Wentao Qiu

Coreless side-polished fiber: a novel fiber structure for multimode interference and highly sensitive refractive index sensors

A novel fiber structure, coreless side-polished fiber (CSPF), is proposed and investigated to implement multimode interference (MMI) and high sensitive refractive index (RI) sensors. For such CSPF, the part of the cladding and the core of a single-mode fiber are side-polished off so as to make the remained cladding a D-shaped multimode waveguide. The excitation and evolution of MMI in the CSPF are simulated numerically. The simulation results show that the high-order modes excited within the D-shaped multimode waveguide are mainly TE0,1 (TM0,1)~TE0,6 (TM0,6) modes. Moreover, the RI sensing characteristics and the influences of residual thickness and dip wavelength on the sensitivity are investigated both numerically and experimentally. The experimental results show that the CSPF with a residual thickness of 43.1 μm can reach an ultra-high sensitivity of 28000 nm/RIU in the RI range of 1.442~1.444. It is also found that the sensitivity can be further increased by reducing the residual thickness and choosing the dip at a longer wavelength. Thanks to the ultra-high RI sensitivity and the ease of fabrication, the CSPF could provide a cost-effective platform to build high-performance fiber devices of various functions.

Molybdenum disulfide nanosheets deposited on polished optical fiber for humidity sensing and human breath monitoring

One important use of molybdenum disulfide (MoS2) could be in making sensing and detection devices with optical chip or fiber. Here, MoS2 nanosheets coated on side-polished optical fiber (SPF) is proposed, which can enhance the localized interaction between evanescent light of fiber core and MoS2 nanosheets, this can motivate greatly sensing and detection performance. Moreover, the MoS2 nanosheet possesses exceedingly high surface/volume ratio. By combining the MoS2 nanosheets and the side-polished fiber, humidity sensing characteristics has been demonstrated. The optical transmitted power (OTP) of the MoS2-based SPF changes with a negative correlation to the variation of relative humidity (RH) in experiments. The OTP changes of the MoS2-based SPF as an exponential function can reach ~13.5dB (~54 fold enhancement) when the RH ranges from 40%RH to 85%RH. Furthermore, experiments on the monitoring of human breath have also been conducted to evaluate the response time (0.85 s) and the recovery time (0.85 s). The performance comparison between this proposed device and the other recent-developed fiber-optic humidity sensing devices in literature illustrates the superiority of the MoS2-based SPF in humidity sensing and monitoring of human breath, which paves a path for the MoS2 nanosheets to integrate in lab-on-fiber sensing and detection devices.

All light-control-light properties of molybdenum diselenide (MoSe 2 )-coated-microfiber

Molybdenum diselenide (MoSe2) nanosheets are coated on the tapered region of microfiber (MF) to achieve active light control by light with order of mW. The MoSe2 nanosheets are illuminated by 405 nm and 980 nm lasers which change the conductivity of the MoSe2, thus the transmitted power of the guiding light (λ = 1550 nm) within the MF can be controlled. The transmitted optical power of the MF has a relative variation of ~2 dB (0.165 dB/mW) when the 405 nm light is illuminating on the MoSe2 nanosheets with a power ranging from 0 to 11.6 mW. The sensitivities of the 980 nm in-fiber and out-fiber experiments are 0.092 dB/mW and 0.851 dB/mW, respectively. The rise and fall times of the transient response are 0.4s and 0.6s, respectively. Therefore, the guiding light in our MF coated with MoSe2 can be effectively manipulated by the 405 and 980 nm light (order of mW). The MF coated with MoSe2 has potential applications in light sensing and all-optically controllable devices.

Interlinked add-drop filter with amplitude modulation routing a fiber-optic microring to a lithium niobate microwaveguide

We propose and experimentally demonstrate a new electro-optically controllable add-drop filter based on light coupling between a microfiber knot ring (MKR) and a lithium niobate (LN) microwaveguide. In our design, the MKR works as a resonator and routes the resonant light into the LN microwaveguide. The LN microwaveguide, as an excellent intermediary between electronics and optics, is a robust platform that not only enables stable support and manipulation of the MKR but also provides amplitude tunability taking advantage of its electro-optic property. Two add-drop filters with different diameters of the MKR, 1.12 mm, and 560 μm respectively, are studied, and a maximum amplitude tunability of ∼0.139  dB/V is obtained. The results show that this design can be a solution to interconnect a microstructured optical fiber with a microstructured on-chip device and provide an effective method to realize the active on-chip integration of the conventional fiber system.

Azimuth angle orientation by side scattering for side-polishing of photonic crystal fibers

We propose and demonstrate a nondestructive and contamination-free method for azimuth angle orientation of the photonic crystal fiber (PCF) and its application for fiber side-polishing. This technique is based on the interference pattern analysis of the light forward-scattered from the PCF that is side illuminated by a laser beam. The scattering pattern is analyzed by introducing a characteristic value which is the sum over the intensities of the upper-half or lower-half regions of the scattering pattern. The characteristic value correlates closely with the azimuth angle of PCF, which enables characterizing the azimuth angle through scattering pattern analysis. Three kinds of PCFs are studied for the determination of their azimuth angles, and an angular accuracy better than 0.5° is obtained. This method is subsequently applied to orient the angular azimuth in side-polishing of the PCF, and the accuracy of polishing angle is about 0.5°. This technique is nondestructive, contamination-free, easy to implement, and able to serve for in-line angular orientation during the fabrication of PCF-based optical devices and manipulation of the PCF.

Reduced graphene oxide wrapped on microfiber and its light-control-light characteristics

Reduced graphene oxide (rGO) sheet wrapped on the tapered region of microfiber is demonstrated to enhance the interaction between rGO and strong evanescent field of optical fiber. The 405 nm and 980 nm lasers are employed to illuminate the rGO to investigate the response characteristics of the optical transmitted power (λ = 1550 nm) in the MF. The transmitted optical power of the MF with rGO changes with ~1.7 dB relative variation when the violet light is ranging from 0 mW to 12 mW (~0.21dB/mW) in the outside-pumped experiment. And in the inside-pumped experiment, the change of the 980 nm laser power from 0 mW to 156.5 mW makes ~6 dB relative variation power of the transmitted optical powers of the MF with rGO. These results indicate the optical transmitted power of the MF with wrapped rGO can be manipulated by the 405 and 980 nm light (order of mW), which signifies the device can potentially be applied as all optically and versatilely controllable devices.