Quality Enhancement of a Complex Holographic Display Using a Single Spatial Light Modulator and a Circular Grating

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  • ABSTRACT

    This paper proposes an optical system for complex holographic display that enhances the quality of the reconstructed three-dimensional image. This work focuses on a new design for an optical system and the evaluation of the complex holographic display, using a single spatial light modulator (SLM) and a circular grating. The optical system is based on a 4-f system in which the imaginary and real information of the hologram is displayed on concentric rectangular areas of the SLM and circular grating. Thus, this method overcomes the lack of accuracy in the pixel positions between two window holograms in previous studies, and achieves a higher intensity of the real object points of the reconstructed hologram than the original phase-reconstructed hologram. The proposed method provides approximately 30% less NMRS (Normal Root Mean Square) error, compared to previous systems, which is verified by both simulation and optical experiment.


  • KEYWORD

    Holographic recording , Holography , Holographic interferometry , Displays

  • I. INTRODUCTION

    A digital holographic display is a type of display technology that provides full depth information for real objects. The optical field of an object can be recorded and stored in a digital device such as a CCD camera or optical sensor, with the capability to transfer and display it at any time and place. In a digital hologram, reconstruction devices can only be used for a phase hologram or an amplitude hologram, but not both at the same time. Previous reports have proposed several methods that use a spatial light modulator (SLM) to reconstruct a complex hologram. Such complex reconstructed holography with an SLM may use either of two methods: two SLMs [1-3], or a single SLM [4-6]. The method with two SLMs uses a coupled phase and amplitude for each SLM set up on both sides of a beam splitter, for combination into a complex hologram. This solution provides a full-display complex hologram with high spatial resolution, but coupling the two displays with pixel accuracy is very difficult. Using the second method, with a single SLM, some researchers attempted to overcome the pixel-matching problem by using a phase-modulation hologram [4] or an amplitude-modulation hologram [5], or both imaginary and real parts of a complex hologram with two small windows and a 4-f system that integrated the phase or amplitude sinusoidal grating to create a complex hologram where 4-f is a common optical configuration in holographic recording [6]. However, this method only partially avoids the pixel-matching problem and did not yield an entirely complex hologram, with only phase or amplitude information.

    In this paper we show how to overcome the constraints of complex holography by using a 4-f system with an input plane with concentric rectangular data for imaginary and real information, and a circular grating. By mathematically calculating the difference between the two sizes of the concentric rectangular areas in the SLM, we achieve a complex hologram, instead of just adjusting the accuracy of the pixel positions on the SLM, as in previous studies. In our system the optical setup is simple, and the system provides a higher intensity for each reconstructed object point than do previous systems [2-13]. Section II describes the proposed method with size variation of concentric rectangular areas for better reconstruction quality. Our results are described in section III by simulation of and experiment with the newly designed optical system.

    II. PROPOSED METHOD

    The proposed method is based on a 4-f system using a circular grating to implement the display system of a complex hologram. The principle of this method is illustrated in Fig. 1. On the input plane depicted in Fig. 1(a), the SLM is divided into two concentric rectangles such that the outer rectangle contains the real part of the complex hologram, and the inner rectangle contains the imaginary part. The reflected light of the imaginary part from the SLM passes through a device to shift its phase by π/2, before it goes into the 4-f system (device D1 in Fig. 1(e)). In the 4-f system in