Birefringence And Bragg Grating Control In Femtosecond Laser Written Optical Circuits

In this thesis, femtosecond lasers are explored for the fabrication of fiber Bragg gratings (FBGs) in suspended core fibers (SCFs) as well as direct writing of integrated optical devices in bulk fused silica glass. The FBGs fabricated in suspended core fibers with different core geometries were demonstrated with femtosecond laser exposure through a Talbot interferometer. In this case, the use of a femtosecond laser system was crucial as it eliminates the need for the use of photosensitive fibers, which is the case for SCFs, while the Talbot interferometry setup provided flexibility in the definition of the grating periodicity, while simultaneously protecting the optical components used in the fabrication process from the high intensities reached during exposure in the proximity of the fibers. These Bragg gratings were employed to show simultaneous strain and temperature sensing. Using a femtosecond laser direct writing system, novel point-by-point fabrication arrangements, with detailed attention to the computer controlled laser beam modulation, were developed in order to correctly introduce modulation of the refractive index profile during the waveguide fabrication process. This technique enabled the development of phase and frequency control required for advanced Bragg grating waveguide (BGW) fabrication and arbitrary spectral shaping. Procedures were demonstrated for the fabrication of chirped and phased shifted BGWs for applications in temporal pulse shaping and spectral shaping that showed significantly improved feature resolutions for sensing applications. The BGWs were used as a practical sensitive tool to determine and study the waveguide birefringence inherent to the nonlinear absorption processes typical of femtosecond laser-material interaction. The control of form and stress birefringence was developed in order to accomplish the fabrication of integrated optical components for polarization control, like guided wave retarders and polarization beam splitters. Tuning of this waveguide birefringence was achieved by the introduction of stress inducing laser modification tracks that enabled the ability to both enhance or reduce the inherent birefringence. Characterization techniques were developed for the absolute determination of the birefringence based on BGWs spectrum splitting, together with crossed polarizer measurements, while novel data analysis procedures were demonstrated for the study of polarization dependent and polarization independent directional couplers with the introduction of a polarization splitting ratio which is wavelength and coupling length dependent. All of the improvements made in the understanding of waveguide birefringence control provided increased flexibility to simultaneously fabricate low polarization mode dispersion circuits, as well as more efficient and compact polarization dependent devices. The polarization aspects detailed here, together with the point-by-point fabrication system, may be further developed in the future towards the fabrication of more complex integrated devices that combine spectral, temporal, and polarization control, all achievable with the same femtosecond laser writing system. These flexible processing techniques will open new directions for writing additional functionalities in optical circuits with more compact three-dimensional geometries.

Quantum information science has found great experimental success by exploiting single photons. To date, however, the majority of quantum optical experiments use large-scale (bulk) optical elements bolted down to an optical bench, an approach that ultimately limits the complexity and stability of the quantum circuits required for quantum science and technology. The realization of complex optical schemes involving large numbers of elements requires the introduction of waveguide technology to achieve the desired scalability, stability and miniaturization of the device. This thesis reports on surprising findings in the field of integrated devices for quantum information. Here the polarization of the photon is shown to offer a suitable degree of freedom for encoding quantum information in integrated systems. The most important results concern: the quantum interference of polarization entangled photons in an on-chip directional coupler; the realization of a Controlled-NOT (CNOT) gate operating with polarization qubits; the realization of a quantum walk of bosons and fermions in an ordered optical lattice and the quantum simulation of Anderson localization of bosons and fermions simulated by polarization entangled photons in a disordered quantum walk. The findings presented in this thesis represent an important step towards the integration of a complete quantum photonic experiment in a chip.

This book provides a comprehensive overview of the theoretical concepts and experimental applications of planar waveguides and other confined geometries, such as optical fibres. Covering a broad array of advanced topics, it begins with a sophisticated discussion of planar waveguide theory, and covers subjects including efficient production of planar waveguides, materials selection, nonlinear effects, and applications including species analytics down to single-molecule identification, and thermo-optical switching using planar waveguides. Written by specialists in the techniques and applications covered, this book will be a useful resource for advanced graduate students and researchers studying planar waveguides and optical fibers.

Fiber Bragg gratings are flexible, cost-effective and highly efficient, with a vast range of potential applications. This timely new work provides a comprehensive description of the principles and practical applications of this latest technology, which has the potential to revolutionize telecommunications and significantly impact optical fiber sensing. Here the authors explain the underlying physics and practical aspects in a clear and unambiguous manner.

Femtosecond laser micromachining of transparent material is a powerful and versatile technology. In fact, it can be applied to several materials. It is a maskless technology that allows rapid device prototyping, has intrinsic three-dimensional capabilities and can produce both photonic and microfluidic devices. For these reasons it is ideally suited for the fabrication of complex microsystems with unprecedented functionalities. The book is mainly focused on micromachining of transparent materials which, due to the nonlinear absorption mechanism of ultrashort pulses, allows unique three-dimensional capabilities and can be exploited for the fabrication of complex microsystems with unprecedented functionalities.This book presents an overview of the state of the art of this rapidly emerging topic with contributions from leading experts in the field, ranging from principles of nonlinear material modification to fabrication techniques and applications to photonics and optofluidics.

This is the first book dedicated to wavelength filters for fibre optics. It provides a comprehensive account of the principles and applications of such filters, including their technological realizations. It explains the relevant performance parameters, the particular advantages and shortcomings of the various concepts and components, and the preferred applications. There is also in-depth information on the characteristics of commercially available devices.

This book attempts to give a discussion of the physics and current and potential applications of the self-focusing of an intense femtosecond laser pulse in a tra- parent medium. Although self-focusing is an old subject of nonlinear optics, the consequence of self-focusing of intense femtosecond laser pulses is totally new and unexpected. Thus, new phenomena are observed, such as long range lam- tation, intensity clamping, white light laser pulse, self-spatial ltering, self-group phase locking, self-pulse compression, clean nonlinear uorescence, and so on. Long range propagation at high intensity, which is seemingly against the law of diffraction, is probably one of the most exciting consequences of this new sub- eld of nonlinear optics. Because the intensity inside the lament core is high, new ways of doing nonlinear optics inside the lament become possible. We call this lamentation nonlinear optics. We shall describe the generation of pulses at other wavelengths in the visible and ultraviolet (UV) starting from the near infrared pump pulse at 800 nm through four-wave-mixing and third harmonic generation, all in gases. Remotely sensing uorescence from the fragments of chemical and biological agents in all forms, gaseous, aerosol or solid, inside the laments in air is demonstrated in the labo- tory. The results will be shown in the last part of the book. Through analyzing the uorescence of gas molecules inside the lament, an unexpected physical process pertaining to the interaction of synchrotron radiation with molecules is observed.