Researchers advance the field of optical computing

Micromechanical oscillators created by a Brazilian researcher in partnership with U.S. scientists pave the way for the use of light in computer microchips to carry information.

By Elton Alisson

Agência FAPESP – Minuscule quartz crystals exist inside the majority of electronic equipment and when excited by an electrical signal, they produce mechanical vibrations that couple with an electric field. In this manner, they provide the timing basis needed for computer circuits to work in an orderly manner: for example, so that operations are completely synchronized at high speeds.

 

Although widely used for decades, quartz crystals no longer meets the needs of the microelectronics industry, which is seeking a lower-cost solution that offers better performance.

 

One Brazilian researcher, in partnership with U.S. scientists, has developed a device that could replace quartz crystals as the “internal clock” of electronic equipment. This study was published in the December edition of Physical Review Letters and was featured on the cover.

 

The device is a micromechanical oscillator made of silicon nitrate – a material that is compatible with microelectronics – with a diameter of about half of a human hair.

 

In the future, this oscillator could be integrated into microcomputer chips in a monolithic manner, without the need for the coprocessing used for quartz crystals. To insert quartz crystals into the circuits of microelectronic devices, the crystals must be manipulated separately and welded to the boards used in the equipment.

 

Furthermore, unlike quartz crystals, which couple with an electric field, the micromechanical oscillator couples with an optical field – which makes it possible to use light in computer microchips to establish optical communication, which is a general aim of the microprocessor industry. 

 

“There is a lot of interest in creating devices that can transport optical information on a microscopic scale – the scale of microchips – as we saw with the evolution of the internet, which is based on fiber optic models that provide an enormous capacity for the transmission of information ,” said Gustavo Silva Wiederhecker, professor at the Gleb Wataghin Institute of Physics at Universidade Estadual de Campinas (Unicamp) and one of the authors of the study, in an interview with Agência FAPESP.

 

“We don’t yet know why, however, certain devices are more economically feasible or which devices offer the most appropriate performance to achieve this end, ” he said.

 

According to Wiederhecker who has support by FAPESP and did his scientific initiation with a fellowship, when light falls on micromechanical oscillators, mechanical oscillations can be induced that cause light to acquire a modulation of amplitude with the same frequency as the mechanical vibrations of the oscillator – in a manner analogous to what happens with electrical signals in quartz crystal–based systems. 

 

Synchronicity

 

Prior to Wiederhecker’s recently published discovery  discovery, it had not been demonstrated that such devices were capable of vibrating at exactly the same time, like two coupled pendulums, when they communicate with each other via light. In the experiment detailed in the recently published article, the researchers demonstrated for the first time the possibility of two micromechanical oscillators becoming synchronized through light.

 

“No one knew that these oscillators were capable of becoming synchronized through optical coupling. The dynamics could have been so complex that it would difficult to observe synchronism between them,” stressed Wiederhecker. 

 

The phenomenon of synchronism is found in most processes that occur in nature, such as in colonies of flying insects and circadian cycles, and was observed on a macroscopic scale for the first time in the 17th century by Christiaan Huygens (1629-1695), who invented the pendulum watch utilized at the time for navigation. 

 

The Dutch physicist observed that a set of synchronized watches was less susceptible to an external disturbance – such as the vibration of sea waves, which could upset a clock phase – than was a regular clock. Over the past few years, the phenomenon has sparked technological interest because it provides the basis for temporalization  and radiofrequency signal processing and can allow the development of new computing concepts based on nanophotonics (transporting optical information on a nanometer scale, one billionth of a meter).

 

“The synchronism of micro-oscillators has drawn significant attention in recent years, not only for its potential technological applications but also because of the type of physics that micro-oscillators show. And  micromechanical oscillators represent a drop in the  ocean  of possibilities presented by nanophotonics,” predicted Wiederhecker.

 

Increased vibration

 

The study was initiated by the Brazilian researcher and scientists from Cornell University in 2008 when Wiederhecker began his postdoctoral studies at Cornell in the group led by Professor Michal Lipson. The first results of the basic study were published in Nature magazine and resulted in a patent filing.

 

In 2011, upon returning to Brazil, Wiederhecker continued to conduct simulations of synchronism and to analyze the data that have now been published  in Physical Review Letters at the Center for Optical and Photonic Research (CePOF) at Unicamp, which is one of FAPESP’s Research, Innovation, and Dissemination Centers (CEPID). 

 

Now, through the Young Investigators in Emerging Research Centers, Wiederhecker has initiated a project that seeks to develop these micromechanical optoelectronic oscillators in Brazil and to increase the scale of devices in synchronism and their frequency.

 

Currently, the devices vibrate at a frequency of 50 million Hertz – the equivalent of 50 million oscillations per second, which is still far below the 3 giga Hertz (GHz) of computers today.

 

Through a Master’s project conducted with a FAPESP fellowship and under the guidance of Wiederhecker, the Unicamp group (in collaboration with colleagues at Cornell) intends to reach frequencies above at least 1 GHz.

 

“In order to bring the technological application of these optical micromechanical oscillators closer to realization,  it is important that they work at higher frequencies,” explained Wiederhecker. 

 

The article Synchronization of micromechanical oscillators using light (doi: 10.1103/PhysRevLett.109.233906) by Wiederhecker et al can be read by subscribers of Physical Review Letters at prl.aps.org/abstract/PRL/v109/i23/e233906.