M.C. Farries

Bio: M.C. Farries is an academic researcher from University of Southampton. The author has contributed to research in topics: Optical fiber & Fiber laser. The author has an hindex of 14, co-authored 21 publications receiving 714 citations.

Efficient pump wavelengths of erbium-doped fibre optical amplifier

Abstract: By choosing pump wavelengths at which excited state absorption does not occur, efficient high gain operation of erbium-doped fibre amplifiers is possible. Practical pump wavelengths of 532nm and 980nm are identified as optimal, giving gains as high as 1.35 dB/mW and 2.2 dB/mW of pump at the two wavelengths, respectively.

Second harmonic generation in an optical fibre by self written x(2) grating

Abstract: Measurements of the effective length and wavelength selectivity of a second order susceptibility grating written into a fibre are reported. A weak non-phase matched second harmonic signal at 532nm is generated by the allowed quadrupole polarisation. This signal initiates the self-writing of an axially periodic pattern of defect centres in the fibre which lead to the growth of a chi (2) grating. Phase-matching is achieved automatically because the enhanced chi (2) is written periodically into the fibre at spatial locations where the second harmonic signal is the highest and is in phase with the pump. One particular chi (2) grating extends over 12cm of fibre and has a bandwidth of 0.24nm

Distributed temperature sensor using Nd3+ -doped optical fibre

Abstract: We report the measurement of temperature distribution with an Nd3+-doped multimode optical fibre. By exploiting the temperature-sensitive absorption bands of the doped-glass core, temperature was measured to an accuracy of 2°C over the range -50°C to +100°C. A spatial resolution of 15m over a fibre length of 140m was obtained.

Generation of permanent optically induced second-order nonlinearities in optical fibers by poling.

Abstract: It is shown that large permanent enhancements in second-order optical nonlinearity can be induced in germanosilicate fibers (both pure and codoped with phosphorus) by application of a transverse dc electric poling field in the presence of high-intensity light. The macroscopic inversion symmetry of the core material is broken by the excitation and alignment of defect centers. Significant frequency doubling results despite the absence of phase matching. The saturation (with both increasing dc field and increasing intensity) of this effect is investigated.

Samarium3+-doped glass laser operating at 651 nm

Abstract: Laser emission has been observed in a samarium3+-doped silica optical fibre in a Fabry-Perot-type laser cavity. The emission is centred on 651 nm and corresponds to stimulated transitions from the 4G5/2 level to the 6H9/2 level. The fluorescence and absorption associated with the metastable level are seen to be unusually narrow (3nm FWHM) for a trivalent rare earth in a disordered glass structure. The laser has operated in CW and Q-switched modes when pumped with 488 nm light at room temperature.

Quasi-phase-matched second harmonic generation: tuning and tolerances

Abstract: The theory of quasi-phase-matched second-harmonic generation is presented in both the space domain and the wave vector mismatch domain. Departures from ideal quasi-phase matching in periodicity, wavelength, angle of propagation, and temperature are examined to determine the tuning properties and acceptance bandwidths for second-harmonic generation in periodic structures. Numerical examples are tabulated for periodically poled lithium niobate. Various types of errors in the periodicity of these structures are then analyzed to find their effects on the conversion efficiency and on the shape of the tuning curve. This analysis is useful for establishing fabrication tolerances for practical quasi-phase-matched devices. A method of designing structures having desired phase-matching tuning curve shapes is also described. The method makes use of varying domain lengths to establish a varying effective nonlinear coefficient along the interaction length. >

Luminescent probes and sensors for temperature.

Abstract: Temperature (T) is probably the most fundamental parameter in all kinds of science. Respective sensors are widely used in daily life. Besides conventional thermometers, optical sensors are considered to be attractive alternatives for sensing and on-line monitoring of T. This Review article focuses on all kinds of luminescent probes and sensors for measurement of T, and summarizes the recent progress in their design and application formats. The introduction covers the importance of optical probes for T, the origin of their T-dependent spectra, and the various detection modes. This is followed by a survey on (a) molecular probes, (b) nanomaterials, and (c) bulk materials for sensing T. This section will be completed by a discussion of (d) polymeric matrices for immobilizing T-sensitive probes and (e) an overview of the various application formats of T-sensors. The review ends with a discussion on the prospects, challenges, and new directions in the design of optical T-sensitive probes and sensors.

Recent progress in distributed fiber optic sensors.

Abstract: Rayleigh, Brillouin and Raman scatterings in fibers result from the interaction of photons with local material characteristic features like density, temperature and strain. For example an acoustic/mechanical wave generates a dynamic density variation; such a variation may be affected by local temperature, strain, vibration and birefringence. By detecting changes in the amplitude, frequency and phase of light scattered along a fiber, one can realize a distributed fiber sensor for measuring localized temperature, strain, vibration and birefringence over lengths ranging from meters to one hundred kilometers. Such a measurement can be made in the time domain or frequency domain to resolve location information. With coherent detection of the scattered light one can observe changes in birefringence and beat length for fibers and devices. The progress on state of the art technology for sensing performance, in terms of spatial resolution and limitations on sensing length is reviewed. These distributed sensors can be used for disaster prevention in the civil structural monitoring of pipelines, bridges, dams and railroads. A sensor with centimeter spatial resolution and high precision measurement of temperature, strain, vibration and birefringence can find applications in aerospace smart structures, material processing, and the characterization of optical materials and devices.

Fiber optic sensor technology: an overview

Abstract: This work presents an overview of progress and developments in the field of fiber optic sensor technology, highlighting the major issues underpinning recent research and illustrating a number of important applications and key areas of effective fiber optic sensor development.

Large second-order nonlinearity in poled fused silica.

Abstract: A large second-order nonlinearity [ χ(2)~1 pm/V~0.2 χ22(2) for LiNbO3] is induced in the near-surface (~4 μm) region of commercial fused-silica optical flats by a temperature (250–325°C) and electric-field (E ~ 5 × 104 V/cm) poling process. Once formed, the nonlinearity, which is roughly 103–104 times larger than that found in fiber second-harmonic experiments, is extremely stable at room temperature and laboratory ambient. The nonlinearity can be cycled by repeated depoling (temperature only) and repoling (temperature and electric field) processes without history effects. Possible mechanisms, including nonlinear moieties and electric-field-induced second-order nonlinearities, are discussed.