Have you seen the movies predator, ghost in the shell or almost any sci-fi series? at least you might have seen tom n jerry show in cartoon network right, then you know what is clocking. It is bending of light around an object, or displaying the image behind an object on the other side so as to give the illusion of there being nothing in the way. It's kind of being invisible so that a person standing in front of you, can see the scene behind you. This process of invisibility basically relates to an upcoming technology called "Optical Camouflage".

Optical Camouflage delivers a similar experience to Harry Potter's invisibility cloak, but using it requires a slightly more complicated arrangement. First, the person who want be invisible (let's call her person A) dons a garment that resembles a hooded raincoat. The garment is made of a special material. Next, an observer (Person B) stands before a person A at a specific location. At that location, instead of seeing person A wearing a hooded raincoat, person B sees right through the cloak, making person A appear to be invisible. If person B were viewing from a slightly different location, he would simply see person A wearing a silver garment. Still, despite its limitations, this is a cool piece of technology.

Optical camouflage is a kind of active camouflage which completely envelopes the wearer. It displays an image of the scene on the side opposite the viewer on it, so that the viewer can "see through" the wearer, rendering the wearer invisible. Optical camouflage doesn't work by way of magic. It works by taking advantage of something called Augmented-reality technology -- a type of technology first pioneered in the 1960s by Ivan Sutherland and his students at Harvard University and the University of Utah.

Optical camouflage is a hypothetical type of active camouflage currently only in a very primitive stage of development. The idea is relatively straightforward: to create the illusion of invisibility by covering an object with something that projects the scene directly behind that Object. Although optical is a term that technically refers to all forms of light, most proposed forms of optical camouflage would only provide invisibility in the visible portion of the spectrum. Prototype examples and proposed designs of optical camouflage devices range back to the late eighties at least, and the concept began to appear in fiction in the late nineties.

WORKING:

Optical camouflage doesn't work by way of magic. It works by taking advantage of something called Augmented-reality technology -- a type of technology first pioneered in the 1960s by Ivan Sutherland and his students at Harvard University and the University of Utah.

Augmented-reality systems add computer-generated information to a user's sensory perceptions. Imagine, for example, that you're walking down a city street. As you gaze at sites along the way, additional information appears to enhance and enrich your normal view. Perhaps it's the day's specials at a restaurant or the show times at a theater or the bus schedule at the station. What's critical to understand is that augmented reality is not the same as virtual reality. While virtual reality aims to replace the world, augmented reality merely tries to supplement it with additional, helpful content. Think of it as a heads-up display (HUD) for everyday life.

Most augmented-reality systems require a user to look through a special viewing apparatus to see a real-world scene enhanced with synthesized graphics. They also call for a powerful computer. Optical camouflage requires these things as well, but it also necessitates several other components. Here's everything needed to make a person appear invisible:

It is consists of:

 a garment made from highly reflective material

 a digital video camera

 a computer

 a projector

 a special, half-silvered mirror called a combiner.

For using optical camouflage, the following steps are to be followed –

1. The person who wants to be invisible (let's call her Person A) dons a garment

That resembles a hooded raincoat. The garment is made of a special material that we’ll examine more closely in a moment.

2. An observer (Person B) stands before Person

A at a specific location. At that

Location, instead of seeing Person A wearing a hooded raincoat, Person B sees right through the cloak, making Person A appears to be invisible.

RETROREFLECTIVITY:

The cloak that enables optical camouflage to work is made from a special materialknown as retro-reflective material. A retro-reflective material is covered with thousands and thousands of small beads. When light strikes one of these beads, the light raysbounce back exactly in the same direction from which they came.

A retro reflector is a device that sends light or other radiation back where it came from regardless of the angle of incidence, unlike a mirror, which does that only if the mirror is exactly perpendicular to the light beam. Retro reflectors are clearly visible ina pair of bicycle shoes. Light source is a flash a few centimeters above camera lens.

This effect can be commonly obtained in two ways:

1. With reflecting and refracting optical elements arranged so that the focal surface of the refractive element coincides with the reflective surface, typically a transparent sphere and a spherical mirror - this same effect may be achieved with a single transparent sphere provided that the refractive index of the material is exactly 2 times the refractive index of the medium from which the radiation is incident. In that case, the sphere surface behaves as a concave spherical mirror with the required curvature for retro reflection. This is conventionally known as a cat's eye retro reflector in either configuration.