A comparative analysis of phenanthrenequinone-doped poly(methyl methacrylate) materials fabricated at California Institute of Technology and National Chiao Tung University is performed in order to understand the dierences exhibited in their recording and baking dynamics. Ó 2001 Published by Elsevier Science B.V.Keywords: Holography; Photopolymer material; PQ-PMMA; Grating dynamics; Temperature eect Phenanthrenequinone-(PQ-) doped poly(methyl methacrylate) (PMMA) [1,2] has been used as a recording material in optical memories and other holographic systems [3±6]. This material consists of a polymeric basis doped with chromophores, the PQ molecules. This material is lightweight and durable, and does not suer from shrinkage. High optical quality samples of dierent shapes and thicknesses can be obtained. These properties make it an excellent candidate for holographic memory modules. In this paper, we compare the PQ±PMMA samples that we use at California Institute of Technology (Caltech) with those fabricated at National Chiao Tung University (NCTU) and try to understand the dierences in behavior they exhibit.Sample preparation consists of dissolving PQ molecules ( 6 0.7%) in liquid methyl methacrylate (MMA) together with azo-bis-isobutyrolnitrile, a polymerization thermal initiator. This solution is poured into molds and allowed to polymerize in a pressure chamber. The preparation process followed at Caltech diers from the one followed at NCTU in the temperature at which the pressure chamber is set during polymerization. For the Caltech material, the temperature of the chamber is set to 80°C. On the other hand, at NCTU the polymerization process is split into two steps [4,7]. First, the solution is let to rest at room temperature for approximately 120 h until the solution turns homogeneously viscid. At this point, the
Reconfigurable processors bring a new computational paradigm where the processor modifies its structure to suit a given application, rather than having to modify the application to fit the device. The Optically Programmable Gate Array, an enhanced version of a conventional FPGA, utilizes a holographic memory accessed by an array of VCSELs to program its logic. Combining spatial and shift multipexing to store the configuration pages in the memory, the OPGA module is very compact and has extremely short configuration time allowing for dynamic reconfiguration. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and digit classification. ABSTRACTReconfigurable processors bring a new computational paradigm where the processor modifies its structure to suit a given application, rather than having to modify the application to fit the device. The Optically Programmable Gate Array, an enhanced version of a conventional FPGA, utilizes a holographic memory accessed by an array of VCSELs to program its logic. Combining spatial and shift multipexing to store the configuration pages in the memory, the OPGA module is very compact and has extremely short configuration time allowing for dynamic reconfiguration. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and digit classification.
The high data transfer rate achievable in page-oriented optical memories demands for parallel interfaces to logic circuits able to process efficiently the data. The Optically Programmable Gate Array, an enhanced version of a conventional FPGA, utilizes a holographic memory accessed by an array of VCSELs to program its logic. Combining spatial and shift multiplexing to store the configuration pages in the memory, the OPGA module is very compact and has extremely short configuration time allowing for dynamic reconfiguration. The reconfiguration capability ofthe OPGA can be applied to solve more efficiently problems in pattern recognition and digit classification.
The Optically Programmable Gate Array (OPGA). an optical version of a conventional FPGA. benefits from a direct parallel interface between an optical memory and a logic circuit. The OPGA utilizes a holographic memory accessed by an array ol VCSELs to program its logic. An active pixel sensor array incorporated into the OPGA chip makes it possible to optically address the logic in a very short time allowing for rapid dynamic reconfiguration. Combining spatial and shifi multiplexing to store the configuration pages in the memory, the OPGA module can he made compact. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and database search.
No abstract
We show that when a dynamic hologram is read out by illumination at the Bragg nulls of a previously recorded grating the diffracted beam inside the medium can result in the recording of two secondary gratings that alter the final selectivity curve. This is confirmed experimentally. This effect can cause cross talk in hologram multiplexing that is stronger than interpage cross talk when a small number of holograms with high diffraction efficiencies are multiplexed.
Reconfigurable processors, like the Field Programmable Gate Arrays (FPGA's), open new computational paradigms where the processor is able to tailor its internal structure to better . implement a given application. A typical FPGA consists of an array of configurable logic blocks and a mesh of interconnections fully programmable by the user to perform a given application. By just changing its internal connectivity, the FPGA can implement a totally different new function. However in most of the applications, the FPGA is configured only once and used as coprocessor to carry out some highly complex or time-consuming computation. The reason for such limitation is the small communication bandwidth between the FPGA chip and the external memory, usually ROM, where the configuration data is stored.The Optically Programmable Gate Array (OPGA)', figure 1, an enhanced version of a conventional FPGA, can overcome this problem. The OPGA utilizes a holographic memory accessed by an array of VCSELs to program its logic. The on-chip logic has been complemented with an array of photodetectors to detect the configuration template recorded in the memory. Combining spatial and shift multiplexing to store the configuration pages in the memory, the OPGA module is very compact and has extremely short configuration time allowing for dynamic reconfiguration. The reconfiguration capability of the OPGA can be applied to solve more efficiently problems in pattern recognition and database searches. Figure 1. OPGA module package Reference: [I] "Optically
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