Study Of Liquid Refractive Index Sensor Based On Singlemode Fiber With A Micro-hole Created By Femtosecond Laser

The existing liquid refractive index(RI) sensors based on tapered fiber have been widely investigated because of there convenient fabrication, good practicability and high resolution. However, we will have to make long tapered region and small diameter waist region fiber sensors to bring high sensitivity. In the ordinary, the taperded region averages several centimeters in length, may be up to 10 cm. Its disadvantage is difficult to conservation and unfavourblelts to micrometering. Drilling micro-hole on the fiber makes external liquid directly affect optical power in the fiber core. Then the sensitivity of tapered fiber sensing device is improved. Now the fiber based on micro-hole and the tapered fiber have been applied to measure refractive index.In this letter, we present a liquid refractive index(RI) sensor based on single-mode tapered optical fiber with a micro-hole. We drill the hole on the taper region by femtosecond laser. Due to the existence of the hole, the sensitivity of tapered fiber sensing device is improved. According to Snell’s Law, we analyze the effects of the location of the hole in the taper region and the shape of the tapered sensor on the sensor sensitivity. The experimental results indicate that the high sensitivity.Then, we give the new tapered fiber sensor sensing principle and magnetostrictive effect mechanism of a detailed analysis. At the input of taper region, when the core diameter decreases to a certain value, resulting in the normalized frequency V being approximately equal to unity, the light cannot be confined in the core and spreads to the cladding. Thus, the cladding acts as new core, and the material surrounding is now the new cladding. As the new core diameter increases and the larger NA due to the larger refractive difference between the cladding and the air, resulting in the new V, higher order modes can be supported and a multimode interference behavior occurs. Some light not refracts into the cladding and passes through the hole, for ncore> na i r, we introduce the hole as a negative lens diverging the light. Thus, the most of the light in the core entered into the cladding, the cladding acts as new core, and the material surrounding is now the new cladding. At the output taper region, these modes gradually couple back to the mode of the single-mode optical fiber.We presented a liquid refractive index(RI) sensor based on single-mode tapered optical fiber with a micro-hole. We gave the principle of sensing device, the fabricated device, and the calculation method. We studied the effects of the location of the hole in the taper region and the shape of the tapered fiber on the sensor sensitivity according to Snell’s Law. The simple fiber sensor device mainly consisted of 1550-nm laser source and the power meter for monitoring optical power. Moreover, we explored the relationship between external liquid RIs and transmission power in tapered fiber. The higher insertion loss means the higher sensitivity of the device. The experimental results showed that the high sensitivity of 214.29 d B/RIU is realized in the RI operation range of 1.417–1.445.