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A wave for the future in faster computing

August 26, 2013

While most of us use our com­puters for tex­ting friends, watching videos, or reading the news, vir­tu­ally every­thing we do on our elec­tronic devices is actu­ally manip­u­lated by math­e­mat­ical oper­a­tions. Infor­ma­tion, explained elec­trical and com­puter engi­neering pro­fessor Hos­sein Mos­al­laei, is car­ried and processed through devices called logic gates.

For instance, a text mes­sage sent from one person to another is first trans­lated from let­ters into num­bers (binary bits), which are then trans­lated into an elec­tronic signal that moves from the sender’s cell phone to the cell tower to the recipient’s phone. From there it is trans­lated back into bits, and then again into let­ters. Every manip­u­la­tion of the data along the way stems from the output of the pre­ceding math­e­mat­ical operations.

The meta­sur­face that elec­trical and com­puter engi­neering pro­fessor Hos­sein Mos­al­laei and his team cre­ated includes two layers that ind­pened­netly con­trol the phase and ampli­tude of a light wave. Image cour­tesy of Hos­sein Mosallaei.

Elec­tronic com­mu­ni­ca­tion is a rel­a­tively effi­cient mode of infor­ma­tion transfer—but, according to Mos­al­laei, another form of infor­ma­tion transfer has the poten­tial for a 1,000-fold increase in speed and band­width over our cur­rent tech­nolo­gies. That method is called pho­tonic communication.

Because light waves prop­a­gate at 1,000 times greater fre­quen­cies than elec­trons, they have the capacity for fun­da­men­tally offering fas­ci­nating fea­tures. Until recently, one major road­block stood in the way of real­izing pho­tonic com­puters oper­ating on ana­logue waves. In a paper recently released online in the Journal of the Optical Society of America B, Mos­al­laei and his team mem­bers have whisked that road­block aside.

The new work, Mos­al­laei said, “lays both the the­o­ret­ical and phys­ical foun­da­tion for an entirely new form of com­puting that will be faster, will have the capacity to transfer 1,000 times more data, and will open up a range of appli­ca­tions we can’t presently imagine.”

Whereas elec­tronic sig­nals are passed along via binary numer­ical code, pho­tonic sig­nals are light waves and one can per­form ana­logue pro­cessing on them. Just as logic gates do math­e­matics on elec­tronic sig­nals, novel devices can do math on light waves—but only if those devices can inde­pen­dently manip­u­late the var­ious parts of the wave.

A wave is char­ac­ter­ized by three things: its ampli­tude, or how tall each peak is; its phase, or where those peaks occur on a hor­i­zontal axis; and its polar­iza­tion, or the direc­tion­ality of the par­ti­cles con­tained in the wave. If you want to per­form math­e­matics on light waves, you must con­trol each of these ele­ments independently.

In pre­vious research, Mosallaei’s team cre­ated a nanoscopic device that was capable of tai­loring only phase and con­cen­trate the light, and it couldn’t do any­thing to the ampli­tude or polarity. This time around, the team has paired that ear­lier device with other devices, which each per­forms a dif­ferent func­tion. When stacked on top of each other, the result is a sur­face that manip­u­lates all three ele­ments vir­tu­ally simul­ta­ne­ously. “This is the first time we can con­trol ampli­tude, phase, and polar­iza­tion to our desire and inde­pen­dent from each other,” said Mosallaei.

In the new paper, the team stacked these meta­sur­faces in such a way that when a light wave passes through the sur­face, what comes out on the other side is the wave’s deriv­a­tive. “We can use it to get the deriv­a­tive of any func­tion,” said Mos­al­laei, whose team is now working to create sim­ilar struc­tures that output other math­e­mat­ical solu­tions, including sums and inte­grals. “The sur­face does the math­e­mat­ical oper­a­tion on the wave.”