Investigation of adiabatically tapered optical microfiber refractometric sensor

• Main Author: Guan, Weiwei.
• Other Authors: Tjin Swee Chuan
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: http://hdl.handle.net/10356/54611
• Institution: Nanyang Technological University

Two adiabatically tapered microfiber sensors are investigated in this project; one is based on microfiber Bragg grating (MFBG) and the other is based on the theory of surface plasmon resonance (SPR). The main application of these two microfiber sensor discussed here is the environmental sensing (refractive index sensing). MFBG sensor is manipulated by tapering general optical fiber into microfiber. Decreasing the cladding diameter can effectively increase the evanescent field so that the MFBG sensor is sensitive to the variation of ambient refractive index (RI). According to the property of Bragg grating, a sharp peak at the reflection spectrum can be observed. When the ambient RI increases, it influences the effective refractive index of the core grating, thus Bragg wavelength shows a significant shift towards right hand side. It was reported that the sensitivity is non-linearly related with the variation of ambient RI. According to calculation, the sensitivity can be 3 – 5 times at higher RI than the sensitivity at lower RI. Surface plasmon resonance (SPR) microfiber sensor is another topic discussed in this project. SPR describes the coherent oscillation at the interface of metal layer and dielectric. The oscillation leads to large power loss so that a sharp dip shows up on the transmission spectrum at the resonance wavelength. Since the evanescent field is contacting the ambient environment, it is very sensitive to the variation of ambient RI.The sensitivity can be as high as thousands nm/UIR. When there is a slight change of ambient RI, a significant shift of resonance wavelength occurs on the transmission spectrum. This is the theory and the idea of the experiment design about this topic. These two kinds of microfiber sensors can be both applied into detection of solution deterioration or chemical reactions in solution. The application of SPR sensor can be much broader due to its extremely high sensitivity. Except for bio-sensing, other applications can be further explored.