High-Performance ‘Quantum Dot Mode-Locked Laser on silicon – Proven 4.1 Terabit-per-second transmission capacity – The Future of Telecommunications and Data Centers – UC Santa Barbara


Bowers Liu Optica

Ten years into the future.

That’s about how far UC Santa Barbara electrical and computer engineering professor John Bowers and his research team are reaching with the recent development of their mode-locked quantum dot lasers on silicon.

It’s technology that not only can massively increase the data transmission capacity of data centers, telecommunications companies and network hardware products to come, but do so with high stability, low noise and the energy efficiency of silicon photonics.

“The level of data traffic in the world is going up very, very fast,” said Bowers, co-author of a paper on the new technology in the journal Optica. Generally speaking, he explained, the transmission and data capacity of state-of-the-art telecommunications infrastructure must double roughly every two years to sustain high levels of performance. That means that even now, technology companies such as Intel and Cisco have to set their sights on the hardware of 2024 and beyond to stay competitive. quantum-dots-head-672x371

Enter the Bowers Group’s high-channel-count, 20 gigahertz, passively mode-locked quantum dot laser, directly grown — for the first time, to the group’s knowledge — on a silicon substrate. With a proven 4.1 terabit-per-second transmission capacity, it leaps an estimated full decade ahead from today’s best commercial standard for data transmission, which is currently reaching for 400 gigabits per second on Ethernet.

The technology is the latest high-performance candidate in an established technique called wavelength-division-multiplexing (WDM), which transmits numerous parallel signals over a single optical fiber using different wavelengths (colors). It has made possible the streaming and rapid data transfer we have come to rely on for our communications, entertainment and commerce.

The Bowers Group’s new technology takes advantage of several advances in telecommunications, photonics and materials with its quantum dot laser — a tiny, micron-sized light source — that can emit a broad range of light wavelengths over which data can be transmitted.

“We want more coherent wavelengths generated in one cheap light source,” said Songtao Liu, a postdoctoral researcher in the Bowers Group and lead author of the paper. “Quantum dots can offer you wide gain spectrum, and that’s why we can achieve a lot of channels.” Their quantum dot laser produces 64 channels, spaced at 20 GHz, and can be utilized as a transmitter to boost the system capacity.

The laser is passively ‘mode-locked’ — a technique that generates coherent optical ‘combs’ with fixed-channel spacing — to prevent noise from wavelength competition in the laser cavity and stabilize data transmission.

This technology represents a significant advance in the field of silicon electronic and photonic integrated circuits, in which the primary goal is to create components that use light (photons) and waveguides — unparalleled for data capacity and transmission speed as well as energy efficiency — alongside and even instead of electrons and wires. Silicon is a good material for the quality of light it can guide and preserve, and for the ease and low cost of its large-scale manufacture. However, it’s not so good for generating light.

“If you want to generate light efficiently, you want a direct band-gap semiconductor,” said Liu, referring to the ideal electronic structural property for light-emitting solids. “Silicon is an indirect band-gap semiconductor.” The Bowers Group’s quantum dot laser, grown on silicon molecule-by-molecule at UC Santa Barbara’s nanofabrication facilities, is a structure that takes advantage of the electronic properties of several semiconductor materials for performance and function (including their direct band-gaps), in addition to silicon’s own well-known optical and manufacturing benefits.

This quantum dot laser, and components like it, are expected to become the norm in telecommunications and data processing, as technology companies seek ways to improve their data capacity and transmission speeds.

“Data centers are now buying large amounts of silicon photonic transceivers,” Bowers pointed out. “And it went from nothing two years ago.”

Since Bowers a decade ago demonstrated the world’s first hybrid silicon laser (an effort in conjunction with Intel), the silicon photonics world has continued to create higher efficiency, higher performance technology while maintaining as small a footprint as possible, with an eye on mass production. The quantum dot laser on silicon, Bowers and Liu say, is state-of-the-art technology that delivers the superior performance that will be sought for future devices.

“We’re shooting far out there,” said Bowers, who holds the Fred Kavli Chair in Nanotechnology, “which is what university research should be doing.”

Research on this project was also conducted by Xinru Wu, Daehwan Jung, Justin Norman, MJ Kennedy, Hon K. Tsang and Arthur C. Gossard at UC Santa Barbara.

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Materials provided by University of California – Santa BarbaraNote: Content may be edited for style and length.

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Discovery: How groups of cells are able to build our tissues and organs while we are still embryos – Understanding ‘how’ may help us treat Cancer more effectively


 

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Ever wondered how groups of cells managed to build your tissues and organs while you were just an embryo?

Using state-of-the-art techniques he developed, UC Santa Barbara researcher Otger Campàs and his group have cracked this longstanding mystery, revealing the astonishing inner-workings of how embryos are physically constructed.

Not only does it bring a century-old hypothesis into the modern age, the study and its techniques provide the researchers a foundation to study other questions key to human health, such as how cancers form and spread or how to engineer organs.

“In a nutshell, we discovered a fundamental physical mechanism that cells use to mold embryonic tissues into their functional 3D shapes,” said Campàs, a professor of mechanical engineering in UCSB’s College of Engineering who holds the Duncan & Suzanne Mellichamp Chair in Systems Biology. His group investigates how living systems self organize to build the remarkable structures and shapes found in nature.

cell biology UC Santa B download

Cells coordinate by exchanging biochemical signals, but they also hold to and push on each other to build the body structures we need to live, such as the eyes, lungs and heart. And, as it turns out, sculpting the embryo is not far from glass molding or 3D printing. In their new work,”A fluid-to-solid jamming transition underlies vertebrate body axis elongation,” published in the journal Nature, Campàs and colleagues reveal that cell collectives switch from fluid to solid states in a controlled manner to build the vertebrate embryo, in a way similar to how we mold glass into vases or 3D print our favorite items. Or, if you like, we 3D print ourselves, from the inside.

Most objects begin as fluids. From metallic structures to gelatin desserts, their shape is made by pouring the molten original materials into molds, then cooling them to get the solid objects we use.

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A fluid-to-solid jamming transition underlies vertebrate body axis elongation

As in a Chihuly glass sculpture, made by carefully melting portions of glass to slowly reshape it into life, cells in certain regions of the embryo are more active and ‘melt’ the tissue into a fluid state that can be restructured. Once done, cells ‘cool down’ to settle the tissue shape, Campàs explained.

“The transition from fluid to solid tissue states that we observed is known in physics as ‘jamming’,” Campàs said. “Jamming transitions are a very general phenomena that happens when particles in disordered systems, such as foams, emulsions or glasses, are forced together or cooled down.”

This discovery was enabled by techniques previously developed by Campàs and his group to measure the forces between cells inside embryos, and also to exert miniscule forces on the cells as they build tissues and organs. Using zebrafish embryos, favored for their optical transparency but developing much like their human counterparts, the researchers placed tiny droplets of a specially engineered ferromagnetic fluid between the cells of the growing tissue.

The spherical droplets deform as the cells around them push and pull, allowing researchers to see the forces that cells apply on each other. And, by making these droplets magnetic, they also could exert tiny stresses on surrounding cells to see how the tissue would respond.

“We were able to measure physical quantities that couldn’t be measured before, due to the challenge of inserting miniaturized probes in tiny developing embryos,” said postdoctoral fellow Alessandro Mongera, who is the lead author of the paper.

“Zebrafish, like other vertebrates, start off from a largely shapeless bunch of cells and need to transform the body into an elongated shape, with the head at one end and tail at the other,” Campàs said.

UC Santa B II Lemaire

The physical reorganization of the cells behind this process had always been something of a mystery. Surprisingly, researchers found that the cell collectives making the tissue were physically like a foam (yes, as in beer froth) that jammed during development to ‘freeze’ the tissue architecture and set its shape.

These observations confirm a remarkable intuition made by Victorian-era Scottish mathematician D’Arcy Thompson 100 years ago in his seminal work “On Growth and Form.”

Darcy Thompson Ms48534_13Read About: D’Arcy Wentworth Thompson

“He was convinced that some of the physical mechanisms that give shapes to inert materials were also at play to shape living organisms. Remarkably, he compared groups of cells to foams and even the shaping of cells and tissues to glassblowing,” Campàs said. A century ago, there were no instruments that could directly test the ideas Thompson proposed, Campàs added, though Thompson’s work continues to be cited to this day.

The new Nature paper also provides a jumping-off point from which the Campàs Group researchers can begin to address other processes of embryonic development and related fields, such as how tumors physically invade surrounding tissues and how to engineer organs with specific 3D shapes.

“One of the hallmarks of cancer is the transition between two different tissue architectures. This transition can in principle be explained as an anomalous switch from a solid-like to a fluid-like tissue state,” Mongera explained. “The present study can help elucidate the mechanisms underlying this switch and highlight some of the potential druggable targets to hinder it.”

Alessandro Mongera, Payam Rowghanian, Hannah J. Gustafson, Elijah Shelton, David A. Kealhofer, Emmet K. Carn, Friedhelm Serwane, Adam A. Lucio, James Giammona & Otger Campàs

Nature (2018)

DOI: 10.1038%2Fs41586-018-0479-2

Silver nanoclusters inside synthetic DNA to create a programmed, tunable fluorescent array


Silver Nano DNA 0430 150423154807_1_540x360The silver used by Beth Gwinn’s research group at UC Santa Barbara has value far beyond its worth as a commodity, even though it’s used in very small amounts.

The group works with the precious metal to create nanoscale silver clusters with unique fluorescent properties. These properties are important for a variety of sensing applications including biomedical imaging.

The team’s latest research is published in a featured article in this month’s issue of ACS Nano, a journal of the American Chemical Society. The scientists positioned silver clusters at programmed sites on a nanoscale breadboard, a construction base for prototyping of photonics and electronics. “Our ‘breadboard’ is a DNA nanotube with spaces programmed 7 nanometers apart,” said lead author Stacy Copp, a graduate student in UCSB’s Department of Physics.

“Due to the strong interactions between DNA and metal atoms, it’s quite challenging to design DNA breadboards that keep their desired structure when these new interactions are introduced,” said Gwinn, a professor in UCSB’s Department of Physics. “Stacy’s work has shown that not only can the breadboard keep its shape when silver clusters are present, it can also position arrays of many hundreds of clusters containing identical numbers of silver atoms — a remarkable degree of control that is promising for realizing new types of nanoscale photonics.”

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DNA nanotubes were decorated by silver clusters with DNA-programmed color.
Credit: UCSB

The results of this novel form of DNA nanotechnology address the difficulty of achieving uniform particle sizes and shapes. “In order to make photonic arrays using a self-assembly process, you have to be able to program the positions of the clusters you are putting on the array,” Copp explained. “This paper is the first demonstration of this for silver clusters.”

The colors of the clusters are largely determined by the DNA sequence that wraps around them and controls their size. To create a positionable silver cluster with DNA-programmed color, the researchers engineered a piece of DNA with two parts: one that wraps around the cluster and the other that attaches to the DNA nanotube. “Sticking out of the nanotube are short DNA strands that act as docking stations for the silver clusters’ host strands,” Copp explained.

The research group’s team of graduate and undergraduate researchers is able to tune the silver clusters to fluoresce in a wide range of colors, from blue-green all the way to the infrared — an important achievement because tissues have windows of high transparency in the infrared. According to Copp, biologists are always looking for better dye molecules or other infrared-emitting objects to use for imaging through a tissue.

“People are already using similar silver cluster technologies to sense mercury ions, small pieces of DNA that are important for human diseases, and a number of other biochemical molecules,” Copp said. “But there’s a lot more you can learn by putting the silver clusters on a breadboard instead of doing experiments in a test tube. You get more information if you can see an array of different molecules all at the same time.”

The modular design presented in this research means that its step-by-step process can be easily generalized to silver clusters of different sizes and to many types of DNA scaffolds. The paper walks readers through the process of creating the DNA that stabilizes silver clusters. This newly outlined protocol offers investigators a new degree of control and flexibility in the rapidly expanding field of nanophotonics.

The overarching theme of Copp’s research is to understand how DNA controls the size and shape of the silver clusters themselves and then figure out how to use the fact that these silver clusters are stabilized by DNA in order to build nanoscale arrays.

“It’s challenging because we don’t really understand the interactions between silver and DNA just by itself,” Copp said. “So part of what I’ve been doing is using big datasets to create a bank of working sequences that we’ve published so other scientists can use them. We want to give researchers tools to design these types of structures intelligently instead of just having to guess.”

The paper’s acknowledgements include a dedication to “those students who lost their lives in the Isla Vista tragedy and to the courage of the first responders, whose selfless actions saved many lives.”

– See more at: http://www.news.ucsb.edu/2015/015345/silver-lining#sthash.LyFLOWCO.dpuf


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New Catalyst Process Uses Light, Not Metal, for Rapid Polymerization


UC SB Polymer-Hawker-Fors-deAlaniz-Dec2014-webresUC Santa Barbara researchers develop a metal-free Atom Transfer Radical Polymerization process that uses an organic-based photocatalyst ~ January 13, 2015

A team of chemistry and materials science experts from University of California, Santa Barbara and The Dow Chemical Company has created a novel way to overcome one of the major hurdles preventing the widespread use of controlled radical polymerization.

In a global polymer industry valued in the hundreds of billions, a technique called Atom Transfer Radical Polymerization is emerging as a key process for creating well-defined polymers for a vast range of materials, from adhesives to electronics. However, current ATRP methods by design use metal catalysts, a major roadblock to applications for which metal contamination is an issue, such as materials used for biomedical purposes.

This new method of radical polymerization doesn’t involve heavy metal catalysts like copper. Their innovative, metal-free ATRP process uses an organic-based photocatalyst–and light as the stimulus for the highly controlled chemical reaction.

“The grand challenge in ATRP has been: how can we do this without any metals?” said Craig Hawker, Director of the Dow Materials Institute at UC Santa Barbara. “We looked toward developing an organic catalyst that is highly reducing in the excited state, and we found it in an easily prepared catalyst, phenothiazine.”

UC SB Polymer-Hawker-Fors-deAlaniz-Dec2014-webres

“It’s “drop-in” technology for industry,” said Javier Read de Alaniz, principal investigator and professor of chemistry and biochemistry at UC Santa Barbara. “People are already used to the same starting materials for ATRP, but now we have the ability to do it without copper.” Copper, even at trace levels, is a problem for microelectronics because it acts as a conductor, and for biological applications because of its toxicity to organisms and cells.

Read de Alaniz, Hawker, and postdoctoral research Brett Fors, now with Cornell University, led the study that was initially inspired by a photoreactive Iridium catalyst. Their study was recently detailed in a paper titled “Metal-Free Atom Transfer Radical Polymerization,” published in the Journal of the American Chemical Society. The research was made possible by support from Dow, a research partner of the UCSB College of Engineering.

ATRP is already used widely across dozens of major industries, but the new metal-free rapid polymerization process “pushes controlled radical polymerization into new areas and new applications,” according to Hawker. “Many processes in use today all start with ATRP. Now this method opens doors for a new class of organic-based photoredox catalysts.”

Controlling radical polymerization processes is critical for the synthesis of functional block polymers. As a catalyst, phenothiazine builds block copolymers in a sequential manner, achieving high chain-end fidelity. This translates into a high degree of versatility in polymer structure, as well as an efficient process.

“Our process doesn’t need heat. You can do this at room temperature with simple LED lights,” said Hawker. “We’ve had success with a range of vinyl monomers, so this polymerization strategy is useful on many levels.”

“The development of living radical processes, such as ATRP, is arguably one of the biggest things to happen in polymer chemistry in the past few decades,” he added. “This new discovery will significantly further the whole field.”