PC fiber filled with nanomagnetic fluid becomes a magnetic-field sensor

A photonic-crystal (PC) fiber-based magnetic-field sensor created by scientists at the Defence Institute of Advanced Technology and Fergusson College (both in Pune, India) combines the flexibility of optical fiber with the sensing capabilities of optofluidics. The nanomagnetic fluid is prepared by combining an iron-salt solution with distilled water and ammonia, resulting in 20-nm-diameter suspended iron oxide particles. A polarization-maintaining PC fiber with two enlarged air holes is filled with the nanomagnetic fluid via syringe. The 23.5 cm fiber section is terminated on both ends with fiber polarizers (forming a birefringent interferometer), the input polarizer rotated to 45º, and a laser-swept interrogator with a broadband 1510–1590 nm source measures the interference between the two polarization modes at the output end.

The filling process fills only the two larger holes in the PC fiber, resulting in a reduced form birefringence intrinsic to the PC fiber, and the introduction of a magnetic-field-dependent birefringence. The wavelength spacing of the interference fringes after fiber filling is 37.979 nm. Upon application of a DC magnetic field, the fringe pattern shifts toward the blue. A magnetic-field sensitivity of 242 pm/mT was measured in one of the prototype devices.

Contact Harneet Thakur at [email protected].