Fiber Mach-Zehnder Interferometer Research Articles

A Tunable and Switchable Multi-Wavelength Erbium-Doped Fiber Ring Laser Enabled by Adjusting the Spectral Fringe Visibility of a Mach-Zehnder Fiber Interferometer

This paper presents a tunable, switchable multi-wavelength emission from an erbium-doped fiber ring laser, enabled by adjusting the spectral fringe visibility of a fiber interferometer filter. The filter is formed with specially designed concatenated tapered fibers to configure a Mach-Zehnder fiber interferometer (MZFI). The laser emission is highly flexible and reconfigurable, allowing for tuning between single- and dual-wavelength operation. The laser can switch sequentially from one up to six wavelengths by fixing the curvature and adjusting the polarization state. The lasing emission is generated over a stable wavelength range between 1559.59 nm and 1563.54 nm, exhibiting an optical signal-to-noise ratio (OSNR) exceeding ~35 dB. The performance of amplitude and wavelength fluctuations were evaluated, indicating an appropriate stability of ~3 dB and a shift less than 0.1 nm within a 45 min period at room temperature. A detailed comparison with the literature is given.

Displaced thinned single-mode fiber Mach-Zehnder interferometer tested for temperature and curvature applications

This article explains the features and qualities of employing a thinned manufacturing fiber to assemble a Mach-Zehnder interferometer (MZI) for detecting two physical variables: temperature and curvature. The MZI comprises a filter by splicing core-offset sections of a thinned fiber (TF) cladding diameter of 80 μm in an SMF-TF-SMF configuration. The TF splices act as the arms of the MZI, while the mismatch diameter sections serve as optical fiber couplers. The optical spectrum analyzer (OSA) detects the transmitted light and analyzes its optical transmission characteristics, showing 11 peaks of modal interferences into the longitude region. As a result of the experimental arrangement, the curvature and temperature sensitivities are 0.49 nm/m−1, 0.01 nm/°C, and 0.09 nm/°C for temperatures of 0–60 °C and 70–130 °C, respectively. The proposed sensor has potential advantages for measuring refractive index, pH, torsion, curvature, and temperature.

An asymmetric STNS-MZI structure and its applications in temperature and Cd2+ monitoring

In this paper, an asymmetric fiber Mach-Zehnder interferometer (MZI) is presented and investigated. The proposed asymmetric MZI structure is mainly constructed with thin core fiber (TCF) and no core fiber (NCF), sandwiched between single mode fibers (SMFs). Note that the TCF is spliced with a slight offset such that higher order cladding modes could be effectively exited. The SMF-TCF-NCF-SMF (STNS) structure is adjusted by a finite-difference beam propagation method simulation to achieve an optimal interference spectrum. Temperature monitoring performance is addressed and the calculated sensing resolution is about 0.28℃ with high precision of ± 0.3 °C. Moreover, as for the Cd2+ monitoring application, the TCF is further etched and then coated with 1-allyl-2-thiourea (ATU) forming cross-linked “-S-Cd-S-” structure. The results show that the resolution of Cd2+ could reach 2.37 × 10−11mol /L, which shows a four order of magnitude improvement compared with our previous work. Therefore, the proposed asymmetric STNS-MZI interference structure has great potential in future applications.

Ultrahigh Extinction Ratio Leaky-Guided Hollow Core Fiber Mach-Zehnder Interferometer Assisted by a Large Core Hollow Fiber Beam Splitter.

We proposed a novel fiber Mach-Zehnder interferometer (FMZI) that can perform an ultrahigh extinction ratio (ER), ultracompact, and ultra-broadband interference characteristics. The FMZI structure is based on an extremely tiny hollow core fiber (HCF) with a small diameter of 10 μm (named HCF10) connected with a beam splitter of a large core of 50 μm HCF (named HCF50). The refractive index (RI) of the air core is lower than that of the HCF cladding; a leaky-guided fiber waveguide (LGFW) occurs in such a short-section HCF10 waveguide to simultaneously have the core and cladding modes. To achieve better fringe visibility of the interference, the section of HCF50 assists in splitting the optical light into core and cladding beams launched into the HCF10 with appropriate intensities. Experimental and simulation results show that the optical characteristics of the proposed LGFW-FMZI are very similar. Based on the results of the study, the length of the HCF10 primarily influences the free spectral range (FSR) of the interference spectra, and the HCF50 splitter significantly controls the optimal extinction ratio (ER) of the interference fringes. By exactly adjusting the lengths of HCF10 and HCF50, the proposed fiber interferometers can perform the capability of an ultrahigh ER over 50 dB with the arbitrary FSR in the transmitted interference spectra over an ultra-broad wavelength range of 1250 nm to 1650 nm.

GO/MoS2@PVA composite membrane-based optical fiber Mach-Zehnder interferometer for humidity sensing and its non-contact sensing application.

A humidity sensor based on an optical fiber Mach-Zehnder interferometer (MZI) coated with a GO/MoS2@PVA composite membrane was investigated for non-contact sensing. MoS2 was used as a nanospacer to enhance the humidity-sensitive properties of GO, and the adhesion and stability of the composite membrane on the fiber surface could be increased by PVA. The proposed sensor shows a maximum sensitivity of 0.26 dB/%RH with average response and recovery times of 1.62 and 1.11 s, respectively. In non-contact sensing applications, the sensor can effectively recognize a maximum distance of 10 mm for the proximity of a human finger with a distance variation interval of 3 mm. The proposed sensor is expected to be applied in non-contact distance detection and localization or as a non-contact human-computer interaction panel.

Highly Sensitive Optical Fiber MZI Sensor for Specific Detection of Trace Pb2+ Ion Concentration

A novel chitosan (CS) functionalized optical fiber sensor with a bullet-shaped hollow cavity was proposed in this work for the trace concentration of Pb2+ ion detection in the water environment. The sensor is an optical fiber Mach–Zehnder interferometer (MZI), which consists of a sequentially spliced bullet-shaped hollow-core fiber (HCF), thin-core fiber, and another piece of spliced bullet-shaped HCF. The hollow-core fiber is caused to collapse by adjusting the amount of discharge to form a tapered hollow cavity with asymmetric end faces. The bullet-like hollow cavities act as beam expanders and couplers for optical fiber sensors, which were symmetrically spliced at both ends of a section of thin core fiber. The simulation and experiments show that the bullet-like hollow-core tapered cavity excites more cladding modes and is more sensitive to variation in the external environment than the planar and spherical cavities. The ion-imprinted chitosan (IIP-CS) film was fabricated with Pb2+ ion as a template and uniformly coated on the surface for specific recognition of Pb2+. Experimental verification confirms that the developed sensor can achieve high-sensitivity Pb2+ ion detection, with a sensitivity of up to −12.68 pm/ppm and a minimum Pb2+ ion detection concentration of 5.44 ppb Meanwhile, the sensor shows excellent selectivity, repeatability, and stability in the ion detection process, which has huge potential in the direction of heavy metal ion detection in the future.

All fiber Mach-Zehnder interferometer immunosensor based on rabbit anti-human IgG and protein a for human IgG detection

Antibodies produced by the immune system, including immunoglobin G (IgG), are among the important biological biomarkers. Optical fibers are ideal for fabricating biosensors because of their flexibility, weight, biocompatibility, electromagnetic interference immunity, etc. This study proposes a multimode-single mode-multimode (MSM) Mach-Zehnder interferometer immunosensor based on rabbit anti-human IgG and protein A (PA) for human IgG detection. When IgG is trapped by antibodies located on the surface of the fiber, the refractive index (RI) changes, and the wavelength redshift occurs in the transmission spectrum of the interference pattern. Here, for binding the antibody to the pre coated PA surface, a rabbit anti-human IgG has been used, which has stronger binding to PA and as a result higher stability than the goat anti-human IgG on the optical fiber surface. By optimizing the optical configuration and biolayer material, a limit of detection of 0.067 μg/ml and sensitivity of 0.14 nm.ml/μg could be achieved.

Femtosecond laser inscribed fiber Bragg grating and Mach-Zehnder interferometer cascade sensing structure for temperature and relative humidity simultaneous measurement

A femtosecond (fs) laser inscribed cascade structure of a fiber Bragg grating (FBG) and a gap-coupled cladding waveguide Mach-Zehnder interferometer (CWMZI) is proposed and demonstrated, which can be used to simultaneously measure temperature and relative humidity. The structure can also be used as a breathing sensor. Transmission dip wavelength of the FBG is used for the temperature monitoring based on its temperature response. Meanwhile, gap-coupled CWMZI is used for relative humidity monitoring because the gap part of the CWMZI is very close to the cladding surface, it is very sensitive to refractive changes caused by ambient humidity variations. Experiments show a temperature sensitivity of 0.01104 nm/°C in a temperature range of 20 °C to 125 °C, and a high relative humidity sensitivity response of −0.0793 nm/%RH in a relative humidity range of 50 % to 80 %. Breathing signal monitoring is also successfully demonstrated using the FBG-CWMZI cascading structure.

A Wearable Sandwich Heterostructure Multimode Fiber Optic Microbend Sensor for Vital Signal Monitoring.

This work proposes a highly sensitive sandwich heterostructure multimode optical fiber microbend sensor for heart rate (HR), respiratory rate (RR), and ballistocardiography (BCG) monitoring, which is fabricated by combining a sandwich heterostructure multimode fiber Mach-Zehnder interferometer (SHMF-MZI) with a microbend deformer. The parameters of the SHMF-MZI sensor and the microbend deformer were analyzed and optimized in detail, and then the new encapsulated method of the wearable device was put forward. The proposed wearable sensor could greatly enhance the response to the HR signal. The performances for HR, RR, and BCG monitoring were as good as those of the medically approved commercial monitors. The sensor has the advantages of high sensitivity, easy fabrication, and good stability, providing the potential for application in the field of daily supervision and health monitoring.

Optical Feedback FM-to-AM Conversion with integrated Micro-Ring Resonator for Displacement Sensing Applications

In this study, we show the capability of integrated Micro-Ring Resonators (MRRs) to perform frequency-to-amplitude (FM-to-AM) conversion of optical feedback interferometry (OFI) signals with improved signal-to-noise ratio compared to conventional AM OFI signals. Further, contrary to traditional OFI FM-to-AM conversion techniques using gas cell-based edge filters and free-space or fiber Mach-Zehnder Interferometers (MZI), integrated photonic processing offers greater compactness and perturbation resilience, enhancing noise performance through improved temperature control and immunity to parasitic mechanical vibrations. The OFI FM-to-AM conversion was performed with a fabricated silicon nitride MRR of radius 120 μm and a quality factor of 130,000. The FM-to-AM conversion factor achieved was 0.61 GHz−1, with a noise equivalent displacement of only 4.9 nm for a 1 kHz bandwidth. This demonstration highlights the potential of integrated edge filters to replace traditional freespace and fiber architectures, more prone to environmental perturbations, in OFI signal processing for vibrometric applications.

All-optical modulation of Fano-like resonances in apodized fiber Bragg grating using Er/Yb doped fiber

A novel all-optical scheme for fast modulation of Fano-like resonance using Er/Yb doped fiber (EYDF) is proposed and demonstrated experimentally. In the integrated system, an apodized fiber Bragg grating (AFBG) is inserted into one arm of the fiber Mach–Zehnder interferometer (MZI), and the asymmetric Fano-like resonances is generated by the interference between the MZI mode and AFBG mode. In addition, a section of EYDF is inserted into the other arm of the MZI to control the phase difference between the two arms of the MZI. By adjusting the power of optical pump applied to the EYDF, the transmission spectrum lineshapes of the integrated device can be effectively modulated into asymmetric Fano-like resonances, symmetric transmission dip or electromagnetically induced transparency-like resonances, which has a fast response speed. The proposed all-optical Fano-like modulation scheme is simple in structure, and has advantages of remote control and long-term stability, providing potential applications in the fields of fast and slow light, optical filters and fiber sensing.

Label-Free DNA Hybridization Detection Using a Highly Sensitive Fiber Microcavity Biosensor.

A novel label-free optical fiber biosensor, based on a microcavity fiber Mach-Zehnder interferometer, was developed and practically demonstrated for DNA detection. The biosensor was fabricated using offset splicing standard communication single-mode fibers (SMFs). The light path of the sensor was influenced by the liquid sample in the offset open cavity. In the experiment, a high sensitivity of -17,905 nm/RIU was achieved in the refractive index (RI) measurement. On this basis, the probe DNA (pDNA) was immobilized onto the sensor's surface using APTES, enabling real-time monitoring of captured complementary DNA (cDNA) samples. The experimental results demonstrate that the biosensor exhibited a high sensitivity of 0.32 nm/fM and a limit of detection of 48.9 aM. Meanwhile, the sensor has highly repeatable and specific performance. This work reports an easy-to-manufacture, ultrasensitive, and label-free DNA biosensor, which has significant potential applications in medical diagnostics, bioengineering, gene identification, environmental science, and other biological fields.

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).

Fiber Mach-Zehnder interferometer micro-cavity length adjustment in tens of nanometers for sensing system miniaturization

Fiber Mach-Zehnder interferometer (FMZI) micro-cavity length adjustment in tens of nanometers by chemical etching for refractive index sensing system miniaturization was firstly reported. This etching process is capable of adjusting the length of micro-structure at the order of tens of nanometers, and achieving such high precision without involving complicated and expensive nano-fabrication facilities. The chemical etching opens up the fiber micro-cavity and redshifts its resonant wavelength at the rate of 3.6 nm/min, upon an estimated etching speed of 41.5 nm/min. The shift of the micro-cavity’s resonant wave-length close to the LD’s emitting wavelength is achieved by such precise length adjustment for sensing system miniaturization. The miniaturized FMZI is experimentally applied to the refractive index sensing for ethanol solutions. The measured transmission is in good linearity with regards to the solution index and the sensitivity is -12.8 dB for 0.0043 RIU (refractive index unit) difference in this study. The miniaturized FMZI index-sensing system can be portable and operating at a fast speed, which is well suited for practical field applications.

Hyperspectral measurement of dispersion in aqueous solution and its effect on ultra-sensitive interferometer.

Since the reported Sellmeier equation of water is fitted with sparse sampling points in the near-infrared region, the simulated refractive index sensitivity of dispersion enhanced interferometers deviates from the true value. Here, we measure the refractive index of aqueous sample based on hyperspectra, and research the effect of dispersion on ultra-sensitive interferometer. A piece of quartz plate is used to generate hyperspectra in the near-infrared region by building a wavefront splitting fiber Mach-Zehnder interferometer (WFSF-MZIs). The refractive index of saline water is tested after measuring the thickness of the quartz plate. By taking the wavelength of 1450 nm as break-point, the empirical dispersion equations of saline water are piecewise fitted. When the normal and abnormal dispersion are taken into account, the theoretical sensitivity of phase compensated WFSF-MZI is in good agreement with the experimental results. Our methodology provides a good reference in designing dispersion sensitized optical refractive index sensor for detecting aqueous samples.

Investigation of an inline fiber Mach-Zehnder interferometer based on hybrid joints of core-offset and peanut-shape for refractive index sensing

An inline fiber Mach-Zehnder Interferometer (MZI) that consisted of a standard single-mode fiber sandwiched between a core-offset and a peanut-shape joint is fabricated for the purpose of refractive index (RI) sensing. After one of the core-offset joints is replaced by a peanut-shape joint in an inline fiber MZI with the core-offset pair, the influence of the interference performance caused by the relative offset direction of the two core-offsets is avoided. The RI sensing characteristics under different core-offset displacement and interference arm length are studied. After bending the inline fiber MZI, the interference spectra become more stable, and the RI sensing performance is markedly improved. The RI sensitivity of −167.27 nm/RIU with a resolution of 2.39 × 10-4 RIU is achieved within the measured RI range of 1.333–1.373.

Intelligent soft self-twisted shape sensor

This paper introduces an all-fiber flexible soft sensor that combines machine learning methods to acquire the ability to recognize its own twisted shape. The sensor is twisted into various shapes, the recognition accuracy of the shapes can reach 100 %. Unlike existing sensors, which require multiple sensors to form an array, such sensor requires only a single optical fiber MZI (Mach-Zehnder interferometer) embedded inside the flexible material, which makes the sensing structure and wiring connection very simple. At the same time, the sensor presents very good reliability, bend sensitivity and repeatability. Its temperature performance is also investigated. All above highlighting its great potential in intelligent robots, medical rehabilitation, surgical endoscopes, and object recognition.

All-optical group velocity manipulation in Mach-Zehnder fiber interferometers incorporating with Brillouin random lasing resonance

We proposed and experimentally demonstrated a novel scheme of light group velocity control via a Mach-Zehnder fiber interferometer incorporated with Brillouin random lasing resonance in a half-open linear cavity. A theoretical model of the proposed Brillouin random lasing resonance-based Mach-Zehnder interferometer (BRLR-MZI) for the light group velocity manipulation was derived, predicting optical power-dependent transmittance spectrum shift as well as the enhancement of the temporal advancement. Thanks to Brillouin random lasing-induced fast light effect, the proposed scheme not only achieves a flexible all-optical manipulation of its transmittance spectrum but also overcomes the saturation effect for the light speed control based on a traditional MZI. In experimental validation, sinusoidally modulated signals with the modulation frequency of 160 kHz ultimately experienced a maximum advancement of 4031 ns (corresponding to the group index of 0.875), which exhibits an advancement improvement of 1364 ns compared with the traditional MZI-based scheme. It suggests a promising platform for exploring applications in fields of all-optical signal processing, microwave photonic, and ultra-sensitive fiber sensing.

Highly Improved Refractive Index Sensitivity in Fiber Mach-Zehnder Interferometer Based on Two Tapers

Highly Improved Refractive Index Sensitivity in Fiber Mach-Zehnder Interferometer Based on Two Tapers

7-Core Fiber-Based High-Resolution Omnidirectional Vector Bending Sensor Enabled by Microwave Photonics Filter

We proposed and experimentally demonstrated a high-resolution omnidirectional vector bending sensor based on 7-core fiber Mach-Zehnder interferometers (MZIs), which is interrogated by the microwave photonics technique. The sensor is composed of three MZIs in the 7-core fiber, and each MZI consists of two symmetric outer cores. Instead of using the traditional wavelength demodulation method, which has the drawback of very limited resolution due to the used optical spectrum analysis devices, e.g., optical spectrum analyzer (OSA), the proposed sensor is interrogated by high-resolution microwave photonics filter (MPF) system, which is capable of offering up to KHz level measurement resolution. As a result, curvature measurement with resolution of 0.0213 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> is demonstrated when the used resolution of vector network analyzer (VNA) is 500 kHz. Thanks to the ultra-high measurement resolution of VNA (∼KHz), the curvature resolution can achieve 4.27 х 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in theory, which is 2 orders of magnitude higher than the traditional wavelength demodulation-based fiber bending sensors. The measured curvature sensitivity of the MZI exhibits highly bending direction dependence, attributed to different strain variation under distinct bending angle. In addition, owing to the different angular positions of cores of the MZI in the 7-core fiber, the MZIs have differential response to fiber bending. This feature has been used to develop vector bending sensing, which is manage to determine the bending direction by using any two MZIs, and the obtained average relative errors for the retrieved curvature and bending direction are 2.57% and 0.86%, respectively. The proposed sensor possesses the unique advantages of high sensitivity and high resolution over the state-of-the-art technology, which is very promising for omnidirectional vector bending sensing in the future.