Long-period gratings in special geometry fibers for high-resolution and selective sensors

Advantages for sensor applications of long-period gratings (LPGs) in special optical fibers are reported. Two consecutive LPGs separated by 60 to 100 mm interfere to improve the resolution and reduce noise in a highly doped fiber with inner cladding and in a D-shaped fiber. These gratings provide good contrast to increase the resolution for sensing applications, with or without access to the surroundings along the fiber. The mode profiles of the devices were characterized experimentally to gain deeper insight into the improved functionality. © The Authors