  Using optical tweezers and a haptic device, microspheres having diameters
ranging from 3 to 4 um (floating in a fluid solution) are manipulated in order
to form patterns of coupled optical microresonators by assembling the spheres
via chemical binding. For this purpose, biotin-coated microspheres trapped by a
laser beam are steered and chemically attached to an immobilized
streptavidin-coated sphere (i.e. anchor sphere) one by one using an XYZ piezo
scanner controlled by a haptic device. The positions of all spheres in the
scene are detected using a CCD camera and a collision-free path for each
manipulated sphere is generated using the potential field approach. The forces
acting on the manipulated particle due to the viscosity of the fluid and the
artificial potential field are scaled and displayed to the user through the
haptic device for better guidance and control during steering. In addition, a
virtual fixture is implemented such that the desired angle of approach and
strength are achieved during the binding phase. Our experimental studies in
virtual and real environments with 8 human subjects show that haptic feedback
significantly improves the user performance by reducing the task completion
time, the number of undesired collisions during steering, and the positional
errors during binding. To our knowledge, this is the first time that a haptic
device is coupled with OT to guide the user during an optical manipulation task
involving steering and assembly of microspheres to construct a coupled
microresonator.
