Excited-state-absorption cross sections and amplifier modeling inthe 1300-nm region for Nd-doped glasses

The performance of Nd³⁺-doped fibre amplifiers is limited by strong excited-state absorption (ESA) of the signal, and, even for fluorozirconate glasses, ESA prevents the important region below 1320 nm from being used. To quantify this limitation and explore alternative host materials, ESA and stimulated-emission cross sections have been measured for a representative group of glass compositions. These parameters have been used in an accurate fiber-amplifier model to provide the first quantitative comparisons of performance for Nd³⁺ -doped glasses in the 1300-nm band as a function of host     

Gain and noise penalty for detuned 980 nm pumping or erbium-dopedfiber power amplifiers

The impact of altering the fiber length and pump wavelength on the gain and noise performance of erbium-doped fiber power amplifiers pumped in the 980-nm band is examined. A gain penalty of <0.5 dB was experimentally observed over an 18 nm pump wavelength range. Theoretical analysis indicates that increasing the numerical aperture (NA) from 0.15 to 0.25 significantly improves the tolerance for a given gain penalty but has little effect on the noise figure. For a given fiber length, the noise figure increases by 0.1 dB for each 3 nm the pump wavelength deviates from 979 nm     

FM microwave multiplexed broad-band distribution systems using Er3+ fiber amplifiers and preamplifiers

The use of an Er³⁺ fiber preamplifier for microwave multiplexed systems and the use of an inline Er³⁺ amplifier in microwave multiplexed systems for signal distribution are reported. The improvement in receiver sensitivity as a preamplifier, without optical filtering, was 9 dB. No power penalty due to amplified spontaneous emission was found when the amplifier was used in a 30-channel signal distribution system     

Impurity analysis of heavy metal fluoride glass fibres using selectively excited photoluminescence

A technique based on selectively excited fibre impurity luminescence (SEFIL) has been developed and successfully applied to the quantitative analysis of Pr3+, Nd3+ and Fe3+ in heavy metal fluoride glass optical fibres. With fibre standards, SEFIL provides accurate analysis at impurity levels well below the requirements for long-distance fibre applications.     

Fundamental limits on Nd3+-doped fiber amplifierperformance at 1.3 μm

To explore the fundamental limits on performance at 1.3 μm, a model for Nd³⁺-doped fiber amplifiers which includes signal saturation and excited state absorption (ESA) at the signal wavelength has been constructed. Ignoring ESA, the difference in pump efficiency between a low-performance and a high-performance glass host is ≈60%, indicating that ESA is the critical parameter distinguishing experimental results reported for different materials. The pump efficiency for a linear Nd³⁺ amplifier is an order of magnitude less than for an Er³⁺ amplifier without ESA and degrades still further with its inclusion. Applications as power amplifiers are more promising, because, in principle, high power conversion efficiencies can be obtained     

Excited-state absorption cross sections in the 800-nm band for Er-doped, Al/P-silica fibers: Measurements and amplifier modeling

Excited-state absorption (ESA) cross sections were determined for the 800-nm band of Er-doped, Al/P-silica fibers. The oscillator strength of the ESA transition exceeds that of the 800 nm, ground-state absorption (GSA) transition by a factor of approximately= 2.3, in reasonable agreement with a Judd-Ofelt calculation. The extended, long-wavelength tail of the GSA band leads to a region around 820 nm where the GSA cross section approximately= ESA cross section. The cross sections were incorporated into an amplifier model for pumping in the 800-nm band. Codirectional and the bidirectional pumping schemes were analyzed for excitation near the peak and in the long wavelength tail of the GSA band. Pumping in the tail for either pumping scheme or pumping near the peak for the bidirectional scheme are predicted to produce a significant improvement in the small-signal gain.<>     

Erbium-doped glasses for fiber amplifiers at 1500 nm

Material-dependent properties influencing the performance of fiber amplifiers are reviewed together with the available data for Er³⁺ . The major glass types potentially useful in this application are considered and compared to silica. The topics addressed include quenching processes and the solubility of rare-earth ions, transition strengths and bandwidths at the 1500-nm gain transition, and the characteristics at the 800-, 980-, and 1480-nm pump bands. Aluminum is shown to be an extremely useful codopant for silica, improving its ability to dissolve rare-earth ions and providing desirable spectroscopic properties for Er³⁺. For some of the attributes considered, other glasses have advantages over Al silica, but only with respect to gain bandwidth and pumping performance at 800 nm is significantly better than expected from other glass compositions     

1.3 μm fluoride fibre laser

Laser action has been achieved in the 1.33-1.34 μm range using an Nd³⁺-doped fluorozirconate glass multimode fibre. These operating wavelengths are the closest to the important telecommunications channel at 1.3 μm of any reported for a glass laser     

Experimental and theoretical analysis of efficient erbium-dopedfiber power amplifiers

The efficiency of Er³⁺-doped fiber power amplifiers (EDFAs) pumped at 980 nm was experimentally investigated and quantum conversion efficiencies (QCE) up to 0.89 were achieved. The experiment was accurately simulated by a computer model using only measured input parameters. The model was further used in an analysis of power amplifiers pumped at 980 and 1480 nm that included waveguide optimization and Er³⁺ confinement. The QCE can be enhanced by increasing the numerical aperture (NA) and confining the Er³⁺ ions to the central region of the core. At pump powers typically used for packaged EDFAs (25-100 mW). QCE can be improved by up to 60% by increasing the NA from 0.15 to 0.25, and confined Er³⁺ doping can provide an improvement of up to 20%. However, NA and Er³⁺ confinement have insignificant effects on the noise figure when both the cutoff wavelength and the fiber length are optimized with respect to QCE