In-line Fiber Interferometers Research Articles

Control of gas pipeline leakage detection based on hybrid inline fiber interferometer

Hybrid inline fiber interferometers gained attention recently especially in the building control and detection fields due to their hybrid multi-path interferences, multi-parameter measurements, high sensitivity, and high precision. This work used etched multimode fiber (MMF) to introduce a novel medical gas pipeline leakage detector based on hybrid Fabry-Perot/Mach-Zehnder inline fiber interferometer (FP-MZI). The hybrid FP-MZI of this work consisted of two cascaded identical fiber Bragg gratings (FBGs) spliced to coreless fiber sandwiching the MMF. Four samples of different MMF lengths and sizes were used as sensing heads in the detection measurements. Self-imaging and phase-equations of the proposed interferometer were solved analytically to select the required length; then COMSOL software was used to ensure the occurrence of the required interference along the proposed interferometer at the designed wavelength. Two medical gas sources; air compressor and high-pressure gas cylinder, attached to two pipelines of size 15×0.7, and 12×0.6 mm was used to provide the required pressure. Gas leak was introduced to the pipes manually through controlled valves and measured using the proposed hybrid FP-MZI. Both constant and variable gas flowrates was investigated with variable gas pressures. The obtained sensitivity was ranged from 0.17-20.9 pm/bar for all of the investigated cases.

Lab on optical fiber: surface nano-functionalization for real-time monitoring of VOC adsorption/desorption in metal-organic frameworks

Abstract Metal-organic framework (MOF) nanomaterials are emerging porous coordinative polymers with large surface area and high porosity. Their application scenarios highly depend on adsorption/desorption dynamics of guest molecules in the framework. For representative ZIF-8 with framework flexibility, the study of molecule transportation in the pore channels of ZIF-8 will address the ambiguity of unclear application scenarios. In this study, the integration of lab-on-fiber technology and nanotechnology are demonstrated for real-time monitoring of adsorption/desorption dynamics of heterocyclic volatile compounds (VOCs) with kinetic diameters larger than the window aperture of ZIF-8. The in-line fiber interferometer with cascaded long-period gratings is used to monitor the real-time refractive index change of VOC adsorption/desorption. The structure-effect relationship between guest VOCs and framework flexibility is analyzed. It shows that the adsorption dynamics is highly related to the molecular geometry and kinetic diameter. The framework flexibility results in the trapping of guest VOCs toluene, pyridine, and tetrahydrofuran in the frameworks. The methanol adsorption/desorption is an effective strategy for the fast desorption of trapped residual VOCs in the framework. Finally, we conceptually demonstrated the real-time monitoring of trace toluene enrichment using ZIF-8 for indoor air purification. This study paves the way for the in-depth understanding of framework flexibility for MOF’s application.

Coherent Rayleigh Backscatter Phase Noise in Digitally Enhanced Fiber Interferometers

The coupling of Rayleigh backscatter induced phase noise in bi-directional, inline fiber interferometers compromises detection sensitivity for Fourier frequencies less than 1 Hz. Here we report experimental and theoretical work highlighting the coupling of backscatter phase noise, and its subsequent range-gating and suppression using digitally enhanced homodyne interferometry. Between two in-line fiber interferometers, each with a differential arm-length of 8 km, we demonstrate a relative stability of 10 Hz/ $\sqrt{\text{Hz}}$ at a Fourier frequency of 100 mHz.

Error estimation in the analytical modeling of abrupt taper Mach-Zehnder interferometers

In-line fiber interferometers based on abrupt tapers have been shown as a promising low-cost platform for various sensing applications. Many variations have been demonstrated experimentally using combinations and permutations of novel photonic devices such as photonic crystal fibers or multimode fibers. In this manuscript, an analytical model for light propagation in an abrupt taper Mach-Zehnder Interferometer in commercial single-mode fiber based on coupled-mode theory is detailed. The model calculates the mode propagation process, and the result is compared with previous numerical simulations. For experimental verification, an in-line Mach-Zehnder interferometer based on an abruptly tapered fiber is fabricated and tested. The spectrum calculated by the model matches well with the measured spectrum. To reduce the computational complexity, a method for step size estimation and the corresponding error accumulation is discussed and verified. This can serve as a basis to estimate the optical responses of this class of abrupt taper based fiber sensors. With the right packaging, these sensors can play a vital role in rugged and hostile environments.

Cascaded Two-Core PCFs-Based In-Line Fiber Interferometer for Simultaneous Measurement of Strain and Temperature

A new fiber sensor configuration based on the cascaded in-line fiber interferometers has been proposed and experimentally demonstrated for simultaneous measurement of strain and temperature. In order to make the cascaded in-line interferometers, we used two different types of two-core photonic crystal fibers (TCPCFs) having two cores in the symmetry and asymmetry structures. The TCPCFs have different transmission characteristics owing to the distinct geometric structures of the integrated cores, this causes the different strain and temperature sensitivities and thus the two parameters can be discriminated. The measurement resolutions are achieved to be $11.1~\mu \varepsilon $ and 1.10 °C for strain and temperature, respectively, in the 10 pm wavelength resolution.

Micro-structured fibers and their applications in fiber-optic sensors and random fiber lasers

Micro-structured fibers are important devices that have drawn intensive attentions and proved to be powerful platforms for various applications over the past decades due to their remarkable merits and advantages, such as small footprint, immunity to electromagnetic interferences, light weight, high physical flexibility, and low cost. Modifications in optical fibers can be used as light-steering elements to excite and couple back different core and cladding modes and form various in-fiber structures, including in-line fiber interferometer, fiber micro-cantilever, fiber random gratings, and so on. These micro-structures, when applied as fiber-optic sensors in the presence of external disturbances, show high sensitivity in terms of the significant changes in the guided light features. Novel micro-structured bend-insensitive fiber-based in-line fiber interferometer and micro-cantilever have been proposed to realize both static and dynamic parameter measurements, including temperature, axial strain, surrounding refractive index, and vibration. We have also developed a novel fiber random grating along with a spectral correlation algorithm for simultaneous measurement of three static measurands. To move a step forward, random fiber lasers based on fiber random grating are achieved for either improving the laser performances or sensing applications of temperature, strain, and ultrasound measurements with high sensitivity.

A robust fiber inline interferometer sensor based on a core-offset attenuator and a microsphere-shaped splicing junction

A robust inline fiber interferometer sensor based on concatenating a core-offset attenuator and a microsphere-shaped splicing junction is proposed, fabricated and applied for sensing applications. Its transmission spectrum shows multiple resonant dips due to the interference between core and cladding modes. While the interferometer sensor is utilized to test surrounding RI from 1.33 to 1.37, it exhibits a linear relationship between peak wavelength shift and RI change. A maximal sensitivity of −56.325 nm/RIU (refractive index unit) is obtained. For temperature sensing, the sensor presents a fair quadric relationship between peak wavelength shift and temperature from 25 to 650 °C, in which the variation rate of the effective RI difference between core and cladding modes with temperature is nonlinear. In addition, a coefficient matrix is constructed to simultaneously measure RI and temperature. The fiber interferometer sensor offers high potential in sensing applications due to its advantages of low cost, simplicity, and robustness.

Optic fiber sensors fabricated by laser-micromachining

Recent progress in using excimer and femtosecond lasers to fabricate functional fiber-optic sensing devices is reviewed extensively in this paper. The application of femtosecond lasers is to fabricate fiber gratings and in-line fiber-optic interferometers for measurements of strain, temperature and refractive index. The application of 157nm excimer lasers is to create fiber gratings and in-line fiber interferometers for measurements of strain, acceleration, pressure, temperature and refractive index. Compared with conventional optical fiber sensors, these novel micro optical fiber sensors fabricated by laser-micromachining have outstanding advantages, such as fast and direct formation, easy mass-production with ultralow-cost, good reproducibility, excellent optical performance, low temperature cross-sensitivity, etc., which pave a way to form a new generation of miniature fiber-optic sensors for many applications.