Interferometric Optical Sensor Research Articles

Phase Demodulator for the Measurement of Extrinsic Fabry-Perot Interferometric Sensors With Arbitrary Initial Cavity Length

A phase demodulator for fiber optic extrinsic Fabry-Perot interferometric (EFPI) sensors is proposed for dynamic signal (vibration, acoustic, etc.) measurements. Three interferometric signals with phase differences are introduced by three lasers with different wavelengths. The tangent of the desired dynamic signal is extracted from the three interferometric signals. Then, the phase modulation is recovered by the arctangent algorithm and phase unwrapping. For the technique, constant phase differences are not required. Theoretically, the phase demodulator can interrogate EFPIs with arbitrary initial cavity length. The phase demodulator can perform regardless of whether the EFPI is modulated with a phase shift $>{2}\pi $ or not. Dynamic signals are recovered successfully from EFPIs with cavity lengths ranging from $23.065~\mu \text{m}$ to $1094.703~\mu \text{m}$ by the same demodulator. As a passive demodulation method, the proposed demodulator is adapted to the detection of high frequency signals. A sinewave with a frequency of 20 kHz is extracted successfully. The algorithm of the technique is simple, robust, and provides great liberty with respect to choosing different sensors in different applications.

Laser-assisted embedding of all-glass optical fiber sensors into bulk ceramics for high-temperature applications

We develop a laser-assisted sensor embedding process to embed all-glass optical fiber sensors into bulk ceramics for high-temperature applications. A specially designed two-step microchannel was fabricated on an Al2O3 substrate for sensor embedment using a picosecond (ps) laser. An optical fiber Intrinsic Fabry-Perot Interferometer (IFPI) sensor was embedded at the bottom of the microchannel and covered by Al2O3 slurry which was subsequently sintered by a CO2 laser. The sensor spectrum was in-situ monitored during the laser sintering process to ensure the survival of the sensor and optimize the laser sintering parameters. By testing in furnace through high temperature, the embedded optical fiber shows improved stability after CO2 laser sealing, resulting in the linear temperature response of the embedded optical fiber IFPI sensor. To improve the embedded IFPI sensor for thermal strain measurement, a dummy fiber was co-embedded with the sensing fiber to improve the mechanical bonding between the sensing fiber and the ceramic substrate so that the thermal strain of the ceramic substrate can apply on the sensing fiber. The response sensitivity, measurement repeatability and high-temperature long-term stability of the embedded optical fiber IFPI sensor were evaluated in this work.

Information integrated glass module fabricated by integrated additive and subtractive manufacturing.

In this Letter, we report a novel integrated additive and subtractive manufacturing (IASM) method to fabricate an information integrated glass module. After a certain number of glass layers are 3D printed and sintered by direct ${{\rm CO}_2}$CO2 laser irradiation, a microchannel will be fabricated on top of the printed glass by integrated picosecond laser, for intrinsic Fabry-Perot interferometer (IFPI) optical fiber sensor embedment. Then, the glass 3D printing process continues for the realization of bonding between optical fiber and printed glass. Temperature sensing up to 1000°C was demonstrated using the fabricated information integrated module. In addition, the long-term stability of the glass module at 1000°C was conducted. Enhanced sensor structure robustness and harsh temperature sensing capability make this glass module attractive for harsh environment structural health monitoring.

High fringe visibility Mach-Zehnder interferometric sensor based on a Four-Core fiber

An in-line optical fiber Mach-Zehnder interferometer (MZI) sensor with high fringe visibility is reported. The sensor is formed by splicing a short section of four-core fiber (FCF) between two coupling sections. The coupling section is fabricated by cascading very short segment of few mode fiber, multimode fiber (MMF), and large core diameter MMF together. A maximum fringe visibility of approximately 30 dB is obtained in the transmission spectrum. The temperature and curvature sensing response were also experimentally investigated. The temperature sensitivities are 61 pm/°C and 49 pm/°C for dip A and dip B ranging from 30 °C to 80 °C, respectively. The curvature sensitivities for dip A and dip B are 20.77 nm/m−1 and 12.89 nm/m−1 in the range of 0.2983 m−1 to 0.7916 m−1, as well as 9.99 nm/m−1 and 5.38 nm/m−1 from the range of 0.7916 m−1 to 1.039 m−1, respectively. The proposed MZI sensor has the advantage of easy fabrication, compactness, higher fringe visibility, and low cost.

A suspended graphene-based optical interferometric surface stress sensor for selective biomolecular detection.

Graphene-based sensors are of great interest in research due to their high specific surface area and high electron mobility that make them suitable for numerous advanced applications. In this paper, selective molecular detection using an antigen–antibody reaction on suspended graphene with a cavity-sealing structure was demonstrated. The suspended graphene sealed nanocavities in a pre-patterned Si substrate, which increased robustness and allowed the use of wet chemical processes for surface functionalization of the suspended graphene to achieve selective molecular binding. The selectivity was evaluated by nanomechanical deflection induced by molecular adsorption on the suspended graphene, resulting in spectral shifts in the optical interference between the suspended graphene and Si substrate. The chemically functionalized suspended graphene enables the analysis of intermolecular interactions and molecular kinetics by colorimetry using optical interference.

基于法拉第旋光器的光纤干涉仪传感探头的设计与改进

基于法拉第旋光器的光纤干涉仪传感探头的设计与改进

Carbon Dot-functionalized Interferometric Optical Fiber Sensor for Detection of Ferric Ions in Biological Samples.

This work reports an interferometric optical microfiber sensor functionalized with nitrogen- and sulfur-codoped carbon dots (CDs) for the detection of ferric ions (Fe3+). Compared to other CD-based ferric ion sensors, the sensing mechanism of this presented sensor is dependent on the refractive index modulations due to selective Fe3+ adsorption onto the CD binding sites at the tapered region. This is the first study in which CD-based sensing was performed at the solid phase as a chelator, which does not rely on its fluorescence properties. The detection performance of the proposed sensor is not only comparable to a conventional fluorescence-based CD nanoprobe sensor but also capable of delivering quantitative analysis results and ease of translation to a sensor device for on-site detection. The presented sensor exhibits Fe3+ detection sensitivity of 0.0061 nm/(μg/L) in the linear detection range between 0 and 300 μg/L and a detection limit of 0.77 μg/L based on the Langmuir isotherm model. Finally, the potential use of the CD-functionalized optical microfiber sensor in the real environmental and biological Fe3+ monitoring applications has also been validated in this work.

Fiber Optic Interferometric Sensors at Sea

The story of the U.S. Navy’s effort to develop sensors that used optical fiber to detect targets at sea offers a window into how a technology goes from basic research to production.

Study of chitosan layer-based Fabry Perot Interferometer optical fiber sensor properties for detection of Pb2+, Hg2+ and Ni2+

This work presents investigation of properties of optical fiber sensor based on Fabry-Perot interferometer using chitosan to detect Pb2+, Hg2+ and Ni2+. The sensor was fabricated by employing chitosan layer on the tip of single mode optical fiber (SMF) which serves as Fabry-Perot interferometer. Some of the light transmitted in the SMF were reflected back due to multiple reflection in the interferometer. The chitosan was coated on the fiber end by using dip coating technique. Three sensors were fabricated which are sensor A, B and C with coating thickness of 141.85 µm, 105.52 µm and 129.25 µm, respectively. Characterization was done for sensitivity and response time of the sensors. The results showed that sensor B which was characterized for Hg2+ provided the highest sensitivity and the most stable response time.

Low-Coherence Interferometric Fiber Optic Sensor for Humidity Monitoring Based on Nafion® Thin Film.

The main aim of this work was the design and development simple fiber optic Fabry-Perot interferometer (FPI) sensor devices for relative humidity (RH) sensing with emphasis on high sensitivity and good stability. The RH fiber FPI sensor is fabricated by coating the end of a cleaved standard multi-mode (MM) fiber with hydrophilic Nafion® sensing film. The Nafion® thin film acts as an active resonance cavity of the low-coherence interferometric sensing structure. The fringe pattern, which is caused by interfering light beam in the Nafion® thin film will shift as the RH changes because the water molecules will swell the Nafion® film and thus change optical pathlength of the sensing structure. The operating principle of a FPI sensor based on the adsorption and desorption of water vapour in the Nafion® and the limitations of this sensor type are discussed in this work. The fiber optic hygrometer was tested in the visible (400–900 nm) region of spectra for measurement of relative humidity (RH) in the range of 5.5–80% at room temperature (RT) in air. The fiber optic humidity sensor has a very short response time (t90 = 5–80 s) and a fast regeneration time (t10 = 5–12 s) as good as commercial sensors.

Heterogeneous silicon photonics sensing for autonomous cars.

Heterogeneous silicon photonics is uniquely positioned to address the photonic sensing needs of upcoming autonomous cars and provide the necessary cost reduction for widespread deployment. This is because it allows for wafer-scale active/passive integration, including optical sources. We present our recent research and the development of interferometric optical gyroscopes and LiDAR sensors. More specifically, we show a fully integrated gyroscope front-end occupying an area of only 4.5 mm2. We also show the first dense pitch optical phased array using heterogeneous phase shifters. The 4 µm pitch heterogeneous phase shifters provide very low V2π of only 0.35-1.4 V across 200 nm, low residual amplitude modulation of only 0.1-0.15 dB for 2π phase shift, extremely low static power consumption (<3 nW), and high speed (> 1 GHz). All of these factors make them ideal for next-generation LiDAR systems that employ optical phased arrays.

A comparative study and experimental observations of optical fiber sagnac interferometric based strain sensor by using different fibers

Abstract Designing of strain monitoring system is a vibrant topic for the researchers. Strain monitoring systems are required in various fields such as mechanics, aeronautics, metallurgy and health monitoring of complex structures etc. Researchers designed different strain monitoring systems based on requirements. In this paper, we have reported a comparative study of Optical Fiber Sagnac Interferometer (OFSI) based strain sensors using three different types of fiber, i.e Polarization Maintaining Fiber (PMF), Standard Photonic Crystal Fiber (PCF) and High Birefringence Photonic Crystal Fiber (Hi-Bi PCF). The transmission spectrums of the sensors were recorded using Optical Spectrum Analyzer (OSA). We have experimentally analyzed the response and sensitivity of the sensors at different applied strains. The experimental results show that the optical interferometric strain sensor using PMF is having highest sensitivity in comparison to other sensors.

Thermal stability of optical fiber metal organic framework based on graphene oxide and nickel and its hydrogen adsorption application.

The electrochemistry (EC) method was used to synthesize graphene oxide-nickel (GO-Ni) metal organic framework (MOF) that has the thickness of μm-level. The MOF's thermal stability and hydrogen adsorption and desorption capacity were measured by using an optical fiber Mach-Zehnder interferometer (MZI) sensor. This MZI was fabricated by core-offset fusion splicing one section of single mode fiber (SMF) between two SMFs. Experimental results showed that the GO-Ni MOF could be stabilized, even as the environmental temperature reached 125 °C. The MOF showed good hydrogen adsorption ability for the the MOF and hydrogen molecules's interactions.

Coherent optical fiber interferometric sensor for incipient cavitation index detection

Optical fiber sensors (OFSs) are nowadays widely adopted in many different fields and applications. Cavitation in pipeline systems is one of the main concerns of engineers because of its serious consequences for the lifetime of pipelines and on the performance of hydraulic devices. Among other useful parameters the incipient cavitation index is one of the most important because it represents the very beginning of the phenomenon. The present paper discusses the possibility of using optical fiber technology to detect cavitation in a pipeline. The experimental system exploits an interferometric fiber optical sensor based on a coherent demodulation scheme, avoiding the need for working point stabilization systems and coping with the polarization fading. Several dispositions and geometries for the sensors have been tested to select the most efficient solution. The results are then compared with cavitation indexes calculated following the standard procedure, using accelerometer measurements, to prove the optical fiber sensors’ effectiveness.

Pipeline monitoring and leak detection using Loop integrated Mach Zehnder Interferometer optical fiber sensor

Abstract The Loop integrated Mach-Zehnder Interferometer (LMZI) optical fiber vibrational sensor was proposed to be implemented in pipeline monitoring and leak detection. The vibration sensing is based on power demodulation method using the torsion-sensitive LMZI sensor. In the 40 m steel pipeline field test, the LMZI sensor detected a significant leak-induced peak at ∼100 Hz during leak at 2 bar water pressure, whereas an additional ∼288 Hz peak was detected during leak at 3 bar water pressure. Both of the detected leak-induced frequencies were compared to the commercial accelerometer and showed good agreements with percentage errors of 0.4% and 2.64% at 2 bar and 3 bar respectively. The LMZI sensor is an alternative leak detection method which has great potential in replacing current conventional sensors in the future.

Analytical Analysis and Experimental Validation of a Multi-parameter Mach-Zehnder Fiber Optic Interferometric Sensor

Here we report a simple analytical technique to model a Mach–Zehnder fiber optic interferometric sensors that allow us to predict and calculate via computer simulations parameters that are not easily obtained experimentally. This model was calibrated and compared with experimental data using a 120 mm sensor for measurements of temperature, refractive index and water level. For instance, we were able to calculate the effects on the cladding effective index caused by the variation of those physical parameters. Moreover, this analysis could further our understanding of such sensors and allow us to make predictions about their use in different applications and even their behavior with different sensing lengths.

Simultaneous measurement of gas pressure and temperature with integrated optical fiber FPI sensor based on in-fiber micro-cavity and fiber-tip

Abstract In paper, an integrated optical fiber Fabry-Perot interferometer (FPI) sensor is proposed and fabricated. The all-fiber sensor is composed of an in-fiber micro-cavity machined by 193 nm excimer laser and a tiny segment of single-mode fiber (SMF). Due to the production of reflection mirrors, the composite FPI structure with different interference cavity is formed between every two surfaces of micro-cavity and fiber-tip. Resulting from the influences of thermal expansion effect of fiber and the thermo-optic effect of in-cavity gas, the interference spectrum of FPI sensor can shift with the temperature and pressure change with different rules. Experimental researches indicate, the low-frequency interference fringe of air cavity is sensitive to pressure change and insensitive to temperature change, but the high-frequency interference fringe of micro-fiber cavity is sensitive to temperature change and insensitive to pressure change. Through analyzing with fast Fourier transform (FFT) and Fourier band-pass filtering (FBPF) methods, we obtain the temperature and pressure sensitivities of the two different cavities. Owning to the different responses to gas pressure and temperature change, the fiber sensor can be used in simultaneous measurement of them, and has excellent merits of miniature size, strong tip structure, simple manufacturing and low cost.

Feasibility use of in-line Mach–Zehnder interferometer optical fibre sensor in lightweight foamed concrete structural beam on curvature sensing and crack monitoring

This article presents a novel study on curvature sensing and crack monitoring in lightweight foamed concrete structural beam using the packaged fibre-based in-line Mach–Zehnder interferometer curvature sensor. The Mach–Zehnder interferometer sensors which consist of two abrupt biconic tapers were fabricated and packaged into polypropylene slabs to protect the sensors under harsh condition of the real sensing environment, as the sensors were embedded into lightweight foamed concrete structural beams for field tests. Pretest characterizations of Mach–Zehnder interferometer sensors based on the packaging thicknesses at different operating wavelengths (1310, 1490 and 1550 nm) were done before the field tests. Three packages with different thicknesses were prepared to justify the effect of the packaging thicknesses on the curvature sensitivity of sensors. Results showed that the Mach–Zehnder interferometer sensor with a thicker bottom slab has the highest sensitivity of up to 3.53 µW m−1 which is capable of detecting a minimum curvature of 0.25 km−1 and a maximum curvature radius of up to 4 km. In the field tests, three Mach–Zehnder interferometer sensors were embedded into the lightweight foamed concrete structural beams with different polypropylene percentages (0.4%, 0.25% and 0%, respectively) to characterize the sensor performance according to the concrete environments with different tensile capacities. Mach–Zehnder interferometer sensor managed to hold up to a maximum loading force of 26 kN in the concrete environment before stopping functioning. Optical powers in response to the loading forces imposed to the beams were mapped to the strains measured by the lead wire alloy foil strain gauges (brand: TML, model: FLK-6-11) with a good correlation value of up to 0.968. Furthermore, the double-sided sensing property of Mach–Zehnder interferometer sensors preponderates over the conventional strain gauges in detecting the internal cracking within the concretes before any earlier sighting of the macrocracks.

Hardware implementation and comparison of displacement retrieval algorithms for a laser diode-based optical feedback interferometric sensor

Optical feedback interferometer (OFI) lasers, also called self-mixing (SM) lasers, have been widely explored over the last couple of decades due to their low cost, compactness, and self-aligned nature and they provide a very good solution for measurements of displacement, vibration, distance, velocity, etc. The SM effect takes place when a part of the laser beam is fed back to the active laser cavity after reflecting from the target. The reflected beam interferes with the emitted beam and hence the optical and spectral characteristics of the laser get changed. To retrieve the vibration or displacement signal of the target from the SM signal, different postprocessing algorithms have been proposed, such as the phase unwrapping method (PUM). The first step of the PUM leads to the coarse estimation of the laser phase and the final step is an iterative joint estimation of 2 parameters, namely laser coupling coefficient $C$ and linewidth enhancement factor $\alpha $. To make this algorithm applicable for real-time measurements, parallel joint estimation for a wide range of $C$ and $\alpha $ values needs to be done. In this research, 3 algorithms, namely PUM, direct fringe unwrapping (DFU), and improved DFU (IDFU) were tested for FPGA implementation by using Verilog HDL (hardware description language) so that more precise and real-time vibration and displacement signals of targets could be extracted from the SM sensor in an embedded systems environment. These algorithms were developed using Verilog HDL for implementation on the Xilinx Spartan-3 Xcs400-FG320 development board. Our designed IDFU algorithm performed $0.492\, $times better than the parallel PUM algorithm in maximum clock frequency and $1.53$ and $1.21$ times better than the PUM in slice registers and LUT utilization of hardware resources, respectively. The designed DFU algorithm can operate $1.355$ times better than IDFU in maximum clock frequency and $25.34$ and $14.25$ times better than IDFU in slice registers and LUT utilization of hardware resources, respectively.

Contactless Optical Fiber Interferometric Sensor to Monitor Water Content in Ethanol

A simple contactless optical fiber interferometric sensor for real-time measurement of low-level of water content in ethanol is proposed and demonstrated. The sensing head consists of a multi-cavity Fabry–Perot interferometer formed with a fiber tip in close contact with a quartz spectrophotometer cell. Ethanol–water solutions introduced into the cell cavity produce a change in the optical path length of one cavity of the interferometer. The increment of water content induces refractive index changes, but more important the absorption of the light increases. Both effects produce a significant change in the interference spectra that can be easily monitored and quantified in the Fourier domain. We demonstrate that our technique can detect water content (0%–60%) in ethanol with a detection limit as low as 0.5%.