Refractive Index Fiber Laser Sensor by Using a Fiber Ball Lens Interferometer with Adjustable Free Spectral Range

Abstract

In this work, a fiber laser refractometer based on a fiber ball lens (FBL) interferometer is proposed. The linear cavity erbium-doped fiber laser uses an FBL structure acting as a spectral filter and sensing element for determining the RI of a liquid medium surrounding the fiber. The optical interrogation of the sensor is the wavelength displacement of the generated laser line as a function of the RI variations. For the proposed FBL interferometric filter, the free spectral range of its wavelength-modulated reflection spectrum is adjusted to maximum in order to obtain RI measurements in a range of 1.3939 to 1.4237 RIU, from laser wavelength displacements in a range from 1532.72 to 1565.76 nm. The obtained results show that the wavelength of the generated laser line is a linear function of the RI variations on the medium surrounding the FBL with a sensitivity of 1130.28 nm/RIU. The reliability of the proposed fiber laser RI sensor is analytically and experimentally investigated.

Fiber Laser Sensor Configurations for Refractive Index, Temperature and Strain: A Review

“…Several works employ tapered optical fibers WSF for RI sensing purposes [41,42,77,78,[81][82][83]. Other alternatives employ optical fiber structures with miss-match core sections, then the light that interacts with the surrounding medium is higher and provides attractive characteristics [33,41,79,80,[84][85][86][87][88][89]. For example, Bin Yin et al propose an FBG and multimode fiber (MMF) integration to detect three parameters, inclusive of RI [38].…”

“…The fiber laser configuration can be appreciated in Figure 6c. R.I. Álvarez-Tamayo and P. Prieto-Cortes reported a linear fiber laser cavity for refractive index sensing [89]. The linear fiber laser cavity is not intricate, and using a ball lens can estimate the reflective index changes applied at one of the linear fiber laser cavities.…”