In-line Mach-Zehnder Interferometer Research Articles

Femtosecond laser inscribed straight waveguide in no-core fiber for in-line Mach-Zehnder interferometer construction.

A new fiber in-line Mach-Zehnder interferometer based on a straight waveguide along the central axis of the no-core fiber sandwiched between single mode fibers is fabricated by a femtosecond laser. The device can be used for high temperature sensing with a sensitivity of -278.86 pm/°C and for bending sensing with a sensitivity of 0.28 nm/m-1. The high mechanical strength, simple fabrication, and precisely controlled free spectral range make the device attractive for potential applications in high temperature monitoring.

Multi-channel optical fiber refractometer based on tree topology structure.

A multi-channel optical fiber refractometer based on S fiber taper (SFT) cascaded with fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The compact SFT acts as an in-line Mach-Zehnder interferometer (MZI) to be used as a band-pass filter (BPF) to tailor the FBG reflection, whose transmission spectrum is sensitive to the surrounding refractive index (SRI). Thus, the peak power of the FBG reflection is modulated by the SRI. The three-channel SRI monitor can be achieved by discriminating the different center wavelength and peak power variation of the FBG reflections. Experimental results show that the RI sensitivities of Channels 1, 2, and 3 are 345.54, 349.57, and 463.60dB/RIU, respectively. Moreover, the temperature cross-sensitivity can be solved by interrogating the center wavelength of the FBG reflection.

Intensity-modulated directional torsion sensor based on in-line optical fiber Mach-Zehnder interferometer.

In this Letter, we demonstrated an intensity-modulated directional torsion sensor based on an in-line Mach-Zehnder interferometer in single-mode fiber. A non-circular symmetric perturbation is created to excite non-circular symmetric cladding mode and then interference with the core mode at the second perturbation. An initial rotation angle is designed between two perturbations for the purpose of discriminating the torsion direction. Both experimental and theoretical results enforce that the spectral peak/dip turns to be the dip/peak when the fiber is twisted from the counter-clockwise to the clockwise direction. Benefiting from the reversal between peak and dip, an intensity-modulated directional torsion sensor is realized in the range from -50 rad/m to 50rad/m with a sensitivity of 45.3%/(rad/cm).

Single Step Process for Optical Microfiber In-Line Mach-Zehnder Interferometers Fabrication

Based on a novel modulated arc-discharge technique, a single step process for taper-functionalized optical microfiber in-line Mach-Zehnder interferometers (MZIs) fabrication is presented. By this process, microfiber and its added down-tapers are fabricated exploiting an amplitude modulated arc-discharge heating in one-step. In this letter, included short-time arc OFF switches during an arc-assisted microfiber fabrication process result in the formation of miniature down-tapers along the microfiber being pulled. The arrangement and time duration of these arc OFF pulses determine the functionality of the resultant microfiber structure. The first single step taper-functionalized microfiber in-line MZI exhibits an extremely high interference dip (~29 dB) with low full width at half maximum (~5 nm) and high external refractive index (RI) sensitivity of 1840 nm per RI unit around 1.368.

Fiber in-line Mach-Zehnder interferometer based on a pair of short sections of waveguide.

A fiber in-line Mach-Zehnder interferometer based on a pair of femtosecond laser inscribed short sections of waveguide is presented. One short waveguide directs part of the propagating light from the fiber core to the cladding-air interface, and experiences multiple total internal reflections before taking back to the fiber core by the other short waveguide. The device is robust in structure, can be fabricated in a fast way and with a flexible manner, and has the capability of ambient refractive index sensing, which makes it highly desirable for many "lab-in-fiber" applications.

Switchable multi-wavelength erbium-doped fiber ring laser based on a tapered in-line Mach–Zehnder interferometer

In this paper, a switchable multi-wavelength erbium-doped fiber ring laser based on a tapered in-line Mach–Zehnder interferometer is proposed. The in-line Mach–Zehnder interferometer is fabricated by splicing a large-core fiber between two segments of single mode fibers, in which the first splicing point is tapered and the second splicing point is connected directly. By carefully rotating the polarization controller, switchable single-, dual-, triple- and quad-wavelength lasing outputs can be obtained with a side mode suppression ratio higher than 50 dB. The maximal peak power difference of multi-wavelength lasing is 3.67 dB, demonstrating a good power equalization performance. Furthermore, the proposed laser is proven to be very stable at room temperature. The wavelength shifts and peak power fluctuations are less than 0.02 nm and 1.3 dB over half an hour. In addition, stable quintuple-wavelength lasing with a side mode suppression ratio higher than 50 dB can also be realized when the filter length is changed.

Design and fabrication of a heterostructured cladding solid-core photonic bandgap fiber for construction of Mach-Zehnder interferometer and high sensitive curvature sensor.

A heterostructured cladding solid-core photonic bandgap fiber (HCSC-PBGF) is designed and fabricated which supports strong core mode and cladding mode transmission in a wide bandgap. An in-line Mach-Zehnder interferometer (MZI) curvature sensor is constructed by splicing single mode fibers at both ends of a HCSC-PBGF. Theoretical analysis of this heterostructured cladding design has been implemented, and the simulation results are consistent with experiment results. Benefiting from the heterostructured cladding design, an enhanced curvature sensing sensitivity of 24.3 nm/m-1 in the range of 0-1.75 m-1 and a high quality interference spectrum with 20 dB fringe visibility are achieved. In order to eliminate the interference of longitudinal strain and transverse torsion on the result of the curvature sensing experiment, we measure the longitudinal strain and transverse torsion sensing properties of HCSC-PBGF, and the results show that the impact is negligible. It is obvious that this high-sensitivity and cost-effective all fiber sensor with a compact structure will have a promising application in fiber sensing.

Fiber optic refractive index and magnetic field sensors based on microhole-induced inline Mach–Zehnder interferometers

A compact microhole-induced fiber optic inline Mach–Zehnder interferometer (MZI) is demonstrated for measurements of refractive index (RI) and magnetic field. Inline MZIs with different etched diameters, different interaction lengths and different sizes of microholes are fabricated and assessed. The optical transmission spectra of the inline MZIs immersed into a series of liquids are characterized and analysed. Experimental results show that liquid RI sensitivity as high as 539.8436 nm RIU−1 in the RI range of 1.3352–1.4113 RIU is achieved and also exhibits good linearity with a correlation coefficient >93%. An inline MZI is also fabricated to be a magnetic field sensor by using magnetic fluid material. The experimental results show that this magnetic field sensor has a high sensitivity of −275.6 pm Oe−1. The inline MZI-based fiber optic sensors possess many advantages, such as small size, simple fabrication, high sensitivity and good linearity, which has a wide application potential in chemical, biological and environmental sensing fields.

Research on dual-parameter optical fiber sensor based on thin-core fiber and spherical structure

A novel dual-parameter optical fiber sensor is proposed and experimentally demonstrated. The proposed sensor is based on a fiber in-line Mach–Zehnder interferometer, which is fabricated by sandwiching a section of thin-core fiber between two spherical structures made of single-mode fibers. The transmission spectrum exhibits the response of the interference between the core and the different cladding modes. Due to the different wavelength shifts of the two selected dips, the simultaneous measurement of temperature and the surrounding refractive index can be achieved. The measured temperature sensitivities are 0.067 nm/°C and 0.050 nm/°C, and the refractive index sensitivities are −119.9 nm/RIU and −69.71 nm/RIU, respectively. In addition, the compact size, simple fabrication and cost-effectiveness of the fiber sensor are also advantages.

INVITED] Sensing properties of micro-cavity in-line Mach-Zehnder interferometer enhanced by reactive ion etching

In this work, we discuss an application of reactive ion etching (RIE) for enhancing the sensing properties of a micro-cavity in-line Mach-Zehnder interferometer (µIMZI). The µIMZI was fabricated using femtosecond laser micromachining in a standard single-mode fiber as a circular hole with a diameter of 54 µm. Next, the structures underwent two kinds of RIE using as reactive gases: sulfur hexafluoride (SF6) and oxygen (O2) mixtures (SF6/O2) or O2 itself. When RIE with SF6/O2 was applied, it allowed for an efficient and well-controlled etching of the fabricated structure at nanometers level observed as an increase in spectral depths of the minima in the µIMZI transmission spectrum. A similar RIE process with O2 alone was ineffective. The well-defined minima obtained with the SF6/O2 RIE significantly improved the resolution of measurements made with the µIMZI. The effect was demonstrated for high-resolution refractive index (RI) measurements of liquids in the cavity. The result of the RIE process was to clean the micro-cavity bottom, increase its depth, and smooth its sidewalls. As an additional effect, the wettability of the micro-cavity surface was improved, making the RI measurements faster and more repeatable. Moreover, we demonstrated that RIE with SF6/O2 results in more stable wettability improvement than when O2 is applied as a reactive gas.

Fiber inline Mach-Zehnder interferometer based on femtosecond laser inscribed waveguides.

A new type of Mach-Zehnder interferometer device based on in-fiber optical waveguides, fabricated by direct femtosecond laser pulse inscription in a single-mode fiber has been demonstrated and successfully employed for temperature and strain measurement. The in-fiber waveguide can couple the light out from the fiber core and guide it along the cladding region before directing it back into the fiber core. Such an inner structured interferometer device is compact and robust, can be constructed in a flexible and precisely controlled manner, and hence is expected to have many potential applications.

Sensitivity amplification of fiber-optic in-line Mach-Zehnder Interferometer sensors with modified Vernier-effect.

In this paper, a novel sensitivity amplification method for fiber-optic in-line Mach-Zehnder interferometer (MZI) sensors has been proposed and demonstrated. The sensitivity magnification is achieved through a modified Vernier-effect. Two cascaded in-line MZIs based on offset splicing of single mode fiber (SMF) have been used to verify the effect of sensitivity amplification. Vernier-effect is generated due to the small free spectral range (FSR) difference between the cascaded in-line MZIs. Frequency component corresponding to the envelope of the superimposed spectrum is extracted to take Inverse Fast Fourier Transform (IFFT). Thus we can obtain the envelope precisely from the messy superimposed spectrum. Experimental results show that a maximum sensitivity amplification factor of nearly 9 is realized. The proposed sensitivity amplification method is universal for the vast majority of in-line MZIs.

Transition between bulk and surface refractive index sensitivity of micro-cavity in-line Mach-Zehnder interferometer induced by thin film deposition.

In this work we discuss the refractive index (RI) sensitivity of a micro-cavity in-line Mach-Zehnder interferometer in the form of a cylindrical hole (40-50 μm in diameter) fabricated in a standard single-mode optical fiber using a femtosecond laser. The surface of the micro-cavity was coated with up to 400 nm aluminum oxide thin film using the atomic layer deposition method. Next, the film was progressively chemically etched and the influence on changes in the RI of liquid in the micro-cavity was determined at different stages of the experiment, i.e., at different thicknesses of the film. An effect of transition between sensitivity to the film thickness (surface) and the RI of liquid in the cavity (bulk) is demonstrated for the first time. We have found that depending on the interferometer working conditions determined by thin film properties, the device can be used for investigation of phenomena taking place at the surface, such as in case of specific label-free biosensing applications, or for small-volume RI analysis as required in analytical chemistry.

Single hole twin eccentric core fiber sensor based on anti-resonant effect combined with inline Mach-Zehnder interferometer

A novel fiber curvature sensor without temperature cross interference based on a single hole twin eccentric core fiber has been proposed. Anti-resonant mechanism combined with inline Mach-Zehnder interference (MZI) structure are applied to the measurands detection. The spectrum is composed of a comb spectrum caused by the inline MZI and several dominant resonant wavelengths induced by anti-resonant effect. The curvature sensitivity of -1.54dB/m-1 can be achieved by intensity demodulation of the selected dip of Gaussian fitting. Similarly, the temperature sensitivity of 70.71pm/°C and 34.17pm/°C are respectively achieved by tracking coherent decrease point obtained by the FFT band pass filter method and Gaussian fit dip. Consequently, a relatively higher resolution of temperature measurement can be realized by the two methods mentioned above. The proposed sensor has a great potential for structural health monitoring, such as buildings, towers, bridges, and many other infrastructures due to its compact structure, easy fabrication and without cross impacts.

Incoherent optical modulation of graphene based on an in-line fiber Mach-Zehnder interferometer.

We investigated the incoherent optical modulation of graphene based on an in-line fiber Mach-Zehnder interferometer fabricated by offset splicing of a D-shaped fiber and single-mode fibers. The D-shaped flat surface was coated with a single-layer graphene whose refractive index can be modulated by an external laser. With a backward pump-probe setup, we found that the incoherent optical modulation occurred independently of the wavelength difference between the pump and probe lasers, supporting the theoretical analysis that the incoherent optical modulation is mainly contributed by the carrier-phonon process of graphene. Further, both the decrease of the pump wavelength and the increase of the pump power would deepen the modulation in an exponential trend. The experimental results are beneficial to understanding the incoherent optical modulation process in graphene. The proposed interferometer covered by graphene can also be used as a compact all-optical intensity modulator.

High-quality Mach-Zehnder interferometer based on a microcavity in single-multi-single mode fiber structure for refractive index sensing.

A fiber inline Mach-Zehnder interferometer (MZI) based on a microcavity with two symmetric openings in single-multi-single mode fiber (SMSF) structure is proposed. By using the finite difference beam propagation method (FD-BPM), the interference spectrum simulation result shows that the MZI can still have high-quality interference even if the microcavity deviates along the radial direction for 3 μm. Therefore, it allows a larger fabrication tolerance and tremendously decreases the fabrication difficulty. Then a microcavity with two symmetric openings in SMSF was fabricated by using femtosecond laser-induced water breakdown. The insertion loss of the microcavity immerged in water is only -8 dB, and the MZ interference peak contrast in the transmission spectrum reaches more than 30 dB. The MZI based on the microcavity in SMSF can be used as a practical liquid refractive index sensor as its high-quality interference spectrum, ultrahigh sensitivity (9756.75 nm/RIU), high refractive index resolution (2×10-5 RIU), good linearity (99.93%), and low-temperature crosstalk (0.04 nm/°C).

In-Line Mach–Zehnder Interferometric Sensor Based on a Seven-Core Optical Fiber

An in-line Mach–Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The sensor is fabricated by splicing a segment of seven-core fiber (SCF) and two segments of very short multi-mode fibers (MMFs). The mode field of the MMF used in our experiments close to the region of hexagonally distributed fiber cores of the SCF, which help to obtain a higher coupling efficiency. A clear interference spectrum of the proposed MZI is obtained by injecting a broadband light into a lead-in single-mode fiber. Such an MZI could be used to realize the measurement of temperature and curvature. The temperature and curvature sensitivities are 55.81 pm/°C and 31.54 nm/ $\text{m}^{-1}$ , respectively.

Envelope-based technique for liquid level sensors using an in-line fiber Mach-Zehnder interferometer.

This paper proposes a sensor interrogation technique based on the analysis of the overall spectrum envelope of an in-line Mach-Zehnder interferometer structure with three different fibers. The interference pattern created by a level sensor of 120 mm was evaluated with both the traditional and the proposed interrogation techniques. The result shows that the technique here proposed improves the sensitivity of the sensor by more than an order of magnitude. Moreover, our new interrogation technique allows the length of an in-line Mach-Zehnder interferometer to be extended up to 470 mm while maintaining high linearity and sensitivity.

Twist and temperature characteristics of the PD-NSN fiber structure based on in-line Mach-Zehnder interferometer

Abstract A novel polarization-dependent (PD) no core-single mode-no core (NSN) fiber structure for twist and temperature sensing has been experimentally investigated. The proposed structure simply involves a section of polarization maintain fiber sandwiched into NSN fiber structure, only using the splicing method. We have analyzed and demonstrated the transmission characteristics of the no core fiber (NCF) with the different lengths. Experimental results indicate that the extinction ratio of the PD-NSN fiber structure comb spectrum based on Mach-Zehnder interferometer (MZI) various with twist rate. The maximum sensitivity of 0.33904 dB/(rad/m) for range from −240° to 360° is achieved. The temperature sensitivity of the proposed structure reaches 41.89 pm/°C for temperature ranging from 20 to 70 °C in the experiment. By using the peak-wavelength discrimination method, the proposed sensor can overcome the temperature and twist cross-sensitivity effects.

Tunable fiber laser based on a cascaded structure consisting of in-line MZI and traditional MZI

A tunable erbium-doped fiber (EDF) laser with a cascaded structure consisting of in-line Mach-Zehnder interferometer (MZI) and traditional MZI is proposed. The transmission spectrum of the in-line MZI is modulated by the traditional MZI, which determines the period of the cascaded structure, while the in-line MZI’s transmission spectrum is the outer envelope curve of the cascaded structure’s transmission spectrum. A stable single-wavelength lasing operation is obtained at 1 527.14 nm. The linewidth is less than 0.07 nm with a side-mode suppression ratio (SMSR) over 48 dB. Fixing the in-line MZI structure on a furnace, when the temperature changes from 30 °C to 230 °C, the central wavelength can be tuned within the range of 12.4 nm.