Mach-Zehnder Interferometer Sensor Research Articles

In-situ and label-free measurement of cytochrome C concentration with a Ti2C-MXene sensitized fiber-optic MZI sensor

BackgroundThe concentration of cytochrome C is demonstrated to be an effective indicator of the microbial corrosion strength of metals. Traditional cytochrome C sensor can detect cytochrome C with a low detection limit, but their use is limited by their high cost, cumbersome operation, and susceptibility to malignant environments. In addition, studies on the monitoring of cytochrome C in the field of microbial corrosion has still not been carried out. Therefore, there is a need for a highly sensitive, selective, low-cost, anti-interference, and stable cytochrome C sensor with online monitoring and remote sensing capabilities for in-situ measurement of microbial corrosion strength. ResultsThis paper proposed a highly sensitive label-free fiber-optic sensor based on Mach-Zehnder interferometer (MZI) for in-situ measurement of the microbial corrosion marker cytochrome C. Two-dimensional Ti2C-MXene material is uniformly immobilized onto the surface of the sensing area to improve the sensitivity, hydrophilicity, and specific surface area of the sensing area, as well as to facilitate the immobilization of specific sensitive materials. The cytochrome C antibody is modified on the surface of Ti2C-MXene to specifically recognize cytochrome C, whose concentration variation can be measured by monitoring the spectral shift of MZI sensor. Results demonstrate a measurement sensitivity of 1.428 nm/μM for cytochrome C concentrations ranging from 0 to 7.04 μM. The detection limit of the sensor is calculated to be 0.392 μM with remarkable performance, including selectivity, stability, and reliability. Besides, the measurement result of the proposed sensor in real microbial corrosive environment is consistent with that of the ideal environment. Significance and noveltyThis is the first instance of achieving in-situ and label-free measurement of cytochrome C by using a fiber-optic MZI sensor, which undoubtedly provides a feasible solution for the effective monitoring of microbial metal corrosion in the environment.

Optofluidic chip with directly printed polymer optical waveguide Mach-Zehnder interferometer sensors for label-free biodetection

Optofluidic devices hold great promise in biomedical diagnostics and testing because of their advantages of miniaturization, high sensitivity, high throughput, and high scalability. However, conventional silicon-based photonic chips suffer from complicated fabrication processes and less flexibility in functionalization, thus hindering their development of cost-effective biomedical diagnostic devices for daily tests and massive applications in responding to public health crises. In this paper, we present an optofluidic chip based on directly printed polymer optical waveguide Mach-Zehnder interferometer (MZI) sensors for label-free biomarker detection. With digital ultraviolet lithography technology, high-sensitivity asymmetric MZI microsensors based on a width-tailored optical waveguide are directly printed and vertically integrated with a microfluidic layer to make an optofluidic chip. Experimental results show that the sensitivity of the directly printed polymer optical waveguide MZI sensor is about 1695.95 nm/RIU. After being modified with capture molecules, i.e., goat anti-human immunoglobulin G (IgG), the polymer optical waveguide MZI sensors can on-chip detect human IgG at the concentration level of 1.78 pM. Such a polymer optical waveguide-based optofluidic chip has the advantages of miniaturization, cost-effectiveness, high sensitivity, and ease in functionalization and thus has great potential in the development of daily available point-of-care diagnostic and testing devices.

Terahertz on-chip sensor based on Mach-Zehnder waveguide interferometer for selective recognition of reducing drug

The selective detection of biochemical substances with high sensitivity in the terahertz (THz) band has emerged as a prominent research area, attracting significant attention. Waveguide-on-chip detection of biochemical substances can effectively enhance the interaction between samples and waves, but there is a lack of reports in the THz band. In this work, a dual-channel metallic parallel-plate waveguide (PPWG) is applied to creatively construct a THz Mach-Zehnder interferometer (MZI) sensor for highly sensitive and selective detection of reducing drug on a chip. This sensor exhibits a strong numerical response of 0.75 THz/RIU, allowing for dynamic sensitivity adjustment through mechanically tuning structural parameters, and it is modified through in-situ growth of Prussian blue (PB) to achieve the selective detection of reducing drug. The experiments confirm that the designed sensor-on-chip possesses exceptional detection sensitivity for cysteamine, reaching an impressive maximum sensitivity of 0.09 GHz/nmol and a low limit of detection of 88 nmol. The modified chip exhibits selective detection of cysteamine, demonstrating a maximum response difference of 4.2 times compared to other configurations. Collectively, a pioneer validates the feasibility of the highly sensitive MZI chip in the THz regime and opens up new possibilities for advancing THz biochemical sensing.

Temperature and Curvature Microfiber Mach-Zehnder Interferometer Sensor Based on Double Peanut-Shaped Structures and Tapered Coreless Fiber

Temperature and Curvature Microfiber Mach-Zehnder Interferometer Sensor Based on Double Peanut-Shaped Structures and Tapered Coreless Fiber

All-fiber MZI hydrostatic pressure sensor

With the rapid development of physical ocean observation, high-performance pressure sensor integrated with stable mechanical strength, sufficient pressure sensitivity as well as negligible temperature crosstalk is highly desirable but still lack of research. This paper proposes an all-fiber optical sensor based on a Mach-Zehnder interferometer (MZI) for hydrostatic pressure measurement, utilizing a multi-mode fiber (MMF)-single-hole-dual-core fiber (SHDCF)-MMF structure. The MMF sections act as a beam splitter and coupler to enhance the Mach-Zehnder interference. The SHDCF serves as the pressure-sensing section. Under the action of the enclosed air hole in SHDCF, hydraulic variations cause changes in the structural parameters of the fiber, especially the refractive index change caused by the elasto-optical effect, which leads to the shift of the interference dips. The experimental results prove that the SHDCF-based MZI sensor has a higher hydrostatic pressure sensitivity than other hole-less silica fiber-based sensors. The max pressure sensitivity is −0.2358 nm/MPa in the range of 0.1 MPa to 16.1 MPa with good linearity and reliability. Moreover, the low temperature–pressure cross-sensitivity of 0.04368 MPa/℃ also proves our sensor more competitive in harsh environment applications.

Thin-core fiber-based Mach-Zehnder interferometer sensor for monitoring temperature, pressure, and humidity

A Mach-Zehnder interferometer (MZI) sensor based on thin-core fiber (TCF) is proposed. Sensitive materials such as polydimethylsiloxane (PDMS) or gelatin are coated on the surfaces of MZIs to achieve temperature, pressure, and humidity measurements. MZI is composed of single mode fiber (SMF), TCF, and multimode fiber (MMF) spliced together to form a “SMF-MMF-TCF-MMF-SMF” structure. The core/cladding diameters of TCF are 3.8 µm and 80 µm respectively. When three types of optical fibers with different core diameters are cascaded together, many cladding modes are excited to form MZI. Firstly, two similar MZI structures were fabricated designated by MZI1 and MZI2. In order to improve the sensitivity and mechanical strength, a layer of PDMS film was coated on the TCF surface of MZI1. Then, a layer of gelatin film is covered on the TCF surface of MZI2. PDMS has the high thermal expansion coefficient, thermal optical coefficient, and elasticity, and gelatin has good humidity sensitivity properties. The experimental results showed that the temperature and pressure sensitivity of MZI1 coated with PDMS reached −340 pm/°C and −14.3 nm/MPa, respectively, while the humidity sensitivity of MZI2 coated with gelatin reached −112.57 pm/% RH. When a fiber Bragg grating is cascaded with the MZI1, the sensor can achieve simultaneous measurement of temperature and pressure, eliminating crosstalk. The proposed sensor has an extremely simple structure and manufacturing method, which only involves the splicing of optical fiber and the coating by the film. In addition, the proposed sensor has a robust structure, good repeatability and stability, and high sensitivity, which has broad application prospects.

Microcavity Mach-Zehnder refractive index sensing in LiTaO3 crystal waveguides by a combination of femtosecond laser inscription and diamond blade dicing

Based on planar waveguides, refractive index sensors have certain advantages over conventional optical fiber sensors, including better mechanical stability and lower cross-responses to factors such as vibrations. In this study, we report for the first time a microcavity Mach-Zehnder interferometric refractive index sensor fabricated within a planar waveguide. The sensor consists of double-line waveguides made of lithium tantalate crystals written by femtosecond laser and microcavities formed by diamond blade dicing. The refractive index sensitivity of the sensor reaches approximately 1856.1 nm/RIU, with extremely low temperature cross-responses. This work provides a new alternative for developing biosensors based on femtosecond laser-written waveguides. In the future, by selecting appropriate materials and optimizing the structure, the sensing performance of this sensor is expected to be further enhanced.

On-chip Mach-Zehnder interferometer sensor with a double-slot hybrid plasmonic waveguide for high-sensitivity hydrogen detection.

An on-chip Mach-Zehnder interferometer (MZI) hydrogen sensor, applying a double-slot hybrid plasmonic (DSHP) waveguide composed of a Si waveguide and two Pd disks on both sides as the sensing arm, is designed. The optical confinement factor of the sensing area can be up to 87%. For the MZI hydrogen sensor with a DSHP waveguide of 14 µm, the sensitivity can be as high as 11.935 nm/%, corresponding to a free spectral range (FSR) of 15 nm. Furthermore, the sensor sensitivity is influenced by the MZI structure parameters, which is highly adjustable. The extinction ratio of the interference spectra can reach over 30 dB. A feasible solution is provided in this paper for highly sensitive hydrogen detection.

A Mach–Zehnder Interferometric Sensor for Contact Temperature Measurement of High Refractive Index Organics Based on a Double-Cladding Tellurite Optical Fiber

A Mach–Zehnder Interferometric Sensor for Contact Temperature Measurement of High Refractive Index Organics Based on a Double-Cladding Tellurite Optical Fiber

In-line open-cavity Mach-Zehnder interferometric refractive-index sensors based on inter-mode and inter-core-mode interferences

We experimentally demonstrated in-line Mach-Zehnder interferometric sensors based on inter-mode interference (IMI) and inter-core-mode interference (ICMI) for refractive index (RI) measurements. The structure of the IMI-based sensor consisted of a C-shaped fiber spliced between two multi-mode fibers (MMF) with the opposite ends spliced to lead-in and lead-out single-mode optical fibers. The ICMI-based sensor has a similar structure as the IMI-based sensor but with an additional in-house fabricated three-core multi-core fiber (MCF) spliced between the MMF and C-shaped fiber. The performance of the two RI sensors was evaluated and compared using water-glycerol solutions with RI values ranging from 1.333 to 1.338. The RI sensitivity, as well as other characteristic properties such as free spectral range and extinction ratio in relation to three lengths of the C-shaped fiber of 2, 2.5 and 3 mm, were investigated in both structures. The open-cavity characteristic of the C-shaped fiber allows the solution to interact with the optical path of the sensors, hence improving their RI measurement sensitivities. Both types of sensors exhibit linear wavelength responses with variation in RI. The RI sensitivity of the IMI-based sensor exhibits minor variations when the length of the C-shaped fiber is altered, with a maximum sensitivity of -7999.76 nm/RIU. In contrast, the RI sensitivity of ICMI-based sensor exhibits variability when changing the C-shaped fiber length, potentially due to variations in the RI distribution among the cores within the MCF, with its maximum sensitivity being -6211.98 nm/RIU. The temperature sensitivity of all the tested sensors was around 0.7 nm/ °C, denoting a low temperature cross-sensitivity of -7.427 × 10−5 RIU/ °C. This work experimentally exhibits a comparison of two sensing effects in the same configuration. The long length (longer than 2 mm) of the sensing element facilitates the fabrication process, and the open-cavity present in the proposed sensors yields a high sensitivity, which is in the same order of magnitude as the IMI-based sensors and is one order of magnitude higher than the ICMI-based sensors, emphasizing their promising candidacy for label-free optical sensing of chemical and biological samples.

Trace detection of canine distemper virus based on surface-functionalized optic-fiber Mach–Zehnder interferometer and the Vernier effect

A surface-functionalized cascaded optic-fiber Mach–Zehnder interferometer (MZI) is proposed and fabricated for trace detection of canine distemper virus (CDV). The Vernier effect is formed based on single-mode fiber (SMF)-dislocation single-mode fiber-SMF. The two MZIs serve as the sensing arm and reference arm, respectively. The CDV antibody is modified on the sensing arm to detect CDV antigen, and the surface structure and morphology are analyzed by the atomic force microscope. The sensitivity of the cascaded MZI sensor is about 12 times than that of a single MZI. In the range of 0.1–104 pg ml−1 CDV, the detection limit of the cascaded MZI sensor is 0.1687 pg ml−1, and the response time is 25 min. The sensor also has good temperature, time stability and excellent selectivity. The biosensor has the advantages of low cost, easy preparation, high sensitivity and good selectivity, and has potential application for trace CDV detection.

Highly sensitive temperature and curvature sensor based on seven-core fiber

A high sensitivity temperature and curvature micro-fiber Mach-Zehnder interferometer (MMZI) sensor is proposed and demonstrated. A peanut structure is fused by a section of seven-core fiber (SCF) and a section of single-mode fiber (SMF). Then the SCF is connected to another SMF and tapered. Finally, the composite structure with the tapered SCF and the SCF-SMF peanut structure is fabricated. The coupling efficiency can be significantly improved, and more high-order modes can be stimulated via the new sensor structure. The experimental results demonstrated that the maximum temperature sensitivity is 836.67 pm/ °C in the range of 35 °C to 40 °C, which is the highest temperature sensitivity of the peanut-shaped MMZI sensor to the best of our knowledge. Furthermore, the sensor can be used for curvature measurement. When the curvature changes from 0 m−1 to 0.0522449 m−1, the sensitivity can achieve 93.33664 nm/m−1. The proposed sensor not only provides a novel method to fabricate a high-sensitivity sensor by combining different types of fibers, but it also has a meaningful application prospect in the fields of biological detection and environmental monitoring.

Simultaneous measurement three parameters of temperature, strain, and curvature by thin-core fiber based-Mach-Zehnder interferometer

A Mach-Zehnder interferometer (MZI) sensor for simultaneous measurement of three parameters is developed. The sensor structure is spliced by single-mode fiber, no-core fiber, thin-core fiber (TCF) and single-mode fiber in turn, where the sensing element is TCF. Due to the different core diameters of three types of optical fibers, the light in the transmission process excites a number of higher-order modes and interacts to form a mode interferometer. The interference spectrum produces many resonance peaks that are sensitive to different parameters. We select three resonant peaks sensitive to temperature, strain and bending for measuring temperature, strain and curvature. The experimental results display that the resonant wavelength of the sensor transmission spectrum drifts linearly as a function of the environmental parameters, with a maximum sensitivity of 248.7 pm/℃ for temperature, −2 pm/με for strain and −24.784 nm/m−1 for curvature. Selecting three resonance peaks to construct a measurement matrix realizes three-parameters simultaneous measurement and eliminates the cross-sensitivity among the three physical quantities. In addition, the proposed sensor possesses appealing characteristics of facile manufacturing process, compact size, high sensitivity, good linear fitting, robustness and low cost, and the sensor has a broad application prospect in the field of multi-parameter simultaneous measurement. In short, only one MZI in the optical fiber can realize the simultaneous monitoring of temperature, strain and bending, which provides a new solution for creating a compact multi-parameter sensor for structural health monitoring.

Sensitive Evanescence-Field Waveguide Interferometer for Aqueous Nitro-Explosive Sensing

The development of novel chemical nitro-explosive sensors with high sensitivity, low cost and a compact size is essential for homeland security, environmental protection and addressing military challenges. Polymeric optical waveguides based on refractive index sensing are widely used in biochemical detection due to their advantages of large-scale integration, low cost, high sensitivity and anti-electromagnetic interference. In this study, we designed and fabricated a polymer waveguide Mach–Zehnder interferometer (MZI) sensor to detect 2,4-dinitrotoluene (DNT) in water. One phase shifter of the MZI waveguide was functionalized by coating a thin cladding layer of polycarbonate with dipolar chromophores and used as the sensing arm; the other arm was coated with passive epoxy resin cladding and used as the reference arm. The phase difference between the two arms of the MZI was modulated using the refractive index (RI) change in the polycarbonate cladding when dipolar chromophores interacted with electro-deficient DNT. The theoretical sensitivity of the designed MZI can reach up to 24,696 nm/RIU. When used for explosive detection, our fabricated sensor had a maximum wavelength shift of 4.465 nm and good linear relation, with an R2 of 0.96 between the wavelength shift and a concentration ranging from 3.5 × 10−5 to 6.3 × 10−4 mol/L. The sensitivity of our device was 6821.6 nm/(mol/L). The design of an unbalanced MZI sensor, together with the sensing material, provides a new approach to using low-cost, compact and highly sensitive devices for in-field explosive detection.

Characterization of laser-induced optothermal effect in magnetic fluids based on a coreless-fiber-coupled microcavity Mach-Zehnder interferometric sensor

We present an integrated coreless-fiber-coupled microcavity Mach-Zehnder interferometric sensor to investigate the optothermal effect of magnetic fluids in the near-infrared wavelength region. The Brownian motion of magnetic nanoparticles and solvent molecules intensifies along with the change of medium refractive index under 473 nm laser illumination, and consequently the interference wavelengths are sensitive to the applied laser power. The maximum wavelength tuning sensitivity is up to 4.7475 nm/(mW/mm2) at a microcavity length of 262.26 µm. Based on interferometric spectral analysis, the refractive index sensitivities of the magnetic fluids are found to be about −3.0909 × 10-4 RIU/(mW/mm2) and −3.3319 × 10-4 RIU/(mW/mm2) for the laser power increase and decrease processes, respectively. The slight difference between the refractive index sensitivities could be attributed to the accumulation of laser energy and Sorét effect. The work presented in this paper provides important references for understanding the optothermal mechanism of magnetic fluids and the design of magnetic-fluids-functionalized laser-controlled photonic devices.

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.