Light focusing microprobes for biomedical and photonics applications based on integrated microsphere arrays

The task of development of compact light-focusing tools for biomedical and photonics applications is challenging due to the multimodal structure of beams propagating in flexible delivery systems of such devices. In this study it is shown that integration of microspheres inside hollow waveguides or capillaries permits compact focusing of light from multimodal sources. Experimental studies were performed for variety of spheres with sizes from 10 to 300 μm with refraction indices ranging from 1.47 to 1.9. It is shown that for high index (1.9) spheres the smallest focused spots can be obtained in chains containing odd number of spheres. It is also demonstrated that increasing the length of such chains generally provides smaller focused spot sizes at the expense of the transmitted power. The underlying optical properties are shown to be based on the filtering of the modes with the best focusing properties in such structures. It is demonstrated that under contact with tissue such structures allow obtaining focused beams with high throughput and wavelength-scale dimensions that can be used for developing novel ultra-precise laser surgical tools.