We present a method of helical long-period fiber grating (H-LPFG) fabrication by use of a CO<sub>2</sub> laser for use as an optical torque sensor. A conventional optical fiber grating has periodic vertical index changes along its fiber axis, but a H-LPFG has a screw-type index modulation. The helical index modulation is obtained with the asymmetric index change caused by a single-side laser beam exposure. The H-LPFG shows peak shifts with codirectional or contradirectional torsion to the helix. Also, the polarization-dependent loss is measured to be relatively small compared with that of a conventional long-period fiber grating.
© 2004 Optical Society of America
Seungtae Oh, Kyung Rok Lee, Un-Chul Paek, and Youngjoo Chung, "Fabrication of helical long-period fiber gratings by use of a CO2 laser," Opt. Lett. 29, 1464-1466 (2004)