Modulated White-LED Interferometer

摘要

ZnSe and InGaN based white-LEDs have been utilized for an interferometer. These white-LED consist of blue-LED light and yellowish green one. When these white-LED were modulated by rectangular wave, there were differences in response speed between blue-LED light and yellowish light. The response speed of blue-LED light of ZnSe type white-LED was 50ns, while that of yellowish light was 5μs. The spectral bandwidths of the blue-LED light and the yellowish light were 10nm and 100nm, respectively. Coherence lengths of these lights were 10μm and 2μm, respectively. Combining the blue-LED light with the yellowish light, we observe an unique interference when scanning the optical path of the low coherence interferometer. We also propose a method for a color separation of an interference in a low coherence interferometer with the ZnSe white-LED modulation. The ZnSe white-LED was modulated with much higher frequency (100kHz) than the Doppler frequency of the above interference. The interference fringe of white light appeared at the upper side on the rectangular modulated light emission, while that of the residual yellowish light was presented at the bottom. The interference fringe of the blue light was derived by subtracting the yellowish light interference from the white light one.