2015 Nov

The World of 3D Imaging

November 3, 2015

Physics of Polarisation

There is almost no one who has not experienced the vivid visual treat of a 3D movie. Every one of us at one point of time or other must have questioned how the scientific world has managed produce such cool technology. Let’s dwell into the properties of light that facilitate this technology and the functioning of eye that guided the design.

Electromagnetic wave theory of light explained that light can be conceived as self-propagating oscillating electric and magnetic fields, which at any given point of time are perpendicular to each other and perpendicular the direction of propagation of light. Now the oscillating electric field and magnetic field are in a plane perpendicular the direction of propagation of light. If you assume the light is coming out a paper, then the magnetic and electric fields are on the paper and can be represented by two perpendicular lines drawn on a paper. Two perpendicular lines can be drawn in infinitely possible ways on a paper. Now lets assume that you are forced to draw the perpendicular lines only in one way. This tells us that at every point along the direction of propagation electric field is oscillating along the same line and so is the magnetic field. Thus electric and magnetic fields are confined to perpendicular planes, and the light that exhibits such property is called as plane polarized light. In order to polarize light, polarizers are used. When light passes through a polarizer, plane polarized light is obtained. In this process, the intensity of light is affected. A polarizer lets light that is parallel to a particular plane pass through it and the rest is filtered out. That particular plane is specific to a polarizer; when light that is polarized in a plane perpendicular to the plane specific to polarizer, no light comes out of the polarizer. This phenomenon is used to reduce the intensity of light in polaroid glasses, and it is discussed during our physics tuition classes as well.

The two eyes of human beings are placed in such a way that the images captured are slightly different from each other and our brain uses the information from the two images to get a feel of the depth of the image. Try closing one of your eyes and it suddenly gets difficult to feel of the distance to the objects. A feel of the distance is perceived only when both eyes are functional and this particular feature of binocular vision is called as stereopsis.

Now coming back to our question on 3D technology in movies, polarization phenomenon in combination with the stereopsis property yields 3D images. In a 3D movie there are two images of every object in the picture, which differ slightly from each other, are projected onto the screen. The light that is employed to produce the two images is plane polarized and the plane of polarization in one image is perpendicular to the other. When a viewer wearing eyeglasses in which each of the eyes sees light that is polarized in a specific plane, such that if right eye sees one image (of the two projected) left eye sees the other. The two different images seen each of the eyes are processed by our brains to get a feel of depth, causing a 3D perception of the image.

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