Sinusoidal wavelength-scanning interferometer with a superluminescent diode for step-profile measurement

摘要

In sinusoidal phase-modulating interferometry an optical path length (OPD) larger than a wavelength is measured by detection of sinusoidal phase-modulation amplitude Z_(b) of the interference signal that is produced by sinusoidal scanning of the wavelength of a light source. A light source with a large scanning width of wavelength is created by use of a superluminescent laser diode for the error in the measured value obtained by Z_(b) to be smaller than half of the central wavelength. In this situation the measured value can be combined with a fractional value of the OPD obtained from the conventional phase of the interference signal. A sinusoidal wavelength-scanning interferometer with the light source measures an OPD over a few tens of micrometers with a high accuracy of a few nanometers.