A Tiny In-Line Coupler Tip with the Half Tapered Dual-Core Photonic Crystal Fibre

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.