Joby Joseph - Academia.edu (original) (raw)
Papers by Joby Joseph
Optics Communications, 2006
We propose and demonstrate a digital holographic technique for 3D object recognition and classifi... more We propose and demonstrate a digital holographic technique for 3D object recognition and classification. One Fresnel digital hologram of each of the 3D objects to be classified is recorded. The electronic holograms are processed digitally to retrieve 3D object information as 2D digital complex images. We use this method to classify four physical objects in a 3D scene into two classes. Results are presented from an experiment to demonstrate the proof of the concept.
Optical Engineering, 2007
The complex Fresnel field that contains three-dimensional (3-D) information about an object can b... more The complex Fresnel field that contains three-dimensional (3-D) information about an object can be retrieved from an optically generated and electronically detected single off-axis Fresnel hologram of a 3-D object. The retrieved complex Fresnel field gives the appearance of a ...
Optical Engineering, 2003
Optical information processing techniques offer many advantages for data security applications. O... more Optical information processing techniques offer many advantages for data security applications. Optics offers several dimensions in which information can be hiddenphase, polarization, wavelength, etc.which makes it possible to encode data more securely. ...
Optics and Lasers in Engineering, 2004
In this paper, we implement a fully phase-encrypted memory system using cascaded extended fractio... more In this paper, we implement a fully phase-encrypted memory system using cascaded extended fractional Fourier transform (FRT). We encrypt and decrypt a two-dimensional image obtained from an amplitude image. The full phase image to be encrypted is fractional Fourier transformed three times and random phase masks are placed in the two intermediate planes. Performing the FRT three times increases the key size, at an added complexity of one more lens. The encrypted image is holographically recorded in a photorefractive crystal and is then decrypted by generating through phase conjugation, the conjugate of the encrypted image. A lithium niobate crystal has been used as a phase contrast filter to reconstruct the decrypted phase image, alleviating the need of alignment in the Fourier plane making the system rugged.
Optics Communications, 2005
We implement a new modulation scheme for inputting digital data pages for content-addressable hol... more We implement a new modulation scheme for inputting digital data pages for content-addressable holographic data storage. This scheme, which is a modification of the hybrid ternary modulation (HTM) scheme, exploits the advantages of both pure phase modulation and hybrid ternary modulation. The technique of using binary phase data pages with equal number of 0 and π using twisted-nematic liquid crystal
Optics Communications, 1991
Optics Letters, 2009
We experimentally investigate the formation of reconfigurable three-dimensional (3D) nonlinear ph... more We experimentally investigate the formation of reconfigurable three-dimensional (3D) nonlinear photonic lattices in an externally biased cerium doped strontium barium niobate photorefractive crystal by a spatial light modulator-assisted versatile simplified single step optical induction approach. The analysis of the generated 3D nonlinear photonic lattices by plane wave guiding, momentum space spectroscopy, and far field diffraction pattern imaging is presented, which points to the embedded potential of these 3D structures as reconfigurable platform to investigate advanced nonlinear light-matter interaction in periodic structures.
Optics and Lasers in Engineering, 2005
We propose and demonstrate the use of phase images for holographic data storage. Use of phase ima... more We propose and demonstrate the use of phase images for holographic data storage. Use of phase images as input leads to uniform diffraction efficiency of multiplexed data pages. Use of binary phase-based data pages with 0 and p phase changes produces uniform spectral distribution at the Fourier plane. This in turn facilitates better recording of higher spatial frequencies. We experimentally demonstrate a phase-based holographic data storage system using shift multiplexing in a Fe:LiNbO 3 crystal, and use it for associative retrieval. Preliminary studies indicate high discrimination capabilities of phase-based holographic data storage system over the amplitude-based system in a content-addressable memory.
Applied Optics, 1998
We implement an optical encryption system based on double-random phase encoding of the data at th... more We implement an optical encryption system based on double-random phase encoding of the data at the input and the Fourier planes. In our method we decrypt the image by generating a conjugate of the encrypted image through phase conjugation in a photorefractive crystal. The use of phase conjugation results in near-diffraction-limited imaging. Also, the key that is used during encryption can also be used for decrypting the data, thereby alleviating the need for using a conjugate of the key. The effect of a finite space-bandwidth product of the random phase mask on the encryption system's performance is discussed. A theoretical analysis is given of the sensitivity of the system to misalignment errors of a Fourier plane random phase mask.
Optical Engineering, 2004
We demonstrate a fully phase encryption system that uses digital holography. The input amplitude ... more We demonstrate a fully phase encryption system that uses digital holography. The input amplitude image to be encrypted is phase encoded, and either its Fourier or Fresnel transform is obtained. Using interference with a wave from a random phase mask, a Fourier or Fresnel ...
Optics Communications, 2002
Use of neural networks (NNs) and diffraction pattern sampling by a ring-wedge detector leads to e... more Use of neural networks (NNs) and diffraction pattern sampling by a ring-wedge detector leads to easier and faster algorithms for pattern recognition. An estimation was made of the optimum dimensions of a digital ring-wedge detector for sampling Fourier transform of random matrices through simulation of digital ring-wedge detector. The modulus squared Fourier transforms of facial images were sampled by ring-wedge geometry, and used for training a neural net for multi-face recognition. Fourier spectral intensities obtained by simulation and experiment were both tested for training and generalization of the network which was studied as a function of learning rate and number of epochs.
Optics Letters, 2009
Security of the conventional Fourier-based double-random-phase encryption (DRPE) technique is pro... more Security of the conventional Fourier-based double-random-phase encryption (DRPE) technique is prone to impulse attacks, as the Fourier transform (FT) of a delta function results in a unity function. To negate such an attack, the phase factors of the lenses are modified by multiplying these with random-phase functions. Owing to this modification of the FT as a result of the randomized lens phase function, a modified FT ͑MFT LR ͒ gives the random output for a delta function input. Employing MFT LR in the DRPE technique enhances the security features and makes the encryption system safer from the impulse attack. Numerical and experimental results are given for the validation of the proposed technique.
Applied Optics, 1992
We describe a real-time image-processing scheme that uses selective erasure of spatial frequencie... more We describe a real-time image-processing scheme that uses selective erasure of spatial frequencies at the Fourier transform plane in an arrangement employing photorefractive two-beam coupling. The versatility of the device results from the use of the Fourier transform of the erasure beam, which counterpropagates to the image-bearing beam. The technique can perform spatial-filtering operations such as edge enhancement, bandpass filtering, and pattern recognition by controlling the information available at the erasure-beam Fourier plane. An experimental demonstration has been made on edge enhancement, bandpass filtering, and character recognition.
Optical Engineering, 2003
We propose a new method to encrypt and decrypt a two-dimensional amplitude image, which uses a ji... more We propose a new method to encrypt and decrypt a two-dimensional amplitude image, which uses a jigsaw transform and a localized fractional Fourier transform. The jigsaw transform is applied to the original image to be encrypted, and the image is then divided into independent ...
Applied Optics, 2008
We make use of a dual beam multiple-exposure (DBME) holographic technique for the formation of al... more We make use of a dual beam multiple-exposure (DBME) holographic technique for the formation of all 14 Bravais lattices of three-dimensional photonic crystal microstructures. For simplicity of experimental implementation, the DBME method has been modified such that, prior to each exposure, once the proper angle between the wave vectors of the interfering beams is chosen, a single axis rotation of the recording medium gives the desired results. The parameters required for the generation of the lattice structures have been derived by appropriate modification of interference of four noncoplanar beams (IFNB) analysis for corresponding implementation in the DBME technique, and the results have been verified by computer simulations. After giving a comparative study of the results with the IFNB method, recording geometries for the DBME approach are also proposed in order to realize all 14 Bravais lattices experimentally.
Optics Communications, 2004
In this paper, we demonstrate a fully digital technique using double random Fourier, and fraction... more In this paper, we demonstrate a fully digital technique using double random Fourier, and fractional plane encryption. The input image to be encrypted is multiplied by a phase mask, and either its Fourier or fractional Fourier transform is obtained. Using interference with a wave from another random phase mask, the encrypted data (Fourier or fractional hologram) is recorded digitally. The decryption key is also recorded as a digital hologram, called the key hologram. An electronic key generated in the PC is multiplied with the encrypted hologram, and a Fourier or fractional Fourier transform (encrypted image) is obtained. This decryption key hologram, the electronically generated key (random phase code), and the encrypted image can be transmitted through communication channels. The retrieval is carried out by all-digital means.
Applied Optics, 2001
We propose and demonstrate a fractional Fourier domain encrypted holographic memory using an anam... more We propose and demonstrate a fractional Fourier domain encrypted holographic memory using an anamorphic optical system. The encryption is done by use of two statistically independent random-phase codes in the fractional Fourier domain. If the two random-phase codes are statistically independent white sequences, the encrypted data are stationary white noise. We exploit the capability of an optical system to process information in two dimensions by using two different sets of parameters along the two orthogonal axes to encode the data. The fractional Fourier transform parameters along with the random-phase codes constitute the key to the encrypted data. The knowledge of the key is essential to the successful decryption of data. The decoding of the encoded data is done by use of phase conjugation. We present a few experimental results.
Optics Communications, 1990
A scheme is described for removal of beam fanning, which is noise in the amplified image, by two-... more A scheme is described for removal of beam fanning, which is noise in the amplified image, by two-beam coupling in a photorefractive BaTiO 3 crystal. The large time constant of the beam fanning is exploited for the success of this scheme. An 8 ms duration pump pulse is used ...
Optics Communications, 2003
We report the use of an electrically addressed liquid crystal spatial light modulator (EALCSLM) o... more We report the use of an electrically addressed liquid crystal spatial light modulator (EALCSLM) operating in the phase mode as a phase-contrast filter (PCF). As an application, an optical phase encryption system has been implemented. We encrypt and decrypt a two-dimensional phase image obtained from an amplitude image. Encrypted image is holographically recorded in a Barium titanate crystal and is then decrypted by generating through phase conjugation, a conjugate of the encrypted image. The decrypted phase image is converted into an amplitude image using an EASLM as a PCF. The idea has been supported by the experimental results.
Optics Communications, 2006
We propose and demonstrate a digital holographic technique for 3D object recognition and classifi... more We propose and demonstrate a digital holographic technique for 3D object recognition and classification. One Fresnel digital hologram of each of the 3D objects to be classified is recorded. The electronic holograms are processed digitally to retrieve 3D object information as 2D digital complex images. We use this method to classify four physical objects in a 3D scene into two classes. Results are presented from an experiment to demonstrate the proof of the concept.
Optical Engineering, 2007
The complex Fresnel field that contains three-dimensional (3-D) information about an object can b... more The complex Fresnel field that contains three-dimensional (3-D) information about an object can be retrieved from an optically generated and electronically detected single off-axis Fresnel hologram of a 3-D object. The retrieved complex Fresnel field gives the appearance of a ...
Optical Engineering, 2003
Optical information processing techniques offer many advantages for data security applications. O... more Optical information processing techniques offer many advantages for data security applications. Optics offers several dimensions in which information can be hiddenphase, polarization, wavelength, etc.which makes it possible to encode data more securely. ...
Optics and Lasers in Engineering, 2004
In this paper, we implement a fully phase-encrypted memory system using cascaded extended fractio... more In this paper, we implement a fully phase-encrypted memory system using cascaded extended fractional Fourier transform (FRT). We encrypt and decrypt a two-dimensional image obtained from an amplitude image. The full phase image to be encrypted is fractional Fourier transformed three times and random phase masks are placed in the two intermediate planes. Performing the FRT three times increases the key size, at an added complexity of one more lens. The encrypted image is holographically recorded in a photorefractive crystal and is then decrypted by generating through phase conjugation, the conjugate of the encrypted image. A lithium niobate crystal has been used as a phase contrast filter to reconstruct the decrypted phase image, alleviating the need of alignment in the Fourier plane making the system rugged.
Optics Communications, 2005
We implement a new modulation scheme for inputting digital data pages for content-addressable hol... more We implement a new modulation scheme for inputting digital data pages for content-addressable holographic data storage. This scheme, which is a modification of the hybrid ternary modulation (HTM) scheme, exploits the advantages of both pure phase modulation and hybrid ternary modulation. The technique of using binary phase data pages with equal number of 0 and π using twisted-nematic liquid crystal
Optics Communications, 1991
Optics Letters, 2009
We experimentally investigate the formation of reconfigurable three-dimensional (3D) nonlinear ph... more We experimentally investigate the formation of reconfigurable three-dimensional (3D) nonlinear photonic lattices in an externally biased cerium doped strontium barium niobate photorefractive crystal by a spatial light modulator-assisted versatile simplified single step optical induction approach. The analysis of the generated 3D nonlinear photonic lattices by plane wave guiding, momentum space spectroscopy, and far field diffraction pattern imaging is presented, which points to the embedded potential of these 3D structures as reconfigurable platform to investigate advanced nonlinear light-matter interaction in periodic structures.
Optics and Lasers in Engineering, 2005
We propose and demonstrate the use of phase images for holographic data storage. Use of phase ima... more We propose and demonstrate the use of phase images for holographic data storage. Use of phase images as input leads to uniform diffraction efficiency of multiplexed data pages. Use of binary phase-based data pages with 0 and p phase changes produces uniform spectral distribution at the Fourier plane. This in turn facilitates better recording of higher spatial frequencies. We experimentally demonstrate a phase-based holographic data storage system using shift multiplexing in a Fe:LiNbO 3 crystal, and use it for associative retrieval. Preliminary studies indicate high discrimination capabilities of phase-based holographic data storage system over the amplitude-based system in a content-addressable memory.
Applied Optics, 1998
We implement an optical encryption system based on double-random phase encoding of the data at th... more We implement an optical encryption system based on double-random phase encoding of the data at the input and the Fourier planes. In our method we decrypt the image by generating a conjugate of the encrypted image through phase conjugation in a photorefractive crystal. The use of phase conjugation results in near-diffraction-limited imaging. Also, the key that is used during encryption can also be used for decrypting the data, thereby alleviating the need for using a conjugate of the key. The effect of a finite space-bandwidth product of the random phase mask on the encryption system's performance is discussed. A theoretical analysis is given of the sensitivity of the system to misalignment errors of a Fourier plane random phase mask.
Optical Engineering, 2004
We demonstrate a fully phase encryption system that uses digital holography. The input amplitude ... more We demonstrate a fully phase encryption system that uses digital holography. The input amplitude image to be encrypted is phase encoded, and either its Fourier or Fresnel transform is obtained. Using interference with a wave from a random phase mask, a Fourier or Fresnel ...
Optics Communications, 2002
Use of neural networks (NNs) and diffraction pattern sampling by a ring-wedge detector leads to e... more Use of neural networks (NNs) and diffraction pattern sampling by a ring-wedge detector leads to easier and faster algorithms for pattern recognition. An estimation was made of the optimum dimensions of a digital ring-wedge detector for sampling Fourier transform of random matrices through simulation of digital ring-wedge detector. The modulus squared Fourier transforms of facial images were sampled by ring-wedge geometry, and used for training a neural net for multi-face recognition. Fourier spectral intensities obtained by simulation and experiment were both tested for training and generalization of the network which was studied as a function of learning rate and number of epochs.
Optics Letters, 2009
Security of the conventional Fourier-based double-random-phase encryption (DRPE) technique is pro... more Security of the conventional Fourier-based double-random-phase encryption (DRPE) technique is prone to impulse attacks, as the Fourier transform (FT) of a delta function results in a unity function. To negate such an attack, the phase factors of the lenses are modified by multiplying these with random-phase functions. Owing to this modification of the FT as a result of the randomized lens phase function, a modified FT ͑MFT LR ͒ gives the random output for a delta function input. Employing MFT LR in the DRPE technique enhances the security features and makes the encryption system safer from the impulse attack. Numerical and experimental results are given for the validation of the proposed technique.
Applied Optics, 1992
We describe a real-time image-processing scheme that uses selective erasure of spatial frequencie... more We describe a real-time image-processing scheme that uses selective erasure of spatial frequencies at the Fourier transform plane in an arrangement employing photorefractive two-beam coupling. The versatility of the device results from the use of the Fourier transform of the erasure beam, which counterpropagates to the image-bearing beam. The technique can perform spatial-filtering operations such as edge enhancement, bandpass filtering, and pattern recognition by controlling the information available at the erasure-beam Fourier plane. An experimental demonstration has been made on edge enhancement, bandpass filtering, and character recognition.
Optical Engineering, 2003
We propose a new method to encrypt and decrypt a two-dimensional amplitude image, which uses a ji... more We propose a new method to encrypt and decrypt a two-dimensional amplitude image, which uses a jigsaw transform and a localized fractional Fourier transform. The jigsaw transform is applied to the original image to be encrypted, and the image is then divided into independent ...
Applied Optics, 2008
We make use of a dual beam multiple-exposure (DBME) holographic technique for the formation of al... more We make use of a dual beam multiple-exposure (DBME) holographic technique for the formation of all 14 Bravais lattices of three-dimensional photonic crystal microstructures. For simplicity of experimental implementation, the DBME method has been modified such that, prior to each exposure, once the proper angle between the wave vectors of the interfering beams is chosen, a single axis rotation of the recording medium gives the desired results. The parameters required for the generation of the lattice structures have been derived by appropriate modification of interference of four noncoplanar beams (IFNB) analysis for corresponding implementation in the DBME technique, and the results have been verified by computer simulations. After giving a comparative study of the results with the IFNB method, recording geometries for the DBME approach are also proposed in order to realize all 14 Bravais lattices experimentally.
Optics Communications, 2004
In this paper, we demonstrate a fully digital technique using double random Fourier, and fraction... more In this paper, we demonstrate a fully digital technique using double random Fourier, and fractional plane encryption. The input image to be encrypted is multiplied by a phase mask, and either its Fourier or fractional Fourier transform is obtained. Using interference with a wave from another random phase mask, the encrypted data (Fourier or fractional hologram) is recorded digitally. The decryption key is also recorded as a digital hologram, called the key hologram. An electronic key generated in the PC is multiplied with the encrypted hologram, and a Fourier or fractional Fourier transform (encrypted image) is obtained. This decryption key hologram, the electronically generated key (random phase code), and the encrypted image can be transmitted through communication channels. The retrieval is carried out by all-digital means.
Applied Optics, 2001
We propose and demonstrate a fractional Fourier domain encrypted holographic memory using an anam... more We propose and demonstrate a fractional Fourier domain encrypted holographic memory using an anamorphic optical system. The encryption is done by use of two statistically independent random-phase codes in the fractional Fourier domain. If the two random-phase codes are statistically independent white sequences, the encrypted data are stationary white noise. We exploit the capability of an optical system to process information in two dimensions by using two different sets of parameters along the two orthogonal axes to encode the data. The fractional Fourier transform parameters along with the random-phase codes constitute the key to the encrypted data. The knowledge of the key is essential to the successful decryption of data. The decoding of the encoded data is done by use of phase conjugation. We present a few experimental results.
Optics Communications, 1990
A scheme is described for removal of beam fanning, which is noise in the amplified image, by two-... more A scheme is described for removal of beam fanning, which is noise in the amplified image, by two-beam coupling in a photorefractive BaTiO 3 crystal. The large time constant of the beam fanning is exploited for the success of this scheme. An 8 ms duration pump pulse is used ...
Optics Communications, 2003
We report the use of an electrically addressed liquid crystal spatial light modulator (EALCSLM) o... more We report the use of an electrically addressed liquid crystal spatial light modulator (EALCSLM) operating in the phase mode as a phase-contrast filter (PCF). As an application, an optical phase encryption system has been implemented. We encrypt and decrypt a two-dimensional phase image obtained from an amplitude image. Encrypted image is holographically recorded in a Barium titanate crystal and is then decrypted by generating through phase conjugation, a conjugate of the encrypted image. The decrypted phase image is converted into an amplitude image using an EASLM as a PCF. The idea has been supported by the experimental results.