Fiber Mach-Zehnder Interferometer Research Articles

Highly sensitive vector magnetic field sensors based on fiber Mach–Zehnder interferometers

A highly sensitive vector magnetic field sensor based on a fiber Mach–Zehnder interferometer (FMZI) is proposed and demonstrated. The FMZI is composed of a micro-cavity that is fabricated in a single-step laser-induced micro-plasma process with a modest-powered nanosecond fiber laser. Combined with a magnetic fluid, the micro-cavity-based FMZI is constructed to a magnetic field sensor for vectorial sensing. The presented magnetic sensor exhibits a maximal strength sensitivity of 64 nm/mT that is the highest among reported vector magnetic field fiber sensors to date, to the best of our knowledge.

High sensitivity curvature sensor based on a double-sphere tapered no-core fiber Mach–Zehnder interferometer

A micro-fiber Mach–Zehnder interferometer (MMZI) based on a double-sphere tapered no-core fiber (DST-NCF) for curvature sensing is proposed and experimentally demonstrated. The sensor is composed of the DST-NCF sandwiched to two single-mode fibers (SMF). The DST-NCF is tapered from a double-sphere structure which is fused by no-core fiber (NCF). When light passes through the DST-NCF from SMF, higher-order modes will be excited, which will improve the sensing performance of the MMZI. This proposed structure achieves a significant improvement in curvature sensitivity for the first time by combining the characteristics of NCF, spherical format, and MMZI. When the central waist region is 2.07 mm, the maximum curvature sensitivity of the sensor is −224.64 nm/m−1, which is the highest curvature sensitivity in the MZI structure based on the spherical structure or the NCF as we have known. In addition, the maximum temperature sensitivity is −5.79 pm/℃ in the range of 40 ℃ − 90 ℃. It shows that this sensor has the characteristics of being insensitive to temperature and avoids the cross-sensitivity effect between temperature and curvature.

Low-cost high-sensitivity pH sensor based on a droplet-shaped single-mode fiber Mach–Zehnder interferometer

In this paper, we present the fabrication of a new fiber-optic pH sensor based on the macro-bending loss properties in a droplet-shaped single-mode fiber (SMF) bending structure for the first time. To form the droplet-shaped probe, a segment of straight SMF is properly bent into a droplet shape using a short length of a thin silica capillary tube and without any splicing. By gradually varying the bending diameter of the droplet-shaped structure, interference results between the core and cladding modes, and a Mach–Zehnder interferometer (MZI) is effectively introduced within the bending section. Sodium hydroxide (NaOH) or hydrochloric acid (HCl) were added to the pH indicator utilizing buffers solution to achieve a wide pH range from 1 to 14. Experimental results show that the proposed sensor exhibits maximum sensitivity of 3.264 nm/pH and 5.336 nm/pH for acidic and alkaline solutions, respectively. In addition to the high sensitivity, the proposed sensor structure provides high sensitivity with a high linear response and good repeatability.

High sensitivity and fast response optical fiber nucleic acid sensor

A label-free optical fiber Mach-Zehnder interferometer (MZI) based biosensor was proposed for the specificity detection of single-stranded nucleic acid (NA). The MZI was made of a fiber sandwich structure by a core-offset fusion splicing means. The piranha solution, APTES (3-Aminopropyltriethoxylsilan) and GA (Glutaraldehyde) were used for the chemical modification of the optical fiber surface, and then the single-stranded probe NA with the known sequence was fixed on the optical fiber surface by covalent fixation method. The specificity of complementary target NA could be detected through the changing of the spectra of the MZI. Thanks to the high sensitivity of the MZI and the high fixation efficiency of the covalent fixation method, the optical fiber MZI based NA sensor showed a fast response of 30 s and a high sensitivity of 0.175 dB/nM with a minimum detection concentration of 1 nM.

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.

A label-free lateral offset spliced coreless fiber MZI biosensor based on hydrophobin HGFI for TNF-α detection.

A real-time label-free lateral offset spliced coreless fiber (CF) Mach-Zehnder interferometer (MZI) biosensor functionalized with hydrophobin Grifola frondosa I (HGFI) was proposed for the detection of cytokine tumour necrosis factor alpha (TNF-α). The nanolayer self-assembled on the optical fiber surfaces by HGFI rendered the immobilization of probe TNF-α antibody and recognition of antigen TNF-α. Trifluoroacetic acid was utilized to remove the HGFI layer from the glass surface, which was validated by field emission scanning electron microscopy (FESEM) and water contact angle (WCA). Results demonstrated that the processes of HGFI modification, antibody immobilization and specific antibody detection can be monitored in real time. The proposed biosensor exhibited good specificity, repeatability and low detection limit for TNF-α, extending its application in inflammation and disease monitoring.

Highly sensitive humidity sensor based on tapered dual side-hole fiber

We proposed and demonstrated a highly sensitive humidity sensor based on a fiber Mach-Zehnder Interferometer (MZI). This sensor is composed of a short section of tapered dual side-hole fiber (DSHF) sandwiched between two single mode fibers. At the tapered section, both the fundamental and higher order cladding modes are stimulated and interfere with each other, forming an inter-modal MZI. The existence of air holes in the DSHF makes the cladding mode more easily excited and has higher refractive index sensitivity. In addition, by coating graphene oxide (GO) film with large specific surface area on the tapered DSHF, the humidity sensitivity of the sensor has been further improved. Experimental results show that the humidity sensitivity of the sensor can reach − 0.142 nm/%RH, which increased 7.9 times than that without GO coating. In addition, the rising and falling time of respiration were 0.23 s and 2.19 s, respectively. The excellent performance demonstrates it is a good candidate for humidity measurement.

High-Sensitivity Liquid Level Sensor Based on the Balloon-Shaped Fiber Optic MZI

We demonstrated a high-sensitivity liquid level sensor based on the balloon-shaped fiber Mach-Zehnder interferometer (MZI). To make an optical fiber MZI sensor, a bare single mode fiber (SMF) is bent into a balloon shape. The sensor is attached to a stiff support and linked to a buoyancy ball floating on the liquid surface via a thin thread. The change in liquid level will bend the fiber and lead to a wavelength shift of transmission spectrum. This is a novel method of measuring liquid levels. We comprehensively studied the sensing performance of the sensor, and applied the ridge regression algorithm to optimize the fitting results of the experimental data. The maximum sensitivity of liquid level and temperature are 5.245 nm/mm and 40.3 pm/°C respectively, and the sensor has a low temperature cross-sensitivity of 0.00768 mm/°C. Furthermore, the sensor has the advantages of real-time response, convenient manufacture, low cost and high reliability, which broadens the application area of balloon-shaped MZI and makes it appropriate for liquid level sensing.

Highly sensitive refractive index sensing based on a novel Mach-Zehnder interferometer with TCF-PCF composite structure

We have proposed and demonstrated a highly sensitive refractive index (RI) sensor based on photonic crystal fiber Mach-Zehnder interferometer (PCF-MZI), which was obtained by splicing a piece of thin core fiber (TCF) and PCF with the same length between two single mode fibers (SMFs). The proposed MZI exhibited good fringe visibility as high as 21 dB in air and a highly RI sensitivity of 252.88 nm/RIU in the range of 1.3735 ∼ 1.3994. Additionally, the RI sensing properties of different length of PCF were also investigated experimentally. It was found that the RI sensitivities were weekly dependent on the length of MZI. The measured sensitivities of the MZI with 35 mm PCF, 40 mm PCF, 45 mm PCF were 112.99 nm/RIU, 119.25 nm/RIU, and 117.52 nm/RIU in the range of 1.3333 ∼ 1.3735 and 228.77 nm/RIU, 252.88 nm/RIU and 183.66 nm/RIU in the range of 1.3735 ∼ 1.3994, respectively. Moreover, the RI sensitivities were increased by about 62% and 2.4 time than the MZI with SMF-PCF-SMF structure in the above RI intervals, respectively. In addition, the sensor shown advantages of simple fabrication, high fringe visibility, high sensitivity and low temperature sensitivity, which was attractive for the development of RI sensing application.

Optical curvature sensor with high resolution based on in-line fiber Mach-Zehnder interferometer and microwave photonic filter.

Curvature measurement plays an important role in structural health monitoring, robot-pose measuring, etc. High-resolution curvature measurement is highly demanded. In this paper, an optical curvature sensor with high resolution based on in-fiber Mach-Zehnder interferometer (MZI) and microwave photonic filter (MPF) is proposed and experimentally demonstrated. The in-fiber MZI is constructed with a ring-core fiber (RCF) which is fusion spliced between two coreless fibers (CLFs). The structure of CLF-RCF-CLF is then sandwiched between two segments of single-mode fiber (SMF), making the whole interferometer structure of SMF-CLF-RCF-CLF-SMF. The operating principle is that different curvatures will cause the variations of the interference spectrum of MZI due to elastic-optic effect, and then the variations are converted into the frequency-shift of the MPF. The factors affecting the visibility of the interference spectrum are researched. A preliminary exploration of the multiplexing demodulation for the in-fiber-MZIs is also investigated and discussed, which is for the first time to the best of our knowledge, holding great potential to pave the way for constructing the sensing network composed of interferometric sensors. The curvature measurement sensitivity is -147.634 MHz/m-1, and the resolution is 6.774 × 10-6 m-1 which is the highest value up to now.

Highly Modulated In-Fiber Mach-Zehnder Interferometer Based on an Ultracompact Leaky-Guided Liquid Core.

We proposed a novel sensor based on an ultracompact leaky-guided liquid core fiber Mach–Zehnder interferometer (LLCFMZI) for high modulation of an interference spectrum. The sensor structure is based on a micro-sized hollow-core fiber (HCF) splicing a tilt end face single-mode fiber (SMF) to create a miniature oblique gap for the effective access of different liquids. The liquid core with a relatively lower refractive index (RI) than the cladding can achieve a leaky-mode optical waveguide (LMOW) mechanism, and its volume is only approximately 7.85 pL. In addition, the utilized micro-length HCF can reduce the energy loss of core in the LMOW to obtain an acceptable extinction ratio (>30 dB) with high temperature (T) sensitivity in the interference spectra. Experimental results show that the interference spectra can be highly modulated within the wide measurement range of 1250–1650 nm with a steadily linear response for thermal effect. The measured temperature sensitivities (T-sensitivities) of various liquids of DI water, ethanol, and Cargille-liquid (nD = 1.305) are 0.8869, 4.4754, and 4.8229 nm/°C, and the corresponding measured thermal optics coefficient (TOC) are −4.16 × 10−5, −2.11 × 10−4, and −3.6 × 10−4 °C−1, respectively. Measurement results demonstrate that the used liquids with a higher TOC can obtain better T-sensitivity modulation. The highest experimental sensitivity of the liquid-core filled with Cargille-liquid (nD = 1.40) is up to +13.87 nm/°C with a corresponding TOC of −4.07 × 10−4 °C−1. Furthermore, the experimental and theoretical values are in good agreement according to FSR the measuring scheme that investigates the effectiveness of the proposed LLCFMZI.

Tunable Brillouin-erbium fiber laser producing multiwavelength cylindrical vector beams

A multiwavelength Brillouin-erbium fiber laser producing cylindrical vector beams with tunable central wavelength and wavelength spacing is presented and experimentally investigated. Owing to the inhomogeneous broadening characteristic of the Brillouin gain, stable multiwavelength lasing is achieved by combination of the cascaded stimulated Brillouin scattering in the ultra-long single mode fiber and the wavelength selection of the fiber Mach-Zehnder interferometer. Multiwavelength lasing with tunable wavelength spacing of about 0.09, 0.11, 0.17, 0.24 and 0.3 nm is achieved by adjusting the optical delay line in the Mach-Zehnder comb filter. With the sufficient pump power, multiwavelength lasing with more than 10 channels is obtained when the wavelength spacing is tuned to be about 0.09 nm. Through adjusting the flat-top tunable bandpass filter, the central lasing wavelength can be tuned from 1534.37 nm to 1570.06 nm continuously. Cylindrical vector beams with purity higher than 93% are produced through regulating polarization controllers on either side of the two-mode long-period grating serving as the mode convertor. Multiwavelength cylindrical vector beams with the largest number of channels and tuning range are obtained to the best of our knowledge.

Interference of Two Gaussian Beam with Arbitrary Polarization Based on Fiber Mach-Zehnder Interferometer

Interference of Two Gaussian Beam with Arbitrary Polarization Based on Fiber Mach-Zehnder Interferometer

Temperature dependence of a refractive index sensor based on a bent core-offset in-line fiber Mach-Zehnder interferometer

A bent core-offset in-line fiber Mach-Zehnder Interferometer (MZI) as a refractive index (RI) sensor was fabricated by using a commercial fusion splicer. The temperature dependence on the so-obtained sensor was investigated. It showed that not only the RI sensitivity, but also the temperature sensitivity could be enhanced by reducing the bending radius. The variation of RI and the temperature hardly affected the sensitivity of each other within the margin of error. The wavelength-related measurement was used to realize the simultaneous measurement of RI and temperature. The highest temperature sensitivity of 0.11745 nm/°C and the highest RI sensitivity of −115.5646 nm/RIU was obtained by the sensor with a length of 30 mm, a core-offset of 6 µm, and a bending radius of 25.42 mm.

Ultra-compact in-core-parallel-written FBG and Mach-Zehnder interferometer for simultaneous measurement of strain and temperature.

An ultra-compact in-core-parallel-written fiber Bragg grating (FBG) and Mach-Zehnder interferometer (MZI) for simultaneous measurement of strain and temperature is described. The FBG and MZI are written spatially parallel in the same section of fiber core using a femtosecond laser, forming an ultra-compact device, which is different from the previously developed axial cascade of different structures. Due to the weak coupling between the FBG and the MZI, their individual extinction ratios are traded off by optimizing their writing position and separation, and extinction ratios of 5.9 dB for the FBG and 10 dB for the MZI are achieved. Experimental results show that the FBG and MZI have different sensitivities for strain and temperature, allowing this device to measure strain and temperature simultaneously. In addition, since both the FBG and MZI are written in the fiber core, this ultra-compact device is proven to be impervious to ambient humidity, making it a promising candidate for accurate industrial strain and temperature measurements.

Alkali etched fiber Mach-Zehnder interferometer with compact sensor head.

We demonstrate a scheme for fabricating compact fiber Mach-Zehnder interferometer (MZI). A section of Ge-doped fiber (GDF) is sandwiched between two single-mode fibers. The sandwich structure is side polished to make the core of GDF exposed to the surroundings. Alkali solution is utilized to etch the core of GDF. A compact fiber MZI is achieved when about half of the core is etched. Compared with the traditional ones, our scheme for fabricating fiber MZI has the characteristics of low cost, environmentally friendly, and regular transmission spectrum. This fiber MZI not only reduces the consumption of the sample, but also brings forth a good potential for micro-scale detection of refractive index.

Optical Fiber Interferometer Based on Inner Air-Cavity With an Open Channel for Gas Pressure Sensing

An optical fiber Mach-Zehnder interferometer based on an inner air-cavity with an open micro-channel structure is presented. The device is fabricated by using femtosecond laser to inscribe a cavity structure in the optical fiber core, followed by discharging the cavity area with a fusion splicer to form an inner air-cavity in the fiber core, and finally create an open micro-channel with the help of hydrofluoric acid corrosion. The fiber in-line interferometric device is miniature, robust, and stable in operation and exhibits a high pressure sensitivity of ~3351 pm/MPa, with an extremely low temperature cross-sensitivity of 2.58 kPa/°C.

Carboxymethyl Cellulose/Graphene Oxide Composite Film-Coated Humidity Sensor Based on Thin-Core Fiber Mach-Zehnder Interferometer

In this paper, a carboxymethyl cellulose (CMC)/graphene oxide (GO) composite film-coated humidity sensor was proposed based on thin-core fiber Mach-Zehnder interferometer (TCMZI). A segment of thin-core fiber (TCF) was spliced between two segments of single-mode fiber (SMF), and the TCF cladding was first corroded with hydrofluoric acid and then coated with a layer of CMC/GO film via optical driven deposition method. The relative humidity (RH) sensing characteristics of the sensor were experimentally investigated by observing the wavelength shift of resonant dips in the transmission spectrum, which showed that the CMC/GO composite film-coated TCMZI has good repeatability and stability in the measurement of humidity. A maximum average humidity sensitivity of −75.6 pm/%RH was obtained in the RH range of 35%-80%, nearly 2.048 and 3.237 times higher than that of CMC and GO single film coated ones. To the best of our knowledge, this is the first report on using the CMC/GO composite film for humidity measurement, and its excellent performance is expected to be extended to humidity sensitization of more fiber-optic sensors. The proposed sensor has the advantages of simple structure, easy fabrication, low cost, good stability and high performance, which can be applied to the fields of bio-chemical and medicine.

High-sensitivity optical fiber hydrogen sensor based on the metal organic frameworks of UiO-66-NH2.

A hydrogen sensor with high sensitivity was demonstrated by coating the metal organic frameworks of ${\rm{UiO}}\! -\! {\rm{66 \!-\! N}}{{\rm{H}}_2}$ on an optical fiber Mach-Zehnder interferometer (MZI). The MZI was made of a fiber mismatch structure by using a core-offset fusion splicing method. The effective refractive index of the ${\rm{UiO}}\! -\! {\rm{66\! -\! N}}{{\rm{H}}_2}$ film varied with the absorption and release of hydrogen, and the interference resonant dip wavelength and the intensity of the MZI changed with the variations of the concentration of hydrogen. The experimental results showed that the proposed sensor had a high hydrogen sensitivity of 8.78 dB/% in the range from 0% to 0.8%, which is almost seven times higher than the existing similar hydrogen sensor.

A MMF-TSMF-MMF Structure Coated Magnetic Fluid for Magnetic Field Measurement

An optical fiber Mach-Zehnder interferometer (MZI) coated by magnetic fluid (MF) is fabricated for magnetic field measurement. The interferometer is composed of multimode fiber-taper single mode fiber-multimode fiber (MTSM). The two MMFs play the role of a beam splitter and a coupler. The TSMF induces the generation of high-order cladding mode and enhances the re-coupling ability of the interferometer. The transmission spectrum and cladding modes with different taper waist diameter are theoretically analyzed. Interference dips are sensitive to the alteration of magnetic field intensity when the taper waist diameter of interferometer is 34 μm. The highest sensitivity is up to -0.81 nm/mT at the magnetic field range of 8-17 mT.