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We propose an experimental setup to measure the refractive index (RI) of two independent liquid samples by analyzing a single optical signal. We spliced a section of a seven-core fiber (SCF) into each arm of a 1 × 2 fiber coupler and spliced additional single mode fiber (SMF) to use as fiber probe tips. As the spatial frequency of the characteristic sinusoidal response of an SCF is a function of the fiber length, we used two different lengths (3 and 10 cm) in our realization. A superluminescent diode (SLD) is used as the light source, and the reflected light by both fiber tips is acquired through an optical circulator. An optical spectrum analyzer (OSA) is used to analyze the spectral response of the combined signals from both fiber tips. We characterized this sensing system by immersing the fiber tips in liquid samples with a RI between 1.3175 and 1.4040. We show that the two independent RI measurements can be retrieved by performing a Fourier transform on the recorded optical spectrum. In particular, we demonstrate that with adequate calibration, the Fresnel coefficients can be calculated independently. The presented approach represents a straightforward and cost-effective fiber implementation for multipoint sensing.

In this paper, we propose a highly sensitive temperature sensor based on two cascaded Mach–Zehnder interferometers (MZIs) that work using the Vernier effect. The all-fiber MZIs were assembled by splicing a segment of capillary hollow-core fiber (CHCF) between two sections of multimode fibers (MMFs). This cascaded configuration exhibits a temperature sensitivity of 1.964 nm/°C in a range from 10 to 70 °C, which is ~67.03 times higher than the sensitivity of the single MZI. Moreover, this device exhibits a high-temperature resolution of 0.0153 °C. A numerical analysis was carried out to estimate the devices’ temperature sensitivity and calculate the magnification of the sensitivity produced by the Vernier effect. The numerical results have an excellent agreement with the experimental results and provide a better insight into the working principle of the MZI devices. The sensor’s performance, small size, and easy fabrication make us believe that it is an attractive candidate for temperature measurement in biological applications.

A simple to fabricate, cost-effective, robust, and highly accurate fiber optic temperature sensor is proposed and experimentally demonstrated. The sensor head consists of an in-fiber Fabry–Perot interferometer (FFPI) embedded in a mold made of a polyester resin. FFPI, which in general present good strain sensitivity and low-temperature sensitivity, was assembled by splicing a microsegment of capillary fiber of 14.66 μ m between two single-mode fibers. The reflected spectrum of the FFPI exhibited a single interference dip within a span of 80 nm. The dimensions of the resin mold can be modified by changing the ambient temperature, which in turn changes the length of the FFPI air-cavity. The dip of the reflected spectrum is shifted toward shorter (larger) wavelengths when external temperature is decreased (increased). The large free spectral range (FSR) allowed to monitor the temperature changes by either a wavelength or an intensity interrogation scheme. Using a laser and an optical power meter it was possible to demonstrate a real-time temperature sensor with a sensitivity of −60.79 nW/°C and a resolution of 0.5 °C, in the range of 10–30 °C. We believe that the practicality of this real-time sensor can be very attractive for environmental sensing application.

A simple method to construct a dual-channel in a prism-based surface plasmon resonance sensor for dual-parameter monitoring is proposed. The metal layer (sensing area), attached to the prism, is half-covered with a polymer in order to generate two individual sensing sections. In this paper, eight different sensor structures (prism/metal/polymer) were analyzed. The prisms are made of NSK16 or SF10 glass and coated with gold or silver films. Half section of the metal films is covered with Polydimethylsiloxane (PDMS) or Poly-methyl methacrylate. The sensor is based on angle interrogation, the laser beam is aligned to be incident upon the interface of the bare and polymer sections. The resonance conditions are different at each pad, due to the refractive index (RI) mismatch, thus the intensity of the reflected signal presents a pair of well-defined resonance dips in series. The sensitivity of these dips to RI and temperature (T) changes was numerically analyzed. Finally, to demonstrate the feasibility to monitor RI and T, simultaneously, a surface plasmon resonance sensor was constructed using a NSK16 glass prism coated with a thin gold film, which was half-covered with PDMS.

In this paper, a narrow spectral linewidth and wavelength-tunable erbium-doped fiber laser based on a Mach-Zehnder interferometer (MZI) as a filter is proposed and experimentally demonstrated. The filter is fabricated by splicing a short length of capillary hollow-core fiber (CHCF) between two small sections of multimode fibers (MMF). The interference pattern generated by the filter has a free spectral range of 10.5 nm and a maximum extinction ratio of 36 dB at 1560 nm. Then, by incorporating the filter inside a ring cavity laser, a single laser emission centered at 1566.46 nm with a spectral width around 0.03 nm and a high SNR of 66 dB (also has a SMSR of 53 dB) is obtained. By changing the temperature of the filter, the wavelength emission of the laser can be tuned from 1566.46 to 1570.09 nm. Considering that the fabrication process of the filter is relatively simple and can be easily implemented in an EDFL, we strongly believe that it can have a great deal of interest in telecom applications.

In this work, a temperature sensor based on an asymmetric core-offset Mach-Zehnder Interferometer (MZI) coated with aluminum is proposed and experimentally demonstrated. The interferometer is fabricated by core-offset splicing three sections of single mode fiber, and by coating it with aluminum using a thermal evaporation technique. The temperature sensitivity of the device increases by a factor of 3.4 to 120 pm/°C after coating, while the interferometric fringe pattern shows an augmented contrast of 8.5 dBm. The experimental results are compared to those obtained with the uncoated MZI to point out the enhancement in the sensibility.

A surface plasmon resonance-based fiber-optic sensor for simultaneous measurement of refractive index and temperature of liquid samples is proposed and experimentally demonstrated. The sensor consists of a gold-coated MM-SM-MM optical fiber structure, whose sensitive section was partially covered with polydimethylsiloxane (PDMS) to generate two independent SPR resonance dips in the fiber transmission spectrum. One of the dips is generated by the bare gold-coated fiber section whose wavelength resonance is tuned by the refractive index and temperature of the surrounding medium. The other dip that is exclusively used to monitor the temperature variations of the liquid sample, whose central wavelength at 900 nm corresponds to PDMS refractive index at 20 °C, is produced by the polymerized gold-coated fiber section. The high refractive index and temperature sensitivity achieved, 2323.4 nm/RIU and −2.850 nm/°C respectively, the small size, the ease fabrication process, and the bio-compatibility of the proposed device are appealing characteristics that makes it ideal for practical bio-sensing applications.

A compact, simple-to-fabricate, low-cost, and highly sensitive optical fiber temperature sensor based on surface plasmon resonance (SPR) is reported. The sensor consists of a core mismatch fiber structure fabricated by splicing a small piece of single-mode fiber (SMF) between two multimode fibers (MMF). SPR is generated when evanescent field interacts with the gold layer deposited over the SMF cladding. Then, the sensor was embedded in polydimethylsiloxane (PDMS), which acts as a temperature to refractive index transducer. Due to PDMS high thermooptic coefficient, the SPR dip underwent a noticeable wavelength shift when a variation of temperature occurred. The device was tested in the 20–60 °C range showing a linear response and a sensitivity of 2.60 nm/°C. This sensor is appealing for temperature monitoring in microfluidic devices made of PDMS due to its high performance and simply fabrication process.

Light-induced deposits of carbon nanotubes (CNTs) are obtained in multimodal interference (MMI) fiber tips. Differences between deposits obtained with solutions with and without surfactant were observed.

The output signal of Mach-Zehnder curvature sensor was Fourier transformed to increase its curvature range to high value of 1.69 m-1, relative to the traditional fringe contrast measurement 1.09 m-1.

A multimode interference (MMI) sensor was designed and experimentally demonstrated for simultaneous measurement of curvature and temperature. A typical fiber structure of single-mode fiber – multimode fiber – single-mode fiber (SMS), mounted in a long and thin carbon steel sheet, and then coated with polydimethylsiloxane (PDMS) was manufactured and tested in curvature and temperature. Bending laboratory results showed that the proffered sensor has a curvature sensitivity of -0.9835 dB/m-1 over a range from 0 m-1 to 1.3652 m-1 , measurements were taken by keeping a constant temperature of 30°C. The laboratory temperature response was -119 pm/°C at a temperature range from 30°C to 60°C, showing an improvement in temperature response, temperature measurements were taken by keeping a constant bending of 0 m-1 . The results show that PDMS coatings are a good way to improve multimode interferometer sensitivity during temperature measurement while keeping a good curvature measuring response, moreover the device shows a linear response within the curvature and temperature ranges. Another advantage of the PDMS coating is that it makes the sensor insensitive to refractive index changes, it gives the sensor robustness and protection against dust.

In this paper, we propose and experimentally demonstrate a simple technique to enhance the curvature sensitivity of a bending fiber optic sensor based on anti-resonant reflecting optical waveguide (ARROW) guidance. The sensing structure is assembled by splicing a segment of capillary hollow-core fiber (CHCF) between two single-mode fibers (SMF), and the device is set on a steel sheet for measuring different curvatures. Without any surface treatment, the ARROW sensor exhibits a curvature sensitivity of 1.6 dB/m−1 in a curvature range from 0 to 2.14 m−1. By carefully coating half of the CHCF length with polydimethylsiloxane (PDMS), the curvature sensitivity of the ARROW sensor is enhanced to −5.62 dB/m−1, as well as an increment in the curvature range (from 0 to 2.68 m−1). Moreover, the covered device exhibits a low-temperature sensitivity (0.038 dB/°C), meaning that temperature fluctuations do not compromise the bending fiber optic sensor operation. The ARROW sensor fabricated with this technique has high sensitivity and a wide range for curvature measurements, with the advantage that the technique is cost-effective and easy to implement. All these features make this technique appealing for real sensing applications, such as structural health monitoring.

An easy to construct curvature sensor is proposed and experimentally demonstrated. The device was fabricated splicing a segment of hollow core fiber (HCF) between two segments of coreless fiber (CLF) forming a Mach-Zehnder interferometer (MZI).

We proposed and demonstrated a compact, simple-to-construct and highly sensitive optical fiber sensor capable of simultaneously measuring refractive index (RI) and temperature (T) based on surface plasmon resonance (SPR) effect. The device structure consists of a single mode fiber (SMF) spliced between two multimode fibers where whole SMF was coated with chromium and gold. The thicknesses of the layers of chromium and the gold were 5 nm and 30 nm, respectively. By covering half of the sensing region of the device with a polymer with high thermo-optic coefficient (TOC), it is feasible to detect RI and T changes with sensitives of 2664.540 nm/RIU and -2.852 nm/°C, respectively.

A simple-to-fabricate and highly sensitive optical fiber temperature sensor is presented. The device consists of an optical microfiber mode interferometer embedded in a polymer with high thermo-optic coefficient which is also used as a packaging material. Temperature modifies the refractive index of the polymer, hence the phase difference between the interfering modes, which results in a prominent wavelength shift of the interference pattern. The sensor was tested in the 20 °C–48 °C range. The temperature sensitivity was found to be 3101.8 pm/°C. The simplicity and the performance of our device make it attractive for several applications.

A fiber optic Fabry-Perot interferometer (FPI) was proposed and demonstrated. The sensor was constructed by splicing a single mode fiber (SMF) and a hollow core fiber (HCF), cleaving the HCF to a length of 15 ± 1 μm and filling it with polydimethylsiloxane (PDMS). The sensitivity of the sensor tip was 0.61 nm/°C and was caused by a combined effect of the thermo-optical and expansion coefficients.

We compare the behavior of three temperature sensors based on fiber optic Fabry-Perot interferometers (FPI). The length of the cavities were 30 ± 2 µm and they were filled with polydimethylsiloxane (PDMS), poly(methyl methacrylate) (PMMA), and the optical adhesive NOA61. The sensitivities for each sensor were 2.20 nm/°C, 0.42 nm/°C, and 0.57 nm/°C, respectively. The refractive index (RI) sensitivity showed by these devices was caused by an integrated consequence of the thermo-optical and expansion coefficients.

An in-fiber Mach–Zehnder Interferometer (MZI), based on hollow core fiber (HCF), for measuring curvature is fabricated and experimentally demonstrated. The sensing part was fabricated by splicing a section of HCF between two sections of multimode fiber (MMF), and different HCF lengths were investigated in order to achieve the highest curvature sensitivity. These devices were tested in a transmission configuration using lead-in and lead-out single mode fibers (SMF). The sensor was attached to a steel sheet by using the polymer Polydimethylsiloxane (PDMS) for accurate control of the applied curvature. The modal analysis was carried out using a commercial software based on finite element method (FEM) and by incorporating some of the experimental data, it was feasible to determine the two dominant modes that interfere in this sensor. The devices were characterized by measuring the fringe contrast variations due to the curvature changes. The interferometer fabricated with a HCF 2.5 mm in length HCF showed the highest curvature sensitivity, −17.28 ± 2.30 dB/m−1, in a range from 1.84 m−1 to 2.94 m−1. Moreover, the sensor that exhibited a better performance was fabricated with a HCF length of 1 mm, combining the most extensive curvature range (from 0.95 m−1 to 2.68 m−1) and an adequate sensitivity (−11.80 ±1.30 dB/m−1). The analysis of the interferometric signal of this device in Fourier domain, allows us to establish a one to one relationship between the contrast and the curvature in a broader range (from 0 m−1 to 2.94 m−1). Moreover, the fringe contrast showed a very low dependency on temperature (from 30 °C to 90 °C), depicting that this device was not affected by temperate fluctuation.

Multimode interference (MMI) devices have attracted a great deal of interest due to their simplicity of fabrication. The MMI device is ready for testing after splicing a section of multimode fiber (MMF) between two single-mode fiber (SMF). In this chapter we provide an overview of the fundamentals behind the formation of self-images in MMI fiber devices, as well as the basic mechanisms for tuning their operational wavelength which is related with their application for sensing applications. The sensitivity enhancement of these MMI fiber sensors is also investigated by reducing the diameter of the MMF via wet chemical etching, as well as coating the MMF with a high refractive index overlay. The MMI fiber sensors are applied to the quality control of gasolines and in particular the real time monitoring of gasohol, mixtures of gasoline and ethanol, which is critical for the proper operation of flexible-fuel vehicles (FFV). The results demonstrate that MMI fiber sensors are well suited for such applications, as well as other applications were the binary mixture of liquids has to be controlled or monitored.

A hybrid mode-locked Erbium-doped fiber laser that provides very short pulse-widths while achieving high repetition rates is proposed and experimentally demonstrated. This hybrid configuration is realized by using a thin film of polydimethylsiloxane (PDMS) doped with single wall carbon nanotubes (SWCNT). This PDMS/SWCNT composite acts as a saturable absorber and is inserted within an active mode-locked laser system using angled connectors. Therefore, the effect of the PDMS/SWCNT composite is to effectively narrow the width of the pulses generated by the active system without modifying its repetition rate. A pulse-width of 730 fs was generated at a repetition rate of 4 GHz, while achieving an average output power of 4 mW. A reduction in the noise of the photodetected RF spectrum was also observed in the hybrid system.

A new technique of ultrafast analogue-to-digital (A-D) conversion for an all-optical data processing is proposed. This technique is based on the Kerr nonlinearity-induced cross-phase modulation in single-mode Mach–Zehnder interferometer configurations arranged in a specific way. Two schemes, capable of realizing both sequential and parallel A-D conversions of optical signals are considered. The potential for an extremely high-bit-rate processing, up to 1 THz in each converter, is due to a femtosecond time response of Kerr effect in fused silica glass. Optical schemes of proposed devices are presented and algorithmically estimated; their functional capabilities are discussed.

A temperature sensor consisting of two three-core-fiber segments is demonstrated. Ratiometric measurements of the signals provide a sensitivity of 0.036/oC which is two orders of magnitude higher than their individual signals.

As information technologies move from electron-to photon-based systems, the need to rapidly modulate light is of paramount importance. Here, we study the evolution of the electric-field-induced ali ...

Microstructured optical fibers present unique properties that enable a number of novel applications. This is due to their particular geometry, which includes an array of holes that runs along their axis, parallel to the core. The possibility of inserting nanoparticles in this type of fiber, especially in photonic crystal fibers, gives rise to novel applications in several areas. In particular, the insertion of luminescent semiconductor nanocrystals has been studied for temperature sensing applications. In this work, we present the development of an all-fiber optical circuit that is able to excite CdSe/ZnS nanocrystals, as well as to efficiently collect their emission, via a double-clad fiber. The nanocrystals were suspended in a polymer, which was inserted into the hollow core of a PCF. Two versions of this setup are discussed and have the advantage of being robust, simple, and of not requiring free-space optics. As a next step, the setup will be tested as a temperature sensor based on the monitoring of the luminescence spectrum.

An ultracompact, cost-effective, and highly accurate fiber optic temperature sensor is proposed and demonstrated. The sensing head consists of Fabry-Perot microcavity formed by an internal mirror made of a thin titanium dioxide (TiO2) film and a microscopic segment of single-mode fiber covered with Poly(dimethylsiloxane) (PDMS). Due to the high thermo-optic coefficient of PDMS the reflectance of the fiber-PDMS interface varies strongly with temperature which in turn modifies the amplitude of the interference pattern. To quantify the changes of the latter we monitored the visibility of the interference pattern and analyzed it by means of the fast Fourier transform. Our sensor exhibits linear response, high sensitivity, and response time of 14 seconds. We believe that the microscopic dimensions along with the performance of the sensor here presented makes it appealing for sensing temperature in PDMS microfluidic circuits or in biological applications.

Compact sources of short pulses with high-repetition-rates are highly desirable for a wide range of applications such as optical coherent tomographic, metrology, optical communication, two photon microscopy, and optical clocks. This thesis is focus on the research and development of fiber lasers that emit short optical pulses. Here we purpose to use Polydimethylsiloxane (PDMS) and SU8-2075 polymers to fabricate thin films doped with SWCNTs that work like a saturable absorber. Moreover, the nonlinear behavior of these films was investigated by using an all-fiber power dependent transmission setup. Using this setup a PDMS/SWCNT film (thickness 200 μm) and SU8-2075 film (thickness 100 μm) were tested. The saturation intensity and the modulation depth of the PDMS/SWCNT and SU8-2075 films are 5.1 MW/cm2, 0.7MW/cm2, 12.3 % and 10 %, respectively. Passively mode-locked Erbium fiber ring lasers have been implemented by using PDMS/SWCNT and SU8-2075 films, the first one produces pulses at a repetition rate of 22.73 MHz with a pulse duration of 1.26 ps assuming a sech2 pulse profile. The second one has a repetition rate of 21.27 MHz with a pulse duration of 871 fs assuming a sech2 pulse profile. A hybrid mode-locked Erbium-doped fiber laser that provides very short pulse-widths while achieving high repetition rates is proposed and experimentally demonstrated. This hybrid configuration is realized by using a PDMS/SWCNT thin film composite as saturable absorber, which is inserted within an active mode-locked laser system using angled connectors. Therefore, the effect of the PDMS/SWCNT composite is to effectively narrow the width of the pulses generated by the active system without modifying its repetition rate. A pulse-width of 730 fs was generated at a repetition rate of 4 GHz, while achieving an average output power of 4 mW. A reduction in the noise of the photodetected RF spectrum was also observed in the hybrid system. Finally, a passively-Q-switching laser has also been built up by using a SU8-2075/SWCNT film. The maximum average power, peak power, and pulse energy were 160 μW, 7.3 mW, and 5.1 nJ, respectively.

We report the fabrication of a saturable absorber made of a novel polymer SU8 doped with Single Wall Carbon Nanotubes (SWCNTs). A passive mode-locked ring cavity fiber laser was built with a 100 μm thick SU8/SWCNT film inserted between two FC/APC connectors. Self-starting passively mode-locked lasing operation was observed at 1572.04 nm, with a FWHM of 3.26 nm. The autocorrelation trace was 1.536 ps corresponding to a pulse-width of 871 fs. The time-bandwidth product was 0.344, which is close enough to transform-limited sech squared pulses. The repetition rate was 21.27 MHz, and a maximum average output power of 1 mW was also measured.

A hybrid mode-locked fiber laser was built by using a PDMS/SWCNTs film as a saturable absorber. The system allows for a high repetition rate of 4 GHz, while achieving pulse widths of 730 fs.

We report the fabrication of novel SU8/SWCNT composite materials as saturable absorbes. The film can be easily inserted between two FC/APC connectors in order to have an inline saturable absorber. A passive mode-locked laser is created by placing this device in an Erbium doped fiber (L-band) ring cavity laser. The laser produces 871 fs pulses with a repetition rate of 21.26 MHz.

A stable optofluidically tunable fiber laser based on Multimode Interference (MMI) effect is experimentally demonstrated. The tuning mechanism relies on modifying the effective width of the multimode fiber (MMF) using a liquid with a specific refractive index, which in turns tunes the peak wavelength of the filter. We easily demonstrate a tunability of almost 40 nm with a side-mode suppression ratio (SMSR) of 47 dBm, and a 3dB bandwidth of 0.4 nm. The laser was operated at room temperature without any thermal control and the wavelength peak was very stable.

An optofluidically tunable multimode interference (MMI) bandpass filter is demonstrated. This scheme allows for a tuning range of almost 40 nm, which can be made continuous by increasing the liquid level around the multimode fiber.

El efecto de fuerza foto-electromotriz se ha empleado para determinar amplitudes de vibración (desplazamiento) ocasionadas por una onda ultrasónica al propagarse a través de un material. En el presente trabajo se propone introducir una señal de referencia para cuantificar los desplazamientos. Debido a que van a existir dos señales en el efecto de fuerza fotoelectromotriz, se hace un análisis experimental que consiste en observar el espectro de frecuencias de la señal y compararlo con el espectro de un interferómetro de Mach-Zehnder con dos frecuencias (se modula la fase de cada haz por medio de una señal senoidal). Otros resultados de este análisis son: Se obtienen las curvas que exhiben la relación entre la corriente de la señal del efecto de fuerza foto-electromotriz y la amplitud de modulación para dos moduladores; se observa que estas dos curvas son iguales dentro de los errores experimentales. Además, se muestra experimentalmente que el cociente entre los voltajes de las señales de salida del efecto de fuerza foto-electromotriz son independientes de la intensidad. Por último, se exponen los resultados obtenidos al determinar la amplitud de vibración de una onda ultrasónica al emplear el efecto de fuerza foto-electromotriz con una señal de referencia.

We demonstrate the capability of an air cavity Fabry-Perot interferometer (FPI), built with a tapered lead-in fiber tip, to measure three parameters simultaneously, distance, group refractive index and thickness of transparent samples introduced in the cavity. Tapering the lead-in fiber enhances the light coupling back efficiency, therefore is possible to enlarge the air cavity without a significant deterioration of the fringe visibility. Fourier transformation, used to analyze the reflected optical spectrum of our FPI, simplify the calculus to determine the position, thickness and refractive index. Samples made of 7 different glasses; fused silica, BK7, BalF5, SF2, BaF51, SF15, and glass slides were used to test our FPI. Each sample was measured nine times and the results for position, thickness and refractive index showed differences of ± 0.7%, ± 0.1%, and ± 0.16% respectively. The evolution of thickness and refractive index of a block of polydimethylsiloxane (PDMS) elastomer due to temperature changes in the range of 25°C to 90°C were also measured. The coefficients of the thermal expansion and thermo-optic estimated were α = 4.71x10(-4)/°C and dn/dT = -4.66 x10(-4) RIU/°C, respectively.

We report the fabrication of a saturable absorber based on SU8 single wall carbon nanotube (SWCNT) composite material. Thin films with a controllable thickness can be fabricated using a simple and reliable process. These films can be inserted between two FC/APC connectors in order to have an inline saturable absorber. A passive mode-locked laser was built by interleaving the fiberized saturable absorber in an erbium-doped fiber (L-band) ring cavity laser. The laser produces 871 fs pulses with a repetition rate of 21.27 MHz and a maximum average power of 1 mW.

We present a novel technique to fabricate a saturable absorber thin film based on Polydimethylsiloxane doped with Single Wall Carbon Nanotubes. Using this film a passive mode-locked fiber laser in a standard ring cavity configuration was built by inserting the film between two angled connectors. Self-starting passively mode-locked laser operation was easily observed. The generated pulses have a width of 1.26 ps at a repetition rate of 22.7 MHz with an average power of 4.89 mW.

A fiber optic vibration sensor based on Multimode Interference (MMI) effects is demonstrated. The proposed sensor is tested by characterizing its bending response, impulse response, and its response to fixed external frequencies. Induced vibration is measured in the range from 0 Hz to 2.5 kHz; the main frequency component overcomes on the first and second harmonics with a difference of 32.4 dB and 37.2 dB, respectively.

Simultaneous measurement of refractive index (RI) in liquids is demonstrating by using multicore fibers to spectrally encode the intensity changes observed when the fiber tip is immersed in the tested liquid.

A Refractive Index sensor based on a Two-Core optical fiber is demonstrated. The sensor response and sensitivity can be easily adjusted by simply controlling an etching process to expose the off-axis core. The proposed RI sensor exhibits a sensitivity exceeding 2,100 nm/RIU.

Here we report a fiber bending sensor based on multimode interference effects. Sensing is achieved through losses induced in the propagating modes, which directly affects the intensity of the imaged formed by the multimode fiber.

A Mach-Zehnder curvature sensor with enhanced contrast based on lateral-offset splicing is proposed. The highest contrast was obtained at 2 µm lateral-offset. Using the Fourier Transform, amplitude changes were traced from 0 m-1 to 2.68 m-1.