Category Archives: Photonics Business

A group of scientists from Hong Kong University of Science and Technology; the University of California, Santa Barbara; Sandia National Laboratories and Harvard University were able to fabricate tiny lasers directly on silicon — a huge breakthrough for the semiconductor industry and well beyond.

For more than 30 years, the crystal lattice of silicon and of typical laser materials could not match up, making it impossible to integrate the two materials — until now.

As the group reports in Applied Physics Letters, from AIP Publishing, integrating subwavelength cavities — the essential building blocks of their tiny lasers — onto silicon enabled them to create and demonstrate high-density on-chip light-emitting elements.

To do this, they first had to resolve silicon crystal lattice defects to a point where the cavities were essentially equivalent to those grown on lattice-matched gallium arsenide (GaAs) substrates. Nano-patterns created on silicon to confine the defects made the GaAs-on-silicon template nearly defect free and quantum confinement of electrons within quantum dots grown on this template made lasing possible.

The group was then able to use optical pumping, a process in which light, rather than electrical current, “pumps” electrons from a lower energy level in an atom or molecule to a higher level, to show that the devices work as lasers.

“Putting lasers on microprocessors boosts their capabilities and allows them to run at much lower powers, which is a big step toward photonics and electronics integration on the silicon platform,” said professor Kei May Lau, Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology.

Traditionally, the lasers used for commercial applications are quite large — typically 1 mm x 1 mm. Smaller lasers tend to suffer from large mirror loss.

But the scientists were able to overcome this issue with “tiny whispering gallery mode lasers — only 1 micron in diameter — that are 1,000 times shorter in length, and 1 million times smaller in area than those currently used,” said Lau.

Whispering gallery mode lasers are considered an extremely attractive light source for on-chip optical communications, data processing and chemical sensing applications.

“Our lasers have very low threshold and match the sizes needed to integrate them onto a microprocessor,” Lau pointed out. “And these tiny high-performance lasers can be grown directly on silicon wafers, which is what most integrated circuits (semiconductor chips) are fabricated with.”

In terms of applications, the group’s tiny lasers on silicon are ideally suited for high-speed data communications.

“Photonics is the most energy-efficient and cost-effective method to transmit large volumes of data over long distances. Until now, laser light sources for such applications were ‘off chip’ — missing — from the component,” Lau explained. “Our work enables on-chip integration of lasers, an [indispensable] component, with other silicon photonics and microprocessors.”

The researchers expect to see this technology emerge in the market within 10 years.

Next, the group is “working on electrically pumped lasers using standard microelectronics technology,” Lau said.

An international team of researchers from Lomonosov Moscow State University and the Australian National University in Canberra created an ultrafast all-optical switch on silicon nanostructures. This device may become a platform for future computers and permit to transfer data at an ultrahigh speed. The article with the description of the device was published in Nano Letters journal and highlighted in Nature Materials.

This work belongs to the field of photonics — an optics discipline which appeared in the 1960-s, simultaneously with the invention of lasers. Photonics has the same goals as electronics does, but uses photons — the quanta of light — instead of electrons. The biggest advantage of using photons is the absence of interactions between them. As a consequence, photons address the data transmission problem better than electrons. This property can primarily be used for in computing where IPS (instructions per second) is the main attribute to be maximized. The typical scale of eletronic transistors — the basis of contemporary electronic devices — is less than 100 nanometers, wheres the typical scale of photonic transistors stays on the scale of several micrometers. Nanostructures that are able to compete with the electronic structures — for example, plasmonic nanoparticles — are characterized by low efficiency and significant losses. Therefore, coming up with a compact photonic switch was a very challenging task.

Three years ago several groups of researchers simultaneously discovered an important effect: they found out that silicon nanoparticles are exhibit strong resonances in the visible spectrum — the so-called magnetic dipole resonances. This type of resonance is characterized by strong localization of light waves on subwavelength scales, inside the nanoparticles. This effect turned out to be interesting to researches, but, according to Maxim Shcherbakov, the first author of the article published in Nano Letters, nobody thought that this discovery could create a basis for development of a compact and very rapid photonic switch.

Nanoparticles were fabricated in the Australian National University by e-beam lithography followed by plasma-phase etching. It was done by Alexander Shorokhov, who served an internship in the University as a part of Presidential scholarship for studying abroad. The samples were brought to Moscow, and all the experimental work was carried out at the Faculty of Physics of Lomonosov Moscow State University, in the Laboratory of Nanophotonics and Metamaterials.

“In our experimental research me and my colleague Polina Vabishchevich from the Faculty used a set of nonlinear optics methods that address femtosecond light-matter,” explains Maxim Shcherbakov. “We used our femtosecond laser complex acquired as part of the MSU development program”.

The "device": a disc 250 nm in diameter capable of switching optical pulses at femtosecond rates. (Maxim Scherbakov et al)

The “device”: a disc 250 nm in diameter capable of switching optical pulses at femtosecond rates. (Maxim Scherbakov et al)

Eventually, researchers developed a “device”: a disc 250 nm in diameter that is capable of switching optical pulses at femtosecond rates (a femtosecond is one millionth of one billionth of a second). Switching speeds that fast will allow us to create data transmission and processing devices that will work at tens and hundreds terabits per second. This can make possible downloading thousands of HD-movies in less than a second.

The operation of the all-optical switch created by MSU researchers is based on the interaction between two femtosecond pulses. The interaction becomes possible due to the magnetic resonance of the silicon nanostructures. If the pulses arrive at the nanostructure simultaneously, one of them interacts with the other and dampers it due to the effect of two-photon absorption. If there is a 100-fs delay between the two pulses, the interaction does not occur, and the second pulse goes through the nanostructure without changing.

“We were able to develop a structure with the undesirable free-carrier effects are suppressed,” says Maxim Shcherbakov. “Free carriers (electrons and electron holes) place serious restrictions on the speed of signal conversion in the traditional integrated photonics. Our work represents an important step towards novel and efficient active photonic devices– transistors, logic units, and others. Features of the technology implemented in our work will allow its use in silicon photonics. In the nearest future, we are going to test such nanoparticles in integrated circuits”.

Electrons are so 20th century. In the 21st century, photonic devices, which use light to transport large amounts of information quickly, will enhance or even replace the electronic devices that are ubiquitous in our lives today. But there’s a step needed before optical connections can be integrated into telecommunications systems and computers: researchers need to make it easier to manipulate light at the nanoscale.

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have done just that, designing the first on-chip metamaterial with a refractive index of zero, meaning that the phase of light can travel infinitely fast.

In this zero-index material there is no phase advance, instead it creates a constant phase, stretching out in infinitely long wavelengths. (Credit: Peter Allen, Harvard SEAS)

In this zero-index material there is no phase advance, instead it creates a constant phase, stretching out in infinitely long wavelengths. (Credit: Peter Allen, Harvard SEAS)

This new metamaterial was developed in the lab of Eric Mazur, the Balkanski Professor of Physics and Applied Physics and Area Dean for Applied Physics at SEAS, and is described in the journal Nature Photonics.

“Light doesn’t typically like to be squeezed or manipulated but this metamaterial permits you to manipulate light from one chip to another, to squeeze, bend, twist and reduce diameter of a beam from the macroscale to the nanoscale,” said Mazur. “It’s a remarkable new way to manipulate light.”

Although this infinitely high velocity sounds like it breaks the rule of relativity, it doesn’t. Nothing in the universe travels faster than light carrying information — Einstein is still right about that. But light has another speed, measured by how fast the crests of a wavelength move, known as phase velocity. This speed of light increases or decreases depending on the material it’s moving through.

When light passes through water, for example, its phase velocity is reduced as its wavelengths get squished together. Once it exits the water, its phase velocity increases again as its wavelength elongates. How much the crests of a light wave slow down in a material is expressed as a ratio called the refraction index — the higher the index, the more the material interferes with the propagation of the wave crests of light. Water, for example, has a refraction index of about 1.3.

When the refraction index is reduced to zero, really weird and interesting things start to happen.

In a zero-index material, there is no phase advance, meaning light no longer behaves as a moving wave, traveling through space in a series of crests and troughs. Instead, the zero-index material creates a constant phase — all crests or all troughs — stretching out in infinitely long wavelengths.  The crests and troughs oscillate only as a variable of time, not space.

This uniform phase allows the light to be stretched or squished, twisted or turned, without losing energy. A zero-index material that fits on a chip could have exciting applications, especially in the world of quantum computing.

“Integrated photonic circuits are hampered by weak and inefficient optical energy confinement in standard silicon waveguides,” said Yang Li, a postdoctoral fellow in the Mazur Group and first author on the paper. “This zero-index metamaterial offers a solution for the confinement of electromagnetic energy in different waveguide configurations because its high internal phase velocity produces full transmission, regardless of how the material is configured.”

The metamaterial consists of silicon pillar arrays embedded in a polymer matrix and clad in gold film. It can couple to silicon waveguides to interface with standard integrated photonic components and chips.

“In quantum optics, the lack of phase advance would allow quantum emitters in a zero-index cavity or waveguide to emit photons which are always in phase with one another,” said Philip Munoz, a graduate student in the Mazur lab and co-author on the paper.  “It could also improve entanglement between quantum bits, as incoming waves of light are effectively spread out and infinitely long, enabling even distant particles to be entangled.”

“This on-chip metamaterial opens the door to exploring the physics of zero index and its applications in integrated optics,” said Mazur.

The paper was co-authored by Shota Kita, Orad Reshef, Daryl I. Vulis, Mei Yin and Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering.

An important step towards next-generation ultra-compact photonic and optoelectronic devices has been taken with the realization of a two-dimensional excitonic laser. Scientists with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) embedded a monolayer of tungsten disulfide into a special microdisk resonator to achieve bright excitonic lasing at visible light wavelengths.

“Our observation of high-quality excitonic lasing from a single molecular layer of tungsten disulfide marks a major step towards two-dimensional on-chip optoelectronics for high-performance optical communication and computing applications,” says Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division and the leader of this study.

Zhang, who also holds the Ernest S. Kuh Endowed Chair at the University of California (UC) Berkeley and is a member of the Kavli Energy NanoSciences Institute at Berkeley (Kavli ENSI), is the corresponding author of a paper describing this research in the journal Nature Photonics. The paper is titled “Monolayer excitonic laser“. The lead authors are Yu Ye and Zi Jing Wong, members of Zhang’s research group, plus Xiufang Lu, Xingjie Ni, Hanyu Zhu, Xianhui Chen and Yuan Wang.

A single molecular layer of tungsten (W) and sulfide (S) is widely regarded as one of the most promising 2D semiconductors for photonic and optoelectronic applications. (Credit: Xiang Zhang, Berkeley Lab)

A single molecular layer of tungsten (W) and sulfide (S) is widely regarded as one of the most promising 2D semiconductors for photonic and optoelectronic applications. (Credit: Xiang Zhang, Berkeley Lab)

Among the most talked about class of materials in the world of nanotechnology today are two-dimensional (2D) transition metal dichalcogenides (TMDCs). These 2D semiconductors offer superior energy efficiency and conduct electrons much faster than silicon. Furthermore, unlike graphene, the other highly touted 2D semiconductor, TMDCs have natural bandgaps that allow their electrical conductance to be switched “on and off,” making them more device-ready than graphene. Tungsten disulfide in a single molecular layer is widely regarded as one of the most promising TMDCs for photonic and optoelectronic applications. However, until now, coherent light emission, or lasing, considered essential for “on-chip” applications, had not been realized in this material.

“TMDCs have shown exceptionally strong light-matter interactions that result in extraordinary excitonic properties,” Zhang says. “These properties arise from the quantum confinement and crystal symmetry effect on the electronic band structure as the material is thinned down to a monolayer. However, for 2D lasing, the design and fabrication of microcavities that provide a high optical mode confinement factor and high quality, or Q, factor is required.”

In a previous study, Zhang and his research group had developed a “whispering gallery microcavity” for plasmons, electromagnetic waves that roll across the surfaces of metals. Based on the principle behind whispering galleries – where words spoken softly beneath a domed ceiling can be clearly heard on the opposite side of the chamber – this micro-sized metallic cavity for plasmons strengthened and greatly enhanced the Q factor of light emissions. In this new study, Zhang and his group were able to adapt this microcavity technology from plasmons to excitons – photoexcited electrons/hole pairs within a single layer of molecules.

In this 2D excitonic laser, the sandwiching of a monolayer of tungsten disulfide between the two dielectric layers of a microdisk resonator creates the potential for ultralow-threshold lasing. (Credit: Xiang Zhang, Berkeley Lab)

In this 2D excitonic laser, the sandwiching of a monolayer of tungsten disulfide between the two dielectric layers of a microdisk resonator creates the potential for ultralow-threshold lasing. (Credit: Xiang Zhang, Berkeley Lab)

“For our excitonic laser, we dropped the metal coating and designed a microdisk resonator that supports a dielectric whispering gallery mode rather than a plasmonic mode, and gives us a high Q factor with low power consumption,” says co-lead author Ye. “When a monolayer of tungsten disulfide – serving as the gain medium – is sandwiched between the two dielectric layers of the resonator, we create the potential for ultralow-threshold lasing.”

In addition to its photonic and optoelectronic applications, this 2D excitonic laser technology also has potential for valleytronic applications, in which digital information is encoded in the spin and momentum of an electron moving through a crystal lattice as a wave with energy peaks and valleys. Valleytronics is seen as an alternative to spintronics for quantum computing.

“TMDCs such as tungsten disulfide provide unique access to spin and valley degrees of freedom,” says co-lead author Wong. “Selective excitation of the carrier population in one set of two distinct valleys can further lead to lasing in the confined valley, paving the way for easily-tunable circularly polarized lasers. The demand for circularly polarized coherent light sources is high, ranging from three-dimensional displays to effective spin sources in spintronics, and information carriers in quantum computation.”

This research was supported by the United States Air Force Office of Scientific Research and by the DOE Office of Science through the Light-Material Interaction in Energy Conversion Energy Frontier Research Center.

Invention of the first integrated circularly polarized light detector on a silicon chip opens the door for development of small, portable sensors that could expand the use of polarized light for drug screening, surveillance, optical communications and quantum computing, among other potential applications.

The new detector was developed by a team of Vanderbilt University engineers directed by Assistant Professor of Mechanical Engineering Jason Valentine working with researchers at Ohio University. The work is described in an article published on Sept. 22 in the online journal Nature Communications.

Wei Li, left, and Jason Valentine in the lab. (Anne Rayner / Vanderbilt)

Wei Li, left, and Jason Valentine in the lab. (Anne Rayner / Vanderbilt)

“Although it is largely invisible to human vision, the polarization state of light can provide a lot of valuable information,” said Valentine. “However, the traditional way of detecting it requires several optical elements that are quite bulky and difficult to miniaturize. We have managed to get around this limitation by the use of ‘metamaterials’ — materials engineered to have properties that are not found in nature.”

Polarized light comes in two basic forms: linear and circular. In a ray of unpolarized light, the electrical fields of individual photons are oriented in random directions. In linearly polarized light the fields of all the photons lie in the same plane. In circularly polarized light (CPL), the fields lie in a plane that continuously rotates through 360 degrees. As a result there are two types of circularly polarized light, right-handed and left-handed.

Humans cannot readily distinguish the polarization state of light, but there are a number of other species that possess “p-vision.” These include cuttlefish, mantis shrimp, bees, ants and crickets.

Cuttlefish also produce varying patterns of polarized light on their skin, which has led scientists to hypothesize that they use this as a secret communication channel that neither their predators or prey can detect. This has led to the suggestion that CPL could be used to increase the security of optical communications by including polarized channels that would be invisible to those who don’t have the proper detectors.

Unlike unpolarized light, CPL can detect the difference between right-handed and left-handed versions of molecules. Just like hands and gloves, most biological molecules come in mirror-image pairs. This property is called chirality. For example, cells contain only left-handed amino acids but they metabolize only right-handed sugars (a fact utilized by some artificial sweeteners which use left-hand forms of sugar which taste just as sweet as the right-hand version but which the body cannot convert into fat).

Illustration of how circularly polarized light passes through the silicon chip and is absorbed by the metamaterial. (Valentine Lab / Vanderbilt)

Illustration of how circularly polarized light passes through the silicon chip and is absorbed by the metamaterial. (Valentine Lab / Vanderbilt)

Chirality can be dramatically important in drugs because their biological activity is often related to their handedness. For example, one form of dopamine is effective in the management of Parkinson’s disease while the other form reduces the number of white blood cells. One form of thalidomide alleviates morning sickness while the other causes birth defects. The number of chiral drugs in use today is estimated to be 2,500 and most new drugs under development are chiral.

“Inexpensive CPL detectors could be integrated into the drug production process to provide real time sensing of drugs,” said Vanderbilt University doctoral student Wei Li, who played a key role in designing and testing the device. “Portable detectors could be used to determine drug chirality in hospitals and in the field.”

The metamaterial that the researchers developed to detect polarized light consists of silver nanowires laid down in a sub-microscopic zig-zag pattern on an extremely thin sheet of acrylic fixed to an optically thick silver plate. This metamaterial is attached to the bottom of a silicon wafer with the nanowire side up.

The nanowires generate a cloud of free-flowing electrons that produce “plasmon” density waves that efficiently absorb energy from photons that pass through the silicon wafer. The absorption process creates “hot” or energetic electrons that shoot up into the wafer where they generate a detectable electrical current.

The zig-zag pattern can be made either right-handed or left-handed. When it is right-handed, the surface absorbs right circularly polarized light and reflects left circularly polarized light. When it is left-handed it absorbs left circularly polarized light and reflects right circularly polarized light. By including both right-handed and left-handed surface patterns, the sensor can differentiate between right and left circularly polarized light.

Three images of the same surface demonstrate the new detector's capability. The researchers coated the surface with right- and -left-handed metamaterial in the form of the Vanderbilt logo. The image on the left was taken in plain polarized light. The one in the center was taken with left-handed circularly polarized light. And the image on the right was taken with right-handed circularly polarized light. (Valentine Lab / Vanderbilt)

Three images of the same surface demonstrate the new detector’s capability. The researchers coated the surface with right- and -left-handed metamaterial in the form of the Vanderbilt logo. The image on the left was taken in plain polarized light. The one in the center was taken with left-handed circularly polarized light. And the image on the right was taken with right-handed circularly polarized light. (Valentine Lab / Vanderbilt)

There have been two previous efforts to make solid-state polarized light detectors. According to Li, one used chiral organic materials that are unstable in air, worked only in a narrow range of wavelengths and had a limited power range. Another was based on a more complicated multilayer design that only worked at low temperatures.

“That is the beauty of metamaterials: You can design them to work in the fashion you desire,” said Li.

The efficiency of their prototype is 0.2 percent — too low to be commercially viable. Now that they have proven the viability of their approach, however, they have a number of ideas for how they can boost the efficiency to a level comparable to conventional photodetectors.

The research was supported by National Science Foundation grant CBET-1336455, Office of Naval Research grant N00014-14-1-0475, U.S. Army Research Office grant W911NF-12-1-0407 and the Volkswagen Foundation.


When the world’s leading scientists and engineers in micro/nanoelectronics convene in Washington, D.C. this December for the 61st annual IEEE International Electron Devices Meeting (IEDM), the subjects under discussion will encompass a range of topics critical to the continuing progress of the industry:

  • how to make transistors that are vanishingly small
  • a growing emphasis on low-power devices for mobile & Internet of Things (IoT)
  • alternatives to silicon transistors
  • 3D IC technology
  • a broad range of papers that address some of the fastest-growing specialized areas in micro/nanoelectronics, including silicon photonics, physically flexible circuits and brain-inspired computing.

The 2015 IEDM will take place at the Washington D.C. Hilton Hotel from December 7-9, 2015, preceded by day-long short courses on Sunday, Dec. 6 and a program of 90-minute tutorials on Saturday, Dec. 5. In addition to a technical program of some 220 papers, other events will take place during the meeting, including evening panels, special focus sessions, IEEE awards, and an entrepreneurial luncheon sponsored by IEDM and IEEE Women in Engineering.

Back for the third year, the 2015 IEDM will feature a slate of designated focus sessions on topics of special interest. This year’s topics are:

  • Neural-Inspired Architectures: From Ultra-Low Power Devices To Applications
  • 2D Layered Materials And Applications
  • Power Devices And Their Reliability On Non-Native Substrates
  • Flexible Hybrid Electronics
  • Silicon-Based Nano-Devices For Detection Of Biomolecules And Cell Functions

“From its inaugural meeting until today, the IEDM conference has been the place where breakthroughs that drive the electronics industry forward are unveiled,” said Mariko Takayanagi, IEDM 2015 Publicity Chair and Senior Manager at Toshiba. “For example, at the IEDM in 1975 Intel’s Gordon Moore gave a talk that refined his earlier prediction of transistor scaling into what has since become known as Moore’s Law. That tradition of attracting the best speakers and a large, diverse audience from around the world continues, with a focus this year on devices intended to support the Internet of Things and other emerging areas of importance that depend upon advances in semiconductor technology.”

Rectennas in Baratunde A. Cola's NEST (NanoEngineered Systems and Transport) lab

Rectennas in Baratunde A. Cola’s NEST (NanoEngineered Systems and Transport) lab

Using nanometer-scale components, researchers have demonstrated the first optical rectenna, a device that combines the functions of an antenna and a rectifier diode to convert light directly into DC current.

Based on multiwall carbon nanotubes and tiny rectifiers fabricated onto them, the optical rectennas could provide a new technology for photodetectors that would operate without the need for cooling, energy harvesters that would convert waste heat to electricity–and ultimately for a new way to efficiently capture solar energy.

In the new devices, developed by engineers at the Georgia Institute of Technology, the carbon nanotubes act as antennas to capture light from the sun or other sources. As the waves of light hit the nanotube antennas, they create an oscillating charge that moves through rectifier devices attached to them. The rectifiers switch on and off at record high petahertz speeds, creating a small direct current.

Billions of rectennas in an array can produce significant current, though the efficiency of the devices demonstrated so far remains below one percent. The researchers hope to boost that output through optimization techniques, and believe that a rectenna with commercial potential may be available within a year.

“We could ultimately make solar cells that are twice as efficient at a cost that is ten times lower, and that is to me an opportunity to change the world in a very big way” said Baratunde Cola, an associate professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech. “As a robust, high-temperature detector, these rectennas could be a completely disruptive technology if we can get to one percent efficiency. If we can get to higher efficiencies, we could apply it to energy conversion technologies and solar energy capture.”

The research, supported by the Defense Advanced Research Projects Agency (DARPA), the Space and Naval Warfare (SPAWAR) Systems Center and the Army Research Office (ARO), is reported September 28 in the journal Nature Nanotechnology.

Developed in the 1960s and 1970s, rectennas have operated at wavelengths as short as ten microns, but for more than 40 years researchers have been attempting to make devices at optical wavelengths. There were many challenges: making the antennas small enough to couple optical wavelengths, and fabricating a matching rectifier diode small enough and able to operate fast enough to capture the electromagnetic wave oscillations. But the potential of high efficiency and low cost kept scientists working on the technology.

“The physics and the scientific concepts have been out there,” said Cola. “Now was the perfect time to try some new things and make a device work, thanks to advances in fabrication technology.”

Using metallic multiwall carbon nanotubes and nanoscale fabrication techniques, Cola and collaborators Asha Sharma, Virendra Singh and Thomas Bougher constructed devices that utilize the wave nature of light rather than its particle nature. They also used a long series of tests–and more than a thousand devices–to verify measurements of both current and voltage to confirm the existence of rectenna functions that had been predicted theoretically. The devices operated at a range of temperatures from 5 to 77 degrees Celsius.

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Fabricating the rectennas begins with growing forests of vertically-aligned carbon nanotubes on a conductive substrate. Using atomic layer chemical vapor deposition, the nanotubes are coated with an aluminum oxide material to insulate them. Finally, physical vapor deposition is used to deposit optically-transparent thin layers of calcium then aluminum metals atop the nanotube forest. The difference of work functions between the nanotubes and the calcium provides a potential of about two electron volts, enough to drive electrons out of the carbon nanotube antennas when they are excited by light.

In operation, oscillating waves of light pass through the transparent calcium-aluminum electrode and interact with the nanotubes. The metal-insulator-metal junctions at the nanotube tips serve as rectifiers switching on and off at femtosecond intervals, allowing electrons generated by the antenna to flow one way into the top electrode. Ultra-low capacitance, on the order of a few attofarads, enables the 10-nanometer diameter diode to operate at these exceptional frequencies.

“A rectenna is basically an antenna coupled to a diode, but when you move into the optical spectrum, that usually means a nanoscale antenna coupled to a metal-insulator-metal diode,” Cola explained. “The closer you can get the antenna to the diode, the more efficient it is. So the ideal structure uses the antenna as one of the metals in the diode–which is the structure we made.”

The rectennas fabricated by Cola’s group are grown on rigid substrates, but the goal is to grow them on a foil or other material that would produce flexible solar cells or photodetectors.

Cola sees the rectennas built so far as simple proof of principle. He has ideas for how to improve the efficiency by changing the materials, opening the carbon nanotubes to allow multiple conduction channels, and reducing resistance in the structures.

“We think we can reduce the resistance by several orders of magnitude just by improving the fabrication of our device structures,” he said. “Based on what others have done and what the theory is showing us, I believe that these devices could get to greater than 40 percent efficiency.”


This work was supported by the Defense Advanced Research Projects Agency (DARPA), the Space and Naval Warfare (SPAWAR) Systems Center, Pacific under YFA grant N66001-09-1-2091, and by the Army Research Office (ARO), through the Young Investigator Program (YIP), under agreement W911NF-13-1-0491. The statements in this release are those of the authors and do not necessarily reflect the official views of DARPA, SPAWAR or ARO. Georgia Tech has filed international patent applications related to this work under PCT/US2013/065918 in the United States (U.S.S.N. 14/434,118), Europe (No. 13847632.0), Japan (No. 2015-538110) and China (No. 201380060639.2)

CITATION: Asha Sharma, Virendra Singh, Thomas L. Bougher and Baratunde A. Cola, “A carbon nanotube optical rectenna,” (Nature Nanotechnology, 2015).

The first all-optical permanent on-chip memory has been developed by scientists of Karlsruhe Institute of Technology (KIT) and the universities of Münster, Oxford, and Exeter. This is an important step on the way towards optical computers. Phase change materials that change their optical properties depending on the arrangement of the atoms allow for the storage of several bits in a single cell. The researchers present their development in the journal Nature Photonics.

Light determines the future of information and communication technology: With optical elements, computers can work more rapidly and more efficiently. Optical fibers have long since been used for the transmission of data with light. But on a computer, data are still processed and stored electronically. Electronic exchange of data between processors and the memory limits the speed of modern computers. To overcome this so-called von Neumann bottleneck, it is not sufficient to optically connect memory and processor, as the optical signals have to be converted into electric signals again. Scientists, hence, look for methods to carry out calculations and data storage in a purely optical manner.

Scientists of KIT, the University of Münster, Oxford University, and Exeter University have now developed the first all-optical, non-volatile on-chip memory. “Optical bits can be written at frequencies of up to a gigahertz. This allows for extremely quick data storage by our all-photonic memory,” Professor Wolfram Pernice explains. Pernice headed a working group of the KIT Institute of Nanotechnology (INT) and recently moved to the University of Münster. “The memory is compatible not only with conventional optical fiber data transmission, but also with latest processors,” Professor Harish Bhaskaran of Oxford University adds.

The new memory can store data for decades even when the power is removed. Its capacity to store many bits in a single cell of a billionth of a meter in size (multi-level memory) also is highly attractive. Instead of the usual information values of 0 and 1, several states can be stored in an element and even autonomous calculations can be made. This is due to so-called phase change materials, novel materials that change their optical properties depending on the arrangement of the atoms: Within shortest periods of time, they can change between crystalline (regular) and amorphous (irregular) states. For the memory, the scientists used the phase change material Ge2Sb2Te5 (GST). The change from crystalline to amorphous (storing data) and from amorphous to crystalline (erasing data) is initiated by ultrashort light pulses. For reading out the data, weak light pulses are used.

Permanent all-optical on-chip memories might considerably increase future performance of computers and reduce their energy consumption. Together with all-optical connections, they might reduce latencies. Energy-intensive conversion of optical signals into electronic signals and vice versa would no longer be required.

A*STAR‘s Institute of Microelectronics (IME) and Lumerical Solutions, Inc. (Lumerical), a global provider of photonic design software, today announced they have co-developed a calibrated compact model library (CML) for IME’s silicon photonics platform and process design kit (PDK). The CML will help photonic integrated circuit (PIC) designers who use IME’s silicon photonics process to improve the accuracy and reliability of their designs.

IME’s 25G silicon photonics platform and PDK are built on validated processes and devices. They offer state-of-the-art performance and enable PIC designers to build reliable devices, system architectures and achieve prototyping and product manufacturing with ease.

PIC design is often manual and iterative, and is based on custom component libraries and workflows, which may lead to errors and multiple design revisions. Leveraging IME’s capabilities in silicon photonics process and device technology, and Lumerical’s expertise in integrated photonics device simulation and circuit design tools, the collaboration overcame these challenges by adding calibrated simulation models to IME’s silicon photonics PDK. The CML enables designers to accurately simulate and optimize the performance of complex PIC designs prior to fabrication.

The CML includes 15 active and passive elements, from waveguides to modulators and photo detectors, and forms part of IME’s silicon photonics PDK, along with process data, layer tables, cells for device layout and design rules.

“With silicon photonics emerging as a leading technology platform for high bandwidth optical communication, R&D is critical in addressing the industry’s needs for increasingly complex photonic-electronic circuits. I am confident that the combined strengths of IME’s capabilities in silicon photonics technologies for integration and manufacturing, and Lumerical’s experience in innovating design tools will enable designers to produce quality photonic integrated circuits, and accelerate the production of next generation devices”, said Prof. Dim-Lee Kwong, Executive Director, IME.

“The addition of calibrated models to IME’s photonic PDK is a compelling step forward in establishing the design and fabrication ecosystem necessary for photonic circuit designers to realise the commercial potential of integrated photonic technologies,” stated Todd Kleckner, co-founder and Chief Operating Officer, Lumerical. “We are excited to work with a renowned and innovative research institute like IME and support joint users of IME’s MPW services and our design tools to confidently scale design complexity and deliver on their next ambitious design challenge.”


Bipartisan passage this week by the U.S. House of Representatives of a bill designed to stimulate development and commercialization of new technologies and promote growth of high-value jobs is being praised by leaders of SPIE, the international society for optics and photonics. The bill, the Revitalizing American Manufacturing and Innovation (RAMI) Act, now moves to the full Senate for a vote. The bill’s authors have said they are optimistic that it will win passage there as well this year, and will be signed into law by the President.

RAMI (S. 1468 and H.R. 2996) was introduced by Senators Roy Blunt (R-Missouri) and Sherrod Brown (D-Ohio) and Representatives Tom Reed (R-New York) and Joe Kennedy (D-Massachusetts). The bill would authorize the Secretary of Commerce to establish manufacturing institutes through a Network for Manufacturing Innovation (NMI).

The institutes – known as Innovation Manufacturing Institutes (IMIs) — would function in public-private partnerships including the federal government, local governments, universities, research institutes, and industry to accelerate manufacturing innovation in technologies with commercial applications. The partnerships would facilitate bridging the gap between basic research performed at U.S. universities and research laboratories, and product development by U.S. manufacturers.

“We are pleased with the bipartisan leadership evidenced with the passage of the RAMI bill, “ said James McNally, chair of the SPIE Engineering, Science, and Technology Policy committee. “This action supports and aligns with the continued commitment of SPIE, driven by its membership, to advocate for photonics R&D and job creation.”

The bill’s acknowledgement that optics and photonics are pervasive in our everyday lives is important as well, McNally said. “Light-based innovations and products can provide significant improved quality of life throughout the world in health care, energy efficiency, lighting, and clean water. Enactment of this bill would position U.S. manufacturing consortiums at the forefront of providing these innovative products to the world, while creating high-quality domestic manufacturing jobs.”

Inclusion of optics and photonics sections in the bill has been advocated by SPIE and other organizations working through the National Photonics Initiative (NPI), a collaborative alliance seeking to raise awareness of photonics and drive U.S. funding and investment in key photonics-driven fields. SPIE, in its role as a Founding Sponsor of the NPI, continues to work toward its long-held mission of advocating for the photonics industry, noted SPIE CEO Eugene Arthurs.

“Our constituents see first-hand how important their work is in enabling inventions that meet society’s many needs, while creating new jobs and generating new revenue,” Arthurs said. “Their research, reported through SPIE events and publications, shows the technology’s vast potential. The products and systems we see at SPIE’s exhibitions are evidence that the technology is already a sizable piece of the economy.”

Photonics scientists, researchers, engineers, and technicians are responsible for developing light-based technologies for earlier and better diagnosis, treatment, or monitoring of conditions such as cancer, diabetes, Alzheimer’s disease, stroke, and epilepsy, Arthurs said. “Their work in integrated photonics will enable the next generation of computing and further evolution of the internet — which exists and functions because of photonics. They are developing sustainable energy sources, more efficient lighting, and other technologies to meet the world’s growing energy needs. In short, photonics is improving our lives and strengthening the economy in the process.”