With real-time sensing and label-free nature, optical sensors based on the resonance wavelength shift with respect to the refractive index change have drawn significant attention for biochemical sensing. Among those RI sensors, one-dimensional photonic crystal nanobeam laser provides extremely high Q-factor, small mode volume, and small footprint and so various types of NBs have been investigated and researched. However, as long as the NB is on the parent chip, the portability and the utility as a sensor is limited. In this thesis, an optical fiber is selected as a substrate platform for the NB to enhance its functionality as an RI sensor. Furthermore, by introducing a second gating to the NB, a band-folding effect is obtained, and so the power collection efficiency of the fiber is improved. With calculated Q-factor and observed sensitivity of ~152nm/RIU, the figure-of-merit of ~570 is achieved.