Mach-Zehnder Interferometer Sensor Research Articles

An Mach-Zehnder Interferometer Refractive Index Sensor Based on Self-phase Modulation Effect in a Tapered Double-cladding Highly Nonlinear Fiber

An Mach-Zehnder interferometer (MZI) sensor based on self-phase modulation (SPM) effect in a tapered double-cladding highly nonlinear fiber (DCHNLF) was proposed and experimentally verified for refractive index (RI) measurement. The DCHNLF was tapered and the SPM spectrum generated in its untapered region acted as the broadband light source for the sensor. The integration of the SPM effect and the RI detection not only simplified the structure of the sensor, but also enhanced its long-term stability and reliability. Since the effective RI of the outer cladding mode of the tapered DCHNLF was affected by the RI variation, a spectral shift would occur in interference spectrum between the core mode and the outer cladding mode. The tapering treatment enhanced the evanescent wave on the surface of DCHNLF, making the sensor more sensitive to external RI. In the external RI range of 1.3333 ~ 1.3972, the sensor achieved an excellent sensitivity of 238.51nm/RIU. In addition, the effect of average pump power and pump wavelength on the sensor performance were experimentally discussed. The results showed that the sensitivity was not affected by the pump condition. This MZI RI sensor has advantages of excellent performance, simple structure and easy fabrication, demonstrating broad application prospects in biomedical research, marine environment monitoring, and human health detection.

PDMS-assisted Mach–Zehnder interferometer for simultaneous sensing of strain and temperature based on hollow-core fibers

A PDMS-assisted Mach-Zehnder interferometric (MZI) fiber-optical sensor based on hollow-core fibers (HCF) is proposed and experimentally demonstrated for the simultaneous detection of strain and temperature. The transmission spectral evolution in response to the applied strain and temperature sensor are investigated. Experimental results suggest that our proposed sensor exhibits strain and temperature sensitivities up to −40.95 dB/N and 2.5 nm/°C for the sensing ranges of 0.01 N to 0.08 N and 35 °C to 42 °C, respectively. Moreover, crosstalk analyses were performed to discriminate the strain and temperature measurement. The proposed sensor possesses desirable advantages such as high sensitivity, easy-fabrication, and low-crosstalk, which paves new way toward developing photonic devices for strain/temperature dual-parameter sensing and related applications.

High-Sensitivity Microfluidic Mach-Zehnder Interferometric Salinity Sensor Based on C-Type Dual-Core Eccentric-Hole Fibers

High-Sensitivity Microfluidic Mach-Zehnder Interferometric Salinity Sensor Based on C-Type Dual-Core Eccentric-Hole Fibers

Slow-wave-enhanced on-chip Michelson interferometer sensor: erratum.

The device described in our earlier paper [Opt. Lett.48, 5968 (2023)10.1364/OL.500033] as a slow wave enhanced on-chip Michelson interferometer sensor is correctly designated as a slow wave enhanced on-chip loop terminated Mach-Zehnder interferometer sensor. In the earlier paper, we experimentally demonstrated slow wave enhanced phase and spectral sensitivity in asymmetric loop-terminated Mach-Zehnder interferometer (LT-MZI) sensors. Compared to Mach-Zehnder interferometers (MZI) that experimentally demonstrated a phase sensitivity 84,000 rad/RIU-cm, the reflected path enhancement of the optical path length coupled with slow light enhancement with photonic crystal waveguides in on-chip slow light loop-terminated Mach-Zehnder interferometer sensors resulted in experimentally demonstrated phase sensitivity 277,750 rad/RIU-cm with theoretical phase sensitivity as high as 461,810 rad/RIU-cm, at the same form factor as the MZI of identical interferometer arm lengths.

A Mach-Zehnder interferometric acoustic sensor using incomplete symmetry 3×3 coupler-based phase shifting demodulator

A Mach-Zehnder interferometric (MZI) acoustic sensor and an incomplete symmetry 3×3 coupler-based phase shifting demodulator are presented. The demodulator is used to recover the acoustic signal detected by the proposed sensor. To eliminate interfering signals loaded on the transmission path, all couplers and interference arms constituting the sensing MZI are packaged into the sensor. Therefore, a path-matched interferometer (PMI) is used to separate the sensor from the demodulator and to compensate for the optical path difference in order to generate interference. The 3×3 coupler of the PMI is used to introduce phase differences of interferometric signals. Two constant large-amplitude carrier signals with a phase difference of π are loaded on the PMI to ensure normalization of the interferometric signals. By normalizing interferometric signals, fluctuations in both fringe visibility and received power are eliminated. The measurement errors caused by the incomplete symmetry of the 3×3 coupler are reduced through phase compensation. The sensor and PMI are designed to be insensitive to environmental disturbances. The phase shifting demodulation technique is then performed to recover the measurand. The proposed sensor is experimentally demonstrated to be able to detect acoustic signals with frequencies between 200 Hz and 20 kHz. This sensor exhibits a linear response to the sound pressure with a sensitivity of 9.101 nm/mPa. The minimum detectable pressure is 9.74 μPa/Hz1/2 at 20 kHz. The proposed sensor has high sensitivity, high robustness, low cost and anti-interference properties.

Large measurement range curvature sensor based on all-fiber Mach-Zehnder interferometer using triple-ring-core few-mode fiber.

This study experimentally demonstrates a large measurement range curvature sensor based on a Mach-Zehnder interferometer (MZI) in a triple-ring-core fiber (TRCF). The sensor is fabricated by fusion splicing a segment of TRCF between two pieces of single-mode fiber (SMF), forming the SMF-TRCF-SMF sandwich structure. Since the TRCF can support the propagation of a few guided modes, the fundamental mode interferes with high-order modes in the sensing part to produce a periodic interference spectrum. Bending causes the effective refractive index of the mode to change, which shifts the interference spectrum. The bending measurement is achieved by monitoring the wavelength variation of interference dips. The proposed sensors can realize curvature measurements up to 100 m-1, with a bending sensitivity of -225.9 pm/m-1. It is believed that the proposed MZI sensor may have potential applications in robot hand gesture recognition and control.

Refractive insensitive directional bend sensor based on specialty microstructure optical fiber with dumbbell shape core

With the development of information society, more and more special occasions are calling for a wide range of sensors with special properties. In this work, a refractive index insensitive directional bend sensor is proposed based on a specialty microstructure optical fiber with dumbbell shape core, which works as a dual core fiber (DCF). Firstly, this specialty microstructure optical fiber with dumbbell shape core has been fabricated with self-pressurised drawing technique. Then, it has been constructed as a Mach-Zehnder interferometer (MZI) sensor. Consequently, its bend sensing characteristics has been investigated from both theory and experiment. The response of the proposed sensor to the bending evidently displays the directional dependence. In the bending along x direction, the interference peak wavelength is almost insensitive to the curvature. But the transmission is sensitive, which almost obeys the exponential function. Correspondingly, in the bending along y direction the wavelength almost linearly varies with curvature, giving out an averaged sensitivity of 2.44 nm/m−1 in the curvature range of 0–3.79 m−1. But the peak transmission fluctuates without typical principle. In addition, the response of the proposed sensor to the refractive index variation has been checked. It is found that the peak wavelength is almost insensitive to the change of refractive index from 1.33 to 1.45, and the peak transmission fluctuates without clear principle. All these results demonstrate that the proposed sensor has great potential for future internet of things (IoT) applications.

High sensitivity Mach-Zehnder interferometric fiber-optic humidity sensor based on multimode interference enhancement

Variations in humidity can significantly disrupt the proper functioning of precision instruments and meters across various industrial, medical, and scientific applications, thereby necessitating real-time humidity monitoring. Here, a high sensitivity fiber-optic relative humidity (RH) sensor based on Mach-Zender interferometer (MZI) is proposed and demonstrated. The humidity sensor consists of single-mode fiber (SMF), peanut structure (PS), and multi-mode fiber (MMF). A multi-mode interference (MMI) enhanced fiber-optic MZI was constructed using a SMF-PS-SMF-MMF-SMF-PS-SMF cascade structure to detect small changes in the refractive index (RI) and expansion force of gelatin film caused by humidity variation. PS, as a beam splitter and combiner of MZI, provides the possibility for simple, economical, and efficient manufacturing of the fiber-based part of humidity sensors. The addition of MMF will excite higher-order core and cladding modes, laying the foundation for achieving high-sensitivity fiber-optic humidity sensors. The fiber-optic RH sensor prototype demonstrate a high sensitivity of about 0.633 nm/% RH in the RH range of 50 % RH to 80 % RH, and a low temperature cross-sensitivity of 0.165 % RH/°C. This sensor has the advantages of safe and easy manufacturing process, low manufacturing cost, and high sensitivity, providing continuous high accuracy humidity measurement results for humidity sensing in different fields.

Theoretical and Experimental Analysis of Single-Arm Bimodal Plasmo-Photonic Refractive Index Sensors.

In this paper, we study both theoretically and experimentally the sensitivity of bimodal interferometric sensors where interference occurs between two plasmonic modes with different properties propagating in the same physical waveguide. In contrast to the well-known Mach-Zehnder interferometric (MZI) sensor, we show for the first time that the sensitivity of the bimodal sensor is independent of the sensing area length. This is validated by applying the theory to an integrated plasmo-photonic bimodal sensor that comprises an aluminum (Al) plasmonic stripe waveguide co-integrated between two accessible SU-8 photonic waveguides. A series of such bimodal sensors utilizing plasmonic stripes of different lengths were numerically simulated, demonstrating bulk refractive index (RI) sensitivities around 5700 nm/RIU for all sensor variants, confirming the theoretical results. The theoretical and numerical results were also validated experimentally through chip-level RI sensing experiments on three fabricated SU-8/Al bimodal sensors with plasmonic sensing lengths of 50, 75, and 100 μm. The obtained experimental RI sensitivities were found to be very close and equal to 4464, 4386, and 4362 nm/RIU, respectively, confirming that the sensing length has no effect on the bimodal sensor sensitivity. The above outcome alleviates the design and optical loss constraints, paving the way for more compact and powerful sensors that can achieve high sensitivity values at ultra-short sensing lengths.

High-sensitivity robust Mach-Zehnder interferometer sensor in ultra-compact format

A new type of fiber sensor called the mini-two-path Mach-Zehnder interferometer (MTP-MZI) sensor has been proposed and demonstrated for high-sensitivity curvature and temperature detection. The sensor is created by fusing two sections of single-mode fibers (SMFs) with an electric-arc technology. In the curvature experiment, the maximum intensity sensitivity is 112.6 dB/m−1 when the curvature changes from 0.005224 m−1 to 0.052245 m−1. As far as our knowledge, it has the highest sensitivity with the same scale in the MZI fiber sensors. Additionally, a temperature sensing performance has been measured within the range from 30 °C to 70 °C, and the maximum temperature sensitivity is 162 pm/°C. Compared with the two-path MZI with traditional meter-scale, the proposed MZI has the advantages of robustness, compact size, easy preparation, and packaging, which can open up new avenues for MZI in the application of multi-dimensional and multi-parameter sensing.

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

Optical fiber sensing for monitoring chloride ion concentration and pH in concrete structures

This paper presents the development and assessment of two individual optical fiber sensing systems either for monitoring chloride concentration or pH range in structural health monitoring of concrete structures. Excessive chloride ions possess the ability to corrode the steels of reinforced concrete structures that affect the safety and health of concrete structures. In addition, the pH of concrete structures decreases to a value close to 9.5 that externally exhibits carbonation and durability problems. The optical fiber Mach-Zehnder interferometer (MZI) sensing platform setup for chloride ion concentrations and the spectral responses of the MZI for the aqueous samples of fresh concrete supernatant (W/C = 0.35 and W/C = 0.65) with salt water solutions in different concentration ranges from 0.015% to 12.5% were measured. An optical fiber pH sensing system is proposed to implement structural health monitoring of concrete especially in pH measurement, which is composed of a fiber optical sensing system with a Visible-NIR bifurcated fibers, a CUV-UV cuvette holder, a broadband light source, a HR 4000 UV-NIR spectrometer, and a personal computer for data acquisition. We measured different pHs of the standard solutions with different pHs of 1, 4.08, 4.95, 5.99, 7.09, 8.07, 9.75. The optical fiber MZI sensing platform has shown the capacity for monitoring of chloride ion concentrations in the ranges from 150 ppm to 125000 ppm. A linear fit (adj. R-Square = 0.87207 and 0.97876 for fresh concrete supernatant with W/C = 0.35 and W/C = 0.65, respectively) for the graph of sensing response, light intensity or transmission loss, as a function of the chloride solution concentration for this 8-cm MZI sensor. Furthermore, based on the optical fiber pH sensing results, we found a linear increase in the maximum intensity (counts) as the pH of standard solution increased from1 to 9.75 (adj. R-Square = 0.91367).

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