Single-polarization fiber lasers using Bragg gratings in Hi-Bi fibers

Cavities of high birefringence (Hi-Bi) Nd³⁺ doped fiber lasers have been closed by an intracore Bragg grating reflector and a dichroic mirror. The spectral characteristics of the laser emissions have been investigated using a measurement accuracy of 100 MHz. Two oscillating frequencies corresponding to two orthogonal linear polarization states of the laser emissions have been observed. The orientations of the two linearly polarized emissions were found parallel to the Hi-Bi fiber axes, respectively. Laser thresholds, slope efficiencies and differences between these frequencies were found to depend on the conditions of the Bragg grating inscription. Multimode single polarization Hi-Bi fiber lasers using two Bragg gratings were fabricated and characterized for the first time to our best knowledge. Wavelength tuning of this single polarization fiber laser has been demonstrated under temperature rise of the two gratings. Polarization and frequency stabilities of the emissions from these Hi-Bi fiber lasers were studied and compared to those from lasers built in a conventional fiber (fiber with no polarization holding property)