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A method for the construction of a tiny in-line coupler tip is presented. An in-line coupler tip was manufactured by tapering a dual-core PCF and cleaving half of the waist region. Even and odd supermodes with different propagation constants are produced in the tapered region, which results in the inter-mode interference. The interferometric spectrum depends on both the length of the tapered region and the refractive index. Due to the thermo-optics coefficient and thermal expansion coefficient of the pure silica, the temperature of the external environment can be measured by interrogating the optical reflection spectrum. Therefore, the in-line coupler can be constructed for the measurement of temperature. The experimental results show that the temperature sensitivity of 0.024nm/°C and operation range of 1425°C are achieved. Compared with other expensive methods, the proposed method possesses wide operation range and tiny size. Thus the microstructured fibre sensor technique appears to have potential applications in industry, medicine, biology, and chemistry. [ABSTRACT FROM AUTHOR]

A method for simultaneous measurement of geometric thickness and refractive index of an optical wafer is presented. By using a fiber optic Mach–Zehnder interferometer (MZI) with a free space, the transmission spectrum of a MZI for the optical wafer at different incidence angle is interrogated, and the geometric thickness and the refractive index of the optical wafer are measured simultaneously. With the transmission spectrum, we can obtain a clear interferogram with a high visibility no matter how small the measurement range of the refractive index. Therefore the proposed technique possesses a broad measurement range and low cost. The experimental results show that the maximum errors of the geometric thickness and the refractive index are only 0.007 mm and 0.008, respectively, and that a broad measurement from 1.316 to 3.503 can be achieved. [ABSTRACT FROM AUTHOR]