| The erbium-doped superfluorescent fiber source (SFS) has become the broadband light source of choice for the fiber optic gyroscope (FOG), in particular to meet the one-part-per-million mean wavelength stability required for inertial navigation. Our efforts have focused on source modeling, and improving both the source efficiency and the mean wavelength stability.; We have developed a computer model of erbium-doped fiber (EDF) devices which has proved extremely useful in studying the vast array of possible SFS architectures and source design parameters. Our model also includes polarization and temperature effects. Various techniques used to determine the EDF simulation parameters were examined, with special attention given to the absorption and emission cross-sections.; Using the simulator, we designed a polarized SFS with nearly the same efficiency as a standard, unpolarized SFS. Since an FOG typically includes a polarizer at the input to the fiber sensing coil, this doubles the usable source output power. Experimental demonstration of polarized forward and backward SFSs incorporating a discrete polarizer yielded output extinction ratios of over 17.5 dB and power improvements greater than 75%, verifying the efficacy of this technique.; Significant progress was also made in the area of source mean wavelength stability. The parameters that affect the mean wavelength are pump power, pump wavelength, optical feedback, temperature, and fiber birefringence. Modeling was used to demonstrate source operating conditions that result in sub-ppm mean wavelength stability over reasonable variations in the pump power, pump wavelength and optical feedback. An experimental demonstration was also made of a filter-compensated SFS with tenfold improvement in thermal mean wavelength variations. In addition, polarization changes caused by fiber birefringence perturbations were found to affect the mean wavelength by more than 100 ppm. Two novel source designs that correct this problem were demonstrated experimentally. One includes Lyot depolarizers and the other a Faraday rotator mirror; both result in polarization induced mean wavelength variations under 10 ppm. |
