Suppose, you have a transparent bottle filled with water. You pin a hole on it & the water stream starts flowing from that hole. From the backside, you put a laser beam. In the bottle, the light goes straight but from the hole, it starts bending following the water flow!
Light is following a curve!
Well, let go through some concepts here. It's known that light bends. When light rays pass from air into water, for instance, they take a sharp turn & that's why a stick dipped in a water-filled jar appears to tilt toward the surface. Out in space, light rays passing near very massive objects(eg. stars) are seen to travel in curves. In each instance, light-bending has an external cause: For water, it is a change in an optical property called the refractive index, and for stars, it is the warping nature of gravity.
Late 70's: Physicists Michael Berry (University of Bristol, UK) and Nandor Balazs (State University of New York, Stony Brook) discovered that a so-called Airy waveform, a wave describing how quantum particles move, can sometimes bend by a small amount. That work was largely ignored until 2007 when Demetri Christodoulides and other physicists (University of Central Florida, Orlando) generated optical versions of Airy waves by manipulating laser light and found that the resultant beam curved slightly as it crossed a detector.
How did this self-bending work?
Light is a bunch of waves, and their peaks and troughs can interfere with one another. For example, a peak passing a trough cancels each other out to create darkness; a peak passing another peak interferes constructively to create a bright spot. Now, imagine light emitted from a wide strip—perhaps a fluorescent tube or, better, a laser whose output has been expanded. By carefully controlling the initial position of the wave peaks—the phase of the waves—at every step along the strip, it is possible to make the light traveling outward interfere constructively at only points on a curve and cancel out everywhere else. The Airy function, which contains rapid but diminishing oscillations, proved an easy way to define those initial phases—except that the resultant light would bend only up to about 8°.
Physicist Mordechai Segev and fellows at Technion, Israel Institute of Technology, in Haifa say they have a technique for making light self-bend through any angle, even through a complete circle. The problem with the Airy function, says Segev, is that the shape of its oscillations specify the right phases only at small angles; at angles much greater than 8°, the shape becomes a crude approximation. So his group turned to Maxwell's equations, which describe the propagation of electromagnetic waves such as light. After mathematics and guesswork, the researchers found solutions to Maxwell's equations that precisely describe the initial phases required for truly self-bending light, as they report in the 3rd week of April 2012 in Physical Review Letters.
The work of Segev's group was theoretical but, by coincidence, a group led by John Dudley (University of Franche-Comté, Besançon, France) has been performing its own experiments on self-bending light. By modifying the existing Airy function, Dudley's group managed to find initial phase values that match the Israeli group's solution, even though they were unaware of it. Using a device called spatial light modulator to pre-adjust the phase of an expanded beam of laser light, the French group found that the resultant light self-bent by up to 60°, as it was reported later in April 2012 in Optics Letters.
Physicist Pavel Polynkin (University of Arizona, Tucson) suggests another application: Burning a curved hole through a material, which would be impossible with a regular laser. But despite such applications, he points out that the light itself doesn't actually curve, it only appears to, because of the way in which the interference bright-spots line up. In fact, he says, most of the light's power does not go toward the bright curve, but into the dim areas that have been canceled out.
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