1,720,996 research outputs found
2 x 2 optical switching fibre polarisation switch and polarisation controller
No full textA liquid crystal based optical fibre polarisation switch is demonstrated. Switching voltages of about 3V were used and switching speeds of a few Hz obtained. In addition, the device may be used as the basis for a polarisation controller in coherent optical detection schemes
Fibre lasers and amplifiers
No full textA brief review is given of the current status of research in the field of rare-earth doped fibre lasers and amplifiers. The merits of making such devices in fibre form are discussed, together with their potential applications
Q-switching in fibre lasers
No full textThis chapter is aimed at providing a detailed description of the techniques involved in Q-switching fibre lasers. In view of the potential of these sources, particular emphasis is placed on diode-pumped operation. In addition, the present status of this type of laser is reviewed, current limitations discussed and possible future progress outlined.There are many applications where it is preferable to operate lasers in a pulsed mode. For example, as sources for distributed sensing and for range finding. Diode lasers, although convenient and compact, are inherently poor at this due to the low damage thresholds of semiconductor materials. Glass on the other hand can withstand high optical intensities (typically x 103) without damage. A compromise is thus to pump a fibre-laser with a laser diode. In this way a compact, all solid-state device can still be made. Direct modulation of the fibre-laser in the form of Q-switching allows significant peak powers and short duration pulses to be generated
Highly tunable and efficient diode pumped operation of Tm<sup>3+</sup> doped fibre lasers
No full textThe characteristics of a Tm3+ doped fibre laser pumped by a laser diode are reported. Operating at a wavelength of 1.94µm the laser had a threshold of 4.4mW, a launched power slope efficiency of 17% and 1mW output power. Measurements on the tuning rang of Tm3+ are presented and lasing is found to be possible from 1.65-2.0µm, the specific range depending on the fibre type. The largest range for a single laser was 300nm
Detailed characterization of Nd<sup>3+</sup> doped SiO<sub>2</sub> - GeO<sub>2</sub> glass fibre lasers
No full textSeveral basic parameters of Nd3+ in a SiO2 - GeO2 glass fibre have been determined. The stimulated emission cross-section for the 4F3/2 to 4I11/2 transition has been evaluated experimentally both by a laser technique and spectroscopically. Comparison is made between the two methods and a nonradiative decay process inferred. The efficiency of the 800nm pump band was determined from measurements of laser slope efficiencies. Branching ratios for the different fluorescent bands have been measured and cavity losses determined
Highly efficient Er<sup>3+</sup> doped fibre lasers pumped at 980nm
No full textThe Er3+ fibre laser operates at a wavelength between 1.5 and 1.6 microns and is thus of interest for both telecommunication purposes and, since it can be Q-switched to give high pulse powers, in eye-safe range-finding systems. To date, ~810nm has been the preferred pump wavelength owing to the ready availability of laser diodes. However, the 810nm pump band of Er3+ suffers from the serious disadvantage of pump excited-state absorption (ESA). As a result much of the pump light is wasted in exciting ions from the metastable level to a still higher energy level, rather than producing stimulated emission. This is reflected in the best reported slope efficiency of 17%, obtained for Er3+ sensitized with Yb3+
Q-switching in fibre-lasers
No full textOne of the most attractive features of fibre lasers is their ability to produce significant pulse powers when Q-switched. Potential applications for such lasers include non-linear switching, OTDR measurements, materials processing and range-finding. We have, already demonstrated 100W:15ns pulses from a diode pumped Nd3+ fibre-laser and have obtained 15W:70ns at 1.56µm with a diode pumped Er3+/Yb3+ system. Pulses of 8W:155ns have been obtained in the visible from a Sm3+ fibre-laser (although this required an Ar+ pump laser). Considerably higher powers than these are predicted for diode-pumped lasers. In particular, theoretical analysis shows that the Er3+ laser is capable of producing pulses in excess of 1kW. To date the performance of the Q-switched fibre laser has been limited by the modulator used to effect the Q-switching. problems involved in Q-switching will be discussed and we will look at ways of overcoming them. Theoretical modelling allows us to predict many of the properties required of a modulator and the results of such calculations will be presented. In addition, Q-switched pulses are seen experimentally to be modulated at the round trip frequency - for some applications this effect may be very important and its origin will be discussed
Absorption and emission cross-section of Er<sup>3+</sup> doped silica fibres
No full textA detailed set of measurements is presented on determining the emission and absorption cross sections of Er3+ doped fibers for the 4 I 13/2 to 4 I 15/2 transition. Two techniques are employed: the Füchtbauer-Ladenberg analysis, based on spectroscopic data; and a more direct technique involving optical saturation of the transition. The cross sections, and in particular their ratio, are significantly different for the two techniques. Possible reasons for this are discussed, and we conclude that the Füchtbauer-Ladenberg approach is inappropriate in this situation
High power ytterbium (Yb<sup>3+</sup>)-doped fibre laser operating in the 1.12µm region
No full textResults are presented for high power (>0.5W) Yb3+ fibre laser operating at a wavelength of around 1120nm pumped either by Nd:YAG (1.064µm) or Nd:YLF (1.047µm) lasers. The use of this laser as a single-wavelength pump for a Tm3+ ZBLAN upconversion fiber laser is also demonstrated
High-power sensitised erbium optical fibre amplifier
No full textMuch of the recent discussion regarding the systems deployment of erbium-doped fiber optical amplifiers has focussed on the pump source. Ideally, when choosing which pump band to use, one desires high efficiency, quantum limited noise performance, and the availability of a long-lived semiconductor based pump source. Initial experiments focussed on the 800 nm pump band of erbium due to its coincidence with commercially-available high-power AlGaAs diode lasers. Unfortunately, the presence of a strong excited state absorption (ESA) in this pump band severely limits the gain performance and degrades the amplifier noise figure. The pump wavelengths of 980 and 1480 nm have their advantages and disadvantages with regards to gain efficiency, amplifier noise figure and overall system advantages. However, there still remain questions with regard to pump laser reliability at both of these wavelengths. We describe here the operation of the sensitized erbium (Er3+/Yb3+) optical amplifier using a diode-pumped Nd3+ laser (DPL) as the pump source at 1064 nm. This approach indirectly utilizes highly non-diffraction limited high-power AlGaAs diode laser arrays and is easily power scalable, a notable advantage for a power optical amplifier. This pumping scheme operates without any noticeable ESA and exhibits a near quantum-limited noise figure. Previous work has focussed on the use of frequency-doubled DPL's at 532 nm as a pump source for erbium fiber amplifiers. In terms of overall efficiency, the utilization of the Nd3+ DPL fundamental as the pump source is a significant improvement and avoids the operational complexities of the nonlinear frequency-doubling process
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