SMART - Singapore MIT Alliance for Research and Technology

Singapore-MIT Alliance for Research & Technology

Biosystems and Micromechanics

BioSystems and Micromechanics (BioSyM) Inter-Disciplinary Research Group

Dielectric metamaterial magnifier for far-field imaging

Biological imaging at the molecular and cellular scales requires resolving of features in the order of 10’s of nanometers. However, the fundamental diffraction limit restricts the resolution of a conventional optical microscope to about half a wavelength (≈200 nm in air) due to the loss of high spatial frequency information carried in the evanescent waves. To break this diffraction limit, near-field scanning microscopy and far-field time-sequential fluorescence nanoscopy have been developed, but a generally slow scanning or sequentially recording procedure in principle prevents users from observing dynamical processes which are of fundamental importance in many biological and medical studies. It is strongly desirable, therefore, to develop a real time imaging technique that can capture subwavelength information, especially on the scale of sub-100 nm.

SMART researchers have proposed (as described in a recent publication: Zhang Baile and George Barbastathis, Optics Express, 18, 11216, (2010)) a dielectric metamaterial magnifier with a novel gradient refractive index (GRIN) design that magnifies subwavelength details and deliver information into the far field. Different from the previous superlens and hyperlens, this magnifier produces a virtual image containing magnified subwavelength details, rather than a real image in front of the object. Our design does not rely on surface plasmon resonance between metal and dielectric, and thus isotropic dielectric materials with negligible loss can be used. Moreover, it works over broadband, creating a color image, which is suitable for molecular fluorescence imaging.

(a) Geometry of the 2D GRIN magnifier. (b) A stratified medium created from
transformation. (c) The layer with extended thickness pushes the left half part of the stratified
medium to the left. (d) Profiles of refractive index in terms of e˜ x. The blue solid line
represents the case in (b). The red dotted line corresponds to the case in (c).