Seminar on Photonic Band Gap Materials: Light Trapping Crystals

Photonic Band Gap (PBG) materials are artificial, periodic, dielectrics that enable engineering of the most fundamental properties of electromagnetic waves. These include the laws of refraction, diffraction, and spontaneous emission of light. Unlike traditional semiconductors that rely on the propagation of electrons through an atomic lattice, PBG materials execute their novel functions through selective trapping or localization of light. This is a fundamentally new and largely unexplored property of Maxwell's equations. This is also of practical importance for alloptical communications, information processing, efficient lighting, and solar energy trapping. Three dimensional (3D) PBG materials offer a unique opportunity to simultaneously (i) synthesize micron-scale 3D circuits of light that do not suffer from diffractive losses and (ii) engineer the electromagnetic vacuum density of states in this 3D optical micro-chip. This combined capability opens a new frontier in integrated optics as well as the basic science of radiation-matter interactions. I review recent approaches to micro-fabrication of photonic crystals with a large 3D PBG centered near 1.5 microns. These include direct laser-writing techniques, holographic lithography, and a newly invented optical phase mask lithography technique. I discuss consequences of PBG materials in classical and quantum electrodynamics.

Power transformers

Power transformers are the most significant pieces of equipment for electrical power delivery systems. One of the key parameters to be monitored in a power transformer is the internal temperature. High temperature accelerates the aging of winding paper insulation and increases the risk of bubbling under severe load conditions. Temperature is also an important parameter for transformer cooling system. The transformer winding hottest-spot temperature is one of a number of limiting factors for the loading capability of transformers. One way to increase the loading capability is to increase the efficiency of the cooling system by using fans and pumps. This research focuses on the investigation of the effect of the cooling system parameters, in particular the oil flow rate, on the thermal performance of power transformers.

Seminar on Optical Isolator: Application to Photonic Integrated Circuits

Optical active devices fail to operate in a desired manner, when unwanted reflections are launched into them. An optical isolator plays an essential role in protecting optical devices from unwanted reflections. Commercially available optical isolators based on a magneto-optic Faraday effect, which are provided with optical fiber and optical beam interfaces, are hard to be integrated with other optical devices. In case of waveguide isolators, it is quite unrealizable to use a rotation of polarization, because the precise control of waveguide birefringence is needed. Several approaches have been developed to avoid the precise control of waveguide geometry, like a nonreciprocal radiation and a nonreciprocal loss isolator. An interferometric waveguide isolator, which uses a nonreciprocal phase shift provided by the first-order magneto-optic effect, has the advantages of a single polarization operation and a wide operational wavelength range. Also, the interferometric isolator is realizable in several waveguide platforms by using a magneto-optic material in a cladding layer. To achieve this, we developed a direct bonding technique of magneto-optic garnet on III-V compound semiconductors and silicon waveguides. In this talk, the integration of optical isolators will be addressed, which includes a non-magneto-optic approach. 

reference :http://www.eng.monash.edu.au

Advanced Optical Functionalities in Photonic Crystals

High-quality self-assembled three-dimensionally-ordered photonic crystals have been synthesized with inorganic and polymeric colloids. These crystals display a pseudo bandgap in the UV / visible / near-IR regions with high values of reflectance combined with low transmission. The stop band characteristics have been modified after infiltrating these passive photonic crystals with materials such as ZnO as well as by synthesizing active photonic crystals directly from colloids made of organic dye-polymer composites. The emission characteristics of these active species are modified by the photonic crystal    environment due to the anisotropic stop band. It has been possible to fabricate photonic crystal heterostructures as well as photonic crystal waveguides for building functionalities into photonic integrated circuits.  BJ93GJCCMXAR

2010 seminar topic Multi-wavelength and Broadband Optical Sources for Fiber-Optic Communication

Tunable lasers in the C and L bands of fiber-optic communication have been designed with erbium-doped fiber. Tunability has been achieved without using an intra-cavity filter, merely by changing the intro-cavity parameters in an appropriate manner. Also, mode-locking at GHz frequencies with a very simple economical design is a highlight of this work. The large tuning range possible in this design is further utilized in demonstrating a broadband source by introducing a dispersion shifted fiber as an intra cavity element. The multiple four-wave mixing processes occurring between the longitudinal modes in this fiber result in a spectral broadening throughout the gain spectrum of the EDF. This is a simple and elegant design to realize a tunable broadband source at pump powers less than 200 mW. The mechanism of broadband generation and the utility of the source for applications will be discussed.

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reference :http://dspace.cusat.ac.in

Cryptography

Security of information results from the need for Private transmission of messages. It is very essential that Security coverage should be provided to the computer systems, including to security to communication channels

Cryptography means hidden writing. Cryptography is used to protect information to which illegal access is possible and where other protective measures are inefficient

The basic idea in cryptography is to take a message in ordinary language, called plain text. This is transformed in some way to produce cipher text. The cipher text can now be sent to the correspondent. He uses another transformation to recover the plain text from the cipher text. The plain text is encrypted or hidden by the first transformation to obtain the cipher text. The cipher text is decrypted by another transformation to obtain the plain text once again. After encryption, cipher text can be transmitted over a data link or stored in a file

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