Tianlong Man

Quantitative evaluation of spatial phase light modulator characteristics in Fresnel incoherent correlation holography

Fresnel incoherent correlation holography (FINCH) is one of the methods for recording holograms of 3D samples under incoherent illumination. The FINCH combines the theory of spatial self-coherence and the in-line phase-shift technology together to form a complex hologram. A spatial phase light modulator (SPLM) plays important roles as the dynamic diffraction optical element (DOE) and phase shifter. When the incoherent light generated from each object point of the 3D samples incidents to a SPLM, it can be split into two spatial self-coherent beams with different curvatures. The hologram caused by these two beams can then be captured by an image detector. Three holograms with different phase shift are recorded sequentially for eliminating the zero-order and twin image, and then a complex valued hologram is obtained by superposing the three holograms. In this paper, the modulation characteristics of SPLM and phase shift error in FINCH are investigated. Based on digital holography, phase modulation characteristics of SPLM are measured under coherent and narrow-bandwidth incoherent illumination respectively. Phase shift error due to quasi monochromatic light illumination is then analyzed in FINCH. The effect of phase shift error on the quality of reconstructed image is also investigated. It is demonstrated the FINCH setup has a smaller phase shift error by experiment.

Effect of phase-shift step on hologram reconstruction in Fresnel incoherent correlation holography

Fresnel Incoherent Correlation Holography (FINCH) enables holograms to be created from incoherent light illumination of 3D objects. The optical setup of FINCH is usually simple and compact owe to its in-line geometry while the reconstruction of hologram suffers from the obstruction of zero-order item and twin image. Phase-shift technology is combined with FINCH in order to obtain zero-order-free and twin-image-free reconstruction. Three-step phase-shifting is adopted in all the publications of FINCH and the application of other multi-step phase-shift technology in FINCH are not investigated yet. The Fresnel holograms are sequentially recorded with different multi-step phase-shifting (including four, three, and two-step) to form the complex hologram and the quality of the reconstructed images are compared by simulations and experiments respectively in this study. Several parameters including resolution, SNR and normalized cross-correlation are applied to evaluate the quality of reconstruction images. Although various noises would be introduced by the optical elements and the experimental environment in practice, four-step phase-shifting provides the best quality of the reconstructed image but the system resolution is not different from others. In addition, the influence of different phase shift plus to the quality of reconstruction images in the three-step phase-shifting FINCH is investigated and the results show that the quality of reconstruction images which use the π/2 is better than that 2π/3.

Self-interference compressive digital holography with improved axial resolution and signal-to-noise ratio

Fresnel incoherent correlation holography (FINCH) was proposed to break the barrier of spatial incoherent digital holographic imaging and show the potential of super-resolution imaging preferences. We developed FINCH as a compressive sensing modality and reconstruction procedure as an inverse problem in order to realize 3D tomographic imaging. Improved axial resolution is obtained via compressive reconstruction. Reconstruction guarantees and accuracy of the proposed method are discussed. Compared with the real-valued signal operation, the signal-to-noise ratio of the results is increased when reconstructing from the complex-valued hologram obtained from the FINCH system.

Axial localization of fluorescence samples using single-shot self-interference digital holography

Application of self-interference digital holography for axial localization is demonstrated. The axial coordinates of the fluorescence sample are extracted from a single-shot hologram and localization accuracy of the proposed method is discussed in the paper.

Compressive self-interference Fresnel digital holography with faithful reconstruction

We developed compressive self-interference digital holographic approach that allows retrieving three-dimensional information of the spatially incoherent objects from single-shot captured hologram. The Fresnel incoherent correlation holography is combined with parallel phase-shifting technique to instantaneously obtain spatial-multiplexed phase-shifting holograms. The recording scheme is regarded as compressive forward sensing model, thus the compressive-sensing-based reconstruction algorithm is implemented to reconstruct the original object from the under sampled demultiplexed sub-holograms. The concept was verified by simulations and experiments with simulating use of the polarizer array. The proposed technique has great potential to be applied in 3D tracking of spatially incoherent samples.

Effect of optical surface flatness performance on spatial-light-modulator-based imaging system

Spatial light modulator (SLM) has various of applications in the field of imaging, beam shaping, adaptive optics and so on. While SLM is used as an aberration correction element in super-resolution microscopy, the surface flatness of SLM could affect the imaging performance of the system due to the higher sensitivity to aberrations of these kind microscopic techniques. In this paper, the optical surface flatness of SLM is measured experimentally by employing the image plane digital holography. The topography of SLM is retrieved from the captured hologram. Aiming to the application of SLM as an adaptive correction element in super resolution microscopy, the aberrations introduced by the surface flatness of SLM are further evaluated and corrected in the same optical system.

Imaging characteristics of self-interference digital holography with structured illumination

Self-interference digital holography enables holographic recording of object illuminated with spatially incoherent light. While Fresnel incoherent correlation holography (FINCH) has great potential in super-resolution microscopic imaging, structured illumination can be implemented simultaneously to further improve the imaging resolution. In this paper, the imaging characteristics of FINCH with structured illumination are investigated in detail. The basic principle of FINCH with structured illumination is discussed. Effects of characteristics of structured light pattern, such as the period, orientation and modulation depth on lateral-resolution are investigated. The potential of structured illuminated FINCH in three-dimensional super-resolution imaging was demonstrated in the paper.

Temporal and Axial Resolution Improvement of Self-interference Digital Holography Combing Compressive Sensing

Self-interference digital holography is combined with compressive sensing for purpose of improving temporal and axial resolution. Simulations demonstrate accurately object reconstruction from under-sampled spatial-multiplexed holograms and 3D tomographic imaging of self-interference digital compressive holography, respectively.

Compressive holographic imaging by self-interference Digital holography

The self-inference incoherent Fresnel digital holography was verified obeying well compressive sensing framework. Compressive holographic imaging of incoherently illuminated colorful objects by Michelson interferometer is demonstrated experimentally, thus the great potential of the technology for multidimensional imaging is showed.

Spatial-identification image encryption based on digital holography

We present a new method of realizing the spatial-identification image encryption based on digital holography in order to improve the encryption degree and increase encryption freedom. Both the object beam and the reference beam are modulated with random phase respectively. The random phase displayed on the spatial light modulator (SLM) in the reference arm is being refreshed synchronously when the aperture is scanning over the original image. The original image is divided into many subareas by the scanning aperture, and the object beam from each subarea interferes with a reference beam with unique random phase. Therefore, many sub-holograms are captured and each sub-hologram is encrypted with its own sub-key. The spatial position of the aperture becomes additional secret key because it is necessary that each sub-key should match with each encrypted sub-hologram for obtaining a completely decrypted image. This method greatly improves the image encryption degree and guarantees the security of the information. The whole original image is retrieved by superposition of all decrypted subareas. The encryption and decryption are demonstrated by simulations.