An experimental study of pH optical sensor using a section of no-core fiber

• An optical fiber structure with a section of no-core fiber for measuring pH is presented.
• Precursor TEOS and pH-sensitive indicators are used to form the pH coating on the no-core fiber by dip-coating.
• The structure with 2 cm no-core fiber has a high pH sensitivity of 0.6 dBm/pH at 1550 nm and a better linearly response from pH 1 to 13.

A simple optical fiber structure with a section of no-core fiber for measuring pH is presented. Precursor TEOS and pH-sensitive indicators are used to form the pH coating on the no-core fiber by dip-coating method. The pH induced refractive index changes on the outside coating of no-core fiber will lead to the variations of the optical output power. The results show that a high pH sensitivity of 0.6 dBm/pH at 1550 nm and a good linear response with a wide pH operation range, from 1 to 13, are obtained. Through monitoring the optical output powers, the responses demonstrate the good stability and repeatability of our proposed structure. At last, the measured data can be obtained with a rapid response time of less than 40 s.