Diluted magnetic semiconductor probe for magnetic field sensing using improved common-mode noise reduction scheme

An optical magnetic field measuring system using diluted magnetic semiconductors (DMS) probes is presented. The attractive features of DMS for building current/ magnetic field sensors are outlined. The system configuration includes a common-mode noise rejection scheme (CMR) to eliminate optic intensity noise induced in the fibre links by environmental vibrations. The CMR scheme relies on a pulse delay method based on the creation of two relatively delayed replicas of the photodetector output signal and their subsequent subtraction (division). Theoretical and experimental analyses of the system operation are developed and noise rejection methods using subtraction and division are presented and compared. Although CMR by division seems to be more appealing from the theoretical viewpoint (due to the rejection of intensity noise caused both by environmental vibrations and laser source output power fluctuations). in practical terms the subtraction is more reliable and easier to implement. The noise rejection figure measured experimentally is about 17 dBV for CMR both by subtraction and by division. A system calibration curve is presented. The minimum magnetic flux density detected with the system is 0.06 mT rms.