Polarization-maintaining, double-clad fiber amplifier employing externally applied stress-induced birefringence

We report a new approach to obtaining linear-polarization operation of a rare-earth-doped fiber amplifier in which the gain fiber is coiled under tension to induce birefringence. We demonstrated this method by constructing an Er/Yb-doped, double-clad, single-mode fiber amplifier with an output power of 530 mW and a polarization extinction ratio of >17 dB (when seeded with linearly polarized light) at a wavelength of similar to 1.5 mu m. The technique is achromatic, permits single- or multiple-pass operation of the amplifier, requires no additional components in the optical path, leaves the fiber ends unobstructed, and is inexpensive to implement. (C) 2000 Optical Society of America OCIS codes: 060.2420, 060.2320, 260.1440, 140.4480, 140.3510.