Robert G. Ahrens

Spectroscopic properties of Er doped silica glasses

We have carried out a systematic study of optical emission in Er doped silica glass materials with different codopants. The stimulated emission cross-sections of these materials have been calculated. The wavelength dependence of emission of these materials has been studied. The different spectral shapes and hence broadening observed in this model is primarily due to different Stark splitting of the upper and lower levels of the Er ion in the glass matrix in the presence of different codopants. Inhomogeneous broadening which may be important at low temperatures is not discussed here. The peak emission cross section in Er doped pure silica glass is 5.4 pm2 and the peak wavelength is at 1535 nm. Codopants broaden the Er amplifier spectrum and vary the wavelength of peak stimulated emission cross section.

Radiation effects on optical fibers and amplifiers

The effects of gamma radiation on rare-earth doped optical fibers have been investigated over the range of 0.01 to 145 kilorads(Si) per hour to total doses exceeding 100 kilorads(Si). The effects of 3 to 4 MeV protons have also been investigated. The level of radiation induced damage has been found to be strongly dependent on radiation dose rate and fiber composition. The existence of dose rate dependence is explained by the process of simultaneous creation of color center defects and annihilation via thermal annealing. Through the use of a suitable kinetic analysis technique, we have determined appropriate rate constants for this process and have developed an empirical model based on our experimental results. In addition to these results, we present the effects of gamma radiation on the performance of operational high power erbium-ytterbium optical amplifiers.

Optical gain of single mode short Er/Yb doped fiber.

Optical gain and output power as a function of pump power has been calculated for short Er/Yb doped single mode fibers for various fiber parameters. The calculation shows that long fiber lengths provide both higher small signal gain and higher output power. Gain of 14 dB has been observed in a 30 mm long fiber at 400 mW of input pump power. The observed small signal gain is found to be linearly proportional to the length of the fiber with a slope of 0.44 dB/mm at 400 mW of pump power.

Analysis of recovery in radiation-induced loss in rare-earth-doped fibers through master curve/demarcation energy diagrams

Radiation-induced losses in rare-earth-doped fibers are analyzed in a novel manner. The mastercurve approach is used for analyzing stability of defects induced by radiation. This method can be applied to examine fibers for space applications.

Failure mode analysis of high-power laser diodes

In this paper, we present the results of a preliminary investigation on the reliability of high power optical diodes. Commercially available 970 nm optical diodes were subjected to various levels of stress, including: operating current, optical power and operating temperature. Optical diodes that failed during testing were subsequently analyzed using a variety of techniques, including: optical microscopy, scanning electron microscopy, eletroluminescence, and near-field profiling. It has been observed that the major cause of optical failure can be attributed to damage on the emitting facet of the optical diodes. Preliminary evidence suggests that facet damage is a result of catastrophic optical damage.

Gain calculation for Er/Yb-doped fiber amplifiers

Gain and output power as a function of pump power has been calculated for short Er/Yb doped single mode fibers for various fiber parameters. The calculation shows (i) small signal gain increases with increasing Er concentration, (ii) long fiber lengths provide both higher gain and higher output, (iii) calculated gain is larger for higher Er emission cross section, and, (iv) >25 dB gain is feasible for 5 cm long fiber for Er and Yb concentrations of 3 X 1026 m-3 and 1.2 X 1027 m-3.

Optical gain of single-mode short Er/Yb doped fibers

Gain and output power as a function of pump power has been calculated for short Er/Yb doped single mode fibers for various fiber parameters. The calculation shows (i) small signal gain increases with increasing Er concentration, (ii) long fiber lengths provide both higher gain and higher output, (iii) calculated gain is larger for higher Er emission cross section, and, (iv) > 25 dB gain is feasible for 5 cm long fiber for Er and Yb concentrations of 3 X 1026 m-3 and 1.2 X 1027 m-3 . Gain of 14 dB has been observed in a 30 mm long fiber at 400 mW. The observed gain is found to be linearly proportional to the length of the fiber with a slope of 0.44 dB/mm at 400 mW of pump power.