Absolute measuring interferometric high-speed profilometer using wavelength modulation at ultrasonic frequencies

Abstract

We present a laser interferometric approach for absolute distance measurements based on current-modulated laser diodes. The proposed system employs a point-wise measuring interferometer operating with two lasers of slightly different wavelengths in the telecommunications spectral range. By exploiting the modulated interference signals, absolute distance information can be obtained without mechanical scanning or additional reference stages. A multistage signal-processing algorithm is introduced that combines absolute frequency estimates with phase-based evaluation to improve the precision of the measurement. In a first step, coarse absolute distance values are determined from the frequency estimation of the modulated interference signals. Subsequently, these estimates are refined by incorporating phase information, enabling enhanced distance resolution while maintaining unambiguous absolute ranging capability. The presented concept combines interferometric precision with absolute distance determination using compact and cost-efficient components. Owing to the use of telecommunications laser diodes and computationally efficient evaluation methods, the system represents a promising approach for high-precision optical metrology and fast distance sensing applications.