Fiber-Based Helical Channels Refractive Index Sensor Available for Microfluidic Chip

We propose and demonstrate a refractive index (RI) sensor based on a dual-hole elliptical core fiber (DHECF), which is available for microfluidic chips. By using the heating-twisting technology, we fabricate a helical long period grating (HLPG) structure in the DHECF. This sensor is convenient for microfluidic chips because of the dual-hole structure in the fiber, which is the natural microfluidic channels. The heating-twisting technology ensures that the fabrication of the gratings sensor is easy and low-cost. In addition, the dual-hole structure contributes to one internal sensing channel which contains two sensing routes (two holes), and one external sensing channel. Experimental results indicate that the testing sensitivity of the internal sensing channel can be 584 nm/RIU (RI range 1.385-1.405), and the sensitivity of the external sensing channel can be 1108.8 nm/RIU (RI range 1.385-1.405).