Tuesday, August 30, 2011

About the latest Technology called " The Fiber optic"

                            Introduction 

An optical fiber is made up of the core (Carries the light pulses), the cladding (reflects the light pulses back into core) and the buffer coating (protects the core and cladding from moisture, damage, etc). Together, all of this creates a fiber optic which can carry up to million messages at any time using light pulses.

Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication.

Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.

Joining lengths of optical fiber is more complex than joining electrical wire or cable. The ends of the fibers must be carefully cleaved, and then spliced together either mechanically or by fusing them together with an electric arc. Special connectors are used to make removable connections.

                                                Pee Pantsy



Fiber optics, through used extensively in the modern world, is a fairly simple and old technology. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel colladon and Jacque Babinet in Paris in the early 1840s.
The use of optic fibers for communication purposes were first carried out in western Europe in the late 19th and early 20th century, such as they were used to diagnose a patient’s stomach by a doctor, and those communications within short ranges. Especially, transfer of images by optical fiber was largely popularized at the beginning of 21st century, Due to the growing medical and television demands.

In 1991, the emerging field of photonic crystals led to the development of photonic- crystal fiber which guides light by means of diffraction from a periodic structure, rather than total internal reflection. The first photonic crystal fibers become commercially available in 2000. Photonic crystal fibers can be designed to carry higher power than conventional fiber, and their wavelength dependent properties can be manipulated to improve their performance in certain applications.
                                               
Applications


1.      Optical fiber communication

Optical fiber can be used as a medium for telecommunication and network because it is flexible and can be bundled as cables. It is especially advantageous for long- distance communications, because light propagates through the fiber with little attenuation compared to electrical cables. This allows long distances to be spanned with few repeaters. Additionally, the per- channel light signals propagating in the fiber have been modulated at rates as high as 111 gigabits second by NTT, although 10 or 40 Gb/s is typical in deployed systems. Each fiber can carry many independent channels, each using a different wavelength of light. The net data rate per fiber is the per channel data rate reduced by the FEC overhead, Multiplied by the number of channels.

For short distance applications, such as creating a network within an office building, fiber –optic cabling can be used to save space in cable ducts. This is because a single fiber can often carry much more data than many electrical cables, such as 4 pair of cat- 5 Ethernet cabling. Fiber is also immune to electrical interference; there is no cross- talk between signals in different cables and no pick up of environmental noise. Non-armored fiber cables do not conduct electricity, which makes fiber a good solution for protecting communications equipment located in high voltage environments such as power generating facilities, or mental communication structures prone to lightning strikes.



2.      Fiber optic sensors

Fibers have many uses in remote sensing. In some applications, the sensor is itself an optical fiber. In other cases, fiber is used to connect a non- fiber optic sensor to a measurement system. Depending on the application, fiber may be used because of its small size, or the fact that no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fiber by using different wavelengths of light for each sensor, or by sensing the time delay as light passes along the fiber through each sensor.
Optical fibers can be used as sensors to measure strain, temperature, pressure and other quantities by modifying a fiber so that the quantity to be measured modulates the intensity, phase, polarization, and wavelength or transit time of light in the fiber. Sensors that vary the intensity of light are simplest, since only a simple a simple sources and detector are required. A particularly useful feature of such fiber optic sensors is that they can, if required, provide distributed sensing over distances of up to one meter.

A major benefit of extrinsic sensors is their ability to reach places which are otherwise inaccessible. An example is the measurement of temperature inside aircraft jet engines by using a fiber to transmit radiation into a radiation pyrometer located outside the engine. Extrinsic sensors can also be used in the same way to measure the internal temperature of electrical transformers, where the extreme electromagnetic field present makes other measurement techniques impossible. Extrinsic sensors are used to measure vibration, rotation, displacement, velocity, acceleration, torque, and twisting.


3.      other uses of optical fibers
Fibers are widely used in illumination applications. They are used as light guides in medical and other applications where bright light needs to be shone a target without a clear line-of-sight path. In some buildings, optical fibers are used to route sunlight from the roof to other parts of the building (see non-imaging optics). Optical fiber illumination is also used for decorative applications, including signs, art and artificial Christmas trees. Swarovski boutiques use optical fibers to illuminate their crystal showcases from many different angels while only employing one light source. Optical fiber is an intrinsic part of the light-transmitting concrete building product, LiTraCon.

In spectroscopy optical fiber bundles are used to transmit light from a spectrometer to a substance which cannot be placed inside the spectrometer itself, in order to analyze it composition.

An optical fiber doped with certain rare earth elements such as erbium can be used as the gain medium of a laser or optical amplifier. Rare-earth doped optical fibers can be used to provide signal amplification by splicing a short section of doped fiber into a regular optical fiber line both wavelengths of light are transmitted through the doped fiber, which transfers energy from the second pump wavelength to the signal wave.

The process that causes the amplification is stimulated emission.

Optical fiber can be used to supply a low level of power (around one watt) to electronics situated in a difficult electrical environment.

Examples of this are electronics in high-powered antenna elements and measurement devices used in high voltage transmission equipment.

Principle of operation

An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process of total internal reflection. The fiber consists of a core surrounded by a cladding layer, both of which are made of dielectric materials. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The boundary between the core and cladding may either be abrupt, in step-index fiber, or gradual, in graded-index fiber.

Total internal reflection

When light travelling in a dense medium hits a boundary at a steep angle (larger than the “critical angle” for the boundary), the light will be completely reflected. This effect is used in optical fibers to confine light in the core. Light travel along the fiber bouncing back and forth off the boundary. Because the light must strike the boundary with an angle greater than the critical angle, only light that enters the fiber within a certain range of angles can travel down the fiber without leaking out. This range of angels is called the acceptance cone of the fiber.

In simpler terms, there is a maximum angle from the fiber axis at which light may enter the fiber so that it will propagate, or travel, in the core of the fiber. The sine of this maximum angle is the numerical aperture (NA) of the fiber. Fiber with a larger NA requires less precision to splice and work with than fiber with a smaller NA. Single-mode fiber has a small NA.

Total internal reflection
Multi-mode fiber

The propagation of light through a multi-mode optical fiber.

Fiber with large core diameter (greater than 10 micrometers) may be analyzed by geometrical optics. Such fiber is called multi-mode fiber, from the electromagnetic analysis (see below). In a step-index multi-mode fiber, rays of light are guided along the fiber core by total internal reflection. Rays that meets the core-cladding boundary at a high angle (measured relative to a line normal to the boundary), greater than the critical angle for this boundary, are completely reflected.

The critical angle (minimum angle for total internal reflection) is determined by the difference in index of refraction between the core and cladding materials. Rays that meet the boundary at a low angle and refracted from the core into the cladding, and do not convey and hence information along the fiber. The critical angle determines the acceptance angle of the fiber, often reported as a numerical aperture.

A high numerical aperture allows light to propagate down the fiber in rays both close to the axis and at various angles, allowing efficient coupling of light into the fiber.
However, this high numerical aperture increases the amount of dispersion as rays at different angles have different path lengths and therefore take different times to traverse the fiber.

In graded-index fiber, the index of refraction in the core decreases continuously between the axis and the cladding. This causes light rays to bend smoothly as they approach the cladding, rather than reflecting abruptly from the core-cladding boundary. The resulting curved paths reduce multi-path dispersion because high angle rays pass more through the lower-index periphery of the core, rather than the high-index center. The index profile is chosen to minimize the difference in axial propagation speeds of the various rays in the fiber.
Single- mode fiber

Single-mode fiber

The structure of a typical single-mode fiber.
1.      Core: 8 um diameter
2.      Cladding: 125 um dia.
3.      Buffer: 250 um dia.
4.      Jacket: 400 um dia.
Fiber with a core diameter less than about ten times the wavelength of the propagating light cannot be modeled using geometric optics. Instead, it must analyze as an electromagnetic structure, by solution of Maxwell’s equations as reduced to the electromagnetic. The electromagnetic analysis may also be required to understand behaviors such as speckle that occur when coherent light propagates in multi-mode fiber. As an optical waveguide, the fiber supports one or more confined transverse modes by which light can propagate along the fiber. Fiber supporting only one mode is called single-mode or mono-fiber. The behavior of larger-core multi-mode fiber can also be modeled using the wave equation, which shows that such fiber supports more than one mode of propagation (hence the name). The results of such modeling of multi-mode fiber approximately agree with the predictions of geometric optics, if the fiber core id large enough to support more than a few modes.

The waveguide analysis shows that the light energy in the fiber is not completely confined in the core. Instead, especially single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding as an evanescent wave.

Special-purpose fiber

Some special-purpose optical fiber is constructed with a non-cylindrical core and/or cladding layer, usually with an elliptical or rectangular cross-section. These include polarization-maintaining fiber and fiber designed to suppress whispering gallery made propagation.

Photonic-crystal fiber is made with a regular pattern of index variation (often in the form of cylindrical holes that run along the length of the fiber). Such fiber uses diffraction effects instead of or in addition to total internal reflection, to confine light to the fiber’s core. The properties of the fiber can be tailored to a wide variety of applications.

Mechanisms of attenuation
Light attenuation by ZBLAN and silica fibers

Attenuation in fiber optics, also known as transmission loss, is the reduction in intensity of the light beam (or signal) with respect to distance traveled through a transmission medium. Attenuation coefficients in fiber optics usually use units of dB/km through the medium due to the relatively high quality of transparency of modern optical transmission media.

Light scattering and specular reflection at the back

Defuse reflection
The propagation of light through the core of an optical fiber is based on total internal reflection of the light wave. Rough and irregular surfaces, even at the modular level, can cause light rays to be reflected in random directions. This is called diffuse reflection or scattering, and it is typically characterized by wide variety of reflection angles.

Light scattering depends on the wavelength of the light being scattered. Thus, limits to spatial scales of visibility arise, depending on the frequency of the incident light –wave and the physical dimension (or spatial scale) of scattering center, which is typically in the form of some specific micro-structure feature. Since visible light has a wavelength of the order of one micron (one millionth of a meter) scattering centers will have dimensions on a similar spatial scale.

Similarly, the scattering of light in optical quality glass fiber is caused by molecular level irregularities (compositional fluctuations) in the glass structure. In deed, one emerging school of thought is that a glass is simply the limiting case of polycrystalline solid. Within this framework, “domains” exhibiting various degrees of short – range order become the building blocks of metals and alloys, as well as glasses and ceramics.

UV- Vis – IR absorption
In addition to light scattering, attenuation or signal loss also occur due to selective absorption of specific wavelengths, in a manner similar to that responsible for the appearance of color. Primary material considerations include both electrons and molecules as follows.
1)     At the electronic level, it depends on whether the electron orbitals are spaced (or “quantized”) such that they can absorb a quantum of light ( or photon) of a specific wavelength or frequency in the ultraviolet (UV) or visible ranges. This is what gives rise to color.

2)     At the atomic or molecular level, it depends on the frequencies of atomic or molecular vibrations or chemical bonds, how close- packed its atoms or molecules are, and weather or not the atoms or molecules exhibit long- range order. These factors will determine the capacity of the material transmitting longer wavelengths in the infrared (IR), far IR, radio and microwave ranges.

Normal modes of vibration in a crystalline solid.

Thus, multi- phonon absorption occurs when two or more phonons simultaneously interact to produce electric dipole moments with which the incident radiation may couple. These dipoles can absorb energy from the incident radiation, reaching a maximum coupling with the radiation when the frequency is equal to the fundamental vibrational mode of the molecular dipole (e.g Si-O bond) in the far – infrared, or one of its harmonics.

The selective absorption of infrared (IR) light by a particular material occurs because the selected frequency of the light wave matches the frequency (or an intergral multiple of the frequency) at which the particles of that material vibrate. Since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies (or portions of the spectrum) of infrared (IR) light.

Reflection and transmission of light waves occurs because the frequencies of the light wave do not match the natural resonant frequencies of vibration of the objects. When IR light of these frequencies strikes an object, the energy is either reflected or transmitted.





To be Continue in next session.............

Wednesday, August 24, 2011

A NEW BALL GAME
Blackberry PlayBook

Listen, I’ll be straight with you. I realize tablets are crazy hot right now, that 2011 is the year of the iPad clone and that every company and its brother is rushing one to market. But I’m sorry. I’m not going to review every one of the 85 tablets that will arrive this year; its online may, and I ‘have already got tablet fatigue. I’m sorry, I am not going to review the Electrolux tablet, the Polaroid table, the Sunoco tablet, the Kellogg’s tablet….The blackberry tablet, though, seems worth a look. The tech world has been hyperventilating over this thing. It’s called the playbook, and it’s a seven-inch touch screen tablet.

The ipad, of course, is a 10-incher, but seven has its virtues. It’s much easier to hold with one hand, for example. In principle, you ought to be able to slip the playbook into the breast pocket of a jacket-but incredibly, the playbook is about half an inch too wide. Still, it looks and feels great: hard rubberized back, brilliant, super-responsive multi-touch screen, solid heft (0.9 pounds). Its software is based on an operating system called QNX,which Research in Motion, the Blackberry’s maker, bought for its industrial stability.(“ It runs nuclear power plants,” says a product manager without a trace of current- events irony.) Nor is QNX the only other company that lent a hand .Palm and Apple were also involved, although they didn’t know it. The Playbook software is crawling with borrowed ideas. For example, to remove or rearrange apps. You hold our finger down on one app icon until all icons begin to pulse (hello, pad!) And to close a program, you swipe your finger upward from the bottom bezel to turn all app window into “Card “, and then flick one upward off the screen( Hello, Palm Pre!)

There are no buttons on the front at all, and the top edge has only on. Play/ Pause and volume keys .Instead ,you navigate by swiping left or right cycles among open multitasking apps.And swiping down reveals an apps toolbar, if it has one.Unfortunately,there’s no way of knowing beforehand if a toolbar exists. so you often swipe futilely and feel silly. Similarly, if app icons completely fill the home screen, you can swipe upward to reveal what’s below the screen-but you won’t know if there are more below the screen.
But the PlayBook does three impressive things that its rivals-the iPad and the Android tablets-can only dream about. First with a special HDMI cable (not included), you can hook it up to a TV or projector, which is a great for power point presentations.( Apparently they still do those in corporations.) The iPad does that, but the TV image is identical to the iPad’s screen image. The PlayBook, However, can show two different things, On the TV, the audience sees your slides; on the PlayBook, You get to see the traditional PowerPoint Cheat sheet of notes and slide thumbnails.

The second cool feature has to do with loading the tablet with your photos and music. Unfortunately, There’s no iTubes-like software to do this automatically .You have to drag files manually from your computer into the playbook’s folder (music, Photos and so on).But once you have set up this process using a USB cable, You can do it thereafter over Wi-fi .The Playbook can even accept such wireless transfer when it’s in sleep mode, sitting in your purse or briefcase across the room.
Finally, there’s a wild, wireless Bluetooth connection features called Blackberry Bridge. In this setup, the playbook’s much roomer screen-a live, encrypted two way link.
At the moment, Blackberry Bridge is the only way to do e-mail, calendar or address book apps of its own. You read that right: RIM has just shipped a Blackberry product that cannot do email. It must be skating season in hell.

What you do get are built –in versions of documents to go, for creating and editing word excel and PowerPoint documents .And you get a nice web browser that plays flash videos online. The playbook’s front and back cameras (3 and 5 megapixels) can record stabilized stills and hi-def video. You should also be aware that this Playbook is Wi-Fi only. You don’t have the option to get online via a cellular network, as with arrivals from Apple, Motorala and Samsung. RIM says that 4G versions of the Playbook will arrive by the end of 2011.


You’re in control

When Microsoft beefed up its Xbox 360 gaming console with an add-on called Kinect, it changed forever the way video games are played-adding a new physical element and putting the player firmly and literally in control.
The technology takes gaming requirements beyond a supple wrist and speedy thumb work on a console: now it’s about arms, legs knees, waist, hips and voice. Tom cruise in minority report controlling the action with his hand movements is so yesterday. With Kinect, you kick and so does the character in the game; you deliver a jab with your fist and a boxer in the game mimics your movements.
A seeming spin-off from the motion capture technology that animation studios routinely use, kinect deploys a motion censor and a color camera to track your entire body, and creates a digital skeleton of you. It uses this to remember you and your playing style the next time you play the same game. Also, four carefully placed micro-phones help you control the game vocally.
Kinect can distinguish up to six players, after each of them just looked at the camera. You need some 2-3 meters of clear space in-front of the television or display as your ‘stage’.
In India, Microsoft has inexplicably launched just four games for kinect, though the list has more than dozen in other markets. The best of the bunch is Dance central, where players are guided to master the choreography for a number of popular dance tunes and more than 600 steps. The game even tacks the calories you burn while performing. So it’s a cool alternative to your exercise routine.
Kinect sports include football, beach volleyball, bowling, boxing, table tennis and athletics. You can compete against your own ‘avatar’ or work in a team. This is possibly the game with the most realism built in. Kinect joyride has go-karting and car racing segments that allow you to flip, twist and swerve with the car. Kinectimals, aimed at children, allows players to train pets using voice recognition.
The kinect device is a 9,900 add-on for existing owners of the Xbox 360 console. It comes integrated with the latest editions of Xbox 360 costing 22,900 for the 4GB version and about 32000 for 250 GB.All kinect games are priced 1999.