Non-contact refractive index measurement based on fiber optic beam-through technique

H. A. Rahman, S. W. Harun, M. Yasin, H. Ahmad

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


A simple refractive index sensor for various concentrations of sodium chloride (NaCl) in de-ionized water is proposed and demonstrated. The beam-through technique is used to obtain output voltage of liquids with known refractive indices, namely methanol, de-ionized water, acetone and ethanol. Based on the output voltage of these liquids, the sensor characteristic curve is determined and the refractive indices of 2 % to 12 % sodium chloride concentrations are obtained. A sensitivity and detection limit of 23.07 mV/refractive index unit (RIU) and 2.28 × 10-3 RIU have been derived from measurements, respectively, with a linearity of more than 97 %. The fiber optic sensor is a promising alternative to other well-established methods for the measurement of liquid refractive index due to its simplicity of design, linearity, non-contact sensing, ruggedness and low fabrication cost.

Original languageEnglish
Pages (from-to)1035-1038
Number of pages4
JournalOptoelectronics and Advanced Materials, Rapid Communications
Issue number10
Publication statusPublished - 2011


  • Beam-through technique
  • Fiber optic
  • Fiber optic displacement sensor
  • Refractive index measurement
  • Sodium chloride in de-ionized water


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