An ambient refractive index (RI) sensor based on a microfiber coil resonator (MCR) is proposed. Using the coupling wave theory, the resonant properties of the MCR are theoretically studied. And then, using the finite difference time-domain method, the sensing characteristic of the sensor is investigated and the dependence of sensing characteristic on the MCR parameters is examined as well. Results show that the sensor is extremely sensitive to the ambient RI variation. And, the microfiber diameter determines both the sensitivity and detection limit of the sensor. Further, the rod diameter determines the free spectral range of the MCR resonance spectrum and influences the detection range of the sensor. However, the sensor sensitivity is almost constant with the rod diameter change. So, for ensuring a good performance in actual experiment, the microfiber diameter should range from 400 nm to 1 μm, and the rod diameter should range from 20 μm to 2 mm. This work provides a guideline for future research on the RI sensor based on MCR.
We propose and demonstrate an application of microfiber knot resonator (MKR) in the generation of a stable and uniform single-wavelength erbium-doped fiber laser (EDFL). An MKR was fabricated using a microfiber a few micrometers in diameter. By embedding the MKR to the ring cavity of the EDFL, a laser with a wavelength of 1558.818 nm and a 3-dB linewidth of 0.0149 nm is demonstrated. The side mode suppression ratio of the laser is about 30 dB, and the maximum power fluctuation is about 0.85 dB. The results demonstrate that the MKR can be employed as a high-performance comb filter to realize a stable and uniform fiber laser.
At present, miniaturized, low loss and integrated slow-light elements are the urgent needs for the slow-light technology development. In this paper, we study the slow-ight effects in a compact microfiber coil resonator (MCR) structure and fabricate the compact MCR slow-light element. Furthermore, we test its slow-light properties and find that the optical pulse propagating in the MCR can be delayed about 30 ps. By caculating, we find that the group velocity of the light pulse propagating in the MCR slow-light element can be reduced to about 0.47c (c is the speed of light in vacuum) and the shape of the light pulse passing through the MCR keeps well.
A nanofiber-plane-grating composite slow-light waveguide to achieve wideband slowlight propagation with no distortion is proposed. The waveguide is formed by embedding a tapered nanofiber into a V-groove on a plane-grating surface. By optimizing the waveguide structural parameters, a slow-light effect with bandwidth of about 1453 GHz is obtained. Based on finite-difference time-domain (FDTD) method, we analyze the waveguide’s optical properties and slow-light characteristics. Simulation results show that a picosecond optical pulse propagating in the slow-light waveguide can be delayed for about 980 fs and without distortion. The group velocity of the optical pulse can be reduced to about 0.3c (c is the speed of light in vacuum). This study will provide important theoretical basis and innovative ideas for the development of new-type slow-light elements.
We numerically investigated the pulse trapping in high nonlinear silicon waveguides. The two orthogonally polarized components of the pulse can trap and copropagate as a unit in a silicon waveguide. Our numerical results show that the trapping pulse can stably propagate when the polarization mode dispersion is compensated by shifting the frequencies of two orthogonally polarized components. We also analyze the effects of the free-carrier absorption and initial polarization angles on the pulse propagation in a silicon waveguide. The proposed on-chip trapping pulse in the silicon waveguide exhibits compact configuration and can potentially have important applications in integrated optics.