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5. Celebrating holography anniversaries: a historical perspective

Author

Beléndez, Augusto, Sheridan, John T., Pascual, Inmaculada, Universidad de Alicante. Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante. Departamento de Óptica, Farmacología y Anatomía, Universidad de Alicante. Instituto Universitario de Física Aplicada a las Ciencias y las Tecnologías, University College Dublin. School of Electrical and Electronic Engineering. College of Arquitecture and Engineering, Holografía y Procesado Óptico, and GITE - Física, Óptica y Telecomunicaciones

Subjects
Física Aplicada, Gabor, Holography, Leith, Denisyuk, Hologram, Óptica
Abstract

The year 2022 marks the 75th anniversary of Dennis Gabor’s invention of the holographic method, what he called “microscopy by reconstructed wave-fronts”, as well as the 60th anniversary of the publication in 1962 of two seminal papers in the field of holography: the introduction of the reflection hologram by Yuri Denisyuk, and the description of the holographic process from the point of view of communication theory by Emmett Leith and Juris Upatnieks. Within the framework of these celebrations, a historical review of the origins of holography is presented with special emphasis on the contributions of Gabor, Denisyuk and Leith to the development of holography. This work was supported by the by “Generalitat Valenciana” of Spain (projects PROMETEO/2021/006 and IDIFEDER/2021/014, cofunded by European Union through the FEDER Programme) and by the “Ministerio de Ciencia e Innovación” of Spain (projects FIS2017-82919-R and PID2019-106601RB-I00).

Published
2022

39. Capture, encryption, compression, and display of digital holograms of three-dimensional objects

Author

Gopinathan, Unnikrishnan, Monaghan, David S., Shortt, Alison, Naughton, Thomas J., Sheridan, John T., and Javidi, Bahram

Abstract

Digital holography can be used to capture the whole Fresnel field from a reflective or transmissive object. Applications include imaging and display of three-dimensional (3D) objects, and encryption and pattern recognition of two-dimensional (2D) and 3D objects. Often, these optica l systems employ discrete spatial light modulators (SLMs) such as liquid-crystal displays. In the 2D case, SLMs can encode the inputs and keys during encryption and decryption. For 3D processing, the SLM can be used as part of an optical reconstruction technique for 3D objects, and can also represent the key during encryption an d decryption. However, discrete SLMs can represent only discrete levels of data necessitating a quantisation o f continuous valued analog information. To date, many such optical systems have been proposed in the literature, y et there has been relatively little experimental evaluation of the practical performance of discrete SLMs in these systems. In this paper, we characterise conventional phase-modulating liquid-crystal devices and examine thei r limitations (in terms of phase quantisation, alignment tolerances, and nonlinear response) for the encryption of 2D and 3D data. Finally, we highlight the practical importance of a highly controlled discretisation (optimal quantisation) for compression of digital holograms.

Published
2006

43. Digital image watermarking spread-space spread-spectrum technique based on Double Random Phase Encoding

Author

Liu, Shi, Hennelly, Bryan M., Sheridan, John T., Liu, Shi, Hennelly, Bryan M., and Sheridan, John T.

Abstract

In this paper a digital invisible image watermarking technique is proposed based on the numerical simulation of optical Double Random Phase Encoding (DRPE). This technique utilizes the capability of the DRPE to spread the energy of the input information in both the space and the spatial frequency domains using two diffusers. The watermark is in the form of a digital barcode image which is numerically encrypted using a simulation of the optical DRPE process. This produces a random complex image, which is then processed to form a real valued random image with a low number of quantization levels. This signal is added to the host image. Extraction of the barcode, involves applying an inverse DRPE process to the watermarked image followed by a low pass filter. The results presented indicate the feasibility and robustness of the proposed method and it is demonstrated that even when using very few quantization levels, i.e. 2-levels, the watermark can still be extracted with very small errors.

Published
2012

44. Cost Function Statistical Analysis in Double Random Phase Encoding

Author

Monaghan, David S., Gopinathan, Unnikrishnan, Situ, Guohai, Naughton, Thomas J., Sheridan, John T., Monaghan, David S., Gopinathan, Unnikrishnan, Situ, Guohai, Naughton, Thomas J., and Sheridan, John T.

Abstract

We examine the Amplitude-Encoding (AE) case of the Double Random Phase Encoding (DRPE) technique. A cost function is the function we use to evaluate an attempted decryption with our original input image. For systems with a relatively small key-space we can evaluate the output of every key to get an overall idea of the spread of these keys in key-space. However for larger systems this is not practical. Based on a normalised root mean squared cost function we wish to identify expressions for the mean and variance of the output (decrypted) intensity for a sample set of keys in a large system (256x256 pixels).

Published
2008

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