Michael LuValle

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.

Radiation reliability of rare earth doped optical fibers for laser communication systems (LT)

The use of an optical communication system in a radiation environment poses unique reliability issues. These issues include the effects of radiation dose rate and total radiation exposure on optical fiber performance. For a radiation reliability study, one must investigate these effects along with mitigating effects such as thermal and optical annealing. We present results from an ongoing reliability investigation of the effects of ionizing radiation on rare earth doped optical fiber designed for use in optical fiber amplifier systems.

A Theoretical Framework for Accelerated Testing

A minimal criteria for building a model that is to be used for extrapolating from experimental data taken at accelerated conditions, to expected degradation or failure at operating conditions is that the model be consistent with both the data and existing physical knowledge. In order to be able to check whether a model is consistent with physical knowledge, it must be expressed as a physical hypothesis.

Configurability of a three-wavelength Raman fiber laser for gain ripple minimization and power partitioning

The performance of a 3/spl lambda/RFL with variable OC reflectivities was investigated in 60 km, 100 km and 140 km transmission spans. The data indicates that this device is practical and can provide stable broadband optical amplification. A gain ripple minimum of 1.1 dB in a 100 km span, in agreement with simulations, is achieved with an OC voltage precision of 25 mV. The gain ripple /spl Delta/G and power partition deviation /spl Delta//spl rho/ voltage sensitivities were found to be /spl sim/0.01 dB/mV and /spl sim/0.04%/mV, respectively. This low sensitivity means control of the output powers of a multi wavelength RFL is not considerably more complicated than controlling multiplexed individual lasers.

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.

Reliability concerns for double clad fiber lasers for space based laser communications

This paper reviews present reliability issues for double clad fiber lasers that could be used as part of a space based laser communication system. Effects of radiation, environmental conditions and operation at high optical powers are reviewed.

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.

Integrating computational models with experimental data in reliability

In this paper we define what we consider the current defacto paradigm for accelerated testing, discuss what is wrong with it, introduce a more rigorous paradigm, and develop some theory for the new paradigm. Examples used for illustration include modeling degradation of connectors under cyclic stress, modeling degradation of metal films, and a pure Arrhenious thermal model of failure.

Optical reliability of cladding pump fiber for high power communication networks

High power lasers and amplifiers for communication networks based on cladding pump fiber operate at unprecedented power levels. The high power and unique structure of cladding pump fiber present new challenges to the optical reliability of lasers and amplifiers based on these novel fibers. In this paper we present results on the reliability of cladding pump fiber under high power both in the multimode pump waveguide and in the rare earth doped core.

Kinetic modeling of hydrogen induced degradation in erbium doped fiber amplifiers

In this paper we describe a single kinetic model consistent with current experimental results of the effect of hydrogen on erbium doped fiber, and derive three approximations to the model that can be used to fit data from fiber. Fits to data are shown for two of the three models.