Micromachined optical fiber current sensor

We describe a micromachined optical fiber current sensor. The sensing eleme nt consists of a squared silicon membrane (8 mm long and 20 mu m thick) tha t has a cylindrical permanent magnet (NdFeB alloy, 3-mm diameter, 1.5 mm hi gh) fixed on its central region. This structure allows the permanent magnet to vibrate in the presence of the magnetic field gradient generated by an ac. A Linear relation between the electrical current and the magnet displac ement was measured with white-light interferometry with an optical fiber lo w-finesse Fabry-Perot microcavity. A measurement range of 0-70 A and a mini mum detectable intensity of 20 mA were obtained when distance D between the membrane and the electrical power line was 5 mm. The output signal directl y shows a linear response with distance D. (C) 1999 Optical Society of Amer ica. OCIS codes: 060.2370, 120.3180.