The instability of the mean wavelength of a superfluorescent fiber source (SFS) is reduced by randomizing the polarization of light from a pump source or by using polarization maintaining components. In one embodiment, the polarization of a pump source is made more random, leading to greater stability of the mean wavelength of the SFS, with an output mean wavelength that is stable to better than 3 ppm for full rotation of the pump polarization state. In another embodiment, the polarization of optical radiation throughout the device is kept substantially constant by using polarization maintaining fiber and components, thereby leading to enhanced mean wavelength stability of the SFS.