Metasurfaces have gradually represented powerful abilities to manipulate the amplitude, phase, polarization as well as orbital angular momentum of output light with subwavelength resolution. Due to the subwavelength pixel size, the reconstructed images of metasurface holography can obtain higher resolution and large field of view compare to traditional holography based on spatial light modulator. Meanwhile, the unwanted diffraction orders can also be eliminated.
Benefiting from the powerful multi-dimensional light field manipulation ability provided by the metasurfaces, multiple independent holograms can be encoded into single metasurface and enhance the information capabilities successfully. Besides, the metasurface holographic imaging method also paves the way to realize beam shaping in miniaturized optical systems. Therefore, metasurface holography is of the great research value.
With the development of quantum information, it is a natural idea to apply the metasurface holography technology to the compact quantum information systems. The single photon light source, as a typical quantum light source, has a special property: wave-particle duality. The spatial distribution of single-photon wave packets could be described by the quantum wave function. When quantum observation is performed on a single photon, the quantum wave function will collapse to a certain eigenstate.
Most of the current research on metasurface holography imaging are realized under laser illmumination. However, acquiring holographic images with single-photon light source illumination has not been realized. In addition, how wave-particle duality is reflected in the interaction of single photon with the metasurface also needs to be further investigated.
To solve the above problems. The research group led by Prof. An-Ning Zhang cooperated with Prof. Ling-Ling Huang from the Beijing Institute of Technology. They worked together to reduce the loss of quantum light source by optimizing the experimental light path and using quantum state modulation theory to realize metasurface holography based on quantum light source. The relevant research results are published in Photonics Research, Volume. 10, Issue 11, 2022 (Jia-Zhi Yang, Rui-Zhe Zhao, Zhe Meng, Jian Li, Qing-Yuan Wu, Ling-Ling Huang, An-Ning Zhang. Quantum metasurface holography[J]. Photonics Research, 2022, 10(11): 2607).
Based on a modified Gerchberg–Saxton algorithm, multiple holograms with quantified phase relations are generated and encoded into different polarization channels of single metasurface. The reconstructed holographic images are successfully obtained under laser illumination firstly. Then a metasurface holographic experimental device under quantum light source illumination as well as raster scan detection is built, as shown in Fig. 1.
The quantum light source used in this work is heralded single photon source. One signal photon is used to predict the existence of another idle photon and can be detected by a detector. In addition, we employ another detector to monitor the photon count rate reflected by the polarization beam splitter before the metasurface. By adjusting the reflected photon count rate to the minimum, we achieved high photon utilization.
Fig. 1. Metasurface holographic experimental setup using quantum light source and raster scan.
By controlling the polarization states of input and output, the reconstructions of images in different areas can be realized, and the results are shown in Fig. 2. For a single photon, its propagation satisfies the description of the quantum wave function. The choice of the input and output polarization state is to project the quantum wave function to a specific measurement basis. As a result, the quantum state will collapse. It will cause a change in the quantum wave function of the single photon, not just a strength reduction.
As shown in Fig. 2, the reconstructed images under quantum light source are basically consistent with the results under laser illumination. This result shows that the quantum light will interact with the entire metasurface sample when passing through it. In other words, a single photon will be modulated by the entire metasurface sample. This phenomenon satisfies the description of quantum wave function, indicating that quantum wave function can be modulated by subwavelength structure. This conclusion will effectively expand the application of metasurface in quantum control.
Fig. 2. Imaging results. The first line is the simulation result, the second line is the result of laser illumination and CCD imaging, and the third line is the result of quantum light source illumination and raster scan imaging.
Professor Ling-Ling Huang believes that the use of quantum light sources in metasurface computer-generated holography is of great significance to metasurfaces fields and quantum imaging fields. Metasurface has attracted much attention in recent years due to its special subwavelength structure and light field manipulation ability. Quantum light sources have also received more and more attention with the development of quantum technology. Combining quantum light sources and metasurface holography will expand the application field of quantum light sources, and is expected to provide new ideas and visions for the design of metasurface.