Long-period gratings in special geometry fibers for high-resolution and selective sensors

Abstract

Abstract. Advantages for sensor applications of long-period gratings (LPGs) in special optical fibers are reported. Two consecutive LPGs separated by 60 to 100 mm interfere to improve the resolution and reduce noise in a highly doped fiber with inner cladding and in a D-shaped fiber. These gratings provide good contrast to increase the resolution for sensing applications, with or without access to the surroundings along the fiber. The mode profiles of the devices were characterized experimentally to gain deeper insight into the improved functionality.

Drug-Induced T-Wave Morphology Changesn

“…In both figures the flat-side is located at the top (away from the viewer) near the edge of the mode-profiles. [91] Based on the data in figure 42 and figure 43 the intensity distribution of the modes in the core, cladding and air can be approximated. Figure 44 shows a cross section of the core-mode intensity perpendicular to the flat-side.…”

“…"Long-Period Gratings in Special Geometry Fibres for High Resolution and Selective Sensors" [91,114].…”

“…The model is based on experiments and describes the TE-TM_like couplings between the core-and claddings-modes, to predict the resonance wavelengths in the spectrum, including the ones outside our detection equipment range. To measure the mode-profiles in the D-shape fibre, sensor 3 was cleaved at the end of the second grating and mounted in front of an infrared camera, with a collimation lens (x20 microscope objective) between the cleaved fibre end and the camera [91]. The mode-field patterns, in transmission, were measured when launching a 2 mW tuneable laser source into the fibres through the SMF-28 fibre (~ 1550 nm, resolution: 0.1 nm step size, 100 kHz linewidth).…”

“…The dip in the core, is typically, and due to germanate loss (diffusion/evaporation) during the preform collapse, and is typically smoothened during drawing (diffusion through homogeneous material). Figure 14 -Index profile at position 107 mm of the preform, from [91] The preform was divided into a number of 6 sections PA to PF. The first section PA 70 -140 mm and second section PB 140 -210 mm were milled into a D-shape preform using a LECO VC-50 cutting machine.…”

“…Precise measurements of the parameters and simulations are required in the development phase to optimize the sensor for the given application. Furthermore, a design could include two inner-claddings, which might optimize the robustness, for more details see Appendix A [91].…”