Linear Cavity Fiber Laser Intracavity Refractive Index Sensor

Although single-mode tapered optical fiber (SMTF) sensors have shown excellent performance, it is dependent on spectral analysis which typically involves costly and bulky equipment. The main focus of this work was the integration of SMTF into linear cavity fiber laser to simplify the sensing output. The optimum dimension of the tapered optical fiber used was 5mm transition length, waist length of 10mm and waist diameter of $12\mu \mathrm{m}$, which was able to produce a single lasing wavelength with suppressed side modes. Linear shifts to the laser with R2 value of 0.970 was observed as the sensor was introduced to increment in the NaCl concentration from 0 to $10\mu \mathrm{M}$. The integrated SMTF yielded a sensitivity of $0.455\mathrm{nm}1\mu \mathrm{M}$. This work has demonstrated the simplification of the sensing output which makes it more feasible for optoelectronic integration and eventually produce a handy, simple, and cost-effective tapered optical fiber sensor system in future.