Development of Low Noise-Broadband Raman Amplification Systems Based on Photonic Crystal Fibers for High Capacity DWDM Networks

The increased demand from IP traffic, video application and cell backhaul has placed fiber routes under severe stains. The high demands for large bandwidth from enormous numbers from cell sites on a network made the capacity of yesterday’s networks not adequate for today’s bandwidth demand. Carries considered Dense Wavelength Division Multiplexing (DWDM) network to overcome this issue. Recently, there has been growing interest in fiber Raman amplifiers due to their capability to upgrade the wavelength-division-multiplexing bandwidth, arbitrary gain bandwidth. In addition, photonic crystal fibers have been widely modeled, studied, and fabricated due to their peculiar properties that cannot be achieved with conventional fibers. The focus of this thesis is to develop a low-noise broadband Raman amplification system based on photonic crystal Fiber that can be implemented in high capacity DWDM network successfully. The design a module of photonic crystal fiber Raman amplifier is based on the knowledge of the fiber cross-sectional characteristics i.e. the geometric parameters and the Germania concentration in the dope area. The module allows to study different air-hole dimension and disposition, with or without a central doped area. In addition the design integrates distributed Raman amplifier and nonlinear optical loop mirror to improve the signal to noise ratio and overall gain in large capacity DWDM network

Limits of performance of chirped- pulse phase-sensitive OTDR

Distributed acoustic sensing is an emerging field of research which aims to develop methods capable of using a single optical fiber as a long, dense, and high-sensitivity sensor array. Currently, the most promising implementations measure the interference of Rayleigh backscattered light, obtained by probing the fiber with light from a source of high coherence. These methods are known as Phase-sensitive Optical Time-Domain Reflectometers (φOTDR), and are currently undergoing a period of active research and development, both academically and industrially. One of its variants, known as the Chirped-Pulse φOTDR (CP-φOTDR), was developed in 2016. This technique has proven to be remarkably sensitive to strain and temperature, with an attractively simple implementation. In this thesis, we delve into the intricacies of this technique, probing its fundamental limits and addressing current limitations. We discuss the implications of estimation on the performance statistics, the impact of different noise sources and the origin of cross-talk between independent measured positions. In doing so, we also propose methods to reach the current fundamental limitations, and overcome the upper bound of measurable perturbations. We then demonstrate new potential applications of the technique: in seismology, by exploiting the high spatial density of measurements for array signal processing; in the fast characterization of linear birefringence in standard single-mode fibers; and on the measurement of sound pressure waves, by using a special flat cable structure to embed the fiber under test. Finally, we summarize and comment on the aforementioned achievements, proposing some open lines of research that may originate from these results.Distributed acoustic sensing is an emerging field of research which aims to develop methods capable of using a single optical fiber as a long, dense, and highsensitivity sensor array. Currently, the most promising implementations measure the interference of Rayleigh backscattered light, obtained by probing the fiber with light from a source of high coherence. These methods are known as Phase-sensitive Optical Time-Domain Reflectometers (φOTDR), and are currently undergoing a period of active research and development, both academically and industrially. One of its variants, known as the Chirped- Pulse φOTDR (CP-φOTDR), was developed in 2016. This technique has proven to be remarkably sensitive to strain and temperature, with an attractively simple implementation. In this thesis, we delve into the intricacies of this technique, probing its fundamental limits and addressing current limitations. We discuss the implications of estimation on the performance statistics, the impact of different noise sources and the origin of cross-talk between independent measured positions. In doing so, we also propose methods to reach the current fundamental limitations, and overcome the upper bound of measurable perturbations. We then demonstrate new potential applications of the technique: in seismology, by exploiting the high spatial density of measurements for array signal processing; in the fast characterization of linear birefringence in standard single-mode fibers; and on the measurement of sound pressure waves, by using a special flat cable structure to embed the fiber under test. Finally, we summarize and comment on the aforementioned achievements, proposing some open lines of research that may originate from these results

Low threshold random lasing from phase separated optical fibers.

In this thesis, a low threshold novel random fiber laser, integrating a passive optical fiber with a phase separated aluminosilicate core – silica cladding as the feedback medium, is proposed and presented. The core exhibits greatly enhanced Rayleigh scattering, therefore requiring a significantly reduced length of scattering fiber (4 m) for lasing. The enhanced Rayleigh scattering was verified through measurements and a new figure of merit called effective power reflectivity was also developed to quantify random feedback. With a Yb-doped fiber as the gain medium, the fiber laser operates at 1050 nm with low threshold power, with a tractable lasing wavelength and maximum linewidth, and possesses an output that can be amplified through conventional means. Furthermore, the laser was found to have a high degree of spatial coherence, spectral broadening with increasing input power, and temporal spectral variation. The random lasing action was confirmed both by the use of RF beat spectra measurements and the trends in the Lévy exponent α obtained from the statistics of spectral intensity variation. Cutback experiments carried out shed light on the evolution of lasing behavior with P-SOF length and the impact of feedback on the lasing behavior. The minimum length of P-SOF required for maximum Rayleigh-distributed feedback was also determined to be ~ 2.5 m. This facile setup and results herein pave the way for further study and applications based on low threshold and compact random fiber lasers