Abstract

The fabrication of an all-fiber Faraday rotator has been achieved in spite of the small Verdet constant of fused silica. The rotation in a straight fiber is obtained through the enhanced field produced by pairs of permanent Nd-Fe magnets in altering polarities separated by pressure-induced halfwave segments. Whereas the all-fiber optical isolators already proposed use curved segments and at least 2 m of fiber, the present design requires only 40 cm of single-mode fiber at a wavelength of 632.8 nm. As the rotation is directly proportional to the magnitude of the magnetic field and to the length of the fiber, it is important to maximize the intensity of the field by an appropriate design. The number of pairs yielding 45° of rotation is an important factor since it determines the simplicity of the device and the throughput losses caused by the pressure-induced halfwave segments. The experimental apparatus consists of thirty-six pairs of Nd-Fe magnets of 12 mm high by 6 mm wide by 10 mm long with a transverse gap of 0.6 mm that allows us to insert the low birefringence LB600 fiber. Rotation off 49.5° is observed for the thirty-six pairs, which corresponds to 1.38°/pair. This is in good agreement with the theoretical prediction of 1.48°/pair. Throughout losses of only 0.02-0.03 dB/contact are measured and a linearity of at least 25 dB is achieved.

© 1991 Optical Society of America