states, the loop-gain dependency on the component characteristics and timedelays and the transient dynamics, i.e., perturbation decay rate and the frequency of perturbation decay. Thus the generalized theory allows a deeper understanding of a PLL's response. The model covers PLLs of arbitrary order and number of inputs.

IEEE Access, 2022

Coordinated and efficient operation in large, complex systems requires the synchronization of the... more Coordinated and efficient operation in large, complex systems requires the synchronization of the rhythms of spatially distributed components. Such systems are the basis for critical infrastructure such as satellite navigation, mobile communications, and services like the precision time protocol and Universal Coordinated Time. Different concepts for the synchronization of oscillator networks have been proposed, in particular mutual synchronization without and hierarchical synchronization from a reference clock. Established network synchronization models in electrical engineering address the role of inevitable cross-coupling time delays for network synchronization. Mutual synchronization has been studied using linear approximations of the coupling functions of these models. We review previous work and present a general model in which we study synchronization taking into account nonlinearities and finite time delays. As a result, dynamical phenomena in networks of coupled electronic oscillators induced by time delays, such as the multistability and stabilization of synchronized states can be predicted and observed. We study the linear stability of nonlinear states and predict for which system parameters synchronized states can be stable. We use these results to discuss the implementation of mutual synchronization for complex system architectures. A key finding is that mutual synchronization can result in stable in-and anti-phase synchronized states in the presence of large time delays. We provide the condition for which such synchronized states are guaranteed to be stable. INDEX TERMS Synchronization, delay effects, systems engineering and theory, control theory, phase locked loops, mutual coupling.

This work presents synchronization of two bidirectionally delay-coupled phase locked loop (PLL) s... more This work presents synchronization of two bidirectionally delay-coupled phase locked loop (PLL) systems with voltage controlled oscillator frequencies of 24 GHz to validate a non-hierarchical clock distribution approach. For this purpose, a PLL architecture that allows mutual coupling between two such nodes is introduced. An existing phase domain model is extended to include the nonlinear response of the oscillator to the tuning signal. With this extension the frequencies and phase-relations of self-organized synchronized states can be precisely predicted. This is verified by measurements obtained from two synchronized PLLs for different time delays and division factors. The predictions of the model are in good agreement with the measurements. For time delays up to 14 ns it is shown that self-organized synchronization is feasible at microwave frequencies.

2022 IEEE BiCMOS and Compound Semiconductor Integrated Circuits and Technology Symposium (BCICTS)

2022 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

We have numerically studied the formation of frequency comb in a silicon nitride microring resona... more We have numerically studied the formation of frequency comb in a silicon nitride microring resonator with a single-mode waveguide and normal group velocity dispersion (GVD). Various dark pulses such as soliton, breather, and complex soliton have been obtained. The waveform shape in the time domain and the optical spectrum of several dark frequency combs have been presented. Recently, optical microresonator have been studied to be used for wide range of applications. Frequency combs have been initially shown in a resonator with anomalous GVD where the formation of bright soliton(s) and Turing roll is occurred [1–3]. Compared to bright pulses, dark frequency combs in normal-dispersion microresonator have some advantages. First, precise laser detuning is not substantial to overcome the thermal instability issue, which has a vital role in the anomalous-dispersion regime. Furthermore, since the formation of dark pulses is dominantly the result of mode interaction and not the broadband chaotic states, they can be obtained repeatedly in experiment [4]. In order to reach stable dark frequency comb and high order of family-mode interaction, multimode waveguide microresonators have been considered before [4–6]. However, in this study, we have considered a single-mode thin silicon nitride waveguide for the microring resonator (Fig. 1a). The formation of various dark frequency pulses, have been numerically simulated using Lugiato-Lefever model.

2020 European Conference on Circuit Theory and Design (ECCTD), 2020

This paper presents a generalization of the classical phase-locked loop (PLL) theory. It includes... more This paper presents a generalization of the classical phase-locked loop (PLL) theory. It includes the effects of timedelays and mutual coupling between PLLs. Two methods for finding stable solutions to locked states and their transient dynamics are discussed. The theoretical predictions of these methods are verified by experimental measurements obtained of a classical PLL entrained by a clock. For entrainment the generalized and classical PLL theory overlap. The analysis correctly predicts the phase-relations of phase-locked states, the loop-gain dependency on the component characteristics and timedelays and the transient dynamics, i.e., perturbation decay rate and the frequency of perturbation decay. Thus the generalized theory allows a deeper understanding of a PLL's response. The model covers PLLs of arbitrary order and number of inputs.