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     

Characterization of the approach to steady state and the steady-state properties of multimode optical fibers using LED excitation

A simple technique has been developed to characterize the approach to steady state and the steady-state properties of multimode fibers using LED excitation. Results are given for 6 mil Selfoc fibers whose far-field pattern for the steady state is in excellent agreement with a calculation by Marcuse. To first order, the steady-state mode distribution fits a simple model of uniform modal excitation of a fiber with a reduced numerical aperture.     

Deep radiative transitions in AlxGa1−xAs:Sn

Deep radiative transitions in LPE-grown Al_xGa_1?xAs:Sn (0?x?0.28) have been studied at temperatures T between 78 and 297 K using photoluminescence. Each sample has a broad, featureless, saturable spectrum with a peak energy which has an x-dependence similar to that of the L-conduction band minima. The asymmetry of the line shape is similar for all x, and the T dependence of the spectral width fits an electron-lattice interaction type equation. Thermal quenching is observed and studied by measuring the photoluminescent decay time as a function of temperature. A configuration coordinate model is proposed to explain the observed spectral data.     

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.<>     

Evaluation of the 800 nm pump band for erbium-doped fiberamplifiers

Performs a comprehensive experimental and theoretical investigation of methods for overcoming the excited-state absorption (ESA), which is the main obstacle to efficient pumping of erbium-doped fiber amplifiers (EDFAs) at 800 nm. The effects of ESA on gain can be reduced at the cost of an additional noise penalty by adopting bidirectional pumping or by pumping in the long-wavelength tail of the ground-state absorption (GSA) band. The GSA and ESA cross-section spectra on the glass host material. One of the most promising hosts, fluorophosphate, is compared to Al/P silica in a detailed analysis based on a quantitative numerical model. It is predicted that 2-3 dB less pump power is required for the fluorophosphate EDFA. For Al/P-silica EDFAs, it is found that ~7-dB-higher power is required when pumping in the 800 nm band than for pumping at 980 and 1480 nm     

Power requirements for erbium-doped fiber amplifiers pumped in the800, 980, and 1480 nm bands

The authors examine relative merits of exciting Er³⁺ amplifiers at the three wavelengths for which high-power laser diodes are available at 800, 980, and 1480 nm. Model calculations are confirmed by a detailed experimental comparison of the power requirements for pumping in the 800-nm band and at 980 nm. To obtain comparable performance with respect to gain and noise figure, 7-8 dB more power is required when pumping in the 800-nm-band     

Analysis of erbium-doped fiber amplifiers pumped at 800 nm

The performance and efficiency of erbium-doped fibers pumped in the 800-nm band has been analyzed using a quantitative amplifier model. Both a silica and a fluorophosphate host were investigated. The analysis showed that under optimized conditions the fluorophosphate is superior to the silica with higher gain and up to 60% higher quantum conversion efficiency. Only with respect to noise figure is the fluorophosphate poorer because of the shorter lifetime of the metastable state.     

Decay of transmitted light during fiber breaks-implications forbreak location

The accuracy of a bit-counting method for locating fiber breaks in an optical communication system proposed by Rosher et al. is limited in part by the decay time of the transmitted light during fiber failure. In order to understand the nature of this limitation, decay times were measured for individual fibers using a variety of failure mechanisms. The mechanics of the break processes were considered and the implications for break location using the bit-counting technique were assessed. The fastest decay times (≈14 ns) occurred when fibers broke catastrophically under stress levels greater than 0.7×109 N/m². The decay times in this case implied a small break-location uncertainty of 3 m when employing the bit-counting scheme. Since the strength members of fiber cable break at much greater tensions, decay times for cable failures (for example, caused by a backhoe) should not significantly limit the break-location accuracy assuming that the fibers do not bend severely before breaking. For stresses below 0.7×109 N/m² the decay times increase as the stress decreases, attributable to a corresponding decrease in the speed with which the cores of the broken fiber sections tilt with respect to each other and/or separate