Imaging represents the most direct and pervasive method by which individuals can obtain, record, and transmit information. In the contemporary era, in which a single mobile phone is ubiquitous, the traditional method of imaging is not a foreign concept to the general public. In the conventional imaging process, the light source illuminates the object, the reflected light of the object carries the information of the object into the array detector, and the array detector responds and generates an image. The term "ghost imaging" is derived from the fact that in this imaging system, the object to be imaged and the surface array detector are positioned in two distinct ways. The light emitted by the illuminated object is not incident on the array detector; rather, it is collected by the single-pixel detector, which is not spatial-resolved. Furthermore, the light incident on the array detector never directly interacts with the object. The fundamental principle underlying ghost imaging is the second-order correlation of the light source. The second-order correlation of the light source is reflected in the joint measurements of the two detectors, which means that the image of the object can only be reconstructed by the joint measurements of the two detectors and not by either of the two detectors individually.
The most commonly utilised light sources in ghost imaging systems are entangled photon pairs, which are prepared through a spontaneous parametric down-conversion process, and pseudo-thermal light sources, which are generated by laser incidence on a rotated ground glass. Ghost imaging systems based on entangled photon pairs apply the quantum properties of entangled photon pairs to the field of imaging, thereby providing a novel platform for the study of the fundamental principles of quantum mechanics and enhance imaging performance by taking advantage of the quantum advantages of entangled sources. The evolution of classical ghost imaging has led to the emergence of computational ghost imaging, which has been integrated with computer techniques such as compressed perception and deep learning, thereby offering solutions to numerous real-world applications.
In response to the current research status, Prof. Baoqing Sun's group at Shandong University and Prof. Lixiang Chen's group at Xiamen University have traced the origin and development of ghost imaging and focused on reviewing the application of ghost imaging in the field of holographic imaging as well as the technological advances brought about by ICCD. The related research has been published in Chinese Optics Letters, Volume. 22, Issue. 11, 2024 (P. Li, et al., "Ghost imaging, development, and recent advances."), and was selected as the cover paper of the issue. Prof. Baoqing Sun of Shandong University and Prof. Ideal Chen of Xiamen University are the corresponding authors of the paper, and Dr. PeiMing Li, Postdoc. Xiaodong Qiu and Dr. Xiao-Jin Chen are the co-first authors.
The paper reviews the work in the field of ghost imaging over the past three decades from three main aspects: the origin of ghost imaging, its application in holography, and the application of ICCD cameras in ghost imaging systems. The paper begins with a summary of the development of ghost imaging in the decade since its inception. During this period, the controversy over the nature of ghost imaging has been the focus of research. The first realization of ghost imaging used entangled photon pairs prepared by a spontaneous parametric down-conversion process as a light source, which led to the discussion of whether entanglement is a necessary condition for ghost imaging. With experimental and theoretical work, ghost imaging based on pseudo-thermal light sources was realized, and it was gradually recognized that the essence of ghost imaging is the second-order correlations of the light field, not entanglement. This phase of work facilitated the understanding of the higher-order coherence of light fields and paved the way for the subsequent development of ghost imaging. The paper then reviews the latest findings of ghost imaging extended from pure amplitude target objects to complex amplitude objects, i.e., ghost holography. Utilizing the correlative nature of quantum light sources, traditional holography is reproduced at the single-photon level. Ghost holography broadens the application of ghost imaging to amplitude and phase acquisition of complex-amplitude objects. Ghost holography is also of interest in the field of quantum state measurements due to its ability to efficiently acquire phase information. Finally, the paper reviews the boost brought by ICCD to ghost imaging. Using ICCD to obtain full-field-of-view images in only one shot completely escapes the constraints of single-pixel scanning and facilitates fast and accurate capture of signaling photons. The application of ICCD in ghost imaging improves detection efficiency and provides a great impetus to the development of ghost imaging.
It is our intention that this review will prove an invaluable source of information for anyone seeking to gain insight into the historical development, current status and potential future applications of ghost imaging. It is our hope that our work will be perceived as impressive and will have broad appeal to those working in related fields.
