1,721,023 research outputs found
Spectroscopic properties of Nd<sup>3+</sup> in fluoroaluminate glasses for an efficient 1.3 µm optical amplifier
No full textIn the majority of Nd3+-doped glasses the amplifier gain is shifted out of the second telecom window (1.3 µm) as a result of long-wavelength emission and signal excited-state absorption (ESA). In this paper we describe new fluoroaluminate glasses developed as hosts for the 1.3 µm Nd3+-doped fibre amplifier. Nd3+ emission peaks at 1310–1317 nm were demonstrated in glasses. Gain in the 1310–1320 nm region was measured in unclad fibres, with evidence of reduced ESA. The paper also examines thermal and viscous properties of the core and cladding glasses for preform and fibre fabrication
Progress in the development of efficient 1.3µm fibre amplifiers
No full textProgress in the development of the elusive pump-efficient 1.3µm optical fibre amplifier is reviewed. Four possibilities exist, all in non-silica glass. At present, there is no clear winning technology, but the availability of high-power pump diodes could favour the more conventional approaches. The telecommunications industry is currently undergoing a rapid transformation towards all-optical systems and networks. The upgrade to all-optical operation is well advanced in the long-haul 1.5µm networks which take advantage of the highly successful Er3+-doped optical fibre amplifier (EDFA) introduced in 1987 [1]. The result is a global optical amplifier market expected to be worth nearly £1 billion pa by 2004, despite the fact that EDFAs are not appropriate for operation at the 1.3µm zero-dispersion window that dominates existing terrestrial fibre systems. An optical amplifier at 1.3µm is required to upgrade presently installed optical links and to promote a balanced evolution of the optical network and to support the expected traffic requirements needed for interactive video and multimedia services. It is worth noting that with development in optical fibre manufacturing, there is now a need for amplifiers spanning the full transmission window from 1.2µm to 1.7µm. The research in fibre amplifiers at 1.3µm encompasses study of active ions with suitable transitions like rare-earth ions Pr3+, Dy3+ and Nd3+ in different host glasses such as in fluorides, chlorides and chalcogenides. The first generation of 1.3µm praseodymium-doped fluoride fibre amplifiers (PDFFAs) based on Pr3+-doped ZBLAN is already available on the market. It is characterised by a gain peak at 1300nm and 3dB bandwidth of 25-40nm depending on input power.[2] The ground state absorption (GSA) to the metastable state is broad, 950-1060nm with line centre at 1010nm, allowing use of different pump wavelengths. However, the absorption is weak and a PDFFA fibre is normally at least 10 metres long. The PDFFA's biggest limitation is in pump efficiency owing to a high nonradiative decay rate from the metastable to an intermediate level which dominates the 1.3µm emission. A 30dB gain amplifier requires 300mW pump power around 1017nm. This cannot be easily achieved with a single semiconductor pump laser. For this reason, PDFFA devices have been pumped by expensive Nd:YLF lasers at 1047nm, away from the peak absorption wavelength, and the pump requirement is further increased to 600mW levels.[3] The development of sufficiently intense semiconductor lasers for peak absorption LD pumping of PDFFAs will encourage the realisation of the second generation of such amplifiers based on lower phonon energy glasses than ZBLAN, such as Pb-Ga-In (PGI) fluoride glass, with thermal stability against crystallisation and a fibre loss similar to stable ZrF4-based glasses. The amplifier pump efficiency improves dramatically when the quantum efficiency is increased by placing Pr3+ in very-low phonon-energy glass to reduce multiphonon quenching. Sulphide-based chalcogenide glasses have phonon energies of ~400cm in ZBLAN, the radiative quantum efficiency can be greater than 50% (c.f. ~4% in ZBLAN, ~7% in PGI). Gain measurement results using Ga-Na-S fibre report a peak net gain at 1.34µm and a gain coefficient (bi-directional pumping configuration) of 0.81dB/mW, compared to the best PGI fluoride fibre of 0.36dB/mW. The amplifier is thus able to deliver 30dB net gain with less than 100mW of 1017nm pump power.[5] However, the biggest drawback is that the gain peak is red-shifted in a sulphide host to about 1.34µm, so that the gain is well down at 1310nm, the preferred operating wavelength. Dysprosium in low phonon energy glasses such as sulphides and chlorides has a suitable transition at 1.3µm.[6,7] The emission is centered at 1310nm with FWHM of 40nm and the quantum efficiency is expected to be around 70%. However, Dy3+ exhibits a significant GSA, which must be bleached in order to achieve net gain, i.e., it behaves like a 3-level amplifier. To date, no fibre gain measurements have been reported. Nd3+ is another active dopant. Novel glass design has resulted in a glass composition based on AlF3 such that the gain peak is inside the second telecom window at 1310nm (near the zero-dispersion region of silica at 1317nm). It is a four-level system and the transition from the metastable level is purely radiative. In order to achieve a high gain amplifier, the competing 1050nm amplified-stimulated-emission must be filtered out. The use of gratings is one possible means of achieving the desired filter characteristics. In Nd3+-doped AlF3-glass fibre, there is the potential for an efficient and inexpensive optical amplifier able to deliver 30dB gain using <100mW pump power in a single pass.[8] It has a convenient pump wavelength at 800nm where inexpensive laser diodes are commercially available. The strong absorption of Nd3+ at 800nm and the high solubility of the ion in the glass gives a short device. Conclusion: Although there are four candidate fibres for 1.3µm doped fibre amplifiers (Pr3+ in ZBLAN, PGI or sulphide, Nd3+ in AlF) each has disadvantages compared to the EDFA operating at 1.53µm. Many of these disadvantages are fundamental and lead to an amplifier which is expensive, or has compromised performance. The commercial development which can change this is the availability of high-power pump sources which would ease the current preoccupation with pump efficiency
Q-switched neodymium-doped phosphate glass fibre lasers
No full textThe operation of a short-pulse, Q-switched, neodymium-doped fiber laser operating at 1.054µm is described experimentally and theoretically. The laser is efficiently pumped with a single-stripe AlGaAs laser diode and emits >1kW pulses. It is seen that due to high gain, short pulses with high energy extraction efficiency can be obtained. The feature of broad emission lines associated with rare-earth-doped glasses is exploited to demonstrate tunable, Q-switched operation over a 40 nm tuning range. <br/
795 nm and 1064 nm dual pump thulium-doped tellurite fibre for S-band amplification
No full textGain measurement in thulium-doped tellurite fibre is demonstrated with a maximum internal gain of 7 dB at 1480 nm. An improvement in gain by a factor of 2 is achieved using a 795 nm and 1064 nm dual pump scheme. Gain in tellurite fibres extends to longer wavelength than in fluorides, showing improved overlap with the C-band EDFA
Evaluation of neodymium doped fluoride glass films deposited by pulsed laser deposition
No full textPulsed laser deposition (PLD) has been evaluated as a technique for the realisation of neodymium doped fluoride glass waveguides. In contrast to other high energy techniques such as sputtering and molecular beam epitaxy, pulsed laser deposition appears to reliably reproduce the bulk stoichiometry of the doped glass in thin film form. However, characteristically for this deposition technique, the film topography is dominated by micron size particulates generated during fabrication. Film uniformity appears to be improved by depositing the film with a laser beam fluence close to the ablation threshold of the material. Unfortunately, this is at the cost of a significantly reduced film thickness which ultimately limits the usefulness of PLD for depositing waveguides from this material
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
Chemical etching of AlF-based glasses
No full textAluminium fluoride based glass [AlF3-M(II)F2-xPO3 M=Mg, Ca, Ba, Sr] fibres have potential for use as 1.3µm amplifiers, but successful application depends on improving their poor mechanical strength. Surface contamination of the preform is a major factor contributing to the lack of strength; it can be improved by chemical etching. As the glass components are highly unreactive, few etching studies have been reported in the literature. In this work, two multicomponent etches have been identified for the purpose and characterised. Optimum working compositions are 0.4M AlCl3 - 6 H2O / 1M HCl and 50% HF (48%) / 30% HNO3 (68%) / 20% H2O plus 3M H3BO3. Both yield fibres of significantly improved strength and quality, although the former etch tends to perform slightly better. Furthermore, an etch procedure has been developed for the aluminium chloride mixture which enables good strength fibre to be pulled in a controlled and reproducible manner
Diode-pumped 1.36µm Nd-doped fibre laser
No full textLaser emission has been observed at 1.363µm on the 4F3/2 to 4 I 13/2 transition from a diode-pumped Nd-doped phosphate glass single-mode fibre. Normally, this transition is strongly suppressed in an oxide glass host due to excited state absorption effects which reduce the efficiency of this transition. We observe both the lowest lasing threshold (5 mW) and the highest slope efficiency (10.8%) reported for a fibre laser in the 1.3µm spectral region
High-gain superfluorescent neodymium-doped single-mode fibre source
No full textHigh brightness, low coherence sources are required in a number of optical sensor applications, particularly the fibre-optic gyro. An efficient superfluorescent, neodymium-doped phosphate glass fibre source has been developed which fulfils this requirement. The fibre shows a high gain efficiency at 1.053µm of 1dB/mW pump power and this permits pumping with an 810nm single-stripe AlGaAs laser diode to obtain > 5mW CW output power at a wavelength of 1.053µm for only 45mW of pump power
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