  Confocal microscopy, a critical advancement in optical imaging, is widely
applied because of its excellent anti-noise ability. However, it has low
imaging efficiency and can cause phototoxicity. Optical-sectioning structured
illumination microscopy (OS-SIM) can overcome the limitations of confocal
microscopy but still face challenges in imaging depth and signal-to-noise ratio
(SNR). We introduce the concept of confocal imaging into OS-SIM and propose
confocal structured illumination microscopy (CSIM) to enhance the imaging
performance of OS-SIM. CSIM exploits the principle of dual photography to
reconstruct a dual image from each pixel of the camera. The reconstructed dual
image is equivalent to the image obtained by using the spatial light modulator
(SLM) as a virtual camera, enabling the separation of the conjugate and
non-conjugate signals recorded by the camera pixel. We can reject the
non-conjugate signals by extracting the conjugate signal from each dual image
to reconstruct a confocal image when establishing the conjugate relationship
between the camera and the SLM. We have constructed the theoretical framework
of CSIM. Optical-sectioning experimental results demonstrate that CSIM can
reconstruct images with superior SNR and greater imaging depth compared with
existing OS-SIM. CSIM is expected to expand the application scope of OS-SIM.
