A novel operation system to detect train vibration and train weight using FBG sensing network has been designed and tested in Hong Kong. The purpose of the system is for real time condition monitoring of trains. Because of the fast response of optical systems, the trains can be monitored in real-time during its normal service without any special arrangement. Hence, the condition checking can be realized without any disruption on the operating condition of the railway system.

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A new method for fabricating Long Period Grating (LPG) using a microlens array is introduced. Instead of blocking the excimer laser beam, this new method convergences the UV laser beam into an intensity modulated profile and the writing efficiency is improved. This method enables shorter grating writing time and also suitable for batch production of LPGs, thus providing an efficient method with potential in the mass production of LPGs.In this paper, we report a new method which uses microlens array for fabricating Long Period Gratings (LPGs). In comparison with other reported methods, namely, the point-by-point inscription and the chromium-plated amplitude mask technique, this method is much more energy efficient and the writing process for each LPG is also shorter. Using a 248 nm excimer laser with pulse energy 150 mJ/cm2 and pulse repetition rate of 50 Hz, more than 50 gratings can be batchproduced in less than 1 minute. Therefore, this method has the potential for the mass production of LPGs. LPGs are generally fabricated by irradiating hydrogen-loaded, germanosilicate fiber with a 193 nm or 248 nm excimer laser through an amplitude mask [1]. Writing time varying from several minutes to more than an hour [2] are required. The optical power of the excimer laser is limited to 100 mJ/cm2 , beyond which the amplitude mask can be damaged. Therefore, this technique need to increase its writing time to compensate for the power shortage. 0277-786X/98/$1O.Oo SPIE Vol. 3491 /301 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx