Anh-Hoang Phan

Generation speed and reconstructed image quality enhancement of a long-depth object using double wavefront recording planes and a GPU

A method for fast computer hologram generation for long-depth objects using double wavefront recording planes (WRPs) and a graphics-processing unit (GPU) is presented. The WRPs are placed between the object and the hologram plane. Each WRP records the wavefront from a section of the object. Double WRPs can provide a shorter calculation time and enhanced reconstructed image quality compared with a single WRP, especially for long-depth objects. The average generation speed of two WRPs is 2.5 times that of one WRP. The correlation efficiency of the reconstructed layer relative to the original is 94% for two WRPs and 88.3% for one WRP at the close depth layer.

Synthesis of computer-generated spherical hologram of real object with 360° field of view using a depth camera.

A method for synthesizing a 360° computer-generated spherical hologram of real-existing objects is proposed. The whole three-dimensional (3-D) information of a real object is extracted by using a depth camera to capture multiple sides of the object. The point cloud sets which are obtained from corresponding sides of the object surface are brought into a common coordinate system by point cloud registration process. The modeled 3-D point cloud is then processed by hidden point removal method in order to identify visible point set for each spherical hologram point. The hologram on the spherical surface is finally synthesized by accumulating spherical waves from visible object points. By reconstructing partial region of the calculated spherical hologram, the corresponding view of the 3-D real object is obtained. The principle is verified via optical capturing using a depth camera and numerical reconstructions.

Multiple-image encryption based on triple interferences for flexibly decrypting high-quality images

We propose a multiple-image encryption (MIE) scheme based on triple interferences for flexibly decrypting high-quality images. Each image is discretionarily deciphered without decrypting a series of other images earlier. Since it does not involve any cascaded encryption orders, the image can be decrypted flexibly by using the novel method. Computer simulation demonstrated that the proposed methods running time is less than approximately 1/4 that of the previous similar MIE method. Moreover, the decrypted image is perfectly correlated with the original image, and due to many phase functions serving as decryption keys, this method is more secure and robust.

Error analysis in parallel two-step phase-shifting method

This paper presents an analysis of error in parallel two-step phase-shifting method. From the analysis, it is clarified that the maximum bandwidth of the object that this technique can capture is a half bandwidth of recording devices. Also, the recording distance must be two times longer than the conventional method to have a good reconstruction image. The analysis was verified by simulations and experimental results.

Super-Resolution Digital Holographic Microscopy for Three Dimensional Sample Using Multipoint Light Source Illumination

In this paper, we use multipoint light source illumination to enhance the resolution of digital holographic microscopy. The specimen is sequentially illuminated from many directions by using multipoint light sources which are created by a lens-array. The high spatial frequency information of the specimen is directed to the limited numerical aperture of the objective lens and captured at a fixed position of image sensor. The three-dimensional information of the specimen can be reconstructed with enhanced resolution by reconstructing the captured holograms.

Fast hologram generation of long-depth object using multiple wavefront recording planes

In this paper we present the method for fast computer generation hologram (CGH) of the long depth object using multiple wavefront recording planes (WRP). The wavefront recording planes are placed between object plane and hologram plane. Each WRP records the wavefront from a section of object. For a long depth object, multiple WRPs can reduce the calculation time and also enhance the quality of reconstruction object in comparison with those ones of single WRP. The hologram of object can be real time generated by out proposed method.

Input-output Coupler System with 45-degree Slant Angle Based on Bragg Hologram

In this paper, we designed and fabricated an input-output coupler system using two or three volume gratings at 632.8nm wavelength. The additional third grating is added at the output coupler to enhance the overall efficiency. The experimental results show that the total system throughput reaches 63% with two-grating and 75% with three-grating input-output coupler. We also present a design method to obtain the desired output power ratio between the gratings.

Optical Image Split-encryption Based on Object Plane for Completely Removing the Silhouette Problem

We propose a split-encryption scheme on converting original images to multiple ciphertexts. This conversion introduces one random phase-only function (POF) to influence phase distribution of the preliminary ciphertexts. In the encryption process, the original image is mathematically split into two POFs. Then, they are modulated on a spatial light modulator one after another. And subsequently two final ciphertexts are generated by utilizing two-step phase-shifting interferometry. In the decryption process, a high-quality reconstructed image with relative error

Analysis on the space-bandwidth product of digital holography for video hologram recording and reconstruction

RE=7.6061{\times}10^{-31}

Super-resolution digital holographic microscopy using multi-point light sources illumination

can be achieved only when the summation of the two ciphertexts is Fresnel-transformed to the reconstructed plane. During the verification process, any silhouette information was invisible in the two reconstructed images from different single ciphertexts. Both of the two single REs are more than 0.6, which is better than in previous research. Moreover, this proposed scheme works well with gray images.