In-fiber Michelson Interferometer Research Articles

In-fiber Michelson interferometric sensor fabricated by single CO2 laser pulse.

An in-fiber Michelson interferometric sensor was presented by fabricating a concavity on the end face of a single mode fiber using a single CO2 laser pulse. Reflected beams from the bottom and air-cladding boundary of the concavity are coupled into the fiber core and superimpose to generate a two-beam in-fiber Michelson interferometer. Compared with other laser-machining methods where multiple scanning cycles with precise manipulation are needed, the proposed method is more straightforward because only a single laser pulse is used to construct the sensor. The concavity constructed by the CO2 laser is very smooth, and its shape could be controlled flexibly by changing the position of the single mode fiber and the parameters of the CO2 laser pulse, so the fringe visibilities of the proposed sensors could be more than 15 dB, which is higher than that of the most reported laser-machining in-fiber Michelson interferometers. The proposed sensor was demonstrated by measuring the temperature with a sensitivity of 11.13 pm/°C. Furthermore, the proposed device is compact (<100 µm), economical, and robust. These advantages make it a promising candidate in practical applications.

Orientation-dependent fiber-optic inclinometer based on core-offset michelson interferometer

An in-fiber Michelson interferometer (MI)-based inclinometer, which consists of misalignment-spliced fiber with end coating, is proposed and experimentally demonstrated. The incident light divided at the misalignment-spliced joint is reflected at the end coating, and then re-coupled into the fiber core. Due to the phase difference between the core mode and the m{text{th}} cladding mode, a typical MI is formed. The fiber near the misalignment-spliced joint is inserted in two capillary quartz tubes. The tilt of the capillary quartz tube leads to a significant deformation and curvature of the misalignment-spliced joint, which causes the wavelength and intensity of the MI spectrum to change. The experimental results indicate a good response within the angle range of 0°–50°. Both the wavelength modulation and intensity modulation are realized, with sensitivities of 0.55 nm/deg and 0.17 dB/deg, respectively. Moreover, the sensor shows a strong orientation dependence due to the asymmetric structure in the misalignment-spliced joint.

A High-Sensitivity Low-Temperature Sensor Based on Michelson Interferometer in Seven-Core Fiber

An in-fiber Michelson interferometer (MI) formed by seven-core fiber (SCF) for low-temperature sensing is proposed and experimentally demonstrated. The sensor head is constructed by a section of seven-core fiber splicing a single-mode fiber (SMF) with a taper. When the external temperature changes, the interference spectrum of the MI will shift due to thermal expansion and thermo-optic effects. By measuring the wavelength variations of the interference dip, the external temperature can be determined. Experimental results proves that the sensor exhibits a maximum linear temperature sensitivity of −0.0775 nm/°C in the temperature range of −60 °C to 15 °C, and the standard deviation is 5% in stability test. The sensor possesses high sensitivity and easy fabrication, which makes it could be a good candidate in low-temperature sensing application.

An Intensity-Modulated In-Fiber Liquid Lever Sensor Based on Intermodal Michelson Interferssometer

A compact in-fiber Michelson interferometer (MI) for liquid level measurement is proposed and demonstrated. The interferometer is fabricated by simply splicing a section of multimode fiber (MMF) with a standard singlemode fiber (SMF). The reflection spectrum of the MI is dependent on the portion of the length of the MMF which is immersed in liquid. The sensing characteristics of the liquid level and temperature are theoretically and experimentally investigated. The experimental results show that the liquid level sensitivity is −1.20 dB/mm when the liquid is water, and the liquid level measurement error induced by temperature is 0.004 mm/°C. The advantages of temperature-immune, cost-effective and reflective intensity demodulation offer the prospective application in chemical and petroleum industrial sensing.

Dynamic bending and rotation sensing based on high coherence interferometry in multicore fiber

Bending and rotation sensing based on high coherence interferometry in seven-core fiber (SCF) is proposed here for the first time. In the suggested scheme, distinct optical paths are formed from the selected cores, thus creating a very compact in-fiber Michelson interferometer. The interferometer consists of an in-line taper structure fabricated on the SCF for a light splitting/coupling element, and a Faraday rotating mirror used as a reflective element. Different strains are exerted on the reference and sensing cores because of the dissimilar distance from the neutral axis. The phase difference between these two interferometer arms resulting from the variations in strain is resolved using a fringe counting technique. The proposed sensor is revealed to be extremely sensitive for curvature and rotation measurement, with sensitivities of 629fringe/m−1 and 6.2fringe/°, respectively. The sensor is capable of detecting the smallest curvature of 0.0032 m−1 or radius of 312 m. The sensor also responds linearly to rotation, with a sensitivity of 6.2fringe/°. This response is highly repeatable; linear; insensitive to slow-varying parameters, such as temperature; and promising for the detection of direction. The proposed sensor is particularly attractive for robotics, wearable medical devices, and structural health-monitoring applications.

Large core-offset based in-fiber Michelson interferometer for humidity sensing

A humidity sensor based on Michelson interferometer (MI) is proposed and demonstrated. The sensor achieves intermodal interference by a large core-offset between two single mode fibers (SMFs) through arc fusion splicing. Experimental results show the sensor with a length of 25 mm and core-offset of 50 μm exhibits a linear humidity sensitivity of −0.083 dB/%RH in the humidity range of 35–95 %RH, which is comparable to that of intensity-modulated humidity sensors with coating humidity sensitive materials. The temperature response and stability is also investigated, a linear temperature sensitivity of 9.5 pm/°C in the temperature range of 20–180 °C is obtained. The low manufacturing cost, easy fabrication and good stability make the sensor has great potential in many applications.

A liquid refractive index sensor based on 3-core fiber Michelson interferometer

A liquid refractive index (RI) sensor based on in-fiber Michelson interferometer (MI) is proposed and experimentally demonstrated, which consists of a segment of 3-core fiber (3CF) fusion spliced with a short piece of multimode fiber (MMF). The operation principle of the MI lies in the intermodal interference of the 3CF via employing MMF to excite high-order modes, and the 3CF end face reflects the interference spectrum which loaded the surrounding RI information. By measuring the reflection spectrum variation, the RI can be determined. Experimentally, a linearly RI sensitivity of -151.56 dB/RIU is achieved in the sensing range of 1.3335-1.3720 RIU, and the temperature sensitivity in water is 0.048 nm/°C.

High stability Michelson refractometer based on an in-fiber interferometer followed with a Faraday rotator mirror

We demonstrated an optical fiber refractive index (RI) sensor based on an in-fiber Michelson interferometer (MI), which is fabricated by splicing a Faraday rotator mirror (FRM) to a singlemode-thin core-singlemode (STS) optical fiber interferometer. From our experiments, it can be found that thus a FRM as reflector can eliminate the polarization random fluctuation of interference spectrum, which makes the sensor exhibit a high stability. Core to core splicing of thin core to standard single mode optical fibers and high reflectivity mirror of FRM can reduce the optical power loss and improve the fringe contrast of sensor spectrum. Both high stability and low power loss are very important in such kinds of reflection interference spectrum modulation and high resolution sensors. This sensor wavelength and intensity RI sensitivity is −48.858nm/RIU and −6.548dB/RIU at the liquid RI from 1.38 to 1.435, respectively. The temperature sensing performance of this sensor is also studied, the sensor wavelength versus temperature sensitivity is 66.18pm/ °C and intensity hardly change with temperature, which means that the temperature cross sensitivity can be eliminated when intensity modulated, and this sensor also has compact size, simple structure, easy fabrication and good repeatability.

Continuous liquid level sensor based on a reflective long period fiber grating interferometer

A continuous liquid level sensor (LLS) based on an in-fiber Michelson interferometer is proposed and experimentally demonstrated. The in-fiber Michelson interferometer is formed by a single long period grating (LPG) together with a reflective mirror at the end of the fiber. The portion between the mirror and LPG is immersed in the liquid to be measured as an LLS sensing probe, and the liquid level can be measured by monitoring the wavelength of interference fringes of the in-fiber Michelson interferometer. The experimental results show that the proposed LLS has a good sensing linearity and sensitivity.

Temperature-insensitive refractive index sensor based on in-fiber Michelson interferometer

A novel intensity-modulated refractive index sensor based on an in-fiber Michelson interferometer is demonstrated by splicing a section of thin core fiber between two standard single mode fibers. Such a refractive index sensor exhibits an ultrahigh sensitivity of −208.24 and 125.44dB/RIU at the refractive index of 1.440 and 1.500, respectively. The refractive index sensor is insensitive to temperature and thus solves the cross-sensitivity problem between temperature and surrounding refractive index. Moreover, the promising RI sensor has the advantages of short size (less than 2mm) and easy fabrication.

In-Fiber Michelson Interferometer Based on Thin-Core Fiber Combined with an End-Face Mirror

An in-fiber Michelson interferometer (IFMI) is proposed and experimentally demonstrated. The configuration is formed by a thin-core fiber (TCF) following with a single mode fiber whose end tip is covered by a thick silver film as a mirror. The TCF excites cladding modes into downstream SMF via the mismatch-core splicing interface, and the low-order cladding modes can be reflected back to the fiber core via the mirror. A well-defined interference pattern is obtained due to the interference of between core and cladding modes. Experimental results represent that the device is linearly sensitive to the ambient temperature variation, and the selected interference dip of 1530nm represents a temperature sensitivity of 67.59pm/oC. The IFMI is compact and simple, and is a good candidate for ambient temperature measurement.

Label-Free Fiber Optic Biosensors With Enhanced Sensitivity

A sensitivity-enhanced long-period grating in-fiber Michelson interferometer with diameter-reduced cladding was proposed for the first time, and was also demonstrated as a label-free biosensor based on refractive index measurement. The cladding structure dependence of the sensitivity for antibody-antigen immuno-sensing was studied experimentally. The proposed biosensor has shown an 8.5-fold sensitivity enhancement as compared to sensors without cladding reduction.