Digital holograms of three-dimensional objects We have developed three different methods of generating digital Fresnel holograms of 3-D real-existing objects illuminated by incoherent light. In the first method, a scanning hologram is generated by a unique scanning system in which Fresnel zone plates (FZP) are created by a homodyne rather than the common heterodyne interferometer. During the scanning, the FZP projected on the observed object is frozen rather than varied as previously. In each scanning period, the system produces an on-axis Fresnel hologram. The twin image problem is solved by a linear combination of at least three holograms taken with three FZPs with different phase values. The second hologram developed here is the digital incoherent modified Fresnel hologram. To calculate this hologram, multiple-viewpoint projections of the 3-D scene are acquired, and a Fresnel hologram of the 3-D scene is directly computed from these projections. This method enables to obtain digital holograms by using a simple digital camera, which operates under regular light conditions. The third digital hologram developed here is the Fresnel incoherent correlation hologram. In this motionless holographic technique, light is reflected from the 3-D scene, propagates through a diffractive optical element (DOE), and is recorded by a digital camera. Three holograms are recorded sequentially, each for a different phase factor of the DOE. The three holograms are superposed in the computer, such that the result is a complex-valued Fresnel hologram that does not contain a twin image.
Noninvasive optical imaging by speckle ensemble During the past decade, optical imaging through scattering medium has proved to be a powerful technique for many applications. It is especially effective in medical diagnostic, since it is safe, noninvasive and low-cost compared with the conventional radiation techniques. Based on a similar principle of the fly’s visual system, we show a novel method of optical imaging through scattering medium. An image of bones hidden between two biological tissues (chicken breast) is recovered from many noisy speckle pictures obtained on the output of a multi-channeled optical imaging system. The operation of multiple imaging is achieved using a microlens array. Each lens from the array projects a different speckled image on a digital camera. The set of speckled images from the entire array are first shifted to a common center and then accumulated to a single average picture in which the concealed object is exposed.
Spatial coherence profilometry and tomography Optical coherence profilometry and tomography are fundamentally new types of optical imaging that generate high resolution images using echoes of light. They have a number of features that make them attractive for a broad range of applications, including the fact that they enable real time, visualization of microstructures in a nondestructive manner. Most existing methods of optical coherence profilometry and tomography are based on the physics of temporal coherence. Our recently invented method is based on the spatial, rather than the temporal, coherence phenomenon. Therefore, the proposed interferometric system is illuminated by a quasi-monochromatic spatial incoherent source instead of a broadband light source. The surface profile is measured by means of shifting the spatial degree of coherence gradually along its longitudinal axis while keeping the optical path difference between the measured surface and a reference plane constant. Currently, we explore novel methods to use the 3-D properties of the coherence function for analyzing surface profiles.
Three-dimensional electro-optical correlation 3-D optical correlators open opportunities for processing 3-D images directly and rapidly. Targets distributed in 3-D space can be recognized or tracked by optical correlators in the same fast and parallel manner that the well-known two-dimensional correlators have demonstrated for the past three decades. Recently we have developed a few methods to perform spatial 3-D electro-optical correlation. We have proposed an electro-optical pattern recognition system, which can identify an object and its location in the three-dimensional observed space. These novel methods enable one to implement many operations of signal processing on three-dimensional images. XX
Security and encryption optical systems Optical technologies have recently been employed in data security. Compared with traditional computer and electrical systems, optical technologies offer primarily two types of benefits. (1) Optical systems have an inherent capability for parallel processing, that is, rapid transmission of information. (2) Information can be hidden in any of several dimensions, such as phase or spatial frequency; that is, optical systems have excellent capability for encoding information. Recently we have proposed several security systems that are based on existing optical correlators but have some additional benefits over those of the present generation. These systems have better security level more functions and they might be useful for more purposes.
Longitudinal beam shaping Recently we have started to explore the field of longitudinal holography. Longitudinal holography is the method to shape the light distribution along the propagation axis. While an ordinary hologram is a transmission mask, typically employed to construct a desired transverse image, the longitudinal hologram is a special transmission mask that is used to achieve a desired longitudinal light distribution. For example, by inserting the longitudinal hologram in the propagation path of the laser beam, its divergence can be avoided so that the beam radius remains constant along an arbitrary axial distance. Currently we extend our research to the 3-D computer generated holography. The goal of this project is to find efficient methods of computing synthetic holograms, which are capable of creating artificial 3-D images in the observer eyes.

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