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Tunable Lasers

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Abstract

Tunable lasers as the name suggests are lasers whose wavelengths can be tuned or varied. They play an important part in optical communication networks. Recent improvements in tunable laser technologies are enabling highly flexible and effective utilization of the massive increases in optical network capacity brought by large-scale application of dense wavelength division multiplexing. 

The outlined approach of full-band tunable lasers based on DFB technology meet the existing performance specifications and possess a cost structure that will ultimately displace static- wavelength DFBs, making tunability ubiquitous.

Introduction

Tunable lasers as the name suggests are lasers whose wavelengths can be tuned or varied. They play an important part in optical communication networks. Recent improvements in tunable laser technologies are enabling highly flexible and effective utilization of the massive increases in optical network capacity brought by large-scale application of dense wavelength division multiplexing.

In a wavelength-division multiplexed (WDM) network carrying 128 wavelengths of information, we have 128 different lasers giving out these wavelengths of light. Each laser is designed differently in order to give the exact wavelength needed. Even though the lasers are expensive, in case of a breakdown, we should be able to replace it at a moment's notice so that we don't lose any of the capacity that we have invested so much money in.

Tunable Lasers Enable Next-g Capabilities

Beyond the ability to address today’s problems, tunable lasers will play a central role in allowing service providers to offer entirely new value-added services and generate new revenue streams.  Next-generation services and functionality will initially be implemented in a new generation of optical add-drop modules (OADMs) and optical cross-connects (OXCs) that incorporate tunable lasers.

Tunable Lasers Seminar PPT


Current-generation OADMs, which rely on fixed-wavelength lasers, are limited in their ability to add channels to the network. Changing traffic patterns, customer requirements, and new revenue opportunities require greater flexibility than static OADMs can provide, complicating network operations and planning. Incorporating tunable lasers removes this constraint altogether by allowing any channel to be added by the OADM at any time. With the deployment of tunable line cards at OADM sites, sparing and restoration capabilities become more economical as well. Optical cross-connects (OXCs) represent another opportunity for tunable lasers to improve network system efficiency. Line cards with widely tunable lasers covering the full C band enable physical-layer provisioning and switching in the optical domain, allowing an “any channel to any channel” connection to be made at network nodes. Widely tunable lasers simplify OXC planning, since all wavelength channels are available from any tunable line card. Even if a particular channel is already in use, wide tenability allows a18   flexible, potentially automated determination of wavelength conversion, which further simplifies  system planning by complementing and adding value to electrical-level provisioning, grooming, and switching. While today’s networks are large and complex, future networks are expected to be greatly simplified and more purely optical in nature, with significant reductions in both capital and operating costs. One scenario shows a “mesh” architecture in which nodal points on the network are designed to route signals on the basis of wavelength. In this example, tunable lasers can be deployed to route signals to their destination on the basis of wavelength. Tunable lasers will play a key role in these advanced telecom networks, since this type of architecture is unlikely to be fully realized with current-generation fixed-wavelength or even narrowly-tunable lasers.

The Distributed Feedback Laser

Among the most common diode lasers used in telecommunications today are distributed feedback (DFB) lasers. They are unique in that they incorporate a diffraction grating directly into the laser chip itself, usually along the length of the active layer (the gain medium).As used in DFB lasers, the rating reflects a single wavelength back into the cavity, forcing a single resonant mode within the laser, and producing a stable, very narrow-bandwidth output.

DFB lasers are tuned by controlling the temperature of the laser diode cavity. Because a large temperature difference is required to tune across only a few nanometers, the tuning range of a single DFB laser cavity is limited to a small range of wavelengths, typically under 5 nm. DFB lasers with wide tuning ranges therefore incorporate multiple laser cavities.

Better Use Of Expensive Network

Bandwidth Tunable lasers provide an advantage over fixed sources even when  service providers employ an alternative “hot-backup” approach to sparing  that  is, maintaining idle channels which are only activated when a backup is required.  In this application, upto 50% of the system bandwidth can be rendered unusable when using fixed wavelength lasers because network carriers must maintain a spare channel for each wavelength used. With tunable lasers, however, only a small  number of line cards are held in reserve slots, since each spare can tune to any  required wavelength. Thus tunable lasers can restore usable system bandwidth to 90% or better.

Moreover, in the event of a channel failure, a tunable backup card can be quickly configured to resume communications, providing nearly seamless restoration in the event of malfunction and allowing SONET protection to be implemented entirely in the optical domain. As a further guarantee of service continuity, tunable lasers therefore present additional opportunities for revenue generation.

Conclusion

Recent advances in tunable laser technology have brought the promise of tunable networks into clear focus. Widespread adoption of tunable lasers will not only eliminate logistical and inventory problems and the associated costs that result from fixed-wavelength line cards but will also enable novel network architectures with dynamic functionality such as dynamic add-drop, thus enabling new value-added services and creating new sources of top-line revenue for system providers.

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Google Glass

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Abstract

Project Glass is a research and development program by Google to develop an augmented reality Head-Mounted Display (HMD). The intended purpose of Project Glass products would be the hands-free displaying of information currently available to most smartphone users, and allowing for interaction with the Internet via natural language voice commands. These glasses will have the combined features of virtual reality and augmented reality. Google glasses are basically wearable computers that will use the same Android software that powers Android smartphones and tablets.

Introduction

Virtual reality is often used to describe a wide variety of applications commonly associated with immersive, highly visual, 3D environments. The development of CAD software, graphics hardware acceleration, head mounted displays, database gloves, and miniaturization.

Wearable Computing

Wearable computers, also known as body-borne computers are miniature electronic devices that are worn by the bearer under, with or on top of clothing. This class of wearable technology has been developed for general or special purpose information technologies and media development. Wearable computers are especially useful for applications that require more complex computational support than just hardware coded logics.

Google Glass

Eye Tap Technology

An EyeTap is a device that is worn in front of the eye that acts as a camera to record the scene available to the eye as well as a display to superimpose a computer-generated imagery on the original scene available to the eye. This structure allows the user's eye to operate as both a monitor and a camera as the EyeTap intakes the world around it and augments the image the user sees allowing it to overlay computer-generated data over top of the normal world the user would perceive. The EyeTap is a hard technology to categorize under the three main headers for wearable computing for while it is in theory a constancy technology in nature it also has the ability to augment and mediate the reality the user perceives.

Future Scope

Google Glass is as futuristic a gadget seen in recent times. It’s limited in scope right now, but the future, Google believes, is bright and the device itself is “incredibly compelling”.


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Bittorrent

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What Is Bittorrent?

                 BitTorrent is a protocol designed for transferring files. It is peer-to-peer in nature, as users connect to each other directly to send and receive portions of the file. However, there is a central server (called a tracker) which coordinates the action of all such peers. The tracker only manages connections, it does not have any knowledge of the contents of the files being distributed, and therefore a large number of users can be supported with relatively limited tracker bandwidth. The key philosophy of BitTorrent is that users should upload (transmit outbound) at the same time they are downloading (receiving inbound.) In this manner, network bandwidth is utilized as efficiently as possible. 

What Bittorrent Does?

                  When a file is made available using HTTP, all upload cost is placed on the hosting machine. With BitTorrent, when multiple people are downloading the same file at the same time, they upload pieces of the file to each other. This redistributes the cost of upload to downloaders, (where it is often not even metered), thus making hosting a file with a potentially unlimited number of downloaders affordable. Researchers have attempted to find practical techniques to do this before. It has not been previously deployed on a large scale because the logistical and robustness problems are quite difficult. Simply figuring out which peers have what parts of the file and where they should be sent is difficult to do without incurring a huge overhead. In addition, real deployments experience very high churn rates. Peers rarely connect for more than a few hours, and frequently for only a few minutes. 

Bittorrent


Pareto Efficiency

                  Well known economic theories show that systems which are pareto efficient, meaning that no two counter parties can make an exchange and both be happier, tend to have all of the above properties. In computer science terms, seeking Pareto efficiency is a local optimization algorithm in which pairs of counter parties see if they can improve their lot together, and such algorithms tend to lead to global optima. Specifically, if two peers are both getting poor reciprocation for some of the upload they are providing, they can often start uploading to each other instead and both get a better download rate than they had before.

Abstract

              Torrent refers to the small metadata file you receive from the web server (the one that ends in .torrent.) Metadata here means that the file contains information about the data you want to download, not the data itself. This is what is sent to your computer when you click on a download link on a website

Conclusion

             Legitimate P2P use is here and has a definite role to play in the future of the Internet. It is without a compromise between the copyright holders and the file sharers, that there will be an ever-escalating arms race of technology versus legal maneuvers. BitTorrent is a nifty program that works in a simple, if counter-intuitive.

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A Plan For No Spam

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 Introduction
 
        Unwanted and irrelevant mass mailings, commonly known as spam are becoming a serious nuisance that if left unchecked may soon be regarded as a Denial of Service Attack against the email infrastructure of the Internet itself.

Best Practices

        The traditional response of the internet to problem uses administrators of deployed protocols is to specify some form of 'Best Practices'. Spam is an attack on the Internet community. The short survey and prosecutions by the FTC and others show that the spam senders are in many cases outright criminals, how then can best practices help? One area in which best practices can provide concrete benefit is in ensuring that the vast majority of Internet users who are acting in good faith do not inadvertently make the problem worse by poorly chosen or poorly coordinated mitigation strategies. 

 
Naive Keyword Inspection  

        Messages are scanned for the presence of words or phrases that occur frequently in spam messages such as HGH or multi-level marketing. This type of filtering is implemented in many common email clients such as Outlook [MSFT].    Keyword Inspection alone is simple to implement but tends to have very high rate of false positives.

Authentication And Authorization

        Practically all spam messages sent today attempt to evade anti-spam measures by use of false header information. None of the spam messages that were examined in the writing of this paper carried a genuine sender address. Most of the massages contained from addresses that were obviously fake. In some cases the addresses were not even valid. Some contained no sender address at all. 

Legislation And Litigation

        The purpose of criminal legislation in a democratic is to deter persons from engaging in prohibited conduct. While it is unlikely that the criminal legislation alone would eliminate spam. Such legislation would certainly create a deterrent for both the spam senders and the advertisers seeking their services. The legislative process is very slow & time consuming. Legislators are reluctant to pass any legislation until they are confident that the implications are fully understood. Legislators will have to be convinced that any new legislation to address the problem of spam will bring benefits that significantly outweigh both the cost of enforcement and the political cost of committing the scarce resource of legislative time to the problem of spam rather than to other pressing problems.

Conclusion

        There are many techniques that address a part of the spam problem. No currently known technique provides a complete solution and it is unlikely that address a part of the problem. No currently known technique provides a complete solution and it is unlikely that any technique will be found in the future that provides a complete and costless solution.


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3D Optical Data Storage

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Introduction

                3D Optical Data Storage is the term given to any form of opticaldata storage in which information can be recorded and/or read with three dimensionalresolution (as opposed to the two dimensional resolution afforded, for example, by CD). This innovation has the potential to provide petabyte-level mass storage on DVD-sized disks. Data recording and readback are achieved by focusing lasers within the medium. However, because of the volumetric nature of the data structure, the laser light must travel through other data points before it reaches the point where reading or recording is desired. Therefore, some kind of nonlinearity is required to ensure that these other data points do not interfere with the addressing of the desired point.

Drive Design

        A drive designed to read and write to 3D optical data storage media may have a lot in common with CD/DVD drives, particularly if the form factor and data structure of the media is similar to that of CD or DVD. However, there are a number of notable differences that must be taken into account when designing such a drive.


Destructive Reading

         Since both the reading and the writing of data are carried out with laser beams, there is a potential for the reading process to cause a small amount of writing. In this case, the repeated reading of data may eventually serve to erase it (this also happens in phase change materials used in some DVDs).

Commercial Development

        In addition to the academic research, several companies have been set up to commercialize 3D optical data storage and some large corporations have also shown an interest in the technology. However, it is not yet clear how the technology will perform in the market in the presence of competition from other quarters such as hard drives, flash storage, and holographic storage.

Data Recording During Manufacturing

        Data may also be created in the manufacturing of the media, as is the case with most optical disc formats for commercial data distribution. In this case, the user cannot write to the disc - it is a ROM format. Data may be written by a nonlinear optical method, but in this case the use of very high power lasers is acceptable so media sensitivity becomes less of an issue.

Comparison With Blu-Ray Disc


        Blu-ray Disc (official abbreviation BD) is an optical discstorage medium designed to supersede the DVD format. The disc diameter is 120 mm and disc thickness 1.2 mm plastic optical disc, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB (23.31 GiB) per layer, with dual layer discs (50 GB) being the norm for feature-length video discs. Triple layer discs (100 GB) and quadruple layers (128 GB) are available for BD-XL Blu-ray re-writer drives.


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3d Password

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Introduction

        Normally the authentication scheme the user undergoes is particularly very lenient or very strict. Throughout the years authentication has been a very interesting approach. With all the means of technology developing, it can be very easy for 'others' to fabricate or to steal identity or to hack someone’s password. Therefore many algorithms have come up each with an interesting approach toward calculation of a secret key. Therefore we present our idea, the 3D passwords which are more customizable and very interesting way of authentication. Now the passwords are based on the fact of Human memory. Generally simple passwords are set so as to quickly recall them.

Brief Description Of System

        The proposed system is a multi factor authentication scheme. It can combine all existing authentication schemes into a single 3D virtual environment .This 3D virtual environment contains several objects or items with which the user can interact. The user is presented with this 3D virtual environment where the user navigates and interacts with various objects. The sequence of actions and interactions toward the objects inside the 3D environment constructs the user’s 3D password.

Existing System

        Current authentication systems suffer from many weaknesses. Textual passwords are commonly used. Users tend to choose meaningful words from dictionaries, which make textual passwords easy to break and vulnerable to dictionary or brute force attacks. Many available graphical passwords have a password space that is less than or equal to the textual password space. Smart cards or tokens can be stolen.

Well-Studied Attack

         The attacker tries to find the highest probable distribution of 3D passwords. In order to launch such an attack, the attacker has to acquire knowledge of the most probable 3D password distributions. This is very difficult because the attacker has to study all the existing authentication schemes that are used in the 3D environment. It requires a study of the user’s selection of objects for the 3D password. Moreover, a well studied attack is very hard to accomplish since the attacker has to perform a customized attack for every different 3D virtual environment design.

Conclusion


        The 3D password is a multi factor authentication scheme that combines the various authentication schemes into a single 3D virtual environment. The virtual environment can contain any existing authentication scheme or even any upcoming authentication scheme or even any upcoming authentication schemes by adding it as a response to actions performed on an object. Therefore the resulting password space becomes very large compared to any existing authentication schemes.


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