In this paper, we report a new type of refractometer based on a D-shaped fiber Bragg grating (FBG) integrated in a loop-mirror optical fiber laser. This proposed sensor is used in wavelength interrogation method, in which the D-shaped FBG is applied as a refractive index (RI) sensing probe and a mirror to select mode of laser. The D-shaped FBG is prepared by the removal of a portion of the fiber cladding covering the FBG by means of side-polishing technique. The D-shaped FBG sensing probe integrated in a loop-mirror optical fiber laser with saturated pump technique, the characteristics of sensing signals have been improved to obtain stable intensity, narrower bandwidth and higher optical signal-to-noise ratio compare to normal reflection configuration. The limit of detection (LOD) of this sensor can be achieved to 2.95 x 10-4 RIU in the refractive index (RI) range of 1.42-1.44. Accordingly, we believe that the proposed refractometer has a huge potential for applications in biochemical-sensing technique.
This work reports the optical properties of surface plasmon resonance (SPR) based on the metal-insulator-metal (MIM) structure towards a refractive index sensor. The MIM-SPR structure operating near infrared region consists of lateral periodicity of subwavelength gold patterns placed on a stack of thin silica spacer and silver film (acting as a reflector) on a silicon substrate. The reflection spectra and the electric field distributions of MIM-SPR structures can be tuned by modifying the geometrical properties and have been numerically investigated by using Lumerical’s finite-difference time-domain (FDTD) solutions. The square lattice configuration of 1200 nm to 1400 nm pitch of gold micro-disks of thickness from 80 nm to 120 nm have been conducted. The size of these considered gold patterns, i.e., the diameter of the micro-disks is in the range of 900 nm to 1000 nm. The proposed MIM-SPR structure possessing sensitivity of 370 nm per refractive index unit (RIU), can be applicable for a wide variety of plasmonic sensing, in particular for refractometric biosensors.
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