VIS-SWIR wideband lens-free imaging

Abstract

Lens-free imaging (LFI) has become an important microscopy tool in many life science and industrial applications. Due to the absence of optical lenses (such as objectives) and accompanying lens aberrations (such as chromatic aberrations), the LFI modality is well suited for optical inspection of microscopic objects in a wide spectral range. However, the relatively restricted spectral sensitivity of CMOS imagers, i.e. from visible (~400 nm) up to near-infrared range (~900 nm), limits the wide spectral use of the technique. Many microscopic samples contain valuable information both in the visible and in the short wave infra-red (SWIR), sometimes in addition to visible (VIS) and near-infrared (NIR). With the recent emergence of cost-effective image sensor technologies such as quantum-dot and graphene-based image sensors with high quantum efficiency in SWIR, new lens-free imaging opportunities are emerging for wideband and high throughput microscopy. We demonstrate for the first time an LFI system based on a quantum-dot image sensor, capable of operating in both the visible and short-wave infrared range. The holograms of the samples are obtained through multiple partially coherent illumination sources in both visible and short-wave infrared (ranging from 405 nm to 1550 nm). The captured holograms are reconstructed to obtain images of the sample in focus. We demonstrate an optical resolution of 3.48 micron in a field of view of 9.6 mm² over the whole spectral range. Our technique mitigates the need for bulky and expensive achromatic imaging optics and offers significant improvements in cost, field-of-view, scalability, and optical resolution to achieve microscopic imaging in both the visible and short-wave infrared spectral range with a simple imaging system. We present in this paper a performance analysis of the system and several potential applications and use cases.