All-fiber Mach-Zehnder Interferometer Research Articles

“Visible range curvature fiber-optic sensor with low strain-temperature dependence”

This manuscript introduces and demonstrates a visible curvature fiber optic sensor using an all-fiber Mach-Zehnder interferometer. The all-fiber interferometer was constructed using an in-line optical fiber sandwich structure, utilizing fibers specifically designed for the visible range. We demonstrate the reproducibility of the curvature sensor fabricating several distinct interferometers. These devices were subjected to curvature testing, exhibiting suitable wavelength shifts and achieving a maximal sensitivity of −10.44 nm/m−1. The hysteresis analysis shows minimal path deviation, and the statistical ANOVA analysis reveals a consistent mean trend with a minimal Prob > F value of 9.30472 × 10−55. Consequently, the hysteresis analysis indicates that the error in the curvature direction has a minimal impact on the measurement, and the low Prob > F value ensures that the curvature measurements cannot overlap. Then, accurate and high reproducibility of the curvature measurements can be expected. The results validate that the optical fiber structure is among the limited approaches to phase modulation interference within the visible range, representing a competitive alternative for curvature measurement.

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.

Temperature and strain simultaneous sensing measurement based on an all-fiber Mach-Zehnder interferometer and fiber Bragg grating.

We designed and fabricated what we believe to be a novel dual-parameter fiber optic sensor for simultaneous measurement of temperature and strain, which was composed of a femtosecond laser inscribed fiber Bragg grating (FBG), three segments of a single-mode fiber (SMF), and two segments of a multimode fiber (MMF), forming a SMF-MMF-FBG-MMF-SMF structure. The FBG and Mach-Zehnder interferometer (MZI) were present in this structure so that the changes of the temperature and strain parameters can be sensed by the shifts of the reflection center wavelength of the FBG and the interference valley wavelength of the MZI. We simulated the light field distribution of the sensor structure, compared the shapes of the interference spectra formed by the MZI structure with different sensing arm lengths of 25, 35, and 45mm, and analyzed the spectra in the spatial frequency domain. The simulation results showed that the interference spectrum of the MZI structure with a 25mm length sensing arm was clearer and more suitable for the experiment. The experimental results showed that the temperature sensitivity of the FBG and MZI was 14.81 and 43.54pm/°C in the range of 80°C to 240°C, and the strain sensitivity was 1.49 and -2.58pm/µε in the range of 0 to 1200µε, with a high linearity and excellent repeatability. The sensor is economical, sensitive, and convenient to fabricate, and exhibits promising applications in the fields of biochemical medical detection and industrial production monitoring.

Wavelength-tunable mode-locked fiber laser based on an all-fiber Mach–Zehnder interferometer filter

Wavelength-tunable dissipative solitons and amplifier similaritons have been obtained by inserting all-fiber Mach–Zehnder interferometer (MZI) filters with different free spectral ranges (FSRs) in a Yb-doped mode-locked fiber laser. The MZI filter is fabricated by splicing one segment of seven-core fiber (SCF) between two segments of single-mode fibers. The bandwidth of the filter depends on the FSR of the modulated interference curve and consequently depends on the tapered fiber diameter. Inserting MZI filters with bandwidths in a fiber laser and applying a tensile strain on the tapered SCF, both wavelength-tunable dissipative solitons and amplifier similaritons have been obtained.

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.

High sensitivity detection of SARS-CoV-2 by an optofluidic hollow eccentric core fiber.

Since the outbreak of coronavirus disease 2019 (COVID-19), efficient real-time monitoring has become one of the challenges faced in SARS-CoV-2 virus detection. A compact all-fiber Mach-Zehnder interferometer optofluidic sensor based on a hollow eccentric core fiber (HECF) for the detection and real-time monitoring of SARS-CoV-2 spike glycoprotein (SARS-CoV-2 S2) is proposed, analyzed and demonstrated. The sensor is comprised of fusion splicing single mode fiber (SMF), hollow core fiber (HCF) and HECF. After the incident light passes through the HCF from the SMF, it uniformly enters the air hole and the suspended micrometer-scale fiber core of the HECF to form a compact all-fiber Mach-Zehnder interferometer (MZI). HECF is side polished to remove part of the cladding that the suspended fiber core can contact the external environment. Subsequently, the mouse anti SARS-CoV-2 S2 antibody is fixed on the surface of the suspended-core for the sake of achieving high sensitivity and specific sensing of SARS-CoV-2 S2. The limit of detection (LOD) of the sensor is 26.8 pM. The proposed sensor has high sensitivity, satisfactory selectivity, and can be fabricated at low cost making it highly suitable for point-of-care testing and high-throughput detection of early stage of COVID-19 infection.

An Ultra-Coherent Semiconductor Laser Locked to a Short Delay Fiber Mach-Zehnder Interferometer With Active Fiber Noise Cancellation

We propose and demonstrate a technique to vastly reduce the linewidth of a commercially available semiconductor laser operating at 1550 nm by locking it to an all-fiber Mach-Zehnder interferometer (MZI) with a short path length imbalance. The long term linewidth was reduced from 20 kHz to the single and even sub Hz level. Very narrow linewidths can only be measured by beating two separate, nominally identical lasers. To this end, we employ two lasers configured in a unique, counter propagating configuration, both locked to two different fringes of the MZI. The beat between the two locked lasers proves the extremely narrow linewidth of each laser. In order to detect and compensate for the noise caused by mechanical and thermal fluctuations of the fibers, we use the beat signal as an input to a servo loop that feeds a piezo electric fiber stretcher stabilizing the MZI.

High-performance all-fiber Mach-Zehnder interferometer based on D-shaped two-mode fiber coated with polydimethylsiloxane for temperature sensing

A novel fiber sensor, an all-fiber Mach-Zehnder interferometer based on D-shaped two-mode fiber (DTMF-MZI) coated with polydimethylsiloxane (PDMS), is proposed and demonstrated. When light is incident from a single-mode fiber (SMF) to a two-mode fiber (TMF), two modes will be excited in the TMF and interfere with each other, just like a two-beam fiber Mach-Zehnder interferometer (MZI). Due to the high negative thermo-optical coefficient, the proposed sensor is sensitive to temperature. Our theoretical analysis and experimental results prove that as the temperature increases, the dips in the transmitted spectrum of DTMF-MZI will blue-shift. Furthermore, we demonstrate the influences of the distance from the center of the fiber core to the polished plane (parameter h) and the length of the polished area (parameter Lpo) of TMF on the temperature sensitivity. In the experiments, the maximum temperature sensitivity of the proposed sensor reaches −305.6 pm/°C in the temperature range of 30 ∼ 80 °C, and the linearity is as high as 0.9890. In addition, the sensor shows good stability at 30 °C and 80 °C in 60 min with the maximum variations of 0.16 nm. The proposed sensor has many advantages, such as being highly temperature-sensitive, compact, and stable.

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

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

Sensing Characteristics of Polarization-Dependent Helical Long-Period Grating-Based Interferometer

We demonstrate an all-fiber Mach-Zehnder interferometer (MZI) by cascading a pair of helical long-period gratings (HLPGs) inscribed in a Panda-type polarization-maintaining fiber (PMF) using a CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -laser. By cascading two grating with different lengths, a serial of polarization-dependent MZIs with different free spectral ranges have been demonstrated. The maximum polarization-dependence loss of the MZI was measured to be more than 35 dB. Two orthogonal interference spectra corresponding to fast axis mode and slow axis mode can be observed. The sensing characteristics of the polarization-dependent MZI we investigated experimentally. For liquid level sensing, the maximum wavelength shifts of the fast and slow axis interference dips were measured to be 11.03 and 3.25 nm when the surrounding refractive index is 1.424 and the interference length is 12.0 cm, respectively. The fast and slow axis interference dips have good linearity and opposite response with the temperature and strain change, the measured temperature and strain sensitivities of the fast and slow axis interference dips were 103.43 pm/°C, −31.26 pm/°C and −2.13 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , 1.68 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , respectively. Based on the high polarization extinction ratio, narrow resonant bandwidth, and low insertion loss, the demonstrated MZI has potential application in polarization-dependent multi-parameter sensing or multi-channel polarization filter.

Ring core few-mode fiber sensor for curvature measurement.

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

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

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

Comparative spectral tuning and fluctuation analysis of an all-fiber Mach–Zehnder interferometer and micro Mach–Zehnder interferometer

This paper presents a comparative spectral analysis for tuning all-fiber directional coupler-based Mach–Zehnder Interferometer (MZI) and all-fiber inline Micro Mach–Zehnder Interferometer (MMZI) configurations. The analytical background is necessary to estimate the change in the differential path length for tuning the channel (peak) wavelengths and inter-channel spacing (i.e. free spectral range) of the MZI. We briefly describe the method used to adjust the spectral response experimentally. The spectral tuning of all-fiber MZI and MMZI has been successfully implemented in different applications of fiber optic communication and sensing (Ramachandran et al (2014 IEEE Sens. J. 15 1270–4; 2017 Opt. Fiber Technol. 36 195–8), Kumar and Ramachandran (2013 Opt. Commun. 289 92–96; 2014 Opt. Laser Technol. 63 144–7)). The spectral tuning of the MMZI is based on the interference length. Compared to MZI, miniaturized MMZI does not deal with any spectral fluctuation when employed in dense wavelength division multiplexing (DWDM) application and a sensing scheme. Research during the past year has surveyed the different MZI structures from an application perspective to infer that MMZI might be the most suitable configuration for sensing applications, and MZI may prove to be more useful in DWDM optical networks.

Multi-wavelength tunable ring cavity fiber laser incorporated with a Mach–Zehnder interferometer filter based on waist-enlarged fiber bitapers

In this study, a multi-wavelength tunable ring cavity erbium-doped fiber laser based on an all-fiber Mach–Zehnder interferometer (MZI) is proposed and demonstrated experimentally. For the proposed fiber laser, the MZI is composed of two waist-enlarged fiber bitapers, and the free spectral range is 10.8 nm. In the experiment, the length of the gain medium erbium-doped fiber is 4 m, the laser threshold is 40 mW, and a 1556.8 nm single-wavelength laser is generated. When the pump power is 200 mW, the single-wavelength tunable laser can be tuned within the range of 1554.4–1563.5 nm by adjusting the polarization controller (PC). In addition, the wavelength spacing is less than 1.2 nm, the peak power difference is less than 1.1 dB, and the 3 dB linewidth is 0.04 nm. For the proposed fiber laser, four types of dual-wavelength lasing outputs are generated by adjusting the polarization controller, and the wavelength intervals are changed from 0.9 to 8.1 nm. The single-, dual- and triple-wavelength laser power fluctuations are less than 0.15, 0.37, and 0.53 dB, respectively, over a 20 min monitoring period.

Ultrasensitive Refractive Index Sensor Based on Mach–Zehnder Interferometer and a 40μm Fiber

An ultra-high sensitivity refractive index (RI) sensor, based on an in-line fiber Mach-Zehnder interferometer (MZI) and utilizing a special 40 μm fiber which has been specifically designed for the purpose, supporting only the LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> modes propagating in the fiber, has been proposed and numerically demonstrated in this work. The all-fiber MZI, based on LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode interference, was fabricated by utilizing a special design with two gradually tapered joints at both sides of this multi-clad thin diameter fiber (TDF). When the TDF diameters varied from 40 μm to 5 μm, a sudden change in the direction of the wavelength shift in the transmission spectrum of the TDF-MZI devices was observed both in liquid RI and air relative humidity (RH) monitoring experiments, as the surrounding RI or RH was seen to increase monotonically. Ultra-high sensitivity values of 5942.8nm/RIU (1.335-1.342) and 21292.2nm/RIU (1.4000-1.4025) were obtained in the experiments carried out, through the use of a tapered TDF-MZI device with TDF diameters of ~5 μm and ~9 μm, respectively. The maximum RH sensitivity of 1.084nm/%RH was obtained by the use of the TDF-MZI device with a TDF diameter of ~12 μm. A compact all-fiber TDF-MZI sensor was thus created with an overall sensing length of <; 4mm, showing the advantages of high sensitivity, low loss, and flexibility in the tunable monitoring direction of the wavelength shift. This design is well suited to various applications, where the high sensitivity RI and RH measurements are required at precise locations.

In-Line Mach-Zehnder Interferometers Based on a Capillary Hollow-Core Fiber Using Vernier Effect for a Highly Sensitive Temperature Sensor.

In this paper, we propose a highly sensitive temperature sensor based on two cascaded Mach–Zehnder interferometers (MZIs) that work using the Vernier effect. The all-fiber MZIs were assembled by splicing a segment of capillary hollow-core fiber (CHCF) between two sections of multimode fibers (MMFs). This cascaded configuration exhibits a temperature sensitivity of 1.964 nm/°C in a range from 10 to 70 °C, which is ~67.03 times higher than the sensitivity of the single MZI. Moreover, this device exhibits a high-temperature resolution of 0.0153 °C. A numerical analysis was carried out to estimate the devices’ temperature sensitivity and calculate the magnification of the sensitivity produced by the Vernier effect. The numerical results have an excellent agreement with the experimental results and provide a better insight into the working principle of the MZI devices. The sensor’s performance, small size, and easy fabrication make us believe that it is an attractive candidate for temperature measurement in biological applications.

Dual sensing points Mach–Zehnder interferometer for refractive index and discrete liquid level sensing

An in-line all-fiber Mach–Zehnder interferometer (MZI) based on the combination of etched single mode fiber (ESMF) and double cladding fiber (DCF) is proposed for refractive index and discrete liquid level sensing. In the proposed structure, two sensing points are devised using two ESMF section of length. The two sections are separated by a refractive index insensitive region formed by DCF section. The sensor may be deployed to measure refractive index in single- or dual-point configuration. The experimental work revealed maximum refractive index (RI) sensitivity at − 37.2 nm/RIU for 1.305–1.335 RI range, with 1 mm compact sensor size. Additionally, the sensor performed as a two-point liquid level sensor with wavelength shift ranging between 0.84 nm and 1.44 nm. The proposed sensor displayed great potential to be deployed in liquid chemical storage to monitor liquid quality and level.

Realization and Modulation of Fano-Like Lineshape in Fiber Bragg Gratings

Optical fiber Bragg gratings (FBGs) featured with narrowband transmission dips (or reflection peaks) have been maturely employed in technologies of optical communications, lasers and sensors. Here, we report a simple strategy to control the lineshapes of FBG's transmission dip by inserting the FBG in one arm of an all-fiber Mach-Zehnder interferometer (MZI). The transmission dip could be modulated into an asymmetric Fano-like lineshape or a transmission peak, which is controlled by the phase difference between the two arms of the MZI. It works for the uniform, chirped, and phase-shifted FBG. We experimentally verify it with a uniform FBG, showing freely modulated asymmetric Fano-like lineshape with the optical delay line, strain and temperature. Due to the modulation, the maximal slope rate is 49.1 dB/nm, and the Fano parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> can be tuned from -∞ to +∞. The tunable lineshapes of the FBGs might open up a new window for the applications of traditional FBGs in lasers, communications and sensors.

All-fiber phase modulator and switch based on local surface plasmon resonance effect of the gold nanoparticles embedded in gel membrane.

All-fiber modulators and switches have drawn great interest in the photonics domain, and they are applied in viable photonic and optoelectronic devices. In this work, with the assistance of an agarose membrane, aspherical gold nanoparticles are embedded on the surface of the microfiber treated with the piranha solution. An all-fiber Mach-Zehnder interferometer was used to realize a low-cost, low-loss, and conveniently prepared all-fiber phase modulator. By taking advantage of the local surface plasmon resonance effect of gold nanoparticles embedded in the agarose membrane, under the excitation of near-infrared region light, the gold nanoparticles were excited to change the effective refractive index of one arm of the Mach-Zehnder interferometer. A maximum phase shift of ∼6π at 1550 nm was obtained from the device. In addition, an all-optical switch was achieved with a rising edge time of 47 ms and falling edge time of 14 ms. The proposed all-fiber modulator and switch based on the local surface plasmon resonance effect of gold nanoparticles embedded in agarose membrane will provide great potential in all-optical fiber systems.

Time-Stretched Femtosecond Lidar Using Microwave Photonic Signal Processing

A real-time ranging lidar with 0.1 Mega Hertz update rate and few-micrometer resolution incorporating dispersive Fourier transformation and instantaneous microwave frequency measurement is proposed and demonstrated. As time-stretched femtosecond laser pulse passing through an all-fiber Mach-Zehnder Interferometer, where the detection light beam is inserted into the optical path of one arm, the displacement is encoded to the frequency variation of the temporal interferogram. To deal with the challenges in storage and real-time processing of the microwave pulse generated on a photodetector, we turn to all-optical signal processing. A carrier wave is modulated by the time-domain interferogram using an intensity modulator. After that, the frequency variation of the microwave pulse is uploaded to the first order sidebands. Finally, the frequency shift of the sidebands is turned into transmission change through a symmetric-locked frequency discriminator. In experiment, A real-time ranging system with adjustable dynamic range and detection sensitivity is realized by incorporating a programmable optical filter. Standard deviation of 7.64 {\mu}m, overall mean error of 19.10 {\mu}m over 15 mm detection range and standard deviation of 37.73 {\mu}m, overall mean error of 36.63 {\mu}m over 45 mm detection range are obtained respectively.