Fiber Mach-Zehnder Interferometer Research Articles

GO/MoS₂@PVA Composite Membrane based optical fiber Mach-Zehnder Interferometer for Humidity Sensing and its Non-Contact Sensing Application

GO/MoS₂@PVA Composite Membrane based optical fiber Mach-Zehnder Interferometer for Humidity Sensing and its Non-Contact Sensing Application

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.

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.

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.

Vector Bending Sensor Based on Hole-Assisted Three-Core Fiber Mach-Zehnder Interferometer

A vector bending sensor based on hole-assisted three-core fiber (HATCF) Mach-Zehnder interferometer (MZI) is demonstrated. The sensor is composed of multi-mode fiber (MMF) - HATCF - MMF structure embedded between two single-mode fibers (SMFs). The bending curvature and direction can be identified by interrogating the wavelength of the interference peak, and the maximum bending sensitivity of -28.726 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> is obtained at the 220° direction. In addition, the sensor has a temperature sensitivity of 44 pm/°C and is insensitive to the external refractive index (RI).

A taper-in-etch based hybrid fiber Mach-Zehnder interferometer hydrogen sensor

A hydrogen (H2) sensing application is proposed and experimentally demonstrated using a multimode fiber (MMF)–tapered-in-etch single-mode fiber (SMF)–MMF (MMF–TiESMF–MMF)-based Mach–Zehnder interferometer (MZI). The MZI is made of an SMF segment placed between two MMF segments. The MMF segments function as mode couplers, splitting and combining light due to a core diameter discrepancy between the MMF and the SMF. The SMF segment undergoes cladding modification by chemically etching to achieve a 50 µm diameter over a 2 cm length, followed by the tapering to obtain a 15 µm waist diameter with a 1 cm length. A layer of palladium–graphite nanofibers is applied to the modified area of the TiESMF to produce H2 adsorption. The sensor is investigated against H2 over the 0.25–1% concentration range at room temperature. When H2 molecules were desorbed on the sensing layer, its index of refraction was changed so that the output spectrum resulting from the MZI is blue-shifted due to H2 molecules desorption. The MMF-TiESMF-MMF MZI exhibits a sensitivity of 0.332 nm/vol% and a linear fit coefficient of 99.72% for H2 concentrations in the range selected. MZI based sensors showed a linear, stable, and repetitive response.

All-fiber modulator derived from the large-transverse-offset Mach-Zehnder interferometer coated with ITO

In this paper, we first propose a fiber electrothermal modulator derived from the large-transverse-offset Mach-Zehnder interferometer (MZI) coated with transparent and conductive indium-tin-oxide (ITO). The fiber MZI was fabricated by welding single-mode fiber (SMF) with large-transverse-offset fusion. The fiber modulator is that the thermo-optic effect of the ITO film on the surface of the fiber leads to a change in the refractive index, which in turn causes the shift of the interference spectrum. Specifically, it is based on the thermo-optic effect of a large-transverse-offset MZI coated with ITO. Through the external electric potential, the ITO film generates Joule heat and then changes the effective refractive index of the cladding to realize fiber phase modulation. In the experiment, the spectrum is significantly shifted by 5.55 nm at the wavelength of 1650 nm and can obtain an optical modulator with a rise (fall) time of 0.65 (0.5) s. The proposed fiber modulator shows great performance in the optical switches and sensing.

High-sensitive and temperature-immune curvature sensor based on bitaper sandwiching in SMS fiber structure

A high-sensitive and temperature-immune curvature sensor based on all fiber Mach–Zehnder interferometer (MZI) is proposed and experimentally investigated. The sensor is constructed by sandwiching a short section of multimode fiber (MMF) between two single-mode fibers (SMFs) with two bitapers. Experimental results show that the sensor can achieve a maximum sensitivity of -34.3935 nm/m−1 in the curvature range of 2.96-4.19 m−1 and a low temperature cross-sensitivity of -0.0003 m−1/∘C in the temperature range of 30-100 °C. The stability test reveals that the standard error of instability is 0.0004 m−1, indicating the sensor’s capacity of long-term operation. The sensor has advantages of low cost, easy fabrication, large curvature detection range, high curvature sensitivity and temperature immunity, makes it has broad application prospects in the curvature sensing field.

All fiber Mach–Zehnder interferometer for simultaneous measurement of temperature and refractive index

An all fiber Mach–Zehnder interferometric (MZI) sensor for measuring temperature and refractive index (RI) is proposed and experimentally demonstrated. The proposed sensor is fabricated with a coreless–few mode–coreless fiber structure. Variations in ambient temperature and RI cause changes in phase differences between the fundamental mode and the higher-order modes, leading to shifts in interference spectrum. The two resonance dips shifts within the wavelength spectrum are used to investigate the temperature and RI characteristics of the sensor. Experimental results show that the two dips have different responses to temperature and RI, indicating that the sensor can realize simultaneous measurement of temperature and RI; the maximum sensing sensitivities are 0.0739 nm/°C and −25.29 nm/RIU, respectively. The proposed sensor has potential applications in physical, biological, and chemical sensing owing to its low cost, good linearity, and simple fabrication.

Quantum-enhanced optical precision measurement assisted by low-frequency squeezed vacuum states

Stable low-frequency squeezed vacuum states at a wavelength of 1550 nm were generated. By controlling the squeezing angle of the squeezed vacuum states, two types of low-frequency quadrature-phase squeezed vacuum states and quadrature-amplitude squeezed vacuum states were obtained using one setup respectively. A quantum-enhanced fiber Mach–Zehnder interferometer (FMZI) was demonstrated for low-frequency phase measurement using the generated quadrature-phase squeezed vacuum states that were injected. When phase modulation was measured with the quantum-enhanced FMZI, there were above 3 dB quantum improvements beyond the shot-noise limit (SNL) from 40 kHz to 200 kHz, and 2.3 dB quantum improvement beyond the SNL at 20 kHz was obtained. The generated quadrature-amplitude squeezed vacuum state was applied to perform low-frequency amplitude modulation measurement for sensitivity beyond the SNL based on optical fiber construction. There were about 2 dB quantum improvements beyond the SNL from 60 kHz to 200 kHz. The current scheme proves that quantum-enhanced fiber-based sensors are feasible and have potential applications in high-precision measurements based on fiber, particularly in the low-frequency range.