An optical fiber refractive index (RI) sensor based on open microcavity Mach-Zehnder interferometer (OMZI) and fiber ring laser (FRL) is proposed and demonstrated experimentally. The OMZI is manufactured by splicing a tiny single mode fiber (SMF) segment with multi-mode fiber (MMF) joints laterally. The large offset structure forms an open microcavity which can be filled with the liquid under test. Through inserting the OMZI into an erbium-doped FRL, the RI measurement can be achieved by discriminating the lasing wavelength, and the detection limit (DL) can be effectively improved owing to the laser sensing spectrum with narrower 3-dB bandwidth and higher optical signal-to-noise ratio (OSNR). Experimental results show that the output laser wavelength has a linear response to the RI change with a sensitivity of −2947.818 nm/RIU during the range of 1.33302~1.33402, and the DL is as low as 5.89×10−6 RIU. Compared with other optical fiber RI sensors, the proposed fiber laser RI sensor with an open microcavity has the advantages of small size, high sensitivity and low DL, making itself a competitive candidate for the microfluidic RI measurement in biochemistry.
We propose and demonstrate single optical fiber tweezers based on graded-index multimode fiber (MMF) which can adjust captured microparticles position in pendulum-style. The optical fiber tweezers can capture the yeast cell stably in three dimensions and swing the yeast cell 57.5 degrees around the fiber tip like a pendulum. The optical fiber tweezers are fabricated by asymmetrical fiber heating fused and tapered method. The capture and swing functions of the proposed optical fiber tweezers provide a new manipulation method for biomedical field.
A fiber-optic distributed acoustic sensing method based on phase-sensitive optical time domain reflectometry combined with dual-chirped pulse and micro-reflective fiber Bragg grating (FBG) is proposed. The sensing fiber consists of a micro-reflective FBG with uniform spatial interval. The micro-reflective FBG help to gain a high signalto-noise ratio light signal, comparing with the Rayleigh backscattering (RBS) light of optical fiber itself. The dualchirped pulses are generated by a time delay, whose corresponding spatial interval approximately equal to twice the spatial interval of adjacent micro-reflective FBG. A beating signal is generated due to the interference of the two identical chirped pulses reflected by the micro-reflective FBG array. Acoustic disturbance between the microreflective fiber gratings will change the phase of the beating signal and the interference waveform will shift. Quantitative measurement can be achieved by directly demodulating the beating signal through using a crosscorrelation algorithm. By using such a method to perform the sensing for the micro-reflective FBG array, distributed quantitative measurement can be realized with only direct detection scheme and simple demodulation algorithm. Experiment are carried out with 2km fiber and PZT vibration simulation and the results verified the effectiveness of our method.
Coherent Anti-Stokes Raman Scattering (CARS) microscopy has attracted lots of attention because of the advantages, such as noninvasive, label-free, chemical specificity, intrinsic three-dimension spatial resolution and so on. However, the temporal overlap of pump and Stokes has not been solved owing to the ultrafast optical pulse used in CARS microscopy. We combine interference spectrum of residual pump in Stokes path and nonlinear Schrodinger equation (NLSE) to realize the temporal overlap of pump pulse and Stokes pulse. At first, based on the interference spectrum of pump pulse and residual pump in Stokes path, the optical delay is defined when optical path difference between pump path and Stokes path is zero. Then the relative optical delay between Stokes pulse and residual pump in PCF can be calculated by NLSE. According to the spectrum interference and NLSE, temporal overlap of pump pulse and Stokes pulse will be realized easily and the imaging speed will be improved in CARS microscopy.
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