Random Rotational Entire-Angle Sensor Using Two Chemical Etching Intrinsic Fabry–Pérot Interferometers

We demonstrate a full range rotational angle sensor system using two chemical etching intrinsic Fabry-Pérot interferometers (FPIs) fabricated by an electrical arc discharge technique. The use of magnetic scale, combined packaged FPI detectors, allows the exploration of position characteristic with direction discrimination. Numerical simulation is employed for optimizing the distance (d) between the detector and the circle magnetic scale. Experiments and numerical simulation show the interference dip shifts of FPI have sinusoidal relation with the rotational angle, as d ranging from 1 to 2.5 mm. Measurements showed five times (d = 1) and four times (d = 1.5) of magnitude greater than FBG detectors, with the linearity of 0.993 and 0.999, respectively. The sinusoidal function variations are displayed by two detectors with a phase difference of 90 degrees, which help to discriminate rotational direction. Moreover, two detectors have a low temperature cross-sensitivity of 2.3 pm/C°. The important advantage of our rotational angle sensor is their angle measurement range without limitation.