Lensless single-pixel imaging by using LCD: application to small-size and multi-functional scanner

Single-pixel imaging commonly uses a spatial light modulator (SLM) to encode a scene's spatial information into a one-dimensional light signal sequence so that a single-pixel detector can be used to capture a scene. Digital micromirror device, liquid crystal on silicon, or light emitted diode matrix is a common choice of SLM, but it requires a certain lens system in order to project the structured light pattern that is generated by the SLM onto the scene. Using a lens would not only lead to aberration but also result in difficulty for establishing a compact imaging system. Therefore, we propose to use a liquid crystal display (LCD) as an intensity-only SLM to conduct structured illumination. As such, single-pixel imaging can be performed in a lensless way. As an instance of the proposed technique, a small-size and multi-functional scanner is designed and established to prove the lensless single-pixel imaging concept. As experimentally demonstrated, the single-pixel scanner can not only achieve grayscale and true-color scanning as a typical scanner does, but also achieve distinctive functionalities, such as accurate optical character recognition from under-sampled data, on-the-fly encryption, and genuine document identification. This compact scanner is as thin as 2.48 millimeters. The proposed lensless single-pixel imaging technique might find applications in various fields.