AJP	ISSN : 0971 – 3093 Vol 23, No. 3, July – Sept, 2014

Vol. 23, No 3 (2014) 303-332

Introduction to optical signal processing

 

Shi Liu^a, Changliang Guo^a and John T Sheridan^a

^aSchool of Electrical, Electronic and Communication Engineering, College of Engineering and Architecture,

This paper presents an overview of recent developments in the area of linear optical signal processing (OSP) under the paraxial approximation. The availability of high quality spatial light modulators (SLM) and high resolution digital cameras make it more feasible to implement many OSP functions. Some fundamental concepts concerning basic Fourier analysis and functions are described for such systems. Then the Fourier transform (FT), the optical Fourier transform (OFT), the discrete Fourier transform (DFT), the fractional Fourier transform (FRT), the Fresnel transform (FST), and the general case of the linear canonical transform (LCT) are discussed. In particular two significant applications of OSP, i.e. optical encryption systems and digital watermarking techniques, are reviewed including basic optical systems and numerical algorithms. Some publications indicating how these concepts have been successfully applied over many years by Kehar Singh et al are referenced. © Anita Publications. All rights reserved.

Total Refs : 210

 

 Vol. 23, No 3 (2014) 333-342

Holography: Rediscovery, Development, and Beyond

 

Francis T S Yu

There are basically two-types of holography that have been developed and they are : Leith’s transmission-type holography and Denisyuk’s reflection-type holography. Nevertheless, the rediscovery of holography must be due to the discovery of laser. In other words, without the discovery of this coherent light source, holography may not have been rediscovered! Nevertheless, the original purpose of the development of holography was to produce a true three-dimensional image by means of wave front reconstruction. Since the rediscovery, it has offered a much wider application beyond its legacy! © Anita Publications. All rights reserved.

 Vol. 23, No 3 (2014) 343-351

Non-linear Fourier optics in computers: a challenge for hybrid digital-optical image processors

 

L Yaroslavsky

Department of Physical Electronics, School of electrical Engineering,

In the paper, a family of methods that work in the domain of Discrete Fourier and Discrete cosine transforms and proved to be very efficient for adaptive and local adaptive image restoration and target location is reviewed and possible ways for their implementation in analog optical image processors that work with the speed of light are discussed. ©Anita Publications reserved. All rights reserved.

Total Refs : 8

Vol. 23, No 3 (2014) 353-362

From optical neural networks to the art of learning

 

Francis T S Yu

 Emeritus Evan Pugh Professor of Electrical Engineering

Common sense tells us that, if we knew the basic constraints and abilities of our neural network, then more efficient learning and educational methods can be devised. There are a couple of fundamental questions: Are we educating our students efficiently? The answer to this question is apparently no! How can we improve it? It can be improved with innovative educational methods, as will be discussed in this paper. © Anita Publications. All rights reserved.

 Vol. 23, No 3 (2014) 363-402

Pupil filters in optical systems. Implementation in liquid crystal spatial light modulators

 

Juan Campos¹, Juan C Escalera¹, Andrés Márquez^2,3, and María J Yzuel¹

¹Departamento de Física, Universidad Autónoma de Barcelona, 08193 Bellaterra, Spain;

²Depto de Física, Ingeniería de Sistema y Teoría de la Señal, Universidad de Alicante, Ap. 99, E-03080 Alicante, Spain

In this paper we review the use of liquid crystal spatial light modulators (LC-SLM) for implementing pupil filters in optical systems. We intend to cover three topics. Firstly, we will study different types of amplitude, phase and complex filters and their effects onto the transverse and axial behavior of an optical system. Secondly, we will describe how to control the amplitude and the phase in an LC-SLM in order to be capable of implementing pupil filters on it. Finally, we will show experimental results of these set-ups improving diverse features of the response of an optical system. © Anita Publications. All rights reserved.

Total Refs : 103

Vol. 23, No 3 (2014) 403-414

About the future of optical computing

 

Joseph Shamir

Interest in signal processing and computing using light was triggered by the invention of the laser and flourished during about three decades starting in 1960. Optical methods were first introduced for analog signal processing paradigms but early attempts toward optical digital processing failed due to fundamental misconceptions. To assess the trends for the future, the first part of the paper is devoted mainly to a historical overview while the second part shows that some novel concepts and advanced technology may revitalize optical signal processing also within the digital computing world. This latter development is demonstrated by digital logic functions implemented on simple electro-optic networks. © Anita Publications. All rights reserved.

Total Refs : 46

Vol. 23, No 3 (2014) 415-424

Novel zoom systems using a vortex pair

 

Jorge Ojeda-Castaneda, Cristina M Gómez-Sarabia and Sergio Ledesma

Electronics Department and Digital Arts Department, University of Guanajuato

We describe the use of two refractive elements that have helical phase variations, here denoted as a vortex pair, for implementing varifocal lenses. Next, we employ vortex pairs for setting several nonconventional optical zoom systems. First, we discuss the Gaussian optics characteristics of single lens zoom system. Then, we describe a tunable afocal attachment, which is later employed for implementing a telephoto system whose elements are at fixed positions. Finally, we discuss a nonconventional zoom system, and we unveil a confocal device that scans axially a volumetric sample. © Anita Publications. All rights reserved.

Total Refs : 13

 Vol. 23, No 3 (2014) 425-432

 Optical scattering of anisotropic nanocylinder evaluated by T-matrix mehod

 

Yunlong Sheng

Center for Optics, Photonics and Lasers,

Department of Physics, Physical Engineering and Optics

The T-matrix method with the Vector Spherical Wave Function (VSWF) expansions represents some difficulties for computing optical scattering of anisotropic particles. As the divergence of the electric field is nonzero in the anisotropic medium and the VSWFs do not satisfy the anisotropic wave equations one questioned whether the VSWFs are still a suitable basis in the anisotropic medium. We made a systematic and careful review on the vector basis functions and the VSWFs. We found that a field vector in Euclidean space can be decomposed to triplet vectors {L, M, N}, which is non-coplanar. Especially, the vector L is designed to represent non-zero divergence component of the vector solution, so that the VSWF basis is sufficiently general to represent the solutions of the anisotropic wave equation. The mathematical proof can be that when the anisotropic wave equations is solved in the Fourier space, the solution is expanded in the basis of the plane waves with angular spectrum amplitude distributions. The plane waves constitute an orthogonal and complete set for the anisotropic solutions. Furthermore, the plane waves are expanded into the VSWF basis. These two-step expansions are equivalent to the one-step direct expansion of the anisotropic solution to the VSWF basis. We used direct VSWF expansion along with the point-matching method in the T-matrix, and applied the boundary condition to the normal components displacement field in order to compute the stress and the related forces and torques and to show the mechanism of the optical trap of the anisotropic nano-cylinders.©Anita Publications. All rights reserved.

Keywords: Optical Scattering; Anisotropic medium, T-matrix,Vector spherical wave functions, Vector field expansion, Complete function set.

Vol. 23, No 3 (2014) 433-450

Optical state machine and nano spheres

 

Eyal Cohen¹, Shlomi Dolev¹ and Michael Rosenblit²

¹Department of Computer Science

Ben Gurion University of the Negev, 653 Be’er Sheva 84105, Israel

²Ilze Katz Institute for Nanoscale Science and Technology, Ben Gurion University of the Negev, 653 Be’er Sheva 84105, Israel

We propose a nano optical state machine. We use an optical vector-matrix multiplication technique to perform an optical state transition. We design a reflective-diffractive element for the implementation of such multiplier. We design this element using nano-spheres. ©Anita Publications. All rights reserved.

Vol. 23, No 4 (2014) 451-456

Image retrieval of turbulence affected stellar objects and its interface with medical image analysis

 

Swapan K Saha

Formerly with Indian Institute of Astrophysics, Bangalore-560 034, India

Single aperture speckle interferometry, a method that deciphers diffraction limited spatial Fourier spectrum and image features of stellar objects by counteracting blurring effect caused by the atmospheric turbulence, pupil- plane techniques, as well as hybrid methods (speckle interferometry with non-redundant pupils) have made impacts in several important fields in astrophysics. Image processing with triple correlation technique retrieves diffraction limited information from the short exposure images of the object. The medical images typically suffer from the imperfections as well. The reconstruction based on the bispectrum technique will be discussed. © Anita Publications. All rights reserved.

 Vol. 23, No 3 (2014) 457-471

Common mistakes, misusage, and other observations in aberrated imaging

 

Virendra N Mahajan

The Aerospace Corporation, El Segundo, CA 90245 USA

Some of the common mistakes in aberrated imaging and misuse of some of the terms are described. They include the sign of a wave aberration, the additive nature of the wave aberrations of a multisurface system versus its lack for the ray aberrations, order of a wave and a ray aberration, root mean square radius of the ray spot instead of its standard deviation, rms value of an aberration instead of its standard deviation, Strehl ratio definition and obtaining it from the modulation transfer function instead of the optical transfer function, use of the Zernike circle polynomials for analysis of wavefronts for noncircular pupils, and obtaining the Seidel coefficients of an aberration function from its Zernike coefficients. We also point out that the so-called Fourier-transform lens does not perform the Fourier transformation. © Anita Publications. All rights reserved.

Vol. 23, No 3 (2014) 473-490

Optical asymmetric cryptosystems: A Review

 

Sudheesh K Rajput and Naveen K Nishchal*

From the cryptography point of view, symmetric encryption schemes suffer from several problems; such as, key distribution, management, delivery and various kinds of attacks. In order to overcome these problems, various asymmetric image encryption schemes have been reported in literature during past few years. In this paper, at first, we present an overview of some of the basic image encryption schemes and then we review all the optical asymmetric cryptosystems based on amplitude- and phase-truncation and phase retrieval approach in different encryption domains like Fourier, Fresnel, and fractional Fourier transform domains. The input image/data used are gray-scale and color patterns. ©Anita Publications. All rights reserved.

Keywords: Image encryption, optical asymmetric cryptosystems, Fourier transform, Fresnel transform, fractional Fourier transform, Phase retrieval algorithm.

Total Refs : 95

Vol. 23, No 3 (2014) 491-496

Nanosecond reverse saturable absorption in graphene-metal porphyrin composites and its application to all-optical logic

 

Chandresh Yadav and Sukhdev Roy

We theoretically analyze reverse saturable absorption (RSA) in graphene and its composites with metal porphyrins in nanosecond regime based on nonlinear intensity induced excited-state absorption (ESA). RSA with 100% modulation can be achieved for graphene-porphyrin composites due to strong two-photon absorption (TPA) and ESA in comparison to pure graphene. Theoretical results are in good agreement with reported experimental results. The RSA characteristics that are sensitive to pump intensity, concentration and TPA coefficient have been used to design all-optical NOT and the universal NOR and NAND logic gates. RSA at relatively lower pump intensities (MW/cm2) compared to other organic materials opens up exciting prospects for all-optical information processing with graphene and graphene composite materials. © Anita Publications. All rights reserved.

 Vol. 23, No 3 (2014) 497-502

Characterizing the passive modelocker for an ultrafast laser

 

An economic, solid state device for effcient modelocking the ultrafast lasers is the contemporary area of research. In this paper we have studied the nonlinear optical properties of a standard dye IR26 by using the Z-scan technique at 1064 nm as a function of its concentration. A prominent contribution of nonlinear absorption is observed in the Z-scan profles.

The commercial laser has been checked for its modelocking effciencies at various concentrations to provide the typical values for a standard modelocker. © Anita Publications. All rights reserved.

PACS. 42.65.k, 42.65.Jx, 42.60.Fc. 42.55.-f

Keywords: nonlinear optics, Z-scan, saturable absorber, modelocking.