Picometer positioning system based on a zooming interferometer using a femtosecond optical comb

A positioning system based on a new zooming interferometer was developed for calibrating ultrahigh-resolution linear encoders. In the system, the positioning resolution is scaled down from that of the driving stage to that of the controlled stage by a zooming ratio that is determined by the ratio bettween the wavelengths of the optical sources for the zooming interferometer, so that the resolution in the controlled stage becomes very high. A femtosecond optical comb is used to stabilize two external-cavity diode lasers that are used as optical sources for the interferometer. The system realized a resolution of better than 30 pm and a stability of 1 nm. (c) 2008 Optical Society of America.