In-Line Mach Zehnder Interferometer Based on Ytterbium Doped Fiber with Up-Taper Structure in Fiber Ring Laser and Its Application in Sensing

Abstract

We report an ytterbium (Yb) doped fiber Mach Zehnder interferometer (MZI) based on the up-taper fiber structure in a fiber ring laser (FRL) cavity. Different from the traditional FRL sensing system, in which additional filters are required, the designed structure simultaneously acts as a filter, sensor and gain medium. Furthermore, thanks to the high thermal–optical coefficient of Yb doped fiber, the temperature sensitivity of 0.261 nm/°C can be achieved in the range of 10–50 °C. In addition, benefiting from the unique characteristics of the laser system itself, the designed structure has a narrower linewidth (−0.2 nm) and a higher signal-to-noise ratio (SNR) (−40 dB) than the sensor system based on a broadband light source (BBS). Meanwhile, the refractive index (RI) response and stability of the system are measured. The RI sensitivity is up to 151 nm/RIU, and the wavelength fluctuation range within two hours is less than 0.2 nm. Therefore, the designed structure is expected to play a significant role in human life safety monitoring, aircraft engine temperature monitoring, etc.

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

“…In contrast, wavelength demodulation is insensitive to source variations; however, the demodulation process implies an intricate or exp stage. Recently, Weihao Lin et al achieved an RI ring fiber laser sensor with modest sensitivity close to 150 nm/RIU [81]. Although this sensitivity is not competitive for interferometric fiber optic structures, its demodulation and the ring fiber laser configuration are not intricate (see Figure 6a); moreover, the principle of operation and the elements involve being similar than as previously described in Figure 1a.…”

“…These structures act as a wavelength selective filter (WSF) into the fiber laser cavity and provide a tunable effect or, in some cases, intensity modulation. 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].…”

Adaptive Fiber Ring Laser Based on Tapered Polarization Maintaining Fiber in Sagnac Loop for Temperature and Salinity Sensing

“…By utilizing the advantages of good SNR and the narrow bandwidth of a fiber ring laser (FRL) cavity, an intensity demodulation scheme with a detection limit of 0.0023‰ has been achieved. Our research team proposes that doped optical fibers inside the FRL structure be used to directly monitor temperature and refractive index [24,25], eliminating the need for an extra filter and sensor head design. Comparatively, the material properties of optical fibers result in low refractive index sensitivity.…”