Sensing and Exploiting Static Femto-Newton Optical Forces by a Nanofiber with White-Light Interferometry

Optical force determines the fundamental process of momentum exchange between light and matter. However, owing to the weak mechanical effect of the optical force and relatively large stiffness of optomechanical devices, pico-Newton (10(-12) N) optical force is required to manipulate micro/nanoparticles and the optical response of optical devices. It is still extremely challenging to sense static femto-Newton (fN) optical forces and exploit such forces to actuate micro-optical devices. Here, using a tapered nanofiber (TNF) with a high mechanical efficiency of 2.13 nm/fN, a sensitive and cost-effective scheme is demonstrated to generate, sense, and exploit fN optical force. Strong light coupling from the TNF to a glass substrate can result in a fN repulsive optical force, which can induce a TNF deformation of up to 425.6 nm. Such a large deformation allows white-light interferometry to detect a fN static optical force (5.2 fN). Moreover, the high optomechanical efficiency (15.6 nm/mu W) allows us to all-optically control the signal power at values ranging from 0.09 to 17.1 mu W with only microwatt pump power, which paves the way toward microwatt and fN-optical-force optomechanical devices.