Jefferson L. Wagener

EFFECTS OF CONCENTRATION AND CLUSTERS IN ERBIUM-DOPED FIBER LASERS

We report a low-threshold, high-conversion-efficiency erbium-doped fiber laser in a 100-parts-in-106 fiber pumped at 1.48 μm. The threshold and efficiency are found to deteriorate noticeably as the erbium concentration is increased. We propose that this is due mostly to rapid cross relaxation between ion pairs or clusters, and through modeling we show that the cluster content increases with concentration.

A Mueller matrix formalism for modeling polarization effects in erbium-doped fiber

The effects of erbium anisotropy in erbium-doped fiber lasers, sources, and amplifiers are examined. Starting from basic ion properties, inversion and gain equations are derived analytically to describe polarization dependencies. A novel matrix form of the Er/sup 3+/ rate equations is presented to propagate powers and polarization states. These equations are then numerically integrated and compared to experimentally observed polarization hole burning and polarization dependent gain. The theoretical predictions agree strongly with experiment in all cases.

Evidence and modeling of paired ions and other loss mechanisms in erbium-doped silica fibers

To explain the sub-optimal performance of erbium-doped resonant fiber lasers and superfluorescent fiber sources observed experimentally, the effects of potential loss mechanisms are explored via computer simulations. Pump excited-state absorption (ESA) at 980 nm and 1.48 micrometers , and signal ESA are unable to explain the dependence of the observed effects on concentration. Cooperative upconversion among uniformly distributed erbium ions fails to explain the observed reduction in source slope efficiency with increasing concentration. On the other hand, rapid cross-relaxation between paired ions, which might form in high concentration fibers, can produce the observed dependences. Rate equations for paired ions are used to understand their saturation behavior and their effect on the slope and threshold of fiber sources. Methods to assess the fraction of paired ions are discussed. Measurements suggest that about 18% of the ions in an aluminum co-doped silica fiber with 5 X 1019 Er3+/cm3 are paired. The effects of paired ions on the gain of Er-doped fiber amplifiers are also briefly discussed.

Novel fiber sensor arrays using erbium-doped fiber amplifiers

We examine the signal-to-noise ratio (SNR) performance of a novel type of time domain multiplexed sensor arrays in which low gain (1-10 dB) fiber amplifiers are incorporated to compensate for splitting losses between sensors. The system noise figure for passive and amplified sensor arrays is presented, along with expressions to optimize the array parameters for high SNRs. We show that practical amplified sensor arrays exhibit low system noise figures that allow much larger arrays (hundreds of sensors) than passive arrays.

Optimization of large-scale fiber sensor arrays incorporating multiple optical amplifiers. I. Signal-to-noise ratio

We report on optimizing the signal-to-noise ratio (SNR) of large-scale fiber sensor arrays employing erbium-doped fiber amplifier (EDFA) telemetry with respect to the number of sensors per rung, the number of amplifiers per array, and the coupling ratio between the fiber buses and the rungs. Broad optimum regions are found, providing design flexibility to minimize pump power requirements. Simulations predict that 300 sensors can be multiplexed on a fiber pair while maintaining a high sensitivity (1 /spl mu/rad//spl radic/(Hz)) for all sensors with a moderate input pump power (<1 W).

Optimization of large-scale fiber sensor arrays incorporating multiple optical amplifiers. Part II: pump power

For part I see, ibid., p. 218, 1998. We discuss how to minimize the pump power required for large-scale fiber sensor arrays employing erbium-doped fiber amplifier (EDFA) telemetry with respect to the number of amplifiers per bus, number of sensors per rung, and the gain per amplifier. For a large array, the pump power requirement is dominated by passive component losses along the array. We investigate several methods, including alternative array topologies, to reduce the power requirement while minimizing the impact on the signal-to-noise ratio (SNR). We define an optimum topology which requires less than 1 W of 1480 nm pump power per bus to support 200 high sensitivity (1 /spl mu/rad//spl radic/(Hz)) sensors on a pair of fiber buses, a power requirement that is reasonable and attainable with available laser diodes.

Modeling of ion pairs in erbium-doped fiber amplifiers

The effects of Er-Er pairs on the characteristics of Er-doped fiber amplifiers are analyzed theoretically. Pairs are found to have little effect on the amplifier optimum length, signal saturation power, and noise figure (at constant gain) but to cause significant reduction in the gain, even at residual levels, quantitatively consistent with fiber laser measurements. A maximum tolerable fraction of paired ions near 8%, corresponding to approximately 400 mole parts in 10(6) Er(2)O(3), is predicted for near-optimum gain efficiency in Al-Ge silica fibers.

A high-stability fiber amplifier source for the fiber optic gyroscope

We demonstrate an erbium-doped fiber amplifier (EDFA) source for the fiber gyroscope with an overall mean wavelength stability of four parts per million. This source, which amplifies the gyroscope signal before detection, is shown to be more stable than a similar single-pass source in a standard configuration. The effects of varying the fiber temperature, pump power, pump wavelength, gyroscope feedback power and signal polarization state on the output mean wavelength are individually explored. Experimental results are in excellent agreement with simulations.

Polarized superfluorescent fiber source.

We report the demonstration of a polarized superfluorescent fiber source (SFS) that increases the power output in the desired linearly polarized component by a factor of 1.76 over that of a standard, unpolarized SFS that uses the same pump power. This increase in efficiency is accomplished by insertion of a low-loss polarizer at an optimum point in the erbium-doped fiber of a standard SFS.

Effect of concentration on the efficiency of erbium-doped silica fiber lasers

Comparison of the output characteristics of different erbium doped fiber lasers show that the threshold pump power increases (by a factor of 4.6) and the conversion efficiency decreases (by a factor of 1.5) as the erbium concentration is increased from around 150 to 1040 mole ppm Er2O3. We propose that these two effects are mostly due to rapid interaction (perhaps upconversion) between a subset of paired ions. This work suggests that for Al-Ge- doped silica fibers, concentrations of 150 mole ppm or less should be used for optimum output power. A fiber with this concentration produced a low-threshold laser with a total power conversion efficiency of 90.4%.