A simple and highly sensitive temperature sensor based on an isopropanol-sealed optical microfiber coupler (OMC) is reported. Due to the high thermo-optic coefficient of isopropanol, the temperature sensitivity of the OMC can be effectively improved by immersing the OMC into isopropanol. The refractive index change of isopropanol is caused by the surrounding temperature variation which in turn allows highly sensitive temperature sensing. Theoretical analysis demonstrates that the temperature sensitivity increases quickly with the decreasing OMC waist diameter. Temperature sensitivities at different waist diameters exhibit high consistency with the theoretical results. When used for temperature sensing, the transmission spectrum blueshifts as the surrounding temperature increases. The highest sensitivity of −5.89 nm/°C is achieved at the waist diameter of 2.2 μm. This is the most sensitive OMC based temperature sensing device reported so far. Such a compact size, low cost, and highly sensitive device may widen the application range of OMC.

A temperature and refractive index simultaneous measurement sensor based on an optical microfiber coupler (OMC) combined with a polarization maintaining fiber (PMF) is proposed and experimentally demonstrated. The OMC-PMF sensor is fabricated by inserting a section of PMF between two output ports of the OMC. The interference spectrum of the OMC-PMF sensor has different responses to temperature and refractive index variations. Temperature and the refractive index can be measured by monitoring the dip intensity variation and the dip wavelength shift of the interference spectrum, respectively. The experimental results show that the refractive index sensitivity is 12 020 nm/RIU, and the temperature sensitivity is 0.88 dB/°C upon increasing temperature from 35 °C to 41 °C.

Using optical fiber devices at the terminal is an important means to improve the performance of free space optical communication systems. We proposed a Fraunhofer diffraction integral based method to calculate the coupling efficiency between spatial light and few-mode fiber, and studied the influences of alignment tolerance on coupling efficiency. Numerical simulations confirm that the results obtained by this new method are consistent with the traditional calculation method. What is more, a few-mode fiber has flatter response characteristics to F-number mismatch, fiber lateral offset and defocus. Compared with single mode fiber, few-mode fibers can not only improve the maximum coupling efficiency, but also their coupling efficiency is much less sensitive to deviations from ideal conditions, thereby making them a more practical option for real world applications.

We report on the first demonstration of a single-fiber optical tweezer that is utilized to stabilize and control the liquid droplet for dye lasing. In order to trap a liquid droplet with a diameter of 15-30 μm, an annular core micro-structured optical fiber is adopted. By using wavelength division multiplexing technology, we couple a trapping light source (980 nm) and a pumping light source (532 nm) into the annular core of the fiber to realize the trapping, controlling, and pumping of the oil droplet. We show that the laser emission spectrum tunes along the same size as the oil droplet. The lasing threshold of the oil droplet with the diameter of 24 μm is 0.7 μJ. The presented fiber-based optical manipulation of liquid droplet micro-lasers can be easily combined with the micro-fluidic chip technology and also may extend the application of optical fiber tweezers for micro-droplet lasing technology in the biological field.

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