The application of digital pixel hologram (DPH) as anti-counterfeiting technology to consumer products is growing important nowadays. Recently, a very high-resolution DPH has been fabricated successful using the electron beam lithography (EBL) facilities housed in Optoelectronics Research Center, City University of Hong Kong. In this paper, we propose an optical encryption technique, called Optical Transform Coding (OTC), which can be used to further enhance the anti-counterfeiting performance of DPH. Details in coding and decoding processes are described. Two DPHs of resolution 2540 dpi are fabricated to demonstrate the technique using a City University (CityU) and Hong Kong Special Administrative Region (HKSAR) logos as examples.
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