Low Noise, High Repetition Rate Semiconductor-based Mode-locked Lasers For Signal Processing And Coherent Communications

This dissertation details work on high repetition rate semiconductor mode-locked lasers. The qualities of stable pulse trains and stable optical frequency content are the focus of the work performed. First, applications of such lasers are reviewed with particular attention to applications only realizable with laser performance such as presented in this dissertation. Sources of timing jitter are also reviewed, as are techniques by which the timing jitter of a 10 GHz optical pulse train may be measured. Experimental results begin with an exploration of the consequences on the timing and amplitude jitter of the phase noise of an RF source used for mode-locking. These results lead to an ultralow timing jitter source, with 30 fs of timing jitter (1 Hz to 5 GHz, extrapolated). The focus of the work then shifts to generating a stabilized optical frequency comb. The first technique to generating the frequency comb is through optical injection. It is shown that not only can injection locking stabilize a mode-locked laser to the injection seed, but linewidth narrowing, timing jitter reduction and suppression of superfluous optical supermodes of a harmonically mode-locked laser also result. A scheme by which optical injection locking can be maintained long term is also proposed. Results on using an intracavity etalon for supermode suppression and optical frequency stabilization then follow. An etalon-based actively mode-locked laser is shown to have a timing jitter of only 20 fs (1Hz-5 GHz, extrapolated), optical linewidths below 10 kHz and optical frequency instabilities less than 400 kHz. By adding dispersion compensating fiber, the optical spectrum was broadened to 2 THz and 800 fs duration pulses were obtained. By using the etalon-based actively mode-locked laser as a basis, a completely self-contained frequency stabilized coupled optoelectronic oscillator was built and characterized. By simultaneously stabilizing the optical frequencies and the pulse repetition rate to the etalon, a 10 GHz comb source centered at 1550 nm was realized. This system maintains the high quality performance of the actively mode-locked laser while significantly reducing the size weight and power consumption of the system. This system also has the potential for outperforming the actively mode-locked laser by increasing the finesse and stability of the intracavity etalon. The final chapter of this dissertation outlines the future work on the etalon-based coupled optoelectronic oscillator, including the incorporation of a higher finesse, more stable etalon and active phase noise suppression of the RF signal. Two appendices give details on phase noise measurements that incorporate carrier suppression and the noise model for the coupled optoelectronic oscillator

Phase Noise Reduction in an Oscillator Using Harmonic Mixing Technique

This thesis presents a new technique of injection of multi-harmonics into an oscillator, study the behavior and response of the oscillator. First general locking equations are derived using the feedback model of an oscillator. Second, using the Laplace domain modeled phase noise analysis giving insight into the phase noise model of an oscillator under multiple harmonics are analytically studied and experimentally validated with good agreement. From the locking process and phase noise analysis we can observe when compared to single tone injection there is a substantial improvement of phase noise under multi-harmonic injection, enhancement in the locking range. We present Injection Locked Frequency Divider (ILFD) circuit under multi-harmonic injection (2nd and 3rd harmonics injected) with simulation, theoretical validation. The proposed circuit is designed using the UMC library by using Op-Amp based feedback current reference circuit. The amplitude dependency of the injection signals on the phase noise is observed as increase in the injection levels decreases the phase noise

RFID SIMULATION IN MATLAB I SIMULINK

Nowadays, Radio Frequency Identification (RFID) applications are widely used in daily application and also in industries. RFID is an automatic identifications method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. The RFID tag is an object that can be placed into a product or person for the purpose of identification using radio waves. RFID uses wireless communication technique, found application in many areas such as attendance tracking system in campus or in a big factory and also for inventory tracking and management. In this project, the work of Yifen Han, Qiang Li and Hao Min from Auto-ID Labs at Fudan University, Shanghai, China will be reproduced so that further simulation result can be generated. Special attention is emphasized on the development of transmitter, receiver, wireless channel and tag for the system simulation environment because these four elements are the most important subsystems to produce an RFID simulation environment. This project will evaluate the system performance by changing the coding method and operation distance. At this point, half of transmitter subsystems have been done. The subsystems developed so far are source coding, raised cosine Hilbert and digital to analog converter

Periodically Disturbed Oscillators

By controlling the timing of events and enabling the transmission of data over long distances, oscillators can be considered to generate the "heartbeat" of modern electronic systems. Their utility, however, is boosted significantly by their peculiar ability to synchronize to external signals that are themselves periodic in time. Although this fascinating phenomenon has been studied by scientists since the 1600s, models for describing this behavior have seen a disconnect between the rigorous, methodical approaches taken by mathematicians and the design-oriented, physically-based analyses carried out by engineers. While the analytical power of the former is often concealed by an inundation of abstract mathematical machinery, the accuracy and generality of the latter are constrained by the empirical nature of the ensuing derivations. We hope to bridge that gap here. In this thesis, a general theory of electrical oscillators under the influence of a periodic injection is developed from first principles. Our approach leads to a fundamental yet intuitive understanding of the process by which oscillators lock to a periodic injection, as well as what happens when synchronization fails and the oscillator is instead injection pulled. By considering the autonomous and periodically time-varying nature that underlies all oscillators, we build a time-synchronous model that is valid for oscillators of any topology and periodic disturbances of any shape. A single first-order differential equation is shown to be capable of making accurate, quantitative predictions about a wide array of properties of periodically disturbed oscillators: the range of injection frequencies for which synchronization occurs, the phase difference between the injection and the oscillator under lock, stable vs. unstable modes of locking, the pull-in process toward lock, the dynamics of injection pulling, as well as phase noise in both free-running and injection-locked oscillators. The framework also naturally accommodates superharmonic injection-locked frequency division, subharmonic injection-locked frequency multiplication, and the general case of an arbitrary rational relationship between the injection and oscillation frequencies. A number of novel insights for improving the performance of systems that utilize injection locking are also elucidated. In particular, we explore how both the injection waveform and the oscillator's design can be modified to optimize the lock range. The resultant design techniques are employed in the implementation of a dual-moduli prescaler for frequency synthesis applications which features low power consumption, a wide operating range, and a small chip area. For the commonly used inductor-capacitor (LC) oscillator, we make a simple modification to our framework that takes the oscillation amplitude into account, greatly enhancing the model's accuracy for large injections. The augmented theory uniquely captures the asymmetry of the lock range as well as the distinct characteristics exhibited by different types of LC oscillators. Existing injection locking and pulling theories in the available literature are subsumed as special cases of our model. It is important to note that even though the veracity of our theoretical predictions degrades as the size of the injection grows due to our framework's linearization with respect to the disturbance, our model's validity across a broad range of practical injection strengths are borne out by simulations and measurements on a diverse collection of integrated LC, ring, and relaxation oscillators. Lastly, we also present a phasor-based analysis of LC and ring oscillators which yields a novel perspective into how the injection current interacts with the oscillator's core nonlinearity to facilitate injection locking.</p

Low-Power High-Data-Rate Transmitter Design for Biomedical Application

Ph.DDOCTOR OF PHILOSOPH

On the 1/f Frequency Noise in Ultra-Stable Quartz Oscillators

The frequency flicker of an oscillator, which appears as a 1/f^3 line in the phase noise spectral density, and as a floor on the Allan variance plot, originates from two basic phenomena, namely: (1) the 1/f phase noise turned into 1/f frequency noise via the Leeson effect, and (2) the 1/f fluctuation of the resonator natural frequency. The discussion on which is the dominant effect, thus on how to improve the stability of the oscillator, has been going on for years without giving a clear answer. This article tackles the question by analyzing the phase noise spectrum of several commercial oscillators and laboratory prototypes, and demonstrates that the fluctuation of the resonator natural frequency is the dominant effect. The investigation method starts from reverse engineering the oscillator phase noise in order to show that if the Leeson effect was dominant, the resonator merit factor Q would be too low as compared to the available technology.Comment: 20 pages, list of symbols, 1 table, 6 figures, 43 reference

Cascaded Microwave Photonic Filters for Side Mode Suppression in a Tunable Optoelectronic Oscillator applied to THz Signal Generation & Transmission

We demonstrate experimentally an optoelectronic oscillator (OEO) in which high side-mode suppression is achieved by cascading a phase modulator-based single passband tunable microwave photonic (MWP) filter with an optoelectronic feedback loop-based infinite impulse response (IIR) MWP filter. The OEO provides an RF oscillation that can be tuned from 6.5 GHz to 17.8 GHz with a phase noise lower than -103 dBc/Hz. Experimental results show that inclusion of the IIR section leads to a 20 dB reduction of phase noise close to the carrier and an increase of 10 dB in side mode suppression, compared to the equivalent OEO without an IIR section. The OEO was used to drive an optical frequency comb generator to generate a THz signal at 242.6 GHz by optical heterodyning; inclusion of the IIR section increases suppression of the side modes neighboring the THz carrier. A radio over fiber link was then implemented at a 242.6 GHz carrier frequency, with transmission of a 24 Gbps signal over 40 km of fiber and a 30 cm wireless path at a bit error rate below the forward error correction limit. The proposed system may be applied to frequency reconfigurable THz links and radars