Metasurfaces & Flat Optics
Structured interfaces with sub-wavelength features enable modulations of phase, amplitude, polarization, dispersion, etc. on demand, leading to a plethora of flat optics and metasurfaces. By controlling the phase-shifting of each meta-atom at wavelength scale, one can realize metasurfaces that would enable complex wavefront engineering. Looking back upon the 9 years development of metasurfaces, several functions and physics of elements or meta-atoms were investigated and used as metasurfaces to improve commercial optical components (lenses, waveplates, filters, and the like).
Imaging & Sensor
Improvement in the accuracy of endoscopic biopsy for small peripheral lesions is necessary if bronchoscopy will play a major role in lung cancer diagnosis. Endoscopic optical coherence tomography (OCT) with commercial catheters that rely on graded-index (GRIN) lenses or ball lenses, however, exhibit strong astigmatism and spherical aberration and thus deviate from diffraction-limited focusing. Shown is an artistic impression of the nano-optic endoscope that uses a metalens, with the ability to modify the phase of incident light at subwavelength level, to enable high-resolution endoscopic imaging at extended depth-of-focus by avoiding monochromatic aberrations. High-resolution three-dimensional images are captured by inserting the nano-optic endoscope into the lungs endo-bronchially visualize airway tissue microstructures. The combination of the superior resolution and higher imaging depth of focus of the nano-optic endoscope is likely to increase the clinical utility of endoscopic optical imaging.
SEM image of a metalens
An individual metalens building block consisting of an amorphous silicon nanopillar on a glass substrate
Structural features of lung tissue are clearly visible, , including moderately scattering epithelium (epi), highly scattering basement membrane (bm), cartilage (car), blood vessel (ves) and alveoli (alv)
Comparison with the state of the art
The ability to tailor the phase at will allows metalenses to be free of spherical aberration and astigmatism.
Structured light refers to the tailoring or shaping of light in all its degrees of freedom, which can be used for micromanipulation and enhancing the capacity of optical communication channels. Chiral light is foremost among the family of structured light fields which carries spin angular momentum and orbital angular momentum (OAM). The metasurface J-plate is a metasurface converter for optical states that couples between arbitrary spin and optical angular momentum states of light in a compact planar. J-plates overcome a key limitation in alternative technologies such as Q-plates and spatial light modulators: conjugate symmetry of light’s angular momentum. And the relatively small pixel size of J-plates improves the beam quality, efficiency, and capability of generating higher OAM states.
Using a J-plate, a new metasurface laser that produces high-purity and non-symmetric super-chiral light never yet observed from lasers, creating of arbitrary spin-orbital chiral states of structured light at the source. Our laser conveniently outputs in the visible, offering a compact and power-scalable source that harnesses intra-cavity structured matter for the creation of arbitrary chiral states of structured light. The metasurface-enhanced laser is a new milestone in the history of structured light lasers as it breaches spin-orbit coupling symmetry as well as sets up a novel record for what high-purity and high-order OAM states can be created from a laser.