Cross-talk prevention in optical dynamic measurement

In interferometry-based optical dynamic measurement, single high-speed camera or photodetector is normally adopted to avoid critical alignment and synchronization problems. Due to the rapid development of high-speed cameras and photodetectors, the signal obtained is sufficient to encode different dynamic informations. However, cross-talk problem always exists. In order to avoid the influence of cross-talk, well-designed carriers must be adopted in either spatial or temporal domain. In this paper, we will present two applications on cross-talk prevention in optical dynamic measurement. The first one is a camera-based dual-wavelength image-plane digital holography. In this application, the direction of two spatial carriers is designed to encode information of two wavelengths at different areas of the spectrum. Two phase maps can be retrieved from one hologram. The second application is a spatially encoded multi-beam laser Doppler vibrometry using a single detector. It encodes vibration information of 20 points on separated frequency ranges. Three methods that can bypass the cross-talk are discussed. The experiment verifies it is possible to do a precise vibration measurement on a 4×5 matrix simultaneously using a single photodetector.