Rotation of microscopic objects in fiber optic trap

Due to easy integration with microfluidic devices, fiber optical trapping is finding increasing use to immobilize microscopic objects for physical and spectroscopic analysis of samples in solution. Though conventional microscope objective based laser spanners (based on transfer of spin or orbital angular momentum) are being employed for rotational manipulation of microscopic objects, the working distance inside microfluidic channel is limited in depth. Recently, we have demonstrated fiber optic tweezers for in-depth trapping of microscopic objects. Here, we demonstrate the development of a fiber optic spanner for rotation of microscopic objects. This single-mode fiber optics based method does not require special structure or optical properties of the sample to be rotated. Trapping and simultaneous rotation of microscopic objects around axis perpendicular to optic axis could be achieved. The rotation speed of the trapped object could be changed by adjusting the laser beam power coupled to the fiber optic trap. Since the fiber optic spanner could be easily integrated onto a microfluidic platform, the proposed configuration can find potential applications in lab-on-achip devices and tomographic imaging.