Unusual fluorescent materials could be used for rapid light-based communications systems.
|In this image, light strikes a molecular lattice deposited on a metal substrate. The molecules can quickly exchange energy with the metal below, a mechanism that leads to a much faster response time for the emission of fluorescent light from the lattice. Courtesy of the researchers|
Two-dimensional materials called molecular aggregates are very effective light emitters that work on a different principle than typical organic light-emitting diodes (OLEDs) or quantum dots. But their potential as components for new kinds of optoelectronic devices has been limited by their relatively slow response time. Now, researchers at MIT, the University of California at Berkeley, and Northeastern University have found a way to overcome that limitation, potentially opening up a variety of applications for these materials.
The findings are described in the journal Proceedings of the National Academy of Sciences, in a paper by MIT associate professor of mechanical engineering Nicholas X. Fang, postdocs Qing Hu and Dafei Jin, and five others.
The key to enhancing the response time of these 2-D molecular aggregates (2DMA), Fang and his team found, is to couple that material with a thin layer of a metal such as silver. The interaction between the 2DMA and the metal that is just a few nanometers away boosts the speed of the material’s light pulses more than tenfold.
Read more at the MIT News Office.
David L. Chandler | MIT News Office
Sept. 18, 2017
2010 Summer Scholar Jessica Morrison develops micro controller for variable light output.
|Helux Technologies founder Jessica [Shipman] Morrison pioneered a new kind of controllable solid-state lighting using a micro-electromechanical system while pursuing her PhD at Boston University. The former 2010 MIT Summer Scholar started a two-year fellowship in April 2017 at the Cyclotron Road incubator at Lawrence Berkeley National Laboratory, where she hopes to commercialize her product.|
Helux Technologies founder Jessica [Shipman] Morrison looks back on her 2010 Summer Scholar internship as laying the foundation for her current work. “When I was at the University of Cincinnati, I worked in a high-energy particle physics lab, so it was a big jump,” she says. “At MIT, I worked quite a bit in the clean room in the electronics and nano fab facility and that was what defined what I really wanted to go into. I’ve changed a little since then, but the basic idea stuck. I went into graduate school knowing that I wanted to do something with some sort of micro- or nano-fabrication.”
After graduating with a degree in physics from the University of Cincinnati, Morrison earned a PhD at Boston University, where she pioneered a new kind of controllable solid-state lighting using a micro-electromechanical system with support from the NSF Engineering Research Center [ERC] for Lighting Enabled Systems and Applications. Her device uses a circular array of tiny wedge-shaped mirrors, made up of contrasting materials that are both moveable and bendable, to reshape the direction and the degree of softness or harshness of the light. The mirrors themselves are less than a millimeter in diameter.
“My hope is to start pushing forward some of the laser-based lighting systems because this technology is the perfect fit for it,” Morrison says. “Using the mirrors to provide dynamic lighting would be a functionality that’s not been seen before. I’m already talking to designers in a space where, at least as a first market, we would be able to pull in some revenue.”
Boston University Professor of Electrical and Computer Engineering Thomas Little, who is Associate Director of the NSF Smart Lighting ERC, says, “With energy-efficient lighting as a goal, the approach to using MEMS mirrors for directional control of lighting emerged as a core system requirement that led to the invention. Jessica drove efforts to model, simulate, and fabricate the device within the center.”
“The multiple degrees of freedom of the device can be readily computer controlled. It is low cost (less than $0.25 in quantity) and can integrated into consumer products,” Little explains, noting that the variable focus, lotus-shaped MEMS mirror can tilt, tip, focus, and “piston.” “The applications of this core technology continue to emerge, but begin with energy efficient lighting, high-speed optical wireless links for data access and data center interconnects, measurement instrumentation, and vehicle-to-vehicle networking,” he says.
|Helux Technologies founder Jessica [Shipman] Morrison hopes to commercialize her adaptable lighting controlled by a micro-electromechanical system.|
In April 2017, Morrison joined the Cyclotron Road incubator at Lawrence Berkeley National Laboratory as a fellow for two years. The fellowship enabled Morrison to bring on a research fellow to work on her project. “My long-term goal is to make something that the general public can use starting with high-end, multi-functional lighting systems,” Morrison says.
During her 2010 internship working on Optimization of Superconducting Nanowire under Professor Karl Berggren, Morrison says, her life was anything but that of a normal college student. “My grandparents raised me, and the day I found out I got into the program my grandmother passed away, suddenly, overnight. Then the first week that I was there, I found out my grandfather had terminal cancer. It was a long summer.” She found lots of support among her fellow Summer Scholars. “I made a lot of friends. They provided the support that I really needed at the time,” she says. It was also the summer she married, changing her name from Shipman to Morrison. “I went back to Ohio and got married immediately after that program,” she says.
As an undergraduate, Morrison had other research experiences with the Air Force Institute of Technology and Case Western Reserve University. Reflecting on her MIT Summer Scholars experience, Morrison says, “One of the biggest differences was that I had a choice. Going into the program they spend the first week presenting to you the available options, and then you get a choice based on what you saw. You don’t necessarily get your first choice every time, but at least you have some choice going into it, so that was pretty awesome from my vantage point.”
The annual Summer Scholars program is co-sponsored by the Materials Processing Center and the Center for Materials Science and Engineering and is supported in part by NSF’s Materials Research Science and Engineering Centers program.
Related: Helux Technologies
Test of cervical mucus may reveal pregnant women’s risk of going into labor too early.
|“Our prediction is that we might be able to identify risk for preterm birth ahead of time, before labor sets in,” says Katharina Ribbeck, an associate professor of biological engineering at MIT and the senior author of the study. “Diagnostic tools for this are missing.” Photo, Bryce Vickmark|
Up to 18 percent of babies born worldwide arrive before they are full-term, defined as 37 weeks of gestation. About 1 million of those babies do not survive, and those who do can face developmental problems such as impaired vision or hearing, defects in the heart or lungs, or cognitive impairments.
Currently there is no reliable way to predict whether a woman with a normal pregnancy will go into labor before 37 weeks. However, a study from MIT offers a new approach to evaluating this risk, by analyzing the properties of cervical mucus. The researchers found that cervical mucus from women who delivered their babies before 37 weeks was very different from that of women who delivered later.
This type of analysis could offer an easy way to calculate the risk of early labor, potentially allowing doctors to try to intervene earlier to prevent preterm births.
“Our prediction is that we might be able to identify risk for preterm birth ahead of time, before labor sets in,” says Katharina Ribbeck, an associate professor of biological engineering at MIT and the senior author of the study. “Diagnostic tools for this are missing.”
Ribbeck worked on the study with Michael House, an associate professor at Tufts University School of Medicine. MIT postdoc Kathryn Smith-Dupont is the first author of the paper, which appears in the Sept. 4 issue of Scientific Reports.
Read more at the MIT News Office.
Anne Trafton | MIT News Office
September 4, 2017
|As a 2016 MPC-CMSE Summer Scholar, Michael Concepción-Santana synthesized hydrogels that can indicate changes in pH near a patient’s tumor in an MRI scan. He received a 2017 New Faces of Engineering College Edition award from DiscoverE. Photo, Denis Paiste, Materials Processing Center.|
Michael Concepción-Santana was honored as one of 11 winners of DiscoverE’s sixth annual New Faces of Engineering College Edition awards, which recognize students who exemplify the vision, innovation and leadership skills needed for a successful engineering career.
Concepción Santana served as an intern in the lab of Michael J. Cima, David H. Koch Professor of Engineering at MIT in 2016 through the Materials Processing Center-Center for Materials Science and Engineering Summer Scholars program.
A Biomedical Engineering major at the Polytechnic University of Puerto Rico, Concepción-Santana was nominated for the DiscoverE award by the American Institute of Chemical Engineers (AIChE). He is a co-author of “Unusual photophysics of anticancer azapodophyllotoxin: The collective effect of discrete H-bond motif spills the beans,” published online Sept. 1, 2017, by the Journal of Photochemistry and Photobiology A: Chemistry.
The first member of his family to attend college, Concepción-Santana hopes pursue a PhD and perhaps an MD as well. Concepción Santana’s research focuses on developing new cancer drugs and new ways to deliver them to cancer cells.
Summer Scholar Luke Soule interns with MIT team developing new catalyst materials to reduce cancer-causing chemicals in the atmosphere.
Air pollution leads to about 6.5 million deaths worldwide every year, including nearly 200,000 within the United States, MIT graduate student Karthik Akkiraju notes with alarm. MPC-CMSE Summer Scholar Luke Soule joined Akkiraju’s efforts to develop new oxide catalysts to reduce air pollution in W.M. Keck Professor of Energy Yang Shao-Horn's lab.
“The main goal of my project was to develop a novel class of oxide catalysts to reduce noxious chemicals in the atmosphere known to cause cancer,” says Soule, a rising senior at the New Mexico Institute of Mining and Technology. “This involved trying to link electronic structure to the catalyst, to the selectivity, towards these volatiles.”
During his internship in Shao-Horn’s Electrochemical Energy Lab, Soule flows gases through a plug flow reactor with the catalysts inside, and analyzes the gases using an infrared [IR] spectrometer. Soule points to a computer displaying graphs from IR spectra of his samples. “Right now I'm just measuring the concentration of CO2 [carbon dioxide] in the cell,” he says.
Akkiraju, whose field is materials science and engineering, says, “I've been working on oxidation reactions for volatile organic compounds. So in the lab we have two basic parts, so we look at synthesis of new materials, and on the other hand we
look at reaction mechanisms. With the background that Luke has, he fits in well with the synthesis part where using different characterization techniques, he's been exploring this novel set of oxide compounds.”
“In order to address the issue of removal of toxic gases such as carbon monoxide,
nitric oxide, [and other] volatile organic compounds, we've been trying to develop new catalyst materials,” Akkiraju explains. “So Luke has taken lead of the project to set up the gas lines for these new organic compounds, run the calibrations, and now he's been producing pretty impressive results.”
“Luke is an incredible team player,” Akkiraju says. “While he's been working on his own project, he also has been finding time to help other people in the lab characterizing their samples, synthesizing new materials for them, so he has a never-say-die kind of attitude, while he’s always up for everything that comes along his path.”
Soule, a materials science and engineering major, says he joined Shao-Horn’s group because the group seemed like a family, and he was really interested in catalysis. During a visit to the lab, Soule demonstrates how more catalyst is loaded into the reactor [see related video], known as in situ reactor because reactions can be observed as they are occurring. “To classify the crystal structure of these catalysts we are synthesizing, I learned SEM – scanning electron microscopy – to image the different morphologies of these catalysts,” Soule says. “They're skills I've used in the past, but I've definitely learned more about them, and they're skills I'll continue to get better at as my career progresses. So it was a really good choice.”
Soule's internship is supported in part by NSF’s Materials Research Science and Engineering Centers program [grant DMR-14-19807]. Participants in the Research Experience for Undergraduates, co-sponsored by the Materials Processing Center and the Center for Materials Science and Engineering, presented their results at a poster session during the last week of the program. The program ran from June 15, 2017, to August 5, 2017, on the MIT campus in Cambridge, Mass.
– Denis Paiste, Materials Processing Center
August 28, 2017
Carbon nanotubes lower transformation temperature of glassy carbon, MIT researchers report.
|MIT graduate student Ashley L. Kaiser, foreground, and MIT Postdoc Itai Y. Stein report in the Journal of Materials Science that a small fraction of carbon nanotubes added to phenol formaldehyde resin lowers the processing temperature needed to achieve the best combination of hardness and low density by 200 degrees Celsius. Photo, Denis Paiste, Materials Processing Center|
Last winter, MIT researchers discovered that a phenol-formaldehyde polymer that was transformed into a glassy carbon material in a process similar to baking reaches its best combination of higher strength and lower density at 1,000 degrees Celsius [1,832 degrees Fahrenheit]. Now, they have determined that by adding a small fraction of carbon nanotubes (CNTs) to this material, they can achieve a similar glassy transformation, but at a more industrially accessible temperature of 800 degrees Celsius.
As the starting polymeric hydrocarbon, known as a phenol-formaldehyde polymeric resin, is heated from 600 degrees Celsius, the size of its crystallites grows until it reaches a plateau at 1,000 degrees Celsius. Scientific literature shows that this plateau holds until well above 2,000 degrees Celsius, MIT Postdoc Itai Y. Stein notes. Compared to the glassy carbon formed without carbon nanotubes, the addition of 1 percent by volume of aligned carbon nanotubes to the starting material allows it to reach the plateau crystallite size at 800 degrees Celsius, a 200 degrees Celsius reduction.
“What we’re showing is that by adding carbon nanotubes, we reach this plateau region earlier,” Stein says. The findings were reported Aug. 22 in the Journal of Materials Science online, by co-authors Stein, former Materials Processing Center-Center for Materials Science and Engineering Summer Scholars Ashley L. Kaiser  and Alexander J. Constable , Postdoc Luiz Acauan, and senior author Brian L. Wardle, Professor of Aeronautics and Astronautics. Kaiser is now a graduate student in Wardle’s lab.
“This work has the interesting finding that nanostructures assist in fabricating/manufacturing the glassy carbon composites. Early lessons with nano-materials broadly showed that nanostructures impede manufacturing, however, we are finding a theme across several research areas that when controlled, the nanostructures can be utilized to enhance manufacturing, sometime significantly. While the nanostructures (here, aligned carbon nanotubes) are valuable as reinforcement to the glassy carbon, they can also be utilized to improve the manufacturability. Ashley and Itai are taking this work even further to test the limits,” says Professor Wardle.
Crystallite size is strongly tied to hardness, which is a measure of mechanical performance such as strength and toughness, and is one of the most important properties of the glassy carbon material. “If you look at the hardness normalized by the density, we previously found that the first point in the plateau region is the best point, because there the glassy carbon material is the least dense and hardest,” Stein says.
The primary finding of the earlier paper was that more disorder in the arrangement of carbon crystallites led to greater hardness and lower density in this glassy carbon material, which was obtained by “baking” a phenol-formaldehyde polymer in the absence of oxygen. The transformed material is also called pyrolytic carbon (PyC). Although the polymer transforms into a graphite-like material, it never reaches the more highly ordered structure of graphite. This difference is confirmed by X-ray diffraction [XRD] analysis of samples baked with, and without, carbon nanotubes and compared to a standard indicator for graphite known as Bernal stacking order. The type of disorder among crystallites here is called turbostratic stacking, where the planes that comprise the crystallites are randomly rotated with respect to one another due to holes (vacancies) and curvature. XRD studies, which were carried out at the Center for Materials Science and Engineering’s shared experimental facilities, also validated the crystallite size evolution with baking temperature.
To imagine this disorder compared to the perfect hexagonal structure of graphene or repeating layered structure of graphite, Stein suggests, think of a stack of flat square pieces of paper. They easily stack into a perfect square with minimal space between each sheet of paper. Take each piece paper, crumple it, and then lightly flatten it out again. You’ll be frustrated trying to reorder these sheets into a neat stack. Similar disorder occurs in the molecular structure of the glassy carbon, because the precursor phenol-formaldehyde polymer begins with a complicated mix of carbon-rich compounds and the baking temperature isn’t high enough to break down all of them into simpler carbon structures. Raman spectroscopy results confirmed the presence of these defects in the carbon structure. Another technique, Fourier Transform Infrared Spectroscopy [FTIR], confirmed the presence of oxygen and hydrogen groups within the crystallites. “It originates from the polymeric precursor that we use, the phenol-formaldehyde, and they’re just stuck; they can’t leave,” Stein explains.
|Samples of carbon nanotubes and polymeric phenol-formaldehyde materials hardened through baking at high temperature in the absence of oxygen. From left: (a) A carbon nanotube forest; (b) A carbon nanotube/polymer nanocomposite; (c) A charcoal-like carbon nanotube/glassy carbon nanocomposite after baking at high temperature; (d) Pure polymer (phenol-formaldehyde); (e) A charcoal-like glassy carbon block from baking polymer at high temperature. Researchers in Professor of Aeronautics and Astronautics Brian L. Wardle’s lab have conducted a series of studies most recently confirming that adding a small quantity of carbon nanotubes to a polymer lowers the ideal processing temperature of their nanocomposite from 1,000 degrees Celsius to 800 degrees Celsius without losing strength or increasing the weight of the material. Image, Ashley L. Kaiser and Itai Y. Stein.|
The researchers’ earlier paper showed that the presence of these more complex carbon compounds in the material strengthens it by leading to three-dimensional connections that are hard to break. The new work shows that the carbon nanotubes have no effect on these oxygen or hydrogen substructures in the material.
For the current study, Stein says, the goal was to explore what happens when carbon nanotubes are added and the baking temperature is increased; specifically, what effect, if any, the nanotubes have on crystallite growth. They found that the nanotubes influence the crystallite formation process on the meso-scale, which is measured in 10s of nanometers, while everything else remains unchanged. Importantly, only the crystallite size is affected by the addition of the carbon nanotubes. “We were surprised to see no change in the graphitic nature of our polymer as it is being baked in the presence of carbon nanotubes. Nonetheless, that is a very interesting finding because we can reduce the processing temperature without affecting the structure of the resulting glassy carbon. Since the properties of the glassy carbon depend on its structure, this finding could allow an industrial process of this technology to realize significant energy savings,” he says.
Faster structural evolution
“The carbon nanotubes allow the composite’s structure to evolve faster at the meso-scale, so it reaches its final state at a lower processing temperature. These nanotubes also decrease the overall weight of the material,” Kaiser adds. “This way, we are able to produce our composite at a lower temperature while decreasing its density and maintaining its excellent properties.”
Stein notes that the researchers also showed in the earlier work that increasing processing temperature above 1,000 degrees Celsius resulted in a weaker material. “So we are essentially reducing the temperature you need to go to reach the best properties,” Stein says of the new report. The desirable properties researchers seek include hardness and light weight. “If you look at the hardness normalized by the density, this (800 degrees Celsius) is the best point, because this is where the glassy carbon is expected to be the least dense and hardest,” Stein says.
This lower processing temperature may make these phenolic materials more compatible with metals whose melting points are below 1,000 degrees Celsius, which may be useful for 3D printing. “The application we specifically thought of using this in is meta-materials,” Stein says. “If you can use nanotubes to reduce the temperature you bake at, if you want to convert it to carbon, just pure carbon, then that could make it more accessible. That 200 degrees Celsius is a big difference for many processes.”
In the new findings, the researchers experimented on a material with just 1 percent carbon nanotubes by volume. They plan to follow up by studying the impact of increasing the proportion of carbon nanotubes to 20 percent by volume. “We just want to see if the nanotubes make it stronger, “ Stein says. They’ll also look at the effect on size and thickness of the crystallites from the added carbon nanotubes.
MIT Postdoc Itai Y. Stein holds samples of cured phenolic resin, left, and glassy carbon, a charcoal-like block formed from baking phenol-formaldehyde polymer at high temperature. Photo, Denis Paiste, Materials Processing Center
“A whole range of structural composites would benefit from this study, particularly next-generation ultra-lightweight nano-structures,” says Piran R. Kidambi, Assistant Professor of Chemical and Biomolecular Engineering at Vanderbilt University, who was not involved in this research. “The study found that aligned carbon nanotube-glassy carbon matrix nanocomposites at the meso-scale evolved much faster with a plateau in crystallite sizes (an important quality metric) at a temperature up to 200 degrees Celsius lower compared to having a pure glassy carbon matrix. Lower temperatures are good news for manufacturing to minimize heating costs in processing, and recent models tell us that slender crystallites are desirable since they increase glassy carbon hardness. Hence a combination of a plateau in crystallite sizes and lower temperatures is very interesting from a manufacturing perspective.”
“This is high quality research that uses fundamental insights to inform and guide manufacturing/synthesis routes for superior composites,” Kidambi adds.
Summer Scholar work
Kaiser’s work as a 2016 MPC-CMSE Summer Scholar makes up the bulk of the paper’s experimental results, all except for the Raman spectroscopy results. “It is a very robust and focused contribution,” Stein says.
“I was thrilled to be involved in this research when I was a Summer Scholar,” Kaiser says. “Now, being able to come back to MIT as a graduate student, rejoin the Wardle group, and publish this work is very exciting. I’m eager to continue working on composites as I pursue my PhD here in Materials Science and Engineering.”
This work received support from the Department of Defense, National Science Foundation MRSEC Program [grant DMR-08-19762], and the MIT Materials Processing Center. Airbus, Embraer, Lockheed Martin, Saab AB, ANSYS, Hexcel, Saertex, and TohoTenax also provided partial support through MIT's Nano-Engineered Composite aerospace STructures (NECST) Consortium. Stein was supported in part by a National Defense Science and & Engineering Graduate Fellowship.
– Denis Paiste, Materials Processing Center
August 28, 2017
AIM Photonics Academy summer intern Ryan Kosciolek creates thin film samples and analyzes their optical, electrical, and material properties.
Active photonic devices, such as waveguides, can be used in lasers, modulators and sensors. AIM Photonics Academy summer intern Ryan Kosciolek is working under Dr. Anuradha Agarwal, MIT principal research scientist, to deposit thin films of amorphous germanium onto silicon to develop lower cost materials for these applications.
“I am working on depositing amorphous germanium on various substrates and characterizing the optical, electrical, and material properties to evaluate its use for photonic applications,” Kosciolek, a rising senior at Rutgers University, explains.
Kosciolek’s work in the lab is supervised by Peter Su, an MIT graduate student in materials science and engineering. “Germanium is a silicon-CMOS [complementary metal oxide semiconductor] compatible material with several active and passive photonic applications,” Su says. “We're looking at specifically amorphous germanium because it is easier to deposit than crystalline germanium, and therefore lower cost.” A crystalline structure is highly ordered at the molecular level, while an amorphous structure is more disordered.
During a visit to the lab, Kosciolek and Su explain the process they use to fabricate these germanium thin films, removing a bare silicon wafer from the process chamber and reapplying tape before reinserting it. To remove the sample from the pressurized main chamber, which is under vacuum, they first have to open the valves connecting the load lock to the process chamber and equalize the pressure. “After we pull the sample out of the process chamber and into the load lock, we can then close the valve and then vent the load lock, so that we can take out the sample. The sample currently is just the silicon wafer,” Kosciolek explains.
“We use a special tool called a profilometer that lets us measure the thickness of the sample,” he says. “An easy way to use it is just apply tape beforehand so that there's a very clear distinct ledge between where the sample is and where it ends.” Su adds, “We're just going to adjust the tape a little bit so that we can get a more distinct edge for that profilometer measurement to measure the thickness. What the tape is doing is securing the sample to our sample holder plate, but we also are simultaneously using that piece of tape to create an edge where we have germanium and then suddenly no germanium, and that ledge right there allows us to measure the thickness using a profilometer.”
|AIM Photonics Academy summer intern Ryan Kosciolek works with amorphous germanium, depositing thin films of that material and characterizing the optical, electrical, and material properties to evaluate its use for photonic applications. Here he stands at the control panel for the thin film, sputter deposition machine. Photo, Denis Paiste, Materials Processing Center.|
After adjusting the sample and the tape, Kosciolek says, they can put it back in the thin film, sputter deposition chamber, first placing it onto the lever arm in the load lock. “After closing the load lock, we can then go back to the control panel and use the pumps to vacuum it down,” he says. He can then move the lever arm containing the sample into the process chamber. “Then we can raise the sample
inside the process chamber, remove the lever arm, and once again close the valve. Once it's at a sufficiently low pressure, we can then run the deposition.” Kosciolek also hopes to fabricate waveguides from the amorphous germanium material.
Kosciolek is a physics and mathematics major at Rutgers. His AIM Photonics Academy internship is part of the “AIM Photonics Future Leaders: Research and Professional Skills Training Program,” with additional support from the Materials Processing Center and the Center for Materials Science and Engineering. AIM Photonics interns from MIT, the University California, Santa Barbara [UCSB], University of Arizona and SUNY Polytechnic Albany convened at UCSB Aug. 10-11, 2017.
– Denis Paiste, Materials Processing Center
August 28, 2017
|AIM Photonics Academy summer intern Ryan Kosciolek presents his research on amorphous germanium materials during the MPC-CMSE Summer Scholars Poster Session on Aug. 3, 2017.|
AIM Photonics Academy summer intern Stuart Daudlin simulates adding a heater to light-filtering ring resonator manufacturing.
Integrated photonic devices that use light rather than electricity to move and process data can increase speeds and reduce waste heat for computers and networks, but variations in ring resonators, waveguides and other light-filtering devices pose manufacturing challenges. AIM Photonics Academy summer intern Stuart Daudlin is running numerical simulations to identify ways to improve consistency in these photonic products.
Working under graduate student Germain Martinez, in the lab of Duane Boning, the Clarence J. LeBel Professor of Electrical Engineering at MIT, Daudlin is simulating photonic device manufacturing using a special type of computer software, a finite difference time domain [FDTD] simulator.
“My goals this summer are to vary the parameters of a ring resonator and define which parameters cause the most variations,” Daudlin explains. “I've built a model for a ring resonator on numerical software, and I have analyzed a few parameters on how the variations might affect the performance of the device. I've had some interesting results so far looking at how only really two parameters stuck out and caused large changes, which is not a good thing, but it's something that we are looking for.” Two factors, the width and the thickness, contributed the most to changes in performance of waveguides and resonators, Daudlin’s simulations show.
“Variations in silicon photonics are very important,” electrical engineering and computer science graduate student Martinez says, “because the eventual goal would be to implement these structures in the same sort of process that we have to make CMOS [complementary metal-oxide semiconductors], for example, transistors and electronics. The idea would be to have both silicon photonics structures and CMOS structures on the same chip at the same time working together.”
“CMOS tends to have metal connectors connecting the different transistors together. Those metal interconnects take up a lot of power, they heat up, especially when you are running at gigahertz frequencies,” Martinez says. “One application of silicon photonics would be to replace some of these metal connectors with silicon waveguides, for example, and the benefit of that would be that you don't dissipate nearly as much heat, because you're not heating up metal anymore. You're using light which doesn't heat up.”
|2017 AIM Photonics Academy summer intern Stuart Daudlin’s project is simulating addition of a heater to light-filtering ring resonator manufacturing. Photo, Denis Paiste, Materials Processing Center.|
Ring resonators and waveguides can play a key role because they can isolate certain wavelengths of light. “Ring resonators directly apply to this data application that Germain was talking about,” Daudlin explains. “They can sort through the wavelengths and essentially modulate the data. That's like what radios do; they modulate a signal.”
Daudlin is incorporating a heater into his manufacturing simulations. “With a heater or with other ways to actively tune these resonators, you can change what
wavelengths they let through,” he says. “For a system on a chip, with theoretically a lot of different cores, that would be perfect for routing these cores together. I currently am working at implementing a heater in the device and in my models, so
I can heat the device, and mitigate these variations and hopefully that will solve these problems in manufacturing.”
Martinez says the best outcome for the project would be finding the key sensitivities that lead to device variation, showing how to mitigate those sensitivities with the heater and characterizing these results with mathematical models. “If we had a way to generate these things more quickly and with less variations, we could make an entire fiber-optic chip that could handle an entire network and put out a bunch of these at once and save the Internet companies a lot more money and a lot more infrastructure,” he says.
Daudlin, a University of Michigan, Ann Arbor, engineering physics major, brings to the project his experience with electricity and magnetism, quantum mechanics and radar. “I've learned a lot since I've got here; I've learned how to use all the software,” Daudlin says. “If I can make a mathematical model to describe the variations of these devices, then that would be very useful for the design of these devices.”
Daudlin’s AIM Photonics Academy internship is part of the “AIM Photonics Future Leaders: Research and Professional Skills Training Program,” with additional support from the Materials Processing Center and the Center for Materials Science and Engineering. AIM Photonics interns from MIT, the University California, Santa Barbara [UCSB], University of Arizona and SUNY Polytechnic Albany convened at UCSB Aug. 10-11, 2017.
– Denis Paiste, Materials Processing Center
August 28, 2017
|2017 AIM Photonics Academy summer intern Stuart Daudlin presents his poster on his project is simulating addition of a heater to light-filtering ring resonator manufacturing. Daudlin worked in the lab of Duane Boning, the Clarence J. LeBel Professor of Electrical Engineering at MIT Photo, Denis Paiste, Materials Processing Center.|