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Kehar Singh

Prof. Kehar  Singh

Emeritus Fellow
Indian Institute of Technology Delhi

Physics Department
IIT Delhi

New Delhi  110016

tel: 011-26591324
E-mail: kehars@physics.iitd.ac.in

Area of Expertise

Information Photonics, Holography, Information Security, Singular Optics, Nanophotonics


Professor Kehar Singh has served as a member of the faculty at IIT Delhi since 1965 in various capacities. He was an academic visitor at the Imperial College of Science & Technology, London during. 1969- 1970. He had been a Professor since January 1984 and during the period 1996 - 1999 served as Head of the Physics Deptt. Prof. Singh held the position of Dean, Post Graduate Studies and Research, IIT Delhi during the period of March 2001-Aug. 2003. He served as CLUSTER Chair at the Swiss Federal Institute of Technology, Lausanne (Switzerland) in Dec. 2002. Currently he is an Emeritus Fellow at IIT Delhi where he continues to teach and carry out research.

Prof. Kehar Singh has been an active researcher and educator and has created infrastructural facilities for teaching and research in his areas of specialization: Photonics/Information Optics (Image formation and evaluation, Dynamic holography, Nonlinear photorefractives, Optical correlators, Holographic storage, Singular optics and Optical encryption). He has published extensively, having authored / co-authored nearly 350 peer reviewed research papers. Besides these there are approx. 65 review articles in books and journals, and 50 papers in conference proceedings.

Research publications by Prof. Singh and coworkers during the period 1965-1985 resulted in 11 Ph.D. theses. Since 1986, 20 students have completed Ph.D. degrees under the supervision of Prof. Singh. Besides these, 75 Master of Technology and M.Sc. students have been guided in their dissertation work. He has been the backbone of the M. Tech. program in Applied Optics at IIT Delhi ever since it started in 1966. This program has produced many scientists who occupy key positions in India and abroad.
Professor Kehar Singh was honoured with Shanti Swarup Bhatnagar Award in Physical Sciences in 1985 by the CSIR, Govt. of India. He has been awarded in 2001, the Galileo Galilei Award of the International Commission on Optics. The Optical Society of India honoured him with the ‘OSI Award’. He was also given ‘Life Time Achievement Award ‘at the OSI symp. held at Tezpur in Dec.2007,and Golden Jubilee ‘Distinguished Service Award’of IIT Delhi in 2011.

He is a Fellow of the Optical Society of America, SPIE (The International Society for Optical Engineering), and Indian National Academy of Engineering, in addition to being a Fellow of the Optical Society of India and the Laser & Spectroscopy Society of India. He was President of the Optical Society of India from 1991 to 1994 and its Vice-President from 1988 to 1991. He also served as the President of ‘Laser and Spectroscopy Society’ of India. He was President, Indian Science Congress Association (Physical Sciences Section) in 2004. Professor Singh is an international advisory member of the editorial board of Optical Review (Japan, 1994 – to date), Member of the editorial boards of Optics & Lasers in Engg. (Elsevier, 1999 – 2006), J. Optics (India, 1974 – to date), Asian J. Phys. (1992 – to date). and Invertis J. Science and Technol (2007- ). He also served as an editorial board member of the Indian J. Pure Appl. Phys. (CSIR, 1986 – 88).

Prof. Singh has been serving as a reviewer of research papers for several journals of repute. He has given approx. 90 invited lectures in various international and national conferences/seminars/workshops and has also been associated as member of organizing/technical/steering committees of several international and national conferences/seminars/ workshops. He was one of the Directors of the II Winter College in Optics held at ICTP, Trieste, Italy during Feb- March, 1995. Professor Singh’s research work has attracted funding for sponsored research in the field of Optics and Photonics from a number of Govt. agencies such as Department of Science and Technology, Ministry of Human Resource Development and Defense Research and Development Organization. He has served on many committees of the Govt. of India, and has been a consultant to some industries.

As technical chair of the International Conference on ‘Optics and Optoelectronics’ held in Dehradun, India in Dec. 1998, Prof. Singh co-edited a two volume proceedings of the conference and SPIE volume 3729, Selected papers from International Conference on Optics and Optoelectronics’98 (Silver Jubilee Symposium of the Optical Society of India). He was technical co-chair of the International conference on Optics and Opto-electronics held in December 2005. He has also edited / co-edited 2 special issues on ‘Photorefractives and their applications’ of J. Optics (India), 3 issues on ‘Optical pattern recognition’ of Asian J. Physics, and a book on ‘Perspectives in Engineering Optics’.

Lecture Title(s)

Dynamic/ Updatable 3-D Displays Using Computer Generated Holograms
Three-dimensional perception is a fundamental aspect of human vision. Though a number of techniques have been developed for 3-D imaging, holography has proven to be the most interesting and successful of them all. Therefore, holography occupies a place of pride among the various methods, and makes it possible to provide highly realistic 3D images with a large viewing angle capability and viewing comfort, without the need for special eye wear. It is indeed well-known that the holograms have 3-D information such as the binocular parallax, the convergence, the accommodation, and so on.
Besides being used in many branches of science and engineering, holography finds applications in creating spectacular displays. In fact, the ideas of the ‘holographic television’ or updatable ‘holographic video display’ existed even in 1965. Holographic displays find applications in the fields of entertainment, education, medical imaging, and technical imaging in civilian and military areas. Major requirements for holographic displays are: Large size, high efficiency, fast recording, image persistence, long lifetime, and resistance to optical and electrical damage. Holography was the inspiration behind the holodeck on Star Trek- the simulated reality facility aboard the star-ship Enterprise- as well as the 3D holographic film of Princess Leia in Star Wars (“Help me, Obi-Wan Kenobi. You are my only hope”).
Computer-generated holograms have made it possible to create holograms for display of arbitrary 3D models, with arbitrarily prescribed amplitude and phase distribution. The processor speed of computers has been steadily increasing over the last decades. New image processing and compression algorithms allow reducing the data amount to manageable levels. However, despite decades of progress in computer technology, the complexity of computations involved in computer-holography for creating 3-D scenes in real-time, poses a formidable challenge. But now recent advances in graphical processing with (GPUs) have brought us closer to realizing the goal than ever before. The calculation speed of the GPU is approx. 1,500 times faster than that of a central processing unit (CPU).
The animation of the 3-D image can be reconstructed by switching the CGH at high speed. HORN (HOlographic ReconstructioN) special-purpose computers have been developed by Japanese scientists for calculating CGHs at high speed. HORN-6 is capable of handling a 3-D image composed of one million points. It is now possible to generate rainbow-, cylindrical-, cylindrical rainbow-, and disk holograms. Electroholography involves the reconstruction of a 3-D image using a device such as a liquid crystal display (LCD) to display the hologram. Photorefractive polymers have also been used to make updatable holograms.
An attempt would be made in the proposed lecture to present the basic principles involved, and the devices used for dynamic holographic displays.

Negatively-Refracting Metamaterials;A Tutorial Introduction
The subject of metamaterials has made spectacular progress during the last decade or so. These man made artificial materials show properties not attainable in naturally occurring materials, and gain their properties from the unit structure rather than the constituent materials. In the proposed lecture, an attempt would be made to introduce the relevant terminology along with a brief historical introduction to the subject. Basics of double negative materials would then be explained by discussing artificial dielectrics and artificial magnetism. Some examples of structures for the near infrared- and visible region would be given along with the relevant fabrication technologies. Finally some examples of applications would be given.

New Methods for High-Density Holographic Data Storage and Reliable Content-Addressable Search
Holographic data storage (HDS) systems have been a subject of much research due to their diverse benefits and applications. This article reports our recent research efforts towards increasing the memory capacity of HDS systems, and also towards performing a faithful content-addressable search with the HDS systems. Initially, we present the results of our investigations on the performance of defocused volume HDS systems in terms of bit-error-rate and content search capability for a photopolymer recording material. New methods are demonstrated in order to perform reliable content-addressable data search in defocused volume HDS systems. Next we present the results of our investigations on gray-scale and sparse-gray-scale data pages. We have proposed new methods for the implementation of gray-scale and sparse-gray-scale modulation codes with a single SLM working in phase mode. An experimental demonstration of the newly developed gray-level phase data page method is presented. These phase mode representations of gray-level and sparse-gray-level data pages ensure a homogenized Fourier spectrum that improves the interference efficiency between the signal and the reference beams. We also explore theoretically the potential storage density improvement while using low-pass filtering and sparse-gray-level phase data pages for holographic storage, and demonstrate the trade-off between the code rate, the block length, and the estimated capacity gain.

Nonlinear Photorefractive Materials for Information Photonics
After its discovery, the photorefractive (PR) effect has attracted many researchers to its vast field of processes, materials, and applications. Starting from the basic physics of the phenomenon to its applications and then the fabrication of the devices, the research is continuing unabated (1-12). Many new theories and applications are coming into prominence. Material research on the other hand, is also on the move. More and more new versatile, stable, and low cost materials have been shown to exhibit the PR effect with impressive response times, and easy processibility for device applications. Special emphasis has been placed on the applications of PR materials in information photonics in which the devices use light as a carrier for information, exploiting its inherent parallel processing capability. All-optical information processing devices are being investigated in recent years, incorporating PR materials as the real-time recording media making near real-time parallel processing possible. Optical correlators play a crucial role in the development of pattern recognition systems. Three-dimensional volume storage of data is achieved in holography through multiplexing of gratings in volume media. The variation in intensity in the interference pattern formed results in a modulation of the refractive index in the volume of the medium, through PR effect. A combination of holography and optical resonator using PR material can be used for the implementation of optical associative memories. In the present era offen called the ‘information age’ the security of information is of paramount importance in almost every field of information technology. P.R. materials also find applications in techniques for optical information security. The present lecture proposes to discuss in brief some of the above-mentioned topics, with special emphasis on the work carried out at IIT Delhi during the past two decades (2-12).

Laser Beams with Phase Singularities (Spinning Light)
During the last decade, laser beams with phase singularities have attracted considerable attention because of their unique properties. The term ‘phase singularity’ or ‘optical vortex’ is uses to represent a point in the wave field with undefined phase and zero amplitude. The phase change on a closed loop surrounding the vortex is an integral multiple of 2π and the integer is also called ‘topological charge’. Such beams have helical wave front and possess orbital angular momentum which is different from spin angular momentum arising due to polarization.
Singular beams can be produced in a number of ways such as by using frequency locking of lasers, mode converters, diffractive optical elements/ holographic optical elements, spiral phase plates, and plain wave interference. Such beams have found applications in a number of areas.
In the present lecture, it is proposed to outline a brief historical development of the subject followed by a description of basic properties and characteristics of singular beams. In this context Hermite- Gaussian and Laguerre-Gaussian laser modes would also be discussed. Subsequently methods of generation and testing of such beams would be described. Propagation of such beams in free-space, and through apertured system in presence of astigmatism, coma, and spherical aberration would be discussed. Finally some application areas (optical trapping, optical testing, speckle metrology, high resolution microscopy, digital holography, image processing, pattern recognition, astronomy, quantum teleportation, quantum cryptography, dark solitons, and wave guiding) would be listed. Of these areas, trapping, optical testing, image processing, and astronomical applications are proposed to be discussed in brief.

Photonic Band Gap Structures; An Exciting Area of Nanophotonics
The term ‘Nanophotonics’ can be conceptually understood as resulting from marriage between nanotechnology and photonics, and deals with interactions between light and matter at a scale shorter than the wavelength of light. The field of nanophotonics is a multidisciplinary one, involving physics, chemistry, engineering, biology, and biomedical technology etc. Some prominent areas of nanophotonics include: Near‐field interactions, Near‐field microscopy, Plasmonics, Nanomaterials, Photonic crystals, Negative refractive index matamaterials, and Nanolithography.
The present lecture aims at introducing the basic concepts in photonic bandgap structures. After listing similarities and dissimilarities between electronics and photonics, an attempt would be made to discuss 1‐D, 2‐D and 3‐D photonic bandgap structures. Various techniques for fabricating such structures would be listed, with an emphasis on holographic lithographic technique. Finally some application areas would be enumerated, and examples from the nature would be pointed out.

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