**9. References**


LCTV SLM. Fig. 20(a) is the experimentally reconstructed image and the nurerical

(a) (b)

Fig. 20. Experimental result of optical phase-coding method. (a) Optical and (b) simulation

We have studied optical security systems for practical applications in verification of the authenticity, such as in a card system. The advantages of the optical method in a security are the fast decoding of an encrypted image and the identification of it. Firstly, we study a common method of joint transform correlation for optical security systems and the optimization of binary holograms and proved that the optimization of a hologram will be a powerful tool in the systems. As an alternative method, a phase-coding technique is introduced to congenital with the uses of real optical devices in optical security systems. Originally, the merit of optical systems is fast processing of decryption of hologram and identification of it. However, the methods discussed here, i.e., not only image encryption, but also decryption of hologram and identification of it, can be applicable in all-digital

Aarts E.; & Korst J. (1990). *Simulated Annealing and Boltzmann Machines*, John Wiley & Sons,

Bättig R. K.; Guest C. C.; Schaefer S. R.; & Toms D. J. (1992). Simulated Annealing of Binary

Holograms for the Interconnection of Single-Mode Sstructures, *Appl. Opt*., Vol.31,

reconstruction image is shown in Fig. 20(b) for comparison.

results.

**8. Conclusion** 

**9. References** 

Chichester

pp.1059-1066

techniques using a recent fast computer.


**Nanophotonic Hierarchical Holograms:** 

**Based on Nanophotonics** 

Naoya Tate et al.\* *The University of Tokyo,* 

*Japan* 

**Demonstration of Hierarchical Applications** 

Recently, Italy's National Committee for Cultural Heritage found some microscopic codes in Mona Lisa's pupils by using a magnifying glass (Lorenzi, 2010). Experts have pointed out that the codes may represent several messages, including the initials of Leonardo Da Vinci, "*LV"*. On the other hand, how and why such microscopic messages were embedded in her pupils has not been revealed yet. The most interesting part of this *other Da Vinci code* is that, although techniques for microscopic fabrication and retrieval had not been generally established in the early 16th century, the concept of embedding secret messages in a macro-scale view already

Present-day techniques for realizing this concept involve the ideas of *covertness* and *overtness*. The former means not showing something openly, and the latter means the opposite. As Da Vinci showed 500 years ago in Mona Lisa's pupils, microscopic optical techniques are suitable for embedding secret messages in a macro-scale optical observation, because the hierarchical structure inherent between different levels of the optical scale can be implemented simply, and the levels are functionally independent of each other. For instance, confidential information can be hidden in any of the physical attributes of light, such as phase, wavelength, spatial frequency, or polarization, so that one kind of anti-counterfeiting is represented (Javidi et al., 1994; Refregier et al., 1995;

Holography, which generates natural three-dimensional images consisting of a number of diffracted light beams, is one of the most common anti-counterfeiting optical techniques (Renesse et al., 1998). In the case of a volume hologram, the surface of the hologram is ingeniously designed into a complicated structure that diffracts incident light in specific directions. A number of diffracted light beams can form an arbitrary three-dimensional image. Because these structures are generally recognized as being difficult to duplicate,

Makoto Naruse1,2, Takashi Yatsui1, Tadashi Kawazoe1, Morihisa Hoga3, Yasuyuki Ohyagi3,

Yoko Sekine3, Tokuhiro Fukuyama3, Mitsuru Kitamura3 and Motoichi Ohtsu1

*2National Institute of Information and Communications Technology, Japan* 

existed—or as we now say, "The best place to hide a leaf is in a forest".

**1. Introduction** 

Rakuljic et al., 1992).

*1The University of Tokyo,Japan* 

*3Dai Nippon Printing Co. Ltd., Japan* 

 \*

Yang H-G.; & Kim E-S. (1996). Practical Image Encryption Sscheme by Real-Valued Data," *Opt. Eng*., Vol.35, pp.2473-2478 **15** 
