  A wavelength-tunable Optical Fiber Tweezer (OFT) based on a Graded Index
Multimode Fiber (GIMF) with a flat endface is proposed. It is shown that the
design can support a trapping position which is far from the tip of the GIMF
compared with other common optical tweezing methods, hence reducing the
possibility of a contact between the trapped particle and the fiber tip.
Moreover, because of the wavelength dependence of the GIMF design parameters
such the Numerical Aperture (NA), the trapping position can become
wavelength-dependent. Therefore, the trapping position can be tuned over a long
range using a common wave-length tunable laser. The proposed OFT differs from
previous fiber-based demonstrations by using a flat-endface fiber making the
fabrication and experiment quite easier than previously proposed
tapered-endface OFTs.
