Long range and nanometric resolution sensor for non-contact position measurement

Miniature high resolution sensors are required in integrated systems. Available high resolution sensors can be separated into two categories: small size sensor but having a limited range; high range sensor but with prohibitive size. The paper describes a miniature position sensor (2 mm diameter, 10 mm length). In the fiber optic displacement sensor the laser diode, photodiode and waveguide are fabricated on the same GaAs substrate and the sensor probe is a five fiber optic bundle. Used in a normal way, this optical sensor has a 1 nm rms resolution, but a linear range less than 200 μm (linearity criterion 1%). We propose to use two optical probes in front of a grating in order to increase the range to a few millimeters while keeping a 15 nm resolution. We describe the sizing method for the grating in order to optimize the sensor performance. The actual performance is verified by experimental results and compared to simulations.