A new concept for a fiber-based wavelength-tunable condensing lens is theoretically and experimentally investigated in terms of its ability to shift the longitudinal focus position as a function of wavelength. By exploiting multimode interference effects with reimaging theory, a compact and robust device, completely contained within a standard FC connector, can be constructed by simply splicing a single-mode fiber (SMF) to a finite length section of multimode fiber (MMF). This paper summarizes the theoretical and experimental results of such a device, with additional results for wavelength sensitivity.

A novel design for an all-fiber bandpass filter based on a multimode interference reimaging phenomenon is presented. The filter has achieved low insertion loss with adequate bandwidth and isolation for coarse wavelength-division multiplexing. The filter can easily be made with any central wavelength that is compatible with the single-mode fiber used for its construction. The measured filter performance matches the theoretical predictions well. The filter can have broad applications in fiber-optic telecommunications, spectroscopy, and sensing.

A new concept for a multimode interference-based fiber-optic displacement sensor is investigated both theoretically and experimentally. By applying multimode interference and reimaging theory to optical fibers, a displacement sensor consisting of only a section of multimode fiber fusion spliced to a single-mode fiber can be readily fabricated. Observation and analysis of the power reflected off of a surface and back through the device over a finite wavelength range provides enough information to use the device as a calibrated displacement sensor over a large displacement range.

This paper describes simulation and experimental methods for designing a D-shaped surface plasmon resonance (SPR) fibre sensor. The sensor consists of two set-up approaches. Finite element method is used in simulation on the fibre sensor device. Two experimental methods for detecting relative intensity are used by varying the wavelength of the optical signal sources and the thickness of gold layer coated on the D-shaped fibre. In the first method, the sensor device works by detecting the relative intensity of two optical signal sources having different wavelengths. In the second set-up, the relative intensity between two D-shaped fibres coated with different thicknesses of gold is measured when a single signal source is launched at the input. The difference in intensities of the signal outputs is used to estimate the refractive index at the sensing region. A prototype SPR D-shaped fibre sensor has been fabricated and the experimental results show good agreement with simulation.

A full-vectorial $\mathbf{H}$-field formulation-based finite element approach is used to optimize a biosensor structure incorporating a horizontal slot waveguide. It is designed to detect DNA hybridization through the change of the effective index of the waveguide structure. The key parameters, such as normalized power confinement, power density, change in effective index, and sensitivity are presented by optimizing the device parameters of the slot waveguide. It is shown here that a 90.0 μm long compact Mach–Zehnder section can be designed with horizontal slot waveguide to detect DNA hybridization and for a ring resonator arrangement a sensitivity of 893.5 nm/RIU is obtained.