Nonlinear dynamics of mode-locking optical fiber ring lasers

We consider a model of a mode-locked fiber ring laser for which the evolution of a propagating pulse in a birefringent optical fiber is periodically perturbed by rotation of the polarization state owing to the presence of a passive polarizer. The stable modes of operation of this laser that correspond to pulse trains with uniform amplitudes are fully classified. Four parameters, i.e., polarization, phase, amplitude, and chirp, are essential for an understanding of the resultant pulse-train uniformity. A reduced set of four coupled nonlinear differential equations that describe the leading-order pulse dynamics is found by use of the variational nature of the governing equations. Pulse-train uniformity is achieved in three parameter regimes in which the amplitude and the chirp decouple from the polarization and the phase. Alignment of the polarizer either near the slow or the fast axis of the fiber is sufficient to establish this stable mode locking

Polarization Properties of the Solitons Generated in the Process of Pulse Breakup in Twisted Fiber Pumped by ns Pulses

Common optical fibers are randomly birefringent, and solitons formatting and traveling in them are randomly polarized. However, it is desirable to have solitons with a well-defined polarization. With pump relatively long pulses, the nonlinear effects of modulation instability (MI) and stimulated Raman scattering (SRS) are dominant at the initial stage of the process of supercontinuum (SC) generation; modulation instability results in pulse breakup and formation of short pulses that evolve finally to a bunch of solitons and dispersive waves. We do the research of the polarization of solitons formed by the pulse breakup process by the effect of modulation instability with pump pulses of nanoseconds in standard fiber (SMF-28) with circular birefringence introduced by fiber twist, and the twisted fiber mitigates the random linear birefringence. In this work, we found that polarization ellipticity of solitons is distributed randomly; nevertheless, the average polarization ellipticity is closer to the circular than the polarization ellipticity of the input pulse. In the experimental setup. 200 m of SMF-28 fiber twisted by 6 turns/m was used. We used 1 ns pulse to pump the fiber. The results showed that at circular polarization of the input pulse solitons at the fiber output have polarizations close to the circular, while in the fiber without twist, the soliton polarization was random

Applications of microstructured fibers : supercontinua and novel components

Microstructured fibers are a special class of pure-silica optical fibers. They consist of a silica core, surrounded by a periodic array of air-holes running along the entire length of the fiber. These air-holes permit guidance of light through total-internal reflection. Diameter and spacing of the air-holes determines the optical properties of the fiber, therefore allowing for tailoring of the fiber according to the intended application. This thesis contains novel results on supercontinuum generation in microstructured fibers. Several critical advances have been made in tailoring of the fiber properties in order to further reduce power requirements hindering miniaturization of supercontinuum sources. In particular, the influence of a second zero-dispersion wavelength of the fiber and the input polarization of highly-birefringent fibers have been studied. Furthermore, a novel two-pump scheme allows for efficient generation of broadband blue-light. The generated supercontinua are applied to characterization of absorption and transmission spectra of novel optical components. The high spectral power density of supercontinuum allows for observation of several new excited-state absorption lines of Erbium-doped fibers and characterization of optical components with strong variations in the transmission spectrum. The second part of the thesis deals with applications developed for microstructured fibers. A tapered microstructured fiber is designed for coupling between standard fibers and photonic-crystal waveguides. An elliptical-core microstructured fiber is proposed as an efficient adapter between standard fibers and highly asymmetric waveguides. In addition, a microstructured fiber based optically bistable fiber cavity is applied to all-optical switching. In particular, an optical flip-flop is numerically studied.reviewe

Theory of lossless polarization attraction in telecommunication fibers

In this work, polarization attraction is meant to be the conservative nonlinear effect that transforms any arbitrary input state of polarization (SOP) of an intense optical signal beam fed to a nonlinear medium into approximately one and the same SOP at the output, provided that the medium is driven by a relatively stronger counterpropagating pump beam. Essentially, the combination of the nonlinear medium and the pump beam serves as a lossless polarizer for the signal beam. The degree of polarization of the outcoming signal beam can be close to 100% (90% in our present simulations). With an eye toward the development of such lossless polarizers for fiber optics applications, we theoretically study the polarization attraction effect in the optical fibers that are used in telecommunication links; i.e., randomly birefringent fibers. A generic model for the fiber-based lossless polarizers is derived, and a statistical scheme for the quantification of their performance is proposed

Bidirectional mode-locked fiber ring laser

In modern day world, advances in technology are constantly pushing the limits of improvement in measurement accuracy. With each passing year, government agencies and contract companies increase investment in research of high precision, ultra sensitive, instruments. Over the last decade, advancements in ultrashort time scale optics have moved the field of metrology to the quantic realm. At this new scientific frontier, mode-locked lasers, with ultra sensitive phase measurement capabilities, have been playing an increasingly significant role. Among these highly sophisticated systems, mode-locked fiber lasers have been extensively explored in an unidirectional mode, while bidirectional remains a promising source for applications with considerable space for experimental innovation. In this project, efforts have been made to contribute to the scientific achievements in this area, with the implementation of an innovative approach for bidirectional mode-locking of fiber lasers, as a potential source for intra-cavity phase interferometry. It consists of a passively driven active mechanism that both stabilizes the laser and controls the location of the crossing points of the counter-circulating pulses. For that purpose, the idea has been developed in both a theoretical and experimental level, with the design, construction, and testing of a fiber ring laser scheme capable of producing stable and independent (frequency unlocked) bidirectional pulses. In this manuscript, the description of the research is presented in seven separate chapters. The first chapter provides an overview of the project itself, the advantages of the controlling mechanism and the importance and practical applications of bidirectional mode-locked fiber lasers. Chapter two introduces the theoretical background necessary to understand pulse propagation in a nonlinear, birefringent, gain saturated optical fiber. In chapter three, the passive mechanism behind bidirectional mode-locking is detailed. Chapter four deals with the systems modeling and computer simulation, and chapter five explains the functional aspects of the self-regenerative system used to stabilize and control the laser pulsing. Chapter six describes the experimental setup itself, and presents the measured data results. Finally, chapter seven summarizes all the work done, emphasizing the consequences of the experimental findings, and laying out the foundations for future work.\u2

Vectorial dark dissipative solitons in Kerr resonators

We report the existence of vectorial dark dissipative solitons in optical cavities subject to a coherently injected beam. We assume that the resonator is operating in a normal dispersion regime far from any modulational instability. We show that the vectorial front locking mechanism allows for the stabilisation of dark dissipative structures. These structures differ by their temporal duration and their state of polarization. We characterize them by constructing their heteroclinic snaking bifurcation diagram showing evidence of multistability within a finite range of the control parameter.Comment: \copyright 2021 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserve

Theory of lossless polarization attraction in telecommunication fibers

In this work, polarization attraction is meant to be the conservative nonlinear effect that transforms any arbitrary input state of polarization (SOP) of an intense optical signal beam fed to a nonlinear medium into approximately one and the same SOP at the output, provided that the medium is driven by a relatively stronger counterpropagating pump beam. Essentially, the combination of the nonlinear medium and the pump beam serves as a lossless polarizer for the signal beam. The degree of polarization of the outcoming signal beam can be close to 100% (90% in our present simulations). With an eye toward the development of such lossless polarizers for fiber optics applications, we theoretically study the polarization attraction effect in the optical fibers that are used in telecommunication links; i.e., randomly birefringent fibers. A generic model for the fiber-based lossless polarizers is derived, and a statistical scheme for the quantification of their performance is proposed. © 2010 Optical Society of America.We thank J. Fatome for sending us a preprint of [16] prior to its publication. This work was carried out with support from the Italian Ministry of the University and Research (MIUR) through the PRIN 2008 project “Nonlinear cross-polarization interactions in photonic devices and systems” and the 2009 Italy–Spain bilateral initiative “Nonlinear Optical Systems and Devices” (HI2008-0075). JN acknowledges funding from the Spanish Ministry of Science and Innovation through an FPI fellowship (TEC2008-05791).Peer Reviewe

Vector-soliton collision dynamics in nonlinear optical fibers

We consider the interactions of two identical, orthogonally polarized vector solitons in a nonlinear optical fiber with two polarization directions, described by a coupled pair of nonlinear Schroedinger equations. We study a low-dimensional model system of Hamiltonian ODE derived by Ueda and Kath and also studied by Tan and Yang. We derive a further simplified model which has similar dynamics but is more amenable to analysis. Sufficiently fast solitons move by each other without much interaction, but below a critical velocity the solitons may be captured. In certain bands of initial velocities the solitons are initially captured, but separate after passing each other twice, a phenomenon known as the two-bounce or two-pass resonance. We derive an analytic formula for the critical velocity. Using matched asymptotic expansions for separatrix crossing, we determine the location of these "resonance windows." Numerical simulations of the ODE models show they compare quite well with the asymptotic theory.Comment: 32 pages, submitted to Physical Review