A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Applications of TOFs as Optical Fiber Sensors <s> A new fibre-optic refractive index sensor is presented. It is based on the radiation losses introduced by the sample medium in a cladded multimode tapered fibre. A simple light transmission measurement setup is used to test some samples. It is demonstrated that the sensor is suitable for measuring RI in the range 1.36 to 1.46, as well as RI changes below 10−4. <s> BIB001 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Applications of TOFs as Optical Fiber Sensors <s> We report a simple optical sensing device capable of measuring the refractive index of liquids propagating in microfluidic channels. The sensor is based on a single-mode optical fiber that is tapered to submicrometer dimensions and immersed in a transparent curable soft polymer. A channel for liquid analyte is created in the immediate vicinity of the taper waist. Light propagating through the tapered section of the fiber extends into the channel, making the optical loss in the system sensitive to the refractive-index difference between the polymer and the liquid. The fabrication process and testing of the prototype sensing devices are described. The sensor can operate both as a highly responsive on-off device and in the continuous measurement mode, with an estimated accuracy of refractive-index measurement of approximately 5 x 10(-4). <s> BIB002 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Applications of TOFs as Optical Fiber Sensors <s> In this paper, the response of a tapered optical fiber humidity sensor is optimized, attending to the thickness of the sensitive coating, the dimensions of the taper, the light source, and the utilization of sensitive materials with different refractive indexes. The main novelty of this study is that the thickness of the sensitive layer is on the order of magnitude of the light wavelength used to excite the sensor. It is shown here that an estimation of the sensor sensitivity can be deducted from the transmitted optical power curve obtained during the layer-by-layer construction process. Theoretical and experimental results are presented <s> BIB003 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Applications of TOFs as Optical Fiber Sensors <s> A large-mode-area holey fiber was tapered to a point in which the airholes collapsed, and its dependence on temperature and strain was studied. The transmission spectrum of such a fiber exhibits a series of peaks owing to the interference between the modes of the solid taper waist. We found that the interference peaks shifted to shorter wavelengths as the taper was elongated. However, the peaks were insensitive to temperature. The fabrication and advantages of our novel wavelength-encoded temperature-independent strain sensor compared with other optical fiber strain sensors are discussed. <s> BIB004 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Applications of TOFs as Optical Fiber Sensors <s> A new concept to measure rotation angles based on a fiber-optic modal Mach-Zehnder interferometer is demonstrated by using a nonadiabatic taper cascaded with a long-period fiber grating. Information about the magnitude of the rotation angle can be obtained from the measurement of the interference pattern visibility, and under certain conditions it is also possible to obtain the sign of the rotation angle from the induced phase variation in the fiber interferometer. <s> BIB005 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Applications of TOFs as Optical Fiber Sensors <s> Abstract A new biosensor has been developed by coating a tapered optical fiber with an anti-gliadin antibodies (AGAs) sensitive nanofilm using the electrostatic self-assembled (ESA) monolayer technique in order to aid the diagnosis of celiac disease. Optical fibers were tapered and then the specific antigen was deposited using the ESA method which allows the construction of nanometric scale recognition surfaces on the fiber optic and helps to create fast response sensors for real time observation of the binding process. Power changes up to 6 dB have been recorded during the antibodies binding process with concentrations in the range 1–15 ppm. Optimal deposition parameters have been selected using an in situ interferometric characterization technique which allows to state the working point of the sensor accurately. The high sensitivity and continuous monitoring of the proposed scheme can reduce importantly the time and serum volume required for celiac disease tests. <s> BIB006 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Applications of TOFs as Optical Fiber Sensors <s> A simple refractive index sensor based on a Michelson interferometer in a single-mode fiber is constructed and demonstrated. The sensor consists of a single symmetrically abrupt taper region in a short piece of single-mode fiber that is terminated by approximately 500 nm thick gold coating. The sensitivity of the new sensor is similar to that of a long-period-grating-type sensor, and its ease of fabrication offers a low-cost alternative to current sensing applications. <s> BIB007 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Applications of TOFs as Optical Fiber Sensors <s> A compact fiber-optic inclinometer based on a fiber-taper Michelson interferometric sensor is constructed and demonstrated. The sensor consist of a single symmetrically taper waist of 80 μm distanced 30 mm from the single-mode fiber end-tip right-angled cleaved. The amplitude of the bending angle of the fiber taper interferometer is obtained by passive interferometric interrogation based on the generation of two quadrature phase-shifted signals from two fiber Bragg gratings with different resonant wavelengths. Optical phase-to-bending sensitivity of ~ 1.13 rad/degree and a bend angle resolution of ~ 0.014 degree/√ Hz were achieved. <s> BIB008 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Applications of TOFs as Optical Fiber Sensors <s> A novel magnetic field sensor using a nonadiabatic tapered optical fiber (NATOF) interacting with magnetic fluid (MF) nanoparticles is proposed and experimentally demonstrated. The NATOF sensitivity when is subjected to refractive index (RI) measurement in the small range from 1.3380 to 1.3510 was 1260.17 nm/RIU as a refractometer sensor. The NATOF is surrounded by a MF whose RI changes with external magnetic field, which MF is as a cladding of tapered fiber. The output interference spectrum is shifted by the change of the applied magnetic field intensity in the range up to 44 mT with a sensitivity of -7.17 × 10 ::: -2 ::: nm/mT, used only 0.1% of the volume concentration of MF nanoparticles. This direct manipulation of light with magnetic fields provides an approach to develop future sensors relying on electromagnetic interactions. <s> BIB009 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Applications of TOFs as Optical Fiber Sensors <s> A new concept for an optical fiber inclinometer based on tapered fiber Bragg grating (TFBG) is presented. The sensor was characterized by the experimental measurement of the dependence of inclination angle on the spectral response in fluctuating temperature conditions. The research showed that the TFBG made it possible to simultaneously measure both the inclination angle and temperature, and to operate as a temperature insensitive 0°–90° tilt sensor, in a different interrogation regime. Inscription of the FBG in the tapered optical fiber section offered not only sensor miniaturization, but also the possibility of temperature sensing by the fiber section adjacent to the inclination area. Moreover, due to the reflective mode of the TFBG, the sensor offers excellent sensitivity due to the double-loss operation. <s> BIB010
A wide variety of high-performance sensors based on TOF structures have been reported, which include RI sensors BIB002 BIB001 BIB007 , temperature sensors, humidity sensors BIB003 , gas sensors  , magnetic field sensors BIB009 , biosensors BIB006 , strain sensors BIB004 and an inclinometer BIB005 BIB008 BIB010 . In this section, we summarize several common sensing applications of the TOF structures which exploit multimodal interference for an enhanced performance. The sections ends with a short overview of the interrogation technologies for the sensors described in this section. A wide variety of high-performance sensors based on TOF structures have been reported, which include RI sensors BIB002 BIB001 BIB007 , temperature sensors, humidity sensors BIB003 , gas sensors  , magnetic field sensors BIB009 , biosensors BIB006 , strain sensors BIB004 and an inclinometer BIB005 BIB008 BIB010 . In this section, we summarize several common sensing applications of the TOF structures which exploit multimodal interference for an enhanced performance. The sections ends with a short overview of the interrogation technologies for the sensors described in this section.