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Optical Image Processing & Optical Scanning Holography
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Optical Scanning Holography (
We continue studying a novel electronic holographic technique (called optical scanning holography) in which 3-D (holographic) information is acquired by a single 2-D laser scanning. Incoherent and partial coherent imaging properties will be studied. Potential applications of the technique include holographic TV, optical scanning cryptography, 3-D holographic microscopy and 3-D optical remote sensing.
Optical Scanning Cryptography (OSC): We study an information security method for secure wireless transmission. By using an encryption key, an image/document is first optically encrypted by optical heterodyne scanning and hence encryption is performed on the fly. The output of the heterodyne encrypted signal is at radio frequency and can be directly sent through an antenna to a secure site for digital storage to be prepared for decryption. In the secure site, an identical optical scanning system to that used for encryption is used, together with a decryption key, to generate an electrical signal. The electrical signal is then processed and sent to a computer to be used for decryption. Utilizing the stored information received from the encryption stage and the electrical information from the secure site, a digital decryption unit performs a decryption algorithm. If the encryption key and the decryption key are matched, the decryption unit will decrypt the image/document faithfully. Further theoretical development, computer simulations and optical experiments are needed. [Click here for a reference publication]
Three-Dimensional Holographic Fluorescence Microscopy: Most commonly used methods for 3-D fluorescence microscopy make use of sectioning techniques which require that the object be physically scanned in a series of 2-D sections along the z-axis. The main drawback in these approaches is the need for these sequential 2-D scans along the depth of the 3-D sample. A novel approach to fluorescence imaging in three dimensions is developed which is based on optical scanning holography. This approach requires only a 2-D scan to record 3-D information. Holograms with better than 1-micron resolution have been recorded by optical scanning holography. The next formidable task is to image true 3-D biological samples with speed faster than confocal methods. [Click here for a reference publication]
Real-Time Optical Pattern Recognition: Current methods for real-time optical correlation employing a joint-Fourier transform approach use a spatial light modulator (SLM) in the focal plane to store the interference intensity which is subsequently read out by coherent light. Because the resolution required for accurate representation of the image transform is extremely high, the SLMs, which meet the specifications, are prohibitively expensive. A novel approach to joint-Fourier transform correlation is studied. The method obviates the use of SLM in the focal plane and still preserves the real time aspects of the measurements. The approach incorporates the use of acousto-optic technology for optical heterodyning, SLMs for image representation and electronically tuned detection of the heterodyne optical signal. [Click here for a reference publication]
Study of Spatial Light Modulators with Applications to 3-D Image Projection and Display, and 3-D TV: 3-D imaging and display is a formidable task. Holography is one of the most important and practical methods for 3-D display as holograms contain depth information of the object. For real-time applications, holograms are displayed or stored on spatial light modulators (SLMs) for display. We study the use of SLMs for 3-D image projection and display. [Click here for a reference publication]
Optical Image Recognition of 3-D objects: A novel three-dimensional (3-D) optical image recognition technique is studied. The technique is based on two-pupil optical heterodyne scanning. A hologram of the 3-D reference object is first created which is then used to spatially modulate one of the pupils of the optical system, with the other pupil being a point source. A 3-D target object to be recognized is then 2-D scanned by optical beams modulated by the two pupils, and the result of the 2-D scan pattern effectively displays the correlation of the holographic information of the 3-D reference object and that of the 3-D target object. A strong correlation peak results if the two pieces of the holographic information are matched. We need to further develop the theoretical model, perform computer simulations as well as further optical experiments. [Click here for a reference publication]
Extended Depth of Field through a Synthesized Difference-of-Gaussians Pupil: Optical systems with extended depth of field are desirable for biomedical applications such as microscopy or endoscopy, machine vision systems, and lithographic systems. The most common way to increase the depth of field is to stop down the lens or use a pupil function which blocks and wastes part of the light, such as an annular pupil. This project is to design and build a prototype using a laser beam-scanning system, acousto-optic hardward for the introduction of the temporal frequency shift between two Gaussian laser scanning beams, electronic mixing and a digital computer to store and process the scanned images. The overall system is to synthesize a difference-of-Gaussians pupil, which does not stop or waste any light as with conventional annular pupils.
Real-Time Programmable Image Processing by Acousto-Optics: The use of acousto-optic modulators (AOMs) for image processing is explored. The novel feature of the technique is that a full 2-D image is inputted to the AOMs for processing. In fact, the 2-D optical image interacts with the sound field produced by the AOM. The scattering or diffraction of the 2-D optical image actually carries the processed versions of the original 2-D input image. Processing is performed in real-time, as the AOM is a real-time device. The processing operation is programmable as the sound amplitude within the AOM can be varied electronically and hence the input image can be modified accordingly. We plan to employ the developed techniques to fully develop real-time and programmable AO-based image and correlation system. [Click here for a reference publication]