Cylinder-type fiber-optic Vernier probe based on cascaded Fabry–Perot interferometers with a controlled FSR ratio

Abstract

We designed a cylinder-type fiber-optic Vernier probe based on cascaded Fabry-Perot interferometers (FPIs) in this paper. It is fabricated by inserting a short single-mode fiber (SMF) column into a large-aperture hollow-core fiber (LA-HCF) with an internal diameter of 150 µm, which structures a length adjusted air microcavity with the lead-in SMF inserted into the LA-HCF from the other end. The length of the SMF column is 537.9 µm. By adjusting the distance between the SMF column and the lead-in SMF, the spectral change is displayed intuitively, and the Vernier spectra are recorded and analyzed. In sensitivity analysis, the probe is encapsulated in the medical needle by ultraviolet glue as a small body thermometer when the length of the air microcavity is 715.5 µm. The experiment shows that the sensitivity of the Vernier envelope is 12.55 times higher than that of the high-frequency comb. This design can effectively reduce the preparation difficulty of the optical fiber Vernier sensor based on cascaded FPIs, and can expand the applied fields by using different fibers and materials.

Optical Harmonic Vernier Effect: A New Tool for High Performance Interferometric Fiber Sensors

“…Hence, the ratios obtained are 1.95, 2.93, and 3.86, respectively, for the first three harmonic orders. As observed, the ratio values are approximately increasing by factors of 1 i  , as predicted by equation (11). Furthermore, it is possible to make a fair comparison between the structures independent of the specific tuning value of the interferometers and to demonstrate more directly the linear enhancement of the M-factor with the order of the harmonics by using a compensated wavelength shift.…”

“…At last, the third group compares the M-factor for each harmonic with the M-factor for the equivalent fundamental optical Vernier effect. It shows the 1 i  factor improvement in the M-factor with the order of the harmonic, as predicted by equation (11).…”

Optical Vernier Effect: Recent Advances and Developments

“…In terms of applications, the configurations using FPIs were mainly used for temperature [15,16,20,23,25,29,30,32,34,38] and strain sensing. [9,12,18,19,35] Apart from these two applications, others such as magnetic field sensing, [9] gas refractive index, [21,26] and pressure sensing, [17,24] airflow sensing, [22] hydrogen sensing, [14] humidity sensing, [13] volatile organic compounds sensing, [28] and refractive index sensing of liquids [31] were also reported.…”

Vernier effect using in-line highly coupled multicore fibers

“…The optical Vernier effect is an efficient yet simple method widely used for enhancing the sensitivity of fiber optic sensors (FOS) 1 , 2 . Essentially, the effect is produced upon combining two interferometric or resonant structures designed with similar free spectral ranges (FSRs) 3 . When the spectral responses of both structures are superimposed, a low spatial frequency envelope is generated, and any spectral shift in one of the optical structures results in an enhanced shift of the envelope’s frequency.…”

“…For example, a Vernier effect-based fiber refractometer has been recently reported with a sensitivity of 500 µm/RIU, a record value for this kind of fiber sensor 5 . Thanks to the inherent advantages of fiber optics, the Vernier effect has been successfully used in temperature 6 – 29 , pressure 30 – 35 , refractive index 36 – 44 , strain 45 – 52 , curvature 53 , 54 , displacement 55 , and humidity 56 FOS. Moreover, mature technologies such as focused ion bean and femtosecond laser micromachining 35 , 48 , photonic crystal fibers 7 , 36 , and fiber tapering 4 , 43 , 46 have been effectively used in the construction of highly-sensitive Vernier devices, thus demonstrating the versatility of Vernier-based sensor schemes.…”