Fiber In-line Mach-Zehnder Interferometer Research Articles

Highly sensitive refractive index fiber inline Mach–Zehnder interferometer fabricated by femtosecond laser micromachining and chemical etching

A High sensitive refractive index (RI) sensor based on Mach–Zehnder interferometer (MZI) in a conventional single-mode optical fiber is proposed, which is fabricated by femtosecond laser transversal-scanning inscription method and chemical etching. A rectangular cavity structure is formed in part of fiber core and cladding interface. The MZI sensor shows excellent refractive index sensitivity and linearity, which exhibits an extremely high RI sensitivity of −17197nm/RIU (refractive index unit) with the linearity of 0.9996 within the refractive index range of 1.3371–1.3407. The experimental results are consistent with theoretical analysis.

Miniature and robust optical fiber in-line Mach-Zehnder interferometer based on a hollow ellipsoid.

An optical fiber in-line Mach-Zehnder interferometer based on a hollow ellipsoid fabricated by femtosecond laser micromachining and fusion-splicing technique is demonstrated. The surface of the hollow ellipsoid acts as an internal mirror that can be utilized for the construction of an interferometer. Such an interferometer device is miniature and robust and can perform external refractive index, curvature, and high-temperature sensing in a mutually independent way, and hence a simultaneous multiple parameter measurement capability can be readily achieved.

Fiber in-line Mach-Zehnder interferometer based on an inner air-cavity for high-pressure sensing.

We demonstrate a fiber in-line Mach-Zehnder interferometer based on an inner air-cavity with open micro-channel for high-pressure sensing applications. The inner air-cavity is fabricated by combining femtosecond laser micromachining and the fusion splicing technique. The micro-channel is drilled on the top of the inner air-cavity to allow the high-pressure gas to flow in. The fiber in-line device is miniature, robust, and stable in operation and exhibits a high pressure sensitivity of ∼8,239 pm/MPa.

Strain Sensor Based on Fiber Ring Cavity Laser With Photonic Crystal Fiber In-Line Mach–Zehnder Interferometer

We experimentally demonstrated a strain sensor based on fiber ring cavity laser with a photonic crystal fiber (PCF) in-line Mach-Zehnder interferometer (MZI) structure, which is used as an optical band-pass filter and acts as the strain sensing component. The fiber ring cavity laser plays the role of enhancing the visibility of the resonant spectrum and narrowing the corresponding 3-dB bandwidth, thus improving the comprehensive sensing performance. The induced axial strain on the structure is measured by monitoring the central wavelengths of the laser output. A high strain sensing sensitivity of 2.1 pm/με is successfully achieved in the linear strain range of 0-2100 με. A parameter Q value describing the overall sensing performance is introduced by including the strain sensing sensitivity, sensing sensitivity relative to 3-dB bandwidth of the resonant spectrum and the corresponding visibility. Comparing with the reported strain measurements based on a PCF in-line MZI structure, the experimental results based on fiber ring cavity laser sensor present more than nine times larger Q value.

Ultracompact Optical Fiber Sensor for Refractive Index and High-Temperature Measurement

An ultracompact microfiber sensor head is demonstrated for refractive index and high temperature sensing. Such a device is a fiber in-line Mach-Zehnder interferometer formed by creating an inner air-cavity along a section of microfiber and exhibits a high refractive index sensitivity of ~4202 nm/refractive index unit and a good temperature sensitivity of 41 pm/°C, with excellent high-temperature sustainability up to 1100 °C.

Intensity-Modulated Strain Sensor Based on Fiber In-Line Mach–Zehnder Interferometer

We demonstrated a novel intensity-modulated strain sensor based on a fiber in-line Mach-Zehnder interferometer with a large fringe visibility of up to 17 dB, which was fabricated by splicing a section of thin core fiber between two sections of single mode fibers with one misalignment-spliced joint. Such a strain sensor exhibited an ultrahigh sensitivity of -0.023 dBm/μe within a measurement range of 500 μe, which is about one order of magnitude higher than that reported in references. Displacement and stress distributions at the misalignment spliced joint were simulated by use of finite element method. In addition, the proposed strain sensor has an advantage of compact size of ~10 mm.

Simultaneous measurement of strain and temperature by employing fiber Mach-Zehnder interferometer

We demonstrated a novel fiber in-line Mach-Zehnder interferometer (MZI) with a large fringe visibility of up to 17 dB, which was fabricated by misaligned splicing a short section of thin core fiber between two sections of standard single-mode fiber. Such a MZI could be used to realize simultaneous measurement of tensile strain and temperature. Tensile strain was measured with an ultrahigh sensitivity of -0.023 dB/μɛ via the intensity modulation of interference fringes, and temperature was measured with a high sensitivity of 51 pm/°C via the wavelength modulation of interference fringe. That is, the MZI-based sensor overcomes the cross-sensitivity problem between tensile strain and temperature by means of different demodulation methods. Moreover, this proposed sensor exhibits the advantages of low-cost, extremely simple structure, compact size (only about 10 mm), and good repeatability.

Fiber in-line Mach–Zehnder interferometer based on near-elliptical core photonic crystal fiber for temperature and strain sensing

A fiber in-line Mach-Zehnder interferometer is fabricated by selectively filling liquid into one air hole of the innermost layer of a photonic crystal fiber (PCF). The refractive index of the liquid is so close to that of the background silica in the wavelength range of 1300-1600 nm that the two-mode PCF evolves into multimode PCF with an elliptically shaped core. Due to the different propagation constants, interference can occur between the fundamental mode and higher-order modes of the liquid-filled PCF. Such a device is applied in temperature and strain measurements with high sensitivities of 16.49 nm/°C and -14.595 nm/N, respectively.

Optical fiber in-line Mach–Zehnder interferometer based on dual internal mirrors formed by a hollow sphere pair

We demonstrate a fiber in-line Mach-Zehnder interferometer based on dual internal mirrors formed by a hollow sphere pair and fabricated by femtosecond laser micromachining together with the fusion splicing technique. The hollow sphere surface adjacent to the fiber core can reflect part of the incident light beam to the air-cladding interface, where the light beam is reflected again before returning to the fiber core by another hollow sphere surface and recombining with the light beam remaining in the fiber core. Such an interferometer is miniature and robust, and is sensitive to environmental variations and allows simultaneous surrounding refractive index, temperature, and curvature measurement.

A strain sensor based on in-line fiber Mach–Zehnder interferometer in twin-core photonic crystal fiber

We experimentally demonstrate a strain sensor realized using a twin-core photonic crystal fiber (PCF). The strain sensor element consists of a 10cm long in-fiber Mach–Zehnder interferometer consisting of twin-core PCF. The output spectra of the sensing element is measured and analyzed under various strain levels. The sensitivity of the strain measurement of −0.31pm/µε is achieved within a range from 0 to 4000µε. The effect of temperature is also analyzed.

Microfiber in-line Mach–Zehnder interferometer for strain sensing

An elegant way of achieving an ultracompact optical fiber in-line Mach-Zehnder interferometer is to create an inner air cavity in a section of microfiber. The sandwich structure splits the light propagating in the fiber into two beams: one passes through the inner air cavity and the other travels along the silica wall of the cavity before recombining at the cavity end, resulting in an interference fringe pattern. Such a device is applied for strain measurement with a high sensitivity of 6.8 pm/με.

Miniaturized fiber in-line Mach–Zehnder interferometer based on inner air cavity for high-temperature sensing

We demonstrate a miniaturized fiber in-line Mach-Zehnder interferometer based on an inner air cavity adjacent to the fiber core for high-temperature sensing. The inner air cavity is fabricated by femtosecond laser micromachining and the fusion splicing technique. Such a device is robust and insensitive to ambient refractive index change, and has high temperature sensitivity of ∼43.2 pm/°C, up to 1000°C, and low cross sensitivity to strain.

Optical fiber strain and temperature sensor based on an in-line Mach–Zehnder interferometer using thin-core fiber

We propose and demonstrate a fiber in-line Mach–Zehnder interferometer using thin-core fibers. This in-line interferometer is composed of a short section of thin-core fiber inserted between two single mode fibers (SMF), and demonstrated as a strain and temperature sensor in this study. A strain sensitivity of −1.83pm/με with a measurement range of 0−2000με, and the temperature sensitivity of −72.89pm/°C with a temperature variation of 50°C are achieved. We also discussed that the influence of strain and temperature change on the relative power ratios among the excited cladding modes in thin-core fibers.

In-line fiber Mach–Zehnder interferometer for simultaneous measurement of refractive index and temperature based on thinned fiber

In this letter, we propose and demonstrate a novel and simple method for simultaneous measurement of refractive index and temperature using all-fiber in-line single-mode-multimode-thinned-single-mode (SMTS) fiber structures based on a small core and cladding diameters thinned fiber Mach–Zehnder interferometer (MZI). The principle of operation relies on the strong effect of the core and cladding mode interference of the thinned fiber through the employing of a multimode fiber. By measuring the shifts of the attenuation peak wavelengths of the two arbitrarily selected interference orders in the transmission spectrum, we can simultaneously measure the refractive index and temperature surrounding the sensor. Results indicate that the selected two interference orders have sensitivities of −2.85×10−3RIU with 3.49×10−1°C, and −1.12×10−3RIU with 4.07×10−1°C respectively at RI range from 1.3325 to 1.3715 and temperature range from 24°C to 84°C. The fabrication is easy, safe and cost effective, and includes only the fusion splicing, making the device properly attractive for physical, biological and chemical sensing in practical applications.

Femtosecond laser fabricated all-optical fiber sensors with ultrahigh refractive index sensitivity: modeling and experiment

All-optical fiber sensors based on ultracompact fiber inline Mach-Zehnder interferometer (MZI) are fabricated by side-ablating a U-shape microcavity in a single-mode optical fiber with the fiber core partially removed using femtosecond (fs) laser pulses, in which the two light paths are accordingly formed in the remaining D-type fiber core and the U-shape microcavity. Beam propagation method (BPM) analysis is utilized to illustrate the dependences of good transmission spectra on parameters including the ablation depth, ablation length and the refractive index of U-shape micocavity, which gives some guidelines to optimize parameters for fs laser micromachining and predicts RI (refractive index) sensitivities within given RI ranges. The modeling results of ultrahigh RI sensitivities for gases and solutions are -3243.75 ± 0.65nm/RIU (refractive index unit) and -10789.29 ± 18.91nm/RIU, respectively. In RI testing experiments, the sensor exhibits ultrahigh RI sensitivities of -3754.79 ± 44.24nm/RIU with refractive indices ranging from 1.0001143 to 1.0002187 by testing different mixture ratios of N2 and He gases, and -12162.01 ± 173.92nm/RIU with refractive indices ranging from 1.3330 to 1.33801 by testing different concentrations of sucrose solutions, which is essentially in agreement with the modeling results.

Ultra-Abrupt Tapered Fiber Mach-Zehnder Interferometer Sensors

A fiber inline Mach-Zehnder interferometer (MZI) consisting of ultra-abrupt fiber tapers was fabricated through a new fusion-splicing method. By fusion-splicing, the taper diameter-length ratio is around 1:1, which is much greater than those (1:10) made by stretching. The proposed fabrication method is very low cost, 1/20–1/50 of those of LPFG pair MZI sensors. The fabricated MZIs are applied to measure refractive index, temperature and rotation angle changes. The temperature sensitivity of the MZI at a length of 30 mm is 0.061 nm/°C from 30–350 °C. The proposed MZI is also used to measure rotation angles ranging from 0° to 0.55°; the sensitivity is 54.98 nm/°. The refractive index sensitivity is improved by 3–5 fold by fabricating an inline micro–trench on the fiber cladding using a femtosecond laser. Acetone vapor of 50 ppm in N2 is tested by the MZI sensor coated with MFI–type zeolite thin film. The proposed MZI sensors are capable of in situ detection in many areas of interest such as environmental management, industrial process control, and public health.

Fiber in-line Mach–Zehnder interferometer constructed by selective infiltration of two air holes in photonic crystal fiber

A fiber in-line Mach-Zehnder interferometer is fabricated through selective infiltrating of two adjacent air holes of the innermost layer in the solid core photonic crystal fiber, assisted by femtosecond laser micromachining. The liquid infiltrated has higher refractive index than that of the background silica, and, hence, the two rods created can support a guide mode with lower effective refractive index than that of silica. The interference is produced by the fiber fundamental mode and the guide mode. The free spectral range (FSR) of the interferometer is found to be dependent on the photonic crystal fiber length, and a large FSR corresponds to a short photonic crystal fiber length. Such an interferometer device is robust and exhibits extremely high temperature sensitivity (∼7.3 nm/°C for the photonic crystal fiber length of 3.4 cm) and flexible operation capability.

Fiber in-line Mach-Zehnder interferometer fabricated by femtosecond laser micromachining for refractive index measurement with high sensitivity

We report a compact fiber in-line Mach-Zehnder interferometer for refractive index sensing with high sensitivity and precise sensing location. One arm of the interferometer contains a microcavity formed by removing part of the fiber core near the core and cladding interface by femtosecond laser micromachining, and the other arm remains in line with the remaining part of the fiber core. Such a fiber in-line Mach-Zehnder interferometer exhibits an extremely high refractive-index-sensitivity of −9370 nm/RIU (refractive index unit) within the refractive index range between 1.31 and 1.335.

Highly sensitive strain and bending sensor based on in-line fiber Mach–Zehnder interferometer in solid core large mode area photonic crystal fiber

We have proposed highly sensitive strain and bending sensor with very low temperature sensitivity based on in-line Mach–Zehnder interferometer (MZI) in solid core large mode area photonic crystal fiber (PCF) and experimentally investigated its novel characteristics. The measured strain and bending sensitivities were −3 pm/με and 36 nm/m −1, respectively. The proposed PCF–MZI shows negligible temperature sensitivity of ∼4.6 pm/°C over the wide temperature range from 25 to 325 °C, eliminating the effect of temperature in optical sensing applications. Furthermore, as the fabrication process of the proposed device does not require photo-inscription or complicate fabrication methods, the proposed device is cost effective and has a great potential to be applied in optical sensing systems.

High-Temperature Sensing Using Miniaturized Fiber In-Line Mach–Zehnder Interferometer

A miniaturized single fiber in-line Mach-Zehnder interferometer is proposed for high-temperature sensing. The interferometer has a microcavity in one of its arms, formed by removing part of the fiber core and cladding, while the other arm remains in the fiber core. Because the fiber core exhibits a temperature coefficient of refractive index which is different from that of air, the interferometer is sensitive to temperature variation. The microcavity structured interferometer also has excellent sustainability to high temperatures up to 1100°C . The system is compact, reliable and can detect the temperature at precise location.