Image-Plane Cylindrical Multiplex Holography

• Main Authors: Ray-Cheng Chang, 張瑞城
• Other Authors: Yih-Shang Cheng
• Format: Others
• Language: en_US
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/84509317499948413724

博士 === 國立中央大學 === 光電科學研究所 === 87 === Many kinds of holographic stereograms (HSs) — stereograms in which a series of 2-D images are holographically recorded — have been developed during the past thirty years. Most of them target on entertaining or advertising displays rather than scientific and engineering applications. The cylindrical holographic stereogram (CHS), benefits from its cylindrical geometric feature, is one exception because its ability to provide 360 degrees of viewing field. This unique characteristic makes it a very good medium for displaying 3-D images with rich information. Traditional CHSs, also known as multiplex holograms, are generally produced by using an anamorphic optical system in a one-step recording process. Images reconstructed from this kind of CHS usually exhibit many shortcomings such as rainbow-colored images, narrow vertical viewing field, and annoying picket-fence effect, which significantly limit the further development of CHSs. This dissertation describes a new approach for producing the CHSs by using a two-step recording process — mastering and transferring — which is also widely used for planar HS. The 2-D photographs are first spatially integrated into the first, or master, hologram, then transferred to the second one. This additional transferring process makes the original 2-D photographs imaged onto the hologram plane, consequently eliminates the picket-fence effect. Other benefits are sharper images due to the nature of image-plane hologram, and less distortion since different integration geometry is adopted. Moreover, this kind of stereograms, called Image-Plane Cylindrical Holographic Stereograms (IPCHSs), has advantages which are wider vertical viewing field and the capability of generating achromatic reconstructed images with white-light illumination. Generally, since the IPCHSs are recorded in the flat format yet viewed in the cylinder format, some modifications have to be made in order to cancel the image blur and distortions. First, the construction reference wave for the master hologram is changed from a divergent light to a collimated one in order to make sure each slice of the hologram (i.e. component hologram) can be illuminated with the same illumination. The synthesizing scheme of each component hologram is also modified to maintain the symmetry. In the transferring process, the construction reference wave is pre-distorted according to the theoretical analysis and numerical simulation. Basically, the reference wave is divergent in one direction but collimated in the other one. This modification compensates the astigmatic effect of the viewing slits therefore restores the aspect ratio of the final images. Furthermore, by introducing the achromatic angle, the color dispersion of the viewed images is significantly alleviated, which consequently increases the sharpness of the images. Other important parameters for IPCHSs, such as the slit width, the slit position, the viewing field, and the vertical size of the light source, are also included in this dissertation. Base on these investigations, the recording systems may be carefully tuned, hence the satisfactory results can be obtained.