Because rare-earth-doped glasses exhibit a large Faraday (or magneto-optical) effect, polarization and birefringence effects within these glasses can be directly correlated to magnetic-field strength, and correspondingly, used to sense electric current. Although single-mode fibers offer a more compact, less expensive alternative to bulk-glass current sensors that require precise alignment and a large number of optical components, the Faraday effect is much reduced, making these devices less sensitive. But by adding cadmium selenide (CdSe) quantum dots to standard single-mode fiber, researchers at the Gwangju Institute of Science and Technology (Gwangju, South Korea) were able to fabricate optical fibers with improved current-sensing capability.
A core of an alumino-germano-silica glass preform was doubly doped with a toluene solution containing CdSe quantum dots. After doping, the preform was dried and an additional glass layer was applied to reduce dopant evaporation. The fiber was drawn to a diameter of 125 µm at 2000°C; average quantum dot size was 5 nm at an estimated concentration of (2.2 × 1024)/m3. Another preform without quantum dots was prepared and drawn into reference fiber. Both fibers were single mode at about 560 nm. A 10 mW 632 nm He-Ne laser source was input to 100 m of the twisted fiber, coiled on a 15 cm drum. Measurements of Faraday rotation angle as a function of current showed that sensitivity of the quantum-dot-doped fiber was roughly twice that of the reference fiber from 0 to 40 A. Contact Won-Taek Han at [email protected].
