Dong-Hoan Seo

Interferometric phase-only optical encryption system that uses a reference wave

An improved image decryption system is proposed that is based on phase-encoded images and the principle of interference and uses a reference wave. A novel technique for generating intensity patterns from the decrypted phase information consists simply of interfering a reference wave with the wave passing through the encrypted image and a phase-only decrypting key. Optical experiments have confirmed the proposed technique as a simple and robust architecture for optical encryption.

Multilevel image encryption by binary phase XOR operations

We propose a multilevel image encryption by using binary phase exclusive-OR(XOR) operations and image dividing technique. The multilevel image can be divided to binary images that have same gray levels. We convert each binary image to binary phase image by phase encoding and encrypt these images with binary random phase images by binary phase XOR operation. We make encrypted gray image by combining each binary encrypted images. We implement the decryption process with joint transform correlator (JTC) and verify the proposed method by computer simulation.

Visual cryptography based on optical interference encryption technique

In this paper, we proposed a new visual cryptography scheme based on optical interference that can improve the contrast and signal to noise ratio of reconstructed images when compared to conventional visual cryptography methods. The binary image being encrypted is divided into any number of n slides. For encryption, randomly independent keys are generated along with another random key based on a XOR process of random keys. The XOR process between each divided image and each random key produces the encryption of n encrypted images. These encrypted images are then used to make encrypted binary phase masks. For decryption, the phase masks are placed on the paths of a Mach-Zehnder interferometer.

In-line fiber optic comb filter using a polished LiNbO/sub 3/ overlay waveguide for a multi-wavelength source

Summary form only given. Wavelength-division multiplexing (WDM) is one of the key solutions for providing greater bandwidth in optical communication networks. Recently, multi-layer dielectric filters, silica waveguides or diffraction gratings have been used to fabricate the WDM devices. In particular, multiwavelength erbium-doped fiber ring lasers using comb filters have been reported. In this paper, we demonstrate a side-polished fiber-optic comb filter and propose its application as a channel isolation filter for a WDM-based multi-wavelength light source.

Optical encryption system based on circular polarization and interferometer

We propose an optical encryption system using circular polarization based on interferometer architecture. The phase-modulated input image, represented as orthogonal linearly polarized states by interferometer, is encrypted into circularly polarized states whose direction of the rotation is random. In the decryption we use the inverse matrix of polarization-modulation key and can recover the original polarization states.

Binary image encryption technique and decryption system using joint transform correlator

In this paper a binary image encryption technique and decryption system based on a joint transform correlation are proposed. IN this method, an encrypted image is obtained by multiplying a phase encoded original binary image with a random phase. A Fourier transform of the encrypted, image is used as the encrypted data and a Fourier transform of the random phase is used as the key code. For decryption, the encrypted data is used for one half of the joint input plane, while the key code is used for the other half. After the joint input plane is inverse Fourier transformed, the original binary image can then be reconstructed on a square law device, such as a CCD camera. The proposed encryption technique does not suffer from strong auto-correlation terms appearing in the output plane. In addition, the reconstructed data can be directly transmitted to a digital system for real-time processing. Based on computer simulations, the proposed encryption technique and decoding system were demonstrated as adequate for optical security applications.

Image Watermark Method Using Multiple Decoding Keys

In this paper, we propose an image watermark method using multiple decoding keys. The advantages of this method are that the multiple original images are reconstructed by using multiple decoding keys in the same watermark image, and that the quality of reconstructed images is clearly enhanced based on the idea of Walsh code without any side lobe components in the decoding process. The zero-padded original images, multiplied with random-phase pattern to each other, are Fourier transformed. Encoded images are then obtained by taking the real-valued data from these Fourier transformed images. The embedding images are obtained by the product of independent Walsh codes, and these spreaded phase-encoded images which are multiplied with new random-phase images. Also we obtain the decoding keys by multiplying these random-phase images with the same Walsh code images used in the embedding images. A watermark image is then made from the linear superposition of the weighted embedding images and a cover image, which is multiplied with a new independent Walsh code. The original image is simply reconstructed by the inverse-Fourier transform of the despreaded image of the multiplication between the watermark image and the decoding key. Computer simulations demonstrate the efficiency of the proposed watermark method with multiple decoding keys and a good robustness to the external attacks such as cropping and compression.

Optical Encryption using a Random Phase Image and Shift Position in Joint Transform Correlation Plane

Most optical security systems use a 4-f correlator, Mach-Zehnder interferometer, or a joint transform correlator(JTC). Of them, the JTC does not require an accurate optical alignment and has a good potential for real-time processing. In this paper, we propose an image encryption system using a position shift property of the JTC in the Fourier domain and a random phase image. Our encryption system uses two keys: one key is a random phase mask and the other key is a position shift factor. By using two keys, the proposed method can increase the security level of the encryption system. An encrypted image is produced by the Fourier transform for the multiplication image, which resulted from adding position shift functions to an original image, with a random phase mask. The random phase mask and position shift value are used as keys in decryption, simultaneously. For the decryption, both the encrypted image and the key image should be correctly located on the JTC. If the incorrect position shift value or the incorrect key image is used in decryption, the original information can not be obtained. To demonstrate the efficiency of the proposed system, computer simulation is performed. By analyzing the simulation results in the case of blocking of the encrypted image and affecting of the phase noise, we confirmed that the proposed method has a good tolerance to data loss. These results show that our system is very useful for the optical certification system.

Hierarchical Image Encryption System Using Orthogonal Method

In recent years, a hierarchical security architecture has been widely studied because it can efficiently protect information by allowing an authorized user access to the level of information. However, the conventional hierarchical decryption methods require several decryption keys for the high level information. In this paper, we propose a hierarchical image encryption using random phase masks and Walsh code having orthogonal characteristics. To decrypt the hierarchical level images by only one decryption key, we combine Walsh code into the hierarchical level system. For encryption process, we first perform a Fourier transform for the multiplication results of the original image and the random phase mask, and then expand the transformed pattern to be the same size and shape of Walsh code. The expanded pattern is finally encrypted by multiplying with the Walsh code image and the binary phase mask. We generate several encryption images as the same encryption process. The reconstruction image is detected on a CCD plane by a despread process and Fourier transform for the multiplication result of encryption image and hierarchical decryption keys which are generated by Walsh code and binary random phase image. Computer simulations demonstrate that the proposed technique can decrypt hierarchical information by using only one level decryption key image and it has a good robustness to the data loss such as random cropping.

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An improved image decryption system is proposed that is based on phase-encoded images and the principle of interference and uses a reference wave. A novel technique for generating intensity patterns from the decrypted phase information consists simply of interfering a reference wave with the wave passing through the encrypted image and a phase-only decrypting key. Optical experiments have confirmed the proposed technique as a simple and robust architecture for optical encryption.