Femtosecond laser fabricated all-optical fiber sensors with ultrahigh refractive index sensitivity: modeling and experiment

Abstract

All-optical fiber sensors based on ultracompact fiber inline Mach-Zehnder interferometer (MZI) are fabricated by side-ablating a U-shape microcavity in a single-mode optical fiber with the fiber core partially removed using femtosecond (fs) laser pulses, in which the two light paths are accordingly formed in the remaining D-type fiber core and the U-shape microcavity. Beam propagation method (BPM) analysis is utilized to illustrate the dependences of good transmission spectra on parameters including the ablation depth, ablation length and the refractive index of U-shape micocavity, which gives some guidelines to optimize parameters for fs laser micromachining and predicts RI (refractive index) sensitivities within given RI ranges. The modeling results of ultrahigh RI sensitivities for gases and solutions are -3243.75 ± 0.65nm/RIU (refractive index unit) and -10789.29 ± 18.91nm/RIU, respectively. In RI testing experiments, the sensor exhibits ultrahigh RI sensitivities of -3754.79 ± 44.24nm/RIU with refractive indices ranging from 1.0001143 to 1.0002187 by testing different mixture ratios of N2 and He gases, and -12162.01 ± 173.92nm/RIU with refractive indices ranging from 1.3330 to 1.33801 by testing different concentrations of sucrose solutions, which is essentially in agreement with the modeling results.

Hydrodynamic simulation of ultrashort pulse laser ablation of gold film

“…Due to its unique characteristics, the femtosecond (fs) laser is a promising tool for the precise micro/nanomachining [1][2][3][4] and surface structure modification [5,6] of solid materials. Compared with picosecond (ps) laser pulses, fs laser pulses induce a fast energy deposition into the electronic system, which takes a few ps to relax with the lattice, simplifying fundamental analyses.…”

BPM analysis of all-optical fiber interferometric sensor based on a U-shape microcavity

“…As for refractive index and temperature sensing applications, FPI and MZI sensors all exhibit good sensitivities and the sensitivities of MZI are better than those of FPI. However, the FPI sensor as a tip structure is smaller and more robust than MZI sensor, since one is of reflectivity spectrum and the other is of transmission spectrum [1,6,7].…”

Femtosecond laser fabricated micro Mach-Zehnder interferometer with Pd film as sensing materials for hydrogen sensing

“…Various structures of microinterferometer cavity have been created by fs laser and used as optical fiber sensors [4][5][6][7][8]. Especially, an ultracompact microcavity Mach-Zehnder interferometer (MMZI) fabricated by fs laser has been used for measuring refractive index (RI) and different mixture ratios of N 2 and He gases [6,9]. MMZI has also been proposed for temperature measurement and the sensitivity achieved is ∼0.046 nm∕°C within the temperature ranging from 100°C to 1100°C [10][11][12][13][14][15][16].…”

“…The RI values of the fiber core n core and the microcavity n cavity are 1.4682 and 1.000132 respectively [9]. Wavelength λ used in the simulations is between 1200 and 1400 nm.…”