November 13, 2013

By gkruckemyer

Researchers at UCF’s College of Optics and Photonics (CREOL) have developed a new way of integrating photonic devices that can potentially revolutionize the technology that runs the Internet and other telecommunication links. The platform can also facilitate scientific breakthroughs in the fields of nonlinear and quantum optics.

The work, led by professor Sasan Fathpour, was recently published in Optics Express, a peer-reviewed publication that emphasizes scientific and technology innovations in optics and photonics.

It is hard to imagine our modern society without electronic microchips. Microelectronics heavily owes its success to silicon – an extraordinary material with unique properties – on which up to billions of tiny devices, mostly transistors, are routinely integrated. The choice for integrated photonic materials has not been as clean-cut as integrated electronics. Integrated photonics is the technology of integrating several photonic devices such as lasers, optical switches, modulators and detectors on a single chip for using light as a means to transmit data over the Internet, between equipment racks of data centers and supercomputers, and perhaps on boards of future laptops and other mobile devices.   

Despite decades of research, there appears to be no ideal photonic material that can play the unifying role that silicon has been dominantly playing for decades in microelectronics. For example, some materials are good for laser light generation, while some are good for electro-optics (an effect useful for switches and modulators). Silicon itself is a good passive optical material to move light around a chip and there are ways to make modulators on it but the performance of the devices is not great because the material is not electro-optic. 

Lithium niobate (an exotic compound of niobium, lithium and oxygen) has a strong electro-optic effect and the vast majority of ultrafast modulators that drive the Internet are based on it.

“Lithium niobate devices are bulky and expensive,” Fathpour said. “If thin films of lithium niobate are developed and the geometrical cross-section of the devices on the films can be reduced to submicron dimensions, the field of integrated photonics can move toward a more unifying platform.”

In addition, if such achieved miniaturized photonic devices are made on silicon wafers that already house electronic circuits, ultrafast photonics and electronics can be seamlessly merged. Such a hybrid platform can pave the path toward using optics to transmit data between microprocessors, graphic and memory chips of future personal computers, game consoles, laptops and tablets. 

Fathpour and his team’s breakthrough results make such a hybrid versatile platform closer to reality. For the first time, they have managed to bond thin films less than half a micrometer thick of lithium niobate to silicon wafers. The films themselves may have applications other than photonics (microelectromechanical systems, microwave filters for cell phones and piezoelectric transducers, to name a few).  For now, Fathpour’s group is more focused on demonstrating basic integrated photonic devices such as low-loss microring resonators and high-performance optical modulators.

Dr. Payam Rabiei, a research scientist at CREOL, and three graduate students have been working for more than a year to make this happen. They have managed to demonstrate electro-optic modulators whose driving voltage is several times less than the best commercial devices.  This has become possible because the dimensions of the devices are less than a micrometer in width and height, compared to tens of microns in conventional devices.  Having smaller devices means less voltage, and less real estate on thin films means less consumption of expensive lithium niobate wafers.

Unlike, conventional lithium niobate waveguides (such as light pipes) that can be hardly bent, the UCF researchers have demonstrated optical rings with diameters less than a third of a millimeter for the first time on the material. All of these will allow integrating several miniaturized modulators and other photonic devices on a single chip for advanced communication formats. The work is funded under the Office of Naval Research Young Investigator Program.

“The advantage of our novel platform is beyond optical telecommunication applications,” Fathpour said. “Lithium niobate is one of the best known nonlinear optical materials but with the lack of small and efficient waveguides, nonlinear photonic chips that can manipulate the color of light, and quantum optics chips that allow quantum-mechanical interaction of light and matter have been hard to achieve.”   

He said he expects these nonlinear and quantum optical chips can become a reality in the near future.

His group plans to start working on building such chips in addition to pursuing their research on advanced photonic devices for optical telecommunication applications.