Surface Plasmon Resonance Sensor Interogation with Cladding Modes Excited by Tilted Fiber Bragg Grating

The objective of this Thesis is to develop novel schemes in surface Plasmon resonance (SPR) sensing with Bragg gratings. The thesis focuses on research studies on the sensing characteristics of four novel configurations of SPR and surrounding refractive indices (SRI) sensors. Firstly, a novel SRI measurement scheme has been demonstrated using a double-clad fiber coupler (DCFC) and a fiber Bragg grating (FBG) to capture cladding modes in reflection. The optical spectra and power in the cladding modes are obtained through the use of a specially designed DCFC spliced to a highly reflective FBG written into slightly cladding-etched standard photosensitive single mode fiber to match the diameter to the inner cladding of the DCFC. The device is capable of capturing low and high order backward propagating cladding modes simply and efficiently. The device is capable of measuring the SRI with an extremely high sensitivity with a total power drop by ≈ 91% of its initial value and a resolution of 1.433×10-5 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. Secondly, a novel optical fiber SPR sensor scheme is demonstrated using reflected guided cladding modes captured by the above mentioned DCFC, and excited in a gold coated fiber with a tilted Bragg grating (TFBG). This new interrogation approach which is 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 spectrum and also in the transmitted spectrum as well, making it far easier in comparison with previous standard techniques which use the transmission spectrum. 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.