High-speed fringe analysis method using frequency demodulation technology

Interferometer fringe-pattern analysis using the fast Fourier transform (FFT) technology is a very precise measuring method. However, this method has not received significant attention in industry, as a result of the long calculation time for an operation, because the method processes an image using sophisticated algorithms. In this work, in order to reduce the calculation time, the fringes imaged on CCD sensor are processed as analog data in the time domain. The fringes are spatial information on a CCD sensor, and can be converted to a synchronous electrical signal by the CCD driving clock pulse at the terminal of CCD output. In the new method, the analog electrical signal, which corresponds to the fringes on the CCD sensor, is analyzed using an electrical circuit in the time domain. The time-instantaneous frequency and phase of the fringes are detected by frequency-demodulating and integrating the signal, respectively. This proposed system can perform high speed fringe analysis operations in 10 ms per raster line of the CCD. The experimental results show that the new fringe analysis has very high speed and is as accurate as the FFT method. (C) 1996 Society of Photo-Optical Instrumentation Engineers.