We present for the first time a wavelength tunable fiber-based optical tweezer using a graded index multimode optical fiber (GIMF). Optical fiber tweezer is a viable replacement for the bulky objective-based tweezers because of the low-cost and user-friendly operation and maneuverability. The proposed optical fiber tweezer consists of a GIMF spliced to a single mode fiber into which a wavelength tunable laser is launched. The exit field at the end-facet of the GIMF is used for tweezing. The GIMF setup is capable of generating a tunable-distance optical trap over a hundred microns by just tuning the laser wavelength. The position of the optical trap can also be customized with the proper design of the GIMF and straining the fiber. The length of the GIMF also plays an important role in the operation of the device. This length needs to be fined-tuned only over less than 500 microns due to the self-imaging properties of the beam propagating in a GIMF; therefore, the necessary length adjustments can be easily done by polishing the end-facet of the fiber. The numerical results also show that as the optical trap moves farther away from the GIMF tip, the optical trap gets weaker. The results also show that the minimum input power to meet the stability conditions for a particle with a radius of 0.1 micron is around 400 mW.
Esmaeil Mobini and Arash Mafi, "Design of a wavelength-tunable optical fiber tweezer (Conference Presentation)," Proc. SPIE 10120, Complex Light and Optical Forces XI, 1012019 (Presented at SPIE OPTO: February 02, 2017; Published: 28 April 2017); https://doi.org/10.1117/12.2252774.5397967380001.
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