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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.

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.

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.

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.

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.

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.