Ghost Identification for QR Codes and Fingerprints with Thermal Light Modulation

Abstract

Ghost imaging with thermal light is a well-known imaging technique in which the light beam used for image reconstruction does not necessarily interact with the object. However, ghost imaging is generally time-consuming due to data acquisition and complex algorithm. Thus a fundamental question arises as to whether we can realize object identification without the need of reconstructing the full ghost images. Here we present a protocol of thermal-light-based object identification in a nonlocal manner, i.e., ghost identification, to answer this question positively. We employ a holography-type method to add an auxiliary planar phase together with the conjugate Fourier spectrum of the test object to the thermal light source, which revives the coherent transfer of complex spectrum from thermal light modulation to the second-order correlation function, regardless of no entanglement. In our experiment, we succeed in demonstrating the fairly good performance of ghost identification for both simple geometric objects and quick response codes, and particularly for fingerprints. Our protocol can find direct applications in secure biosensing and covert detection where very low light illumination levels are needed.