Pixel super-resolution using wavelength scanning

Abstract

Undersampling and pixelation affect a number of imaging systems, limiting the resolution of the acquired images, which becomes particularly significant for wide-field microscopy applications. Various super-resolution techniques have been implemented to mitigate this resolution loss by utilizing sub-pixel displacements in the imaging system, achieved, for example, by shifting the illumination source, the sensor array and/or the sample, followed by digital synthesis of a smaller effective pixel by merging these sub-pixel-shifted low-resolution images. Herein, we introduce a new pixel super-resolution method that is based on wavelength scanning and demonstrate that as an alternative to physical shifting/displacements, wavelength diversity can be used to boost the resolution of a wide-field imaging system and significantly increase its space-bandwidth product. We confirmed the effectiveness of this new technique by improving the resolution of lens-free as well as lens-based microscopy systems and developed an iterative algorithm to generate high-resolution reconstructions of a specimen using undersampled diffraction patterns recorded at a few wavelengths covering a narrow spectrum (10–30 nm). When combined with a synthetic-aperture-based diffraction imaging technique, this wavelength-scanning super-resolution approach can achieve a half-pitch resolution of 250 nm, corresponding to a numerical aperture of ~1.0, across a large field of view (>20 mm²). We also demonstrated the effectiveness of this approach by imaging various biological samples, including blood and Papanicolaou smears. Compared with displacement-based super-resolution techniques, wavelength scanning brings uniform resolution improvement in all directions across a sensor array and requires significantly fewer measurements. This technique would broadly benefit wide-field imaging applications that demand larger space-bandwidth products.

High-resolution imaging: wavelength scanning enhances resolution

A new way to obtain high-resolution images over wide fields of view that involves scanning the wavelength has been demonstrated by a US team. The resolution of many imaging systems, particularly wide-field microscopes, is limited by undersampling and pixelation. Conventionally, this problem has been remedied by physically shifting the light source, sample or detector. Now, Aydogan Ozcan and co-workers at the University of California, Los Angeles propose a new solution—successively illuminating the sample at a few wavelengths over a narrow range (10–30 nanometres). This method has two main advantages over physical scanning: it requires fewer measurements and results in uniform enhancement of the resolution over the entire sample plane. The researchers experimentally demonstrate the technique on both lens-based imaging systems and lensless holographic ones.