Graded-index Optical Fiber Tweezers With Long Manipulation Length Research

With advantages of small size, easy of use, low cost, easy operation and other characteristics, optical fiber tweezers(OFT) can be used to capture, select, manipulate micro and nano particles, and have a wide range of applications in biology, medicine and related fields. It might even damage the biological samples due to a short manipulation distance(MD) of the OFT. Therefore, OFT with a long MD is meaningful for realizing a truly noncontact optical manipulation. Long manipulation length is critical for optical fiber tweezers to enhance the flexibility of non-contact trapping. In this paper, the method of fiber optical tweezers to capture cell with long distance are studied.In this paper a long manipulation distance of more than 40 μm is demonstrated experimentally by the graded-index fiber(GIF) tweezers with a large cone angle of 58°. The long manipulation distance is obtained by introducing an air cavity between the lead-in single mode fiber and the GIF based on the graded-index fiber optical tweezers. By adjusting the length of air cavity to change the distance of focus point near the fiber taper and it can make any length of GIF taper to stable optical trapping. It increase the utilization rate of etched GIF taper. The light field near the tip of the probe and in the cavity are numerically calculated.The influence of the cavity length and the GIF length on the light distribution and the focusing length of the GIF taper is investigated numerically, which is helpful for optimizing the parameters to perform stable optical trapping.Graded-index optical tweezers is fabricated by chemically etching a GIF taper and air cavity is fabricated by capillary glass tube. In the experiment we demonstrated the stable optical trapping of yeast cells. With the air cavity length of 100 μm, the stable optical trapping of a yeast cell was observed at a background flow rate of 12μm/s. The manipulation distance is more than 40 μm and MD is 10 times longer, compared with the previous graded-index optical tweezers experiment. The stable optical trapping of yeast cells can also be demonstrated by suddenly moving the GIF taper towards the cell. In another experiment with the same GIF taper and same cell, the manipulation length is increasing by adjusting the laser power. It proves this optical tweezers can manipulate cells with long distance. With these experiments, the easy-to-use and high repeatability of this optical tweezer can be well proved. By analysising the focuse force distribution in the axis and the Stokes force and comparing the experiment data with calculated data, it proves the long manipulation length is available. This kind of optical fiber tweezers has advantages including low-cost, easy-to-fabricate and easy-touse.