Feature

Ultra-High Resolution Interferometric Sensors

Michael Hercher

An extraordinary variety of measurements can be made using optical interferometry. Cheap laser diodes can lead to inexpensive and accurate sensors for such measurements. In most cases, interferometric measurements are made by interfering two beams so that their phase is proportional to the quantity being measured. There are two basic tasks in building a sensor of this type: (1) design the transducer so that the measured phase is proportional to the desired physical parameter and does not depend on other parameters that are likely to change, and (2) devise an appropriate means for processing the data from the transducer. Figure 1 illustrates four basic types of 2-beam interferometers, differentiated in terms of how they generate detectable phase changes.