1,720,980 research outputs found
A method of increasing the range of 1.65µm long range OTDR system based on Raman amplification
Full text linkOptical Time Domain Reflectometry (OTDR) is an efficient and reliable technique for locating fibre faults and determining the loss distribution along the fibre. An OTDR system operating at a wavelength of 1.65µm is more sensitive to fibre macro-bending and micro-bending losses than those at the region of 1.3/1.55µm, thus providing an early detection of system faults and reducing the risk of total system failure. The current limitation in the maximum dynamic range of OTDR systems is due to the low power of 1.65µm laser diodes. Raman amplification has been employed to amplify a 1.66µm laser diode pulse by 24.8dB before launching it down the end of a sensing fibre. We propose a novel method of increasing the dynamic range of a 1.65µm OTDR system through the use of delayed Raman amplification within the sensing fibre. By delaying the pump pulse with respect to the OTDR pulse, amplification of the latter may be delayed by tens of kilometres
Diode pumped high power simultaneously Q-switched and self mode-locked erbium doped fibre laser
No full textWe report for the first time a diode pumped electro-optically Q-switched and mode-locked Erbium doped fibre laser. Simultaneous Q-switching and mode-locking produces 4 ns pulses of 540 Watts peak power in a 20 ns Q-switched envelope
Novel optical fibre distributed temperature sensor based on the Landau-Placzek ratio
No full textWe report a compact, portable optical fiber distributed temperature sensor based on spontaneous Brillouin backscattered light. The ratio of the Rayleigh and Brillouin backscattered light is known as the Landau-Placzek ratio and gives a measure of temperature. To measure the Landau-Placzek ratio the Rayleigh and Brillouin signals that are separated by a frequency of approximately 10 GHz have to be spectrally resolved. A narrow linewidth Q-switched fiber laser and an inexpensive low loss in-fiber Mach-Zehnder interferometer were developed for this purpose
Narrow linewidth, Q-switched erbium doped fibre laser
No full textWe report a narrow linewidth, diode pumped, high power Q-switched Erbium doped fibre laser for the application of Landau-Placzek temperature sensing. An output coupler consisting of an in-fibre Bragg grating enables narrow linewidth operation. A linewidth of 1.3 GHz is reported with a peak power of 100 Watts and a pulse width of 20 ns at a repetition rate of 200 Hz
1.65µm long range distributed testing of optical fibres using a compact Q-switched fibre laser
No full textA simple Q-switched Erbium-doped fibre laser operating at 1.5µm forms the basis of a high peak power pulsed source at 1.65µm. Applications include monitoring of active telecommunication links, loss measurement at 1.65µm and distributed temperature sensing
Distributed optical fibre sensing at 1.65µm using a Q-switched fibre laser
No full textIt is becoming increasingly vital to monitor telecommunication links during operation and installation process. By using a high peak power source and the optical time domain reflectometry (OTDR) technique operating at the wavelength region of 1.6µm, it is possible to monitor conventional C-band Erbium-doped fibre amplifier (EDFA) systems whilst transmitting data, and to characterise losses at the higher wavelengths of extended bandwidth systems designed around the L-band EDFA systems. We describe a compact design based on Raman shifting the output of an Erbium-doped Q-switched fibre laser operating at 1.5µm for obtaining a pulsed source at 1.6µm. This source was used for an OTDR measurement and also as a source for a 1.65µm Raman-based distributed temperature sensor, in contrast to distributed temperature sensors normally operating at 1.5µm. OTDR measurements at 1.65µm provide more accurate determination of macro and micro-bend losses than at 1.5µm as such losses increase with wavelength. The temperature measurement extracted from the anti-Stokes Raman signal at 1.5µm was made over a sensing range of 10.1km, with a spatial resolution of 10m and temperature resolution of 4°C
Technique for measuring distributed temperature with 35cm spatial resolution utilising the Landau-Placzek ratio
No full textThe authors report a spontaneous Brillouin-based distributed temperature sensing (DTS) system using a short-pulsewidth laser source at 1.5µm, which permits measurements down to an accuracy of 35cm spatial resolution. This DTS system has been demonstrated utilizing conventional single-mode silica fibers for a range of 1km from a single-ended source, and a temperature resolution of 4.3°C was achieve
An all-fiber system for simultaneous interrogation of distributed strain and temperature sensing using spontaneous Brillouin scattering
No full textWe demonstrate a low-loss, long-range, single-ended distributed optical fiber sensor to measure both temperature and strain simultaneously and unambiguously. By using the Landau-Placzek ratio and cascaded Mach-Zehnder interferometric filters, we measure both the intensity and the frequency changes in the Brillouin backscattered signal. Strain and temperature measurements can then be independently resolved. A temperature resolution of 4°C, a strain resolution of 290 µ.epsilon, and a spatial resolution of 10m have been achieved for a sensing length of 15 km
A high power Q-switched erbium fibre laser producing 50mJ pulses
No full textQ-switched fibre lasers have been extensively researched since the first development in 1986. Recent numerical modeling has suggested that two methods can be used to improve the energy storage per unit length within a fibre. One technique is to increase the Erbium concentration which will however, lead to clustering of Erbium ions which decreases the efficiency of the fibre through co-operative up-conversion. The method which we will present is based on using a novel fibre geometry using a large mode field area. Single-mode operation is maintained by decreasing the N.A. of the fibre
A stable narrow linewidth Q-switched Er-doped fibre laser
No full textQ-switched pulses of stable linewidths less than 60MHz were generated for repetition rates up to 1kHz, using low doped erbium fibre as a saturable absorber combined with CW prelase technique
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