International Journal of Scientific Engineering and Technology Volume 2 Issue 3, PP : 112-115
(ISSN : 2277-1581) 1 April 2013
Study of Intensity Modulated Fiber Optic Sensor - Effect of Length of Core Exposed in Guiding Liquid A. Jayanth Kumar1, T. Radha Krishna2, B.S. Bellubbi2 1 2
Institute of Aeronautical Engineering, Dundigal, Hyderabad-500 043, AP, India Advanced Photonics Lab, JNTU College of Engineering, Hyderabad. AP. ,India E-mail: dr.jayanth@gmail.com
Abstract:- In the past two decades fiber optic technology has passed through many analytical stages. Commercially available fiber optic sensors are widely used in mechanical and industrial automation. They are also used in instrumentation and control. In the present work, an intensity modulated fiber optic sensor is used. A small portion of cladding (1cm, 2cm and 3cm) is removed in the middle of the fiber along its length. This portion is totally immersed in known concentrations of common salt solution which acts as guiding medium. One end of the fiber is connected to source of 820nm, 850nm for plastic fiber and 1300nm, 1550nm for silica glass fiber. The second end of the fiber is connected to a power meter through which the output power is measured. The power loss which is the difference of power launched into the fiber and power collected at the second end of the fiber is noted. A relation between the core exposed in guiding solution and the output power at the second end of the fiber is studied. This study helps in deciding the length of core of an optical fiber to be exposed to the environment. I. Introduction: ‘Fiber optic sensors‟ is very promising area for commercial applications due to cost effectiveness, easy realization, sensitivity, small in size and free from EMI[1-4] . In view of the above advantages, fiber optic sensors have become very popular in the areas like process control, avionics, petrochemicals, pharmaceuticals [5-11]. These sensors are based on attenuated total internal reflections. When a ray of light travels from denser medium to rarer medium and if the angle of incidence is greater than the critical angle the ray reflects back in to the denser medium. If the rarer medium is an absorbing medium, the evanescent wave intensity gets attenuated and as a result the intensity of output power at the second end of the fiber decreases
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exponentially [12]. Thus an un-clad optical fiber can be efficiently used as intensity modulated fiber optic sensor. As intensity modulated sensors [13-14] are easy to realize and compact in size, they are being extensively used for sensing mechanism. In most of the intensity modulated sensors the core is exposed to the environment and the change in environment can be studied by measuring the output power at the second end of the fiber which is used as sensor. The output power changes depending on the length of the core exposed in the environment [15-16] In the present work, core of different lengths is exposed in guiding solutions of various concentrations and optimum length of the core to be exposed is determined. The experiment is carried out with common salt solution as guiding solution at wavelengths 820nm and 850nm for plastic fiber and 1300nm and 1550nm for silica glass fiber. II. Experimental Arrangement: The experimental arrangement [16] is shown in figure 1. A white light source that gives wavelength 820nm, 850nm, 1300nm and 1550nm is used in the experiment. A plastic fiber (200 / 230µm) of 1m length and a silica glass fiber (62.5 / 125µm) of length 8800m are used in the present experiment. Using suitable connectors, one end of the plastic fiber is connected a white light source at a wavelength 820nm and the second end connected to a power meter which records the output power at the second end of the fiber. The output power at the second end of the fiber is considered as power launched since the attenuation in one meter fiber is negligible. Now, 1cm cladding is removed in the middle of the fiber, the bare core is immersed in pure (distilled) water which acts as guiding liquid and the output power is noted. The experiment is
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