Field Programmable Gate Arrays (FPGAs) are very versatile devices. 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 FPGAs can implement a totally different new function. This concept of programmable hardware makes the FPGA be faster when compared to a general-purpose processor, but at the same time more flexible than a specific circuit (ASIC).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 bandwith between the FPGA chip and the external memory, usually ROM, where the configuration data is stored. A typical FPGA requires about 1Mbit of configuration data, which results in reconfiguration times of hundreds of milliseconds.To overcome this bandwidth limitation, we use an FPGA that can be very rapidly configured by transferring the configuration data from an optical memory (figure 1). The optical memory can store a very large set of configuration pages in the form of holograms, which can be transferred at once to the FPGA since the readout is page oriented. Therefore, this Optically Programmable Gate Array (OPGA) makes it possible to dynamically reconfigure the FPGA and use more efficiently its logic resources by time and space multiplexing them.
Asymmetric directional coupling between a hybrid plasmonic waveguide with subwavelength field confinement and a conventional dielectric waveguide is investigated. The proposed hybrid coupler features short coupling length, high coupling efficiency, high extinction ratio, and low insertion loss; it can also be integrated into a silicon-based platform. This coupler can be potentially adopted for signal routing between plasmonic waveguides and dielectric waveguides in photonic integrated circuits. Furthermore, it can be exploited to efficiently excite hybrid plasmonic modes with conventional dielectric modes.
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