Single-mode optical fiber | EPFL Graph Search

In fiber-optic communication, a single-mode optical fiber (SMF), also known as fundamental- or mono-mode, is an optical fiber designed to carry only a single mode of light - the transverse mode. Modes are the possible solutions of the Helmholtz equation for waves, which is obtained by combining Maxwell's equations and the boundary conditions. These modes define the way the wave travels through space, i.e. how the wave is distributed in space. Waves can have the same mode but have different frequencies. This is the case in single-mode fibers, where we can have waves with different frequencies, but of the same mode, which means that they are distributed in space in the same way, and that gives us a single ray of light. Although the ray travels parallel to the length of the fiber, it is often called transverse mode since its electromagnetic oscillations occur perpendicular (transverse) to the length of the fiber. The 2009 Nobel Prize in Physics was awarded to Charles K. Kao for his theo

High Performance InP-Based Quantum Dash Semiconductor Mode-Locked Lasers for Optical Communications

Anthony Martinez

Several applications are pushing the development of high performance mode-locked lasers: generation of short pulses for extremely high bit rate transmission at 100 Gb/s and beyond, all-optical clock recovery at 40 Gb/s and beyond, generation of millimeter wave signals through mode-beating on a high speed photodiode, optical sampling for analog-to-digital conversion, and generation of wavelength-division-multiplexing channels. This paper will report on new advances in InP-based quantum dash mode-locked lasers, which largely surpass the performance of their bulk or quantum well counterparts in terms of the mode-beating spectral purity and the bandwidth of optical spectrum. In particular, we will describe the quantum dash nanostructures used for the mode-locked lasers and the dependence of the mode-locking properties on detailed quantum dash structures. We will demonstrate that these quantum dash lasers can be actively mode-locked, generating sub-picosecond or picosecond pulses at different repetition frequencies with extremely low timing jitter. They can also be used to achieve all-optical clock recovery, with timing jitter compliant with International Telecommunication Union (ITU) standards even for highly degraded input optical signal-to-noise ratio. Finally, we demonstrate that, owing to the very wide and flat optical spectrum and the low relative-intensity noise level of the mode-locked laser, error-free transmission over 50 km single mode fiber has been achieved for eight wavelength division multiplexing ITU channels at 10 Gb/s with a channel spacing of 100 GHz. (C) 2009 Alcatel-Lucent.

2009

Investigating Novel Optical Fibres for More Advanced Distributed Optical Fibre Sensing

Malak Mohamed Hossameldeen Omar Mohamed Galal

The ever-growing need for distributed optical fibre sensors (DOFS) in numerous fields and applications demands continuous research towards the advancement of the existing sensing systems. The convenience in the field of DOFS lies in the several degrees of freedom that it offers, such as the scattering mechanism, the interrogation technique, the medium for propagation, and the sensing fibre itself. Even though a vast amount of research is oriented towards the fabrication of novel fibres, in many cases the real benefit of such fibres is not really exploited. Therefore, in this thesis, we use and characterise multiple novel optical fibres with the aim of harnessing their full potential by understanding their ultimate strengths and limitations. To that effect, we perform efficient distributed optical fibre sensing by investigating different scattering mechanisms in different scattering media by means of several interrogation techniques. The thesis is divided into two groups of chapters depending on the type of scattering mechanism and medium. In the first group of chapters, we work on the investigation of the most prominent scattering mechanism in silica-core single-mode optical fibres (SMFs), namely Rayleigh scattering. We interrogate a novel reflection-enhanced fibre (REF) based on fibre Bragg gratings using one of the most widely-utilised interrogation techniques for Rayleigh scattering, which is phase-sensitive optical time-domain reflectometry (f-OTDR). So far, no theoretical expression has been presented to relate the most crucial parameters of Rayleigh-based sensing systems. We, therefore, develop a model, as a figure-of-merit for Rayleigh-based systems, addressing this concern, and we confirm it with experimental results. By performing a distributed temperature measurement as a form of comparison between the REF and an SMF, we yield a 6× lower experimental uncertainty for the REF when compared to the SMF, and this lower uncertainty is directly attributed to the 6× higher signal-to-noise ratio that the REF offers. The model as well as the guidelines for utilising REFs to maximum effect will aid the scientific community in better understanding Rayleigh-based sensing systems and employing them more efficiently.The focus then shifts to the most prominent scattering mechanism in a gaseous medium of high density (at 1 atm for instance), namely Brillouin scattering. The analysis is carried out using several novel hollow-core optical fibres particularly anti-resonant fibres (HC-ARFs) which we fill with gas. We demonstrate for the first time to the best of our knowledge a Brillouin gain measurement in gas-filled HC-ARFs and highlight the square dependence of the Brillouin gain on the gas pressure. We perform a comparison between three hollow-core fibres of different dimensions which we fill with two different gases, and we indicate the trade-offs in terms of Brillouin gain coefficients, gas filling times as well as gas pressure limitations. Additionally, we conduct for the first time to our knowledge a distributed temperature measurement using a gas-filled hollow-core conjoined-tube anti-resonant fibre (HC-CAF) and show a higher sensitivity to temperature change which is about 2× greater than the sensitivity of conventional silica fibres. The results indicate the great potential of gas-filled hollow-core fibres and pave the way for researchers to employ them as promising candidates for lasing,sensing and imaging applications.

EPFL2022

Enhanced Signal-Associated Noise in a φ-OTDR System

Malak Mohamed Hossameldeen Omar Mohamed Galal, Suneetha Sebastian, Luc Thévenaz

Owing to their high sensitivity with respect to external measurands, Rayleigh-based distributed optical fiber sensors (DOFS) find their way into applications in many industrial and academic sectors. To further transcend the limit of these sensors in terms of sensing range, low spatial resolution, speed and accuracy of the measurement, improving the signal-to-noise ratio (SNR) of the system plays a pivotal role. Out of the several existing techniques for enhancing the SNR, one such method, solely dedicated to the Rayleigh-based sensors, is through intrinsically increasing the backreflected signal of the fibers. The enhanced backreflected signal provided by such fibers, generally known as reflection-enhanced fibers (REF), is rigorously analyzed in the present work. It is inferred from the analysis that the enhanced signal is essentially accompanied by enhanced signal-dependent noises, which can adversely affect their performance. For instance, when a performance comparison is carried out between the REF and a standard single-mode fiber (SMF) under identical experimental conditions, due to their different intrinsic backreflected signal levels, the two fibers experience dissimilar noise regimes leading to an erroneous estimation of the performance of the former. This necessitates the optimization of the interrogation system and the experimental parameters while employing such fibers for specific sensing applications. Additionally, a distributed temperature measurement is presented by taking advantage of the enhanced SNR of a 100 m long REF exhibiting a sub-mK temperature uncertainty of 0.5 mK at metric spatial resolution yielding a sixfold improvement compared to the 3 mK uncertainty of an SMF.

2022

Investigating Novel Optical Fibres for More Advanced Distributed Optical Fibre Sensing

Malak Mohamed Hossameldeen Omar Mohamed Galal

EPFL2022