Refractive index monitoring and water content estimation in plants by using optical fiber probe and semiconductor laser
2009
Fukuda, M.(Toyohashi Univ. of Technology, Aichi (Japan)) | Matsuo, A. | Jinno, H. | Farzana, I. | Nakayama, N. | Ooyama, S. | Utsumi, A. | Tanabe, T.
Refractive index inside plant was investigated by combining an optical silica fiber probe with an optical analog transmission system. A mirror facet set at the sensing head of the probe was fabricated by cleaving a fiber (50-microm-core step-index multimode fiber). A laser diode lasing at 650 nm was used as an optical source in this system since the emitted light of 650-nm wavelength is scarcely absorbed in water and sugar solution, and thus suitable for monitoring refractive index inside plants. The sensing head was inserted into vegetables, and the lasing light was guided to the sensing head. The intensity of optical back-reflection generated at the sensing head was monitored for calculating refractive index inside plants. The following results have been clarified in these experiments. (1) The refractive indexes obtained in water and cane sugar solutions well corresponded to those monitored with a commercially available refract-meter. (2) The refractive indexes obtained by the probe tended to be larger than those monitored with the refract-meter because the influence of scattering by soluble solid constituent and fiber contained inside plants was included in the values obtained by the probe. (3) The change in refractive index inside plant before and after LED light illumination or water supply was clearly monitored for leaf lettuce and Chinese cabbage. In addition, water content inside plant could be estimated by using the refractive index experimentally obtained. Based on these results, the newly developed technique has been demonstrated to be applicable to refractive index monitoring at the inside of plants.
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