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Morphology and motility are essential criteria for assessing sperm viability. However, the human sperm head is small (∼3–4 μm) and requires a relatively high-magnification microscope objective, while the sperm flagella (∼45 μm) are poorly visible with complex 3D properties. Microscopic dynamic observation of intact sperm in 3D is challenging. Conventional inspection methods with a limited depth of field are inadequate for this issue. To provide a solution to this critical need, we develop pixelated polarization-based parallel phase-shifting digital holographic microscopy for the 3D dynamic observation of human sperm. Compared to conventional holographic imaging, this approach can effectively separate the object wavefront and avoid image quality degradation while fully exploiting the spatial bandwidth of the camera. We propose the use of the Stokes parameter reconstruction method to reconstruct the object wavefront and investigate the effect of the sampling interval on the system resolution by spectral analysis. The methodology achieves the retrieval of the 3D trajectory and motion parameters of sperm and reconstructs the sperm head orientation and the thin, highly-dynamic flagellum. The system allows for more comprehensive information on sperm motility and morphology, which is significant for male reproductive research. It also has significant potential for 3D dynamic observation of micro-organisms.

Optical tweezers are constantly evolving micromanipulation tools that can provide piconewton force measurement accuracy and greatly promote the development of bioscience at the single-molecule scale. Consequently, there is an urgent need to characterize the force field generated by optical tweezers in an accurate, cost-effective, and rapid manner. Thus, in this study, we conducted a deep survey of optically trapped particle dynamics and found that merely quantifying the response amplitude and phase delay of particle displacement under a sine input stimulus can yield sufficiently accurate force measurements. In addition, Nyquist–Shannon sampling theorem suggests that the entire recovery of the accessible particle sinusoidal response is possible, provided that the sampling theorem is satisfied, thereby eliminating the requirement for high-bandwidth (typically greater than 10 kHz) detectors. Based on this principle, we designed optical trapping experiments by loading a sinusoidal signal into the optical tweezers system and recording the trapped particle responses with 45 frames per second (fps) charge-coupled device (CCD) and 163 fps complementary metal–oxide–semiconductor (CMOS) cameras for video microscopy imaging. The experimental results demonstrate that the use of low-bandwidth detectors is suitable for highly accurate force quantification, thereby greatly reducing the complexity of constructing optical tweezers. The trap stiffness increases significantly as the frequency increases, and the experimental results demonstrate that the trapped particles shifting along the optical axis boost the transversal optical force.

The division-of-focal-plane (DoFP) polarimeter can quickly and effectively obtain the polarization information of light in real time, where Stokes parameter reconstruction is a critical issue. Many reconstruction methods have been proposed to address this; however, their performance tends to degrade in the presence of noise. Thus, it is significant to clarify the noise-induced error in Stokes parameter reconstruction. In this work, we investigate the link between the noise-introduced error and the reconstruction method and develop a simple and effective way to evaluate the noise robustness of reconstruction methods. Furthermore, a novel experimental scheme of noise measurement, to the best of our knowledge, is designed to verify the theory. Based on the criterion, our scheme guides the selection of reconstruction methods and further promotes the practical application of the DoFP technique.