The proposed method adopts a Fourier single-pixel imaging algorithm that includes a differential operation to enable the suppression of out-of-focus background noise. However, due to the utilization of single-pixel imaging, the measurement number of the proposed method is more than that of the traditional multi-mode microscopic imaging method. Through taking the experimental results in our paper as an example and employing Intel(R) Core(TM) i7-10700 CPU @ 2.90 GHz, 32.0 GB memory, it takes about 4 min to reconstruct four multi-mode images with a pixel count of 850×850, and the calculation time depends on the image number of pixels. Therefore, the proposed method is not suitable for dynamic imaging scenes.

In the manufacturing of micro-nano devices such as semiconductor chips, their morphology characterization is helpful for manufacturing process evaluation and defect detection. To obtain complete information on the sample to be tested, one has to use bright field microscopes and dark field microscopes for joint characterization of multiple imaging modes. However, the existing methods to achieve multi-mode imaging need to change the experimental device or adopt a different imaging system, which leads to different fields of view of the acquired multi-mode images and is not conducive to comprehensively analyzing the samples to be tested by synthesizing the multi-mode imaging results. Therefore, it is necessary to develop multi-mode microscopic imaging technology to deal with the above problems. For example, microscopes based on LED array light source and multi-mode microscopic imaging technology using spatial light modulators are utilized to perform different filtering in the spectral plane of traditional microscopes.

Our paper proposes a multi-mode microscopic imaging technology based on the single-pixel imaging principle. It employs wide-field structured light to encode the spatial information of the sample and then leverages each pixel of the camera as a single-pixel detector to reconstruct an Ariy image. Different points on the Airy disk image correspond to different orders of signals diffracted by different object points. Therefore, by designing different digital pinholes to extract the values at different positions on the Airy disk image and arranging them according to the camera pixel coordinates, multi-mode images can be reconstructed, such as bright field images, bias images, and dark field images.

To design the digital pinhole to extract the signals of different diffraction orders of the sample, we should calibrate the conjugate relationship between the camera and the pixels of the spatial light modulator. We adopt an affine matrix to represent the correspondence between the camera and the spatial light modulator, and the calibrated reprojection error is shown in Fig. 7. After the affine matrix is calibrated, digital pinholes can be generated according to the calibrated affine matrix. The proposed method is employed to perform multi-modal imaging on a circuit chip and obtain the multi-modal results shown in Fig. 10. However, due to the directionality of digital pinholes, the reconstructed multimodal results are also anisotropic. To obtain isotropic multi-mode results, we design digital pinholes with the same radius and different directions as shown in Fig. 12 to obtain multiple images and then synthesize these images to obtain isotropic results. The isotropic multi-mode results are shown in Fig. 13. We have also verified through the resolution board experiment (Fig. 14) that the contrast of the bright field images reconstructed by extracting the bias signals is higher than that of the bright field images constructed by extracting the zero-frequency signals.

Our paper proposes a multi-mode microscopic imaging technique based on the single-pixel imaging principle. It adopts each pixel of the camera as a single-pixel detector to reconstruct an Airy disk image, and the values at different positions in the Airy disk image represent different orders of signals diffracted by different object points. The experimental results show that this technology does not need to change the experimental device or replace different microscopes. By designing different digital pinholes, the light intensity values at different positions can be extracted from the single-pixel reconstructed Airy disk images. These light intensity values correspond to different orders of diffraction signals from different object points. By arranging these extracted signals according to the camera pixel coordinates, images of different modes can be reconstructed, such as bright field imaging, bias imaging, and dark field imaging. The fields of view of these multi-mode images are the same, which is conducive to the comprehensive analysis and acquisition of the complete shape characteristics of the samples. As a new computational imaging method, the proposed method is expected to be applied to the offline characterization of micro-nano devices.