D. Szebesta

CW room temperature operation of praseodymium-doped fluorozirconate glass fibre lasers in the blue-green, green and red spectral regions

Abstract We report room temperature, continuous-wave oscillation of Pr3+-doped fluorozirconate fibre lasers at around 491 nm, 520 nm, 605 nm, 635 nm and 715 nm. An output power of 250 mW has been obtained 635 nm for 800 mW of pump power from an argon ion laser operating at 476.5 nm. Tunable operation of the red transitions has been investigated, with output powers in excess of 30 mW being obtained. Q-switched pulses of 75 ns (fwhm) and 20 W peak power at 635 nm have also been generated.

A review of fluoride fibres for optical amplification

Abstract This paper reviews the current world-wide status of fibres based on the fluoride glass system for optical amplification, with particular emphasis on telecom applications. The key feature of fluorozirconate glasses, with the very long wavelength multiphonon edge, is the accompanying relatively low non-radiative decay rate of excited rare-earth dopant ions. This gives unique opportunities compared with the better known oxide glass systems. Amplifiers with high gains have been demonstrated at important wavelengths such as 0.8, 1.3 and 1.5 μm. Improvements to allow the fabrication of more efficient fibres are also discussed.

High output power from an efficient praseodymium-doped fluoride fiber amplifier

A praseodymium doped fluoride fiber amplifier (PDFFA) exhibiting efficient operation in both the large- and the small-signal regimes is described. The amplifier, based on a high NA fluoride fiber, exhibited a maximum small-signal gain of 29 dB and a low-pump small-signal. efficiency of 0.13 dB/mW. In the saturated regime a maximum output power of 212 mW was achieved. In this format, the signal-out versus pump-in characteristic, exhibited a slope efficiency of 30%, representing the most efficient conversion from pump to signal yet reported. Detailed spectral characterization reveals small-signal gain in excess of 20 dB over a wavelength range of almost 50 nm and in excess of 100 mW of saturated output available over a 30-nm wavelength range. >

Quarter-watt output at 1.3 mu m from a praseodymium-doped fluoride fiber amplifier pumped with a diode-pumped Nd:YLF laser

The characteristics of a praseodymium-doped fluoride fiber amplifier (PDFFA) pumped using a high-power diode-pumped Nd:YLF laser operating at 1.047 mu m are described. High small signal gains (29.5 dB) and the highest saturated output yet reported for PDFFAs (250 mW) have been achieved using this commercial diode-pumped source. The spectral characteristics have also been examined in both the large and small signal regimes. It is concluded that there is no significant penalty associated with pumping PDFFAs in the long wavelength wing of their pump band, even though this pump wavelength is almost 40 nm away from the peak of the absorption band.<<ETX>>

High Output Power from an Efficient Praseodymium Doped Fluoride Fibre Amplifier1

A praseodymium doped fluoride fiber amplifier (PDFFA) exhibiting efficient operation in both the large- and the small-signal regimes is described. The amplifier, based on a high NA fluoride fiber, exhibited a maximum small-signal gain of 29 dB and a low-pump small-signal. efficiency of 0.13 dB/mW. In the saturated regime a maximum output power of 212 mW was achieved. In this format, the signal-out versus pump-in characteristic, exhibited a slope efficiency of 30%, representing the most efficient conversion from pump to signal yet reported. Detailed spectral characterization reveals small-signal gain in excess of 20 dB over a wavelength range of almost 50 nm and in excess of 100 mW of saturated output available over a 30-nm wavelength range.<<ETX>>

Quarter Watt Output at 1.3µm From a Praseodymium Doped Fluoride Fibre Amplifier Pumped with a Diode-Pumped Nd:YLF Laser

The fact that most terrestrial optical fibre communications systems installed around the world today operate at 1.3µm means that a practical fibre amplifier operating in this window is of key strategic importance. The primary contender to provide amplification within this window is the praseodymium doped fluoride fibre amplifier(PDFFA). To date high gains (>30dB) and high saturated output powers ( >200mW)[1] have been achieved but have required the use of large- frame ion lasers as primary optical pump sources. The main difficulty in using semiconductor laser diodes as a pump source is the very high level of pump power needed in this comparatively low efficiency system. One approach that has proved successful in erbium doped fibre power amplifiers is to use a solid state crystal laser to convert the large, but spatially incoherent output from 800nm semiconductor laser diode bars into a TEM00 output which can then be efficiently coupled into the doped fibre[2].

Noise and crosstalk characteristics of a praseodymium-doped fluoride fiber amplifier

We report the noise and gain characteristics of a 1.3 micrometers PDFFA, in both the small and large signal regime. The small-signal noise performance shows a value of 5 dB at 1.3 micrometers , reducing to < 4 dB for wavelengths < 1.28 micrometers , and increasing to > 7 dB for wavelengths > 1.32 micrometers . No noise penalty has been observed in saturation for output powers as high as + 17 dBm, corresponding to 10 dB gain compression. Crosstalk measurements show a 3 dB rollover frequency of 6 kHz.

Prospects for ultra-low-loss fluoride fibres at BTRL

Abstract An evaluation of the loss mechanisms operating in fluoride fibres indicates that a minimum loss of 0.035 dB/km could be achieved. However, the current minimum loss reached at BTRL is 0.65 dB/km, measured over 110 m of fibre. The paper concentrates on three stages involved in fibre fabrication, including raw materials, purification, and preform fabrication. In each case, particular attention is paid to the influence on absorption and scatter loss. In addition, the prospects for scaling up to produce long lengths of monomode fibre is discussed.

Rare-earth-doped fluoride fibers for optical amplification (Invited Paper)

Rare earth-doped fluorozirconate fibres show potential as optical amplifiers from the visible to the mid IR. This paper reviews the current status of their application in telecommunications, concentrating on Tm and Er-dopants for the 1st window and Nd and Pr-dopants for the 2nd window. A 1300 nm system operating at 2.5 Gbits/s using a Pr-doped fibre amplifier is described.

Characterization of a first window amplifier using a thulium-doped fluoride fiber

A fully connectorized diode laser pumped first window amplifier has been constructed, for the first time, around a thulium doped fluoride fiber. For a 780/806 nm combination of pump and signal wavelengths intrinsic small signal gains of 25 - 26 dB and gain efficiencies of 2.4 dB/mW have been achieved. In addition output powers approaching +13 dBm from the doped fiber were possible for launched pump powers of 31 mW, which corresponds to a pump to signal conversion efficiency of around 64%. Minimum noise figures of 4 - 5 dB have been achieved with characteristics which mirror the output power performance. The 3 dB gain bandwidth for this transition has been measured at 9 - 10 nm for small signals, increasing to better than 15 nm under signal saturation conditions.