Mach-Zehnder Interferometer Sensor Research Articles

FPI and MZI combined high-sensitivity sensor based on PDMS microcavity

In this paper, an optic-fiber temperature sensor is proposed with an innovative structure design and sensing theory combination. The structure design is consisted of classic SMSMS structure and a polydimethylsiloxane (PDMS) microcavity, which is formed by inserting single mode fibers (SMF) and multimode fibers (MMF) from both ends of a hollow core fiber (HCF) filled with uncured PDMS. By adjusting the length (L) of the cavity into proper value, the reflection temperature sensitivity reaches up to −567.86 pm/℃, and the transmission sensitivity reaches −120.69 pm/℃. Due to the presence of the PDMS microcavity, the reflection spectrum achieved highly sensitive temperature Fabry-Perot interferometer (FPI) sensor. Moreover, a Mach-Zehnder interferometer (MZI) temperature sensor also formed by monitoring the transmission spectrum, and its temperature sensitivity is elevated about 7 and 1.2 times compared with the pure splicing SMSMS and the splicing + PDMS coating structure. By deploying the PDMS microcavity, FPI sensor and MZI sensor were combined inside one device with significant temperature sensing performance, and these two combined sensors can cross-correct within the intersected detection range. With simple manufacture steps, higher temperature sensitivity and bigger sensing range are achieved.

A Ring Core Fiber Sensor Based on Mach–Zehnder Interferometer for Transversal Force Sensing With Solvable Temperature Cross Sensitivity

In this work, we proposed a ring core fiber (RCF)-based all-fiber sensor used for transverse force sensing. The sensor is composed of 1-mm coreless fiber (CLF) and 2.5-cm RCF. Then, the coreless (CL)-ring core (RC) fiber structure is connected to two segments of single-mode fibers to form a Mach–Zehnder interferometer (MZI). The transmission spectrum of the MZI structure has a large extinction ratio (ER) of up to 20 dB with a free spectral range (FSR) of 9.3 nm. After the fabrication, the MZI sensor is packaged for force sensing at different temperatures. The different values of forces are applied on the fiber sensor, which are tuned from around 0.26 to 1.5 N/mm. With the increase of transverse force, the spectra of output signals show a linear redshift. The force sensitivity of the proposed MZI sensor reaches up to 4.109 nm/(N/mm) with a good linearity of 0.9824. By using a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times2$ </tex-math></inline-formula> matrix, the temperature cross sensitivity can be extracted. The proposed force sensor based on the MZI fiber structure shows great potential applications in the field of structural health monitoring and supercapacitor safety detection.

Refractive Index Measurement Based on Thin-Core Fiber In-Line Mach-Zehnder Interferometer and Differential Intensity Demodulation

A compact and reliable thin-core fiber (TCF) based in-line Mach-Zehnder interferometric (MZI) sensor for refractive index (RI) measurement is proposed and experimentally demonstrated. A section of TCF is sandwiched between a multi-mode fiber (MMF) and a single-mode fiber (SMF) to form the sensing head. In addition, the use of the differential intensity demodulation method not only greatly reduces the system cost, but also solves the problem of power fluctuation in the RI interrogation system. Three samples with different sensing lengths have been made, and the maximum sensitivity of 59.9 dB/RIU has been obtained in the range of 1.332–1.411 RIU, which means the measurement resolution is about 1.669 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> RIU. Besides, the proposed MZI-based RI sensor is less sensitive to temperature, thus the cross-sensitivity effect can be greatly weakened.

Enhanced Mach-Zehnder interferometer multimode–single-mode–multimode fiber optic refractive index sensor based on surface plasmon resonance

In this paper, an all-fiber Mach-Zehnder interferometer (MZI) sensor for refractive index (RI) measuring is presented, which is based on Multimode–Single-mode–Multimode (MSM) fiber. The effects of both reducing the radius of the sensing part and the surface plasmon resonance (SPR) on its efficiency are investigated. Increasing the interaction of high-order modes with external media, caused by etching the cladding layer of the single-mode fiber part, significantly improves the sensitivity. Both wavelength and intensity interrogation approaches are employed to study the Multimode–etched Single-mode–Multimode (MESM) fiber sensor. The intensity and the wavelength sensitivities for the RI measurement in the range of 1.428–1.458 are obtained as −2306.754 %/RIU and 1315.74 nm/RIU, respectively. Finally, the MESM-SPR sensor is proposed and characterized. Results exhibit high performance in the RI range of 1.333 to 1.357, in which the sensitivity of 1437.056 nm/RIU is achieved. The advantages like low cost, high sensitivity, and simple fabrication methods make these sensors promising devices for chemical, food industry, and biosensing applications.

A novel method of curvature demodulation for Mach-Zehnder interferometer optical fiber curvature sensors

This paper constructs a novel curvature demodulation method for Mach-Zehnder interferometer (MZI) optical fiber sensors. The method is composed of two parts: spectral curve decomposition and support vector machine regression (SVR) of curvature. The authors fabricated the MZI fiber optic curvature sensor and carried out curvature loading experiments. The curvature demodulation method proposed in this paper includes the following steps: spectral data acquisition, data normalization, coefficient vectors calculation, and curvature calculation. The minimum root mean square errors (RMSE) of the curvature demodulation method is 0.02133 m−1. This method has two characteristics: wide curvature demodulation range and unitive curvature regression expression. The curvature demodulation method is not only limited to the MZI sensor curvature demodulation but also applicable to the demodulation of other physical quantities with the spectral data as input. This paper provides a new idea for solving similar demodulation problems.

In-fiber Mach-Zehnder interferometer based on hollow optic fiber for metal ion detection.

A new, to the best of our knowledge, in-fiber Mach-Zehnder interferometric sensor is proposed and experimentally demonstrated for detecting Cu2+ ions in an aqueous environment. The sensor is fabricated simply and cost-effectively by arc-fusing a short section of hollow optical fiber between two standard single-mode fibers and is functionalized by depositing chitosan and poly(acrylic acid) bilayers using electrostatic self-assembly. The proposed sensor shows a linear response with sensitivity of 42 nm/mM in the Cu2+ ion concentration from 0 to 40 µM. Moreover, the fiber sensor exhibits good reusability and repeatability and is a promising candidate for contamination detection in drinking water and industrial waste water.

A Temperature Sensor Based on Composite Optical Waveguide

We propose a temperature sensor, which consists of a composite optical waveguide (COW) sandwiched between two single mode fibers (SMFs). The COW is formed by side polishing a capillary optical fiber (COF) and filling with polydimethylsiloxane (PDMS). Unlike the conventional fixed sensing structure, the Mach-Zehnder interferometer (MZI) and multimode interferometer (MMI) can be selectively formed by adjusting different fusion splicing parameters, so as to produce a blunt or sharp tapered fusion structure between the SMF and the COF. Because of the high thermo-optic coefficient of PDMS and the high-order modes excited by the tapered fusion structure, the MZI and MMI sensors are very sensitive to temperature. The experimental results show that within the temperature measurement range from 16 °C to 80 °C, several resonance wavelengths of the MZI and MMI sensors exhibit a remarkable blue shift with the increase of temperature. The maximum temperature sensitivities of the MZI and MMI sensors can reach −0.50 nm/ °C and −0.88 nm/ °C, respectively. The humidity sensitivity of the sensor is −0.10 nm/%RH. However, in the process of temperature measurement, humidity has little influence on the sensitivity of the sensor. Due to the advantages of compact size, flexible structure, and high sensitivity, the sensor has great application potential in monitoring the changes of environment and living temperature.

High sensitivity sensor based on mode interference of fiber arc-shaped misaligned welding structure for strain and torsion sensing

We propose a compact and ultrasensitive all-fiber Mach–Zehnder interferometer sensor based on an arc-shaped misaligned structure that can measure strain and torsion sensing. The structure utilizes a single-mode fiber and was fabricated in an optical fiber fusion splicer through simple discharge and fusion splicing steps. The experimental and theoretical investigations of its response revealed an optimal strain sensitivity of up to ~267.17 pm /με¯. In addition, the maximum torsion sensitivities in the clockwise and counterclockwise rotation directions of the fiber cross section were ~ − 1.528 dB/(rad/cm) and ~1.2191 dB/(rad/cm), respectively. Further, the proposed device exhibited low temperature cross sensitivity. Therefore, this single-mode-fiber based core-cladding modal interferometer has great potential in the field of photoelectric sensing due to multiple advantages such as compact size, easy fabrication process, low cost, etc.

High Fidelity MZI-BCG Sensor With Homodyne Demodulation for Unobtrusive HR and BP Monitoring

An all-optical active homodyne detection aided fiber-optic Mach-Zehnder interferometer (MZI) vital signs monitoring system is proposed and investigated. The active homodyne detection is mainly realized by employing a wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) and automatic closed-loop control system (CLCS). It can effectively maintain the MZI sensor to operate around the quadrature point and successfully eliminate the fading effect of output signal induced by low frequency drift. Therefore, high fidelity and high stableness of the ballistocardiograph (BCG) signal is guaranteed. The results show that according to the Bland-Altman and the confidence ellipse analysis, the heart rate (HR) monitoring performance reveals high accuracy and good consistence. What’ more, a multiple linear regression-based blood pressure (BP) estimation model is presented, which shows that the BP is highly correlated with I-J-K complex oriented features, including IJ interval, JK interval and JK amplitude. It indeed offers a potential approach to achieve cuff-less BP estimation merely based on the high-fidelity BCG signal. In conclusion, the proposed MZI-BCG monitoring system is simple to use, and it shows great potential in future unobtrusive cardiac monitoring both in home and hospital.

High-Sensitivity Liquid Level Sensor Based on the Balloon-Shaped Fiber Optic MZI

We demonstrated a high-sensitivity liquid level sensor based on the balloon-shaped fiber Mach-Zehnder interferometer (MZI). To make an optical fiber MZI sensor, a bare single mode fiber (SMF) is bent into a balloon shape. The sensor is attached to a stiff support and linked to a buoyancy ball floating on the liquid surface via a thin thread. The change in liquid level will bend the fiber and lead to a wavelength shift of transmission spectrum. This is a novel method of measuring liquid levels. We comprehensively studied the sensing performance of the sensor, and applied the ridge regression algorithm to optimize the fitting results of the experimental data. The maximum sensitivity of liquid level and temperature are 5.245 nm/mm and 40.3 pm/°C respectively, and the sensor has a low temperature cross-sensitivity of 0.00768 mm/°C. Furthermore, the sensor has the advantages of real-time response, convenient manufacture, low cost and high reliability, which broadens the application area of balloon-shaped MZI and makes it appropriate for liquid level sensing.

Femtosecond laser processing for a high sensitivity fiber MZI microcavity.

An ultra-compact fiber inline Mach-Zehnder interferometer sensor based on femtosecond laser micromachining technology is demonstrated. It is found that the microstructure has an ultra-high refractive index sensitivity of 16660 nm/RIU when a femtosecond pulsed laser is used to remove the upper cladding and part of the core of a standard single-mode fiber. However, its temperature sensitivity is not much different from that of most pure quartz fibers and can be as high as 7.934 nm/°C when the microcavity is coated with a low-refractive-index ultraviolet adhesive, which was originally used for bonding glass. With this coating, however, it demonstrates excellent robustness.

Ring core few-mode fiber sensor for curvature measurement.

An all-fiber Mach-Zehnder interferometer (MZI) using ring core few-mode fiber (RC-FMF) for curvature sensing is proposed and experimentally demonstrated. The MZI was fabricated by splicing a segment of RC-FMF between two pieces of single-mode fiber (SMF). With the benefit of a RC of the central axis of the RC-FMF, the sensor is more sensitive to curvature compared to other fiber sensors based on ordinary SMF or FMF. Curvature measurement can be achieved by monitoring the wavelength shift of interference dips. Experimental results have shown that the sensitivity of curvature sensing can reach up to -4.370nm/m-1, within the range of 1.199-1.549m-1. Also, the temperature sensing characteristics of the sensor are measured, and the maximum temperature sensitivity is 57.6 pm/°C, ranging from 25°C to 45°C. The proposed MZI sensor has excellent potential for curvature measurement of building structural health monitoring, bridge engineering, and more.

A peanut taper based Mach-Zehnder interferometric sensor for strain and temperature discrimination

A Mach-Zehnder interferometric optical fiber sensor is proposed and demonstrated for strain and temperature discrimination. The sensor is fabricated by connecting a standard single mode fiber and a commercialized panda-type polarization maintaining fiber between the lead-in fiber and the lead-out fiber using three peanut-shaped up-tapers. Thanks to the different responses to strain and temperature of the single mode fiber and the polarization maintaining fiber, the sensor is able to achieve strain and temperature discrimination. Experiment results show that the sensor is capable of obtaining low discrimination errors of ±5.48 με and ±0.21 °C for strain and temperature respectively. Besides, the proposed sensor is robust, cost-effective and easy to fabricate, which allows it a potential candidate for implementing simultaneous measurement of strain and temperature.

Investigations on seven-core fiber based interferometric all-fiber sensor for curvature and temperature measurements

An all-fiber Mach-Zehnder interferometer (MZI) sensor structure for measurement of temperature and curvature is proposed and demonstrated experimentally, which consists of two parts of no-core fiber (NCF) and seven-core fiber (SCF) sandwiched between two single-mode fibers (SMF). Since the two no-core fibers are respectively cascaded at both ends of SCF to improve light separation and recombination, the intermodal interference effect can be generated in the fiber inside structure. Based on the theoretical optimization analysis, we confirmed the sensing characteristics of the proposed all-fiber MZI-based sensors. The experiment results demonstrate that the spectral interference dips of proposed sensor have different responses for curvature and temperature. The wavelength shift is sensitive to temperature change and has better linearity, but insensitive to curvature variation. The spectral intensity is not only sensitive to curvature variation but also temperature change with a certain nonlinearity. The maximum temperature and curvature sensitivities of 100.1 pm/℃ in temperature range of 50–100 ℃ and 10.22 dB/m−1 in curvature range of 0.82–1.226 m−1 are obtained respectively. These sensing characteristics and the advantages of simple fabrication, high repeatability and common materials can make the proposed sensor be widely used in building structure detection and engineering.

Study of Intra-Chamber Processes in Solid Rocket Motors by Fiber Optic Sensors.

In this study, an experimental study of the burning rate of solid fuel in a model solid propellant rocket motor (SRM) E-5-0 was conducted using a non-invasive control method with fiber-optic sensors (FOSs). Three sensors based on the Mach–Zehnder interferometer (MZI), fixed on the SRM E-5-0, recorded the vibration signal during the entire cycle of solid fuel burning. The results showed that, when using MZI sensors, the non-invasive control of solid fuel burnout is made possible both by recording the time of arrival of the combustion front to the sensor and by analyzing the peaks on the spectrogram of the recorded FOS signal. The main mode of acoustic vibrations of the chamber of the model SRM is longitudinal, and it changes with time, depending on the chamber length. Longitudinal modes of the combustion chamber were detected by MZI only after the combustion front passed its fixing point, and the microphone was unable to register them at all. The results showed that the combustion rate was practically constant after the first second, which was confirmed by the graph of the pressure versus time at the nozzle exit.

Mach-Zehnder interferometer for multi-parameter measurement sensor based on SMF-NCF-FMF-NCF-SMF

A Mach-Zehnder interferometer sensor is designed, which includes a cascade structure of single-mode fiber (SMF)-no-core fiber (NCF)-few-mode fiber (FMF)-no-core fiber (NCF)- single-mode fiber (SMF) (SNFNS). In this structure, the NCF is used as the input and output coupler, and the FMF is used as the sensing region. In the measurement range, the SNFNS sensor has three interference dips. Among them, temperature and humidity can be measured simultaneously through the dip2 and the dip3, temperature and refractive index can be measured simultaneously by the dip1 and dip2. The temperature sensitivities are 0.063 nm/℃, 0.013 nm/℃ and 0.095 nm/℃ in the range of 30 ℃~85 ℃. When refractive index changes from 1.333 to 1.365, the refractive index sensitivities of the dip1 and the dip2 are 134.17 nm/RIU and 53.76 nm/RIU, respectively, the changes of the dip3 are not noticeable. When humidity changes from 30%RH to 70%RH, the humidity sensitivities of the dip2 and dip3 are 0.034 nm/%RH and 0.025 nm/%RH, respectively, the changes of the dip1 are not noticeable. Furthermore, the structure has the merits of simple construction, good repeatability, and good stability.

Encapsulation Research of Microfiber Mach-Zehnder Interferometer Temperature and Salinity Sensor in Seawater

Encapsulation of microfiber Mach-Zehnder interferometer (MMZI) sensor for temperature and salinity sensing in seawater is developed. It includes a C-shape metal tube with a slit on the bottom and polymer adhesive with large elasticity modulus, by which a more robust sensor with relatively fast response can be obtained. To evaluate the performance of sensor after encapsulation, effects of different polymer adhesives on tension withstanding, temperature and salinity sensitivities are evaluated, and dependence of response time on shape of metal tube is investigated. Results show that sensitivities of the sensor in temperature and salinity sensing can reach to be about −1.77 nm/°C and 1.18 nm/ ‰, and response times are about 219.0 ms and 12.5 ms, respectively. By comparing temperatures and salinities measured by sensor with those measured by commercial device, accuracy of the sensor after encapsulation is proved. In addition, cross-sensitivities of strain/pressure and short/long-term stability after encapsulation are also evaluated. Finally, based on the basic structure, further improvements are attempted, such as double encapsulation with stainless steel mesh and complex encapsulation with two kinds of polymer. Encapsulations of MMZI demonstrated here show advantages of low cost, improved robustness, relatively fast response, long-term stability and easy expandability, which will not only afford a critical support for optical sensors operated in the ocean, but also offer some useful references for microfiber sensors used in other sensing applications.

The Interferometer of Mach Zehnder and Its Applications

Fiber optic interferometers have been studied extensively for sensing various physical characteristics such as temperature, strain, pressure, and refractive index. Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac are the four different types. In this case, in this study, the operational principles of Mach-Zehnder interferometric sensor are examined. fabrication techniques, as well as application sectors. The technologies of interferometric sensors are described in detail to demonstrate their great potential in practical uses. Mach-Zehnder The interferometer is a device that measures the difference in phase shifts Between two coherent collimated beams. According to this fundamental Principle, various devices can be designed. Several devices, including various types of in-line MZI optical sensors, all-optical switches and modulator, can be created using this basic principle are discussed in this paper.

Design of an on-chip sensor operating near the dispersion turning point with ultrahigh sensitivity

In this paper, an on-chip refractive index (RI) sensor based on the asymmetric Mach–Zehnder interferometer (MZI) is proposed for sensitivity enhancement. The outstanding sensing performance is obtained by achieving the dispersion turning point (DTP). We analyze the necessary conditions for DTP formation, the transmission spectrum characteristics, and the sensing performance near the DTP. The results show that when the group index difference between the reference arm and the sensing arm is close to zero, high RI sensitivity can be obtained near the DTP. Since the resonance peaks on both sides of the DTP have different shift directions with the change of RI, by tracing the wavelength shift between the two resonance peaks, the RI sensitivity and the limit of detection can reach 40960 nm/refractive index unit (RIU) and 4.88 × 10 − 7 R I U . The proposed asymmetric MZI sensor provides a potential on-chip platform for high-performance RI sensing.

Waveguide Mach-Zehnder Interferometer for Temperature and Concentration Sensing

Mach-Zehnder interferometer (MZI) based on optical waveguide is proposed and demonstrated, in which a waveguide core with a core expander and a collector is inscribed in a photoresist SU-8 film by ultrafast laser-induced two-photon polymerization (TPP) technique, whereas the cladding of the waveguide is fabricated by the standard photolithographic technique. Interference occurs in this MZI when the light is scattered into the cladding by the core expander and then collected by the core collector, in which the roles of the core expander and the collector are investigated in details. By integrating with a microchannel, a waveguide-based optofluidic MZI sensor is realized, which exhibits a redshift at a sensitivity of 0.618 nm/°C with the increase of temperature, and blueshifts at sensitivities of -0.102 nm/wt% and -0.092 nm/°Bx for concentration measurement of sodium chloride and sucrose solutions, respectively. Experimental results demonstrate the effectiveness of this sensor for temperature and concentration measurement, manifesting its promising potential for biomedical, chemical, and environmental applications.