An inline multichannel surface plasmon resonance (SPR) sensor scheme excited with tilted fiber Bragg gratings (TFBG) in a chromium- and gold-coated fiber is demonstrated. The channels have different operating wavelengths, different TFBG tilt angles, and hence different refractive index operating ranges. The polarization state of each channel based on the TFBG orientation can be used to switch each SPR sensor on or off as required. This system provides an operating range of 1.40-1.44 RIU and a sensitivity of around 500  nm/RIU. The multiplexing in a single optical fiber of a number of TFBG-SPR sensors is demonstrated for the first time.

We present a novel optical fiber surface plasmon resonance (SPR) sensor scheme using reflected guided cladding modes captured by a double-clad fiber coupler and excited in a gold-coated fiber with a tilted Bragg grating. This new interrogation approach, based on the reflection spectrum, provides an improvement in the operating range of the device over previous techniques. The device allows detection of SPR in the reflected guided cladding modes and also in the transmitted spectrum, allowing comparison with standard techniques. The sensor has a large operating range from 1.335 to 1.432 RIU, and a sensitivity of 510.5 nm/RIU. The device shows strong dependence on the polarization state of the guided core mode which can be used to turn the SPR on or off.

We demonstrate the use of fiber Bragg gratings (FBGs) as a monolithic temperature sensor from ambient to liquid nitrogen temperatures, without the use of any auxiliary embedding structure. The Bragg gratings, fabricated in three different types of fibers and characterized with a high density of points, confirm a nonlinear thermal sensitivity of the fibers. With a conventional interrogation scheme it is possible to have a resolution of 0.5 K for weak pure-silica-core FBGs and 0.25 K using both boron-doped and germanium-doped standard fibers at 77 K. We quantitatively show for the first time that the nonlinear thermal sensitivity of the FBG arises from the nonlinearity of both thermo-optic and thermal expansion coefficients, allowing consistent modeling of FBGs at low temperatures.

A simple refractive index sensor based on a small section of fiber damaged by the fiber fuse is proposed and demonstrated with a sensitivity of 350.58 nm/refractive index unit (RIU). For comparison, a hetero-core structure fiber sensor composed of a short no-core fiber (NCF) sandwiched between two pieces of single-mode fibers is demonstrated with a sensitivity of 157.29 nm/RIU. The fiber fuse technique can allow mass production of sensors by incorporating small sections of the damaged fiber of any type into each device. We believe this is the first application of the periodic damage tracks in optical fibers formed by the fiber fuse.

We present a novel measurement scheme using a double-clad fiber coupler (DCFC) and a fiber Bragg grating (FBG) to resolve cladding modes. Direct measurement of the optical spectra and power in the cladding modes is obtained through the use of a specially designed DCFC spliced to a highly reflective FBG written into slightly etched standard photosensitive single mode fiber to match the inner cladding diameter of the DCFC. The DCFC is made by tapering and fusing two double-clad fibers (DCF) together. The device is capable of capturing backward propagating low and high order cladding modes simply and efficiently. Also, we demonstrate the capability of such a device to measure the surrounding refractive index (SRI) with an extremely high sensitivity of 69.769 ± 0.035 μW/RIU and a resolution of 1.433 × 10(-5) ± 8 × 10(-9) RIU between 1.37 and 1.45 RIU. The device provides a large SRI operating range from 1.30 to 1.45 RIU with sufficient discrimination for all individual captured cladding modes. The proposed scheme can be adapted to many different types of bend, temperature, refractive index and other evanescent wave based sensors.