Abstract

We present a fiber-optic refractometer with intensity-type transducer which can operate remotely via long fiber-optic cables. This version of the refractometer is intended for accessing the concentration of aqueous solutions of sodium chloride in the range from zero to about 145‰ (1.327 < n < 1.353 at λ=940 nm and 25°C), which is of significant practical interest for industrial users. We address the relationship between the span and linearity of the intensity-type optical transducer with spherical working surface which we employ in the refractometer. We optimized the transducer for the specified measurement range and achieved good sensitivity and non-linearity as small as 0.05. We significantly reduced the negative effect of the unstable optical loss of the fiber-optic cables, variation of the optical source power and photo-detector response on the readings of the refractometer by using an optical bridge configuration followed by an analogue optoelectronic signal processing unit. The refractometer has a parasitic variation of its output as low as 1.5% under a total variation of the optical source power and a fiber-optic cable loss of 20 dB. Potential applications of this refractometer include the in-situ characterization of various liquids such as the sodium chloride salt-brine solutions in food industry.

© 2011 IEEE

Optical fiber thermo-refractometer

J. J. Imas, C. R. Zamarreño, I. Del Villar, J. C. C. Da Silva, V. Oliveira, and I. R. Matías
Opt. Express 30(7) 11036-11045 (2022)

Polarimetric optical fiber refractometer

Michael Shribak
Appl. Opt. 40(16) 2670-2674 (2001)

Differential optical fiber refractometer based on a path-matching differential interferometer with temperature compensation

Yu-Lung Lo and Chin-Ho Chuang
Appl. Opt. 40(21) 3518-3524 (2001)

Optical refractometer based on a birefringent Bragg grating written in an H-shaped fiber

O. Frazão, T. Martynkien, J. M. Baptista, J. L. Santos, W. Urbanczyk, and J. Wojcik
Opt. Lett. 34(1) 76-78 (2009)

Analysis and design of fiber-optic refractometers

Z. Zhou and F. F. Liu
J. Opt. Soc. Am. A 8(2) 322-329 (1991)